Self-assembly and phase behavior of new (alpha-hydroxyalkyl)phosphorus amphiphiles

Anew series of(alpha -hydroxyalkyl)phosphinic acids I was prepared in good yields from long-chain aldehydes (C-8-C-18) and 50% aqueous hypophosphorous acid under sonication. Oxidation of these phosphinic acids by dimethyl sul foxide in the presence of catalytic amounts of iodine afforded the correspo nding (oc-hydroxyalkyl)phosphonic acids 2. Critical micelle concentrations (cmc) of the amphiphilic monocaternary (alpha -hydroxyalkyl)phosphorus acid ammonium salts 1 and 2, determined by tensiometry and P-31 NMR, showed a g ood correlation between the two methods and indicated their high surfactant properties. The phosphonate salts 2 with two dissociable groups had much h igher cmc values than those of the corresponding phosphinate analogues 1. T he ammonium salts of these phosphorus acids were able to form ordered lyotr opic mesophases in concentrated water solutions, visualized by optical pola rization microscopy. The nature of the observed mesophases (hexagonal or la mellar) depended on the concentration, the temperature, the nature of the p olar head, and the length of the alkyl chain, the hexagonal phase being pro moted for shorter chains (C-8 and C-10). The ability of these acids 1-2 to form stable and compact Langmuir monolayers at the air/water interface was studied. Their conformations at the air/water interface were estimated by a molecular modeling study.