1
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Wang H, Dekel DR, Abruña HD. Unraveling the Mechanism of Ammonia Electrooxidation by Coupled Differential Electrochemical Mass Spectrometry and Surface-Enhanced Infrared Absorption Spectroscopic Studies. J Am Chem Soc 2024. [PMID: 38820130 DOI: 10.1021/jacs.4c02621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2024]
Abstract
Ammonia electrooxidation has received considerable attention in recent times due to its potential application in direct ammonia fuel cells, ammonia sensors, and denitrification of wastewater. In this work, we used differential electrochemical mass spectrometry (DEMS) coupled with attenuated total reflection-surface-enhanced infrared absorption (ATR-SEIRA) spectroscopy to study adsorbed species and solution products during the electrochemical ammonia oxidation reaction (AOR) on Pt in alkaline media, and to correlate the product distribution with the surface ad-species. Hydrazine electrooxidation, hydroxylamine electrooxidation/reduction, and nitrite electroreduction on Pt have also been studied to enhance the understanding of the AOR mechanism. NH3, NH2, NH, NO, and NO2 ad-species were identified on the Pt surface with ATR-SEIRA spectroscopy, while N2, N2O, and NO were detected with DEMS as products of the AOR. N2 is formed through the coupling of two NH ad-species and then subsequent further dehydrogenation, while the dimerization of HNOad leads to the formation of N2O. The NH-NH coupling is the rate-determining step (rds) at high potentials, while the first dehydrogenation step is the rds at low potentials. These new spectroscopic results about the AOR and insights could advance the search and design of more effective AOR catalysts.
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Affiliation(s)
- Hongsen Wang
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
| | - Dario R Dekel
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
- The Wolfson Department of Chemical Engineering, Technion─Israel Institute of Technology, Haifa 3200003, Israel
- The Nancy & Stephen Grand Technion Energy Program (GTEP), Technion─Israel Institute of Technology, Haifa 3200003, Israel
| | - Héctor D Abruña
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States
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2
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Bollmeyer MM, Majer SH, Coleman RE, Lancaster KM. Outer coordination sphere influences on cofactor maturation and substrate oxidation by cytochrome P460. Chem Sci 2023; 14:8295-8304. [PMID: 37564409 PMCID: PMC10411619 DOI: 10.1039/d3sc02288a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 06/22/2023] [Indexed: 08/12/2023] Open
Abstract
Product selectivity of ammonia oxidation by ammonia-oxidizing bacteria (AOB) is tightly controlled by metalloenzymes. Hydroxylamine oxidoreductase (HAO) is responsible for the oxidation of hydroxylamine (NH2OH) to nitric oxide (NO). The non-metabolic enzyme cytochrome (cyt) P460 also oxidizes NH2OH, but instead produces nitrous oxide (N2O). While both enzymes use a heme P460 cofactor, they selectively oxidize NH2OH to different products. Previously reported structures of Nitrosomonas sp. AL212 cyt P460 show that a capping phenylalanine residue rotates upon ligand binding, suggesting that this Phe may influence substrate and/or product binding. Here, we show via substitutions of the capping Phe in Nitrosomonas europaea cyt P460 that the bulky phenyl side-chain promotes the heme-lysine cross-link forming reaction operative in maturing the cofactor. Additionally, the Phe side-chain plays an important role in modulating product selectivity between N2O and NO during NH2OH oxidation under aerobic conditions. A picture emerges where the sterics and electrostatics of the side-chain in this capping position control the kinetics of N2O formation and NO binding affinity. This demonstrates how the outer coordination sphere of cyt P460 is tuned not only for selective NH2OH oxidation, but also for the autocatalytic cross-link forming reaction that imbues activity to an otherwise inactive protein.
