Thermodynamic Properties of the Site-selective Binding of a Bromo-hydrazone and Its Unsubstituted Analogue to Human Serum Albumin

A bromine-substituted hydrazone derivative, named N′-(4-bromobenzylidene)-2-hydroxybenzohydrazide (BBH), and its unsubstituted analogue, named N′-benzylidene-2-hydroxybenzohydrazide (BH), have been synthesized by a simple and effective one-pot synthesis method. Their interactions with human serum albumin (HSA) were comprehensively studied employing spectroscopy, electrochemistry, and molecular docking. Our attention was largely on the thermodynamic properties of their binding to HSA, in order to evaluate the impact of a bromine atom in BBH to its biological activity comparing to BH. BBH is a stronger ligand with a binding constant of 105 L·mol−1 and formed a more stable complex with HSA compared with BH. The binding processes of both BBH and BH are mainly an enthalpy driven process occurring in site I, mainly bound by hydrogen bonding and the van der Waals force.