THERMODYNAMIC AND FLUORESCENCE STUDIES OF THE UNDERLYING FACTORS IN BENZYL ALCOHOL-INDUCED LIPID INTERDIGITATED PHASE

To further investigate factors contributing to the action of alcohol i n the solute-induced lipid interdigitation phase, thermodynamic and fl uorescence polarization measurements were carried out to study the int eraction of benzyl alcohol with dipalmitoyl phosphatidylcholine bilaye r vesicles. The obtained results were compared with those previously r eported for ethanol and cyclohexanol (L. G. Roth and C-H, Chen, Arch. Biochem. Biophys. 296, 207, 1992). Similar to ethanol, benzyl alcohol was found to exhibit a biphasic effect on the enthalpy (Delta H-m) and the temperature (t(m)) of the lipid-phase transition and the steady-s tate fluorescence polarization (P) monitored by 1,6-diphenyl-1,3,5-hex atriene, At a total concentration of benzyl alcohol <30 mg/ml (the alc ohol concentration in lipid phase <21 mg/ml), benzyl alcohol was found to exhibit large increases in Delta H-m and P, which were correlated with the formation of a lipid interdigitated phase, as evidenced by re ported X-ray diffraction data. Combining the results with benzyl alcoh ol and ethanol suggested that simultaneously large changes in Delta H- m and P can be used as an indication of the occurrence of a solute-ind uced lipid interdigitated phase. The overall interacting force in the formation of this lipid phase, as derived from the interactions of the hydroxyl portion of an alcohol with the lipid phosphate head group an d the hydrophobic portion of an alcohol with the lipid hydrocarbon cha ins, may or may not be dominated by hydrophobic interaction, Although lipid/water partition coefficients and the contribution of hydrophobic interaction to the overall interacting force were comparable between benzyl alcohol and cyclohexanol, benzyl alcohol induced lipid interdig itated phase, but not for cyclohexanol, This was due to the ability of benzyl alcohol to be more effective than cyclohexanol in simultaneous ly interacting with the phosphate head group and the hydrocarbon chain s of lipid. (C) 1996 Academic Press, Inc.