Osmium redox reactions

A compound which is a good choice for an artificial electron relay is one which can reach the reduced FADH2 active site, undergo fast electron transfer, and then transport the electrons to the electrodes as rapidly as possible. Electron-transport rate studies have been done for an enzyme electrode for glucose (G) using interdigitated array electrodes (41). The following mechanism for redox reactions in osmium polymer—GOD biosensor films has... 

Polynuclear transition metal cyanides such as the well-known Prussian blue and its analogues with osmium and ruthenium have been intensely studied Prussian blue films on electrodes are formed as microcrystalline materials by the electrochemical reduction of FeFe(CN)g in aqueous solutionThey show two reversible redox reactions, and due to the intense color of the single oxidation states, they appear to be candidates for electrochromic displays Ion exchange properties in the reduced state are limited to certain ions having similar ionic radii. Thus, the reversible... 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

Some interesting chemistry has appeared relating to the ability of the isocyanide ligand to stabilize unusual oxidation states. A series of palladium metal - metal bonded complexes has been synthesized by redox reactions involving two metal complexes in different formal oxidation states (33 -35). Similar ruthenium(I) and osmium(I) dimers have been prepared by an unusual homolytic fission of a ruthenium-carbon bond (36) or by singleelectron oxidation of Os(CNXylyl)5 (18). 

In another report, binding of IgG to anti-IgG immobilized on a Au-coated BK7 chip (sealed by PDMS) was detected by SPR [741]. Lactate was also determined using the SPR method. First, lactate was oxidized by LOX immobilized on an osmium redox polymer to produce H202. This molecule was then reduced by HRP immobilized in the same redox polymer. This surface reaction was detected by SPR [741]. 

Many of these oxo ruthenium (and similar osmium) species can be involved in reversible redox reactions in which OH or H20 participate, for example,... 

Many different redox reactions i acidic solutions are catalyzed by the same substances that catalyze hydrogen peroxide reactions. For example, Bognar and Jellinek determined traces of V(V), Fe(III), and osmium tetroxide using a chlorate-bromide-ascorbic acid-o-tolidine system and the Landolt effect. 

S. Mosseri, P. Neta, P. Hambright, D.Y. Sabry, and A. Harriman, Redox Reactions of Osmium Porphyrins, J. Chem. Soc. Dalton Trans. (1988) 2705. 

L-tryptophan (L-trp) is an essential aminoacid and it is needed to maintain optimum health. Osmium(VIII) acts as an efficient catalyst in many redox reactions [3, 4] involving different complexities due to the formation of different intermediate complexes, free radicals, and multiple oxidation states of osmium. 

Note that the HI value in this case is -1. The value for the former case is twice this value because two diol products are formed, so really the two results are equivalent. Since OSO4 is used as a catalyst, it is recovered and it is the Af-methyhnorpholine oxide that is consumed. This paradoxical situation of using a hypothetical redox reaction in place of the real mechanistically correct one is the only way to satisfy both the tracing of oxygen atoms and the observed net consumption of N-oxide in the overall balanced chemical equation. This will also impact on the determination of/(sac) since the N-oxide will be counted as contributing to the target bond structure map and not osmium tetraoxide. 

Some platinum metals, especially ruthenium but also rhenium, osmium, and iridium, form luminescent complexes with nitrogen-containing ligands, e.g., 2,2 -bipyridine (bpy). These complexes may participate in redox reactions with concomitant chemiluminescence in three different ways. 

Subsequent research on osmium-modified polymers has shown how the redox potential can be controlled by altering bipyridine ligands of the immobilized osmium complexes. The ability to reliably modulate redox potential has significantly broadened the range of enzymes with which osmium redox polymer are compatible and allows for mediation of oxidative enzymatic reactions as well as reductive enzymatic reactions. 

