Effects of phospholipid acyl chain structure on thermotropic phase properties. 3. Phosphatidylcholines with (−), and (±)- anteiso acyl chains

Abstract

We have synthesized a number of anteiso-branched fatty acids, both as racemates and as pure (−)-stereoisomers, as well as the corresponding di- anteiso-acyl phosphatidylcholines (PCs). The phase transition temperatures ( c of the hydrated PCs have been determined by differential thermal analysis (DTA). Consideration of the observed effects of acyl chain length and terminal see-butyl group configuration on anteiso acid melting points and di- anteiso-acyl PC transition temperatures leads us to the conclusion that the terminal branched portions of anteiso acyl chains interact only weakly with adjacent acyl chains in the hydrated phosphatidylcholine bilayer and probably in the anhydrous fatty acid crystal as well. In agreement with this conclusion, we observe that the DTA heating transition endotherms for hydrated di- anteiso-acyl PCs appear to be considerably less strongly endothermic, and occur at much lower temperatures, than do the major transition endotherms for the di- n-acyl PCs of like carbon number. Our findings generally support the proposal that anteiso acyl lipids tend to fluidize membranes, although they do so less effectively than do cis-unsaturated acyl lipids.