1. α-Hydroxy coordination of mononuclear vanadyl citrate, malate and S-citramalate with N-heterocycle ligand, implying a new protonation pathway of iron–vanadium cofactor in nitrogenase
- Author
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Chen, Can-Yu, Chen, Mao-Long, Chen, Hong-Bin, Wang, Hongxin, Cramer, Stephen P, and Zhou, Zhao-Hui
- Subjects
Inorganic Chemistry ,Chemical Sciences ,Algal Proteins ,Bacterial Proteins ,Carboxylic Acids ,Coordination Complexes ,Crystallography ,X-Ray ,Hydrogen Bonding ,Hydrogen-Ion Concentration ,Ligands ,Malates ,Metalloproteins ,Molecular Structure ,Nitrogenase ,Organometallic Compounds ,Protons ,Solutions ,Static Electricity ,Stereoisomerism ,Citrate ,Malate ,Vanadyl ,Crystal structure ,R-homocitrato iron vanadium cofactor ,Theoretical and Computational Chemistry ,Other Chemical Sciences ,Inorganic & Nuclear Chemistry ,Inorganic chemistry - Abstract
Unlike the most of α-alkoxy coordination in α-hydroxycarboxylates to vanadium, novel α-hydroxy coordination to vanadium(IV) has been observed for a series of chiral and achiral monomeric α-hydroxycarboxylato vanadyl complexes [VO(H2cit)(bpy)]·2H2O (1), [VO(Hmal)(bpy)]·H2O (2), [VO(H2cit)(phen)]·1.5H2O (3), [VO(Hmal)(phen)]·H2O (4), and [(Δ)VO(S-Hcitmal)(bpy)]·2H2O (5), [VO(H2cit)(phen)]2·6.5H2O (6), which were isolated from the reactions of vanadyl sulfate with α-hydroxycarboxylates and N-heterocycle ligands in acidic solution. The complexes feature a tridentate citrate, malate or citramalate that chelates to vanadium atom through their α-hydroxy, α-carboxy and β-carboxy groups; while the other β-carboxylic acidic group of citrate is free to participate strong hydrogen bonds with lattice water molecule. The neutral α-hydroxy group also forms strong intermolecular hydrogen bonds with water molecule and the negatively-charged α-carboxy group in the environment. The inclusion of a hydrogen ion in α-alkoxy group results in the formation of a series of neutral complexes with one less positive charge. There are two different configurations of citrate with respect to the trans-position of axial oxo group, where the complex with trans-hydroxy configuration seems more stable with less hindrance. The average bond distances of V-Ohydroxy and V-Oα-carboxy are 2.196 and 2.003Å respectively, which are comparable to the VO distance (2.15Å) of homocitrate in FeV-cofactor of V-nitrogenase. A new structural model is suggested for R-homocitrato iron vanadium cofactor as VFe7S9C(R-Hhomocit) (H4homocit=homocitric acid) with one more proton in homocitrate ligand.
- Published
- 2014