Antisymmetric Band Research Articles

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440 cm −1 is assigned to the ν 3 CO 3 2− antisymmetric stretching vibration. An additional band is resolved at 1335 cm −1. An intense sharp Raman band at 1092 cm −1 is assigned to the CO 3 2− symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442 cm −1 shifting to lower wavenumbers with thermal treatment. A band observed at 870 cm −1 with a band of lesser intensity at 842 cm −1 shifts to higher wavenumbers upon thermal treatment and is observed at 865 cm −1 at 400 °C and is assigned to the CO 3 2− ν 2 mode. No ν 2 bending modes are observed in the Raman spectra for smithsonite. The band at 746 cm −1 shifts to 743 cm −1 at 400 °C and is attributed to the CO 3 2− ν 4 in phase bending modes. Two infrared bands at 744 and around 729 cm −1 are assigned to the ν 4 in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO 6 octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991 cm −1 in both the IE and infrared spectra are attributed to combination bands.

Elastic and Inelastic Electron Tunneling Spectroscopy of a New Rectifying Monolayer

Rectification of electrical current was observed in a Langmuir-Schaefer monolayer of fullerene-bis[ethylthio-tetrakis(3,4-dibutyl-2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate, Au electrodes at room temperature (there are two regimes of asymmetry, at lower bias, i.e., between 0 and +/-2 V, and at higher bias), and also between Pb and Al electrodes at 4.2 K. The latter experiment was coupled with second harmonic detection of the second derivative of the current with respect to voltage (d2I/dV2). The d2I/dV2 spectrum shows intramolecular vibrations, and also two antisymmetric broad bands, centered at +/-0.65 V, due to resonant electron tunneling between the Fermi level(s) of the electrodes and the lowest unoccupied molecular orbital of the molecule.

On the structural parameters and vibrational spectra of CH 3NCS, SiH 3NCS and GeH 3NCS

The infrared spectra (3500–400 cm −1) of CH 3NCS in gas, xenon solution (−60 to −100 °C) and solid phases have been recorded. The effect of free internal rotation of the methyl group is observed on the CH 3 antisymmetric stretch and deformation bands from which zeta values have been obtained. The band centers for the degenerate CH 3 vibrations have also been determined from the low-temperature spectra in liquid xenon and their values are significantly different from the ones in the gas. By combining previously reported rotational constants for CH 3NCS, SiH 3NCS and GeH 3NCS with the ab initio MP2(full)/6-311+G(d,p) predicted parameters, adjusted r 0 parameters have been obtained. The structural parameters for CH 3NCS ( C s) are: r(C N) = 1.441(5), r(N C) = 1.206(5), r(C S) = 1.586(5), r(C H s) = 1.090(2) and r(C H a) = 1.093(2) Å with ∠CNC of 143.9(3) and ∠NCS of 175.5(2)°; for SiH 3NCS ( C 3v): r(Si N) = 1.704(5), r(N C) = 1.197(5), r(C S) = 1.567(5), r(Si H) = 1.476(3) Å with ∠NSiH = 108.5(3)°; for GeH 3NCS ( C s): r(Ge N) = 1.843(5), r(N C) = 1.209(5), r(C S) = 1.576(5), r(Ge H s) = 1.519(3) and r(Ge H a) = 1.517(3) Å with ∠GeNC = 149.9(5) and ∠NCS = 176.5(2)°. These parameters are significantly different from the values previously reported for all three molecules. Ab initio calculations by the Møller-Plesset perturbation method to the second order MP2(full) and density functional theory calculations by the B3LYP method utilizing a variety of basis sets have been carried out for all three molecules to predict barriers to rotation and linearity as well as force constants, vibrational frequencies, infrared intensities, Raman activities, depolarization ratios and centrifugal distortion constants which are compared to the experimental quantities. Some significant changes have been made for the assignments of some of the fundamentals for CH 3NCS which has been clearly shown to have C s symmetry in the ground vibrational state as well as for GeH 3NCS with C s symmetry. The results are discussed and compared to corresponding quantities of some similar molecules.

