Phase behavior of the DOPE + DOPC + alkanol system

Abstract

Small- and wide-angle X-ray diffraction was used to study the effect of 1-alkanols, as simple models of general anesthetics, (abbreviation C_nOH, n = 8–18 is the even number of carbons in the aliphatic chain) on the lamellar to hexagonal L_α → H_II phase transition in the dioleoylphosphatidylethanolamine–dioleoylphosphatidylcholine = 3 : 1 mol/mol (DOPE + DOPC) system. All studied C_nOHs were found to decrease the phase transition temperature of the DOPE + DOPC system in a C_nOH chain length and concentration dependent manner and thus promote the formation of the H_II phase. Anesthetically active C₈OH and C₁₀OH were found to decrease the lattice parameter d of the L_α phase, however longer non-anesthetic C_nOHs increased the parameter d; this effect being more pronounced with increasing C_nOH concentration. The lattice parameter of the H_II phase was decreased in the presence of all C_nOHs, even at the lowest concentrations studied. In the scope of the indirect mechanism of general anesthesia observed changes in the lattice parameter d (reflecting changes in the bilayer thickness) due to the intercalation of C₈OH and C₁₀OH might induce changes in the activity of integral membrane proteins engaged in neuronal pathways.