- Lewis Acid Activation of the Ferrous Heme-NO Fragment toward the N-N Coupling Reaction with NO to Generate N2O
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Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to N2O. We show that BF3 coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate N2O. 15N-isotopic labeling reveals a reversible nitrosyl exchange reaction and follow-up N-O bond cleavage in the N2O formation step. Other Lewis acids (B(C6F5)3 and K+) also promote the NO coupling reaction with (OEP)Fe(NO). These results, complemented by DFT calculations, provide experimental support for the cis:b3 pathway in bacNOR.
- Abucayon, Erwin G.,Khade, Rahul L.,Powell, Douglas R.,Zhang, Yong,Richter-Addo, George B.
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- Nickel-mediated N-N bond formation and N2O liberationvianitrogen oxyanion reduction
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The syntheses of (DIM)Ni(NO3)2and (DIM)Ni(NO2)2, where DIM is a 1,4-diazadiene bidentate donor, are reported to enable testing of bis boryl reduced N-heterocycles for their ability to carry out stepwise deoxygenation of coordinated nitrate and nitrite, forming O(Bpin)2. Single deoxygenation of (DIM)Ni(NO2)2yields the tetrahedral complex (DIM)Ni(NO)(ONO), with a linear nitrosyl and κ1-ONO. Further deoxygenation of (DIM)Ni(NO)(ONO) results in the formation of dimeric [(DIM)Ni(NO)]2, where the dimer is linked through a Ni-Ni bond. The lost reduced nitrogen byproduct is shown to be N2O, indicating N-N bond formation in the course of the reaction. Isotopic labelling studies establish that the N-N bond of N2O is formed in a bimetallic Ni2intermediate and that the two nitrogen atoms of (DIM)Ni(NO)(ONO) become symmetry equivalent prior to N-N bond formation. The [(DIM)Ni(NO)]2dimer is susceptible to oxidation by AgX (X = NO3?, NO2?, and OTf?) as well as nitric oxide, the latter of which undergoes nitric oxide disproportionation to yield N2O and (DIM)Ni(NO)(ONO). We show that the first step in the deoxygenation of (DIM)Ni(NO)(ONO) to liberate N2O is outer sphere electron transfer, providing insight into the organic reductants employed for deoxygenation. Lastly, we show that at elevated temperatures, deoxygenation is accompanied by loss of DIM to form either pyrazine or bipyridine bridged polymers, with retention of a BpinO?bridging ligand.
- Beagan, Daniel M.,Cabelof, Alyssa C.,Carta, Veronica,Caulton, Kenneth G.,Gao, Xinfeng,Pink, Maren
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p. 10664 - 10672
(2021/08/20)
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- Nucleophilic addition reactions of the nitroprusside ion - The case of O-methylhydroxylamine
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The kinetics of the reaction between aqueous solutions of [Fe(CN) 5NO]2- and NH2OCH3 has been studied by means of UV/Vis spectroscopy and complementary solution techniques, FTIR/ATR spectroscopy, mass spectromet
- Gutierrez, Maria M.,Olabe, Jose A.,Amorebieta, Valentin T.
