Quinone complexes, osmium

Quercetinase, 44 281 Quinlol complexes, osmium, 37 270 1,5-Quinoid-7,8-dihydro-6//-L-biopterin, pro-tonated, oxo-Mo(IV) complex, 40 11-12 Quinone complexes... 

Gauvin, R. M. Rozenberg, H. Shimon, L. J. W. Ben-David, Y. Milstein, D. Osmium-mediated C—H and C—C bond cleavage of a phenolic substrate p-quinone methide and methylene arenium pincer complexes. Chem. Eur. J. 2007, 13, 1382-1393. 

A detailed stu of over 45 catalysts, primarily from Group VIII metal salts and complexes, showed palladium(II) compounds to be the most effective in the dehydrogenation of a variety of aldehydes and ketones. Soluble palladium(II) salts and complexes such as dichloro(tTiphenylphosphine)palladium(II) and palladium(II) acetylacetonate have been shown to be optimal, with the salts of rhodium, osmium, iridium and platinum having reduced efficacy. Since the d ydrogenation reaction is accompanied by reduction of the palladium(II) catalyst to palladium(0), oxygen and a cooxidant are required to effect reoxidadon. Copper(II) salts are favored cooxidants, but quinones, and especially p-benzoquinone, are also effective (Scheme 24). - ... 

Figure 5. Donor-acceptor complexes bridged by peptide units composed of polyproline units (a) ruthenium donor, quinone acceptor (161) (b) osmium donor, cobalt acceptor (75, 76),...

When a metal complex like osmium(II) fris(bipyridyl) or a metallocene, as in compound 3, is appended to the ligand, the MLCT excited state is quenched by energy transfer to the adjacent metal center. The rate of this quenching decreases as an anionic substrate binds between the two metal eomplexes. A similar switching mechanism is seen in the calix[4]diquinone-appended complex, 4. In this case, the fluorescence emission is quenched via an intramolecular electron transfer to the quinone. Anion binding between the Ru complex and the quinone blocks the quenching process, and the emission intensity is significantly recovered. 

Electrocatalytic enzyme mediation has been demonstrated using quinones, viol-ogens, 2,2-azinobis(3-ethylbenzothiazohne-6-sulfonate) (ABTS), and complexes of iron, ruthenium, cobalt, osmium, and many other compounds [22-24]. Much early work concerned the GOx anode, intended for a glucose sensor. In 1974, Schlapfer et al. tested 11 different mediators for a GOx electrode with a semipermeable membrane [25]. Ten years later, Cass et al. reported membrane-bound electrodes that operated in whole blood [26]. In 1986, Bourdillon et al. presented an analysis arguing that immobilized enzyme electrodes have higher efficiency than those with free enzyme in solution [27]. These examples demonstrate several possible enzyme/ mediator configurations. Both enzyme and mediator can exist as firee species in the liquid electrolyte, or one or both can be immobilized on the electrode surface. As an alternative to immobilization, enzyme and mediator can also be confined near the electrode by a semipermeable membrane. 

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