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Theoretical Study on Ionization Processes for Ampicillin Drug in Water by DFT and Ab Initio Methods at T = 298.15 K

Authors: 

Zeinab DEHGHAN, Farhoush KIANI, Fardad KOOHYAR*, Seyed B. HOSSEINI, Fatemeh ZABIHI, Le Quoc BAO, Niloofar SOLTANI

Source title: 
Latin American Journal of Pharmacy, 39(2): 231-236, 2020 (ISI)
Academic year of acceptance: 
2019-2020
Abstract: 

In this research we investigated the ionization processes of ampicillin in water at constant temperature (298.15 K) by ab initio and DFT methods. Using this investigation, for ampicillin in water, the value of the first ionization constant, pKa1, and the second ionization constant, pKa2 as well as structural properties such as dihedral angle between the indicated atoms (D), total atomic charge (Muliken) (q), bond lengths between the indicated atoms (d), and bond angle between the indicated atoms (A) were calculated at T = 298.15 K. These structural properties were applied to indicate the strength of hydrogen bonding between ampicillin and water molecules. In this research, it was suggested that in aqueous solution, the anion and neutral species of ampicillin are solvated with four water molecules and also, the cation specie of ampicillin is solvated with three water molecules. In addition, it can be seen in this work that for ampicillin in water, there is a comparable agreement between the experimentally determined and theoretically calculated pKa values at 298.18 K