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Biomedical subjects

I W Levin

Publications and source records attributed to I W Levin.

67 records · Page 4Linked to original sources
PubMed1977

Raman spectra and vibrational assignments for deuterated membrane lipids. 1,2-Dipalmitoyl phosphatidylcholine-d9 and -d62.

Vibrational Raman spectra of polycrystalline 1,2-dipalmitoyl phosphatidylcholine-d9 (fully deuterated choline methyl groups) and 1,2-dipalmitoyl phosphatidylcholine-d62 (fully deuterated acyl chains) were recorded in the 3050- 2800, 2250-2050 and 1800-700 cm-1 regions. The fundamental vibrational modes were assigned primarily on the basis of isotopic frequency shift ratios, group frequency correlations and comparisons with specific model compounds. Since deuterium-substituted lipids provide well-isolated spectral probes, particularly in the carbon-deuterium stretching region, the dependence of the 2250-2050 cm-1 region on lipid phase was examined for the dipalmitoyl phosphatidylcholine-d62 species. The methylene CD2 deformation and twisting modes at 984 and 919 cm-1, respectively, also exhibit intense, isolated vibrational transitions which should prove useful for monitoring molecular order in mixed dueterated and undeuterated lipid systems. Except for the relatively weak choline methyl C-D and C-H stretching modes, the spectrum of 1,2-dipalmitoyl phosphatidylcholine-d9 is not distinguishable from that of the undeuterated system. For both the d9 and undeuterated species, the vibrational modes associated with the lipid head group region are sensitive to slight hydration.

Deuterium↗
PubMed1977

Cooperative unit size in the gel-liquid crystalline phase transition of dipalmitoyl phosphatidylcholine-water multilayers: an estimate from Raman spectroscopy.

The temperature dependence of the Raman spectral transitions assigned to the acyl chain C-C stretching modes of dipalmitoyl phosphatidylcholine was determined for the gel, phase transition and liquid crystalline states of the lipid multilayers. The van't Hoff enthalpy differences delta HVH between trans and gauche rotational isomers were obtained from the Raman spectral data for the temperature region characteristic of each bilayer state. An average size for the cooperative unit undergoing the chain melting process during the phase transition was estimated from the ratio of the appropriate van't Hoff enthalpy to an adjusted calorimetric enthalpy.

Binding Sites↗
PubMed1977

Comment on the carbon-hydrogen stretching region of vibrational Raman spectra of phospholipids.

The broad, environmentally sensitive 2935-2910 cm-1 feature in the vibrational Raman spectra of phospholipids originates primarily from methylene symmetric carbon-hydrogen (C-H) stretching modes. For ordered acyl chains exhibiting local C2h symmetry at low temperatures, the infrared active methylene C-H asymmetric stretching modes become increasingly apparent at higher temperatures in the Raman spectrum as intramolecular chain disorder (trans-gauche isomerization) leads to a loss of chain symmetry. The 2935 cm-1 shoulder, assigned to the acyl chain methyl group C-H symmetric stretching vibration, is difficult to distinguish as a separate spectral transition in the chain disordered state. An ordering of lipid fluidity for several phospholipids is presented in terms of the intensities of features in the 3000-2800 cm-1 region with particular emphasis upon the 2935-2910 cm-1 contour.

Phospholipids↗
PubMed1977

Hydrocarbon trans-gauche isomerization in phospholipid bilayer gel assemblies.

