%0 Journal Article
%T Metal Ion Selectivity of Kojate Complexes: A Theoretical Study
%A Sarita Singh
%A Jyoti Singh
%A Sunita Gulia
%A Rita Kakkar
%J Journal of Theoretical Chemistry
%D 2013
%R 10.1155/2013/342783
%X Density functional calculations have been performed on four-coordinate kojate complexes of selected divalent metal ions in order to determine the affinity of the metal ions for the kojate ion. The complexation reactions are characterized by high energies, showing that they are highly exothermic. It is found that Ni(II) exhibits the highest affinity for the kojate ion, and this is attributed to the largest amount of charge transfer from the ligand to the metal ion. The Ni(II) complex has distorted square planar structure. The HOMOs and LUMOs of the complexes are also discussed. All complexes display a strong band at ~1500£¿cm£¿1 corresponding to the stretching frequency of the weakened carbonyl bond. Comparison of the complexation energies for the two steps shows that most of the complexation energy is realized in the first step. The energy released in the second step is about one-third that of the first step. 1. Introduction Kojic acid, a -pyrone derivative (C6H6O4; 5-hydroxy-2-(hydroxymethyl)-4-pyrone), is a natural heterocyclic chelating agent found in fermented food. It forms stable, water-insoluble chelates with metal cations such as Fe(II) and Cu(II) [1¨C3]. The chelates have reasonable hydrolytic stability, neutral charge, and significant lipophilicity [4]. Anions of kojic acid and its derivatives behave as bidentate ligands and coordinate to iron(III) via the carbonyl and phenolic hydroxyl oxygens [5]. Kojic acid is identified and quantitatively determined gravimetrically by the formation of characteristic light-green copper kojate crystals. Besides its use for analytical purposes, the chelating ability of kojic acid plays a significant role in its antimicrobial, antifungal, and antineoplastic activities [6¨C8]. The in vivo studies of Mn(II) and Zn(II) kojic complexes proved them to be potential radioprotective agents against lethal doses of -irradiation in mice [9]. The polarographic, potentiometric, and zone electrophoresis investigations of chelates of Cd(II) with kojic acid have been reported [10]. Wiley et al. [3] synthesized and determined the magnetic susceptibilities of Cu(II), Ni(II), Co(II), Fe(II), and Mn(II) kojate complexes. The complexing behavior of kojic acid with Cu(II), Zn(II), Ni(II), and Co(II) has also been reported in dioxane-water media [11, 12]. Due to their strong chelating ability, kojic acid and its derivatives play a strong role in Fe(III) and Al(III) overload pathologies. They also behave as tyrosinase inhibitors. Several experimental and density functional theory (DFT) studies on kojic acid complexes have been reported
%U http://www.hindawi.com/journals/jtc/2013/342783/