Spectroscopic and voltammetric characterizations of the interaction of two local anesthetics with bovine serum albumin

The interactions of bovine serum albumin (BSA) with two local anesthetics, procaine hydrochloride (PCH) and tetracaine hydrochloride (TCH) were studied using spectroscopic methods such as fluorescence and ultraviolet visible (UV–vis), and electrochemical techniques including cyclic voltammetry (CV) and differential pulsed stripping voltammetry (DPSV). The results obtained from these techniques turned out that both PCH and TCH could bind to BSA. The binding constants (KA) and the number of binding sites (n) of the two drugs with BSA at different temperatures were determined, respectively. At 291 K, KA was found as 2.40×104 and 1.42×104 L mol−1 and n was 1.03 and 0.99 for PCH–BSA and TCH–BSA, respectively. According to van’t Hoff equation, the thermodynamic parameters, ΔG, ΔH and ΔS, were obtained, showing the involvement of hydrophobic and electrostatic force in these interactions. Based on the theory of the Förster energy transference, the distance between the acceptor (PCH or TCH) and the donor (BSA) were determined as 2.32 and 3.62 nm for PCH and TCH, respectively. The effects of Fe3+, Cu2+, Mg2+, Mn2+, Zn2+ and Ca2+ on the binding of PCH or TCH to BSA were also evaluated.