Thermodynamic Characteristics and Spectral-Luminescent Properties of N-m-Tolylbenzamide in Microheterogeneous Surfactant Self-Assemblies

Abstract

To model the binding to biomembranes, the interactions of potent N-m-toly- lbenzamide (NTB) with a cationic surfactant, cetyltrimethylammonium bromide (CTAB) and an anionic surfactant, sodium dodecyl sulfate (SDS), have been investigated. The study was carried out by quantifying the absorption and fluorescence emission spectra of NTB as a function of pre-micellar to post-micellar surfactant concentrations in the temperature range of 25-50 C. NTB is a strongly fluorescent compound that exhibits intense violet fluorescence. Using mathematical models, the water-micelle partition coefficient (Kx), surfactant-NTB binding constant (Kb), binding capacity (nb) and the degree of counter-ion binding (a) are discussed from the thermodynamic viewpoint, considering the thermody- namic parameters of additive solubilization (DG � p ; DH � p ; DS � p ). The high values of all interactions, especially when the surface charge of the organized medium is cationic, ensure that there are greater interactions between the NTB and CTAB than with SDS. The NTB molecule is found to be located at only one binding site of each surfactant and probably exhibits static quenching rather than a collisional quenching mechanism. These findings have been confirmed by the binding capacity for the NTB-surfactant combina- tional system and Stern-Volmer quenching constant (Ksv) values. The observed depression in binding strength of the counterions with temperature increase favors the promising solubilization of NTB in the palisade layer of micelles leading to penetration binding.