Polar head charge of membrane modifiers and their biological activity: the Monte Carlo simulation studies

On the basis of the 10-state Pink model, the effect of the polar head charge of amphiphilic modifier molecules has been discussed. It was shown, that for small concentrations of anionic and cationic compounds inserted into a layer composed of electroneutral lipids the electrostatic interaction, in spite of the long-range character, can be limited to the nearest neighbour interaction. Computer simulation results suggest, that the gel-fluid transition temperature can be lowered or raised by a proper selection of anionic-cationic amphiphilic modifiers. Moreover, the effect of ionic strength of the membrane medium and dielectric permeability of the hydrophobic part of membrane, where a shift of the dielectric constant from 5 to 80 occurred, has been studied. It was also shown that addition of alkyl molecules to the membrane, which are the counterions of alkyl modifier molecules added earlier, almost doubles the number of incorporated membrane modifiers. Membrane permeability analysis shows that membrane permeability, at temperatures lower than the gel-fluid transition temperature, should be more related to the number of small domains (cluster area) and less to the interfacial area.