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.
In this paper, we present studies concerning phenyltin adsorption onto the dipalmitoylphosphatidylcholine bilayer. Phenyltin compounds are known to be biologically active, and their molecular geometry makes it possible to study the effect of steric constraints on their ability to penetrate the model lipid membrane. Using a fluorescence probe as a reporter of the amount of adsorbed compound, we evaluated their affinity to the membrane as a function of the membrane state. The amount of the adsorbed compound was found to depend on the adsorbing molecule's geometry and lipid bilayer organization. The fluorescence measurements were supported by the density functional theory (DFT) method of quantum mechanical computations. The penetrant location was correlated with the possible relative positions of its polar and hydrophobic moieties to determine if it could adopt structural requirements of the local membrane environment. Molecules were deformed by a model force, mimicking interactions within the membrane interfacial region. Computations show that the diphenyltin molecule can be deformed to such an extent that it can adopt an amphiphilic conformation. Triphenyltin is different, as its bending requires more energy. Born repulsion energies from hydrophobic fluid into water for phenyltins were also computed in an isodensity-polarized continua model of DFT computation. Our results indicate that the phenyltin compounds incorporate into the interface of the lipid membrane, although diphenyltin integrates more deeply than triphenyltin, which locates on the double layer's surface, and this is due to the fact that the main role is played by steric and not electrostatic interactions.
Our earlier studies have shown that the compounds diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT) in the presence of UVC radiation enhanced the degree of phosphatidylcholine liposome membrane oxidation (J. Agric. Food Chem. 2005, 53, 76-83). The prooxidative behavior of the compounds has now been confirmed with the electron paramagnetic resonance method, which proved the possibility that the studied compounds can exist in free radical forms. The present work investigates the possibility of the protective action of quercetin on phosphatidylcholine liposome membranes exposed to the prooxidative action of DPhT and TPhT induced by UV radiation (lambda = 253.7 nm). The concentrations of quercetin and its equimolar mixtures with DPhT and TPhT were determined (and compared with well-known antioxidants as standards-trolox and butylated hydroxytoluene, also in the presence of phenyltins) as those that induce 50% inhibition in oxidation of liposomes radiated with UV. They are 5.1 +/- 0.10, 2.9 +/- 0.12, and 1.9 +/- 0.08 microM (differences between the values are statistically significant), constituting the following sequence of antioxidative activity: quercetin:TPhT > quercetin:DPhT > quercetin. This relation is confirmed by the results on the antiradical ability of quercetin and its mixtures with DPhT and TPhT toward the free radical 1,1-diphenyl-2-pricrylhydrazil. Similar sequences obtained in both studies suggest a possible mechanism of the antiradical action of the mixtures as free radical scavengers. We suggested that (i) quercetin's ability, documented by spectrophotometric, infrared attenuated total reflectance spectroscopy, (1)H NMR, and molecular modeling methods, to form complexes with phenyltins indicates a possible way of protection against the peroxidation caused by the free radical forms of phenyltins and (ii) the differentiation in the action of the quercetin/TPhT and quercetin/DPhT associates (statisticaly significant) may result from a different localization in the liposome membrane, which is indicated by the results of the fluorimetric studies.
When model membranes are prepared by ultrasonic treatment of polyunsaturated phospholipids, radical production can induce a partial degradation of the polyunsaturated fatty acyl chains and the formation of lipid hydroperoxides. A suitable antioxidant employed during liposome preparation is able to protect them against lipid peroxidation. This work contains the results of studies on egg lecithin liposomes with incorporated antioxidants that were supposed to play the protective role mentioned. As it has been shown the antioxidant com pounds used ensured a 40-60% , i.e., satisfactory protection of liposomes after 30 min sonication. Possible practical applications are discussed.
The effect of trialkyllead and trialkyltin on pig erythrocyte hemolysis has been studied and compared. The results o f experiments showed that the hemolytic activity o f organoleads increases with their hydrophobicity and follows the sequence: triethyllead chloride < tri-npropyllead chloride < tributyllead chloride. And similarly in the case of organotins: triethyltin chloride < tri-n-propyltin chloride < tributyltin chloride. Comparison of the hemolytic activity of organoleads and organotins indicates that the lead compounds exhibit higher hemolytic activity. The methods of quantum chemistry allowed to determine the maximum electric potential of the ions R3Pb+ and R3Sn+, and suggest a relationship betw een the potential and toxicity.
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