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) [1–3]. 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 [6–8]. 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
References
[1]
A. Beélik, “Kojic Acid,” Advances in Carbohydrate Chemistry, vol. 48, pp. 145–183, 1956.
[2]
S. A. Sallam, S. S. Haggag, and M. S. Masoud, “Thermodynamic parameters of ionization of kojic acid and its coordinating behaviour towards transition metals,” Thermochimica Acta, vol. 168, pp. 1–7, 1990.
[3]
J. W. Wiley, G. N. Tyson Jr., and J. S. Steller, “The configuration of complex kojates formed with some transition elements as determined by magnetic susceptibility measurements,” Journal of the American Chemical Society, vol. 64, no. 4, pp. 963–964, 1942.
[4]
P. Comba, “The relation between ligand structures, coordination stereochemistry, and electronic and thermodynamic properties,” Coordination Chemistry Reviews, vol. 123, pp. 1–48, 1993.
[5]
J. ？ima, A. Bradiaková, and M. Antalík, “Photochemical properties of systems containing cytochrome c and kojic acid,” Journal of Photochemistry and Photobiology A, vol. 94, pp. 163–166, 1996.
[6]
J. Brtko, L. Rondahl, M. Ficková, D. Hudecová, V. Eybl, and M. Uher, “Kojic acid and its derivatives: history and present state of art,” Central European Journal of Public Health, vol. 12, supplement, pp. S16–S18, 2004.
[7]
J. Bransová, J. Brtko, M. Uher, and L. Novotny, “Antileukemic activity of 4-pyranone derivatives,” The International Journal of Biochemistry & Cell Biology, vol. 27, pp. 701–706, 1995.
[8]
L. Novotny, P. Rauko, M. Abdel-Hamid, and A. Váchalková, “Kojic acid—a new leading molecule for a preparation of compounds with an anti-neoplastic potential,” Neoplasma, vol. 46, pp. 89–92, 1999.
[9]
S. Emami, S. J. Hossemimehr, S. M. Taghdisi, and S. Akhlaghpoor, “Kojic acid and its manganese and zinc complexes as potential radioprotective agents,” Bioorganic & Medicinal Chemistry Letters, vol. 17, pp. 45–48, 2007.
[10]
R. L. Pecsok, R. L. Meeker, and L. D. Shields, “Chelates of cadmium with kojic acid,” Journal of the American Chemical Society, vol. 83, no. 9, pp. 2081–2085, 1961.
[11]
Y. Murakami, “Complexing behavior of Kojic acid with metal ions. I. Mg(II) and Mn(II) Chelates,” Bulletin of the Chemical Society of Japan, vol. 35, pp. 52–56, 1962.
[12]
Y. Murakami and K. Mera, “Complexing behavior of kojic acid with metal ions. III. Infrared studies of bivalent metal-kojate chelates,” Bulletin of the Chemical Society of Japan, vol. 39, pp. 396–397, 1966.
[13]
F. Cecconi, C. A. Ghilardi, A. Ienco et al., “Different complexation properties of some hydroxy keto heterocycles toward beryllium(II) in aqueous solutions: experimental and theoretical studies,” Inorganic Chemistry, vol. 41, no. 15, pp. 4006–4017, 2002.
[14]
A. Zangl, P. Klüfers, D. Schaniel, and T. Woike, “Photoinduced linkage isomerism of {RuNO}6 complexes with bioligands and related chelators,” Dalton Transactions, no. 6, pp. 1034–1045, 2009.
[15]
M. Orio, C. Bochot, C. Dubois et al., “The versatile binding mode of transition-state analogue inhibitors of tyrosinase towards dicopper(II) model complexes: experimental and theoretical investigations,” Chemistry, vol. 17, no. 48, pp. 13482–13494, 2011.
[16]
G. Crisponi, A. Dean, V. D. Marco et al., “Different approaches to the study of chelating agents for iron and aluminium overload pathologies,” Analytical and Bioanalytical Chemistry, vol. 405, pp. 585–601, 2013.
[17]
V. M. Nurchi, J. I. Lachowicz, G. Crisponi et al., “Kojic acid derivatives as powerful chelators for iron(III) and aluminium(III),” Dalton Transactions, vol. 40, no. 22, pp. 5984–5998, 2011.
[18]
V. M. Nurchi, G. Crisponi, J. I. Lachowicz et al., “Iron(III) and aluminum(III) complexes with hydroxypyrone ligands aimed to design kojic acid derivatives with new perspectives,” Journal of Inorganic Biochemistry, vol. 104, pp. 560–569, 2010.
[19]
P. R. Sudhir, H. F. Wu, and Z. C. Zhou, “Probing the interaction of kojic acid antibiotics with iron(III) chloride by using electrospray tandem mass spectrometry,” Rapid Communications in Mass Spectrometry, vol. 19, pp. 209–212, 2005.
[20]
D. Sanna, L. Bíró, P. Buglyó, G. Micerac, and E. Garribba, “Transport of the anti-diabetic VO2+ complexes formed by pyrone derivatives in the blood serum,” Journal of Inorganic Biochemistry, vol. 115, pp. 87–99, 2012.
