Chain Stretch Research Articles

A New Technique to Study Kinetics of Chain Conformation in Polyaniline Films

Conducting polymers are well known to expand/contract upon electrochemical oxidation/reduction. Such dimensional changes induced by an electrochemical stimulus originate from incorporation of solvated dopant ions into the film and/ or conformational change of -conjugated polymer chains. An increasing number of studies have been devoted to the potential-induced deformations of conducting polymers in an effort to fabricate novel actuators and artificial muscles. Polyaniline (PANI) and its derivatives are a family of conducting polymers that exhibit a significant extent of deformations at low voltages. They have been intensively studied by Kaneto et al. as a key element of soft actuators. Recently, we have found a new type of a potential-induced change in film property of PANI and its derivatives, i.e., a change in the intensity of light reflected from the polymer-coated electrode with an applied potential. The change in reflection was interpreted as below. In the reduced state of the PANI film where polymer chains have a coiled structure, a light scattering or a diffuse reflection takes place in the polymer layer and thus a negligible intensity of light reaches the photodetector placed at a right position of specular reflection. By increasing the potential, polymer chains stretch and the coiled structure relaxes as has been demonstrated by MacDiarmid and Epstein. Consequently, Rayleigh or Mie scattering is attenuated in the polymer film and the incident light can go deep into the polymer layer to reach a highly reflective Pt surface. Then, specular reflection at the Pt surface occurs effectively and the reflected light gains its intensity. When the potential is raised further, the PANI film turns a blue-black color. At the higher potentials, therefore, the PANI film starts to absorb the incident 633 nm light and the intensity of light coming to the Pt surface reduces. In the present study, a new method for investigating kinetics of chain conformation for the PANI film is proposed on the basis of the in situ reflection technique. Aniline of reagent grade from Aldrich was distilled under Ar atmosphere and stored in a Schlenck tube filled with Ar gas. PANI was deposited on Pt-coated glass plates by a potential-sweep method with 1.3M aniline in 2.3M perchloric acid (HClO4). Electrode potentials were referred to Ag/AgCl/ NaCl(satd.). After polymerization by cycling the potential between 0:1 and 0.9V at 50mV s , the PANI film was rinsed thoroughly with distilled water, dried in air lightly, and transferred to a thin layer cell of Figure 1 for in situ reflection measurements. Thicknesses of PANI films were evaluated by measuring the amount of electricity during a potential-step doping in HClO4. The oxidation level was defined as the number of unit charges per aniline unit and calculated from the polymer weight, a molecular weight of an aniline unit, and the doping charge. In situ reflection technique with a He-Ne laser (633 nm) is described earlier. The optical arrangement is schematically depicted in Figure 1, where the PANI electrode is slightly tilted from the two parallel glass plates to avoid a light reflected directly at the front glass surface. A current signal of a Si photodiode was converted to a voltage using a current/voltage preamplifier and the voltage signal was fed to a lock-in amplifier. Before starting measurements, the potential of the PANI electrode was kept at a sufficiently negative potential so as to obtain a reduced form of PANI, i.e., leucoemeraldine. Just prior to the measurement, the system was switched to a galvanostatic mode and a constant anodic current was applied to the electrode. A time course of the intensity of a reflected light was measured till the electrode potential reaches 0.5V. The electrode potential was rested at 0:2V till the cathodic current density fell down to 0:2 mAcm 2 or below. Then the next current pulse was applied to the PANI electrode. Figure 2 depicts a set of light intensity vs. charge curves for a PANI film in HClO4 (pH 1) obtained in the galvanostatic Si photodiode Slit PANI/Pt/Cr/glass Electrolyte solution Silicone spacer

Application of reptation models to modeling of rheological behavior of polymer nanocomposites

