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Raman spectroscopic study of saturated mixed chain phosphatidyl choline multi lamellar dispersions

Biophysical Journal 41(2 PART 2): 350A

Raman spectroscopic study of saturated mixed chain phosphatidyl choline multi lamellar dispersions

The thermotropic behavior of a series of mixed-chain saturated phospholipids in fully hydrated multilamellar dispersions was examined by vibrational Raman spectroscopy in both the C.sbd.C stretching (1000-1200-cm-1) and the C.sbd.H stretching (2800-3100-cm-1) mode regions. This lipid series represents phosphatidylcholines [PC] in which the sn-1 acyl chain is fixed in length with 18 C atoms, while the sn-2 acyl chain length is increased in steps of 2 methylene units from 10 to 18 C atoms. The transition temperatures of these mixed-chain PC measured by Raman spectroscopic procedures are in good agreement with those determined by high-sensitivity differential scanning calorimetry. The total change in the Raman spectral intensity ratio .DELTA.(I2935cm-1/I2884cm-1) across the narrow gel .tautm. liquid-crystalline phase transition temperature region is markedly different for the mixed-chain phospholipids in comparison to the symmetric chain systems. For the mixed-chain bilayer dispersions, the data conform to a smooth hyperbolic cosine curve and vary in the order C(18):C(10)PC > C(18):C(12)PC > C(18):C(14)PC < C(18):C(16)PC < C(18):C(18)PC with a minimum chain-chain order/disorder change observed for the C(18):C(14)PC multilamellar assemblies. The change in the spectral intensity ratio determined in the 1000-1200-cm-1 region is similar to that detected in the 2800-3100-cm-1 region; the smallest change in the spectral intensity ratio .DELTA.(I1088cm-1/I1065cm-1) across the phase transition region is again observed for the C(18):C(14)PC dispersions. These data, together with other structural information determined at common reduced temperatures for various gel state, mixed-chain phospholipid dispersions, lead to the conclusion that membrane lipids adopt 2 types of chain conformations in bilayer systems. In the first class, the lipid molecules in the 2 opposing monolayers pack independently, as typified by the C(18):C(18)PC and C(18):C(16)PC bilayers. In contrast, the hydrocarbon chains in the second type of lipid bilayers are assumed to effect an interdigitated packing arrangement which couples the 2 monolayers across the bilayer center. This second type of bilayer is represented by the C(18):C(10)PC, C(18):C(12)PC, and C(18):C(14)PC dispersions.

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Accession: 006255845

PMID: 6871161

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