[21]
D. Sanna, P. Buglyó, L. Bíró, G. Micera, and E. Garribba, “Coordinating properties of pyrone and pyridinone derivatives, tropolone and catechol toward the VO2+ ion: an experimental and computational approach,” European Journal of Inorganic Chemistry, vol. 2012, no. 7, pp. 1079–1092, 2012.
[22]
R. Kakkar, R. Grover, and P. Gahlot, “Metal ion selectivity of hydroxamates: a density functional study,” Journal of Molecular Structure: THEOCHEM, vol. 767, no. 1–3, pp. 175–184, 2006.
[23]
J. P. Perdew, K. Burke, and M. Ernzerhof, “Generalized gradient approximation made simple,” Physical Review Letters, vol. 77, no. 18, pp. 3865–3868, 1996.
[24]
B. Delley, “An all-electron numerical method for solving the local density functional for polyatomic molecules,” The Journal of Chemical Physics, vol. 92, no. 1, pp. 508–517, 1990.
[25]
B. Delley, “Analytic energy derivatives in the numerical local-density-functional approach,” The Journal of Chemical Physics, vol. 94, no. 11, pp. 7245–7250, 1991.
[26]
B. Delley, “Fast calculation of electrostatics in crystals and large molecules,” Journal of Physical Chemistry, vol. 100, no. 15, pp. 6107–6110, 1996.
[27]
B. Delley, “From molecules to solids with the DMol3 approach,” Journal of Chemical Physics, vol. 113, no. 18, pp. 7756–7764, 2000.
[28]
N. Matsuzawa, J. Seto, and D. A. Dixon, “Density functional theory predictions of second-order hyperpolarizabilities of metallocenes,” Journal of Physical Chemistry A, vol. 101, no. 49, pp. 9391–9398, 1997.
[29]
R. Kakkar, P. N. Kapoor, and K. J. Klabunde, “First principles density functional study of the adsorption and dissociation of carbonyl compounds on magnesium oxide nanosurfaces,” Journal of Physical Chemistry B, vol. 110, no. 51, pp. 25941–25949, 2006.
[30]
N. A. Benedek, I. K. Snook, K. Latham, and I. Yarovsky, “Application of numerical basis sets to hydrogen bonded systems: a density functional theory study,” Journal of Chemical Physics, vol. 122, no. 14, Article ID 144102, 2005.
[31]
B. Delley, “Hardness conserving semilocal pseudopotentials,” Physical Review B, vol. 66, Article ID 155125, 2002.
[32]
C. U. Singh and P. A. Kollman, “An approach to computing electrostatic charges for molecules,” Journal of Computational Chemistry, vol. 5, pp. 129–145, 1984.
[33]
I. Mayer, “Bond orders and valences from ab initio wave functions,” International Journal of Quantum Chemistry, vol. 29, pp. 477–483, 1986.
[34]
K. B. Wiberg and P. R. Rablen, “Comparison of atomic charges derived via different procedures,” Journal of Computational Chemistry, vol. 14, pp. 1504–1518, 1993.
[35]
R. Kakkar, R. Grover, and P. Gahlot, “Density functional study of the properties of isomeric aminophenylhydroxamic acids and their copper (II) complexes,” Polyhedron, vol. 25, no. 3, pp. 759–766, 2006.
[36]
R. Kakkar and C. Singh, “Theoretical study of the kojic acid structure in gas phase and aqueous solution,” International Journal of Quantum Chemistry, vol. 111, no. 15, pp. 4318–4329, 2011.
[37]
D. T. Richens, The Chemistry of Aqua Ions, John Wiley & Sons, New York, NY, USA, 1997.
[38]
R. G. Parr and R. G. Pearson, “Absolute hardness: companion parameter to absolute electronegativity,” Journal of the American Chemical Society, vol. 105, no. 26, pp. 7512–7516, 1983.
[39]
R. G. Pearson, “Hard and soft acids and bases,” Journal of the American Chemical Society, vol. 85, no. 22, pp. 3533–3539, 1963.
[40]
R. B. Martin, “A stability ruler for metal ion complexes,” Journal of Chemical Education, vol. 64, p. 402, 1987.
[41]
H. Sigel and D. B. McCormick, “Discriminating behavior of metal ions and ligands with regard to their biological significance,” Accounts of Chemical Research, vol. 3, pp. 201–208, 1970.
[42]
J. P. Glusker, “Structural aspects of metal liganding to functional groups in proteins,” Advances in Protein Chemistry, vol. 42, pp. 1–76, 1991.
[43]
L. Rulí？ek and J. Vondrá？ek, “Coordination geometries of selected transition metal ions (Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Hg2+) in metalloproteins,” Journal of Inorganic Biochemistry, vol. 71, pp. 115–127, 1998.
[44]
J. Bjerrum and C. K. Jorgenssen, “Crystal field stabilization and tendency towards complex formation of first transition group elements,” Recueil des Travaux Chimiques des Pays-Bas, vol. 75, pp. 658–664, 1956.
[45]
L. E. Orgel, An Introduction to Transition Metal Chemistry, Ligand Field Theory, Methuen, London, UK, 1966.
