On the basis of Gortel & Grendel (J. Exp. Med., 1925, 41, 439-494) discovery, the importance of the lipid bilayer as an integral and indispensible component of the cell membrane is discussed. In particular, attention focuses on the interaction between membranes and amphiphilic substances. The effect on membranes of quaternary ammonium salts, both in the form of pesticides and oxidants as well as organic compounds of tin and lead are discussed in greater detail.
The effect of two series of amphiphilic quaternary ammonium salts on some properties of phospholipid membranes was studied. The compounds of one series, N-benzyl-N,N-dimethyl-N-alkyl ammonium bromides, exert a destructive effect on membranes and are treated as reference compounds. The compounds of the other series, N-(3,5-di-t-butyl-4-hydroxy)benzyl-N,N-dimethyl-N-alkyl ammonium bromides, are derivatives of the former ones, exhibit antioxidant properties, and do only relatively slight damage to the membranes. The aim of the work was to explain the difference in molecular interaction with membranes between the two kinds of hydrophobic compounds. Thermodynamic methods, a new mixing technique, and monolayer and quantum calculation methods were used. It has been shown that the antioxidant molecules are less hydrophobic than those of the reference compounds and disturb the membrane organization to a lesser extent. On the basis of monolayer data, we suggest that the studied antioxidant behaves like a substitutional impurity, whereas the reference behaves like an interstitial one.
The effect of four amphiphilic cationic compounds that differ in their polar head properties on the kinetics of calcium ion desorption from unilamellar lecithin liposom e membranes has been studied. The compounds under investigation were: N-benzyl-N,N-dimethyl-N-tetradecy-lammonium chloride (BDTA), N-methyl-N-tetradecylmorpholinium bromide (MTM), N-methyl-N-dodecyloxym ethylenem orpholinium chloride (MDOM) and N,N,N-trimethyl-N-te-tradecylammonium bromide (TMTA). Kinetic constants were determined using the three-compartmental analysis for isotopic labels. For the above mentioned compounds electronic structure calculations were performed and point charges and dipole moments of the molecules determined by using quantum chemistry methods. It was found that the rate of desorption increases with increasing concentration of the compounds studied, and effectiveness of the compounds follows the sequence: BDTA >MTM >TMTA >MDOM . For dipole moments the sequence obtained is somewhat different, namely: BDTA>MTM >MDOM >TMTA. Apparently, the differences in the effectiveness of action of the compounds in the calcium desorption process follow not only from the values of dipole moments of their polar heads but also from the values of point charges on some atoms and from steric properties.
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