Complexation and Thermal Studies of Uric Acid with Some Divalent and Trivalent Metal Ions of Biological Interest in the Solid State

Abstract

Nine new [metal : uric acid] complexes [M(Ua) n ] Á XH 2 O have been synthesized. These complexes have been characterized by elemental analysis, X-ray diraction (XRD), magnetic susceptibility ( e. ), FTIR spectra, thermal analysis (TG & DTA), and electronic spectra (UV/ visible). Uric acid (HUa) coordinates as a bidentate ligand to Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Al(III), Cr(III) and Fe(III) through the protonated N-7 within the imidazole ring and O-6 within the pyrimidine ring. Uric acid forms neutral metal urate complexes with all the above metal ions. The quantitative compositions were determined as [M(Ua) 2 Á (H 2 O) 2 ] Á XH 2 O where M(II) Mn, Fe, Co, Ni, Cu, Zn and X 2, 4, 2, 4, 2, 2, respectively. The M(II) complexes exhibit an isostructural octahedral coordination with N-7, O-6 of two uric acid ligand molecules, and O of two water molecules. Compositions were also determined as [M(Ua) 3 ] Á YH 2 O where M(III) Al, Cr, Fe and Y 6, 3, 3 respectively. All the M(III) complexes form an isostructural octahedral coordination with N-7 and O-6 of three uric acid ligand molecules. Iron(III) complexes prepared with N 1 , N 3 and N 9 -methyl uric acid yielded brown complexes with a metal : ligand ratio of 1 : 3, while N 7 -methyl uric acid did not yield a complex due to blockage of N-7 with a methyl group.

Toxicity of seabird guano to sea urchin embryos and interaction with Cu and Pb

“…Hydrogen urate is the predominant form of uric acid at pH = and it has complexing capacity on Cu or Pb, forming a non-electrolitic complex due to charge neutralization of the cation (Cu +2 or Pb +2 ) (Wilcox et al, 1972;Tak et al, 1981;Moawad, 2002). The solubility product constants (K sp ) of the hydrogen urates were 5.8 × 10 -5 for Cu (Moawad, 2002) and 1.2 × 10 -14 for Pb (Tak et al, 1981). Hydrogen phosphate is the predominant phosphate species at pH = 8 and shows K sp values at 25 ºC of 4.5 × 10 -7 for Cu and 5.3 × 10 -12 for Pb (Markich et al, 2001)..…”

Spectroscopic, thermal and magnetic properties of some transition metal complexes derived from 1-Phenyl-3-Substituted-4-Nitroso-5-Pyrazolones

“…The molar conductivities of 1 mM in DMF (10 -3 A 2g  3 T 1g (P) transitions, respectively, in an octahedral geometry [29] and is almost identical with that of the octahedral [Ni(H 2 O) 6 ] 2+ ion [30]. It is difficult to relate spectra with the structure of Cu 2+ complexes, especially in view of the distorted geometry observed for its complexes [28].…”

Interaction of uranium(VI) with bioligands present in human biological fluids: the case study of urea and uric acid

“…Although the formation constants for both U(VI)-uric acid and U(VI)-urea systems were determined at pH 3 and 4 respectively; but they are still valid for speciation calculation in the biological pH range of human urine (4)(5)(6)(7)(8), since both ligands do not undergo deprotonation in the indicated range of pH.…”

“…Due to their biological importance, both compounds were thoroughly studied especially from the biochemical viewpoint. As a bio-ligand, uric acid interacts with bio-metal ions such as Mg, Ca, Fe, Co, Cu, and Zn to form soluble and/or solid complexes [6,7]. Its salts and complexes have also been obtained with some other cations; Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Al(III), Fe(III) [6], and with Cr(III) as well [6,8].…”