Characteristic rheological behaviors of polymer nanocomposites were studied in shear flow and uniaxial elongational flow. Solid-like plateau storage modulus, strong shear thinning at low frequency regions, and strain hardening at elongational flow were observed. Especially, strain hardening was clearly observed for polymers without long chain branches if nanoparticles were homogeneously dispersed in the polymer matrix and interactions between nanoparticles and surrounding polymer molecules were sufficiently strong. Reptation models were used to model the nanoscale dynamics of nanoparticles and macromolecular chains, and the characteristic rheological behavior of nanocomposites could be explained. Brownian dynamics simulation of Doi-Edwards reptation model was applied and two particle constraint coefficients were introduced to express the influence of nanoparticles on molecular orientation and reptational diffusion of polymer chains. In the simulation, stress tensor including link tension coefficient which characterizes anisotropic friction coefficient of the molecular chain was used to obtain material functions by assuming that the anisotropy of friction was altered by the presence of nanoparticles. Additional frictional force between polymer chains and nanoparticles was considered and the suitable relaxation process and chain stretch were incorporated by considering the full chain geometry of polymer molecular chains. All the reptation models considering the effect of nanoparticles were verified by comparing the theoretical results with experimental data for polymer nanocomposites in shear and elongational flows.

Correlation between mobility enhancement and conformational change in polyaniline and its derivatives: Polaron lattice formation

Conformational changes in polyaniline, poly(methylaniline), and poly(methoxyaniline) are studied in perchloric acid and acetonitrile by means of an in situ reflection technique with oxidation level as a parameter. Stretching of polymer chains leading to enhancement of specular reflection at the polymer-coated electrodes is found to be well correlated with the increase in carrier mobility. The concomitant change in mobility and chain conformation observed with the polyaniline family is explained in terms of the formation of polaron lattice at increased oxidation levels.

Structure and Dynamics of ASC2, a Pyrin Domain-only Protein That Regulates Inflammatory Signaling

Structure and Dynamics of ASC2, a Pyrin Domain-only Protein That Regulates Inflammatory Signaling

Saturation of Shear-Induced Isothermal Crystallization of Polymers at the Steady State and the Entanglement−Disentanglement Transition

To provide insight into the formation of shear-induced precursor structures, three apparently unrelated subjects are analyzed and discussed: the saturation of crystallization from sheared polymer melts, evaluated with a new shear DTA instrument, the steady state in steady shear, and the entanglement-disentanglement transition. It is shown that the same large strains that saturate crystallization also lead to a reversible steady state in steady shear, where the viscosity of the sheared melt is constant in time, and their magnitude is only determined by the temperature of the sheared melt. Features of the melt morphology at this state are discussed, and their importance is highlighted to understand the possible mechanisms behind the formation of shear-induced precursors. Measurements of the reptation time for unsheared samples, and samples sheared up to the steady state, allowed the quantification of the entanglements loss during the transition between these two states (around 2/3), which is interpreted as an entanglement-disentanglement transition. The relevance of this result on assumptions of flow models, particularly the constant number of topological constraints, convective constraint release process, and chain stretch, is discussed.

Model of the toxic complex of anthrax: Responsive conformational changes in both the lethal factor and the protective antigen heptamer

The toxic complex of anthrax is formed when the monomeric protective antigen (PA) (83 kDa), while bound to its cell-surface receptor, is first converted to PA63 heptamers (PA63h) following N-terminal proteolytic cleavage, and then lethal (LF) (90 kDa) or edema factor (EF) binds to the heptamer. We report a "pseudoatomic" model for the complex of PA63h and full-length LF determined by applying the normal-mode flexible fitting procedure to a approximately 18 A cryo-electron microscopy (EM) density map of the complex. The model describes the interacting surface that buries a total area of approximately 10,140 A2 comprising approximately 40% charged, and approximately 30% each of polar and hydrophobic residues. For the heptamer, the buried surface, composed of approximately 110 residues, involves primarily three monomers and includes for two, similar stretches of the polypeptide chain from domain 1. For LF, the interface again involves approximately 110 residues, mostly from the N-terminal domain I (LF(N)), and the structurally homologous C-terminal domain IV. Most interestingly, bound LF displays a marked conformational change resulting from a "collapse" of domains I, III, and IV on domain II, with the largest movement of approximately 9 A noted for domain I. On the other hand, primarily, rigid-body movements, larger than approximately 10 A for three PA63 monomers, cause the hourglass-shaped heptamer lumen to enlarge by as much as approximately 50% near the middle of the molecule. Such concerted structural rearrangements in LF and the heptamer can facilitate ingress of the ligand into the heptamer lumen prior to unfolding and release through the PA63h channel formed in the acidic late endosomal membrane.