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p. 4433 - 4438
(2013/01/14)
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- Electrocatalytic Reductions of Nitrite, Nitric Oxide, and Nitrous Oxide by Thermophilic Cytochrome P450 CYP119 in Film-Modified Electrodes and an Analytical Comparison of Its Catalytic Activities with Myoglobin
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Previous investigations of nitrite and nitric oxide reduction by myoglobin in surfactant film modified electrodes characterized several distinct steps in the denitrification pathway, including isolation of a nitroxyl adduct similar to that proposed in the P450nor catalytic cycle. To investigate the effect of the axial ligand on these biomimetic reductions, we report here a comparison of the electrocatalytic activity of myoglobin (Mb) with a thermophilic cytochrome P450 CYP119. Electrocatalytic nitrite reduction by CYP119 is very similar to that by Mb: two catalytic waves at analogous potentials are observed, the first corresponding to the reduction of nitric oxide, the second to the production of ammonia. CYP119 is a much more selective catalyst, giving almost exclusively ammonia during the initial half-hour of reductive electrolysis of nitrite. More careful investigations of specific steps in the catalytic cycle show comparable rates of nitrite dehydration and almost identical potentials and lifetimes for ferrous nitroxyl intermediate (FeII-NO-) in CYP119 and Mb. The catalytic efficiency of nitric oxide reduction is reduced for CYP119 as compared to Mb, attributable to both a lower affinity of the protein for NO and a decreased rate of N-N coupling. Isotopic labeling studies show ammonia incorporation into nitrous oxide produced during nitrite reduction, as has been termed co-denitrification for certain bacterial and fungal nitrite reductases. Mb has a much higher co-denitrification activity than CYP119. Conversely, CYP119 is shown to be slightly more efficient at the two-electron reduction of N2O to N2. These results suggest that thiolate ligation does not significantly alter the catalytic reactivity, but the dramatic difference in product distribution may suggest an important role for protein stability in the selectivity of biocatalysts.
- Immoos, Chad E.,Chou, Ju,Bayachou, Mekki,Blair, Emek,Greaves, John,Farmer, Patrick J.
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p. 4934 - 4942
(2007/10/03)
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- Stabilization of ammonium dinitramide in the liquid phase
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The kinetics of accumulation of the main products of thermal decomposition of ammonium dinitramide in the melt was investigated. The isotope composition of nitrogen-containing gases evolved by the decomposition of 15NH4N(NO2/su
- Andreev,Anikin,Ivanov,Krylov,Pak
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p. 1974 - 1976
(2007/10/03)
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- Kinetic, isotopic, and 15N NMR study of N-hydroxybenzenesulfonamide decomposition: An HNO source reaction
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Decomposition of N-hydroxybenzenesulfonamide (C6H5SO2NHOH) in alkaline solution to yield N2O and sulfinate (C6H5SO2-) is first order in C6H5SO2NHO-, with rate constant = 2.44 (±0.23) × 10-4 s-1 at 25°C, ΔH? = 94.1 kJ mol-1, and ΔS? = 6.64 J K-1 mol-1. The reaction occurs via reversible release of HNO (and/or its conjugate NO-), followed by rapid dimerization of the intermediate to form N2O. It is shown by 15N tracer methods that this species and the NO- intermediate formed in trioxodinitrate decomposition are capable of codimerization, showing them to be in the same (singlet) electronic state. Protonation of C6H5SO2NHO- brings about a 15N NMR shift of -28.6 ppm. The free acid and its basic anion exhibit identical, large NOEF values (-4.16), showing that the dissociable hydrogen in C6H5SO2NHOH is bound to oxygen rather than to nitrogen, despite contrary literature reports.
- Bonner, Francis T.,Ko, Younghee
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p. 2514 - 2519
(2008/10/08)
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- Nitrogen-tracer Experiments on the Reaction of Hydrazine with an Excess of Nitrous Acid
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Mass-spectrometric analysis of the dinitrogen and dinitrogen monoxide evolved from the reaction between (1+) and excess of HNO2 are consistent with scrambling occurring between two nitrogens of hydrazine and one nitrogen of nitrous acid.A cyclic form of hydrazoic acid is postulated as a reaction intermediate, although other explanations are possible.At low acidities, pH 3.7, substantial yields of ammonia and N2O are formed.This would be expected to disturb the pattern of tracer distribution in the evolved gases, but in fact the isotopic results were virtually the same as at higher acidities.
- Phelan, Kieran G.,Stedman, Geoffrey
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p. 1603 - 1610
(2007/10/02)
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- Nitrogen Tracer Evidence for a Cyclic Azide Species
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Tracer experiments on the reaction of 15N-enriched hydrazine with excess of nitrous acid indicate a scrambling of tracer between the nitrogens of equimolar amounts of hydrazine and nitrous acid; a cyclic azide species is suggested as an intermediate.
- Phelan, Kieran G.,Stedman, Geoffrey
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p. 299 - 300
(2007/10/02)
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