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Affiliation(s)
- Melissa M Bollmeyer
- Baker Laboratory Department of Chemistry and Chemical Biology Cornell University 162 Sciences Drive Ithaca NY 14853 USA
| | - Sean H Majer
- Baker Laboratory Department of Chemistry and Chemical Biology Cornell University 162 Sciences Drive Ithaca NY 14853 USA
| | - Rachael E Coleman
- Baker Laboratory Department of Chemistry and Chemical Biology Cornell University 162 Sciences Drive Ithaca NY 14853 USA
| | - Kyle M Lancaster
- Baker Laboratory Department of Chemistry and Chemical Biology Cornell University 162 Sciences Drive Ithaca NY 14853 USA
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3
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Braley SE, Kwon HY, Xu S, Dalton EZ, Jakubikova E, Smith JM. Buffer Assists Electrocatalytic Nitrite Reduction by a Cobalt Macrocycle Complex. Inorg Chem 2022; 61:12998-13006. [PMID: 35948065 DOI: 10.1021/acs.inorgchem.2c00909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This work reports a combined experimental and computational study of the activation of an otherwise catalytically inactive cobalt complex, [Co(TIM)Br2]+, for aqueous nitrite reduction. The presence of phosphate buffer leads to efficient electrocatalysis, with rapid reduction to ammonium occurring close to the thermodynamic potential and with high Faradaic efficiency. At neutral pH, increasing buffer concentrations increase catalytic current while simultaneously decreasing overpotential, although high concentrations have an inhibitory effect. Controlled potential electrolysis and rotating ring-disk electrode experiments indicate that ammonium is directly produced from nitrite by [Co(TIM)Br2]+, along with hydroxylamine. Mechanistic investigations implicate a vital role for the phosphate buffer, specifically as a proton shuttle, although high buffer concentrations inhibit catalysis. These results indicate a role for buffer in the design of electrocatalysts for nitrogen oxide conversion.
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Affiliation(s)
- Sarah E Braley
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47401, United States
| | - Hyuk-Yong Kwon
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Song Xu
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47401, United States
| | - Evan Z Dalton
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47401, United States
| | - Elena Jakubikova
- Department of Chemistry, North Carolina State University, 2620 Yarbrough Drive, Raleigh, North Carolina 27695, United States
| | - Jeremy M Smith
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47401, United States
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4
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Stroka JR, Kandemir B, Matson EM, Bren KL. Electrocatalytic Multielectron Nitrite Reduction in Water by an Iron Complex. ACS Catal 2020. [DOI: 10.1021/acscatal.0c03600] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Jesse R. Stroka
- Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, United States
| | - Banu Kandemir
- Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, United States
| | - Ellen M. Matson
- Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, United States
| | - Kara L. Bren
- Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, United States
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5
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Brown BN, Robinson KJ, Durfee QC, Kekilli D, Hough MA, Andrew CR. Hydroxylamine Complexes of Cytochrome c': Influence of Heme Iron Redox State on Kinetic and Spectroscopic Properties. Inorg Chem 2020; 59:14162-14170. [PMID: 32970420 DOI: 10.1021/acs.inorgchem.0c01925] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hydroxylamine (NH2OH or HA) is a redox-active nitrogen oxide that occurs as a toxic intermediate in the oxidation of ammonium by nitrifying and methanotrophic bacteria. Within ammonium containing environments, HA is generated by ammonia monooxygenase (nitrifiers) or methane monooxygenase (methanotrophs). Subsequent oxidation of HA is catalyzed by heme proteins, including cytochromes P460 and multiheme hydroxylamine oxidoreductases, the former contributing to emissions of N2O, an ozone-depleting greenhouse gas. A heme-HA complex is also a proposed intermediate in the reduction of nitrite to ammonia by cytochrome c nitrite reductase. Despite the importance of heme-HA complexes within the biogeochemical nitrogen cycle, fundamental aspects of their coordination chemistry remain unknown, including the effect of the Fe redox state on heme-HA affinity, kinetics, and spectroscopy. Using stopped-flow UV-vis and resonance Raman spectroscopy, we investigated HA complexes of the L16G distal pocket variant of Alcaligenes xylosoxidans cytochrome c'-α (L16G AxCP-α), a pentacoordinate c-type cytochrome that we show binds HA in its Fe(III) (Kd ∼ 2.5 mM) and Fe(II) (Kd = 0.0345 mM) states. The ∼70-fold higher HA affinity of the Fe(II) state is due mostly to its lower koff value (0.0994 s-1 vs 11 s-1), whereas kon values for Fe(II) (2880 M-1 s-1) and Fe(III) (4300 M-1 s-1) redox states are relatively similar. A comparison of the HA and imidazole affinities of L16G AxCP-α was also used to predict the influence of Fe redox state on HA binding to other proteins. Although HA complexes of L16G AxCP-α decompose via redox reactions, the lifetime of the Fe(II)HA complex was prolonged in the presence of excess reductant. Spectroscopic parameters determined for the Fe(II)HA complex include the N-O stretching vibration of the NH2OH ligand, ν(N-O) = 906 cm-1. Overall, the kinetic trends and spectroscopic benchmarks from this study provide a foundation for future investigations of heme-HA reaction mechanisms.
