R. Mendelsohn

The effect of sonication on the hydrocarbon chain conformation in model membrane systems: A Raman spectroscopic study☆

Raman spectra are presented for egg lecithin above and below the gelliquid crystal phase transition, and several regions of the Raman spectrum are shown to be sensitive to conformational changes in the hydrocarbon chains. These regions are used to investigate the effect of sonication on the structure of egg lecithin and dipalmitoyl lecithin vesicles. Sonication of both egg lecithin above Tm, and dipalmitoyl lecithin above and below Tm produces no change in the relative population of trans and gauche isomers in any of the systems studied. Sonication does however appear to effect interchain interactions, a possible consequence of imperfect packing towards the center of the bilayers in vesicle systems.

Structural studies of biological membranes and related model systems by raman spectroscopy: Sphingomyelin and 1,2-dilauroyl phosphatidylethanolamine☆

Raman spectra are reported at relatively high resolutions (1.5 cm-1) for sphingomyelin and for 1,2-dilauroyl phosphatidylethanolamine above and below their melting temperatures. The spectra of 1,2-dilauroyl phosphatidylethanolamine below Tm show the hydrocarbon chains to be less ordered in the solid phase than the fatty acid of the same chain length, without the significant occurrence of guache isomers. The spectra of sphingomyelin show significant formation of gauche isomers below Tm, indicating a less rigid environment for this molecule in the solid state.

Resonance Raman spectra of the nickel, cobalt, and copper chelates of mesoporphyrin IX dimethyl ester

Resonance Raman spectra have been obtained for the Ni, Co, and Cu chelates of mesoporphyrin IX dimethyl ester in solution using the tunable Rhodamine 6G dye and Ar+ lasers. Several bands show variation of intensity and depolarization ratio with exciting wavelength. Excitation profiles for some isolated bands peak at the maxima of the corresponding α electronic absorption bands. The variation of depolarization ratio for some anomalously polarized bands (ρl > 3/4) has been interpreted in terms of lowering of the symmetry of metalloporphyrins from D4h. The rigorous symmetry of these chelates is proposed as Cs because of the effect of peripheral substituents. A vibrational assignment is suggested for some of the metal sensitive modes.

Resonance Raman spectra of Cu‐etioporphyrins I, I‐meso‐d4, and IV

Resonance Raman spectra obtained using the Ar+ and tunable Rhodamine 6G dye lasers are presented for the position isomers Cu−etioporphyrin I and IV in dilute (10−4 M) solution. The spectra show significant differences in several vibrations enabling the molecules to be distinguished. Several anomalously polarized (ρl ≳ 3/4) vibrations are observed which show dispersion of the depolarization ratios. The dispersion of ρl is interpreted as arising from reduction of chromophore symmetry from its idealized D4h. The solution data for Cu−etioporphyrin I and Cu−etioporphyrin IV are consistent with C4h symmetry and C2v symmetry, respectively, thereby demonstrating the sensitivity of resonant Raman scattering to slight perturbations of the chromophore due to peripheral substituents. Resonance Raman data are also presented for the deuterated analog Cu−etioporphyrin I (meso−d4). Several shifts in the vibrational modes are observed and possible vibrational assignments are discussed.

Deuterated fatty acids as Raman spectroscopic probes of membrane structure

Raman spectra are reported for the C-D stretching region of stearic acid-d35 bound in egg lecithin multilayers. The temperature dependence of the spectra shows that the linewidth of the C-D stretching bands is a sensitive and non-perturbative probe of membrane hydrocarbon chain conformation. The utility of this approach for studying lipid conformation in membranes containing a significant fraction of non-lipid component is discussed.

Resonance Raman spectra of Cu‐1:3:5:7‐tetramethyl porphin and Cu‐1:2:3:4:5:6:7:8‐octamethyl porphin

Resonance Raman spectra of Cu‐1:3:5:7‐tetramethyl porphin and Cu‐1:2:3:4:5:6:7:8‐octamethyl porphin have been obtained both in dilute CS2 solution and as solids dispersed in KBr matrices using the Ar+ and tunable Rhodamine 6G dye lasers. The solution data for Cu‐octamethyl porphin show that its rigorous molecular symmetry in solution is D4h, while the spectral data for Cu‐tetramethyl porphin are consistent with C4h molecular symmetry. Assignments for some of the stronger bands are discussed by comparing the spectra of these two molecules with other planar metalloporphins and porphyrins.

Raman studies of the C-H and C-D stretching regions in stearic acid and some specifically deuterated derivatives.

Raman spectra of polycrystalline stearic acid-do, stearic acid-d35, 16:16-d2-18:18:18-d3-stearic acid, 18:18:18-d3-stearic acid, 17:17-d2-stearic acid, 17-d1-stearic acid, 16:16-d2-stearic acid, 12:12-d2-stearic acid and 12-d1-stearic acid have been obtained for the region containing the C-D and C-H stretching vibrations. Assignments of the methyl, methyl-d3, methylene, methylene-d2 and methylene-d1 stretching vibrations are discussed.

Thermal denaturation and photochemistry of bacteriorhodopsin from Halobacterium cutirubrum as monitored by resonance raman spectroscopy

Resonance Raman studies of the thermal denaturation of bacteriorhodopsin from Halobacterium cutirubrum show that the N-retinylidenelysine moiety present in the chromophore is N-protonated. This corroborates an earlier suggestion of Lewis et al. ((1974) Proc. Natl. Acad. Sci. U.S., 71, 4462-4466). The widely differing excitation profiles of two -C=C- stretching modes are explained in terms of the light-initiated reaction cycle in the molecule. Glutaraldehyde fixation of bacteriorhodopsin has no effect on the intensity ratio of the two modes, suggesting that no large motion of the protein is necessary for the photoreaction cycle to occur.

Resonance Raman spectroscopy as an analytical probe for biological chromophores: Spectra of four Cu-etioporphyrins*

Summary Resonance Raman spectra have been obtained for the position isomers Cu-etioporphyrins I, II, III, and IV, as solids dispersed in KBr matrices. The spectra of the four molecules differ markedly in the 650–850 cm −1 region, enabling the substances to be distinguished. The potential of resonance Raman spectroscopy as a sensitive and non-destructive analytical tool is illustrated.

Infrared and far-i.r. spectra of Cu-1:3:5:7-tetramethyl porphin and Cu-1:2:3:4:5:6:7:8-octamethyl porphin☆

Abstract Infrared and far-i.r. spectra have been obtained for polycrystalline Cu-1:3:5:7-tetramethyl porphin and Cu-1:2:3:4:5:6:7:8-octamethyl porphin as solids dispersed in KBr and polyethylene matrices. A comparison of the i.r. and Raman data suggest that the two molecules have a center of symmetry in the solid state. The i.r. spectra are compared with the i.r. spectra of the corresponding non-metalloporphyrins in order to gain information about the i.r. active metal—nitrogen vibrations.