Acyl chain packing properties of deuterated lipid bilayer dispersions: Vibrational Raman spectral parameters

Abstract

Abstract The phase, packing and dynamic behavior of model membrane systems consisting of lipids with completely deuterated chains is generally monitored by the temperature dependence of the line width of the methylene (CD 2 ) symmetric stretching modes located at ∼2100 cm −1 1–5 Alternative empirical spectral parameters derived from the peak‐height intensity ratios of spectral features assigned to the chain CD methylene and methyl stretching modes are introduced and evaluated. In particular, specific intensity ratios reflect a sensitivity to average inter‐ and intra‐chain order–disorder properties of the portions of the lipid chains localized either near the methyl termini or near the head‐group–acyl chain interface. The utility of these intensity parameters is evaluated by examining the bilayer behavior of binary mixtures of dipalmitoylphosphatidylcholine with fully deuterated lipid chains (DPPC‐ d 62 ) and dipalmitoylphosphatidylcholine with non‐deuterated chains (DPPC‐ d o ) in various physical states. We also assess the use of intensity parameters for clarifying the effects of ethanol on the inter‐ and intra‐chain interactions of DPPC‐ d 62 bilayers. In the DPPC‐ d 62 –ethanol system particular emphasis is placed on the formation of the novel interdigitated chain gel phase.