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Affiliation(s)
- Brianna N Brown
- Department of Chemistry and Biochemistry, Eastern Oregon University, La Grande, Oregon 97850, United States
| | - Kelsey J Robinson
- Department of Chemistry and Biochemistry, Eastern Oregon University, La Grande, Oregon 97850, United States
| | - Quentin C Durfee
- Department of Chemistry and Biochemistry, Eastern Oregon University, La Grande, Oregon 97850, United States
| | - Demet Kekilli
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, United Kingdom
| | - Michael A Hough
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ, United Kingdom
| | - Colin R Andrew
- Department of Chemistry and Biochemistry, Eastern Oregon University, La Grande, Oregon 97850, United States
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6
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Kiernicki JJ, Norwine EE, Zeller M, Szymczak NK. Tetrahedral iron featuring an appended Lewis acid: distinct pathways for the reduction of hydroxylamine and hydrazine. Chem Commun (Camb) 2019; 55:11896-11899. [PMID: 31528878 DOI: 10.1039/c9cc05720j] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We present the preparation of a nitrogen-based bidentate ligand featuring an appended boron Lewis acid as well as its tetrahedral Fe2+ and Zn2+ complexes. These complexes act as platforms for hydrazine and hydroxylamine capture and reduction chemistry.
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Affiliation(s)
- John J Kiernicki
- University of Michigan, 930 N. University, Ann Arbor, MI 48109, USA.
| | - Emily E Norwine
- University of Michigan, 930 N. University, Ann Arbor, MI 48109, USA.
| | - Matthias Zeller
- H. C. Brown Laboratory, Purdue University, 560 Oval Dr, West Lafayette, IN 47907, USA
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7
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Smith MA, Majer SH, Vilbert AC, Lancaster KM. Controlling a burn: outer-sphere gating of hydroxylamine oxidation by a distal base in cytochrome P460. Chem Sci 2019; 10:3756-3764. [PMID: 31015919 PMCID: PMC6457333 DOI: 10.1039/c9sc00195f] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2019] [Accepted: 02/14/2019] [Indexed: 01/19/2023] Open
Abstract
One amino acid makes the difference between a metalloenzyme and a metalloprotein in two otherwise effectively identical cytochrome P460s.