Structure and Dynamics of ASC2, a Pyrin Domain-only Protein That Regulates Inflammatory Signaling

Pyrin domain (PYD)-containing proteins are key components of pathways that regulate inflammation, apoptosis, and cytokine processing. Their importance is further evidenced by the consequences of mutations in these proteins that give rise to autoimmune and hyperinflammatory syndromes. PYDs, like other members of the death domain (DD) superfamily, are postulated to mediate homotypic interactions that assemble and regulate the activity of signaling complexes. However, PYDs are presently the least well characterized of all four DD subfamilies. Here we report the three-dimensional structure and dynamic properties of ASC2, a PYD-only protein that functions as a modulator of multidomain PYD-containing proteins involved in NF-kappaB and caspase-1 activation. ASC2 adopts a six-helix bundle structure with a prominent loop, comprising 13 amino acid residues, between helices two and three. This loop represents a divergent feature of PYDs from other domains with the DD fold. Detailed analysis of backbone 15N NMR relaxation data using both the Lipari-Szabo model-free and reduced spectral density function formalisms revealed no evidence of contiguous stretches of polypeptide chain with dramatically increased internal motion, except at the extreme N and C termini. Some mobility in the fast, picosecond to nanosecond timescale, was seen in helix 3 and the preceding alpha2-alpha3 loop, in stark contrast to the complete disorder seen in the corresponding region of the NALP1 PYD. Our results suggest that extensive conformational flexibility in helix 3 and the alpha2-alpha3 loop is not a general feature of pyrin domains. Further, a transition from complete disorder to order of the alpha2-alpha3 loop upon binding, as suggested for NALP1, is unlikely to be a common attribute of pyrin domain interactions.

PH-Responsive Nanostructures Assembled from Amphiphilic Block Copolymers

We present a novel route to assemble thin films containing pH-responsive nanostructures of hydrophilic cylindrical domains oriented perpendicular to a silicon substrate. The amphiphilic block copolymer, poly(styrene-b-acrylic acid) (PS-b-PAA), is prepared from the precursor, poly(styrene-b-tert-butyl acrylate) (PS- b-PtBA), by an autocatalytic reaction involving surface hydroxyl groups. The surface morphology and evolution of the nanostructures in aqueous solutions over a pH range of 2.6-9.1 are captured by in-situ atomic force microscopy (AFM). The ordered PS-b-PAA films exhibit unique surface morphologies across three pH regimes. At low pH (pH 6.0) PAA chains stretch strongly to cover the entire surface, leading to a continuous PAA wetting layer decorated by hexagonally packed depressions. The equilibrium film thickness increases as pH increases and is reversibly recovered upon decreasing pH. The water contact angle decreases by 30° as pH increases from 2.6 to 9.1, demonstrating that wettability can be tuned by varying the pH of the surrounding medium. Because of their pH-responsive behavior and small feature size, nanostructured devices designed from amphiphilic block copolymers have potential applications including sensors and membranes.

Myosin heavy chain isoform composition and stretch activation kinetics in single fibres of Xenopus laevis iliofibularis muscle.

Skeletal muscle is composed of specialized fibre types that enable it to fulfil complex and variable functional needs. Muscle fibres of Xenopus laevis, a frog formerly classified as a toad, were the first to be typed based on a combination of physiological, morphological, histochemical and biochemical characteristics. Currently the most widely accepted criterion for muscle fibre typing is the myosin heavy chain (MHC) isoform composition because it is assumed that variations of this protein are the most important contributors to functional diversity. Yet this criterion has not been used for classification of Xenopus fibres due to the lack of an effective protocol for MHC isoform analysis. In the present study we aimed to resolve and visualize electrophoretically the MHC isoforms expressed in the iliofibularis muscle of Xenopus laevis, to define their functional identity and to classify the fibres based on their MHC isoform composition. Using a SDS-PAGE protocol that proved successful with mammalian muscle MHC isoforms, we were able to detect five MHC isoforms in Xenopus iliofibularis muscle. The kinetics of stretch-induced force transients (stretch activation) produced by a fibre was strongly correlated with its MHC isoform content indicating that the five MHC isoforms confer different kinetics characteristics. Hybrid fibre types containing two MHC isoforms exhibited stretch activation kinetics parameters that were intermediate between those of the corresponding pure fibre types. These results clearly show that the MHC isoforms expressed in Xenopus muscle are functionally different thereby validating the idea that MHC isoform composition is the most reliable criterion for vertebrate skeletal muscle fibre type classification. Thus, our results lay the foundation for the unequivocal classification of the muscle fibres in the Xenopus iliofibularis muscle and for gaining further insights into skeletal muscle fibre diversity.

