Interactions of short-chain alcohols with dimyristoylphosphatidylethanolamine bilayers: a calorimetric and infrared spectroscopic investigation

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Abstract
We have investigated the effects of methanol, ethanol, and 1-propanol on the phase transitions of L-.alpha.-dimyristoylphosphatidylethanolamine using differential scanning calorimetry and Fourier transform infrared spectroscopy. Alcohols lower the temperature of the gel (L.beta.) to liquid-crystalline (L.alpha.) phase transition and also lower the temperature of the unhydrated crystalline (Lc) to liquid-crystalline phase transition. When the lipid/alcohol dispersions are incubated at 2.degree.C for 1-18 h, a dehydrated crystalline phase forms, which gives rise to a phase transition at about 55.degree.C. This dehydrated crystalline phase forms more quickly at higher alcohol concentrations. although alcohol at low concentration lowers the enthalpy of the observed melting transition, at high concentrations 1-propanol markedly increases this enthalpy. The phase giving rise to this high-enthalpy melting process is distinct from both the unhydrated crystalline phase and the gel phase. Infrared spectra suggest that this phase contains significant amounts of alcohol in a solid solution with the lipid.