title: 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.
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.
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China; College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, China.
authors.forename: Can-Yu
authors.initials: CY
authors.lastname: Chen
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Mao-Long
authors.initials: ML
authors.lastname: Chen
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
authors.forename: Hong-Bin
authors.initials: HB
authors.lastname: Chen
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States.
authors.forename: Hongxin
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, United States. Electronic address: spjcramer@ucdavis.edu.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Cramer
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China; Department of Chemistry, University of California, Davis, CA 95616, United States. Electronic address: zhzhou@xmu.edu.cn.
authors.forename: Zhao-Hui
authors.initials: ZH
authors.lastname: Zhou
mesh_terms: D020418:Algal Proteins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008293:Malates / Q000737:chemistry*; D008667:Metalloproteins / Q000737:chemistry*; D015394:Molecular Structure; D009591:Nitrogenase / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011522:Protons; D012996:Solutions; D055672:Static Electricity; D013237:Stereoisomerism
chemical_list: D020418:Algal Proteins; D001426:Bacterial Proteins; D002264:Carboxylic Acids; D056831:Coordination Complexes; D008024:Ligands; D008293:Malates; D008667:Metalloproteins; D009942:Organometallic Compounds; D011522:Protons; D012996:Solutions; C055326:iron-vanadium cofactor; C031384:vanadyl citrate; C030298:malic acid; D009591:Nitrogenase; C011729:citramalate
keywords: Citrate; Crystal structure; Malate; Nitrogenase; R-homocitrato iron vanadium cofactor; Vanadyl