Hemolysis by Amphoteric Surfactants with a Phosphate Group

The hemolysis of some amphoteric surfactants with a phosphate group was investigated to clarify the mechanism of antimicrobial activity of 2- (hexadecyldimethylammonio) ethyl hydrogen phosphate (C16C1 C1NC2PO4). C16C1C1NC2PO4 was found to have higher hemolytic activity than some analogues. The hemolytic activity-structure relationship of (trialkylammonio) alkyl hydrogen phosphate showed the following characteristics. C16C1C1NC2PO4 had high hemolytic activity among the homologues. When a methylene bridge between two ionic groups was 2, the highest hemolytic activity was observed in some congeners differing from the length of methylene bridge. This was due to the phosphate group of C16C1 C1 NC2PO2 present in a free form. The phosphate groups of the congeners differing from C16C1C1 NC2PO4 in length of the methylene bridge, interacted intramolecularly or intermoleculaly with the quaternary ammonium groups owing to the large degree of steric freedom. As the carbon number of short alkyl chains increased, hemolytic activity became higher due to hydrophobic effect. This is contrast to cases of antimicrobial activity and binding ability with divalent cations by steric effect.The primary site of hemolytic attack by C16C1C1NC2PO4 thus differs considerably from the active site for antimicrobial action. However, relatively good correlation between hemolytic activity and antimicro-bial activity toward K. pneumoniae was observed. The contribution of the lipophilicity of C16C1C1NC2PO4 is thus important for antimicrobial activity. Sodium 2- [N-methyl (2-hydroxytetradecyl) amino] ethyl hydrogen phosphate, found to show bacteriostatic activity, showed higher hemolytic activity.