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J.-A. Richard, I. Kelly, D. Marion, M. Auger, M. Pézolet*, 2005. Structure of b-Purothionin in Membranes:  A Two-Dimensional Infrared Correlation Spectroscopy Study, Biochemistry, 44, 52-61.


M.-E. Rousseau, T. Lefèvre, L. Beaulieu, T. Asakura, M. Pézolet*, 2004. Study of Protein Conformation and Orientation in Silkworm and Spider Silk Fibers Using Raman Microspectroscopy, Bioacromolecules.

Infrared and Raman spectroscopies are very efficient techniques to characterize molecular orientation in macromolecular systems. In the present paper, two examples of the application of vibrational spectroscopy to the study of molecular orientation in synthetic and natural macromolecules will be presented. In the first example, the dynamics of orientation and relaxation of stretched films of bimodal blends of polystyrene (PS) and deuterated polystyrene (dPS) has been studied in situ by polarization modulation infrared linear dichroism while, in the second one, polarized Raman microspectroscopy has been used to determined quantitatively the orientation of -sheet domains in single filaments of Bombyx mori silk.


C. Pellerin, M.-E. Rousseau, M. Côté, M. Pézolet, 2004. Study of Molecular Orientation by Vibrational Spectroscopy: From Polymers to Silk, Macromol. Symp.

Infrared and Raman spectroscopies are very efficient techniques to characterize molecular orientation in macromolecular systems. In the present paper, two examples of the application of vibrational spectroscopy to the study of molecular orientation in synthetic and natural macromolecules will be presented. In the first example, the dynamics of orientation and relaxation of stretched films of bimodal blends of polystyrene (PS) and deuterated polystyrene (dPS) has been studied in situ by polarization modulation infrared linear dichroism while, in the second one, polarized Raman microspectroscopy has been used to determined quantitatively the orientation of -sheet domains in single filaments of Bombyx mori silk.


I. Pelletier, M. Pézolet*, 2004. Compression-Induced Stereocomplexation of Polylactides at the Air/Water Interface, Macromolecules, 37, 4967-4973.

The conformational and morphological changes occurring at the air/water interface during the compression of pure poly(D-lactide) (PDLA), pure poly(L-lactide) (PLLA) and their equimolar blend have been thoroughly investigated using polarization-modulation infrared reflection absorption spectroscopy and Brewster angle microscopy. The results obtained show that the plateau region observed in the isotherm of the pure polylactides corresponds to an equilibrium between free 103 helices in a fluid phase and 103 helices in unstable solid-like domains. For the blend, this plateau corresponds to an equilibrium between free 103 helices in the fluid phase, 103 helices in unstable solid-like domains of pure polyenantiomers and 31 helices in very stable solid-like domains of PDLA/PLLA stereocomplex. The results obtained also suggest that the proportion of stereocomplex and pure polyenantiomers domains formed during the compression of the monolayer of the blend can be modulated by different experimental parameters such as the molecular weight of the polymers, the subphase temperature, the compression rate, and the “incubation” time.


I. Pelletier, I. Laurin, T. Buffeteau, M. Pézolet*, 2004. Determination of the Molecular Orientation in Biaxially Oriented Ultathin Films, J. Phys. Chem. B, 108, 7162-7169.

Biaxial orientation in ultrathin films is characterized by a preferential orientation of the main molecular axis in the plane of the film in addition to its orientation with respect to the normal of the film. In this paper, analytical expressions allowing the calculation of the molecular orientation in biaxially oriented films from their anisotropic optical constants are presented for the first time. These expressions have been used to calculate the molecular orientation in multilayers of poly(g-benzyl-L-glutamate) and to determine the angles between the main molecular axis and the different transition moments used (a angles). Using the optical constants determined by Buffeteau et al. for PBG multilayers, we have found that the tilt angle of the PBG helices with respect to the monolayer normal is 89° and that the azimuthal angle in the plane is 57°. The calculated α angles for the carbonyl stretching mode of the ester group and the amide I and amide II modes of the amide group are 49, 34 and 74°, respectively. The analytical expressions presented in this paper have also been used to calculate the molecular orientation in Langmuir-Blodgett monolayers of an equimolar blend of poly(D-lactide) and poly(L-lactide). The optical constants of the a monolayer of the polylactide mixture determined using p- and s-polarized transmittance and p-polarized reflection-absorption infrared spectra have shown that the polylactide helices have a tilt angle of 81° and an azimuthal angle of 56°.


T. Lefèvre, K. Arseneault, M. Pézolet, 2004. Study of Protein Aggregation Using Two-Dimensional Correlation Infrared Spectroscopy and Spectral Simulations, Biospectrosc. 73, 705-715.

Two-dimensional correlation spectoscopy establishes correlations between intensity variations in a series of spectra obtained by the application of an external perturbation. However, spectral effects (wavenumber shift or bandwidth change) are known to generate apparent asynchronisms in 2D maps. Surprisingly, spectral effects are often neglected in the literature when interpreting experimental maps, which can lead to erroneous conclusions. In an attempt to evaluate the contribution of these effects and that of true asynchronisms on 2D maps, the heat-induced aggregation of glutamyl-tRNA synthetase (GluRS) was studied as a typical example of the application of FT-IR spectroscopy in the amide I region. The data were compared with those obtained from a mutant protein that differs by one amino acid. To determine whether the aggregation mechanisms are identical for both proteins, the experimental 2D maps were compared to simulations based on curve fitting of the initial and final spectra of the series, which allows change in position and bandwidth of the components to be taken into account. Intermediate spectra were generated using a convenient function that mimicks the spectral evolution. The speed and the delay of each component was controlled. Apart from the appearance of turns that occur for the mutant and not for GluRS, the aggregation mechanisms of both proteins seems to be essentially identical. In particular, the loss of -helices seems to be concomitant with the formation of intermolecular -sheets, whereas the loss of intramolecular -sheets is delayed. Since the experimental maps are satisfactorily simulated when almost all the components are in-phase, it appears that many of the asynchronous features are mainly due to spectral effects. Thus, one has to be aware that true asynchronisms are not necessarily at the origin of peaks observed in asynchronous maps.


T. Lefèvre, M. Pézolet, 2003. Importance of the Reference Spectrum on Generalized Two-Dimensional Correlation Spectroscopy: Relation Between Intensity Variations and Synchronism, J. Phys. Chem. A, 107, 6366-6372.

Generalized two-dimensional correlation spectroscopy (2D-COS) establishes correlations between intensity variations within a series of ordered spectra generated by an external perturbation. The influence of the reference spectrum on the synchronicity has been investigated by using spectral simulations and mathematical analysis. With a two-state model, it is found that for two synchronous bands, 2D asynchronous peaks appear when no reference is used, whereas when the mean or the first spectrum of the series is chosen, no asynchronous peak occurs, as expected. In the latter cases, the intensity ratio of the dynamic spectra is constant throughout the experiment, which is not the case if a reference is not subtracted. The proportionality constant is equal to the ratio of the amplitudes of the intensity variations. This result is mathematically demonstrated and generalized to any form of intensity variation: if the intensity ratio of two bands is constant throughout the experiment, the elements of the 2D asynchronous matrix are zero at any wavenumber. In addition, it is established that any spectrum of the series can be used as a reference to evidence the occurrence of synchronisms. In the case of linear intensity variations, the correlations between two bands are always synchronous as long as a spectrum of the series or the mean spectrum is chosen as the reference. Thus, it is very difficult to determine whether the intensity variations have different variation rates. All the conclusions drawn from the mathematical analysis are confirmed with spectral simulations. These mathematical considerations are applied to absorbance spectra.


C. Pellerin, R.E. Prud'homme, M. Pézolet, B. A. Weinstock, P.R. Griffiths, 2003. Deformation and Relaxation of Polymers Studied by Ultra-Rapid Scanning FTIR Spectrometry, Macromolecules, 36, 4838-4843.

A recently developed ultrarapid scanning Fourier transform infrared (URS-FTIR) spectrometer has been used to study the irreversible deformation of polymer films with a millisecond time resolution for the first time. The evolution of molecular orientation as a function of draw ratio and relaxation time was studied for films of amorphous poly(ethylene terephthalate) (PET) stretched above its glass transition temperature (Tg). Very good agreement was obtained between the results obtained by URS-FTIR and polarization modulation infrared linear dichroism (PM-IRLD) spectrometry. Reversible gauche-to-trans conversions were observed, indicating that the PET chains remain amorphous. The orientation and relaxation of polystyrene (PS) in films of pure PS and of blends of PS with poly(vinyl methyl ether) (PVME) were also studied above Tg. A method allowing the determination of the orientation function of PS using a single p-polarized spectrum is described. Results reveal a significant decrease in PS orientation during the first second following the end of deformation, emphasizing the importance of the experimental time resolution in the characterization of the relaxation behavior of polymers.


P. Vermette, V. Gauvreau, M. Pézolet, G. Laroche, 2003. Albumin and Fibrinogen Adsorption onto Phosphatidylcholine Monolayers Investigated by Fourier Transform Infrared Spectroscopy, Colloids Surf. B: Biointerfaces, 29, 285-295.

Dipalmitoylphosphatidylcholine (DPPC) monolayers were deposited onto a germanium attenuated total reflectance (ATR) crystal using the Langmuir /Blodgett technique. The DPPC-coated crystal was then exposed to human serum albumin or human fibrinogen solutions while measuring the protein adsorption by recording FTIR spectra. The effect of the zwitterionic nature of the DPPC polar headgroup towards protein adsorption has been ascertained by exposing either the phospholipid headgroup or the acyl chains to the protein solution; this was possible by the use of a silanized or a bare germanium crystal. Calibration curves have been made to measure the protein surface concentrations. After 3 h, the albumin surface concentration on DPPC monolayers was about three times higher when the proteins were exposed to the lipid acyl chains instead of the polar headgroups (e.g. 3 vs. 1 g cm-2). As for fibrinogen (FGN) adsorption, when the lipid polar headgroups were exposed to the protein solution, the FGN adsorption was low reaching a maximum value of 0.5 g cm-2. When interacting with the lipid acyl chains, the FGN adsorption reached a plateau at a value of 2.1 g cm-2 after 3 h. Clearly, both albumin and FGN showed a low tendency to adsorb on surfaces where the lipid polar headgroups are exposed toward the protein solution.


C. Pellerin, R.E. Prud'homme, M. Pézolet, 2003. Effect of Thermal History on the Molecular Orientation in Polystyrene/Poly(Vinyl Methyl Ether) Blends, Polymer, 44, 3291-3297.

The effect of thermal history on the orientation and relaxation behavior of blends of polystyrene with poly(vinyl methyl ether) (PS/PVME) has been studied using polarization modulation infrared linear dichroism (PM-IRLD) and differential scanning calorimetry (DSC). DSC shows that miscible PS/PVME blends containing 70% of PS can be physically aged at temperatures above their mean glass transition temperature (Tg). PM-IRLD measurements reveal that both components become more oriented upon stretching at 51 °C (8 °C above Tg) if the sample is aged at the deformation temperature prior to stretching. Room-temperature aging can also lead to an increased orientation if the heating time at 51 °C is kept short. Moreover, PS and PVME develop a larger orientation in phase-separated blends than in miscible ones, and their relaxation is hindered. The results have been interpreted considering the morphology of the samples, including the presence of concentration fluctuations in miscible blends, and the effect of the local environment on the rigidity of the chains.


I. Pelletier, I. Laurin, T. Buffeteau, B. Desbat, M.Pézolet, 2003. Infrared Study of the Molecular Orientation in Ultrathin Films of Behenic Acid Methyl Ester: Comparison Between Single Langmuir-Blodgett Monolayers and Spin-Coated Multilayers, Langmuir, 19, 1189-1195.

Single Langmuir-Blodgett (LB) monolayers of behenic acid methyl ester(BAME)were studied by infrared spectroscopy. Anisotropic optical constants of this system were calculated from a perpendicular-polarized attenuated total reflectance spectrum and a parallel-polarized reflection-absorption spectrum and were compared to those obtained, in a previous article, for spin-coated multilayers (Pelletier, I.; Bourque, H.; Buffeteau, T.; Blaudez, D.; Desbat, B.; Pézolet, M. J. Phys. Chem.B2002, 106, 1968). These optical constants were used to calculate the tilt angle of the alkyl chains in both types of films deposited on solid substrates and to simulate polarization modulation reflection-absorption spectra of the Langmuir film at the air/water interface. The results indicate that the molecular tilt angle is near 30° for spin-coated multilayers, while single LB monolayers have a tilt angle of 11±2°. A similar orientation of the alkyl chains is obtained on single monolayers deposited onto solid substrates or spread at the air/water interface (Langmuir films), showing that no change of molecular orientation results from the Langmuir-Blodgett transfer. The presence in the infrared spectra of several bands due to the methylene wagging and twisting modes and of the splitting of the band due to the methylene bending mode at 1463 and 1473 cm-1 indicates that in all types of films BAME alkyl chains are in the all-trans conformation and packed in an orthorhombic subcell. However, under certain circumstances, the splitting of the methylene bending mode band was not observed. This phenomenon is associated with the roughness of the solid substrates supporting the LB film leading to the formation of gauche defects in the film and thus to a molecular disordering of the monolayer.


