Reduction cyclic

Ferric iron appears to undergo cyclic reduction by O2 to Fe and oxidation of Fe by H2O2... 

Warburg and Christian showed that the color of this old yellow enzyme came from a flavin and proposed that its cyclic reduction and reoxidation played a role in cellular oxidation. When NADP+ was isolated the proposal was extended to encompass a respiratory chain. The two hydrogen carriers NADP+ and flavin would work in sequence to link dehydrogenation of glucose to the iron-containing catalyst that interacted with oxygen. While we still do not know the physiological function of the old yellow enzyme,b the concept of respiratory chain was correct. 

Another means of metabolic activation is the cyclic reduction/oxidation of the parent compound, resulting in high rates of consumption of NADPH and production of superoxide anion. Either the depletion of NADPH and/or the formation of reactive oxygen radicals could lead to cellular injury. 

Fig. 3. Cyclic reduction and oxidation of cytochrome P-450 in adrenal cortical mitochondria. FP. adrenodoxin reductase non-haem iron protein, adrenodoxin SH, substrate SOH. hydroxylated product (from Ref. 24, with permission).

Fig. 4. Technique for monitoring platelet aggregation in the partially obstructed left circumflex coronary artery of the dog. Electromagnetic flow probes measure blood flow. Partial obstruction of the coronary artery with a plastic Lexan cylinder results in episodic cyclical reductions in coronary blood flow that are due to platelet-dependent thrombus formation. Every 2-3 mm the thrombus must be mechanically shaken loose to restore blood. For detailed application of the Folts model, see Sullivan et al. (1992) Folts, Rowe (1974, 1988) and Folts et al. (1976, 1982).

Folts JD, Rowe GG (1974) Cyclical reductions in coronary blood flow in coronary arteries with fixed partial obstruction and their inhibition with aspirin. Fed Proc 33 413... 

P. Amodio, I. Gladwell and G. Romanazzi, Numerical solution of general bordered ABD linear systems by cyclic reduction, JNAIAM J. Numer. Anal. Indust. Appl. Math., 2006, 1(1), 5-12. 

Figure 2. Schematic representation of the cyclic reduction/oxidation of twin pairs of MoOe octahedra between the comer and the edge-sharing arrangements (Boxes represent MoOe octahedra with sharing of oxygen atoms at comers for M0O3 or edges for M0O2). The figure is not completely accurate, because it cannot take into account the fact that the arrangements are not perpendicular to the main axes of the lattice.

Total Mn in soils is highly variable and not closely related to the Mn content of the parent material, probably because of the tendency for cyclical reduction-oxidation to rapidly mobilize, then reprecipitate Mn as oxides in nodules and other deposits. Mn tends to associate with ferric iron in these deposits. 

Dopamine -hydroxylase catalyzes the side-chain hydrox-ylation of dopamine and other phenylethylamine derivatives. Ascorbic acid serves as a specific electron-donating cofactor. The enzyme from bovine adrenal glands contains and a smaller amount of Cu. When the enzyme oxidizes ascorbate to dehydroascorbate, most of the is reduced to Cu Added substrate is hydroxylated, and Cu is reoxidized to Cu This indicates that most of the protein-bound Cu undergoes cyclic reduction and oxidation during hydroxyhtion. The results also rule out an oxygen-carrier function for ascorbate. The possibility that a p-substituted hydroperoxide of the substrate is formed as an intermediate in the reaction has been examined with the use of 13,13 -tritium-labelled substrate. The results indicate that such an intermediate is unlikely. 

Suppose n-butyraldehyde-l- H(CH3CH2CH2CDO) were reduced with aluminum tri-s-butoxide made from optically active s-butyl alcohol. Assuming the cyclic reduction mechanism, would you expect the first 10 per cent of n-butanol-l- H to be optically active Explain. What would be the products at equilibrium ... 

The cyclic reduction mechanism that we are referring to is known as the Meerwein-Ponndorf-Oppenauer-Verly method and it is shown in the following generalized form ... 

The resulting reduced photoproduct acts as the catalytic intermediate for COj reduction (Figure 33). It has been suggested that carbon monoxide ligand dissociation, followed by formation of a rhenium-formate intermediate, leads to cyclic reduction of carbon dioxide to CO. Interestingly, a rhenium(I)-carboxylate complex, /ac-Re(0—C(=0)—H)(bpy)(CO)3, has been isolated as a by-product of the photosystem. The latter complex is inactive in COj reduction to CO, and hence a rhenium-formate intermediate formed by COj insertion into the hydride bond was suggested as the active intermediate for CO formation (Figure 33). 

Since it is well known that at least part of the Cu of ceruloplasmin undergoes cyclic reduction by substrate and oxidation by molecular oxygen (88), the availability of the various Cu binding sites to small solute molecules is of importance. One of the first observations which suggested that at least part of the Cu was... 

Apart from triangular factorization and Gaussian elimination, there exist other effective direct methods for block-banded systems. For instance, the odd-even reduction (the cyclic reduction) is effective for solving symmetric block tridiagonal systems Ax=b with (2 — 1) x (2 — 1), matrices of the form... 

Key intermediate energy-converting steps common to both photosynthesis and respiration are (1) the cyclic reduction and oxidation of nicotinamides and flavins coupled to the pumping of acid (protons) from one side to the other of a membrane and (2) the return of acid (protons) across the membrane coupled to production of ATP. 

If reduction of the oxidized nicotinamide were to occur in an appropriately structured and carboxylate-containing protein within a membrane, however, the pickup of proton by the carboxylate could occur from one side of a membrane, thereby lowering the concentration on that side, and on oxidation the proton release could occur to a confined space on the other side, thereby increasing the proton concentration within the confined space on the other side. Our proposal is that the cyclic reduction and oxidation of redox couples within the thylakoid membrane of chloroplasts and within the inner mitochondrial membrane achieves proton pumping by means of AGap, the aqueous mediated repulsion between oil-like and charged groups that disrupts association of oil-... 

It was briefly mentioned that the same order of reduction likelihood remained also if one Li was introduced. However, focusing on different possible interpretations, the reduction energy order of VC and DMC was interchanged if considering the cyclic reduction products of EC, PC, and VC. In the gas-phase a difference in the relative stability of the linear carbonates was suggested only with linear products, because of a particularly strong stabilization effect of DMC in a continuum. With... 

Another interesting exploitation of DTE derivatives, in this case bearing A-methylpyridinium pendant groups, is based on the fact that the closed isomer behaves as an electron acceptor, while the open state formed by visible light irradiation does not. Thus, a molecularly imprinted matrix is formed by cross-linking yia electropolymerization of thioaniline-functionalized Au nanoparticles in the presence of the closed photoisomer. The system is built in such a way that the closed photoisomer is then released to the electrolyte solution, so that the cyclic reduction and oxidation of the bridging units results in the reversible electrochemically controlled uptake and release of the closed photoisomer. The system finds a number of applications. ... 

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