Ammonia oxidizing bacteria (AOB) use the cytotoxic, energetic molecule hydroxylamine (NH2OH) as a source of reducing equivalents for cellular respiration. Despite disproportionation or violent decomposition being typical outcomes of reactions of NH2OH with iron, AOB and anammox heme P460 proteins including cytochrome (cyt) P460 and hydroxylamine oxidoreductase (HAO) effect controlled, stepwise oxidation of NH2OH to nitric oxide (NO). Curiously, a recently characterized cyt P460 variant from the AOB Nitrosomonas sp. AL212 is able to form all intermediates of cyt P460 catalysis, but is nevertheless incompetent for NH2OH oxidation. We now show via site-directed mutagenesis, activity assays, spectroscopy, and structural biology that this lack of activity is attributable to the absence of a critical basic glutamate residue in the distal pocket above the heme P460 cofactor. This substitution is the only distinguishing characteristic of a protein that is otherwise effectively structurally and spectroscopically identical to an active variant. This highlights and reinforces a fundamental principal of metalloenzymology: metallocofactor inner-sphere geometric and electronic structures are in many cases insufficient for imbuing reactivity; a precisely defined outer coordination sphere contributed by the polypeptide matrix can be the key differentiator between a metalloenzyme and an unreactive metalloprotein.
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Affiliation(s)
- Meghan A Smith
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
| | - Sean H Majer
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
| | - Avery C Vilbert
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
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8
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McQuarters AB, Blaesi EJ, Kampf JW, Alp EE, Zhao J, Hu M, Krebs C, Lehnert N. Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase. Inorg Chem 2019; 58:1398-1413. [PMID: 30623648 DOI: 10.1021/acs.inorgchem.8b02947] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Fungal denitrification plays a crucial role in the nitrogen cycle and contributes to the total N2O emission from agricultural soils. Here, cytochrome P450 NO reductase (P450nor) reduces two NO to N2O using a single heme site. Despite much research, the exact nature of the critical "Intermediate I" responsible for the key N-N coupling step in P450nor is unknown. This species likely corresponds to a Fe-NHOH-type intermediate with an unknown electronic structure. Here we report a new strategy to generate a model system for this intermediate, starting from the iron(III) methylhydroxylamide complex [Fe(3,5-Me-BAFP)(NHOMe)] (1), which was fully characterized by 1H NMR, UV-vis, electron paramagnetic resonance, and vibrational spectroscopy (rRaman and NRVS). Our data show that 1 is a high-spin ferric complex with an N-bound hydroxylamide ligand that is strongly coordinated (Fe-N distance, 1.918 Å; Fe-NHOMe stretch, 558 cm-1). Simple one-electron oxidation of 1 at -80 °C then cleanly generates the first model system for Intermediate I, [Fe(3,5-Me-BAFP)(NHOMe)]+ (1+). UV-vis, resonance Raman, and Mössbauer spectroscopies, in comparison to the chloro analogue [Fe(3,5-Me-BAFP)(Cl)]+, demonstrate that 1+ is best described as an FeIII-(NHOMe)• complex with a bound NHOMe radical. Further reactivity studies show that 1+ is highly reactive toward NO, a reaction that likely proceeds via N-N bond formation, following a radical-radical-type coupling mechanism. Our results therefore provide experimental evidence, for the first time, that an FeIII-(NHOMe)• electronic structure is indeed a reasonable electronic description for Intermediate I and that this electronic structure is advantageous for P450nor catalysis because it can greatly facilitate N-N bond formation and, ultimately, N2O generation.
