Ascorbic acids, reducing action

The polycythemic action of cobalt may be depressed or enhanced by various means which apparently do not act in the same way in different species. In the dog the simultaneous or separate feeding of liver and of choline or the injection of liver extracts or ascorbic acid reduces or... 

The reaction is carried out at a pH of 3 to 4 at this pH the indophenol is stable. At low pH ranges the dye fades and at pH ranges above 4 the action of non-ascorbic acid reducing substances becomes more prominent. 

Mechanisms by which nature in vivo oxidises (Figure 8) unsaturated fatty acids by the action of oxygen, iron and ascorbic acid (reducing agent) are being translated and adopted for usage in both water borne and solvent based alkyd systems. 

FIGURE 18.30 The physiological effects of ascorbic acid (vitamin C) are the result of its action as a reducing agent. A two-electron oxidation of ascorbic acid yields dehy-droascorbic acid. 

It is not clear whether V(V) or V(IV) (or both) is the active insulin-mimetic redox state of vanadium. In the body, endogenous reducing agents such as glutathione and ascorbic acid may inhibit the oxidation of V(IV). The mechanism of action of insulin mimetics is unclear. Insulin receptors are membrane-spanning tyrosine-specific protein kinases activated by insulin on the extracellular side to catalyze intracellular protein tyrosine phosphorylation. Vanadates can act as phosphate analogs, and there is evidence for potent inhibition of phosphotyrosine phosphatases (526). Peroxovanadate complexes, for example, can induce autophosphorylation at tyrosine residues and inhibit the insulin-receptor-associated phosphotyrosine phosphatase, and these in turn activate insulin-receptor kinase. 

A very effective tosylamide cleavage seems to be possible by the cooperative action of the electro-generated anthracene anion radical as electron transfer agent and of ascorbic acid as proton donor and additional reducing agent (Eq. (97))... 

Figure 4. Effect of reducing agents on the mutagenic action of the browning mixture of Glc and Lys. Key . cysteine O, N-acetylcysteine A, penicillamine A, dithiothreitol , triose reductone and , ascorbic acid.

Since ascorbic acid is a strong reducing agent, it is presumed to reduce ferric iron to its ferrous form or to maintain ferrous iron in its reduced state which is more available. However, its action on copper would be to reduce Cu (III) to Cu (I), the less available form of copper (36). Ascorbic acid is also thought to Increase the solubility of iron by decreasing the alkalinity of the intestinal chyme. Effect of ascorbic acid on the availability of zinc has been less extensively studied. 

A comprehensive review of spectrophotometric methods for the determination of ascorbic acid (1) was presented. Most of the methods are based on the reducing action of ascorbic acid, making use of an Fe(III)-Fe(II) redox system, and to a lesser extent Cu(II)-Cu(I), V(V)-V(IV) and phosphomolybdate/phosphotungstate-molybdenum/tungsten blue redox systems. A kinetic spectrophotometric method for the determination of L-ascorbic acid and thiols (RSH) was developed, whereby the absorbance of the Fe(II)-phen complex formed during the reaction of 1 or RSH with Fe(III)-phen was continuously measured at 510 nm by a double beam spectrophotometer equipped with a flow cell. The linearity range for 1 was 4-40 p,M and for RSH 8-80 xM. The method was validated for pharmaceutical dosage forms . 

Free radical scavengers may prove to be successfiil in interfering with the mechanism of action for asbestos. In vitro studies have shown that the effects of asbestos can be diminished by compounds that reduce the levels of reactive oxygen species, such as free radical scavengers (ascorbic acid, bemitil. 

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