J.Y. Klass, G.R. Brown, R.B. Lennox, H. Bourque, M. Pézolet, 2003. Enantiomeric Polylactides at the Air-Water Interface: -A Isotherms and PM-IRRAS Studies of Enatiomers and their Blend, Langmuir, 19, 333-340.

The surface pressure-area (-A) isotherms of enantiomeric polylactides and their equimolar blend reveal differences in the appearance of features and compression rate effects. Surface potential data indicate that the poly(L-lactide) monolayer interacts differently than the 50:50 poly(L-lactide)/poly(D-lactide) blend film with the water subphase. In the case of the 50:50 blend at 25 °C, compression-expansion experiments confirm that the change in the monolayer is irreversible within the time frame of the experiment. In the poly(L-lactide) case, hysteresis is also observed, but the film readily reverts to its original state. Infrared spectra of the polymer monolayers at the air-water interface were obtained using the polarizationmodulation infrared reflection-absorption spectroscopy (PM-IRRAS) technique. PM-IRRAS spectra of a compressed poly(L-lactide) monolayer are consistent with the polylactide helices lying in the plane of the air-water interface. No absorbances are observed in the PM-IRRAS spectra of poly(L-lactide) prior to the plateau in the -A isotherms, suggesting that the helix formation is linked to the increase in surface density which accompanies film compression. The PM-IRRAS spectra establish that the conformation of the poly(L-lactide) helices with respect to the air-water interface is different than the conformation of the D/L blend helices.


C. Pellerin, I. Pelletier, M. Pézolet, R.E. Prud'homme, 2003. Influence of the reference temperature on the orientation and relaxation of miscible polystyrene/poly(vinyl methyl ether) blends, Macromolecules, 36, 153-161.

The deformation and relaxation behavior of polymers depends heavily on temperature. Inmiscible polystyrene/poly(vinyl methyl ether) (PS/PVME) blends, which possess a broad glass transition region, polarization modulation infrared linear dichroism (PM-IRLD) measurements show that when the mean glass transition temperature (Tg) is used as the reference temperature, the orientation and relaxation of orientation of PS in the blends depend significantly on the composition. In contrast, similar values are obtained for blends containing between 40 and 100% PS when the end of the glass transition region (Tgf) is used as the reference temperature. Physical aging experiments made by differential scanning calorimetry indicate that Tgf can be associated with the highest temperature at which enthalpic relaxation occurs, above the mean Tg of the blend. Both series of results have been analyzed, first, by considering the presence of concentration fluctuations in the miscible blends and, second, in the framework of the Lodge-McLeish model.


C. Duchesne, X. Kong, J. Brisson, M. Pézolet et R.E. Prud'homme, 2002. Molecular Orientation and Relaxation of Poly(ethylene Terephthalate) by Polarization Modulation Infrared Spectroscopy, Macromolecules, 35, 8768-8773.

Molecular orientation and relaxation of the trans and gauche conformers of poly(ethylene terephthalate), during and after an uniaxial deformation above the glass transition temperature, between 85 and 100 °C, were investigated using polarization modulation infrared linear dichroism. At all temperatures, it was found that the trans conformers orient much more that the gauche conformers whereas their relaxation rates are comparable. Gauche-trans conformational changes were observed during both stretching and relaxation. At temperatures of 93 °C or below, the relaxation was exponential with time, whereas above 93 °C, the initial decrease was followed by an increase of the orientation function due to crystallization. A reorientation of the gauche conformers, driven by the movement of the trans conformers, was also observed during crystallization.


J.-A. Richard, I. Kelly, D. Marion, M. Pézolet et M. Auger, 2002. Interaction Between b-Purothionin and Dimyristoylphosphatidylglycerol: A 31P NMR and Infrared Spectroscopy Study, Biophys. J., 83, 2074-2083.

The interaction of b-purothionin, a small basic and antimicrobial protein from the endosperm of wheat seeds,with multilamellar vesicles of dimyristoylphosphatidylglycerol (DMPG) was investigated by 31P solid-state NMR and infrared spectroscopy. NMR was used to study the organization and dynamics of DMPG in the absence and presence of b-purothionin. The results indicate that b-purothionin does not induce the formation of nonlamellar phases in DMPG. Twodimensional exchange spectroscopy shows that b-purothionin decreases the lateral diffusion of DMPG in the fluid phase. Infrared spectroscopy was used to investigate the perturbations, induced by b-purothionin, of the polar and nonpolar regions of the phospholipid bilayers. At low concentration of b-purothionin, the temperature of the gel-to-fluid phase transition of DMPG increases from 24°C to ~33°C, in agreement with the formation of electrostatic interactions between the cationic protein and the anionic phospholipid. At higher protein concentration, the lipid transition is slightly shifted toward lower temperature and a second transition is observed below 20°C, suggesting an insertion of the protein in the hydrophobic core of the lipid bilayer. The results also suggest that the presence of b-purothionin significantly modifies the lipid packing at the surface of the bilayer to increase the accessibility of water molecules in the interfacial region. Finally, orientation measurements indicate that the a-helices and the b-sheet of b-purothionin have tilt angles of ~60° and 30°, respectively, relative to the normal of the ATR crystal.


E. Roux, R. Stomp S. Giasson, M. Pézolet, P. Moreau et J.-C. Leroux, 2002. Steric Stabilization of Liposomes by pH-Responsive N-Isopropylacrylamide Copolymer, J. Pharm. Sci., 91, 1795-1802.

The aim of this study was to characterize a pH-sensitive liposome formulation bearing a terminally alkylated N-isopropylacrylamide (NIPAM) copolymer with regard to its pH responsiveness, surface properties, and pharmacokinetics. The interacting forces between two lipid bilayers bearing the anchored NIPAM copolymer were measured with a surface force apparatus. The pH-triggered content release was evaluated in buffer before and after incubation in human serum. The pharmacokinetics was determined in rats following the intravenous injection of 67Ga-loaded liposomes with or without the polymer coating. The force measurements between lipid bilayers showed that NIPAM copolymers provide a steric barrier that was dependent on pH. The pHsensitive liposomes maintained their pH sensitivity after incubation in serum. In vivo, the polymer-coated liposomes exhibited a prolonged circulation time in rats, with an area under the blood concentration–time curve that is 1.6-fold higher than the control formulation. This study showed that liposomes can be rendered pH sensitive by anchoring a terminally alkylated NIPAM copolymer at their surface. At neutral pH, the polymer provides a steric barrier that increases the liposome circulation time in vivo.


I. Pelletier, H. Bourque, T. Buffeteau, D. Blaudez, B. Desbat and M. Pézolet, 2002. Study by Infrared Spectroscopy of Ultrathin Films of Behenic Acid methyl Ester on Solid Substrates and at the Air/Water Interface, J. Phys. Chem. B, 106, 1968-1976.

Ultrathin films of behenic acid methyl ester (BAME) deposited by spin coating on solid substrates or spread at the air/water interface were studied by infrared spectroscopy and Brewster angle microscopy. Anisotropic optical constants of BAME were determined from a transmittance spectrum at normal incidence and a parallelpolarized reflectance spectrum at grazing incidence. A transmittance spectrum recorded at oblique incidence (60°) was used to validate these optical constants. The anisotropic extinction coefficients and the polarized ATR spectra were used to calculate the tilt angle of several transition moments and also the molecular tilt angle of BAME molecules assuming an all-trans conformation of the alkyl chain. The results indicate that the alkyl chain of the fatty acid ester is tilted and that the molecular tilt angle is close to 30°. PM-IRRAS spectra of BAME at the air/water interface were also recorded as a function of the surface pressure. The splitting of the methylene bending mode shows that the all-tans alkyl chains are packed in a quasi-crystalline structure at the air/water interface, even at low surface pressure. This finding was further confirmed by Brewster angle microscopy. Furthermore, the band progression due to the methylene wagging modes was observed for the first time in infrared spectra of a Langmuir monolayer. The simulation of the PM-IRRAS spectrum of a BAME monolayer recorded at 30 mN/m using the optical constants obtained from films prepared by spin coating indicate that, as opposed to the orientation on solid substrates, the alkyl chain of BAME is nearly perpendicular to the air/water interface in Langmuir films.


C. Pellerin, M.-E. Rousseau, R.E. Prud'homme and M. Pézolet, 2002, Orientation and Relaxtion in Thick Poly(ethylene terephtalate) Films by Transmission Infrared Linear Dichroism, Appl. Spectrosc., 56, 17-23.

Infrared spectroscopy is a powerful tool for the study of the orientation in amorphous and semi-crystalline polymers, but it is generally limited to thin samples. In this study, we have used transmission infrared linear dichroism to study the orientation of thick poly(ethylene terephthalate) (PET) films. To overcome the saturation problem of the intense bands of PET, overtones and combination bands in the high-frequency region of the mid-infrared spectrum were used. Using polarization-modulation infrared linear dichroism (PM-IRLD), it was possible to follow in real-time the relaxation of orientation of uniaxially oriented PET films up to 500 mm thick. It was observed that between 30 and 500 mm, the thickness of the films has no effect on the orientation relaxation dynamics. It should, therefore, be possible to use thick films, which are much easier to prepare than thin films, for future infrared studies of the deformation of PET. A very good correlation was also observed for the relaxation curves obtained using high- and low-frequency bands related to gauche and trans conformers in thin and thick films. An example of the application of these high-frequency bands to obtain orientation and structural information is also given in the case of a commercial PET bottle showing a biaxial orientation.


T. Buffeteau, F. Lagugné Labarthet, M. Pézolet and C. Sourisseau, 2001, Dynamics of Photoinduced Orientation of Non-Polar Azobenzene Groups in Polymer Films. Characterization of the cis Isomers by Visible and FTIR Spectroscopies, Macromolecules, 34, 7514-7521.

To better characterize the cis state and the reorientation processes in polymers containing azobenzene groups, the in situ dynamics of photoinduced orientation of a polymer with azobenzene groups bearing no donor and acceptor substituents such as poly[4-[2-(methacryloyloxy)ethyl]azobenzene] polymer (pMEA) was carried out using real-time UV-vis and infrared spectroscopies. Thin films of pMEA were irradiated at 488 nm with either linearly or circularly polarized light (Ipump ) 10 mW/cm2). The different mechanisms occurring during the photoisomerization cycles were revealed by following the time dependence of the normalized average absorbance (T0) and the normalized linear dichroism (T2) during the orientation (laser on) and relaxation (laser off) periods. Therefore, the normalized average absorbance has allowed an estimation of the cis isomer fraction (fcis) at the photostationary state. The photoisomerization is more efficient when the film is irradiated using a circularly polarized light (fcis ) 0.15) than using linearly polarized light (fcis ) 0.11). The cis state has been characterized for the first time in azopolymers by infrared spectroscopy using a band at 1515 cm-1 characteristic of the cis isomers. The time dependence of the intensity of this band during the relaxation period has shown that the cis state is very stable and has a lifetime of about 12 h. Finally, a significant dichroism of the trans and cis isomers has been observed when the films were irradiated with a linearly polarized light.


H. Bourque, I.Laurin, M. Pézolet, J.M. Klass, R.B. Lennox and G.R. Brown, 2001, Investigation of the Poly(L-lactide)/Poly(D-lactide) Stereocomplex at the Air-Water Interface by Polarization Modulation Infrared Reflection Absorption Spectroscopy, Langmuir, 17, 5842-5849.

The polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) technique has been used in situ to determine the orientation and molecular structure of an equimolar mixture of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) spread at the air-water interface. The characteristics of the compression isotherm and of the PM-IRRAS spectra give clear evidence for the presence of a PLLA/PDLA stereocomplex. One of the most striking features in the PM-IRRAS spectra of the stereocomplex is the derivative shape of the band due to the C=O stretching vibration providing a spectral signature of the presence of polylactide helices oriented parallel to the water surface. The positive and the negative components of the C=O band observed at 1749 and 1765 cm-1 are assigned to the A and E modes of the helical structure, respectively. This assigment was confirmed by recording transmission spectra of the transfered stereocomplex at normal and oblique incidence. Compression of the monolayer past 17 Å2/repeat unit results in the formation of a bilayer structure. The surface pressure-area isotherm and the PM-IRRAS features suggest that the structure of the film at the air-water interface is similar to the three-dimensional crystal structure of the PLLA/PDLA stereocomplex. In the bulk crystalline structure, the molecules adopt a 31-helix conformation and a segment of a PLLA molecule is paired with a segment of a PDLA molecule resulting in a racemic unit cell. The PM-IRRAS technique is thus shown to provide detailed insight into the structure of these polymeric Langmuir films and definitely shows that helical polymeric structures can be directly observed at the air-water interface.


Y. Wang, C.G. Bazuin and M. Pézolet, 2001, Investigation of Orientation and Relaxation in a Segmented Zwitterionomer by Fourier Transform Infrared Spectroscopy, Macromolecules, 34, 6344-6352.

