title: Autoxidation-product-initiated dioxygenases: vanadium-based, record catalytic lifetime catechol dioxygenase catalysis.
abstract: In recent work, it was shown that V-containing polyoxometalates such as (n-Bu4N)7SiW9V3O40 or (n-Bu4N)9P2W15V3O62, as well as eight other V-containing precatalysts tested, evolve to a high activity, long catalytic lifetime (> or = 30,000-100,000 total turnovers) 3,5-di-tert-butylcatechol dioxygenase, in which Pierpont's complex [VO(DBSQ)(DTBC)]2 (where DBSQ is 3,5-di-tert-butylsemiquinone and DTBC is the 3,5-di-tert-butylcatecholate dianion) was identified as a common catalyst or catalyst resting state (Yin, C.-X.; Finke, R. G. Vanadium-Based, Extended Catalytic Lifetime Catechol Dioxygenases: Evidence For a Common Catalyst. J. Am. Chem. Soc. 2005, 127 (25), 9003-9013). Herein, those findings are followed up by studies aimed at answering the following questions about this record catalytic lifetime 3,5-di-tert-butylcatechol dioxygenase catalyst: (i) What is the key to how V leaches from, for example, seemingly robust V-containing polyoxometalate precatalysts? (ii) What is the key to the sigmoidal, apparently autocatalytic kinetics observed? (iii) What can be learned about the underlying reactions that form [VO(DBSQ)(DTBC)]2? (iv) Finally, do the answers to (i-iii) lead to any broader insights or concepts? Key findings from the present work include the fact that the reaction involves a novel, autoxidation-product-induced dioxygenase, that is, one in which the undesired autoxidation of the 3,5-di-tert-butylcatechol substrate to the corresponding benzoquinone and H2O2 turns on the desired dioxygenase catalysis via a V-leaching process which eventually yields Pierpont's complex, [VO(DBSQ)(DTBC)]2. Plausible reactions en route to [VO(DBSQ)(DTBC)]2 consistent with the kinetic data, the role of H2O2, and the relevant literature are provided. The results provide a prototype example of the little observed but likely more general concept of an autoxidation-product-initiated reaction. The results also provide considerable simplification of, and insight into, the previously disparate literature of V-based 3,5-di-tert-butylcatechol dioxygenase catalysis.
authors.affiliation: Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
authors.forename: Cindy-Xing
authors.initials: CX
authors.lastname: Yin
authors.forename: Yoh
authors.initials: Y
authors.lastname: Sasaki
authors.forename: Richard G
authors.initials: RG
authors.lastname: Finke
mesh_terms: D002384:Catalysis; D050548:Catechol 1,2-Dioxygenase / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D014639:Vanadium / Q000737:chemistry*
chemical_list: D014639:Vanadium; D006861:Hydrogen Peroxide; D050548:Catechol 1,2-Dioxygenase