Jet-cooled infrared spectroscopy in slit supersonic discharges: Symmetric and antisymmetric CH2 stretching modes of fluoromethyl (CH2F) radical

The combination of shot noise-limited direct absorption spectroscopy with long-path-length slit supersonic discharges has been used to obtain first high-resolution infrared spectra for jet-cooled CH2F radicals in the symmetric (nu1) and antisymmetric (nu5) CH2 stretching modes. Spectral assignment has yielded refined lower- and upper-state rotational constants and fine-structure parameters from least-squares fits to the sub-Doppler line shapes for individual transitions. The rotational constants provide indications of large amplitude vibrational averaging over a low-barrier double minimum inversion-bending potential. This behavior is confirmed by high-level coupled cluster singles/doubles/triples calculations extrapolated to the complete basis set limit and adiabatically corrected for zero point energy. The calculations predict a nonplanar equilibrium structure (theta approximately 29 degrees, where theta is defined to be 180 degrees minus the angle between the C-F bond and the CH2 plane) with a 132 cm(-1) barrier to planarity and a vibrational bend frequency (nu(bend) approximately 276 cm(-1)), in good agreement with previous microwave estimates (nu(bend) = 300 (30) cm(-1)) by Hirota and co-workers [Y. Endo et al., J. Chem. Phys. 79, 1605 (1983)]. The nearly 2:1 ratio of absorption intensities for the symmetric versus antisymmetric bands is in good agreement with density functional theory calculations, but in sixfold contrast with simple local mode CH2 bond dipole predictions of 1:3. This discrepancy arises from a surprisingly strong dependence of the symmetric stretch intensity on the inversion bend angle and provides further experimental support for a nonplanar equilibrium structure.

Infrared Spectra and Intensities of the H2O and N2 Complexes in the Range of the ν1- and ν3-Bands of Water

The IR spectra of complexes of water with nitrogen molecules in the range of the symmetric (nu(1)) and antisymmetric (nu(3)) bands of H(2)O have been studied in helium droplets. The infrared intensities of the nu(3) and nu(1) modes of H(2)O were found to be larger by factors of 1.3 and 2, respectively, in the N(2)-H(2)O complexes. These factors are smaller than those obtained in recent theoretical calculations. The conformation of the N(2)-H(2)O complex was estimated. Spectra and IR intensities of the (N(2))(2)-H(2)O and N(2)-(H(2)O)(2) complexes were also obtained and their structures are discussed.

Raman spectroscopy of dimethyl sulphoxide and deuterated dimethyl sulphoxide at 298 and 77 K

Raman spectroscopy was used to determine the molecular behaviour of DMSO and DMSO-d6, and to compare it with that of DMSO in DMSO-intercalated kaolinites. For DMSO at 298 K two bands are observed at 2994 and 2913 cm−1 and are assigned to the antisymmetric and symmetric CH stretching modes. At 77 K the degeneracy of these bands is lost. Bands are now observed as antisymmetric bands at 3001, 2995 and 2988 cm−1 and symmetric bands at 2923, 2909 and 2885 cm−1, respectively. For the DMSO-intercalated low-defect kaolinite, the 2913 cm−1 band resolves into five component bands at 2882, 2907, 2917, 2920 and 2937 cm−1. The CD antisymmetric and symmetric stretching modes in the 298 K spectrum are found at 2250 and 2125 cm−1, respectively. Both bands show some asymmetry and further bands may be resolved at 2256 and 2244 cm−1 in the antisymmetric stretching region and at 2118 cm−1 in the symmetric stretching region. The spectra of the SO stretching region of DMSO and DMSO-d6 are complex with a band profile centred at 1050 cm−1. Three bands are curve resolved at 1058, 1042 and 1026 cm−1 attributed to the unassociated monomer and the out-of-phase and the in-phase vibrations of the dimer, respectively. Upon cooling to liquid nitrogen temperature, these three bands are observed at 1057, 1038 and 1019 cm−1. The spectra of the SO stretching region of DMSO-d6 are more complex because of the overlap of the DCD deformation modes with the SO stretching modes. The antisymmetric and symmetric stretching CS modes of DMSO are observed at 698 and 667 cm−1, shifting at 77 K to 705 and 672 cm−1. It is concluded that the structure of DMSO in DMSO-intercalated kaolinite is different from those of both liquid DMSO at 298 K and solid DMSO measured at 77 K. Copyright © 2002 John Wiley & Sons, Ltd.

