Amavadin and Homologues as Mediators of Water Oxidation

Abstract

The vanadium(IV) N-hydroxyiminodicarboxylate complexes [V(HIDPA) 2 ] 2À and [V(HIDA) 2 ] 2À ,close models of the amavadin (a natural product from Amanita fungi lacking the V=Og roup but exhibiting ar are NO-bound oxyiminate moiety), are shown to be the first recognized complexes of the early transition metals (up to periodic Group 7) that mediate the oxidation of water.The reactions were analyzed by visible spectrophotometry,m ass spectrometry,a nd measurement of evolved dioxygen using Ce 4+ as sacrificial oxidant. Am echanism proposed on the basis of DFT calculations involves the reversible oxidation to the mononuclear V V -{OṄ <}c enter, where the redox active oxyimino group playsakey role and metal oxidation state variation is only one unit. The more similar model of the metallobiomolecule,[ V(HIDPA) 2 ] 2À , displays alower oxidation rate than [V(HIDA) 2 ] 2À but does not undergo appreciable degradation, in contrast to the latter.

Nitrite Reduction in Aqueous Solution Mediated by Amavadin Homologues: N2O Formation and Water Oxidation

“…Such ac olour change was previously observed with H 2 O 2 [4] or Ce IV [15] as oxidants, and was attributed to the reduction of V V complexes back to V IV as ar esult of the water oxidationp rocess. This behaviour is similarf or samples covered with aluminium foil and, hence,p rotected from light radiation, and for unprotected ones.…”

“…[15] An eightfold increase in dissolvedo xygen (from 0.46 to 4.06 mg L À1 )w as detected after 20 h. The amount of released oxygen is half that of the initial amounto fn itrite in solution (0.11v s. 0.22 mmol L À1 ,r espectively). The releaseo fo xygen is associated with vanadium-mediated water oxidation;aprocess for whicht he mechanism was proposed and investigated previously.…”

“…[15] This was the first ex- ample of such activity by av anadium complex under non-photochemical conditions. [15] This was the first ex- ample of such activity by av anadium complex under non-photochemical conditions.…”

“…[15] The oxidation of [V(HIDA) 2 ] 2À or [V(HIDPA) 2 ] 2À by nitrite strongly depends on the pH of the reactionm ixture. [15] The oxidation of [V(HIDA) 2 ] 2À or [V(HIDPA) 2 ] 2À by nitrite strongly depends on the pH of the reactionm ixture.…”

“…[75,76] Because in the proposed mechanisms the relative stability of the high-and low-spin states was ac rucial issue, the B3LYP* functional was selected for the calculations. [15] The B3LYP* functional was constructed by using the keywords blyp, IOp(3/76 = 1000001500), IOp(3/77 = 0720008500) and IOp(3/78 = 0810010000) in Gaussian. [15] The B3LYP* functional was constructed by using the keywords blyp, IOp(3/76 = 1000001500), IOp(3/77 = 0720008500) and IOp(3/78 = 0810010000) in Gaussian.…”