1
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Ucur B, Shiels OJ, Blanksby SJ, Trevitt AJ. Observation of Solvent-Dependence in the Mechanism of Neutral-Catalyzed Isomerization of para-Aminobenzoic Acid Protomers. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:1128-1137. [PMID: 38523556 DOI: 10.1021/jasms.3c00433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/26/2024]
Abstract
Proton-transfer reactions are commonplace during electrospray ionization (ESI) mass spectrometry experiments and are often responsible for imparting charge to analyte molecules. Multiple protonation-site isomers (protomers) can arise for polyfunctional molecules and these isomers can interconvert via solvent-mediated proton transfer reactions during various stages of the ESI process. Studying the populations and interconversion of protonation isomers provides key insight into the ESI process, ion-molecule interactions, and ion dissociation mechanisms. An archetype molecule to study protomer interconversion fundamentals in this context is para-aminobenzoic acid (pABA), where both the amino and carboxylic acid protomers are typically formed under ESI and the mechanisms for interconversion are still under refinement. Using ion-trap mass spectrometry reaction kinetics (2.5 mTorr, 300 K), this study examines gas-phase interconversion catalysis of pABA protomers by seven neutral species, which are commen solvents and additives used for ESI: water, formic acid, methanol, ethanol, propanol, ammonia, and acetonitrile. Three distinct reaction cases are reported: (i) formic acid, methanol, ethanol, propanol, and ammonia each catalyze the interconversion between the amino and carboxylic acid protomers via a n = 1 solvent-molecule vehicle mechanism; (ii) for water, however, a n = 6 adduct complex is detected and this suggests that the observed protomer interconversion occurs through a Grotthuss mechanism, in accord with literature reports; (iii) acetonitrile inhibits proton transfer by the formation of particularly stable n = 1 and 2 adduct complexes. The second-order rate constants for the protomer interconversion are observed to increase in the following order: H2O < HCO2H < MeOH < EtOH < PrOH < NH3. Potential energy schemes are reported for all neutral-catalyzed proton transfer reactions using the DSD-PBEP86-D3(BJ)/aug-cc-pVDZ level of theory. A central transition state, which connects the protonation site adducts, is shown to be the key rate-limiting step. The energy of this transition state is sensitive to the proton affinity of the neutral solvent, and this is supported by the correlation between the reaction rate and the solvent proton affinity.
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Affiliation(s)
- Boris Ucur
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Oisin J Shiels
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Stephen J Blanksby
- Central Analytical Research Facility and the School of Chemistry and Physics, Queensland University of Technology, Brisbane 4001, Australia
| | - Adam J Trevitt
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
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2
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Ruan XY, Wu DX, Li WA, Lin Z, Sayed M, Han ZY, Gong LZ. Photoinduced Pd-Catalyzed Enantioselective Carboamination of Dienes via Aliphatic C-H Bond Elaboration. J Am Chem Soc 2024; 146:12053-12062. [PMID: 38622809 DOI: 10.1021/jacs.4c01690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2024]
Abstract
Three-component diene carboaminations offer a potent means to access synthetically valuable allylic amines with rapid molecular complexity escalation. The existing literature primarily discloses racemic examples, necessitating the use of halides/pseudohalides as substrates. This paper introduces a photoinduced Pd-catalyzed enantioselective three-component carboamination of aryl-substituted 1,3-dienes, leveraging aliphatic C-H bonds for rapid synthesis. The reaction employs 10 mol % of chiral palladium catalyst and an excess aryl bromide as the HAT reagent. This approach yields diverse chiral allylamines with moderate to excellent enantioselectivities. Notably, it stands as the first instance of an asymmetric three-component diene carboamination reaction, directly utilizing abundant C(sp3)-H bearing partners, such as toluene-type substrates, ethers, amines, esters, and ketones. The protocol exhibits versatility across amines, encompassing aliphatic, aromatic, primary, and secondary derivatives. This method could serve as a versatile platform for stereoselective incorporation of various nucleophiles, dienes, and C(sp3)-H bearing partners.