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Affiliation(s)
- Ashley B McQuarters
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Elizabeth J Blaesi
- Department of Chemistry and Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Jeff W Kampf
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - E Ercan Alp
- Advanced Photon Source (APS) , Argonne National Laboratory (ANL) , Argonne , Illinois 60439 , United States
| | - Jiyong Zhao
- Advanced Photon Source (APS) , Argonne National Laboratory (ANL) , Argonne , Illinois 60439 , United States
| | - Michael Hu
- Advanced Photon Source (APS) , Argonne National Laboratory (ANL) , Argonne , Illinois 60439 , United States
| | - Carsten Krebs
- Department of Chemistry and Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
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9
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Rahman MH, Ryan MD. Insight into Solvent Coordination of an Iron Porphyrin Hydroxylamine Complex from Spectroscopy and DFT Calculations. Eur J Inorg Chem 2018. [DOI: 10.1002/ejic.201800040] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Md. Hafizur Rahman
- Chemistry Department Marquette University PO Box 1881 53201 Milwaukee WI USA
| | - Michael D. Ryan
- Chemistry Department Marquette University PO Box 1881 53201 Milwaukee WI USA
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10
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Kannan B, Kumsa D, Jebaraj AJ, Méndez-Albores A, Georgescu NS, Scherson D. The electrocatalytic properties of adsorbed hemin and its nitrosyl adduct on glassy carbon surfaces toward hydroxylamine in aqueous neutral electrolytes. J Electroanal Chem (Lausanne) 2017. [DOI: 10.1016/j.jelechem.2017.02.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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11
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Malko D, Kucernak A, Lopes T. Performance of Fe–N/C Oxygen Reduction Electrocatalysts toward NO2–, NO, and NH2OH Electroreduction: From Fundamental Insights into the Active Center to a New Method for Environmental Nitrite Destruction. J Am Chem Soc 2016; 138:16056-16068. [DOI: 10.1021/jacs.6b09622] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Daniel Malko
- Department
of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| | - Anthony Kucernak
- Department
of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| | - Thiago Lopes
- Fuel
Cells and Hydrogen Center, Nuclear and Energy Research Institute, IPEN-CNEN/SP, Sao Paulo-SP 05508-000, Brazil
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12
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Subedi H, Brasch NE. Mechanistic studies of the reactions of the reduced vitamin B12 derivatives with the HNO donor Piloty's acid: further evidence for oxidation of cob(I)alamin by (H)NO. Dalton Trans 2016; 45:352-60. [PMID: 26618754 DOI: 10.1039/c5dt03459k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
There is accumulating evidence for the existence of HNO in biological systems. Compared with NO (˙NO), much less is known about the chemical and biochemical reactivity of HNO. Kinetic and mechanistic studies have been carried out on the reaction between the vitamin B12-derived radical complex cob(II)alamin (Cbl(II)˙, Cbl(II)) with the widely used HNO donor Piloty's acid (PA). A stoichiometry of 1 : 2 Cbl(II) : PA was obtained and PA decomposition to HNO and benzenesulfinate (C6H5SO2(-)) is the rate-determining step. No evidence was found for nitrite (Griess assay), ammonia (Nessler's test) or NH2OH (indooxine test) in the product solution, and it is likely that HNO is instead reduced to N2. A mechanism is proposed in which reduction of Cbl(II) by (H)NO results in formation of cob(I)alamin (Cbl(I)(-)) and ˙NO. The Cbl(I)(-) intermediate is subsequently oxidized back to Cbl(II) by a second (H)NO molecule, and Cbl(II) reacts rapidly with ˙NO to form nitroxylcobalamin (NOCbl). Separate studies on the reaction between Cbl(I)(-) and PA shows that this system involves an additional step in which Cbl(I)(-) is first oxidized by (H)NO to Cbl(II), which reacts further with (H)NO to form NOCbl, with an overall stoichiometry of 1 : 3 Cbl(I)(-) : PA. Experiments in the presence of nitrite for both systems support the involvement of a Cbl(I)(-) intermediate in the Cbl(II)/PA reaction. These systems provide the second example of oxidation of cob(I)alamin by (H)NO.
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Affiliation(s)
- Harishchandra Subedi
- Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, USA and Division of Science, Mathematics, and Physical Education, Western Nebraska Community College, Scottsbluff, Nebraska 69361, USA
| | - Nicola E Brasch
- School of Applied Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand.
