Biophysical analysis of triazolium-based protic ionic liquid-incorporated bile salt media

Abstract

Room temperature ionic liquids (RTILs) are unique molecules with synthetic flexibility and good solvation properties. Bile salts (BSs) are naturally occurring solubilizing agents that aggregate in aqueous solution. Both RTILs and BSs are surface active agents, and thereby incorporation of RTILs into BS media can result in a molecular entity of specific importance in encapsulating hydrophobic molecules, enhancing oil recovery, waste water treatment, the detergent industry, etc. In this study, a series of amphiphilic protic 1,2,4-triazolium based RTILs, 1-alkyl-1,2,4-triazolium trifluoroacetate, with varying alkyl chain lengths (from butyl to heptyl) were synthesized and characterized via NMR spectroscopy. Sodium cholate (NaC) and sodium deoxycholate (NaDC) were selected as representative bile salts (BSs) for the investigation. The effect of 1,2,4-triazolium-based RTILs on BSs was investigated using anthracene fluorescence. The anthracene fluorescence detects a progressive step-wise aggregation of BSs, confirming that anthracene is a suitable extrinsic probe for this particular study, and the results were also verified using the electrical conductivity measurements of BSs in water. Experimental results reveal that the presence of RTILs disrupts the characteristic step-wise aggregation behavior of both BSs. At lower concentrations of NaC and NaDC, it is observed that the alkyl chain of RTILs incorporates into the hydrophobic regions of dimeric BSs, whereas at higher concentrations of BSs, addition of RTILs induces gelation of NaDC and NaC, and they form mixed micellar systems. Furthermore, the extent of disruption in BS micellization is found to be dependent on the hydrophobicity of the RTILs.