A QUANTITATIVE ELECTRON-SPIN-RESONANCE LINE-SHAPE STUDY OF THE ORDER-DISORDER TRANSITION IN THE LAMELLAR PHASE OF THE PALMITOYLLYSOPHOSPHATIDYLCHOLINE-WATER SYSTEM

A quantitative slow-motional ESR line shape study is reported of the l amellar phase and the micellar phase of the palmitoyllysophosphatidylc holine (PaLPC)-water system. The lamellar spectra are simulated using the microscopic order-macroscopic disorder (MOMD) model developed by M eirovitch, E., Nayeem, A., and Freed, J. H., 1984, J. phys. Chem., 88, 3454, whereas the micellar spectra are interpreted in terms of a two- dynamics model developed in this laboratory (Liang, Z., and Westlund, P.-O., 1993, J. chem. Phys., 99, 7098). For the lamellar phase, an ord er-disorder transition is observed from the temperature dependence of the spectra and quantized in terms of the model parameters, yielding a transition temperature of about 45 degrees C. A comparison of the mod el parameters is made between the lamellar and the micellar phases, wh ich indicates a phase independence of the local orientational order. A similar comparison is made also between the oleoyllysophospatidylchol ine-water and the PaLPC-water systems in the lamellar phases. It is su ggested that in the lamellar phase of PaLPC there is an interdigitatio n of acyl chains of the PaLPC bilayer.