VIVO Complexes of Bis(imidazol‐2‐yl) Derivatives: A Potentiometric, Spectroscopic and DFT Study

Abstract

AbstractThe 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)