Laser Raman Spectroscopic Study of Specifically Deuterated Phospholipid Bilayers

Raman spectra of 1,2-dimyristoyl-sn-glycero-3- phosphocholines specifically deuterated in the 2 chain at one of positions 3, 4, 6, 10, 12, and 14 have been obtained as a function of temperature. The frequencies of the CD₂ vibrational stretching modes depend on the position of the labeled CD₂ group, being maximum at position 3 of the acyl chain and then decreasing until they become constant beyond position 6. This frequency dependence is interpreted in terms of the inductive effect of the charge distribution of the acyl chain carboxyl group. In both gel and liquid-crystal phases, the Raman line widths depend on the position of the CD₂ group, being minimum at position 6 and increasing toward both ends of the hydrocarbon chain. The width of the CD stretching bands abruptly increases at the phase transition temperature. The magnitude of the increase depends upon the position of the label, increasing almost linearly up to position 10 and then decreasing for positions 12 and 14. The spectra for the CD₂ group at position 3 and the terminal CD₃ group are almost the same in both phases. These results are interpreted in terms of the effects of hydrocarbon chain organization on the vibrational modes.