Raman spectroscopy of dimethyl sulphoxide and deuterated dimethyl sulphoxide at 298 and 77 K

AbstractRaman spectroscopy was used to determine the molecular behaviour of DMSO and DMSO‐d6, and to compare it with that of DMSO in DMSO‐intercalated kaolinites. For DMSO at 298 K two bands are observed at 2994 and 2913 cm−1 and are assigned to the antisymmetric and symmetric CH stretching modes. At 77 K the degeneracy of these bands is lost. Bands are now observed as antisymmetric bands at 3001, 2995 and 2988 cm−1 and symmetric bands at 2923, 2909 and 2885 cm−1, respectively. For the DMSO‐intercalated low‐defect kaolinite, the 2913 cm−1 band resolves into five component bands at 2882, 2907, 2917, 2920 and 2937 cm−1. The CD antisymmetric and symmetric stretching modes in the 298 K spectrum are found at 2250 and 2125 cm−1, respectively. Both bands show some asymmetry and further bands may be resolved at 2256 and 2244 cm−1 in the antisymmetric stretching region and at 2118 cm−1 in the symmetric stretching region. The spectra of the SO stretching region of DMSO and DMSO‐d6 are complex with a band profile centred at 1050 cm−1. Three bands are curve resolved at 1058, 1042 and 1026 cm−1 attributed to the unassociated monomer and the out‐of‐phase and the in‐phase vibrations of the dimer, respectively. Upon cooling to liquid nitrogen temperature, these three bands are observed at 1057, 1038 and 1019 cm−1. The spectra of the SO stretching region of DMSO‐d6 are more complex because of the overlap of the DCD deformation modes with the SO stretching modes. The antisymmetric and symmetric stretching CS modes of DMSO are observed at 698 and 667 cm−1, shifting at 77 K to 705 and 672 cm−1. It is concluded that the structure of DMSO in DMSO‐intercalated kaolinite is different from those of both liquid DMSO at 298 K and solid DMSO measured at 77 K. Copyright © 2002 John Wiley & Sons, Ltd.

Tunneling between Luttinger liquids

We consider the problem of tunneling between spinless 1D Luttinger liquid chains. We show how to map the problem onto the 4-state chiral clock model together with a free boson for the total charge mode. We use a variety of results, some of them exact, from the integrable chiral Potts model and the study of commensurate/incommensurate transitions to deduce the physics of coupled Luttinger liquids. For those intrachain interaction strengths for which interchain tunneling is relevant, we find that it can lead to the formation of symmetric and antisymmetric bands with split Fermi surfaces, depending on the relative strengths of interchain tunneling and interchain interactions. With split Fermi surfaces, the tunneling is coherent. It is not possible to have two gapless Fermi surfaces with the same Fermi momentum when interchain tunneling is relevant. However, interchain interactions can drive the formation of a gap, in which case interchain transport will be incoherent. We comment on the possible relevance of our results to c-axis transport in high-T_c superconductors.

Microstructure, Wettability, and Thermal Stability of Semifluorinated Self-Assembled Monolayers (SAMs) on Gold

The microstructure, wettability, and thermal stability of self-assembled monolayers (SAMs) on gold generated from semifluorinated alkanethiols F(CF2)10(CH2)nSH, where n = 2, 6, 11, 17, and 33 (F10HnSH), were examined by polarization modulation infrared reflection absoprtion spectroscopy (PM-IRRAS) and dynamic contact angle measurements. Analysis by PM-IRRAS revealed that the length of the methylene spacer (Hn) influenced the tilt angle of the fluorocarbon segments in the semifluorinated SAMs. As the length of the methylene spacer was increased, the tilt angle of the perfluorocarbon moiety increased with respect to the surface normal. The longer methylene spacers (Hn, n = 11, 17, and 33) exhibited well-ordered trans-extended conformations as indicated by the position of the antisymmetric methylene band (νaCH2 = 2919 cm-1). Shortening the length of the methylene spacer to n = 6, however, led to a decrease in conformational order (νaCH2 = 2925 cm-1). Dynamic contact angle measurements using the Wilhelmy plate method showed that the semifluorinated SAMs were poorly wet by both water (average θa = 120°) and hexadecane (average θa = 81°). The wettability varied with the length of the methylene spacer; in particular, both the thinnest and the thickest semifluorinated SAMs (derived from F10H2SH and F10H33SH, respectively) exhibited relatively low dynamic contact angle values. In addition, the thermal stability of the semifluorinated SAMs was found to increase as the length of the methylene spacer was increased. Overall, these films exhibited remarkable resistance to thermal degradation (e.g., SAMs derived from F10H33SH sustained a relatively high contact angles after incubation at 150 °C for 1 h in air).