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13
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Subedi H, Brasch NE. Studies on the Reaction of Reduced Vitamin B12Derivatives with the Nitrosyl Hydride (HNO) Donor Angeli's Salt: HNO Oxidizes the Transition-Metal Center of Cob(I)alamin. Eur J Inorg Chem 2015. [DOI: 10.1002/ejic.201500442] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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14
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Youngblut M, Pauly DJ, Stein N, Walters D, Conrad JA, Moran GR, Bennett B, Pacheco AA. Shewanella oneidensis cytochrome c nitrite reductase (ccNiR) does not disproportionate hydroxylamine to ammonia and nitrite, despite a strongly favorable driving force. Biochemistry 2014; 53:2136-44. [PMID: 24645742 DOI: 10.1021/bi401705d] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cytochrome c nitrite reductase (ccNiR) from Shewanella oneidensis, which catalyzes the six-electron reduction of nitrite to ammonia in vivo, was shown to oxidize hydroxylamine in the presence of large quantities of this substrate, yielding nitrite as the sole free nitrogenous product. UV-visible stopped-flow and rapid-freeze-quench electron paramagnetic resonance data, along with product analysis, showed that the equilibrium between hydroxylamine and nitrite is fairly rapidly established in the presence of high initial concentrations of hydroxylamine, despite said equilibrium lying far to the left. By contrast, reduction of hydroxylamine to ammonia did not occur, even though disproportionation of hydroxylamine to yield both nitrite and ammonia is strongly thermodynamically favored. This suggests a kinetic barrier to the ccNiR-catalyzed reduction of hydroxylamine to ammonia. A mechanism for hydroxylamine reduction is proposed in which the hydroxide group is first protonated and released as water, leaving what is formally an NH2(+) moiety bound at the heme active site. This species could be a metastable intermediate or a transition state but in either case would exist only if it were stabilized by the donation of electrons from the ccNiR heme pool into the empty nitrogen p orbital. In this scenario, ccNiR does not catalyze disproportionation because the electron-donating hydroxylamine does not poise the enzyme at a sufficiently low potential to stabilize the putative dehydrated hydroxylamine; presumably, a stronger reductant is required for this.
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Affiliation(s)
- Matthew Youngblut
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin 53211, United States
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15
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Porter TR, Mayer JM. Radical Reactivity of the Fe(III)/(II) Tetramesitylporphyrin Couple: Hydrogen Atom Transfer, Oxyl Radical Dissociation, and Catalytic Disproportionation of a Hydroxylamine. Chem Sci 2014; 5:372-380. [PMID: 24729854 PMCID: PMC3981745 DOI: 10.1039/c3sc52055b] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The chemistry of low-valent iron porphyrin complexes with oxyl radical reagents has been explored. (Meso-tetramesityl porphyrinato) iron(III) hydroxide, (TMP)FeIII(OH) reacts with the hydroxylamine TEMPO-H (1-hydroxy-2,2,6,6-tetramethylpiperdine) to yield the ferrous porphyrin, (TMP)FeII, together with H2O and TEMPO. This reaction has a second order rate constant k1 = 76 ± 5 M-1 1 s-1 and likely occurs by concerted e-/H+ transfer. Hydrazines PhNHNHPh and PhNHNH2 similarly yield (TMP)FeII. A subsequent reaction between TEMPO (2,2,6,6-tetramethylpiperdinyl radical) and (TMP)FeII is observed to reversibly form the TEMPO-ligated ferric porphyrin, (TMP)FeIII(TEMPO). A combination of 1H NMR and optical spectroscopies were used to determine the thermodynamic parameters for TEMPO binding: K4 (25°C) = 535 ± 20 M-1, ΔH°4 = -7.0 ± 1.5 kcal mol-1, ΔS°4= -11 ± 5 cal mol-1 K-1, ΔG‡4(235K) = 21.3 ± 0.5 kcal mol-1, ΔG‡-4(235K) = 16.9 ± 0.5 kcal mol-1. The Fe-O bond is remarkably weak. The stable phenoxyl radical 2,4,6- t Bu3C6H2O• (ArO•) forms a stronger bond to (TMP)FeII to irreversibly make a similar FeIII(OR) complex. Both (TMP)FeII and (TMP)FeIII(OH) are catalysts for the disproportionation of excess TEMPO-H to TEMPO and TEMP-H (2,2,6,6-tetramethylpiperdine). The lack of reactivity between (TMP)FeII and the alkylated TEMPO-H analogue, TEMPO-CH3, suggests that the disproportionation involves a hydrogen atom transfer step. These results highlight the importance and versatility of the heme FeIII/II couple that is often overshadowed by its higher-valent counterparts.
