Versatility of guanidoacetic acid coordination modes and synthesis of its new zinc complex

Abstract

Guanidinoacetic acid (GAA) is an amino acid involved in several biological processes including renal activity since it is synthesized mainly in the kidneys, insulin metabolism, creatine/phosphocreatine synthesis and recently as experimental nutrient for multiple sclerosis treatment. Given its biological role, some interactions between GAA and its complexation with essential and toxic metal ions have been previously investigated, both in aqueous medium with Ni(II), Co(II), Cu(II), Zn(II), Cd(II), and Pb(II), as well as in the synthesis of complexes in solid phase. This study presents the versatile coordination modes of GAA and reports its novel solid zinc complex. GAA complexation ranges from the usual α-nitrogen and oxygen bidentate coordination to a paddlewheel monodentate-oxygen mode in a Cu2GAA4 complex. The novel solid GAA zinc complex has only been succeeded to be synthesized in the presence of copper(II) salt, being characterized by single-crystal structure refinement using X-ray diffraction and mid and far-Fourier Transform Infrared spectroscopy. The results showed that the synthesized complex, (HGAA)[Zn(GAA)Cl3].H2O (1) , exhibits a tetrahedral geometry with an oxygen-carboxylate GAA monodentate coordination complemented by three chloride ligands and a water bridge linked to amonoprotonated GAA species. Hydrogen bonds play a crucial role in the stabilization of1, especially between Zn(GAA)Cl3- and its cation ion, HGAA+.Infrared spectroscopy of 1 presented aband at 412 cm-1 and three bands at 291, 273 and 239 cm-1, corresponding to Zn-O and Zn-Cl stretching modes, respectively. The different coordination modes of guanidinoacetate ion and its complexation with zinc and copper(II), as well as the way the hydrogen bonds stabilize their structures may help to further understand the diverse biochemical processes involved in this amino acid.