Deamination process in the formation of a copper(II) complex with glutamic acid and a new ligand derived from guanidinoacetic acid: Synthesis, characterization, and molecular modeling studies

Autor: Luiza Cristina de Moura, Marcelo H. Herbst, Ricardo Bicca de Alencastro, Jussara L. Miranda, Bruno A. C. Horta, Magaly Girão Albuquerque, Jackeline da Silva Coelho
Rok vydání: 2008
Předmět:
Zdroj: Polyhedron. 27:2386-2394
ISSN: 0277-5387
DOI: 10.1016/j.poly.2008.04.024
Popis: A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (Gaa) and glutamic acids (Glu), forming the binuclear copper(II) complex K2Cu2C16H23N7O12 · 1/2H2O (1), which was characterized by elemental analysis (CHN), spectroscopy methods (IR and EPR), powder X-ray diffraction, thermogravimetric analysis (TGA), and mass spectrometry. A new ligand, namely biguanide-1,5-diethanoate (Bge) (C6H9N5O4), was formed during complexation, probably due to the reaction between two Gaa species and the consequent release of a significant amount of ammonia, thus, characterizing the deamination process. In complex 1, Bge behaved as a tetradentated ligand, using its oxygen and nitrogen atoms as coordinating sites to both Cu(II) ions. In addition, Glu has coordinated to Cu(II) through its α-N and O atoms. Theoretical calculations of the cis–cis, cis–trans, and trans–trans isomers of 1, considering three prototropic forms of the Bge ligand, were carried out using semi-empirical quantum mechanics (PM3/d). DFT (B3LYP and B3P86) calculations of complex 1, in which a hydrogen atom replaced the side chain of Glu, were also carried out using the 6-31G(d) basis set and the LanL2DZ effective core potential for the transition metal. Based on experimental and theoretical data, we concluded that the trans–trans isomer of the binuclear copper(II) complex 1 should be the most stable, although the occurrence of other isomers, even if in minor quantities, should not be disregarded.
Databáze: OpenAIRE
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