Hydroxylamine, reduction

Oximes undergo hydrogenation to hydroxylamines and/or amines depending on reaction conditions. Platinum oxide is the most frequently used catalyst for selective hydrogenation of oximes to hydroxylamines. Reduction of chiral oxime 96 over palladium catalyst (equation 66) proceeds in high yield and stereoselectivity. High stereoselectivity was observed in catalytic hydrogenation of a-alkoxyoximes . 

It was found that underpotentially deposited germanium strongly enhances the reduction rate of nitrate. The reduction of nitrite is enhanced to a lesser extent, whereas germanium is inactive for NO and hydroxylamine reduction. It is of interest that the well-known inhibition of the nitrate reduction at low potentials was absent for germanium-modified electrodes. 

The nitrite reductase of Azotobacter vinelandvi (A. agile) was extracted in soluble form by Nason and his colleagues (537). The preparation reduced nitrite and hydroxylamine in the presence of reduced nicotinamide-adenine dinucleotides and required flavin for maximal activity. FAD was shown to be specific for nitrite reduction, whereas both FAD and FMN were active for hydroxylamine reduction. The hydroxylamine reductase activity of the preparation was enhanced in the presence of Mn +. Ammonia was shown to be the product of nitrite reduction, but the product of hydroxylamine reduction was not identified. Another nitrite and hydroxylamine reductase, which had a Mn requirement, was also isolated and partially purified in Nason s laboratory from soybean... 

The latter inhibition is reversed by light. Urea inactivation-reaclivation studies showed parallel loss and recovery of nitrite and hyroxylamine reductase activities, and nitrite was shown to inhibit hydroxylamine reduction. These results have suggested that the enzyme has a common binding site for nitrite and hydroxylamine. The absorption spectra of the A. fischeri enzyme (oxidized, reduced, and reduced plus nitrite or hydroxylamine) are shown in Fig. 39. 

Selective reductions. Borch et af. have recenlly reported a study of the reduction of various organic functional groups with sodium cyanoborohydride. Under neutral conditions, carbonyl groups are reduced to a negligible extent, but reduction is rapid at pH 3 4. Ketoximes are reduced smoothly at pH 4 to the corresponding alkyl-hydroxylamines. Reduction of aldoximes results mainly in the dialkylhydroxylaminc. 

D.J., and Butt, J.N. (2002) Protein film voltammetry reveals distinctive fingerprints of nitrite and hydroxylamine reduction by a cytochrome c nitrite reductase. Journal of Biological Chemistry, 277, 23374-23381. 

Figure 4-14. Catalytic voltammetry of nitrite reductase is critically dependent on the identity and concentration of the substrate at pH 7. (A) In 1 pM nitrite, reduction of the enzyme successively, turns on, but then attenuates activity. (B) Overlaid derivatives emphasise changes in the waveshape as the nitrite concentration is increased from 1.7 to 265 pM. At higher nitrite concentrations, activity increases upon application of a more negative potential, and this is reflected by the two positive features in the derivative plot. (C) At 1 mM hydroxylamine, reduction of the enzyme does not attenuate the rate of catalysis. (D) Overlaid derivatives show that as the hydroxylamine concentration is raised from 1.1 to 347 mM the waveshape develops two positive features similar to the waveshapes displayed at high rates of nitrite reduction. Reproduced from ref. 70 with permission of the American Society for Biochemistry and Molecular Biology.

With ferrous ion or cathodic reduction, conversion of plutonium from Pu to Pu is so rapid that back extraction of plutonium to the aqueous phase and reduction there to Pu can be carried out simultaneously in a single multistage contactor. With tetravalent uranium, reduction of plutonium is slower, so that additional contactor volume is desirable to complete back extraction. With hydroxylamine, reduction of plutonium is so much slower that it is preferable first to return both uranium and plutonium to the aqueous phase by stripping with dilute nitric acid and then to reduce the plutonium in equipment providing sufficient residence time for reduction to proceed to completion. Finally, the uranium is reextracted by TBP. 

Partially purified nitrite reductase frequently exhibits variable amounts of hydroxylamine reductase activity indicating that the enzyme is not totally specific for nitrite (Hucklesby and Hageman, 1976 Hewitt et al., 1%9). The affinity of the enzyme for nitrite is from 10 to 1000 times greater than for hydroxylamine (Hewitt, 1975). Moreover the inclusirm of hydroxylamine in assays for nitrite reductase does not influence the rate of nitrite conversion to ammonia (Lazzarini and Atkinson, 1%1 Cresswell et al., 1962). If hydroxylamine is a normal intermediate of nitrite reduction, it must be strongly bound to the enzyme and the hydroxylamine reduction site is not readily available to exogenous hydroxylamine. However, preliminary evidence indicates that in vitro ammonia can displace hydroxylamine from nitrite reductase (Loussaert and Hageman, 1976). 

Amino-2-ethylenehydroxylamines. Startg. acetoxyphosphate added under argon to a soln. of N-(2-heptyl)hydroxylamine and a little tetrakis(triphenylphosphine)pal-ladium(O) in THF, stirred at room temp, for 2 h, diethylamine added, stirred again for 3 h, and treated with ether and 2 N HCl - product. Y 90%. F.e., also N-allylation of hydroxylamines, reductive dehydroxylation to 2-ethylene-5cc-amines (with Zn), and conversion to a,p-ethylene-azomethines and -nitrones, s. S. Murahashi et al.. Tetrahedron Letters 29, 2973-6 (1988). 

For example, the iron in plant hemoglobins can remove an oxygen. .. R. Sturms et al. Hydroxylamine reduction to ammonium by plant and cyanobacterial hemoglobins. 2011. Biochemistry 50(50), p. 10829. DOI 10.1021/bi201425f. 

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