Spectroscopic approach of the interaction study of amphiphilic drugs with the serum albumins

The interaction of the amphiphilic drugs, i.e., amitriptyline hydrochloride (AMT) and promethazine hydrochloride (PMT), with serum albumins (i.e., human serum albumin (HSA) and bovine serum albumin (BSA)), has been examined by the various spectroscopic techniques, like fluorescence, UV–vis, and circular dichroism (CD). Fluorescence results indicate that in case of HSA–drug complexes the quenching of fluorescence intensity at 280 nm is less effective as compared to at 295 nm while in case of BSA–drug complexes both have almost same effect and for most of drug–serum albumin complexes there is only one independent class of binding. For all drug–serum albumin complexes the quenching rate constant (Kq) values suggest the static quenching procedure. The UV–vis results show that the change in protein conformation of PMT–serum albumin complexes was more prominent as compared to AMT–serum albumin complexes. The CD results also explain the conformational changes in the serum albumins on binding with drugs. The increase in α-helical structure for AMT–serum albumin complexes is found to be more as compared to PMT–serum albumin complexes. Hence, the various spectroscopic techniques provide a quantitative understanding of the binding of amphiphilic drugs with serum albumins.