An investigation of binding ability of ionic surfactants with trifluoperazine dihydrochloride: insights from surface tension, electronic absorption and fluorescence measurements

Abstract

This work deals with the effect of the ionic surfactants, sodium dodecylsulphate (SDS), dioctylsulphosuccinate sodium salt (AOT), dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB), on the physicochemical properties of the antidepressant phenothiazine drug, trifluoperazine dihydrochloride (TFP). Surface tension, fluorescence and electronic absorption measurements have been done in order to study the nature of interactions between drug–ionic surfactant mixtures. Various interfacial, micellar, spectroscopic and corresponding thermodynamic parameters have been calculated from these techniques. The values of the interaction parameter (β) suggest that cationic surfactants exhibit less synergistic interactions with TFP compared to anionic surfactants. To confirm this we further performed fluorescence quenching and electronic absorption titrations of ionic surfactants with TFP. Anionic surfactants (SDS, AOT) have been observed to bind preferentially with TFP over cationic surfactants (DTAB, DDAB), which supports the presence of a cationic charge on the head group of the drug and signifies that anionic surfactants can act as better drug-carriers than cationic surfactants even at very low concentrations. The blue shift and decrease in fluorescence intensity observed in fluorescence quenching methods for TFP + SDS/AOT mixtures confirms the formation of a new complex between interacting species. Also the number of binding sites for drug molecule has been estimated, which helps to give an insight into the mechanism of the drug–surfactant complexes formed. The results indicate that among electrostatic, hydrophobic and van der Waals forces, the former ones are the predominant intermolecular forces between TFP and ionic surfactants.