Preliminary Assignment of Protonated and Deprotonated Homocitrates in Extracted FeMo-Cofactors by Comparisons with Molybdenum(IV) Lactates and Oxidovanadium Glycolates.

ABSTRACT: A similar pair of protonated and deprotonated mononuclear oxidovanadium glycolates [VO(Hglyc)(phen)(H2O)]Cl·2H2O (1) and [VO(glyc)(bpy)(H2O)] (2) and a mixed-(de)protonated oxidovanadium triglycolate (NH4)2[VO(Hglyc)2(glyc)]·H2O (3) were isolated and examined. The ?C-O(H) (?C-OH or ?C-O) groups coordinated to vanadium were spectroscopically and structurally identified. The glycolate in 1 features a bidentate chelation through protonated ?-hydroxy and ?-carboxy groups, whereas the glycolate in 2 coordinates through deprotonated ?-alkoxy and ?-carboxy groups. The glycolates in 3 coordinate to vanadium through ?-alkoxy or ?-hydroxy and ?-carboxy groups and thus have both protonated ?C-OH and deprotonated ?C-O bonds simultaneously. Structural investigations revealed that the longer protonated V-O?-hydroxy bonds [2.234(2) Å and 2.244(2) Å] in 1 and 3 are close to those of FeV-cofactor (FeV-co) 2.17 Å1 (FeMo-co 2.17 Å2), while deprotonated V-O?-alkoxy bonds [2, 1.930(2); 3, 1.927(2) Å] were obviously shorter. This shows a similar elongated trend as the Mo-O distances in the previously reported deprotonated vs protonated molybdenum lactates (Wang, S. Y. et al. Dalton Trans. 2018, 47, 7412-7421) and these vanadium and molybdenum complexes have the same local V/Mo-homocitrate structures as those of FeV/Mo-cos of nitrogenases. The IR spectra of these oxidovanadium and the previously synthesized molybdenum complexes including different substituted ?C-O(H) model compounds show red-shifts for ?C-OH vs ?C-O alternation, which further assign the two IR bands of extracted FeMo-co at 1084 and 1031 cm-1 to ?C-O and ?C-OH vibrations, respectively. Although the structural data or IR spectra for some of the previously synthesized Mo/V complexes and extracted FeMo-co were measured earlier, this is the first time that the ?C-O(H) coordinated peaks are assigned. The overall structural and IR results well suggest the coexistence of homocitrates coordinated with ?-alkoxy (deprotonated) and ?-hydroxy (protonated) groups in the extracted FeMo-co.

SUBMITTER: Jin WT 

PROVIDER: S-EPMC6813765 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature