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 |
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Authors: | Jussara Lopes de Miranda Jackeline da Silva Coelho Luiza Cristina de Moura Marcelo Hawrylak Herbst Bruno Araújo Cautiero Horta Ricardo Bicca de Alencastro Magaly Girão Albuquerque |
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Institution: | 1. Departamento de Química Inorgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, 21949-900, Rio de Janeiro, RJ, Brazil;2. Departamento de Química Orgânica, Instituto de Química, Universidade Federal do Rio de Janeiro, 21949-900, Rio de Janeiro, RJ, Brazil;3. Departamento de Física dos Sólidos, Instituto de Física, Universidade Federal do Rio de Janeiro, 21949-900, Rio de Janeiro, RJ, Brazil |
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Abstract: | 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. |
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Keywords: | Copper(II) complex Guanidinoacetic acid Glutamic acid Deamination |
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