Chain-melting transition temperatures of phospholipids with acylated or alkylated headgroups (N-acyl phosphatidylethanolamines and O-alkyl phosphatidic acids), or with alpha-branched chains.
The biphasic dependence of the chain-melting transition temperature on chainlength, nN, of the headgroup-attached chain of N-acyl phosphatidylethanolamines and of O-alkyl phosphatidic acids is interpreted in terms of a different linear dependence of the transition enthalpy and entropy on nN for long and short chains, respectively. A consistent expression of the form [equation: see text], where DeltanN is the critical chainlength at which the packing mode of the headgroup-attached chains changes, is found to apply systematically to the transition temperatures for both sets of lipids, over the range nN=2-18. This thermodynamic analysis demonstrates that the headgroup-attached chain is located in an environment that differs for long and short chains. Similar considerations apply also to phosphatidylcholines with alpha-branched glycerol-attached chains.
Marsh
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Max-Planck-Institut für biophysikalische Chemie, Abteilung Spektroskopie, D-37077 Göttingen, Germany.
D019277:Entropy; D008956:Models, Chemical; D010712:Phosphatidic Acids / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
D010712:Phosphatidic Acids; D010714:Phosphatidylethanolamines; D010743:Phospholipids