title: Raman spectroscopic study of an interdigitated lipid bilayer. Dipalmitoylphosphatidylcholine dispersed in glycerol.
abstract: Dipalmitoylphosphatidylcholine (DPPC) dispersed in perdeuterated glycerol was investigated in order to determine the effects on the Raman spectra of hydrocarbon chain interdigitation in gel-phase lipid bilayers. Interdigitated DPPC bilayers formed from glycerol dispersions in the gel phase showed a decrease in the peak height intensity I2850/I2880 ratio, for the symmetric and asymmetric methylene CH stretching modes, respectively, as compared to non-interdigitated DPPC/water gel-phase dispersions. The decrease in this spectral ratio is interpreted as an increase in chain-chain lateral interactions. Spectra recorded in the 700-740 cm-1 CN stretching mode region, the 1000-1200 cm-1 C-C stretching mode region and the 1700-1800 cm-1 C = 0 stretching mode region were identical for both the interdigitated and non-interdigitated hydrocarbon chain systems. At low temperatures the Raman peak height intensity ratios I2935/I2880 were identical for the DPPC/glycerol and DPPC/water dispersions, indicating that this specific index for monitoring bilayer behavior is insensitive to acyl chain interdigitation. The increase, however, in the change of this index at the gel-liquid crystalline phase transition temperature for the DPPC/glycerol dispersions implies a larger entropy of transition in comparison to the non-interdigitated DPPC/water bilayer system.
mesh_terms: D005990:Glycerol; D008051:Lipid Bilayers; D011663:Pulmonary Surfactants; D013059:Spectrum Analysis, Raman; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D011663:Pulmonary Surfactants; D005990:Glycerol