The orientation behavior of a segmented poly(tetramethylene oxide) (PTMO) zwitterionomer, with a narrow polydispersity PTMO segmental molecular weight of 5.2 x 103, a melting point of 17 °C, and elastomeric characteristics, was studied using infrared linear dichroism. The results obtained show that when the amorphous zwitterionomer is stretched at ambient temperature, the PTMO chains orient in the stretch direction. At a draw ratio of approximately 3, strain-induced crystallization occurs and increases with strain amplitude. The chain axis of the crystallized PTMO segments are almost perfectly oriented in the stretch direction, whereas the orientation of the amorphous segments is low and undergoes no further changes during crystallization. The degree of crystallization was also determined from the spectra (22% for a draw ratio of 5.6). The crystallization kinetics were shown to follow the Avrami equation, indicating one-dimensional growth (n ) 0.8). Orientation relaxation following deformation was also studied as a function of temperature at draw ratios and temperatures where strain-induced crystallization is avoided. Little orientation was detected in the ionic regions of the polymer during stretching. The orientation function for the PTMO soft blocks decreases, and the relaxation rate increases with increasing temperature. Time-temperature superposition of the relaxation curves is discussed in relation to the hard (or cluster) phase transition.


A.K. Oultache, X. Kong, C. Pellerin, J. Brisson, M. Pézolet and R.E. Prud'homme, 2001, Orientation and Relaxation of Orientation of Amorphous Poly(Ethylene Terephthalate), Polymer, 42, 9051-9058.

Poly(ethylene terephthalate) (PET) has been uniaxially stretched at different draw ratios and draw rates above its glass transition temperature, in the 80-105 ºC temperature range.  Molecular orientation and relaxation have been followed by birefringence. A decrease in temperature reduces the mobility of the oriented chains resulting in a slow relaxation while an increase in stretching rate results in higher orientation values and rapid relaxation after the extension. The same relaxation behavior has been observed from birefringence and polarization modulation infrared spectroscopy.  Rouse relaxation times have been estimated from rheological master curves and birefringence relaxation data, while retraction and the reptation times have been deduced from the scaling laws proposed by Doi and Edwards.


M.-J. Paquet, M. Laviolette, M. Pézolet and M. Auger, 2001, 2D-IR Study of the Aggregation of Cytochrome c in the Presence of Dimyristoylphosphatidylglycerol, Biophys. J., 81, 305-312.

Two-dimensional infrared correlation spectroscopy (2D-IR) was used in this study to investigate the aggregation of cytochrome c in the presence of dimyristoylphosphatidylglycerol. The influence of temperature on the aggregation has been evaluated by monitoring the intensity of a band at 1616 cm-1, which is characteristic of aggregated proteins, and the 2D-IR analysis has been used to determine the various secondary structure components of cytochrome c involved before and during its aggregation. The 2D-IR correlation analysis clearly reveals for the first time that aggregation starts to occur between nearly native proteins, which then unfold, yielding to further aggregation of the protein. Later in the aggregation process, the formation of intermolecular bonds and unfolding of the -helices appear to be simultaneous. These results lead us to propose a two-step aggregation process. Finally, the results obtained during the heating period clearly indicate that before the protein starts to aggregate, there is a loosening of the tertiary structure of cytochrome c, resulting in a decrease of the -sheet content and an increase of the amount of -turns. This study clearly demonstrates the potential of 2D-IR spectroscopy to investigate the aggregation of proteins and this technique could therefore be applied to other proteins such as those involved in fibrilogenesis.


T. Buffeteau, E. Le Clavez, B. Desbat, I. Pelletier and M. Pézolet, 2001, Quantitative Orientation of a-Helical Polypeptides by Attenuated Total Reflection Infrared Spectroscopy, J. Phys. Chem. B, 105, 1464-1471.

Spectral simulations of polarized attenuated total reflection (ATR) spectra have been used to determine quantitatively the orientation of a-helical polypeptides. Transmittance and polarized ATR spectra of five monolayers of poly-g-benzyl-L-glutamate (PBG) transferred by the Langmuir-Blodgett techniques on germanium crystal have been recorded and the dichroic ratios of the amide I and amide II bands have been calculated. Simulations were performed using anisotropic optical constants of PBG in the molecular coordinate system and using the 4x4 matrix formalism of Berreman. Assuming that the a-helices are parallel to the plane of the ATR crystal, an average angle of 38±1° between the helix axes and the withdrawing direction has been found. Simulated spectra for various orientations of the a-helices are then given and influence of the azimuthal and tilt angles on the dichroic ratios of the amide bands has been investigated.


L. Messé, M. Pézolet and R.E. Prud'homme, 2001, Molecular Relaxation Study of Polystyrene: Influence of Temperature, Draw Rate and Molecular Weight, Polymer, 42, 563-575.

Molecular relaxation curves of five different polystyrene samples, four monodisperse of weight-average molecular weight ranging from 210000 to 2340000, and one polydisperse, have been studied using birefringence and polarization modulation infrared linear dichroism, during and after a step-strain uniaxial deformation at temperatures between Tg and Tg+60°C. Relaxation measurements can be fitted with a set of exponential decay functions, thus defining three different relaxation times. The relaxation times thus obtained with birefringence and polarization modulation experiments are similar, and decrease with an increase in temperature. The first relaxation time (1), which is of the order of seconds, is independent of average molecular weight (Mw), while the second (2) and third (3) relaxation times increase with molecular weight. For example, at Tg+20°C, and for a PS molecular weight of 2340000, values of 0.7, 39 and 16500 s were determined for 1,2 and 3, respectively. The power law dependence found for the third relaxation time scales as Mw1.6 at each temperature. This behavior is consistent with the prediction of the theoretical model of Doi-Edwards and allows the assignment of 1 to the first, and 3 to the second relaxation time of Doi-Edwards (2 is intermediate between those two). The decrease of the relaxation time ratio (3/1) with temperature, noted for all the PS molecular weights investigated, suggests a decrease in the number of entanglement points with an increase in temperature above Tg+20°C. Finally, for a given temperature, a linear dependence is observed between 3 and 1 in agreement with the 3=21N1.6 Doi-Edwards prediction, where N is the number of entanglements.


C. Pellerin, R.E. Prud'homme and M. Pézolet, 2000, Orientation and Relaxation Study of Miscible Polystyrene / Poly(vinyl methyl ether) Blends, Macromolecules, 33, 7009-7015.

The macroscopic deformation and relaxation of orientation of miscible polystyrene/poly(vinyl methyl ether) (PS/PVME) blends containing between 50 and 100% PS have been studied using polarization modulation infrared linear dichroism (PM-IRLD). PS/PVME films were stretched at Tg + 15 to a draw ratio of 2, at constant draw rates of 10 and 100 cm/min. During the deformation, the addition of the lower molecular weight PVME to the blends leads to an important increase of the orientation function of PS. During the relaxation period, a fast decay of the PS orientation function occurs at short times, followed by a slow chain relaxation at longer times. The relaxation rate is faster in pure PS than in the blends, the increase of the PVME content leading to a hindered relaxation. The orientation function of PVME is small in all cases, but we have been able, for the first time, to measure directly its relaxation, which follows closely the trend observed for PS. However, no relaxation coupling can be clearly observed between the two polymers, the relaxation rate of PVME being always faster than that of PS. These results demonstrate the efficiency of PM-IRLD to determine quantitatively the time dependence of the orientation function of several chemical groups in multicomponent systems during the orientation and relaxation processes.


F. Picard, M. Pézolet, P. E. Bougis and M. Auger, 2000, Hydrophobic and electrostatic cardiotoxin-phospholipid interactions as seen by solid-state 31P NMR spectroscopy, Can. J. Anal. Sci. Spectrosc., 45, 72-83.

Cardiotoxins (CTXs) purified from elapid venoms are known to interact strongly with negatively charged phospholipid membranes such as those constituted of dimyristoylphosphatidic acid (DMPA). These interactions have been shown to result in the disappearance of the bilayer structure and in the formation of an isotropic phase. On the other hand, some studies have suggested that cardiotoxins can also interact with zwitterionic membranes such as those constituted of dimyristoylphosphatidylcholine (DMPC). While phosphorus-31 NMR spectroscopy is widely recognized as a powerful method for the study of electrostatic interactions, new tools for the study of phospholipid-protein interactions have recently been developed, namely the precise measurement of the lateral diffusion time by EXSY 31P NMR spectroscopy and the quantitative calculation of the partial orientation of phospholipid membranes from one-dimensional 31P solid-state NMR spectra. These methods appear to be very well suited for the study of hydrophobic protein-phospholipid interactions and are used in the present study to investigate the electrostatic and hydrophobic interactions between cardiotoxin I purified from Naja mossambica mossambica venom and membranes constituted of DMPC or DMPA.


F. Lagugné Labarthet, S. Freiburg, C. Pellerin, M. Pézolet, A. Natansohn and P. Rochon, 2000, Spectroscopic and Optical Characterization of a Series of Azobenzene-Containing Liquid Crystalline Polymers, Macromolecules, 33, 6815-6823.

A series of azobenzene-containing side chain liquid crystalline polymers with various spacer lengths (pXMAN, where X, the number of methylene units, varies from 4 to 12) have been synthesized and characterized. Phases and aggregation have been studied by UV-visible spectroscopy as a function of temperature. Polarized spectra were measured before and after irradiation with a resonant pump light at 488 nm. The annealing process on polymers with short spacers (p4MAN-p8MAN) induces a hypsochromic shift while, for longer spacers (p9MAN-p12MAN), it induces a large bathochromic shift. These effects may be due to the strong dipolar interaction and interdigitation of the side chain chromophores in an antiparallel orientation. The irradiation of such organized films with either circularly or linearly polarized light induces a bathochromic shift by breaking the antiparallel organization. This is a consequence of the angular reorientation of the azobenzene moieties as a result of trans-cis photoisomerization. To estimate the orientation of the side chain azobenzene photoactive group, of the aliphatic spacer and of the main chain, linear dichroism in the infrared spectral range was measured using the polarization-modulation technique with in situ irradiation. From these experiments, a high and stable value of photoinduced linear dichroism reveals a strong interaction and self-organization of azobenzene side chain molecules during the relaxation process. The anisotropic reorientation of the polymer main chain and of the spacer is small when compared to the reorientation of the azobenzene side chains, which become perpendicular to the linearly polarized pump beam. Additional birefringence measurements were carried out with in situ irradiation followed by a relaxation cycle for the whole series of polymers in various phases. The stability and the rate of the induced birefringence depend on the initial degree oforganization within the thin film and on its thermal history. It is noteworthy that annealing can lead to a significant improvement of the birefringence level (+44%). The results obtained on photoinduced orientation and phase organization are correlated with the polymer properties.


A. Nabet, M. Auger and M. Pézolet, 2000, Investigation of the Temperature Behavior of the Bands Due to the Methylene Stretching Vibrations of Phospholipid Acyl Chains by Two-dimensional Infrared Correlation Spectroscopy, Appl. Spectrosc., 54, 948-955.

The temperature-induced gel-to-liquid crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) is characterized by a shift towards high frequencies and an increase of the width of the bands due to the methylene stretching vibrations. These spectral modifications are frequently used to measure the conformational order of lipid acyl chains. However, it is not clear whether these bands contain two spectral components due to trans and gauche conformers or whether they gradually shift with temperature. The temperature-induced gel-to-liquid crystalline phase transition of DPPC has been investigated in the present study by two-dimensional infrared (2D-IR) correlation spectroscopy. Our results show that each methylene stretching band in both the synchronous and the asynchronous maps is characterized by two peaks. The same pattern is also observed when the temperature range is restricted to the gel phase. These results were compared to those obtained by spectral simulations using either a single band that shifts in frequency and gets broader with the increase of temperature (shiftingband model), simulating a continuously evolving one-phase system, or a band made of two components (two-band model), simulating the trans and gauche spectral contributions of a two-phase system. The results obtained for the asynchronous maps of the simulated spectra indicate clearly that the experimental results cannot be modeled by a pure two-phase system and are best simulated by the shifting-band model.


M. Morissette, A. Dicko, M. Pézolet, S. Callier and T. Di Paolo, 1999, Effect of Dehydroepiandrosterone and its Sulfate and Fatty Acid Ester Derivatives on Rat Brain Membranes, Steroids, 64, 796-803.

The effects of dehydroepiandrosterone (DHEA) as well as its sulfate and fatty acid ester derivatives on rat brain membrane fluidity was investigated by fluorescence depolarization of a lipid probe 1,6-diphenyl- 1,3,5-hexatriene and compared to its effect on phospholipid conformation investigated by Fourier transform infrared spectroscopy. In rat brain, membrane fluidity varied rostro-caudally, the frontal cortex showing the highest fluidity compared to the hypothalamus, hippocampus, striatum, thalamus, and hindbrain. As previously reported, it was observed that cholesteryl hemisuccinate and stearic acid rigidify striatal membrane whereas linoleic acid and L-alpha-phosphatidylcholine increase the membrane fluidity. Striatal fluidity was increased in vitro with increasing concentrations of DHEA, this effect was greater with the DHEA fatty acid ester derivatives (DHEA-L), DHEA-undecanoate, and DHEA-stearate, whereas no effect was observed with DHEA-sulfate (DHEA-S). In the frontal cortex only the two DHEA-L derivatives increased membrane fluidity, whereas DHEA and DHEA-S were without effect. The effect of DHEA-L on synthetic dimyristoylphosphatidylcholine-d(54) phospholipid membranes indicates a disordering effect of DHEA-undecanoate and DHEA-stearate as reflected by increased trans-gauche isomerization of the acyl chains of the lipid. Hence, DHEA-L increase the disorder and/or fluidity of brain membranes; interestingly, these compounds are abundant in the brain where they are generally considered as storage compounds that slowly release the active unconjugated steroid hormone.


