Micellar-mediated binding interaction between proflavine hemisulfate and salicylic acid: spectroscopic insights and...

The molecular interactions between salicylic acid (SA) and proflavin hemisulfate (PF) were investigated using fluorescence and UV-VIS absorption spectroscopy in an aqueous micellar environment. Changes in the absorption spectra of SA in the presence of PF indicate a ground state interaction between salicylate and proflavine hemisulfate ions to form a complex. The excitation bands of SA monitored at its emission wavelength reveal a red spectral shift of 8390.54 and 2037.75 cm(-1) when compared with absorption bands. The intensity of both excitation bands decreased in the presence of increasing amounts of PF. The absence of excitation bands of PF rules out the possibility of its direct excitation and suggests energy transfer from excited SA to PF, resulting in quenching of the SA fluorescence. The fluorescence quenching results were found to fit the well-known Stern-Volmer (S-V) relation. S-V plots at different temperatures were used to further evaluate thermodynamic parameters such as ∆G, ∆H and ΔS. The thermodynamic and kinetic data obtained from the quenching results were used to investigate the possible mechanism of binding, the nature of the binding force and the distance between SA and PF molecules. The linear relation between SA fluorescence quenching and PF concentration used to develop an analytical method for the determination of PF from Lorexane (a veterinary cream) using a fluorescence quenching method.