The reduced enzyme is reoxidized by osmium redox couples on the polymer chain close to the active site on the enzyme The electrons from the reaction then propagates to the electrode surface by means of electron hopping between the redox sites in the polymer The polymer is crosslinked by PEGDGE to the electrode surface, where the osmium complex oxidizes and the electrons are transferred to the electrode The electron transfer procedure is shown in figure 1 The current produced is proportional to the rate of glucose conversion, and provides a measure of the substrate concentration... 

The redox polymer has three functions, it communicates with the active site in the enzyme, transfers the electrons to the electrode surface and it forms a matrix in which the enzyme is immobilized [3], This is the reasons which makes the osmium polymer such a successful mediator. A very sensitive and fast biosensor is achieved with the redox polymer bound enzyme. There are no membrane passages that will delay the reaction and the mediator is immobilized in the same matrix and will not diffuse away. An amperometric glucose sensor with the mediator electrostatically bound to a PVP polymer has been studied in a previous paper [4], where the mediator loss seemed to be a problem. The hydrophilicity of the osmium redox polymer also contributes to the rapid response because of the fast transport of water soluble substrates and products. 

Oxidation of aliphatic aldehydes by benzyltrimethylammonium chlorobromate to the corresponding carboxylic acid proceeds via the transfer of a hydride ion from the aldehyde hydrate to the oxidant. The oxidation of aUyl alcohol with potassium bromate in the presence of osmium(Vin) catalyst in aqueous acidic medium is first order in bromate, Os(Vni) and substrate, but inverse fractional order in H+ the stoichiometry of the reaction is 2 3 (oxidantsubstrate). The active species of oxidant and catalyst in the reaction were understood to be BrOs and H2OSO5, respectively, which form a complex. Autocatalysis by Br, one of the products, was observed, and attributed to complex formation between Br and osmium(VIII). First-order kinetics each in BrOs, Ru(VI), and substrate were observed for the ruthenium(VI)-catalyzed oxidation of cyclopentanol by alkaline KBrOs containing Hg(OAc)2. A zero-order dependence on HO concentration was observed and a suitable mechanism was postulated. The oxidation reaction of aniUne blue (AB+) with bromate at low pH exhibits interesting non-linear phenomena. The depletion of AB+ in the presence of excess of bromate and acid occurs at a distinctly slow rate, followed by a very rapid reaction. A 12-step reaction mechanism, consistent with the reaction dynamics, has been proposed. The novel cyclohexane-l,4-dione-bromate-acid system has been shown to exhibit a rapid oscillatory redox reaction superimposed on a slower... 

The redox reaction between the polyelectrolytes in PEM films and specific molecules in solutions has been used to induce responsive film swelhng. To name a few, multilayer films containing a ferrocene-derivatized polyaUylamine hydrochloride (PAH-Fc) [185] and an osmium complex-derivatized polyaUylamine hydrochlorides (PAHOs) [186] can swell by 10% of initial film thickness upon oxidation of the Os(II). Multilayer capsules with layered anionic and cationic polyferrocenylsilanes to form multilayer capsules expand and increase their per-meabihty upon chemical oxidation of the ferrocene units [187]. Additionally, a poly(L-glutamic acid)/PAH multilayer film is reported to take up ferrocyanide ions from solutions and can expand and contract by 5-10% in response to electrochemical oxidation and reduction of the ferrocyanide species [188]. 

For mixed carbonyl adducts, from other groups, redox condensation reactions have been employed to considerable effect. Thus for osmium-cobalt, a range of derivatives has been prepared (241, 248, 249) by reactions of the types ... 

More recently, osmium-based redox polymers of similar structure have been developed as mediators for enzyme-catalyzed reactions relevant to biofuel cells. In this context, the chief development objectives have been tuning the redox potential for both anodes... 

Osmium (continued) carbide, 24 233 dianion, lA. Xil, 317-319 with phosphines and diphosphines, 30 191 protonation/deprotonation, 30 169 raft hexaosmium clusters, 30 180-182 reactions of condensation, 30 145 with hexafluoroacetone, 30 288 redox, 30 184-185 structural transformations, 30 203 sulfur-containing, synthesis of, 30 147 sulfur derivatives, 24 269, 300-310 synthesis... 

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