Investigating the influence of monovalent alkali metal salts on sodium deoxycholate bile salt aggregate system

Bile salts (BSs) are naturally occurring biological surfactants responsible for emulsifying and solubilizing cholesterol, fats, and lipid-soluble vitamins. These are cholesterol-derived facial amphiphiles. Depending on the bile salt concentration, dimers, primary aggregates, and secondary aggregates are formed. The salt-induced gelation study of BSs was reported for NaCl salt. In our current study, the effect of monovalent alkali metal salts on the gelation process of sodium deoxycholate (NaDC), a dihydroxy bile salt, was studied. We have used various techniques, including fluorescence spectroscopy, light scattering, differential scanning calorimetry (DSC), and dynamic light scattering (DLS), to investigate the salt-induced gelation of BSs. For fluorescence studies 1, 6-diphenylhexatriene (DPH) was used as the fluorescent probe. It was observed that the fluorescence anisotropy of DPH increases with increasing monovalent cationic salt concentration, suggesting the viscosity increase is due to the formation of gel in BSs. The anisotropy decreases significantly after a specific salt concentration, probably due to a decrease in viscosity because of the competition between the gelation and precipitation processes. We observed that the salt concentration required to induce the precipitation process depends on the size of the cation. DSC and temperature-dependent viscosity studies show a gel-to-sol phase transition in BSs at a specific temperature