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The change of biological activity of amphiphilic biocides following the change of their hydrophobic parts (the cut-off effect) is discussed. The mechanism of the interaction (between such amphiphiles and model and biological membranes is proposed that explains the cut-off phenomenon. It is proposed, on the basis of experimental studies and theoretical calculations, that the diminished biological activity of amphiphilic compounds upon elongation of thier hydrophobic part can be the result of the appearance of interdigitated structures in the lipid bilayers. On the other hand, weak hydrophobic interactions between amphiphilic compounds of short hydrophobic chins and lipid molecules of model membranes are responsible for the poor biological activity of these compounds.
This paper presents the results of study on the toxic action mechanism of organic derivatives of tin (IV) on black lipid membrane (BLM) as a model of cell membrane. Trimethyltinchloride, tripropyltinchloride, tributyltinchloride, triphenyltinchloride, dimethyltindichloride, dipropyltinchloride, dibutyltin- dichloride, diphenyltindichloride were tested. The compounds were selected to determine the role of their structural elements in the mechanism studied. The measurements were made for the concentrations of investigated compounds ranging from 0 to 12x 10-7 mol/L, i.e. within the range of toxic concentrations, causing the BLM depolarisation. The effects of compounds studied on BLM were strongly dependent on their concentration and structure, which the trans- membrane-potential measurements of model-membrane depolarisation (dynamics and extent) showed the most evidently. The efficiency of the interaction between the black lipid membrane and the tin (IV) derivatives increased as follows: dialkyl > trialkyl > diphenyl > triphenyl. The compounds studied were recognised as having the lipophilic properties-crucial for modification of model and biological membranes.
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Electrolyte efflux, chlorophyll, malondialdehyde content and enzymatic activities (catalase, peroxidase) in cucumber cotyledons as well as stability of model lipid membranes in the presence of some new, acyclic and cyclic, aminophosphonates were studied. They also differed in the substituents at the phosphorus and nitrogen atoms. It was found that the effectiveness of the compounds to influence mentioned parameters depended on their lipophilicity and structural features. The most active compounds were these with isopropyl substituents at the P atom unless their hydrocarbon chains at the N atom were not too long. Butyl substituents at phosphorus significantly decreased aminophosphonates efficiency. Similar effect was observed when trans-type hydrocarbon chain was replaced with a short-branched one. It also seems that cyclic compounds with hexane rings were weaker modifiers of model and biological membranes than these with pentane rings. Results show that aminophosphonates interact with plasma membranes and presumably induce oxidative stress.
The antioxidant activity of two new series of pirolidinium chlorides (PAC-n) and bromides (PAB-n) was studied. The antioxidant functional group was incorporated into the polar part of the compounds. The influence of the compounds on the degree of lipid oxidation in the erythrocyte membrane subjected to UV radiation was studied. It was found that all the salts used protected erythrocyte membranes against oxidation of membrane lipids. Their antioxidant activity increased with alkyl chain length. PAB compounds were stronger oxidation inhibitors than PAC ones. Possible reasons for such behaviour are discussed, taking into account the fluidity changes in erythrocyte membrane caused by the compounds studied. In order to do this, steady-state measurements of fluorescence anisotropy were performed, enabling to calculate the anisotropy coefficient.
The hemolytic activity of some newly synthesized aminomethanephosphonic acid derivatives was studied. The compounds studied differed in their polarity and the hydrophobicity of the electronic substituents at their nitrogen and carbon atoms. It was found that acyclic aminophosphonates exhibited significantly stronger hemolytic properties than cyclic aminophosphonates. To cause the same level of hemolysis of pig erythrocytes, it was necessary to use about a tenfold higher concentration of cyclic aminophosphonates than acyclic ones. The hemolytic activities of the compounds were related to the possibilities of their incorporation into the lipid phase of erythrocyte membranes. Once incorporated, they changed the fluidity of those membranes; the changes were more pronounced in the case of cyclic aminophosphonates. Acyclic compounds were also found to exhibit a slight antioxidative activity, which may be a consequence of their stronger interaction with the membrane lipids. The results obtained in the experiments performed with the use of planar lipid membranes were similar to those obtained in the hemolytic studies, i.e., acyclic aminophosphonates interacted more effectively with those membranes. The general conclusion is that both stereochemistry and hydrophobicity are the factors that determine the efficiency of the interaction of the compounds studied with the model membranes used, and that most likely location of aminophosphonates is the lipid phase of the erythrocyte membrane. Another conclusion is that newly synthesized aminophosphonates may be used as potentially good pesticides.
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