V. Raussens, M. Pézolet, Jean-Marie Ruysschaert and E. Goormaghtigh, 1999, Structural Difference in the H+, K+ - ATPase between the E1 and E2 Conformations: An Attenuated Total Reflection Infrared Spectroscopy, UV Circular Dichroism and Raman Spectroscopy Study, Eur. J. Biochem., 262, 176-183.

Conformational changes taking place in the gastric H+,K+-ATPase when shifting from the K+-induced E2 form to the El form upon replacing K+ ions by Na+ were investigated by different spectroscopic approaches. No significant secondary-structure change or secondary-structure reorientation with respect to the membrane plane could be measured by attenuated total reflection Fourier transform infrared spectroscopy of oriented films. Circular dichroism and Raman spectra obtained on tubulovesicle suspensions indicated no significant secondary structure or tyrosine and tryptophan side-chain environment changes in tubulovesicle suspensions. The smallest observable structural changes are discussed in term of the number of amino-acid residues involved for each technique.


A. Dicko, M. Morissette, S. Ben Ameur, M. Pézolet and T. Di Paolo, 1999, Effect of Estradiol and Tamoxifen on Brain Membranes: Investigation bt Infrared and Fluorescence Spectroscopy, Brain Res. Bull., 49, 401-405.

Nongenomic effects of steroids on rat brain neurotransmitter transporters and receptors have been reported in several laboratories. In the present study, we have investigated possible membrane effects of 17 a- and 17 b-estradiol, as well as tamoxifen, by studying their interactions with synthetic phospholipid membranes using Fourier transform infrared spectroscopy. We have also used the fluidity of rat striatal and frontal cortex membranes, as determined by fluorescence depolarization of the probe 1,6-diphenyl-1,3,5-hexatriene (DPH), to probe the effects of these drugs on membranes. Our results show that tamoxifen induces conformational disorder along the acyl chains of deuterated dimirystoylphosphatidylcholine and decreases the gel to liquid-crystalline phase transition temperature by approximately 10 °C. Similar effects, although less pronounced, were observed with 17 beta-estradiol, whereas 17 a-estradiol had no significant effect. The DPH fluorescence anisotropy of striatum and frontal cortex membranes was decreased in vitro with 17 b-estradiol or tamoxifen and also with 17 a-estradiol, but to a lesser extent. These results suggest a stereospecific estradiol effect on membranes and that the effects of these compounds are not related to their activity on estrogen receptors. These observations support a different mechanism of action of steroids that could be implicated in their neuroprotective activity.


F. Picard, T. Buffeteau, B. Desbat, M. Auger and M. Pézolet, 1999, Quantitative Orientation Measurements in Thin Lipid Films by ATR Infrared Spectroscopy, Biophys. J., 76, 539-551.

Quantitative orientation measurements by attenuated total reflectance (ATR) infrared spectroscopy require the accurate knowledge of the dichroic ratio and of the mean-square electric fields along the three axes of the ATR crystal. In this paper, polarized ATR spectra of single supported bilayers of the phospholipid dimyristoylphosphatidic acid covered by either air or water have been recorded and the dichroic ratio of the bands due to the methylene stretching vibrations has been calculated. The mean-square electric field amplitudes were calculated using three formalisms, namely the Harrick thin film approximation, the two-phase approximation, and the thickness- and absorption-dependent one. The results show that for dry bilayers, the acyl chain tilt angle varies with the formalism used, while no significant variations are observed for the hydrated bilayers. To test the validity of the different formalisms, s- and p-polarized ATR spectra of a 40-Å lipid layer were simulated for different acyl chain tilt angles. The results show that the thickness- and absorption-dependent formalism using the mean values of the electric fields over the film thickness gives the most accurate values of acyl chain tilt angle in dry lipid films. However, for lipid monolayers or bilayers, the tilt angle can be determined with an acceptable accuracy using the Harrick thin film approximation. Finally, this study shows clearly that the uncertainty in the determination of the tilt angle comes mostly from the experimental error on the dichroic ratio and from the knowledge of the refractive index.


M. Pézolet, C. Pellerin, R.E. Prud’homme and T. Buffeteau, 1998, Study of polymer orientation and relaxation by polarization modulation and 2D-FTIR spectroscopy, Vib. Spectrosc., 18, 103-110.

Polarized Fourier transform infrared (FTIR) spectroscopy has been used extensively to study polymer orientation. The dichroic ratio and the dichroic difference are normally obtained from spectra recorded sequentially with the infrared radiation polarized parallel and perpendicular to a reference direction. To improve the sensitivity of this technique and to be able to follow accurately the dynamics of orientation, FTIR spectroscopy has been coupled with the polarization modulation (PM) technique. With this technique, the dichroic difference spectrum is recorded directly, thus minimizing instrumental and sample fluctuations. The results obtained demonstrate the high efficiency of polarization modulation infrared linear dichroism (PM-IRLD) to determine quantitatively the time dependence of the orientation function of several chemical groups during the orientation and relaxation processes. Examples of the application of this technique to study in situ the dynamics of orientation will be presented for both stretched films of polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends and optically oriented copolymers containing azobenzene side chains. The use of the PM-IRLD technique has allowed the direct determination of the relaxation kinetics of the components in polymer blends. In the case of the azopolymers, the time-dependent spectra obtained by PM-IRLD have also been analyzed by two-dimensional Fourier transform infrared (2D-FTIR) spectroscopy. The results obtained with this technique show that the spectral resolution is significantly enhanced in the asynchronous maps that also provide valuable information about the relative movement of the different chemical groups of the polymers.


A. Dicko, H. Bourque and M. Pézolet, 1998, Study by infrared spectroscopy of the conformation of dipalmitoylphosphatidylglycerol monolayers at the air-water interface and transferred on solid substrates, Chem. Phys. Lipids, 96, 125-139.

A parallel investigation of the conformational changes of dipalmitoylphosphatidylglycerol (DPPG) monolayers induced by surface pressure has been studied in situ at the air water interface using polarization modulation external infrared reflection absorption spectroscopy (PM-IRRAS) and on solid substrate by attenuated total reflection (ATR) spectroscopy. For both the ATR and PM-IRRAS spectra of DPPG, the non-linear increase of the intensity of the antisymmetric methylene stretching band of DPPG with molecular surface density, indicates that the compression of the DPPG monolayer induces a change of the conformation and/or orientation of the acyl chains of the phospholipid. At surface pressures between 7 and 20 mN/m, the acyl chains of the DPPG monolayer are found to be more ordered on the germanium substrate than at the air-water interface. At higher surface pressures, the conformation of the lipid acyl chains of DPPG on both substrates are almost similar. In the liquid-condensed phase, the acyl chains are in all-trans conformation and their tilt angle with respect to the normal of the film is approximately 30°. Our results also suggest the presence of DPPG solid domains in the liquid-expanded phase. Investigation of polar head group region indicates that at low surface pressures, the carbonyl groups were more oriented on the water surface than the acyl chains. Finally, the present study shows that intermolecular hydrogen bonding probably occur between the glycerol hydroxyl and the phosphate or carbonyl groups of the phospholipid.


Y. Xiao, H. Bourque, M. Pézolet and A.M. Ritcey, 1998, Polarization modulation IRRAS investigation of a cellulose ether at the air/water interface, Thin Solid Films, 327-329, 299-302.

Spread monolayers of a cellulose alkyl ether (HPC-C16) have been investigated at the air/water interface by polarization modulation infrared reflection-absorption spectroscopy (PM-IR S). Infrared spectra exhibit bands associated with the symmetric and anti-symmetric methylene stretching vibrations, as well as with the methylene scissoring vibration, at 2850, 2917 and 1471-1463 cm-1, respectively. All of these bands appear as positive peaks in the PM-IRRAS spectra, indicating that the hexadecane sidechains have a net orientation perpendicular to water surface. The relatively low frequencies of the methylene stretching bands suggest that the hydrocarbon sidechains adopt a near all-trans conformation. The intensity of these bands increases with decreasing molecular area during monolayer compression. This increase is due not only to an increase in the surface density of the absorbing groups but also to orientational changes. These results indicate that alkyl sidechain orientation at the air/water interface is, to a certain degree, dependent on the surface pressure. Furthermore, no change in orientation is observed during compression through the plateau typically present in surface pressure-area isotherms of these polymers.


M. Subirade, I. Kelly, J. Guéguen and M. Pézolet, 1998, Molecular Basis of the Film Formation from a Soybean Protein: Comparison between the Conformation of Glycinin in Aueous Solution and in the Film State, Int. J. Biol. Macromol., 23, 241-249.

Fourier transform infrared spectroscopy has been used to investigate the conformational changes of glycinin, a major storage protein of soybean seeds, upon film-forming. The results show that the secondary structure of glycinin is mainly composed of a b-sheet (48%) and unordered (49%) structures. The amide I band of glycinin in film-forming conditions, i.e. in alkaline media and in the presence of plasticizing agent, reveals the conversion of 18% of the secondary structure of the protein from the b-sheet (6%) and random coil (12%) to the a-helical conformation due to the helicogenic effect of the ethylene glycol used as the plasticizing agent. Conformational changes also occur upon the film-forming process leading to the formation of intermolecular hydrogen-bonded b-sheet structures. Results obtained from other plant families indicate that, whatever the origin and conformation of protein, formation of films leads to the appearance of intermolecular hydrogen-bonded b-sheet structures, suggesting that this type of structure might be essential for the network formation in films. Thus, it is hypothesized that, in the film state, intermolecular hydrogen bonding between segments of b-sheet may act as junction zones in the film network. This study reveals for the first time that there is a close relationship between the conformation of proteins and the mechanical properties of films.


T. Buffeteau, F. Lagugné Labarthet, M. Pézolet and C. Sourisseau, 1998, Photoinduced Orientation of Azobenzene Chromophores in Amorphous Polymers as Studied by Real-Time Visible and FTIR Spectroscopies, Macromolecules, 31, 7312-7320.

In situ dynamical study of the photoinduced orientation of the DR1 azobenzene derivative in a doped PMMA matrix and in p(DR1A-co-MMA) copolymers was carried out using real-time visible and infrared spectroscopies. The different mechanisms occurring during the photoisomerization cycles were highlighted by following the time dependence of the normalized average absorbance (T0), the normalized linear dichroism (T2) and the order parameter (P2) during the orientation (laser on) and the relaxation (laser off) periods. The thermal cis-trans back-relaxation and the angular redistribution were followed separately from the T0 and T2 relaxation curves, respectively. The orientation and relaxation curves were fitted by the Kohlrausch-Williams-Watts (KWW) function in order to compare the rate constant and the distribution width for various samples. On one hand, the chromophore-matrix interactions were investigated in doped systems by changing the tacticity of the PMMA matrix. On the other hand, the chromophore-chromophore interactions in functionalized polymers were studied by changing the concentration of azobenzene units in copolymer systems.


T. Le Bihan and M. Pézolet, 1998, Study of the Structure and Phase Behavior of Dipalmitoylphosphatidylcholine by Infrared Spectroscopy: Characterization of the Pretransition and Subtransition, Chem. Phys. Lipids, 94, 13-33.

Despite the fact that fully hydrated multilayers of phosphatidylcholines have been extensively studied in the past, phase transitions such as the pretransition and the subtransition are still the object of different interpretations and contradictory observations. In order to obtain more information on the structural changes associated to these transitions for dipalmitoyl phosphatidylcholine (DPPC), a study has been done using both transmission and polarized attenuated total reflection infrared spectroscopy. At the pretransition, we observe that the extended hydrocarbon chains become less tilted with respect to the bilayer normal. The pretransition is also characterized by an increase in the hydration of the DPPC bilayer and the appeareance of the ripple structure. As opposed to previous findings, we do not observe a major variation of the acyl chain packing mode at the pretransition. These observations are supported by the investigation of DPPC with 5 mol% cholesterol, since this sterol is known to be a strong inhibitor of the pretransition. On the other hand, a drastic change in chain packing, characterized by infrared bands due to the methylene scissoring mode, is observed at the subtransition. Also, below the subtransition, we observe an increase of the hydrocarbon chain rotational disorder. Some correlations have also been made between the spectral parameters normally used to characterize the degree of order of the acyl chains. These correlations have allowed us to evaluate more precisely at the molecular level the subtle structural changes tl-lat occur during phase transitions of DPPC.


V. Raussens, H. de Jongh, M. Pézolet, J.-M. Ruysschaert and É. Goormaghtigh, 1998, Secondary Structure of the Intact H+, K+ - ATPase and its Membrane-Embedded Region: An Attenuated Total Reflection Infrared Spectroscopy, UV Circular Dichroism and Raman Spectroscopy Study, Eur. J. Biochem., 252, 261-267.

