Várnagy, Katalin and Csorba, Timea and Kiss, Dóra and Garribba, Eugenio and Micera, Giovanni and Sanna, Daniele (2007) VIVO complexes of bis(imidazol-2-yl) derivatives: a potentiometric, spectroscopic and DFT study. European Journal of Inorganic Chemistry, Vol. 2007 (31), p. 4884-4896. eISSN 1099-0682. Article.
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The complexation of the VIVO ion with four amino acid derivatives of bis(imidazol-2-yl)methylamine [N-glycyl-bis(imidazol-2-yl)methylamine = Gly-BIMA, N-α-aspartyl-bis(imidazol-2-yl)methylamine = α-Asp-BIMA, N-α-glutamyl-bis(imidazol-2-yl)methylamine = α-Glu-BIMA and N-histidyl-bis(imidazol-2-yl)methylamine = His-BIMA] was studied in aqueous solution through the combined application of potentiometric and spectroscopic (UV/Vis and EPR) techniques. For comparison, the complexing capability of three simple bis(imidazol-2-yl) derivatives [bis(imidazol-2-yl)methane = BIM, bis(imidazol-2-yl)methylamine = BIMA and bis(imidazol-2-yl)nitromethane = BINM] and two benzyloxycarbonyl (Z) derivatives (Z-Gly-BIMA and Z-Ala-BIMA) was reported. Mono- and bis-chelated species with the (Nim, Nim) donor set were formed in both acid and neutral pH conditions, with the bis-chelated complexes being characterised by a cis-trans isomerism. In the basic pH range the complexation process continues with the formation of a mono-hydroxo cis-VOL2H-1 complex in systems with BIM, BIMA and BINM, and with the deprotonation and coordination of the amide nitrogen to give VOLH-1 and VOLH-2 in those with Gly-BIMA, α-Asp-BIMA, α-Glu-BIMA and His-BIMA. The results demonstrate that the bis(imidazol-2-yl)methyl residue is an anchoring group of intermediate strength, capable of avoiding extensive hydrolysis of the VIVO ion in the presence of a slight excess of ligand (L/M from 3:1 to 5:1). DFT calculations with progressively more complex basis sets were performed in order to obtain information on the structure of the VOLH-1 and VOLH-2 complexes. Finally, a discussion on the 51V anisotropic parallel hyperfine coupling constant (A||) of VOLH-1 and VOLH-2 and on the EPR properties connected to the V-N-(amide) bond in VIVO complexes is presented.
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