ABSORPTION INTENSITIES, PRESSURE-BROADENING AND LINE MIXING PARAMETERS OF SOME LINES OF NH 3 IN THE ν4 BAND

The intensities and foreign gas broadening coefficients of 57 selected lines of the ν 4 band of NH 3 have been measured in the region of 1550 cm -1 using a high resolution Brucker Fourier transform spectrometer. The line intensities were obtained by using the methods of absorbance at the line center and by fitting Voigt profiles to the measured shapes of the lines. The latter method also provides the collisional widths of the lines. In addition, collision cross relaxation coefficients of O 2 and air foreign gases were measured for 9 doublets of NH 3 in the ν 4 band. The J and K quantum numbers dependencies of pressure-broadening coefficients and line intensities are discussed. The observed air broadening and cross relaxation coefficients were found to be in reasonable quantitative agreement with the concentration-weighted average of the N 2 and O 2 broadening coefficients. The comparison of our present and previous results obtained for the NH 3–H 2, NH 3–air, NH 3–N 2 and NH 3–CO 2 collisions shows an increase of the pressure broadening and cross relaxation coefficients with quadrupole moment of the foreign gas. The analysis of the line intensities was based on the third-order theory of line strengths and yields effective transition moments, vibrational band strengths and correction parameters of the symmetric and antisymmetric partial bands of the fundamental ν 4 band.

NH stretching bands of the hydrogen-bonded C 6H 5NH 2żN(C 2H 5) 3 cluster

The vibrational spectrum of the 1:1 aniline-triethylamine cluster, formed in a supersonic jet, has been observed in the NH stretching region using infrared depletion spectroscopy combined with REMPI/TOF mass spectrometry. The two absorption bands observed at 3328 and 3466 cm −1 are assigned to the hydrogen-bonded and free NH stretching vibrations of the cluster, respectively. The former band is enhanced, broadened and largely red-shifted from the aniline monomer bands, while the latter appears at the middle of the symmetric and antisymmetric bands of the monomer. The vibrational frequencies and intensities of the NH stretching bands are qualitatively reproduced by ab initio calculations at the MP2 level with the 6–31G∗∗ basis set. The calculated geometry is the typical hydrogen-bonded one, where one of the amino hydrogens of aniline interacts with the nitrogen of triethylamine.

Fourier transform infrared analysis of the interaction of azide with the active site of oxidized and reduced bovine Cu,Zn superoxide dismutase.

Binding of azide to the native and arginine-modified bovine Cu,Zn superoxide dismutase in the oxidized and reduced form and to the copper-free derivative has been investigated by Fourier transform infrared spectroscopy. The antisymmetric stretching band of the azide is shifted to higher energy upon coordination to the copper atom of the oxidized form of the native enzyme. Similar spectral changes occur upon interaction of the anion with the Cu-diethylenetriamine model compound. On the other hand, interaction of azide with the native reduced form of the enzyme results in a band shift toward lower energy with respect to the free anion band. The same shift is observed after reaction of the azide with free lysine or arginine but not when it is reacted with other amino acid residues. The antisymmetric band of the azide is not perturbed by addition of the reduced arginine-modified enzyme; it is likely shifted toward higher energy upon addition of oxidized arginine-modified enzyme while it is again shifted toward lower energy in the presence of the copper-free derivative of the unmodified enzyme. It is concluded that azide does not directly coordinate to the copper in the reduced form of Cu,Zn superoxide dismutase but it remains in the active-site pocket in electrostatic interaction with the guanidinium group of Arg141, which is an invariant residue in this class of enzymes.

Antisymmetric Amino-Wagging Band of Hydrazine up toK′ = 13 Levels

A newly recorded high-resolution infrared spectrum of hydrazine has been studied in the 729–1198 cm−1region (the ν12antisymmetric wagging band) with a resolution of 0.002 cm−1. About 1350 transitions withK′ from 7 to 13 have been newly assigned and about 2350 transitions with lower values ofK′ reanalyzed with the improved precision. The effective parameters have been calculated separately for each value ofK′ using the Hougen–Ohashi hamiltonian for hydrazine. The extended assignment completes the analysis of the ν12band of hydrazine.