Sarcoplasmic reticulum Ca2+-ATPase and gastric (H+,K+)-ATPase were cleaved under 3 different proteolysis conditions. After elimination of the protease and of the cleaved peptides, the vesicles contg. the membrane-bound peptides of the ATPases were studied by Fourier-transform attenuated total reflection IR spectroscopy. In the harsher proteolysis conditions, the membrane-associated domain of Ca2+-ATPase represented ~20% of the protein and was mainly comprised of a-helices. Polarized IR spectroscopy showed that these a-helixes were mainly oriented perpendicular to the membrane. However, only 10-20% of (H+,K+)-ATPase was cleaved. The remaining, membrane-associated domain of the protein contained ~30% a-helices and 30% b-sheet structures. The a-helices adopted a mainly transmembrane orientation. Whereas the data on Ca2+-ATPase were in general agreement with the current model of the protein, the results indicated that caution must be used in choosing this protein as a general structural model for all P-type ATPases. The protease-resistant, membrane-associated domain of the (H+,K+)-ATPase was indeed much larger than predicted and also contained b-sheet structures.


T. Buffeteau and M. Pézolet, 1998, Photoinduced Orientation in Azopolymers Studied by Infrared Spectroscopy: Cooperative and Biaxial Orientation in Semicrystalline Polymers, Macromolecules, 31, 2631-2635.

A disperse red 19-containing semicrystalline azopolymer (pDR19T) with phenylene diacrylate (PD) groups within the main chain has been studied by polarization modulation and two-dimensional correlation infrared spectroscopy. The time dependence of the orientation function of azobenzene and PD groups has been followed during the orientation (linearly polarized laser on) and relaxation (laser off) periods. The results show a high degree of orientation of the different groups perpendicular to the direction of the laser polarization and a cooperative orientation of the PD groups with the azobenzene side chains. The azobenzene groups are not randomly oriented in the plane normal to the direction of the laser polarization leading to a biaxial orientation distribution. This photoinduced biaxiality has been quantified for pDR19T united for amorphous copolymers containing azobenzene and methyl polymer methacrylate structural units.


A. Natansohn, P. Rochon, X. Meng, C. Barrett, T. Buffeteau, S. Bonenfant and M. Pézolet, 1998, Molecular Addressing' Selective Photoinduced Cooperative Motion of Polar Ester Groups in Copolymers Containing Azobenzene Groups, Macromolecules, 31, 1155-1161.

Amorphous copolymers with rigid azobenzene and ester side groups form films in which birefringence can be induced using linearly polarized light. When both the azobenzene and the ester groups are polar, cooperative motion occurs and high levels of birefringence can be achieved at relatively low azobenzene content. With less polar ester groups, this cooperative motion is significantly reduced, suggesting that the effect is not dictated by steric factors (as is the case in liquid crystalline copolymers), but by electric interaction between the side group dipoles. The differences in cooperative motion of two copolymer systems: poly{4 prime -[(2-(methacryloyloxy)ethyl) ethylamino]-4-nitroazobenzene (DR1M)-co-4-nitrophenyl 4-[[2-[(2-methyl-1-oxo-2-propenyl)oxy]ethyl] oxy]benzoate (BEM)} (a polar azo/polar ester pair), and poly{DR1M-co-4-phenyl 4-[[2-[2-(2-methyl-1-oxo- 2-propenyl)oxy]ethyl]oxy]benzoate (NBEM)} (a polar azo/less polar ester) have been investigated using birefringence measurements and time dependent infrared spectroscopy. Thus, the 'molecular addressing' concept introduced by Anderle and Wendorff for liquid crystalline copolymers is real. Kinetic analysis using time-dependent infrared spectroscopy clearly shows that the azobenzene groups move first and are followed by the ester groups, which move to a much greater degree when they have similar polarity (BEM with DR1M).


A. Dicko, T. Di Paolo and M. Pézolet, 1998, Interaction of Dehydroepiandrosterone with Phospholipid Membranes: An Infrared Spectroscopy Investigation, Biochim. Biophys. Acta, 1368, 321-328.

The interaction between dehydroepiandrosterone (DHEA) and its sulfate metabolite (DHEA-S) with deuterated dimyristoyl phosphatidylcholine (DMPC-d54) was investigated by FTIR spectroscopy. DHEA, as cholesterol, induces some conformational order in the liq.-cryst. phase of DMPC-d54. Attenuated total reflectance (ATR) measurements performed on oriented DMPC-d54/steroids samples have shown that in the gel phase, the acyl chains of DMPC-d54 become more normal to the bilayer surface in the presence of DHEA or cholesterol. On the other hand, DHEA-S increases the no. of gauche conformers along the hydrocarbon chains of DMPC-d54. No evidence for the presence of hydrogen bond was found between both steroids and the 13C labeled carbonyl group of hydrated DMPC.


D. Blaudez, T. Buffeteau, B. Desbat, P. Fournier, A.-M. Ritcey and M. Pézolet, 1998, Infrared Relection-Absorption Spectroscopy of Thin Organic Films on Nonmetallic Substrates: Optimal Angle of Incidence, J. Phys. Chem., 102B, 99-105.

Infrared external reflectance spectra of a Langmuir-Blodgett film of cadmium arachidate deposited on a glass substrate were recorded for s- and p-polarized radiations at different angles of incidence from 20 to 80°. The peak intensity of the asymmetric CH2 and COO- stretching bands was measured on the difference (D R) and the normalized (D R/R) spectra and compared quantitatively with that simulated using a three-phase model system consisting of air, a uniaxial film, and a semi-infinite glass substrate. The maximum intensity in the D R and D R/R spectra occurs at different angles of incidence. However, when the signal-to-noise ratio is taken into account, the optimal incident angle for both the difference and the normalized spectra is at about 75° for the p- and s-polarizations. Reflectance spectra at different angles of incidence have also been studied as a function of the orientation of the hydrocarbon tail relative to the surface normal. The results show that the accuracy of the determination of the molecular orientation is at least as good at high angles of incidence than near the Brewster angle.


T. Buffeteau and M. Pézolet, 1997, Study of the Dynamics of Photoinduced Orientation of Azopolymers by Infrared Spectroscopy, Mikrochimica Acta, 14, 395-397.

IR spectroscopy coupled with the polarization modulation technique has been used to characterize the mol. orientation in azo polymers irradiated by polarized light. The results obtained with an amorphous azo acrylic polymer contg. Disperse Red-1 side-chains reveal that this technique is highly effective to det. quant. the time dependence of the degree of orientation of several chem. groups during the orientation (laser on) and relaxation (laser off) processes


C.-P. Lafrance, J.-É. Blochet and M. Pézolet, 1997, N-Acylphophatidylethanolamines: Effect of the N-Acyl Chain Length on its Orientation, Biophys. J., 72, 2559-2568.

N-Acylphosphatidylethanolamines, or NAPEs, are found in tissues involved in degenerating processes, such as dehydrated endosperm of seeds, erythrocyte membranes, or cell injury. To det. the conformation and orientation of the acyl chains of these phospholipids, NAPEs with deuterated N-acyl chains of 6 and 16 carbon atoms were synthesized and studied by transmission and attenuated total reflectance (ATR) IR spectroscopy. For N-C16d-DPPE, the ATR measurements show that the N-acyl chain has the same orientation as the two acyl chains attached to the glycerol moiety, while the N-acyl chain of N-C6d-DPPE is randomly oriented. These results demonstrate that for N-C16d-DPPE, the N-acyl chain is embedded into the hydrophobic core of the bilayer, while for the short chain deriv. the N-acyl chain remains in the lipid headgroup region. The anal. of the carbonyl stretching band and of the amide I band suggests that, for the long N-acyl chain lipid, the ester C=O and N-H groups are linked by intermol. hydrogen bonds.


A. Nabet and M. Pézolet, 1997, Two-Dimensional FTIR Spectroscopy: A Powerful Method to Study the Secondary Structure of Proteins Using H-D Exchange, Appl. Spectrosc., 51, 466-469.

Two-dimensional IR spectroscopy has been used for the first time to study the conformation of proteins by hydrogen-deuterium exchange. To generate the two-dimensional synchronous and asynchronous maps, hydrogen-deuterium exchange of the amide protons of proteins deposited on attenuated total reflection crystals has been used as an external perturbation. Owing to the fact that the amide protons assocd. with each conformation are not exchanged at the same rate, the different conformational contributions of the amide bands could be sepd. The use of different sampling time domains turned out to be very helpful to sep. more efficiently the fast kinetics from the slower ones. The results obtained on myoglobin show that this method is particularly useful to unravel the different components under the poorly resolved amide I, II, and II' bands of proteins. The anal. of the synchronous and asynchronous maps of myoglobin demonstrates that the amide I band of this protein is composed of at least four components that could be assigned to a-helical, intermol. b-sheet, b-turn, and random coil conformations.


T. Buffeteau, A. Natansohn, P. Rochon and M. Pézolet, 1996, Study of Cooperative Side Group Motions in Amorphous Polymers by Time Dependent Infrared Spectroscopy, Macromolecules, 29, 8783-8790.

Amorphous copolymers of 4 prime -[(2-(methacryloyloxy)ethyl)ethylammino]-4-nitroazob enzene (DR1M) and 4-nitrophenyl-4-[2-(methacryloyloxy)ethyl]benzoate (BEM) have been studied by time dependent polarization modulation infrared spectroscopy. Bands due to several chemical groups of the copolymers have been analyzed in order to follow simultaneously the time dependence of the photoactive (DR1M) and inert (BEM) groups during the orientation (linearly polarized laser on) and relaxation (laser off) periods. The results show clearly the cooperative orientation of the BEM groups with the azobenzene side chains. The level of orientation and the rate constants of the two types of structural units have been determined for different copolymer compositions by fitting the orientation and relaxation curves with biexponential functions. The fast `writing' rate constant of DR1M increases linearly with the DR1M content while the slow `writing' rate constant is almost constant. The orientation kinetic of BEM groups is rather described by a monoexponential function and is mainly governed by that of photoactive side chains at high DR1M content. During the relaxation process, the fast and slow rate constants of DR1M groups are fairly constant over the whole range of copolymer composition while the degree of orientation of BEM groups is almost completely maintained.


M. Méthot, F. Boucher, C. Salesse, M. Subirade and M. Pézolet, 1996, Determination of Bacteriorhodopsin Orientation in Monolayers by Infrared Spectroscopy, Thin Solid Films, 285, 627-630.

In the present study, Fourier transform infrared-attenuated total reflection spectroscopy has been used to characterize Langmuir-Blodgett films of purple membranes deposited on Ge crystals at different surface pressures. The results obtained indicate that the average angle of the protein's a -helices with respect to the interface normal remains unchanged with increasing lateral pressure. Moreover, the total absorbance of the films as a function of molecular area suggests that a multilayer structure is formed between 40 and 46 mN m-1.


M. Subirade, D. Marion and M. Pézolet, 1996, Comparative Study of the Interaction of Two Lipid Binding Proteins with Membrane Lipids: Monolayer and Infrared Spectroscopy Study, Thin Solid Films, 285, 326-329.


T. Le Bihan, J.-É. Blochet, A. Désormeaux, D. Marion and M. Pézolet, 1996, Determination of the Secondary Structure and Conformation of Puroindolines by Infrared and Raman Spectroscopy, Biochemistry, 35, 12712-12722.

The conformation of puroindoline-a and -b, two basic lipid-binding proteins isolated from wheat seedlings, has been studied for the first time by IR and Raman spectroscopy. The IR results show that puroindoline-a and -b have similar secondary structure composed of approx. 30% a-helixes, 30% b-sheets, and 40% unordered structure at pH 7. The conformation of both puroindolines is significantly pH-dependent. The redn. of the disulfide bridges leads to a decrease of the soly. of puroindolines in water and to an increase of the b-sheet content by about 15% at the expense of the a-helix content. Raman spectroscopy confirms the structure similarity between the two puroindolines with little differences in the side chains' environment. All the disulfide bridges are in a gauche-gauche-gauche conformation, and the unique tyrosine residue present in both puroindolines is hydrogen-bonded to water. Raman spectra have been recorded in both H2O and D2O media, thus providing addnl. information concerning the accessibility of certain residues to water. We have also obsd. that puroindoline-a tends to form some aggregates under acidic and high ionic strength conditions. Near-UV CD measurements suggest that the tryptophan-rich domain is involved in this aggregate formation. Finally, on the basis of a combined IR and sequence conformational anal., we propose a secondary structure assignment for both puroindolines. The results show that puroindolines exhibit a similar folding pattern with plant nonspecific lipid-transfer protein and some amylase-protease inhibitors. These proteins could form a homogeneous structural family of plant proteins involved in the defense against pathogens that are probably derived from a common "helicoidal" protein ancestor.


T. Buffeteau and M. Pézolet, 1996, In Situ Study of Photoinduced Orientation in Azopolymers by Time Dependent Polarization Modulation Infrared Spectroscopy, Appl. Spectrosc., 50, 948-955.

