Comparative Studies on the Interaction of Rhodamine B with Bovine Serum Albumin Using Fluorescence Method and Synchronous Fluorescence Method

The reaction mechanism of rhodamine B (RHB) with bovine serum albumin (BSA) was investigated using fluorescence spectroscopy and synchronous fluorescence spectroscopy at different temperatures (298 K, 310 K and 318 K). The results showed that electrostatic force played a major role on the conjugation reaction between BSA and RHB, and the type of quenching was static quenching. Primary binding site for RHB was sub-hydrophobic domain IIA, and the number of binding sites was 1. The order of magnitude of binding constants (Ka) was 104. The value of Hill’s coefficients (nH) was approximately equal to 1, which suggested no cooperativity in BSA-RHB system. The donor-to-acceptor distance r < 7 nm indicated that the static fluorescence quenching of BSA by RHB was also a non-radiation energy transfer process. The results of two methods were consistent that showed the synchronous fluorescence spectroscopy could be used to study the reaction mechanism between drug and protein, and was a useful supplement to the conventional fluorescence quenching method