A tube-based constitutive equation for polydisperse entangled linear polymers

We present a tube-based constitutive model for polydisperse entangled linear polymers. The model is constructed as the non-linear extension of a linear model [A. Leygue, C. Bailly, R. Keunings, A differential tube-based model for predicting the linear viscoelastic moduli of polydisperse entangled linear polymers, J. Non Newton. Fluid Mech., in press] capable of predicting quantitatively the linear viscoelasticity of polydisperse linear systems. The constitutive equation accounts for the major linear and non-linear phenomena thought to be important in the description of entangled linear polymers: reptation, contour-length fluctuations, thermal constraint release, convective constraint release and chain stretch effects. In the non-linear regime convective constraint release couples the relaxation of the different masses and provides a non-linear mixing rule for the model. The predictive capabilities of the model are tested on published results for mono- and bi-disperse entangled solutions [C. Pattamaprom, R.G. Larson, Constraint release effects in monodisperse and bidisperse polystyrenes in fast transient shearing flows, Macromolecules 34 (2001) 5229–5237; X. Ye, R.G. Larson, C.J. Pattamaprom, T. Shridar, Extensional properties of monodisperse and bidisperse polystyrene solutions, J. Rheol. 47 (2) (2003) 443–468], both in shear and extension.

Specific Interactions versus Counterion Condensation. 2. Theoretical Treatment within the Counterion Condensation Theory

Polyuronates such as pectate and alginate are very well-known examples of biological polyelectrolytes undergoing, upon addition of divalent cations, an interchain association that acts as the junction of an eventually formed stable hydrogel. In the present paper, a thermodynamic model based on the counterion condensation theory has been developed to account for this cation-induced chain pairing of negatively charged polyelectrolytes. The strong interactions between cross-linking ions and uronate moieties in the specific binding site have been described in terms of chemical bonding, with complete charge annihilation between the two species. The chain-pairing process is depicted as progressively increasing with the concentration of cross-linking counterions and is thermodynamically defined by the fraction of each species. On these bases, the total Gibbs energy of the system has been expressed as the sum of the contributions of the Gibbs energy of the (single) chain stretches and of the (associated) dimers, weighted by their respective fractions 1 - theta and theta. In addition, the model assumes that the condensed divalent counterions exhibit an affinity free-energy for the chain, G(C)(aff,0), and the junction, G(D)(aff,0), respectively. Moreover, a specific Gibbs energy of chemical bonding, G(bond,0), has been introduced as the driving force for the formation of dimers. The model provides the mathematical formalism for calculating the fraction, theta, of chain dimers formed and the amount of ions condensed and bound onto the polyelectrolyte when two different types of counterions (of equal or different valence) are present. The effect of the parameter G(bond,0) has been investigated and, in particular, its difference from G(C,D)(aff,0) was found to be crucial in determining the distribution of the ions into territorial condensation and chemical bonding, respectively. Finally, the effect of the variation of the molar ratio between cross-linking ions and uronic groups in the specific binding sites, sigma0, was evaluated. In particular, a remarkable decrease in the amount of condensed counterions has been pointed out in the case of sigma0 = 1/3, with respect to the value of sigma0 = 1/4, characterizing the traditional "egg-box" structure, as a result of the drop of the charge density of the polyelectrolyte induced by complete charge annihilation.

Short‐time stretch relaxation of entangled polymer solutions investigated using full Rouse model predictions

AbstractWe conduct a systematical investigation into the short‐time stretch relaxation behavior (i.e., shorter than the Rouse time but sufficiently longer than the glassy time) of entangled polymer liquid in single‐step strain flows, on the basis of theory/data comparisons for a broad series of type‐A entangled polymer solutions. First, within existing normal‐mode formulations, the Rouse model predictions on a full‐chain stretch relaxation in single‐step strain flows are derived for a popular 1‐D model proposed within the Doi–Edwards tube model, as well as for the original 3‐D model for nonentangled systems. In addition, an existing formula for the aforementioned 1‐D model that, however, rested upon a consistent‐averaging or the so‐called uniform‐chain‐stretch approximation is simultaneously examined. Subsequently, the previously derived formulas on chain stretch relaxation are directly incorporated into a reliable mean‐field tube model that utilizes the linear relaxation spectrum and the Rouse time constant consistently determined from linear viscoelastic data. It is found that the predictions of the 1‐D model differ substantially from that of the original 3‐D model at short times. Theory/data comparisons further indicate that the 1‐D model without approximations seems able to describe fairly well the nonlinear relaxation data under investigation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1199–1211, 2006

