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Phase separation of five amphiphilic drugs in 10 mM phosphate buffer with added phospholipids has been studied. The drugs used are tricyclic antidepressants (amitriptyline hydrochloride, imipramine hydrochloride, and clomipramine hydrochloride) and phenothiazines (promethazine hydrochloride and promazine hydrochloride). Depending on the nature and structure of studied compounds, the phospholipids caused different effects on the clouding behavior. Cardiolipin decreased the cloud point for all drugs. With amitriptyline, all the additives lowered the cloud points, whereas the clomipramine showed opposite ten dency. Imipramine and promethazine led to similar extremal behaviour of cloud point, although promazine, which is structurally similar to promethazine, did not show the same tendency. Thermodynamic analysis of the experimental data suggested that the process of clouding is entropically driven.

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The interaction between cationic gemini hexanediyl-1,6-bis(dimethylcetylammonium bromide) (16-6-16, abbreviated as G6) with conventional cationic cetylpyridinium chloride (CPC), anionic sodium bis(2-ethyl hexyl)sulfosuccinate (AOT) and nonionic polyoxyethylene 10 cetyl ether (Brij56) in aqueous medium has been investigated at 25 degrees C. Different physicochemical properties such as critical micelle concentration (cmc), surface excess concentration (Gamma(max)), minimum area per molecule (A(min)), and interaction parameters (beta(m), beta(sigma)) as well as other thermodynamic and micellar properties have been determined. The interfacial and bulk behaviors were explored using theoretical models of Clint, Rubingh, Rosen, Motomura, and Maeda for justification and comparison of results of different binary combinations with the geminis of alkanediyl-alpha,omega-bis(dimethylcetylammonium bromide) series. Synergism was observed in all the binary combinations in the micelle and at interface with lowering of packing parameter due to slight expansion of A(min). The results of the present study could be of interest for selection of surfactant mixtures for surfactant-enhanced remediation (SER) of soils and aquifers contaminated by hydrophobic organic compounds (HOCs).