Isotopes nitric oxides

TABLE V-8. Relative Vapor Pressures of Isotopic Nitric Oxides ... 

Table I. Isotopic Composition of Butenes Produced in Radiolysis of C2H4-C2D4 Nitric Oxide Mixtures...

Sigman et al. [134] have described a bacterial method for measuring the isotopic composition of seawater nitrate at the natural-abundance level. The method is based on the analysis of nitrous oxide gas (N2O) produced quantitatively from nitrate by denitrifying bacteria. The classical denitrification pathway consists of the stepwise reduction of nitrate (NOp to nitrite (N02), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) ... 

A very remote secondary H/D isotope effect has been measured for the 2 + 2-cycloaddition of TCNE to 2,7-dimethylocta-2,fran -4,6-triene. The reaction of nitric oxide with iV-benzylidene-4-methoxyaniline to produce 4-methoxybenzenediazonium nitrate and benzaldehyde is thought to proceed via a 2 + 2-cycloaddition between nitric oxide and the imine double bond. A novel mechanism for the stepwise dimerization of the parent silaethylene to 1,3-disilacyclobutane involves a low-barrier [1,2]-sigmatropic shift. Density functional, correlated ab initio calculations, and frontier MO analysis support a concerted 2 + 2-pathway for the addition of SO3 to alkenes. " The enone cycloaddition reactions of dienones and quinones have been reviewed. The 2 + 2-photocycloadditions of homochiral 2(5H)-furanones to vinylene carbonate are highly diastereoisomeric. ... 

New derivatives of 4-amino and 2,4-diaminopteridines have been synthesized and their capability to inhibit neuronal nitric oxide synthase evaluated <99JMC4108>. The synthesis of folic acid multiply labeled with stable isotopes, for bioavailability studies in human nutrition, has been reported <99JCS(P1)1311>, Synthesis and antiviral evaluation of several 6-(methylenecarbomethoxy)pteridine-4,7-diones have been described <99JHC435>. Synthesis and biochemical evaluation of bis(6,7-dimethyl-8-D-ribityllumazines) as potential bisubstrate analog inhibitors of riboflavin synthase have been reported <99JOC4635>. Synthesis and cyclization of novel lumazine-enediyne chimeras have been reported <99H13>. 

In summary, a considerable body of enzymatic, genetic, and analytical data supports the view that the major, if not sole, pathway of denitrification involves NO as an obligatory intermediate and requires the action of nitric oxide reductase. On the other hand, the ability of nitrite to modify nitrosyl transfer ratios and the N isotope fractionation factor during its reduction, are consistent with the reductive scheme of Averill and Tiedje (1982). It was suggested (Goretski... 

Firestone, M. K., Firestone, R. B., and Tiedje, ]. M. (1979). Nitric oxide as an intermediate in denitrification Evidence from nitrogen-13 isotope exchange. Biochem. Biophys. Res. Commun. 91, 10-16. 

Goretski, J., and Hollocher, T. C. (1990). Tire kinetic and isotopic competence of nitric oxide as an intermediate in denitrification. J. Biol. Chem. 265, 889-895. 

Ye, R. W., Toro-Suarez, 1., Tiedje, J. M., and Averill, B. A. (1991). H2 0 isotope exchange studies on the mechanism of reduction of nitric oxide and nitrite to nitrous oxide by denitrifying bacteria. J. Biol. Chem. 266, 12848-12851. 

Back and Mui17 studied the reaction with isotopically labeled nitric oxide to test the proposal that active nitrogen contained vibra-tionally excited molecules capable of dissociating nitric oxide. This reaction was proposed by Winkler and his co-workers133,435... 