Telechelic associative polymers: Interaction potential and high frequency modulus

Previous studies establish that adsorbed layers of telechelic polymers can exchange ends, increasing the entropy and allowing the loops to relax. The resulting entropic attraction amounts to approximately 1kT per bridging chain for ideal chains but decreases with increasing degree of stretching. From the interactions between planar brushes of highly stretched chains, we calculate the pair potential between spheres via the Derjaguin approximation. The softness of the repulsion and the depth of the attraction depend on the degree of stretching of the chains, the aggregation number or adsorption density, and the ratio of the overall size to the layer thickness. From the interaction potential, second virial coefficients in the osmotic pressure and the high-frequency modulus, characterizing dilute micellar solutions, follow directly. The second virial coefficient in the osmotic pressure is very negative with modest stretching but approaches the hard sphere limit as the chains become very strongly stretched. Th...

Molecular Structure of a 9-MDa Icosahedral Pyruvate Dehydrogenase Subcomplex Containing the E2 and E3 Enzymes Using Cryoelectron Microscopy

The pyruvate dehydrogenase multienzyme complexes are among the largest multifunctional catalytic machines in cells, catalyzing the production of acetyl CoA from pyruvate. We have previously reported the molecular architecture of an 11-MDa subcomplex comprising the 60-mer icosahedral dihydrolipoyl acetyltransferase (E2) decorated with 60 copies of the heterotetrameric (alpha(2)beta(2)) 153-kDa pyruvate decarboxylase (E1) from Bacillus stearothermophilus (Milne, J. L. S., Shi, D., Rosenthal, P. B., Sunshine, J. S., Domingo, G. J., Wu, X., Brooks, B. R., Perham, R. N., Henderson, R., and Subramaniam, S. (2002) EMBO J. 21, 5587-5598). An annular gap of approximately 90 A separates the acetyltransferase catalytic domains of the E2 from an outer shell formed of E1 tetramers. Using cryoelectron microscopy, we present here a three-dimensional reconstruction of the E2 core decorated with 60 copies of the homodimeric 100-kDa dihydrolipoyl dehydrogenase (E3). The E2E3 complex has a similar annular gap of approximately 75 A between the inner icosahedral assembly of acetyltransferase domains and the outer shell of E3 homodimers. Automated fitting of the E3 coordinates into the map suggests excellent correspondence between the density of the outer shell map and the positions of the two best fitting orientations of E3. As in the case of E1 in the E1E2 complex, the central 2-fold axis of the E3 homodimer is roughly oriented along the periphery of the shell, making the active sites of the enzyme accessible from the annular gap between the E2 core and the outer shell. The similarities in architecture of the E1E2 and E2E3 complexes indicate fundamental similarities in the mechanism of active site coupling involved in the two key stages requiring motion of the swinging lipoyl domain across the annular gap, namely the synthesis of acetyl CoA and regeneration of the dithiolane ring of the lipoyl domain.

Simultaneous stress and birefringence measurements during uniaxial elongation of polystyrene melts with narrow molecular weight distribution

Tensile stress and flow-induced birefringence have been measured during uniaxial elongation at a constant strain rate of two polystyrene melts with narrow molecular weight distribution. For both melts, the stress- optical rule (SOR) is found to be fulfilled upto a critical stress of 2.7 MPa, independent of strain rate and temperature. Estimation of the Rouse times of the melts, from both the zero-shear viscosity and the dynamic-shear moduli at high frequency, shows that the violation of the SOR occurs when the strain rate multiplied by the Rouse time of the melt exceeds by approximately 3. The presented results indicate that in contrast to current predictions of molecular theories, the regime of extensional thinning observed by Bach et al. (2003) extends well beyond the onset of failure of the SOR, and therefore the onset of chain stretch in the non-Gaussian regime.