FT-Raman and infrared spectroscopic study of aragonite-strontianite (Ca xSr 1 − xCO 3) solid solution

Synthetic aragonite-strontianite solid-solution samples have been studied using dispersive IR and FT-Raman spectroscopy. In addition to the end-members, nine samples over a range of composition from Ca 0.9Sr 0.1CO 3 to Ca 0.1Sr 0.9CO 3 were analysed. Carbonate anion internal modes are examined in detail by means of band-shape analysis and component fitting procedures. Positional disorder induced by the random cationic substitution results in strong increase of the halfwidth in several vibrational bands. Results obtained for the doubly degenerate modes (antisymmetric stretching and bending, ν 3 and ν 4) reveal the presence of three components both in the IR antisymmetric stretching band as well as in the Raman antisymmetric bending band. These observations are interpreted in terms of an overtone 2 ν 4 in possible Fermi resonance with the corresponding ν 3 fundamental in the IR spectra, and the presence of Davidov (factor group) splitting in the FT-Raman ν 4 band. Lattice modes in the FT-Raman spectra demonstrate weaker cohesion between the cation/carbonate/cation layers in aragonite ( synth) than in strontianite ( synth).

RNA-Diethylstilbestrol Interaction Studied by Fourier Transform Infrared Difference Spectroscopy

Diethylstilbestrol (DES), a synthetic estrogen, is known to be a carcinogen in human and in animals. This study was designed to examine the interaction of DES with yeast RNA in aqueous solution at physiological pH with drug/RNA-phosphate (P) molar ratios of 1/80, 1/40, 1/20, 1/10, 1/4, and 1/2. Fourier transform infrared (FTIR) difference spectroscopy was used to determine the drug binding mode, the binding constant, the sequence selectivity, and RNA secondary structure in the RNA.DES complexes. Spectroscopic evidence showed that at low drug concentration (1/80 and 1/40), DES is intercalating through both Gua-Cyt and Ade-Urd base pairs with minor interaction with the backbone PO2 group (external binding). The calculated binding constant of K approximately 8.5 x 10(4) M-1 at a drug concentration of 3.12 x 10(-4) M shows that DES is a weaker intercalator than those of the methylene blue, acridine orange, and ethidium bromide. At high drug content (r > 1/40, where r represents the DES/RNA-phosphate molar ratio), a partial helix destabilization occurs with no alteration of RNA conformation upon drug complexation. However, a comparison with DNA.DES complexes showed that drug intercalation causes major reduction of the B-DNA structure in favor of A-DNA with no participation of the backbone PO2 group in the DES. DNA complexation.

Comparison of the effects of amikacin and kanamycins A and B on dimyristoylphosphatidylglycerol bilayers: An infrared spectroscopic investigation

Aminoglycoside antibiotics are very effective against severe Gram-negative infections, but their clinical use is associated with nephrotoxic side-effects. The cascade of events leading to acute renal failure involves an impairment of lysosomal phospholipase activity, which is thought to result from the direct interaction of the drugs with the head group of negative phospholipids. Fourier transform infrared spectroscopy was used to study the effects of three aminoglycosides from the kanamycin family (amikacin and kanamycins A and B) on dimyristoylphosphatidylglycerol (DMPG) bilayers at lysosomal pH. The results obtained were consistent with a tightening of the lipidic network caused by the neutralization of the negative head groups of DMPG by the positive charges of the aminoglycosides. These antibiotics induced an increase of the transition temperature of DMPG, a decrease of both the frequency and relative intensity of the hydrogen-bonded carbonyl component, and a decrease of the phosphate antisymmetric band frequency. Kanamycin B, which is known to be the most nephrotoxic drug of the three, exhibited the greatest effects on the transition temperature and on the carbonyl stretching band. A comparison of the nature and extent of the spectral changes led us to conclude that amikacin lies flat on the bilayer surface, whereas kanamycin B is located between the lipidic head groups and quite close to some of the carbonyl groups. Finally, a possible correlation between the importance of bilayers perturbation and the respective inhibitory potency against phospholipases was examined.

