QM and QM/MM study on inhibition mechanism of polyphenolic compounds as non-classical inhibitors of alpha-human carbonic anhydrase (II)

Phenolic and polyphenolic compounds are distributed in plant tissues as a secondary metabolite which are compromised in multiple and imperative physiological phenomena. Herein, inhibition mechanism of human carbonic anhydrase isoform II, hCAII, with seven phenolic compounds including phenol, catechol, resorcinol, 4-methyl catechol, vanillic acid, trans-cinnamic acid and ortho-coumaric acid has been investigated using quantum mechanical and ONIOM calculations. B3LYP-D3/6-311++G** method has been employed to calculate the electronic structure and electronic energy of different species through the reaction mechanism path. The model system of hCAVII has been used that includes the core of the catalytic center, Zn2+, binds to three histidine residues and a hydroxide ion or water molecule forming a first coordination shell. Thr199 and Glu106 were considered as neighboring residues to the ones binding zinc. All thermodynamic functions through the reaction path are evaluated in different phases. The calculated results indicate that all phenolic inhibitors do not directly interact with the zinc ion in the CA active center, and the presence of aromatic moieties was associated with more effective inhibition. In addition, the implicit and explicit solvent effect has been considered for water solvent using QM and ONIOM (QM/MM) calculations.