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Affiliation(s)
| | - James M. Mayer
- Department of Chemistry, University of Washington, Seattle, WA
98195-1700
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16
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McQuarters AB, Goodrich LE, Goodrich CM, Lehnert N. Disproportionation of O-Benzylhydroxylamine Catalyzed by a Ferric Bis-Picket Fence Porphyrin Complex. Z Anorg Allg Chem 2013. [DOI: 10.1002/zaac.201300125] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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17
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Plymale NT, Dassanayake RS, Hassanin HA, Brasch NE. Kinetic and Mechanistic Studies on the Reactions of the Reduced Vitamin B12 Complex Cob(I)alamin with Nitrite and Nitrate. Eur J Inorg Chem 2011. [DOI: 10.1002/ejic.201100992] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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18
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Doctorovich F, Bikiel D, Pellegrino J, Suárez SA, Larsen A, Martí MA. Nitroxyl (azanone) trapping by metalloporphyrins. Coord Chem Rev 2011. [DOI: 10.1016/j.ccr.2011.04.012] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Gutiérrez MM, Olabe JA, Amorebieta VT. Disproportionation of O-methylhydroxylamine catalyzed by aquapentacyanoferrate(II). Inorg Chem 2011; 50:8817-25. [PMID: 21859073 DOI: 10.1021/ic2007155] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The aquapentacyanoferrate(II) ion, [Fe(II)(CN)(5)H(2)O](3-), catalyzes the disproportionation reaction of O-methylhydroxylamine, NH(2)OCH(3), with stoichiometry 3NH(2)OCH(3) → NH(3) + N(2) + 3CH(3)OH. Kinetic and spectroscopic evidence support an initial N coordination of NH(2)OCH(3) to [Fe(II)(CN)(5)H(2)O](3-) followed by a homolytic scission leading to radicals [Fe(II)(CN)(5)(•)NH(2)](3-) (a precursor of Fe(III) centers and bound NH(3)) and free methoxyl, CH(3)O(•), thus establishing a radical path leading to N-methoxyamino ((•)NHOCH(3)) and 1,2-dimethoxyhydrazine, (NHOCH(3))(2). The latter species is moderately stable and proposed to be the precursor of N(2) and most of the generated CH(3)OH. Intermediate [Fe(III)(CN)(5)L](2-) complexes (L = NH(3), H(2)O) form dinuclear cyano-bridged mixed-valent species, affording a catalytic substitution of the L ligands promoted by [Fe(II)(CN)(5)L](3-). Free or bound NH(2)OCH(3) may act as reductants of [Fe(III)(CN)(5)L](2-), thus regenerating active sites. At increasing concentrations of NH(2)OCH(3) a coordinated diazene species emerges, [Fe(II)(CN)(5)N(2)H(2)](3-), which is consumed by the oxidizing CH(3)O(•), giving N(2) and CH(3)OH. Another side reaction forms [Fe(II)(CN)(5)N(O)CH(3)](3-), an intermediate containing the nitrosomethane ligand, which is further oxidized to the nitroprusside ion, [Fe(II)(CN)(5)NO](2-). The latter is a final oxidation product with a significant conversion of the initial [Fe(II)(CN)(5)H(2)O](3-) complex. The side reaction partially blocks the Fe(II)-aqua active site, though complete inhibition is not achieved because the radical path evolves faster than the formation rates of the Fe(II)-NO(+) bonds.
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Affiliation(s)
- María M Gutiérrez
- Department of Chemistry, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes y Roca, Mar del Plata B7602AYL, Argentina
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