Infrared spectroscopy has been coupled with the polarization modulation technique in order to characterize the molecular orientation in films of azopolymers irradiated in situ with polarized visible light. The results obtained on disperse red 1-containing amorphous azopolymer (pDR1A) demonstrate the high efficiency of polarization modulation infrared linear dichroism to determine quantitatively the time dependence of the orientation function of several chemical groups during the orientation (laser on) and relaxation (laser off) processes. The difference dichroic spectra show that polarized visible light induces a preferential orientation of the azobenzene groups perpendicular to the direction of the polarization of the writing laser. This orientation of the side chains also results in a slight cooperative orientation of the C = O ester groups of the main chain of the polymer. The time dependence of the orientation function shows that the orientation and relaxation processes could be described by a biexponential function involving `fast' and `slow' response modes. The rate constants associated with these modes are the same for the main chain and the side chains of the polymer. Finally, we have observed that the level of orientation and the rate constants of the orientation and relaxation processes depend strongly on the film thickness.


A. Nabet, J.M. Boggs and M. Pézolet, 1996, Study by Infrared Spectroscopy of the Interdigitation of C26:0 Cerebroside Sulfate into Phosphatidylcholine Bilayers, Biochemistry, 35, 6674-6683.

The insertion mode of the long fatty acid chain of the asym. glycosphingolipid C26:0-cerebroside sulfate (C26-CBS) in sym. matrixes of phosphatidylcholines of different acyl chain length has been investigated by transmission and attenuated total reflectance (ATR) IR spectroscopy. The concn. of C26-CBS in myelin is increased in the demyelinating disease adrenoleukodystrophy. The conformational order and the orientation of the chains of the asym. glycosphingolipid have been evaluated for C26-CBS incorporated at 8 mol % in perdeuterated dimyristoylphosphatidylcholine (DMPC-d54) and perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62). The results, for the gel phase, are consistent with interdigitation of the C26-CBS long acyl chain across the bilayer center of an all-trans-DMPC bilayer in which DMPC is less tilted than in the absence of CBS. In contrast, in DPPC the results suggest that although the CBS long chain interdigitates across the center of the bilayer, it does not change the tilt angle of the DPPC mols. in the gel phase. Furthermore, in DPPC, C26-CBS is less well oriented than the host DPPC mols. and it increases the gauche content of the DPPC acyl chains. The observation of the amide spectral region indicates that exposure of the sphingosine amide moiety to buffer is greater in the longer chain length DPPC bilayer than in the shorter chain length DMPC bilayer. The thermotropic behavior of the lipid mixts. of C26-CBS at 8 mol % in DMPC or DPPC shows that the glycosphingolipid stabilizes the gel phase of the short chain length bilayer while it destabilizes the long chain length one. Our results further demonstrate that, at this concn., C26-CBS is completely miscible in DMPC and DPPC in the gel and the liq. cryst. phases. The difference in behavior of C26-CBS in DMPC and DPPC is a consequence of the greater mismatch between the C26 chain length and the bilayer thickness of DPPC relative to DMPC. They may help to understand the deleterious effects of glycosphingolipids with very long chain fatty acids in adrenoleukodystrophy.


F. Picard, M. Pézolet, P.E. Bougis and M. Auger, 1996, Model of Interaction Between a Cardiotoxin and Dimyristoylphosphatidic Acid Bilayers Determined by Solid State 31P NMR Spectroscopy, Biophys. J., 70, 1737-1744.

The interaction of cardiotoxin IIa, a small basic protein extd. from Naja mossambica mossambica venom, with dimyristoylphosphatidic acid (DMPA) membranes has been investigated by solid-state 31P NMR spectroscopy. Both the spectral lineshapes and transverse relaxation time values have been measured as a function of temp. for different lipid-to-protein molar ratios. The results indicate that the interaction of cardiotoxin with DMPA gives rise to the complete disappearance of the bilayer structure at a lipid-to-protein molar ratio of 5:1. However, a coexistence of the lamellar and isotropic phases is obsd. at higher lipid contents. In addn., the no. of phospholipids interacting with cardiotoxin increases from about 5 at room temp. to approx. 15 at temps. above the phase transition of the pure lipid. The isotropic structure appears to be a hydrophobic complex similar to an inverted micellar phase that can be extd. by a hydrophobic solvent. At a lipid-to-protein molar ratio of 40:1, the isotropic structure disappears at high temp. to give rise to a second anisotropic phase, which is most likely assocd. with the incorporation of the hydrophobic complex inside the bilayer.


M.C. Godet, M. Pézolet, V. Tran, P. Colonna and A Buléon, 1995, Inclusion/Exclusion of Fatty Acids in Amylose Complexes as a Function of the Fattty Acid Chain Length, Int. J. Biol. Macromol., 17, 405-408.

Structural models are proposed for amylose-fatty acid complexes depending on the resp. chain lengths of their constituents. The three studied fatty acids induce the Vh amylose cryst. type. However, in contrast to lauric and palmitic acids, caprylic acid is not present in crystals. On the basis of the relative amts. of amylose and fatty acid detd. in coplexes and previous results of mol. modeling, inclusion of lauric and palmitic acids inside the amylose helixes is proposed; the acyl chains are included in cryst. areas and the caroboxylic groups in amorphous areas. The absence of caprylic acid in crystals could be due to the soly. of this compd. in the crystn. medium.


M. Subirade, C. Salesse, D. Marion and M. Pézolet, 1995, Interaction of a Nonspecific Wheat Phospholipid Transfer Protein wih Lipid Monolayers Imaged by Fluorescence Microscopy and Studied by Infrared Spectroscopy, Biophys. J., 69, 974-988.

The interaction of a nonspecific wheat lipid transfer protein (LTP) with phospholipids has been studied using the monolayer technique as a simplified model of biol. membranes. The mol. organization of the LTP-phospholipid monolayer has been detd. by using polarized attenuated total internal reflectance IR spectroscopy, and detailed information on the microstructure of the mixed films has been investigated by using epifluorescence microscopy. The results show that the incorporation of wheat LTP within the lipid monolayers is surface-pressure dependent. When LTP is injected into the subphase under a dipalmytoylphosphatidylglycerol monolayer at low surface pressure (<20 mN/m), insertion of the protein within the lipid monolayer leads to an expansion of dipalmytoylphosphatidylglycerol surface area. This incorporation leads to a decrease in the conformational order of the lipid acyl chains and results in an increase in the size of the solid lipid domains, suggesting that LTP penetrates both expanded and solid domains. By contrast, when the protein is injected under the lipid at high surface pressure (³20 mN/m), the presence of LTP leads neither to an increase of mol. area nor to a change of the lipid order, even though some protein mols. are bound to the surface of the monolayer, which leads to an increase of the exposure of the lipid ester groups to the aq. environment. The conformation of LTP, as well as the orientation of a-helixes, is surface-pressure dependent. At low surface pressure, the a-helixes inserted into the monolayers are rather parallel to the monolayer plane. In contrast, at high surface pressure, the a-helixes bound to the surface of the monolayers are neither parallel nor perpendicular to the interface but in an oblique orientation.


C.-P. Lafrance, A. Nabet, R.E. Prud'homme and M. Pézolet, 1995, On the Relationship between the Order Parameter <P2(cosq )> and the Shape of the Orientation Distributions, Can. J. Chem., 73, 1497-1505.

The mol. orientation is generally expressed by an order parameter, WP2V, which depends on both the angular position and the shape of the orientation distribution. This parameter is an av. made over all orientations of the structural units studied in a sample and, consequently, a given <P2> value can correspond to different orientation distributions. In this article, model distributions are used to show the relationship between the shape, width, and angular position of the center of the orientation distribution on the <P2> coeff., for the case where the distribution of the mol. chains exhibits cylindrical symmetry with respect to the ref. direction. A significant difference is obsd. between the order parameters calcd. for distributions of Gaussian and Lorentzian shapes with similar width at half-height. The variation of the <P2> coeff. as a function of the width at half-height, W1/2, and of the position of the center of the distribution, qC, is analyzed. Figures showing the range of W1/2-qC coordinates that can correspond to a given  <P2> value are presented. As an example, the influence on the order parameter of the disorder between the different domains of phospholipid samples (mosaic spread) and of the conformational disorder in the acyl chains of these mols. is also studied. This example permits the evaluation of the magnitude of the errors that can be introduced in calcns. of the tilt angle of the mol. chains in the case of distributions of finite widths or of bimodal character.


R. Savoie, M. Pézolet, S. Dallaire and C. Simard, 1995, Raman Spectrometer Modification for CCD Multichannel Detection, Can. J. Appl. Spectrosc., 39, 164-173.

The various steps needed for the addn. of a CCD multichannel detector to a com. Raman spectrometer are described. Options in the choice of the components required by this transformation are presented, and the necessary corrections needed to transform raw spectra obtained in this manner into a more conventional format are discussed. The advantages and limitations of this type of detection are evaluated by comparison with the conventional dispersive method of data recording using a photomultiplier detection system.


A. Nabet, J.M. Boggs and M. Pézolet, 1994, Study by FTIR Spectroscopy of the Interaction of Bovine Myelin Basic Protein with Phosphatidic Acid, Biochemistry, 33, 14792-14799.

The effect of bovine myelin basic protein (MBP) on dimyristoylphosphatidic acid (DMPA) and phosphatidic acid prepd. from egg yolk phosphatidylcholine (EPA) has been investigated by transmission and attenuated total reflectance (ATR) Fourier transform IR spectroscopy. Interaction of MBP with DMPA and EPA dispersions decreases the lipid acyl chain conformational disorder as a consequence of hydrophobic interactions of the protein with the lipids. Since these effects are more important for EPA dispersions than for DMPA, MBP is believed to penetrate more into EPA bilayers. This could be due to the fact that the hydrogen bond network formed by the charged polar headgroups of EPA is weaker than that of DMPA. This is supported by the spectra of the phosphate region showing that the phosphate groups of EPA are less hydrogen bonded than DMPA. In the presence of MBP, the hydrogen bond network is replaced by electrostatic interactions of the protein with the polar headgroups of the lipid. IR spectra of the polar headgroup region also show evidence that MBP enhanced the second ionization state of the phosphate group at neutral pH, this effect being more important for EPA than for DMPA bilayers. Also, IR spectra of the lipid carbonyl stretching region show evidence that MBP limits the accessibility of water mols. to the interfacial part of the lipid bilayer. Finally, ATR measurements on oriented films of lipid/protein complexes indicate that the penetration of the protein into the lipid bilayer is followed by a reorientation of the lipid acyl chains toward the normal to the bilayer in the case of EPA. Assuming a narrow distribution of conformation, the authors calcd. that the mean angle of the C:O amide bonds of the protein with regard to the bilayer normal is around 65°. Since the conformation of MBP is rather complex and composed of several secondary structure elements, it is difficult to assoc. this angle with an overall orientation of the protein.


Y. Popineau, S. Bonenfant, M. Cornec and M. Pézolet, 1994, A Study by Infrared Spectroscopy of the Conformation of Gluten Proteins Differing in their Gliadin and Glutenin Compositions, J. Cereal Sci., 20, 15-20.

The conformations of gluten proteins extd. from three near-isogenic lines of the wheat cultivar Sicco, which differed in their high Mr glutenin subunit compns., were studied by IR spectroscopy. Whole gluten and gluten fractions prepd. by sequential extn. were analyzed in soln. and in the doughly hydrated state by transmission and attenuated total reflectance spectroscopy, resp. In the hydrated viscoelastic state, the b-sheet content, esp. that of intermol. b-sheet conformation, of gluten proteins was higher than that in soln. In viscoelastic gluten fractions, the proportion of intermol. b-sheet increased as the glutenin content increased. In addn., the a-helix content was lowest and the intermol. b-sheet content highest when disulfide bonds were reduced in the hydrated state because interactions between gluten polypeptides can be maximized under these conditions. These results suggest that the interactions between subunits in glutenin polymers and aggregates involve intermol. b-sheets located in their repetitive domains or in the region of chain entanglements that are responsible for the viscoelastic properties of gluten proteins.


Z. Zhang, M. King, R. Guidoin, M. Therrien, M. Pézolet, A. Adnot, P. Ukpabi and M.H. Vantal, 1994, Morphological, Physical and Chemical Evaluation of the Vascugraft® Arterial Prosthesis: Comparison of a Novel Polyurethane Device with other Microporous Structures, Biomaterials, 15, 483-501.

In this study the morphology, physical properties, surface chemical characteristics and microstructure of the Vascugraft® arterial prosthesis have been investigated. This is a novel microporous polyurethane device, recently developed by the company Braun-Melsungen AG in Germany for use as a small calibre arterial substitute. This comparative study included two other synthetic grafts: the Mitrathane® prosthesis, a hydrophilic prototype polyetherurethane urea graft with closed internal pores, and the commercially successful expanded polytetrafluoroethylene reinforced Goretex® prosthesis with an open microporous structure. The Vascugraft® prosthesis contains a network of fused microfibres of varying thickness and orientation which provide open and communicating pores similar in size to those in the Goretex® material. In addition, they extend from one side of the graft wall to the other. As well as having superior longitudinal and radial compliance to the reinforced Goretex® device, the Vascugraft® prosthesis has more than adequate bursting and suture retention strengths. Through the use of contact angle measurements, electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and molecular weight analysis by size exclusion chromatography, the surface of the Vascugraft® prosthesis has been shown to be uniquely hydrophobic, as well as containing carbonate groups within an aliphatic polyesterurethane polymer. In addition, variations in micro-phase separation structure of hard and soft segment domains between different sizes and batches of product are marginal. Because of the interesting physical and chemical properties, it is recommended that in vitro biocompatibility and biostability studies be undertaken prior to using the prosthesis in animal or clinical trials.


