Nitrite complexes reaction with

Besada [12] described a spectrophotometric method for determination of penicillamine by reaction with nitrite and Co(II). Penicillamine is first treated with 1 M NaN02 (to convert the amino-group into a hydroxy-group), then with 0.1 M CoCl2, and finally the absorbance of the brownish-yellow complex obtained is measured at 250 nm. The process is carried out in 50% aqueous ethanol, and the pH is adjusted to 5.4— 6.5 for maximum absorbance. The calibration graph is linear over the concentration range of 0.25-2.5 mg per 50 mL, and the mean recovery (n = 3) of added drug is 99.7%. Cystine, cysteine, methionine, and other amino adds do not interfere. 

The benzyl ligand of benzylbis(dimethylglyoximato)pyridine cobalt complex has been selectively converted to 3,5-dibenzyl-l,2,4-oxadiazole by a reaction with alkyl nitrite in the presence of light (426). The reaction proceeds by the in situ formation of an oxime and a nitrile oxide (Scheme 1.44). 

Samples of natural water should either be analysed immediately or be stored (not for a very long time) at a decreased temperature to suppress microbial processes. For the determination of nitrate and nitrite it is useful to conserve the samples by addition of 1 ml chloroform or 0.1% phenylmercuric acetate per Utre. To prevent oxidation of sulphide and some other substances in water samples, reductants are added [5, 147]. If the distribution of a species between the f ree ionic form and various complexes is to be studied, as is of ten the case, care must be taken not to shift the equiUbrium by adding substances that would enter into side reactions with the studied species. 

The donor types D3, D4, and D6 of Keilin and Nicholls (37) all reduce compound I of Type A enzymes directly to the ferric state in a two-electron process without detectable intermediates. Each of these donors is probably also able to bind in the heme pocket of the free enzyme. Alcohols (type D3) form complexes with free ferric Type A enzymes whose apparent affinities parallel the effectiveness of the same alcohols as compound I donors (39). Formate (type D3) reacts with mammalian ferric enzyme at a rate identical to the rate with which it reduces compound I to free enz5mie (22). Its oxidation by compound I may thus share an initial step analogous to its complex formation with ferric enzyme. Formate also catalyzes the reduction of compound II to ferric enzyme by endogenous donors in the enz5mie (40, 41). Both compound I and compound II may thus share with the free enzyme the ability to ligate formate in the heme pocket. Nitrite, which is oxidized to nitrate by a two-electron reaction with compoimd I (type D4), also forms a characteristic complex with free enzyme (42). In both cases the reaction involves the donor in its protonated (HNO2) form. 

A benzofuran ring replaces one of the benzene rings of the biphenyl moiety present in many of the sartans in the rather more complex drug saprisartan (80-10). It is of note, further, that the acidic proton is provided in this case by a trifluorosulfo-namide instead of the more common tetrazole ring. Construction of the imidazole fragment begins by nitrosation of the (3-ketoester (79-1) by means of sodium nitrite in acid to afford the oxime (79-2). Reaction with acetyl chloride leads to the ester (79-3). Reaction of this last intermediate with the iminoether from propionitrile then affords the imidazole (79-4). 

Thus, antioxidant effects of nitrite in cured meats appear to be due to the formation of NO. Kanner et al. (1991) also demonstrated antioxidant effects of NO in systems where reactive hydroxyl radicals ( OH) are produced by the iron-catalyzed decomposition of hydrogen peroxide (Fenton reaction). Hydroxyl radical formation was measured as the rate of benzoate hydtoxylation to salicylic acid. Benzoate hydtoxylation catalyzed by cysteine-Fe +, ascorbate - EDTA-Fe, or Fe was significantly decreased by flushing of the reaction mixture with NO. They proposed that NO liganded to ferrous complexes reacted with H2O2 to form nitrous acid, hydroxyl ion, and ferric iron complexes, preventing generation of hydroxyl radicals. 

