Generation of a cis-[MoVO(OH)] center: proton- and oxygen-17 superhyperfine parameters relevant to molybdoenzymes

Studies by electron paramagnetic resonance spectroscopy of xanthine oxidase enriched with molybdenum-95 and with molybdenum-97

“…These conclusions are consistent with the structure proposed by Morpeth et al (1984) from the ligand hyperfine couplings, which is shown in Figure 5D. Confidence that the Rapid signal-giving species possess a structure similar to Figure 5d is strengthened by recent model compound work (Farchione et al, 1986;Dowerah et al, 1987).…”

The inorganic biochemistry of molybdoenzymes

“…In 1981, hydroxyl ligands of Mo(v) were generated by irradiating single crystals of molybdate, and gave (Yamase et al 1981) proton splittings analogous to those in the enzymes. Eventually in 1986, the long awaited model compound m-[MoO(OH)L], where LH 2 = (HSCH 2 CH 2 N(Me)CH 2 -) 2 , was generated in solution and the exchangable proton found (Farchione et al 1986) to have A( 1 H) av 1-50 mT. More detailed later work (Dowerah et al 1987), involving -SH as well as -OH ligands and including frozen solution studies, utilizing the ligand…”

“…data on molybdenum(v) compounds relevant as enzyme models has proliferated rapidly in the last few years (e.g. Scullane et al 1979;Hanson et al 1981;Kaul et al 1985;Farchione et al 1986;Dowerah et al 1987;Cleland et al 1987;Young et al 1987). One of these publications (Dowerah et al 1987) describes for the first time a series of compounds, based on a single polydentate ligand, that mimic to a most useful degree many of the e.p.r.…”

Complexes Containing cis-[MoVO2]+ and cis-[MoVO(OH)]2+ Centers

“…Elimination and/or condensation reactions, initiated by coupled electron−proton transfer reactions involving an oxo ligand in the reduced complex, account for the formation of these thermodynamically favored species. , Kinetically controlled syntheses, which exploit ligands capable of retarding elimination and the close approach of molybdenum centers, are required for the generation of long-lived cis -[Mo V O 2 ] + complexes. Only a small number of cis- [Mo VI O 2 ] 2+ complexes are known to undergo a reversible, one-electron reduction on the cyclic voltammetric time scale. − The reduction products, which can be chemically generated in many cases, are formulated as cis- [Mo V O 2 ] + complexes on the basis of EPR studies. Some of these complexes protonate to form cis- [Mo V O(OH)] 2+ species, but the coligands are effective in retarding further reactions. − These formulations are consistent with extensive multifrequency EPR studies of [(L-N 2 S 2 )MoO 2 ] - and (L-N 2 S 2 )MoO(OH) complexes and their 95,97 Mo-, 98 Mo-, 1 H-, 2 H-, and 17 O-labeled analogues. ,,, Possible geometries and electronic structures for these species were predicted recently using ab initio and INDO molecular orbital methods, and in most cases, the results were concordant with those obtained from solution EPR studies 2h.…”

“…Only a small number of cis- [Mo VI O 2 ] 2+ complexes are known to undergo a reversible, one-electron reduction on the cyclic voltammetric time scale. − The reduction products, which can be chemically generated in many cases, are formulated as cis- [Mo V O 2 ] + complexes on the basis of EPR studies. Some of these complexes protonate to form cis- [Mo V O(OH)] 2+ species, but the coligands are effective in retarding further reactions. − These formulations are consistent with extensive multifrequency EPR studies of [(L-N 2 S 2 )MoO 2 ] - and (L-N 2 S 2 )MoO(OH) complexes and their 95,97 Mo-, 98 Mo-, 1 H-, 2 H-, and 17 O-labeled analogues. ,,, Possible geometries and electronic structures for these species were predicted recently using ab initio and INDO molecular orbital methods, and in most cases, the results were concordant with those obtained from solution EPR studies 2h. None of these complexes have been isolated in substance, and no structural information is available.…”