The vibrational Raman spectra of dimyristoyl (DMPC)-, dipalmitoyl (DPPC)-, and distearoylphosphatidycholine (DSPC)-water bilayer system were used to probe lipid hydrocarbon chain trans-gauch isomerization dynamics below the gel-liquid crystalline phase transition temperature. In addition to the 1090-1085 cm-1 vibrational transitions, which appear with increasing temperatures and are characteristic of gauche conformers within the acyl chains, a new feature arises in all three bilayer systems at approximately 1122 cm-1. This carbon-carbon stretching mode is associated with the formation of the gauche bond rotation of the terminal methyl group oriented toward the center of the bilayer. Estimates of the enthalpy differences (deltaH) between hydrocarbon chains in an all-trans conformation and chain configurations containing gauche forms may be made from peak height intensities of vibrational features associated with the appropriate rotational isomers. For the DMPC-H2O, DPPC-H2O, and DSPC-H2O assemblies, the Raman data yield enthalpy differences of 2.9 +/- 0.6, 3.4 +/- 0.5, and 9.9 +/- 1.2 kcal/mol, respectively. These values are interpreted to reflect approximately two gauche bonds per lipid molecule for the DMPC-H2O and the DPPC-H2O gels and six gauche bonds per molecule for the DSPC-H2O gels.

Hydrocarbons↗
PubMed1977

Vibrational Raman spectra of lipid systems containing amphotericin B.

Resonance-enhanced and normal vibrational Raman spectra were observed for both multilamellar and single-wall vesicle assemblies of dimyristoyl phosphatidylcholine containing amphotericin B, a channel-forming polyene antibiotic, and cholesterol. The decrease in the frequency of the polyene antibiotic C = C stretching mode at 1556 cm-1 and the increase in intensity of the C-C-H in-plane deformation mode at 1002 cm-1 indicate that amphotericin B is ordered in a lipid-cholesterol medium similarly to the solid, but is surrounded by a slightly more polar environment. The intensity of the C = C stretching mode I1556 decreases 4-fold during the broadened gel to liquid crystalline phase transition (16--32 degrees C) of dimyristoyl lecithin-cholesterol (4 : 1) multilayers. Other resonance-enhanced vibrations of amphotericin B exhibit similar behavior. For amphotericin B in pure dimyristoyl lecithin multilayer or vesicle systems, however, the vibrational intensity associated with the C = C stretching mode remains constant during the melting of lipid hydrocarbon chains. In addition, a third effect occurs in liquid crystalline egg lecithin-cholesterol (4 : 1, mol ratio) multilayers in which I 1556 first increases by 25% between 3 and 25 degrees C, in parallel with the loss of active channels, and then remains constant as the temperature increases from 25 to 42 degrees C. This latter intensity pattern is masked in the dimyristoyl lecithin-cholesterol system by the overwhelming effect upon the C = C mode from changes in the lipid chain packing characteristics which occur during the phase transition. The broadened phase transition in 4 : 1 dimyristoyl lecithin-cholesterol multilayers (16--32 degrees C), as followed by the ratio of intensities at 2880 and 2850 cm-1 (asymmetric and symmetric methylene C-H stretching modes, respectively) is slightly narrowed by the addition of amphotericin B, and effect from which a binding stoichiometry at 24 degrees of 1 : 1 amphotericin B: cholesterol is estimated. This stoichiometry was confirmed by differential calorimetric scans, which also show the presence of a peak proportional to cholesterol content. Raman I2880/2850 peak height ratios in pure dimyristoyl lecithin bilayers were increased over the 14--38 degrees C range by amphotericin B, a spectral effect which suggests an ordering of the lipid matrix perhaps as a consequence of the polyene binding to the bilayer surface. For bilayers containing cholesterol, the ratios of intensities of the 2935 cm-1 feature, composed mainly of acyl chain terminal methyl and underlying methylene C-H stretching modes, to the 2850 cm-1 feature are significantly increased by amphotericin B. This effect indicates that the antibiotic penetrates the bilayer in the lipid-sterol system.

Amphotericin B↗
PubMed1976

Effect of bilayer curvature on vibrational Raman spectroscopic behavior of phospholipid-water assemblies.

