Mixed micellization of dimeric surfactant–amphiphilic drug systems: effect of surfactant structure

Abstract

In order to explore their applications as drug delivery vehicles, the mixed interfacial/micellar behaviour of a number of dimeric surfactants (zwitterionic, cocogem and anionic) with an amphiphilic antidepressant drug imipramine hydrochloride (IMP) in aqueous solutions has been investigated. The cmc values of mixed surfactants, estimated from surface tension measurements, decrease with mole fraction (α) and tail length of the surfactants. The values in most of the cases are lower than cmc_id. This indicates that mixed micelles are formed due to attractive interactions among the components. A number of simple models (those of Rosen, Rubingh, Motomura) that combine pseudophase approximation with the regular solution theory, have been used to estimate some important physicochemical parameters needed for such applications (like compositions of mixed monolayers (X^s)/mixed micelles (X^m) and the interaction parameters (β)). The values of the micellar interaction parameter (β^m) come out to be negative with the magnitude order being: anionic dimerics > zwitterionic dimerics > cocogems. This is explained in light of the different structures of surfactants; IMP is positively charged and with anionic surfactants it experiences stronger attractive interactions while with cocogems its interactions are weak. With zwitterionic dimerics, the drug experiences intermediate interactions.