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Affiliation(s)
- Xiao-Yun Ruan
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Dan-Xing Wu
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Wen-Ao Li
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Zihan Lin
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Mostafa Sayed
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Zhi-Yong Han
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Liu-Zhu Gong
- Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
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3
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Tang K, Brown MR, Risko C, Gish MK, Rumbles G, Pham PH, Luca OR, Barlow S, Marder SR. Beyond n-dopants for organic semiconductors: use of bibenzo[ d]imidazoles in UV-promoted dehalogenation reactions of organic halides. Beilstein J Org Chem 2023; 19:1912-1922. [PMID: 38116245 PMCID: PMC10729154 DOI: 10.3762/bjoc.19.142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Accepted: 11/28/2023] [Indexed: 12/21/2023] Open
Abstract
2,2'-Bis(4-dimethylaminophenyl)- and 2,2'-dicyclohexyl-1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazole ((N-DMBI)2 and (Cyc-DMBI)2) are quite strong reductants with effective potentials of ca. -2 V vs ferrocenium/ferrocene, yet are relatively stable to air due to the coupling of redox and bond-breaking processes. Here, we examine their use in accomplishing electron transfer-induced bond-cleavage reactions, specifically dehalogenations. The dimers reduce halides that have reduction potentials less cathodic than ca. -2 V vs ferrocenium/ferrocene, especially under UV photoexcitation (using a 365 nm LED). In the case of benzyl halides, the products are bibenzyl derivatives, whereas aryl halides are reduced to the corresponding arenes. The potentials of the halides that can be reduced in this way, quantum-chemical calculations, and steady-state and transient absorption spectroscopy suggest that UV irradiation accelerates the reactions via cleavage of the dimers to the corresponding radical monomers.
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Affiliation(s)
- Kan Tang
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Megan R Brown
- Department of Chemistry & Center for Applied Energy Research (CAER), University of Kentucky, Lexington, Kentucky, 40506, United States
| | - Chad Risko
- Department of Chemistry & Center for Applied Energy Research (CAER), University of Kentucky, Lexington, Kentucky, 40506, United States
| | - Melissa K Gish
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
| | - Garry Rumbles
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States,
| | - Phuc H Pham
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Oana R Luca
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Stephen Barlow
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
| | - Seth R Marder
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States,
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
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Uchikura T, Tsubono K, Hara Y, Akiyama T. Dual-Role Halogen-Bonding-Assisted EDA-SET/HAT Photoreaction System with Phenol Catalyst and Aryl Iodide: Visible-Light-Driven Carbon–Carbon Bond Formation. J Org Chem 2022; 87:15499-15510. [DOI: 10.1021/acs.joc.2c02032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Tatsuhiro Uchikura
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1, Mejiro,
Toshima-ku, Tokyo 171-8588, Japan
| | - Kazushi Tsubono
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1, Mejiro,
Toshima-ku, Tokyo 171-8588, Japan
| | - Yurina Hara
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1, Mejiro,
Toshima-ku, Tokyo 171-8588, Japan
| | - Takahiko Akiyama
- Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1, Mejiro,
Toshima-ku, Tokyo 171-8588, Japan
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5
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Wang J, Ye Y, Sang T, Zhou C, Bao X, Yuan Y, Huo C. C(sp 3)-H/C(sp 3)-H Dehydrogenative Radical Coupling of Glycine Derivatives. Org Lett 2022; 24:7577-7582. [PMID: 36214657 DOI: 10.1021/acs.orglett.2c02951] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Here we report a general C(sp3)-H/C(sp3)-H dehydrogenative coupling strategy for the preparation of various natural or unnatural amino acids from readily available glycine derivatives and hydrocarbons through a combination of SET and HAT process.
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Affiliation(s)
- Jiayuan Wang
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
| | - Youwan Ye
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
| | - Tongzhi Sang
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
| | - Chenxing Zhou
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
| | - Xiazhen Bao
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
| | - Yong Yuan
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
| | - Congde Huo
- Gansu International Scientific and Technological Cooperation Base of Water-Retention Chemical Functional Materials, Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China
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6
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Zhao ZW, Ran YS, Hou YJ, Chen X, Ding XL, Zhang C, Li YM. Free Radical Cascade Carbochloromethylations of Activated Alkenes. J Org Chem 2022; 87:4183-4194. [PMID: 35234480 DOI: 10.1021/acs.joc.1c03024] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Free radical carbochloromethylations of ortho-cyanoarylacrylamides and N-(arylsulfonyl)acrylamides have been developed by employing simple alkyl chlorides as the chloromethyl source. The transformations are characterized by wide functional group compatibility and utilizing readily available reagents, thus providing efficient methods for constructing polychloromethyl-substituted quinoline-2,4-diones and α-aryl-β-polychloromethylated amides.