Fe2(SR)2(CO)6], which are readily available from the reactions of R2S2 with [Fe3(CO)12] (33) and of RSH with [Fe2(CO)9] (34), can be nitrosylated in reactions which replace three carbonyl ligands by two nitrosyl ligands. Nitrosylation can be effected either by use of nitric oxide gas (27,29) or by use of sodium nitrite in aqueous ethanol (27) or, better, in dimethylformamide (DMF) (25). It is usually more convenient to employ nitric oxide if complexes of normal isotopic composition are required, but for 15N labeling the use of sodium nitrite in DMF is the more convenient and economical route. 

Other aspects of the report (42) on [Fe3S2(NO)5] are surprising. Elemental analysis of the ammonium salt was reported to distinguish between iron(II) and iron(III) in [Fe3S2(NO)5] , but to find these two types of iron present in equal numbers is most unusual for a triiron complex. Second, the molecular weight of the potassium salt was measured as 420 by mass spectrometry. This value is close to the M/Z of 421 calculated for the most abundant isotopic form of the ion-pair cation [KFe3S2(NO)5] +. Finally, the ESR spectrum reported is that of a dini-trosyliron species, which bears a remarkable resemblance to that reported (22) for a complex formed from Fe(II) and nitric oxide in aqueous alkaline solution. 

Figure 2. Changes in the isotopic composition of gas phase oxygen and declines of 0 isotope content of gaseous oxygen or nitric oxide as a function of illumination time for preoxidized Ti02 samples.

Wolthers, Kirsten R., Schimerlik, Michael I. (2002) Neuronal nitric oxide synthase substrate and solvent kinetic isotope effects on the steady-state kinetic parameters for the reduction of 2, 6-dichloroindophenol and cytochrome C3+, Biochemistry 41, 196-204. 

Studies on the photolysis of simple aliphatic and alicyclic nitrites have confirmed the need for a six-membered transition state, which decides the point of attack on a carbon chain [ 18]. The photolysis of a nitrite (9) gives an active alkoxy radical and a molecule of nitric oxide, which is itself a stable free radical. These radicals must at first be confined within a solvent cage (lo), for no significant scrambling of isotopic nitrogen occurred when a mixture of the nitrite (14) and... 

The nitric oxide results were originally interpreted in terms of the hypothesis that the reaction which is uninhibitable by nitric oxide is a molecular reaction. As was indicated earlier (p. 42), however, the isotopic mixing experiments of Rice and Varnerin render this idea untenable, and indicate the reaction to proceed almost entirely by a free-radical mechanism. 

Staveley and Hobbs and Hinshelwood studied the inhibition of the reaction by nitric oxide, and found under certain conditions that some 13 % was uninhibitable. Several investigations have shown that this residual reaction is not a molecular reaction. Stevenson et al studied the pyrolysis of propane containing radioactive carbon, and concluded that isotopic mixing took place at the same rate, relative to the pyrolysis rate, when the reaction was completely inhibited as when it was uninhibited Hinshelwood et al obtained a similar result. Poltorak and Voievodsky showed that when propane is pyrolyzed in the presence of D2, D atoms appear in the hydrocarbon fraction at a rate, relative to the rate of decomposition, that is independent of the amount of nitric oxide present. All of these results show that free radicals are still important in the reaction occurring in the presence of nitric oxide, and provide no support for the view that a molecular mechanism plays a significant role in the propane pyrolysis. Evidence reading to the same conclusion is provided by the experiments of Niclause et which show that in certain reaction vessels the propane pyrolysis is completely... 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

The fact that the rates of organic pyrolyses are affected by nitric oxide and other added substances has been referred to in Section 4. It was there noted that certain reactions maximally inhibited by nitric oxide cannot be molecular processes, since isotopic mixing still occurs. In this section the question of the mechanism of pyrolyses occurring in the presence of nitric oxide will be considered only very briefly, since at the present time (1969-70) the situation is by no means clear and some further investigations are under way. 

The spectroscopic constants were taken from Gillette and Eyster (5), who measured and analyzed the fundamental rotation-vibration band of nitric oxide using a grating spectrometer. The constants used in this calculation were adjusted to correspond to the naturally occurring isotopic mixture. 

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