title: Effects of short-chain alcohols on the phase behavior and interdigitation of phosphatidylcholine bilayer membranes.
abstract: Solute effects on the polymorphism and phase transitions in the suspensions of dipalmitoylphosphatidylcholine (DPPC) were studied by means of carboxyfluorescein (CF) and phosphatidylethanolamine rhodamine (PERho) fluorescence, differential scanning calorimetry, and X-ray diffraction. Specifically, the shifts of the lipid chain-melting phase transition, pretransition and subtransition temperature as a function of the bulk alcohol concentration were determined calorimetrically. The chain-melting phase transition temperature, Tm, was found to depend on the chain-length of the added alcohol: for short-chain alcohols (up to n-propanol), Tm first decreases and then increases with increasing alcohol concentration. For longer-chain alcohols, however, Tm decreases over the whole investigated alcohol concentration range. The pretransition and the subtransition temperature of DPPC both decrease monotonously (but non-linearly) with increasing alcohol concentration, but the former transition disappears at some characteristic, chain-length dependent alcohol concentration, cL beta i. This point in the solute-dependent phase diagram of DPPC is diagnostic of the complete hydrocarbon interdigitation. It was determined for a series of short-chain alcohols ranging from methanol through to 1-hexanol. A quantitative formula for the calculation of such limiting alcohol concentration is introduced. This formula relates the cL beta i values to the free energy of transfer of alcohols from the aqueous sub-phase into the DPPC sub-phase. By using the concept of an apparent chain-length this formalism can also be used for the alcohols with polar OH-groups at the second or third position on the hydrocarbon chain. Alcohol-induced hydrocarbon interdigitation in the phospholipid bilayers is thus shown to result chiefly from the solute-induced perturbation (lateral expansion) in the lipid headgroup region. Longer-chain alcohols, which balance this effect by disordering the phospholipid chains, therefore do not induce chain interdigitation.
authors.affiliation: Technische Universität München, Klinikum r.d. Isar, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Löbbecke
authors.forename: G
authors.initials: G
authors.lastname: Cevc
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000438:Alcohols / Q000494:pharmacology*; D002152:Calorimetry, Differential Scanning; D005456:Fluorescent Dyes; D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000438:Alcohols; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D015060:1,2-Dipalmitoylphosphatidylcholine