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Affiliation(s)
- Zhi-Wei Zhao
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
| | - Yu-Song Ran
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
| | - Yu-Jian Hou
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
| | - Xin Chen
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
| | - Xue-Ling Ding
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
| | - Cui Zhang
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
| | - Ya-Min Li
- Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P. R. China
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7
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Nolte TM, Hendriks AJ, Novák LA, Peijnenburg WJGM. A universal free energy relationship for both hard and soft radical addition in water. J PHYS ORG CHEM 2022. [DOI: 10.1002/poc.4317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Tom M. Nolte
- Department of Environmental Science, Institute for Water and Wetland Research Radboud University Nijmegen Nijmegen The Netherlands
| | - A. Jan Hendriks
- Department of Environmental Science, Institute for Water and Wetland Research Radboud University Nijmegen Nijmegen The Netherlands
| | - Laurie A. Novák
- Department of Environmental Science, Institute for Water and Wetland Research Radboud University Nijmegen Nijmegen The Netherlands
| | - Willie J. G. M. Peijnenburg
- Department of Environmental Science, Institute for Water and Wetland Research National Institute of Public Health and the Environment Bilthoven The Netherlands
- Institute of Environmental Sciences (CML) Leiden University Leiden The Netherlands
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8
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Shiels OJ, Turner JA, Kelly PD, Blanksby S, da Silva G, Trevitt A. Modelling Reaction Kinetics of Distonic Radical Ions: A Systematic Investigation of Phenyl-type Radical Addition to Unsaturated Hydrocarbons. Faraday Discuss 2022; 238:475-490. [DOI: 10.1039/d2fd00045h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Gas phase ion−molecule reactions are central to chemical processes across many environments. A feature of many of these reactions is an inverse relationship between temperature and reaction rate arising from...
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9
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Ding D, Feng E, Kotha RR, Chapman NC, Jiang H, Nash JJ, Kenttämaa HI. Spin-Spin Coupling Controls the Gas-Phase Reactivity of Aromatic σ-Type Triradicals. Chemistry 2021; 28:e202102968. [PMID: 34786768 DOI: 10.1002/chem.202102968] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2021] [Indexed: 11/11/2022]
Abstract
Examination of the reactions of σ-type quinolinium-based triradicals with cyclohexane in the gas phase demonstrated that the radical site that is the least strongly coupled to the other two radical sites reacts first, independent of the intrinsic reactivity of this radical site, in contrast to related biradicals that first react at the most electron-deficient radical site. Abstraction of one or two H atoms and formation of an ion that formally corresponds to a combination of the ion and cyclohexane accompanied by elimination of a H atom ("addition-H") were observed. In all cases except one, the most reactive radical site of the triradicals is intrinsically less reactive than the other two radical sites. The product complex of the first H atom abstraction either dissociates to give the H-atom-abstraction product and the cyclohexyl radical or the more reactive radical site in the produced biradical abstracts a H atom from the cyclohexyl radical. The monoradical product sometimes adds to cyclohexene followed by elimination of a H atom, generating the "addition-H" products. Similar reaction efficiencies were measured for three of the triradicals as for relevant monoradicals. Surprisingly, the remaining three triradicals (all containing a meta-pyridyne moiety) reacted substantially faster than the relevant monoradicals. This is likely due to the exothermic generation of a meta-pyridyne analog that has enough energy to attain the dehydrocarbon atom separation common for H-atom-abstraction transition states of protonated meta-pyridynes.
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Affiliation(s)
- Duanchen Ding
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
| | - Erlu Feng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
| | - Raghavendhar R Kotha
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
| | - Nathan C Chapman
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
| | - Hanning Jiang
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
| | - John J Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA
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10
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Milton JR, Jankiewicz BJ, Max JP, Vinueza NR, Kirkpatrick LM, Campbell K, Gallardo VA, Reece JN, Kenttämaa HI. Study on the Gas-Phase Reactivity of Charged Pyridynes. J Org Chem 2021; 86:9979-9993. [PMID: 34242505 DOI: 10.1021/acs.joc.1c00618] [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
The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyridinium cations, were examined in the gas phase using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of selected product ions were probed using collision-activated dissociation (CAD) experiments in a linear quadrupole ion trap (LQIT) mass spectrometer. Mechanisms based on quantum chemical calculations are proposed for the formation of all major products. The products of the reactions of the charged ortho-pyridynes in the gas phase were found to closely resemble those formed upon reactions of neutral ortho-arynes in solution, but the mechanisms of these reactions exhibit striking differences. Additionally, no radical reactions were observed for any of the charged ortho-pyridynes examined, in contrast to previous proposals that ortho-benzyne can occasionally react via radical mechanisms. Finally, the relative reactivities of those charged gaseous ortho-pyridynes that yielded similar product distributions were found to be affected mainly by the (calculated) vertical electron affinities of the dehydrocarbon sites, which suggests that the reactivity of these species is controlled by polar effects.