Diazotization is a complex reaction (Scheme 1). When performed in acidic media with sodium nitrite, NOx or nitrosyl halides, its kinetics are dependent upon the acidity of the medium in media with a Hammett acidity constant (-H0) from — 1 to 3 the reaction rate increases with acidity and the formation of the nitroso cation is the rate-limiting step, in more acidic media (-H0 > 4) the reaction rate decreases when acidity increases and the deprotonation of intermediate 6 is the rate-limiting step.6-9... 

Kinetic studies on the reaction of [L(H20)Mo(OH)2Mo(H20)L]4+ with Cl- (0.11 M-1 s-1 at 25 °C) and CIO4 (a redox process) (2.0 x 10 3 M 1 s-1 at 21 °C) give rate constants independent of [H+] in the range 0.05-1.0 M. It is proposed that the CIO4 reaction is substitution controlled. This reaction proceeds Mo 1— anti-MoY (red-purple) — syn-Mo (yellow). No intermediates were identified. The reaction with N03 has also been studied (again strictly air-free), when quantitative formation of the red-purple fl fi -[L2Mo204]2+ complex and nitrite is observed (equation 16).67... 

Upon reaction with nitrous acid, indole produces a complex mixture of products. In addition to 3-oximino-3H -indole (16), which is the stable tautomeric form of 3-nitrosoindole (17), dimeric products of the type (18) and (19) are also formed. In contrast, (16) appears to be the sole product of the nitrosation of indole with amyl nitrite and sodium ethoxide (72HC(25-2)537). Studies of the nitrosation of pyrrole are somewhat indecisive. The mononitrosopyrrole, obtained from the reaction of pyrrole with nitrous acid, has not been fully characterized, but there is some evidence that nitrosation of pyrrole with amyl nitrite and sodium ethoxide leads to the sodium salt of the 3-nitroso derivative. However, upon the addition of acid, the product rearranges to give the oxime of 3-formylisoxazole (20) (B-77MI30502). 

Nitrite complexes of platinum can be formed, and complexes are known where the N02 ligand is N- or O-bonded. For platinum(II) the compounds are N-bonded, but for platinum(IV) complexes can be synthesized which are O- or N-bonded. Synthetic methods involve substitution reactions with nitrite ion or addition of NO to Pt02(PPh3)2 (equations 477 and... 

Complexes of stoichiometry ZnLX2 (X = N02 or N03) have been isolated from the reaction of zinc nitrite or nitrate with 1,2-dimorpholinoethane and 1,2-dipiperidinoethane.647 The complexes contain zinc in a distorted octahedron of two ligand nitrogens and two bidentate O-bonded nitrite or nitrate anions. The nitrite complexes show greater stability than the... 

The mechanism of the reaction of [Fe2(SR)2(CO)6] with nitric oxide does not seem to have been investigated. The corresponding reaction with nitrite in DMF proceeds (25) via the mononuclear complex [Fe(NO)2(SR)2] (see Section II,B,1), but it is not yet known how this complex is formed from [Fe2(SR)2(CO)6],... 

Butler, A.R., Glidewell, C. and Glidewell, S.M. (1992) Formation of the dinuclear iron-nitrosyl complex [Fe2(SMe)2(NO)4] by incorporation of SMe groups from methionine in reactions with iron(II) salts and nitrite. J. Chem. Soc. Chem. Commun., 141-142. 

The electrochemical transformation of a molybdenum nitrosyl complex [Mo(NO)(dttd)J [dttd = 1,2-bis(2-mercaptophenylthio)ethane] (30) is rather interesting (119). Ethylene is released from the backbone of the sulfur ligand upon electrochemical reduction. The resulting nitrosyl bis(dithiolene) complex reacts with O2 to give free nitrite and a Mo-oxo complex. Multielectron reduction of 30 in the presence of protons releases ethylene and the NO bond is cleaved, forming ammonia and a Mo-oxo complex (Scheme 15). The proposed reaction mechanism involves successive proton-coupled electron-transfer steps reminiscent of schemes proposed for Mo enzymes (120). 

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