Structure-activity relationships, anionic surfactants

The quaternary ammonium compounds (qv) are manufactured by the reaction of an alkyl halide with a tertiary amine. The alkyl halide may be short-chain, long-chain, or benzyl. Selection of a long-chain alkyl group yields structures with variable composition and greatly adds to the chemical complexity inherent in this group. Investigation of structure-activity relationships has led to claims for superior efficacy or compatibility, most notedly with anionic surfactants in disinfectant-detergent cleaner systems, of closely related compounds in the family. 

Gullikson, G.W., et al. 1977. Effects of anionic surfactants on hamster small intestinal membrane structure and function Relationship to surface activity. Gastroenterology 73 501. 

The role of surfactants in stabUizing emulsions, as well as the relationship between demulsifier structure and performance, has been identified for over 50 years [J9]. The classification of surfactants as well as demulsifiers is quite arbitrary, but a commonly used one is based on chemical structure [20, 21], Chemical types include nonionic, anionic, and cationic. A brief summary of the evolution in demulsifier chemistry over the years and the effective concentration range is presented in Table 1. The development of chemicals which are more surface active has allowed for reductions in the average dosages. 

Such interactions are directly relevant to the effect of surfactants on drug absorption. Fig. 10.5a shows the relationship between absorption of salicylate or L-valine across rat jejunal tissue in vivo and release of protein and phospholipid by a series of surfactants. Fig. 10.5b shows the relative activity of a series of non-ionic surfactants of the Brij series and sodium taurodeoxycholic acid (NaTDC), sodium dodecyl sulphate (NaDS) and CTAB [30]. An association between protein release and increased absorption of solutes has also been reported by Feldman and Reinhard [31] and Walters et al. [32]. Anionic, non-ionic and cationic surfactants tended to accelerate the breakdown of the mucous layer covering the epithelium and at high concentrations were thought to interfere with the structure of the mucosal surface itself. Exposure of various anionic and nonionic surfactants to rabbit intestinal mucosa causes epithelial desquamation and necrosis [33]. 

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