DNA Molecules in Microfluidic Oscillatory Flow

The conformation and dynamics of a single DNA molecule undergoing oscillatory pressure-driven flow in microfluidic channels is studied using Brownian dynamics simulations, accounting for hydrodynamic interactions between segments in the bulk and between the chain and the walls. Oscillatory flow provides a scenario under which the polymers may remain in the channel for an indefinite amount of time as they are stretched and migrate away from the channel walls. We show that by controlling the chain length, flow rate and oscillatory flow frequency, we are able to manipulate the chain extension and the chain migration from the channel walls. The chain stretch and the chain depletion layer thickness near the wall are found to increase as the Weissenberg number increases and as the oscillatory frequency decreases.

Low Swelling Capacity of Highly Stretched Polystyrene Brushes

We report the unusually low swelling capacity of highly stretched polystyrene chains grown on a silicon surface using “living” free radical polymerization. The control over the lateral density leads to brushes with a very high grafting density (up to >1.0 chain/nm2). Neutron reflectivity measurements have evidenced two specific features of such brushes: (i) the controlled nature of the surface polymerization through a very homogeneous growth of homopolymer and copolymer chains; (ii) the highest volume fraction in good solvent Φ(z=0) = 0.85 ever seen due to the highly stretched configuration of the dry chains, hindering a complete swelling of the layers and suggesting a significant deviation from predicted scaling laws.

Hydrophobic chains near hydrophobic surfaces—simulations in three dimensions

The behaviour of a hydrophobic chain near a hydrophobic wall is studied in threedimensions by numerically simulating a modified version of the decorated lattice model ofWidom and co-workers. The effective hydrophobic interaction is temperaturedependent. The chain stretches and adheres to the hydrophobic wall in a pancake likeconformation at intermediate temperatures, whereas it collapses upon itself at slightlyhigher temperatures. At lower or higher dimensions it is in a random coil state.

Failure property distributions for conventional and highly crosslinked ultrahigh molecular weight polyethylenes

To make stochastic (probabilistic) failure predictions of a conventional or highly crosslinked ultrahigh molecular weight polyethylene (UHMWPE) material, not only must a failure criterion be defined, but it is also necessary to specify a probability distribution of the failure strength. This study sought to evaluate both parametric and nonparametric statistical approaches to describing the failure properties of UHMWPE, based on the Normal and Weibull model distributions, respectively. Because fatigue and fracture properties of materials have historically been well described with the use of Weibull statistics, it was expected that a nonparametric approach would provide a better fit of the failure distributions than the parametric approach. The ultimate true stress, true strain, and ultimate chain stretch data at failure were analyzed from 60 tensile tests conducted previously. The ultimate load and ultimate displacement from 121 small punch tests conducted previously were also analyzed. It was found that both Normal and Weibull models provide a reasonable description of the central tendency of the failure distribution. The principal difference between the Normal and Weibull models can be appreciated in the predicted lower-bound response at the tail end of the distribution. The data support the use of both parametric and nonparametric methods to bracket the lower-bound failure prediction in order to simulate the failure threshold for UHMWPE.

Study of Protein−Lipid Interactions at the Bovine Serum Albumin/Oil Interface by Raman Microspectroscopy

The interface of 10 or 25% (w/v) bovine serum albumin (BSA), pH 7, buffered solution against mineral or corn oil was studied with a Raman microscope. A gradient of distribution of protein and oil at the interface was observed. The difference spectrum obtained by subtracting the spectrum of mineral or corn oil from that of the BSA/oil interface indicated interactions involving different functional groups of the BSA and the oil molecules. Against mineral oil, the BSA spectrum showed reduced intensity of the tryptophan band at 750 cm(-1) and reduced intensity ratio of the tyrosine doublet at 850-830 cm(-1), indicating changes in the microenvironment of these hydrophobic residues. A negative band at 2850 cm(-1) indicated the involvement of the CH groups in the mineral oil. However, the amide regions, normally assigned to protein secondary structure, were not significantly changed. When the spectrum of BSA was subtracted from the BSA/mineral oil interface spectrum, the resultant difference spectrum showed changes of symmetric and antisymmetric CCC stretches at 980 and 1071 cm(-1), respectively. In contrast, the difference spectrum of BSA/corn oil interface - BSA showed a decrease of CH(2) symmetric stretching at 2850 cm(-1) and a decrease of unsaturated fatty acid hydrocarbon chain stretch at 3010 cm(-1). Raman spectroscopy is a useful tool to study the nature of protein-lipid interactions.