D. Blaudez, T. Buffeteau, J.C. Cornut, B. Desbat, N. Escafre, M. Pézolet and J.M. Turlet, 1994, Polarization Modulation FTIR Spectroscopy at the Air-Water Interface, Thin Solid Films, 242, 146-150.

Mid-infrared spectra of monolayers spread at the air-water interface have been obtained, completely devoid of strong water vapor absorptions, using polarization modulation infrared reflexion absorption spectroscopy (PM-IRRAS). On normalized difference (covered vs. uncovered water) PM-IRRAS spectra, the monolayer absorption bands appear upwards or downwards depending on the orientation of their transition moment with respect to the water surface. Vibrational modes of the water subphase contribute to these difference spectra as broad dips. Study of a monolayer of cadmium arachidate has allowed observation of the vibrational modes of the polar heads and provides some evidence of their symmetrical anchoring at the water surface. Under surface compression, a monolayer of deuterated arachidic acid undergoes a molecular reorganization leading to a better ordering of the deuterated chains.


A. Natansohn, P. Rochon, M. Pézolet, P. Audet, D. Brown and S. To, 1994, Azo Polymers for Reversible Optical Storage. 4. Cooperative Motion of Rigid Groups in Semicrystalline Polymers, Macromolecules, 27, 2580-2585.

Polarized light induces a preferred orientation of azobenzene groups through photochemical trans-cis-trans processes. Stronger orientation tendencies exist if the azo-containing polymers are crystalline or liquid crystalline and the cooperative reorientation of nonactive mesogens of similar shape has been demonstrated. This paper shows that cooperative reorientation is a more general phenomenon and can take place even for a nonactive rigid group of a different shape which is bonded in the main chain while the azobenzene groups are in the side chains. Comparison is made between a disperse red 1-containing amorphous azo polymer (pDR1A) and a disperse red 19-containing semicrystalline azo polymer (pDR19T) with phenylene diacrylate (PD) groups within the main chain. Dichroic ratios are obtained from infrared and electronic spectra and are correlated with a writing/erasing/rewriting sequence performed with an argon laser. A maximum birefringence of 0.08 can be obtained on pDR1A, while on pDR19T the birefringence is 0.27 in similar conditions. This is the result of a combination of the semicrystallinity of pDR19T and of the cooperative orientation of PD groups along with the azobenzene groups. The drawback in terms of optical storage is the longer time required to write or erase the induced birefringence in pDR19T.


M. Subirade, J. Gueguen and M. Pézolet, 1994, Conformational Changes upon Dissociation of a Globular Protein from Pea Characterized by Fourier Transform Infrared Spectroscopy, Biochim. Biophys. Acta, 1205, 239-247.

Fourier transform IR spectroscopy shows that the secondary structure of legumin, a globular protein from pea seeds, is composed of 41% b-sheets and 16% a-helixes and furthermore reveals the presence of b-turns. The conformation prediction from the anal. of the amino acid sequence of legumin using hydrophobic cluster anal. reveals that the C-terminal part of the a-polypeptide is devoid of defined secondary structures, whereas the b-polypeptide is highly ordered. Comparison with analogous 11S globulins from other plant families indicates that ordered domains are highly preserved, phenomenon that may be assocd. with the similarity of the quaternary structure of these proteins. The results also reveal the presence of a large hypervariable region, located at the surface of the protein, that could be at the origin of the different functional properties of the 11S type globulins. The step-by-step destruction of the quaternary oligomeric structure of the native protein is accompanied by conformational changes that depend on the dissocn. conditions. Whereas acylation leads to a decrease of the a-helix content by 10% at the expense of the b-sheet content, addn. of sodium perchlorate results in the conversion of 10% of the protein secondary structure from b-sheet to unordered. These observations provide further evidence of the existence of different monomeric states that differ from their secondary structure and, therefore, exhibit different surface-active properties.


C.-P. Lafrance, P. Chabot, M. Pigeon, R.E. Prud'homme and M. Pézolet, 1993, Study of the Distribution of Molecular Orientation in Thick Polyethylene Samples by X-Ray Diffraction and Infrared and Raman Spectroscopy , Polymer, 34, 5029-5037.

The molecular orientation in thick polyethylene samples has been studied by wide-angle X-ray diffraction, i.r. dichroism and Raman spectroscopy. The original specimens, with dimensions of the order of a centimetre, were cut to obtain 1 mm thick platelets on which the measurements were made. The mean coefficient of the second-order Legendre polynomial, <P2>, was calculated from X-ray diffraction and from the 1894 cm-1 i.r. band for the crystalline phase, from the 909 cm-1 i.r. band for the vinyl end groups and from the 1130 and 1060 cm-1 Raman bands for the all-trans C-C conformers. The fourth-order coefficient, <P2>, was also determined from X-ray diffraction and Raman spectroscopy for a series of cylindrical rods of draw ratios l ranging from 6 to 20. An excellent correlation is observed between the <P2> coefficients measured from different X-ray reflections and from the 1894 cm-1 i.r. band. The Raman spectroscopy results show that the all-trans bonds located in the amorphous phase are aligned perpendicular to the extrusion direction for the l = 6 rod, and gradually reorient towards the fibre axis for &lambda; values up to 20, while <P2> and <P4> coefficients calculated for the crystalline phase remain constant at l = 12. The variation of the orientation through the thickness of the samples was investigated for the cylindrical rods and for an H-shaped moulding produced by extrusion and rolling. Minor differences in the degree of molecular orientation were detected between the centre and the surface of the rods, whereas important variations were measured for the H-shaped sample.


J. Liu, S.-X. Lin, A. Brisson, J.-É. Blochet, M. Pézolet and J. Lapointe, 1993, The Glutamyl-tRNA Synthetase of Escherichia Coli Contains One Atom of Zinc Essential for its Native Conformation and its Catalytic Activity, Biochemistry, 32, 11390-11396.


D. Blaudez, T. Buffeteau, J.-C. Cornut, B. Desbat, N. Escafre, M. Pézolet and J.-M. Turlet, 1993, Polarization Modulation FTIR Spectroscopy of a Spread Monolayer at the Air-Water Interface, Appl. Spectrosc., 47, 869-874.

This study devoted to FTIR spectroscopy of monolayers spread at the air/water interface is, to our knowledge, the first one presenting complete mid-infrared monolayer spectra devoid of strong water vapor absorptions. This has been possible by using the PM-IRRAS method combining polarization modulation with two channel simultaneous acquisition. Due to its differential character, the detected signal is not sensitive to the isotropic absorptions of the sample environment. From theoretical simulations and experiments, the best angle of incidence was found to be near 76° for the detection of intrasurface as well as out of surface transition moments. Under these experimental conditions, the absorption bands of the monolayer appear upwards or downwards in the normalized difference (covered vs uncovered) PM-IRRAS spectra depending on the orientation (parallel or perpendicular) of their transition moments with respect to the interface.


T. Buffeteau, B. Desbat, M. Pézolet and J.-M. Turlet, 1993, Mesure de l'orientation des polymères en dichroïsme linéaire infrarouge par modulation de polarisation: procédure expérimentale et analyse quantitative, J. Chim. Phys., 90, 1467-1489.

L’analyse de l’orientation d’un polymère par mesure du dichroïsme linéaire infrarouge a été améliorée en modulant la polarisation du faisceau incident. Après avoir décrit la procédure expérimentale utilisée, nous présentons une analyse quantitative du signal détecté permettant de remonter à la différence dichroïsque de l’échantillon. L’application à l’étude de films étirés de poly(chlorure de vinyle) et de poly(méthacrylate de méthyle ) montre la grande sensibilité de cette méthode, en particulier pour de très faibles élongations de ces polymères. La précision obtenue sur l’évolution de la fonction d’orientation <P2(cosq )> permet de mettre en évidence de très faibles réarrangements des chaînes macromoléculaires.


J.-É. Blochet, C. Chevalier, É. Forest, É. Pebay-Peyroula, M.-F. Gautier, P. Joudrier, M. Pézolet and D. Marion, 1993, Complete Amino Acid Sequence of Puroindoline, a New Basic Cystine-Rich Protein with a Unique Tryptophan-Rich Domain, Isolated from Wheat Endosperm by Triton X114 Phase Partitioning, FEBS Letters, 329, 336-340.

A new basic protein has been isolated from wheat endosperm by Triton X-114 phase partitioning. It contains five disulfide bridges and is composed of equal amts. of a polypeptide chain of 115 amino acid residues and of the same chain with a C-terminus dipeptide extension. The most striking sequence feature is the presence of a unique tryptophan-rich domain so that this protein isolated from wheat seeds has been named puroindoline. The similar phase partitioning behavior in Triton X-114 of this basic cystine-rich protein and of purothionins suggests that puroindoline may also be a membranotoxin that might play a role in the defense mechanism of plants against microbial pathogens.


A. Désormeaux, G. Laroche, P.E. Bougis and M. Pézolet, 1992, Characterization by Infrared Spectroscopy of the Interaction of a Cardiotoxin with Phosphatidic Acid and with Binary Mixtures of Phosphatidic Acid and Phosphatidylcholine, Biochemistry, 31, 12173-12182.

The effect of cardiotoxin IIa from Naja mossambica mossambica, a small basic protein extd. from snake venom, on dimyristoylphosphatidic acid (DMPA) and on equimolar mixts. of DMPA and dimyristoylphosphatidylcholine (DMPA) was studied by Fourier-transform IR spectroscopy. The interaction of cardiotoxin with DMPA dispersions decreases both the cooperativity of the phase transition of the lipid and the mol. order of the lipid acyl chains in the gel phase. This effect increases with the proportion of the toxin in the complexes and leads to the total abolition of the phase transition of DMPA at a lipid-to-protein molar ratio of 5. Small-angle x-ray results demonstrate that the structure of the lipid-protein complexes is poorly ordered and gives rise to broad diffusion peaks rather than to well-resolved diffraction patterns. IR spectra of oriented cardiotoxin-DMPA films show that the protein is not homogeneously oriented with respect to the bilayer surface. The destabilization of the gel-phase structure of DMPA by cardiotoxin also results in a deeper water penetration in the interfacial region of the lipid since more carbonyl ester groups appear to be hydrogen bonded in the presence of the toxin. The IR results on the phosphate group vibrations also indicate clearly that the basic residues of cardiotoxin interact strongly with the phosphate group of DMPA that becomes partly doubly ionized at a pH as low as 6.5. The results obtained on the interaction of cardiotoxin with an equimolar mixt. of DMPA and DMPC clearly demonstrate the ability of this toxin to induce lateral phase sepn. in this mixt. with one phase contg. DMPA-rich domains perturbed by cardiotoxin while the second phase is composed of regions enriched in DMPC. Comparison of the results of the current study with those obtained on other basic proteins and polypeptides suggests that charge-induced phase sepn. occurs only when the charge d. on certain regions of the protein structure is high enough to lead to efficient electrostatic interactions with anionic phospholipids. This condition occurs only when the conformation of the protein or polypeptide is well-ordered at the lipid interface.


M. Pézolet, S. Bonenfant, F. Dousseau and Y. Popineau, 1992, Conformation of Wheat Gluten Proteins: Comparison between Functional and Solution States as Determined by Infrared Spectroscopy, FEBS Letters, 299, 247-250.

The conformation of wheat gluten proteins in their functional hydrated solid state (doughy state) has been studied for the first time using attenuated total reflection IR spectroscopy. The amide I band of functional gluten proteins reveals that, in addn. to b-turns and a-helixes, these proteins contain a significant amt. of intra- and intermol. extended b-sheet structures. It appears that the solubilization of gluten proteins results in a major decrease of the amt. of b-sheet structures accompanied by an increase of the content of the b-turn and a-helical conformations. In addn., the a-helixes appears to be more distorted in soln. than in the functional state. Furthermore, spectra of w- and g-gliadins, which are two types of prolamins of differing amino acids sequence and conformation, confirm the results obtained on the functional protein system. These results suggest that viscoelastic gluten proteins may interact through aligned b-sheets corresponding to their repetitive domains.


A. Désormeaux, J.-E. Blochet, M. Pézolet and D. Marion, 1992, Amino Acid Sequence of a Non-Specific Wheat Phospholipid Transfer Protein and its Conformation as revealed by Infrared and Raman Spectroscopy . Role of Disulfide Bridges and Phospholipids in the Stabilization of the Helix Structure, Biochim. Biophys. Acta, 1121, 137-152.

