title: Temperature and solvent structure dependence of VO2+ complexes of pyridine-N-oxide derivatives and their interaction with human serum transferrin.
abstract: The behaviour of the systems formed by VO(2+), 2-hydroxypyridine-N-oxide (Hhpo) and 2-mercaptopyridine-N-oxide (Hmpo) was studied both in solution and in the solid state through the combined application of spectroscopic (EPR and UV-Vis spectroscopy) and DFT methods. The geometry of solid bis-chelated complexes [VOL(2)], with L = hpo and mpo, is square pyramidal, but it can change to cis-[VOL(2)S], where S is a solvent molecule, when these are dissolved in a coordinating solvent. The equilibrium between the square pyramidal and cis-octahedral forms is strongly affected by solvent and temperature. At room temperature, the predominant species is [VOL(2)], which gives a pink colour to the solutions; at lower temperatures, the equilibrium is shifted--partially or completely--toward the formation of cis-[VOL(2)S], which is green. In an acidic environment and in the presence of an excess of ligand, [VOL(2)] can transform into the tris-chelated complex [VL(3)](+), in which vanadium loses the oxido ligand and adopts a hexa-coordinated geometry intermediate between octahedral and trigonal prismatic. 1-Methylimidazole (1-MeIm), which represents a model for His-N coordination, forms mixed complexes with stoichiometry cis-[VOL(2)(1-MeIm)], occupying an equatorial position. In the ternary systems VO(2+)-Hhpo-hTf and VO(2+)-Hmpo-hTf at room temperature and pH 7.4, besides (VO)hTf and (VO)(2)hTf, the mixed species cis-VO(hpo)(2)(hTf) and VO(mpo)(hTf) are observed, with the equatorial binding of an accessible histidine residue. Finally, the contribution of the N-oxide group to (51)V A(z) and A(iso) hyperfine coupling constants, which can be important in the characterisation of similar species, is discussed.
authors.affiliation: Istituto CNR di Chimica Biomolecolare, Trav. La Crucca 3, I-07040 Sassari, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Sanna
authors.forename: Valeria
authors.initials: V
authors.lastname: Ugone
authors.forename: Giovanni
authors.initials: G
authors.lastname: Micera
authors.forename: Eugenio
authors.initials: E
authors.lastname: Garribba
mesh_terms: D004121:Dimethyl Sulfoxide / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry*; D013696:Temperature; D014168:Transferrin / Q000378:metabolism*; D014638:Vanadates / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D009942:Organometallic Compounds; D011725:Pyridines; D012997:Solvents; D014168:Transferrin; D014867:Water; D014638:Vanadates; C013229:pyridine N-oxide; D004121:Dimethyl Sulfoxide