In order to clarify the effect of bilayer curvature upon phospholipid conformation, vibrational Raman spectra were recorded for dipalmitoyl and dimyristroyl phosphatidylcholine in the gel state for both multilayer and single-wall vesicle assemblies. An intensity comparison, based upon a nonperturbing internal standard, between the two classes of bilayrer systems reflected a decrease in peak height intensity for the observed hydrocarbon chain transitions in the single shell vesicle form. No intensity change between bilayer form was detected, however, for the two observed head group modes. Trends in the peak height intensity rations for the 1100 cm-1 carbon-carbon stretching vibrations indicated an increase in hydrocarbon chain transgauche isomerization for the vesicle in comparison to the multilayer arrangements. The sensitivity of the methylene carbon-hydrogen stretching modes to interchain interactions was demonstrated by comparisons of the intensity patterns in the 2900 cm-1 region to the intensity characteristics of the carbon-carbon stretching region for polycrystalline, multilayer and vesicle materials. Examination of various carbon-carbon stretching mode intensity ratios for cholesterol doped dipalmitoyl phosphatidylcholine bilayers indicated that while 25 mol% cholesterol increased the transgauche acyl chain isomerization in multilayers, no comparable effect was observed for the vesicle forms. In contrast, the methylene twisting/methylene deformation intensity ratios for the cholesterol containing systems suggested that some further type of interchain perturbation occurs in the vesicle aggregations.

Membranes, Artificial↗
PubMed1976

Use of phospholipid-clay complexes for determining vibrational spectra of membrane related systems.

For determining the infrared and Raman spectra of membrane related systems, a method is developed to incorporate phospholipid bilayer assemblies in a clay matrix to form ultra-thin, self-supporting films. These films, containing stabilized bilayers arranged between the silicate layers of hectorite, are in the shape of discs which measure about 2 cm in diameter and 25 microns thick and require approximately 2 mg of phospholipid for preparation. Although several spectral regions below 1100 cm-1 are masked by the host clay, both head group and acyl chain vibrations may be conveniently observed and monitored for phospholipid conformational changes.

Membranes, Artificial↗
PubMed1976

Phase transitions of phospholipid single-wall vesicles and multilayers. Measurement by vibrational Raman spectroscopic frequency differences.

Raman spectroscopic frequency differences between selected carbon-carbon stretching modes of lipid hydrocarbon chains were determined as a function of temperature for use in monitoring lipid phase transition behavior and acyl chain disorder in both multilamellar and single-wall vesicles. Transition temperatures detected by this procedure for pure dipalmitoyl phosphatidylcholine and dimyristoyl phosphatidylcholine multilayers were observed at 39 +/- 1 degrees C and 23 +/- 1 degrees C, respectively. Although the phase transition for unilamellar vesicles of dipalmitoyl phosphatidylcholine occurred at nearly the same temperature as the multilayers, the crystal-liquid crystalline transition for the single-shell vesicles appeared to span a slightly broader temperature range, a characteristic consistent with irregularities in the packing arrangement of the hydrocarbon chains. Within the precision of the Raman spectroscopic method, however, the temperature behavior of both the multilamellar and the unilamellar dimyristoyl phosphatidylcholine assemblies appeared nearly identical. The temperature profile for the Raman frequency differences of an excess water sonicate of 25 mol percent cholesterol in dipalmitoyl phosphatidylcholine served as an example of the effect upon lipid phase transition characteristics of a bilayer component intercalated between the acyl chains. For this particular cholesterol-lipid system the phase transition was broadened over a 30 degrees C temperature range, in contrast to the marrow 2-4 degrees C range observed for pure multilayer and single-shell vesicle particles.

Binding Sites↗
PubMed1975

Raman spectra and vibrational assignments for dipalmitoyl phosphatidylcholine and structurally related molecules.

Raman spectra of dipalmitoyl phosphatidylcholine and structurally related molecules are examined and vibrational transitions assigned for the C-C, phosphate and C-H stretching modes of these molecules. Particular emphasis is placed on the characteristics of the Raman spectra in the 2800-3000, 1000-1150 and 700-800 cm-minus 1 regions. It is found that hydrocarbon transitions dominate the spectra at the expense of those of the phosphate and choline groups. The methyl and methylene C-H stretching assignments have been clarified for the Raman spectra of phospholipid systems.

Cholesterol↗