A wheat nonspecific phospholipid transfer protein has been isolated from wheat seeds and its amino acid sequence reveals that it is composed of 90 residues for a mol. wt. of 9607. From the comparison of its sequence with those of the eight known proteins of the same family, hypotheses on the role of some conserved residues in the transfer activity can be made. The conformation of this protein has been studied by Raman and Fourier transform IR spectroscopy and this is the first report on the structure of non specific plant phospholipid transfer proteins. As opposed to previous studies on the structure prediction from the amino acid sequence, the results obtained show that plant non specific phospholipid transfer proteins are not almost entirely composed of b-sheets. Instead, IR results show that the wheat protein contains 41% a-helix and 19% b-sheet structures, while 40% of the conformation is undefined or composed of turns. Raman spectroscopy shows that three disulfide bridges adopt a gauche-gauche-gauche conformation while the other exhibits a gauche-gauche-trans conformation, and that the two tyrosine residues are hydrogen bonded to water mols. The cleavage of the disulfide bonds affects significantly the conformation of the protein, the extended conformation being increased by 15% at the expense of the a-helix content. On the other hand, the binding of 1-palmitoyllysophosphatidylcholine to the protein leads to an increase of 8% of the a-helix content compared to the free protein. Secondary structure predictions from the amino acid sequence suggest that the binding of a phospholipid stabilizes helicity of the amphipathic helices while the redn. of disulfide bonds would affect the stability of the N-terminal helix. The extended structure located at the C-terminus is not affected. Finally, the wheat phospholipid transfer protein has no effect on the thermotropic behavior of large unilamellar vesicles of dimyristoylphosphatidylcholine while it increases the conformational order of the acyl chains of large unilamellar vesicles of dimyristoylphosphatidylglycerol in the liq.-cryst. state. No major conformational changes of the protein are obsd. when it is adsorbed to phospholipid vesicles. These results suggest that the helical structure is essential for the transfer activity without excluding a possible role of the C-terminal extended structure on the adsorption to phospholid vesicles.


M. Pigeon, R.E. Prud'homme and M. Pézolet, 1991, Characterization of Molecular Orientation in Polyethylene by Raman Spectroscopy, Macromolecules, 24, 5687-5694.

The polarization dependences of several Raman bands of roll-drawn high-density polyethylene of uniaxial symmetry were investigated at different draw ratios between 7.0 and 11.7. When the right-angle scattering geometry was used, it was possible to determine quantitatively the principal components of the Raman tensors of the 1080, 1130, and 1170-1 vibrations. The orientation coefficients <P2(cos q )> and <P4(cos q )> of the C-C bonds with trans conformation and gauche defects were also calculated by using these bands. The results obtained from the 1080cm-1 band show that the orientation of gauche structures does not vary much with the draw ratio (between 7.0 and 11.7). On the other hand, the polarization behavior of the 1130-cm-1 band indicates that trans conformers in the amorphous phase orient more readily in the draw direction. When the components of the Raman tensors obtained from right-angle scattering were used, it was found that backscattering measurements could yield good estimates of <P2(cos q)> and <P4(cos q )> orientation averages. Finally, a method is proposed for the rapid evaluation of these parameters from calibration curves obtained from backscattering spectra measured with the polarization direction of both the incident and scattered light parallel to the draw direction. This method should be particularly useful for the determination of the distribution of the orientation of trans bonds in thick processed samples of polyethylene.


M. Lafleur, I. Samson and M. Pézolet, 1991, Investigation of the Interaction between Melittin and Dipalmitoylphosphatidylglycerol Bilayers by Vibrational Spectroscopy, Chem. Phys. Lipids, 59, 233-244.

Melittin is shown to affect the structure of the charged phospholipid dipalmitoylphsophatidylglycerol (DPPG). In the gel phase, the presence of melittin leads to (i) an increased lipid interchain vibrational coupling, (ii) a shift of the rectangular to hexagonal lipid packing transition toward low temps., (iii) a very small conformational disordering effect, (iv) a decrease of the polarity or hydrogen bonding capability of the lipid ester group surrounding, (v) an important decrease of the water content in the complexes where the remaining water has a more disordered structure than bulk water, and (vi) an interlamellar repeat distance of 79 Å. All these observations are rationalized by the following model: adjacent bilayers of DPPG are bridged by tetramers of melittin through electrostatic interactions inducing surface charge neutralization and partial dehydration of the complexes. Melittin also affects the thermotropic behavior of DPPG. When a small amt. of the toxin is present, its affinity for charged lipids is such that a phase sepn. occurs, the domains being stable enough to have their own gel to liq.-cryst. phase transition. In the fluid state, a deeper penetration into the lipid matrix is proposed based on the downshift of the phase transition and the low vibrational interchain coupling. This study brings out general features of cationic species/anionic lipid complexes. The charge neutralization leads to stronger interchain coupling, and electrostatic bridging of adjacent bilayers seems to be common. The hydrophobicity of the peptide is a key factor in the modulation of the gel to liq.-cryst. phase transition and in its insertion in the fluid lipid matrix.


C.-P. Lafrance, M. Pézolet and R.E. Prud'homme, 1991, Study of the Distribution of Molecular Orientation in Highly Oriented Polyethylene by X-Ray Diffraction, Macromolecules, 24, 4948-4956.

High-density polyethylene (HDPE) cylindrical rods produced by ram extrusion were studied by wide-angle X-ray diffraction. Even order <P2(cosq)> coefficients of the Legendre polynomial series describing the orientation distribution of the 110, 200, 020, 011, 211, and 002 crystal planes were calculated from the X-ray data for n up to 32. It is shown that high order <P2(cosq)> values can be used to characterize the evolution of the orientation at high draw ratios, whereas the commonly used 'orientation function', <P2(cosq)>, reaches a constant value close to unity at draw ratios over approximately 12. The <P2(cosq)>c values describing the c axis or molecular orientation distribution were computed from the different planes: the correlation between the coefficients thus calculated is excellent. It is concluded that the molecular orientation may be calculated from any arbitrary reflection for uniaxially oriented samples. Finally, the average <P2(cosq)>c coefficients are used to compare the experimental distributions with those calculated from the pseudoaffine deformation model and from Gaussian, Lorentzian, and 'most probable' distribution functions.


G. Laroche, E.J. Dufourc, J. Dufourcq and M. Pézolet, 1991, Structure and Dynamics of Dimyristoylphosphatidic Acid-Calcium Complexes by 2H-NMR, Infrared and Raman Spectroscopy, and Small Angle X-Ray Diffraction, Biochemistry, 30, 3105-3114.

The structural and dynamic properties of complexes of dimyristoylphosphatidic acid (DMPA) and Ca ions have been characterized by 2H NMR, Raman, and IR spectroscopies and small-angle x-ray diffraction. All techniques used show that these complexes do not undergo a cooperative thermotropic phase transition. Small-angle x-ray diffraction unambiguously demonstrates that the structure of the lipid mols. of the DMPA/Ca2+ complexes remains lamellar even at a temp. as high as 85°. Raman results indicate that within this temp. range, only a few trans-gauche isomerizations of the C-C bonds of the phospholipid acyl chains arise in this system. The 2H NMR spectra indicate that the DMPA chains are highly motionally restricted up to 65° and that higher temps. might acivate some low-frequency overall motions of entire lamellar domains. Small-angle x-ray scattering and 2H NMR spectroscopy of 2H2O also show that the interaction of Ca with DMPA promotes an important dehydration of the lipid assembly, even though the latter technique clearly demonstrates that some water mols. remain strongly bond in the DMPA/Ca2+ complexes. The carbonyl stretching mode region of the IR spectrum of DMPA/Ca2 complexes suggests that these water mols. are trapped near the interfacial region of the lipid membrane and are hydrogen bonded with the carbonyl groups of the lipid. Finally, comparison of the phosphate stretching mode region of the IR spectra of complexes of DMPA with Ca ions with those of model compds. provides strong evidence that Ca ions bind to both charges of the phosphate group of DMPA and form bridges between adjacent bilayers.


F. Dousseau and M. Pézolet, 1990, Determination of the Secondary Structure of Proteins in Aqueous Solution from the Amide I and II Infrared Bands. Comparison between Classical and Partial Least Squares Methods, Biochemistry, 29, 8771-8779.

A method for estg. protein secondary structure from IR spectra has been developed. The IR spectra of H2O solns. of 13 proteins of known crystal structure have been recorded and cor. for the spectral contribution of water in the amide I and II region by using the algorithm of F. Dousseau et al. (1989). This calibration set of proteins has been analyzed by using either a classical least-squares (CLS) method or the partial least-squares (PLS) method. The pure-structure spectra calcd. by the classical least-squares method are in good agreement with spectra of poly(L-lysine) in the a-helix, b-sheet, and undefined conformations. The results show that the best agreement between the secondary structure detd. by x-ray crystallog. and that predicted by IR spectroscopy is obtained when both the amide I and II bands are used to generate the calibration set, when the PLS method is used, and when it is assumed that the secondary structure of proteins is composed of only four types of structure: ordered and disordered a-helices, b-sheet, and undefined conformation. Attempts to include turns in the secondary structure estn. have led to a loss of accuracy. The std. deviation of the difference between x-ray and IR secondary structure ests. with this method is 4.8% for the a-helix, 3.7% for the b-sheet, and 5.1% for the undefined structure, whereas the regression coeffs. are 0.95, 0.96, and 0.56, resp. The spectra of the calibration proteins were also recorded in 2H2O soln. After correction for the contribution of the combination band of 2H2O in the amide 1' band region, the spectra were analyzed with PLS, but the results were not as good as for the spectra obtained in H2O, esp. for the a-helical conformation.


G. Laroche, E.J. Dufourc, M. Pézolet and J. Dufourcq, 1990, Coupled Changes Between Lipid Order and Polypeptide Conformation at the Membrane Surface. A 2H-NMR and Raman Study of Polylysine-Phosphatidic Acid Systems, Biochemistry, 29, 6460-6465.

Thermotropism and segmental chain order parameters of sn-2-perdeuteriated dimyristoylphosphatidic acid (DMPA)-water dispersions, with and without poly(L-lysine) (PLL) of different mol. wts. were investigated by solid-state 2H NMR spectroscopy. The segmental chain order parameter profile of this neg. charged lipid is similar to that already found for other lipids. Addn. of long PLL (MW = 200,000) increases the temp., Tc, of the lipid gel-to-fluid phase transition, whereas short PLL (MW = 4000) has practically no effect on Tc. In the fluid phase both varieties of PLL increase the plateau character of segmental order parameters up to C position 10. At a reduced temp., long PLL more significantly increases the segmental ordering, esp. at the Me terminal position. Thus, polar head-group capping and charge neutralization by PLL induce severe changes in lipid chain ordering, even down to the bilayer core. The structure of PLL bound to the lipid bilayer surface was monitored by Raman spectroscopy, following the amide I bands. Results show that the lipid gel-to-fluid phase transition triggers a conformational transition from ordered b-sheet to random structure of short PLL, whereas it does not affect the strongly stabilized b-sheet structure of long PLL. It is concluded that both short and long PLL can efficiently cap and neutralize lipid head groups, whatever their structure, and that peptide length is a key parameter in whether lipids or peptides are the driving force in conformationally coupled changes of both partners in the membrane.


D. Lafrance, D. Marion and M. Pézolet, 1990, Study of the Structure of N-acyl Dipalmitoylphosphatidylethanolamines in Aqueous Dispersion by Infrared and Raman Spectroscopies, Biochemistry, 29, 4592-4599.

The effect of the headgroup chain length on the structure and on the thermotropic behavior of N-acyldipalmitoylphosphatidylethanolamines (N-acyl-DPPEs) was studied by IR and Raman spectroscopies. The N-acyl-DPPEs can be divided in 2 classes depending on the N-acyl chain length. When the N-acyl chain contains ³10 C atoms, DPPE penetrates into the bilayer, whereas it remains at the level of the glycerol backbone for shorter N-acyl chains. For both classes of N-acyl-DPPEs, the rotation of the lipid chains in the liq.-cryst. phase is hindered by the presence of the N-acyl group. In addn., the disruption of the H bonds between the amino and phosphate groups by the N-acylation of the amino group results in an increase of the hydration of the phosphate group compared to that in DPPE. The hydration occurred at both the phosphate and amide group levels: the phosphate group is more hydrated for phospholipids with long N-acyl chains whereas in the case of short-chain derivs. both the phosphate and amide groups are hydrated. This higher degree of hydration coupled with the immobilization of the lipid mol. may contribute to the bilayer stabilizer role of N-acyl-PEs, since hydration is an important factor in bilayer stability.


P. Chabot, R.E. Prud'homme and M. Pézolet, 1990, Study of Segmental Orientation in Poly(vinyl chloride)/Poly(methyl- n-propyl-propiolactone) Blends by Fourier-Transform Infrared Spectroscopy, J. Polym. Sci., Polym. Phys. Ed., 28, 1283-1296.

Fourier-transform infrared (FTIR) spectroscopy has been used to investigate the segmental orientation of poly(vinyl chloride) (PVC)/poly(a -methyl-a -n-propyl-b -propiolactone (PMPPL) blends in uniaxially stretched samples over a wide range of compositions and draw ratios. The results indicate that for pure PVC, syndiotactic segments reach a higher degree of orientation than isotactic segments and gauche conformations. Similarly, for pure PMPPL, crystalline segments orient more than amorphous segments at any given elongation. Thus, for both polymers, the higher orientation is obtained for the more rigid segments or those located in a more rigid (crystalline) phase.


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