Probing the adverse temperature dependence in the static fluorescence quenching of BSA induced by a novel anticancer hydrazone

Abstract

A novel hydrazone, 2-hydroxy-N′-(3-hydroxybenzylidene) benzohydrazide (HHB), has been designed, synthesized and characterized. HHB was designed to be an analogue of 311 and PIH with potential anticancer activity, and the IC₅₀ towards HeLa cell was about 3.46 × 10⁻⁵ mol⁻¹ L. The interactions of HHB with bovine serum albumin (BSA) had been investigated systematically by spectroscopy, electrochemistry, and molecular modeling under simulative physiological conditions. HHB bound BSA in the sub-domains IIA to form a ground-state complex, inducing the quenching of the intrinsic fluorescence emission, the change of absorption spectrum and the increase of electrical resistance of BSA. An adverse temperature dependence in the fluorescence quenching was detected and discussed to be a reasonable consequence of the big E_a requirement to overcome the obstructive amino acid residues in the entrance to the binding site, which were closely related to the natural structure of BSA and the molecular shape of HHB. The impact of metal ions, including Fe²⁺, Fe³⁺, Cu²⁺, Mg²⁺, Zn²⁺, Ca²⁺ and Al³⁺, towards the interactions of HHB and BSA has been investigated and they were found to affect the HHB–BSA interactions in a mild way.