Amphiphilic derivatives of betaine esters as modifiers of macrovesicular BLM

A series of amphiphilic derivatives of betaine esters (V-n), with the chemical structure (CH3)3N+COOCnH2n + 1Cl- (n = 10, 12, 14 or 16) were studied with respect to their effects on the electrical properties of lecithin macrovesicular membranes. Normalized resistance and breakdown voltage were found to depend on the V-n concentration in the membrane and on the alkyl chain length (n). Resistance decreases up to about 10(4) ohm.cm2 and breakdown voltage decreases by 111 mV were detected in the V-n: lecithin molar ratio range measured (0.005-0.05). Maximal decrease in breakdown voltage was observed for V-14. These findings together with the featured anionic selectivity suggest that, due to the interaction of V-n with phospholipids, hydrophilic pores are formed in the lipid bilayers. This assumption is supported by the results obtained by electron paramagnetic resonance (EPR) measurements which showed no collective changes in bilayer dynamics or ordering. In particular, rotational correlation times and order parameters of the spin probe molecules dissolved in the membrane did not change in the concentration range tested. Since a large number of defects in the membrane can be expected to influence the collective ordering and dynamics, this observation also suggest that the number of pores formed is small.