PubMed · 5697033
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B Piccolo, R T O'Connor. 1968. Atomic absorption spectroscopy.. https://doi.org/10.1007/bf02631956
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Intramolecular excimer formation in pyrene-labeled phosphatidylcholine was used as a tool to determine thermodynamic characteristics of the lamellar to hexagonal phase transitions in a binary lipid system dilinoleoylphosphatidylethanolamine (DLPE)/palmitoyloleoylphosphatidylcholine (POPC). Upon an L alpha/HII phase transition, the activation energy Ea for excimer formation increased from 5.6 +/- 0.2 kcal/mol to 6.3 +/- 0.2 kcal/mol, while the activation entropy delta S decreased from -40.0 +/- 0.8 cal/K.mol to -38.4 +/- 0.8 cal/K.mol. The results are consistent with the idea of molecular splaying of the acyl chains in the hexagonal phase. It is estimated that the molecular area at the terminal carbon of the lipid acyl chains increases by a factor of 2.2 upon the L alpha HII transition in DLPE/POPC.
We propose a conformational nomenclature for amphiphilic lipid molecules that is general and compatible with the stereospecific numbering scheme, in contrast to earlier methods in which discrepancies with the sn-scheme lead to contradictory assignments of the absolute configuration of the system. The present method can be rationally extended to different classes of lipids, both natural and synthetic. It is simple and provides a convenient framework for conformational studies on widely varying classes of lipids.
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