Iranian Journal of Catalysis (IJC) Gas contaminants capturing by gamma-carbonic anhydrase catalyst: A quantum chemical approach Volume 4 (2014) Issue 3, September 2014 2024 02 03 Gas contaminants capturing by gamma-carbonic anhydrase catalyst: A quantum chemical approach EN Mina Ghiasi Department of chemistry, Faculty of science, Alzahra University, 19835-389, Vanak, Tehran, Iran. Nahal Majdoddin 5th floor, Tehran Province Gas Company, No. 701, 15946-53415, Valiasr St, above Valiasr Sq., Tehran, Iran. Ebrahim Esalati 3rd floor, Gas 6th Building, 15988-66515, Amani Ave., Gharani St., Tehran, Iran. Journal Article 2024 02 03 In this paper, we used quantum chemical approach to shed light on the catalytic mechanism of γ-carbonic anhydrase (γ-CA) to convert carbon dioxide to bicarbonate ion. Density functional theory (DFT) using B3LYP and UB3LYP functional and three split-valance including 6-31G*, 6-311G** and 6-311++G** basis sets were used to calculate the details of electronic structure and electronic energy of active and inactive forms of γ-CA enzyme active center, and complex between γ-CA and carbon dioxide. The catalytic mechanism involved the nucleophilic attack of cobalt bound hydroxide ion to CO2. In the following, the five coordinate cobalt complex as a transition state is formed and then the produced bicarbonate is displaced by a water molecule and give cobalt bound hydroxide for the next turn of catalysis. The activation energy barrier for this mechanism is about 7.9 kcal/mol.