Characterization of the pretransition in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine by Fourier transform infrared spectroscopy

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Abstract
Fourier transform IR spectroscopy was used to study the IR-active acyl chain vibrational modes of fully hydrated multibilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (L-DPPC) over the temperature range 0.degree.-55.degree. C. Frequencies, bandwidths and other spectral parameters were measured as a function of temperature for the methylene scissoring, rocking and wagging modes, as well as for the C-H stretching modes; they were used to monitor the packing of the acyl chains. Particular emphasis was placed on determining the nature of the pretransition event. Between 36.degree. and 38.degree. C the spectral changes are indicative of a phase change in the acyl chain packing from an orthorhombic to a hexagonal subcell. In the gel phase, at all temperatures below the main transition, the acyl chains are predominantly in all-trans conformations. The temperature-dependent variations of spectral parameters apparently result from changes in interchain interactions.

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