Interaction of acridine orange with bile salts: a spectroscopic approach

Abstract

Acridine orange (AO) is a metachromic cationic dye and its photophysical property is extremely sensitive to its environment and surrounding pH conditions. One of the most important applications of AO is its photosensitizing ability and thus extensively employed in photodynamic therapy. AO exhibits excellent potential towards selective anti-cancer cell activity often considered as a "Magic Bullet" for cancer treatment. The photosensitizer when administered intravenously reaches to the target tissue by circulating through blood, which emphasizes its interaction with various biomolecules such as proteins, DNAs, biosurfactants etc. Moreover, the interactions between dyes and surfactants, in general, are interesting for their complex nature governed and influenced by the chemical structure of dye and physicochemical properties of the surfactants. Bile salts are referred to as biosurfactants taking into account their capacity to solubilize and emulsify cholesterol, bilirubin, lecithin, lipids and fat soluble vitamins in living organisms. The focus of the present study is to study the interaction AO with two variants of bile salts deoxycholates (sodium deoxycholate, sodium taurodeoxycholate) and cholates (sodium cholate, sodium taurocholate) by spectroscopic technique. These bile salts below CMC induce aggregation of the dye whereas AO gets solubilised in monomeric form in the bile salt micellar cavity above their CMC. Dihyroxy bile salts induce the aggregation of AO more efficiently as compared to the corresponding trihydroxy bile salts. The binding constant and partition coefficient were determined and the order was found to be NaDC > NaTDC > NaTC > NaC. The negative values of standard free energy and enthalpy indicates towards the spontaneity and exothermic nature of these processes. The effect of ionic strength and cosolvents was also studied on the micellisation and aggregation behaviour of AO.