Infrared spectroscopy, infrared photoconversion, and ultraviolet photodissociation of NO dimers in neon and nitrogen matrices

The nitric oxide dimers isolated in neon or nitrogen matrices have been irradiated in the infrared by selected lines of a cw CO laser and in the UV at 193 nm by an ArF excimer laser. IR excitation of the antisymmetric mode of the cis dimer in neon induces a conversion to a special van der Waals dimer. At T<6 K UV irradiation dissociates the dimers mainly to NO monomers and, in smaller proportion, to NO2 in the neon matrix or to N2O in the nitrogen matrix. NO2 is formed exclusively from the cis dimer and N2O from the trans dimer. At higher temperature in nitrogen, the oxygen atoms produced in the N2O formation migrate and react with NO to form NO2. The vibrational spectroscopy in nitrogen reveals several new features. The symmetrical vibrational mode of planar trans-(NO)2, normally IR inactive, becomes observable at 5.8 K owing to the matrix strain. cis-(NO)2 is trapped in two sites and the energy difference between them changes abruptly around 14 K, suggesting a structural transformation in the neighborhood of the sites. Cooling at 5.8 K induces a reversible decrease of the cis dimer bands, correlated with the appearance of vdW dimer bands. In both matrices, the antisymmetric band of the cis dimer is broadened by a predissociation effect as in the gas phase.

Further Analysis of the Fourier Transform Spectrum of the Antisymmetric Amino-Wagging Band of Hydrazine

The Fourier transform spectrum of the antisymmetric amino-wagging band of hydrazine has been extensively reanalyzed. About 1700 transitions from 18 subbands with K′ from 0 to 6 were newly assigned. In place of a global fit, which proved unsuccessful, individual subband fits were made for each K′ value to obtain sublevel parameters for each K sublevel of the antisymmetric amino-wagging state. Sublevel parameters other than the subband origins are found to have very irregular K dependences.

Interaction of calf-thymus DNA with trivalent La, Eu, and Tb ions. Metal ion binding, DNA condensation and structural features.

The interaction of calf-thymus DNA with La3+, Eu3+ and Tb3+ has been investigated in aqueous solution at pH 6.5, using metal/DNA(P) molar ratios(r) 1/80, 1/40, 1/20, 1/10, 1/4 and 1/2. Correlations between FTIR spectral changes and DNA structural properties have been established. At low metal/DNA(P) (r) 1/80, the metal ions bind mainly to the PO2- groups of the backbone, resulting in increased base-stacking interaction and duplex stability. At (r) 1/40 and 1/20, metal ion binding to the PO2- and the guanine N-7 site (chelation) predominates with minor perturbations of the A-T base pairs. Evidence for this comes from the displacement of the band at 1712 cm-1 (T,G) towards a lower frequency and the PO2- antisymmetric band at 1222 cm-1 towards a higher frequency. At higher metal/DNA(P) ratio, r > 1/20, DNA begins to condensate and drastic structural changes occur, which are accompanied by the shift and intensity changes of several G-C and A-T absorption bands. No major departure from B-DNA conformation was observed before and after DNA condensation even though some local structural modifications were observed. A comparison with the Cu-DNA complexes (denaturated DNA) shows some degree of helical destabilization of the biopolymer in the presence of lanthanide ions.

An infrared spectroscopic study of specifically deuterated fatty-acyl methyl groups in phosphatidylcholine liposomes

The region of the infrared spectrum corresponding to C- 2H stretching vibrations (2050–2250 cm −1) has been examined for liposomes composed of dimyristoylphosphatidylcholine deuterated specifically at the methyl ends of either one ( sn-2) or both the fatty acyl chains. This label is intended to provide information on lipid dynamics in the contact region between monolayers. The two most prominent bands observed correspond, respectively, to antisymmetric (2212 cm −1) and symmetric (2075 cm −1) C- 2H stretching vibration. The antisymmetric band consists of two overlapping peaks, whose positions vary with the gel or liquid-crystalline state of the lipid. The separation between the peaks making up the antisymmetric band increases with temperature, and is maximum above the T c transition temperature; this rules out the previously proposed assignment of these two peaks to different rotational modes of the methyl group relative to the adjacent methylene. The position and width of the symmetric band at 2075 cm −1 are also sensitive to the physical state of the lipid. The presence of cholesterol at an equimolar ratio with the phospholipid abolishes all the phase-dependent changes observed. The intrinsic polypeptide gramicidin A, at a 5:1 lipid/peptide mol ratio, is seen to enlarge the lipid thermotropic transition, with small effects above T c. Cytochrome c, an extrinsic protein, at a 10:1 mole ratio, does not modify the phase-dependent behaviour of the terminal methyl groups, but consistently shifts all the observed bands to lower-frequency positions, which suggests a long-range effect of the protein along the phospholipid fatty acyl chains.