The Spectroscopic and Conductive Properties of Ru(II) Complexes with Potential Anticancer Properties

Hindawi Publishing Corporation Journal of Spectroscopy Volume 2014, Article ID 656830, 14 pages http://dx.doi.org/10.1155/2014/656830 Research Article The Spectroscopic and Conductive Properties of Ru(II) Complexes with Potential Anticancer Properties Adebayo A. Adeniyi and Peter A. Ajibade Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa Correspondence should be addressed to Peter A. Ajibade; Received 15 February 2014; Accepted 4 May 2014; Published 14 July 2014 Academic Editor: Stephen Cooke Copyright © 2014 A. A. Adeniyi and P. A. Ajibade. This 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. Different density functional methods (DFT) have been used to optimize and study the chemistry of five potential anticancer complexes in terms of their electronic, conductive, and spectroscopic properties. Many of the computed properties in addition to the IR and QTAIM analysis of the NMR are dipole moment vector (𝜇𝑖 ), linear polarizability tensor (𝛼𝑖𝑗 ), first hyperpolarizability tensors (𝛽𝑖𝑗𝑘 ), polarizability exaltation index (Γ), and chemical hardness (𝜂) of the complexes. Stable low energy geometries are obtained using basis set with effective core potential (ECP) approximation but, in the computation of atomic or molecular properties, the metal Ru atom is better treated with higher all electron basis set like DGDZVP. The spectroscopic features like the IR of the metal-ligand bonds and the isotropic NMR shielding tensor of the coordinated atoms are significantly influenced by the chemical environment of the participating atoms. The carboxylic and pyrazole units are found to significantly enhance the polarizabilities and hyperpolarizabilities of the complexes while the chloride only improves the polarity of the complexes. Fermi contacts (FC) have the highest effect followed by the PSO among all the four Ramsey terms which defined the total spin-spin coupling constant J (HZ) of these complexes. 1. Introduction Ruthenium-based organometallic complexes are widely applied in medical research field as anticancer compounds [1–13]. Two of the ruthenium complexes, KP1019 [14, 15] and NAMI-A [16–19], have passed through the phase two medical tests as potential anticancer drugs and might rival cisplatin which has been the most effective and widely used anticancer agent [20–24]. Many other applications for ruthenium complexes in addition to study as anticancer agents are as photoluminescence, electrochemiluminescence, catalyst, and photochemical complexes [25–30]. The complexes used in this work are designed to play a dual role as anticancer and nonlinear optical (NLO) materials. Docking study of some of these complexes has been found to be promising than many of the RAPTA complexes [31]. The most widely screened ruthenium complexes as anticancer are the halfsandwich complexes [2, 3, 32–37]. RAPTA complexes as type of the half-sandwich ruthenium complexes under Dyson research teams have been experimentally proven as potential anticancer agents [22–24, 38–42]. The complexes (Figure 1) studied in this work have similar structures with another type of half-sandwich ruthenium anticancer complexes [43–52]. The main differences in these models of complexes compared to the type of complexes from the Sandler research team are the pyrazole and carboxylic units of interest that are incorporated into the bidentate or tridentate ligands coordinating to the metal through the nitrogen atoms. Our interest in this work is to compute the chemical properties of these complexes in relation to the unique features of the carboxylic or pyrazole units, total stability, conductivity, and reactivity either as anticancer or NLO materials. Besides the limitation of the unknown targets of ruthenium anticancer complexes [14, 20, 39, 53–56] which is limiting their rational design and approval, other limitations in their application are the complexity of their reaction and instability [20]. In drug design there is need for a clear understanding of the physicochemical properties of the drug 2 Journal of Spectroscopy Ru N N N N N N Cl H O HO N O N O 1 N N 4 N N O ∙ N N Ru N O N N N N N H N O O 5 3 O H 2 O H O O H Figure 1: The schematic features showing all the bidentate ligands of complexes 1, 2, and 3 and tridentate ligands of complexes 4 and 5. candidates [57] which will enhance their rational design. To understand the chemistry of these complexes, the IR spectroscopic differences, the isotropic NMR shielding (𝜎Iso ), magnetizabilities (𝜒Iso ), the hardness (𝜂), hyperpolarizability (𝛽), polarizability exaltation index (Γ) dipole (𝜇), and anisotropy polarizations (⟨𝛼⟩, Δ𝛼1 , Δ𝛼2 , Δ𝛼3 ) of these five complexes are computed. In addition to the spectroscopic features of these complexes, many factors computed in this work like the polarizabilities, hyperpolarizabilities [58], hardness [59, 60], and polarizability exaltation index [59], have been linked to the stability, reactivity, or selectivity [61] and conductivity of molecules. The main aim is to characterize and analyze the electric, conductive, and spectroscopic properties of the complexes in relation to the number and position of the carboxylic and pyrazole units. There is little known information about the hyperpolarizabilities of ruthenium metal complexes but many of the computed properties in this study have not been reported for these types of metal complexes to the best of our knowledge. 2. Computational Method The geometries of the complexes were optimized twice using PBE0 hybrid density functional [62] and combined basis set SBKJC VDZ [63] with effective core potential (ECP) (for ruthenium and chloride atoms where applicable) while other atoms are treated with basis set 6-31G∗ in the first optimization that will be subsequently referred to as ECP(Ru,Cl)|6-31G∗ systems. In the second optimization, only the ruthenium atom is treated with SBKJC VDZ ECP basis set while other atoms are treated with improved basis set 6-31+G(d,p) and this will be referred to as ECP(Ru)|631+G(d,p) systems. The PBE0 is obtained by casting the functional and correlation of Perdew, Burke, and Ernzerhof in a hybrid HF/DFT scheme with a fixed 1/4 ratio [64]. In application of SBKJC VDZ ECP basis set, 28 core electrons were removed from Ru (1s, 2s, 2p, 3s, 3p, and 3d) and 10 from Cl (1s, 2s, and 2p) atoms (where applicable) and were treated with pseudopotential while the valence electrons were treated with a double zeta quality functions. The choice of SBKJC VDZ ECP basis set is necessary for large systems of our type which also contain heavy metal like ruthenium. The choice combination of ECP basis set with PBE0 functional for the optimization is due to the past records of their effectiveness in computational study of metal clu (...truncated)