Self-organization properties of new (α-aminoalkyl)phosphonic- and (α-aminoalkyl)phosphonocarboxylic acid amphiphiles in water and at the air/water interface

We have studied the surfactant properties of a series of single- and double-chain (alpha-aminoalkyl)-phosphonocarboxylic- and (alpha-aminoalkyl)-phosphonic acid amphiphiles, prepared in nearly quantitative yields by one-pot selective hydrolysis of the mixture obtained by reacting P-H bond tetraoxyspirophosphorane and long-chain aldimines. Disodium salts of monocatenary derivatives are soluble in water and the cmc's were determined by tensiometry, showing surfactant properties for all compounds. Thermodynamic calculations confirmed the tensiometry results, in the sense that phosphonocarboxylates present much more electrostatic destabilizing repulsions favoring micellization less than phosphonates. The disodium salts of these phosphonic acids were able to organize into ordered lyotropic mesophases in concentrated water solutions, visualized by optical polarizing microscopy. The nature of the observed mesophases seems to be strongly dependent on the polar head structure. All compounds were studied using the Langmuir technique. The more hydrophobic derivatives formed stable monolayers versus time at the air/water interface. The areas occupied per molecule depend on the polar head structure and the number of alkyl chains. The conformations at the air/water interface were estimated by a molecular modeling study.