Aqueous V(V)-Peroxo-Amino Acid Chemistry. Synthesis, Structural and Spectroscopic Characterization of Unusual Ternary Dinuclear Tetraperoxo Vanadium(V)-Glycine Complexes

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Abstract
Vanadium participation in cellular events entails in-depth comprehension of its soluble and bioavailable forms bearing physiological ligands in aqueous distributions of binary and ternary systems. Poised to understand the ternary V(V)-H2O2-amino acid interactions relevant to that metal ion’s biological role, we have launched synthetic efforts involving the physiological ligands glycine and H2O2. In a pH-specific fashion, V2O5, glycine, and H2O2 reacted and afforded the unusual complexes (H3O)2[V2(O)2(μ2:η2:η1-O2)2(η2-O2)2(C2H5NO2)]·5/4H2O (1) and K2[V2(O)2(μ2:η2:η1-O2)2(η2-O2)2(C2H5NO2)]·H2O (2). 1 crystallizes in the triclinic space group P1̅, with a = 7.805(4) Å, b = 8.134(5) Å, c = 12.010(7) Å, α = 72.298(9)°, β = 72.991(9)°, γ = 64.111(9)°, V = 641.9(6) Å3, and Z = 2. 2 crystallizes in the triclinic space group P1̅, with a = 7.6766(9) Å, b = 7.9534(9) Å, c = 11.7494(13) Å, α = 71.768(2)°, β = 73.233(2)°, γ = 65.660(2)°, V = 610.15(12) Å3, and Z = 2. Both complexes 1 and 2 were characterized by UV/visible, LC-MS, FT-IR, Raman, NMR spectroscopy, cyclic voltammetry, and X-ray crystallography. The structures of 1 and 2 reveal the presence of unusual ternary dinuclear vanadium-tetraperoxo-glycine complexes containing [(VV=O)(O2)2]− units interacting through long V−O bonds and an effective glycinate bridge. The latter ligand is present in the dianionic assembly as a bidentate moiety spanning both V(V) centers in a zwitterionic form. The collective physicochemical properties of the two ternary species 1 and 2 project the chemical role of the low molecular mass biosubstrate glycine in binding V(V)-diperoxo units, thereby stabilizing a dinuclear V(V)-tetraperoxo dianion. Structural comparisons of the anions in 1 and 2 with other known dinuclear V(V)-tetraperoxo binary anionic species provide insight into the chemical reactivity of V(V)-diperoxo species in key cellular events such as insulin mimesis and antitumorigenicity, potentially modulated by the presence of glycinate and hydrogen peroxide.