Research Article A DFT Study of Structural and Bonding Properties of Complexes Obtained from First-Row Transition Metal Chelation by 3-Alkyl-4-phenylacetylamino-4,5-dihydro-1H-1,2,4-triazol-5-one and Its Derivatives Hubert Jean Nono, 1 Désiré Bikélé Mama, 2 Julius Numbonui Ghogomu, 1 and Elie Younang 3 1 Department of Chemistry, Faculty of Science, University of Dschang, P.O. Box 67, Dschang, Cameroon 2 Department of Chemistry, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon 3 Department of Inorganic Chemistry, Faculty of Science, University of Yaound´ e I, P.O. Box 812, Yaound´ e, Cameroon Correspondence should be addressed to D´ esir´ e Bik´ el´ e Mama; bikelemama@yahoo.fr and Julius Numbonui Ghogomu; ghogsjuju@hotmail.com Received 12 December 2016; Accepted 3 May 2017; Published 3 July 2017 Academic Editor: Konstantinos Tsipis Copyright © 2017 Hubert Jean Nono et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Density functional calculations were used to explore the complexation of 3-alkyl-4-phenylacetylamino-4,5-dihydro-1h-1,2,4- triazol-5-one (ADPHT) derivatives by frst-row transition metal cations. Neutral ADPHT ligand and mono deprotonated ligands have been used. Geometry optimizations have been performed in gas-phase and solution-phase (water, benzene, and N,N- dimethylformamide (DMF)) with B3LYP/Mixed I (LanL2DZ for metal atom and 6-31+G(d,p) for C, N, O, and H atoms) and with B3LYP/Mixed II (6-31G(d) for metal atom and 6-31+G(d,p) for C, N, O, and H atoms) especially in the gas-phase. Single points have also been carried out at CCSD(T) level. Te B3LYP/Mixed I method was used to calculate thermodynamic energies (energies, enthalpies, and Gibb energies) of the formation of the complexes analyzed. Te B3LYP/Mixed I complexation energies in the gas phase are therefore compared to those obtained using B3LYP/Mixed II and CCSD(T) calculations. Our results pointed out that the deprotonation of the ligand increases the binding afnity independently of the metal cation used. Te topological parameters yielded from Quantum Teory of Atom in Molecules (QTAIM) indicate that metal-ligand bonds are partly covalent. Te signifcant reduction of the proton afnity (PA) observed when passing from ligands to complexes in gas-phase confrms the notable enhancement of antioxidant activities of neutral ligands. 1. Introduction In recent years, the repercussion of free radicals and reac- tive oxygen species (ROS) in neurodegenerative disorder is more sensitive [1–4]. Te contribution of these ROS to the pathophysiology of myocardial reperfusion damage. Tese ROS can be oxygen-centered radicals [5] or oxygen- centered nonradicals [6]. Te removal of electrons from cellular membranes by these ROS and the reaction between these latter ones and proteins [7] provoke the alteration of the structures of these membranes and proteins. Such alterations justify the frailty of these cellular membranes that expose them to be attacked by invaders (viruses and bacteria). Nevertheless, each cell is naturally equipped by defense systems against any destructive efect of ROS. Tis statute of protective mechanism against ROS in humans is attributed to antioxidant molecules [8, 9]. In general, antioxidant molecules (tocopherol (vitamin E), ascorbic acid (vitamin C), carotenoids, favonoids, and polyphenols) prevent the proliferation of free radical reactions in all cell membranes. Tis explains the emergence of studies on the investigation of antioxidant activities of biologically active compounds. Tis has led to increased pressure on the need for the newer Hindawi Bioinorganic Chemistry and Applications Volume 2017, Article ID 5237865, 15 pages https://doi.org/10.1155/2017/5237865