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Affiliation(s)
- Jacob R Milton
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Bartłomiej J Jankiewicz
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States.,Institute of Optoelectronics, Military University of Technology, gen. S. Kaliskiego 2, 00-908 Warsaw, Poland
| | - Joann P Max
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Nelson R Vinueza
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Lindsey M Kirkpatrick
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States.,Ryan White Center for Pediatric Infectious Disease, Indiana University School of Medicine, 705 Riley Hospital Drive, Room 3032, Indianapolis, Indiana 46202, United States
| | - Karinna Campbell
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Vanessa A Gallardo
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Jennifer N Reece
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, United States
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11
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Uchikura T, Hara Y, Tsubono K, Akiyama T. Visible-Light-Driven C-S Bond Formation Based on Electron Donor-Acceptor Excitation and Hydrogen Atom Transfer Combined System. ACS ORGANIC & INORGANIC AU 2021; 1:23-28. [PMID: 36855634 PMCID: PMC9954416 DOI: 10.1021/acsorginorgau.1c00007] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Developed herein is a visible-light-driven synthesis of sulfides by an electron donor-acceptor/single electron transfer and hydrogen atom transfer combined system without transition metals and strong oxidants. This reaction proceeds through the excitation of an electron donor-acceptor complex between a thiolate and an aryl halide, followed by the hydrogen atom transfer from an alkane to the generated aryl radical.
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12
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Shiels OJ, Kelly PD, Bright CC, Poad BLJ, Blanksby SJ, da Silva G, Trevitt AJ. Reactivity Trends in the Gas-Phase Addition of Acetylene to the N-Protonated Aryl Radical Cations of Pyridine, Aniline, and Benzonitrile. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:537-547. [PMID: 33444019 DOI: 10.1021/jasms.0c00386] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
A key step in gas-phase polycyclic aromatic hydrocarbon (PAH) formation involves the addition of acetylene (or other alkyne) to σ-type aromatic radicals, with successive additions yielding more complex PAHs. A similar process can happen for N-containing aromatics. In cold diffuse environments, such as the interstellar medium, rates of radical addition may be enhanced when the σ-type radical is charged. This paper investigates the gas-phase ion-molecule reactions of acetylene with nine aromatic distonic σ-type radical cations derived from pyridinium (Pyr), anilinium (Anl), and benzonitrilium (Bzn) ions. Three isomers are studied in each case (radical sites at the ortho, meta, and para positions). Using a room temperature ion trap, second-order rate coefficients, product branching ratios, and reaction efficiencies are measured. The rate coefficients increase from para to ortho positions. The second-order rate coefficients can be sorted into three groups: low, between 1 and 3 × 10-12 cm3 molecule-1 s-1 (3Anl and 4Anl); intermediate, between 5 and 15 × 10-12 cm3 molecule-1 s-1 (2Bzn, 3Bzn, and 4Bzn); and high, between 8 and 31 × 10-11 cm3 molecule-1 s-1 (2Anl, 2Pyr, 3Pyr, and 4Pyr); and 2Anl is the only radical cation with a rate coefficient distinctly different from its isomers. Quantum chemical calculations, using M06-2X-D3(0)/6-31++G(2df,p) geometries and DSD-PBEP86-NL/aug-cc-pVQZ energies, are deployed to rationalize reactivity trends based on the stability of prereactive complexes. The G3X-K method guides the assignment of product ions following adduct formation. The rate coefficient trend can be rationalized by a simple model based on the prereactive complex forward barrier height.
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Affiliation(s)
- Oisin J Shiels
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - P D Kelly
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Cameron C Bright
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Berwyck L J Poad
- Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology, Brisbane, Queensland 4001, Australia
| | - Stephen J Blanksby
- Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology, Brisbane, Queensland 4001, Australia
| | - Gabriel da Silva
- Department of Chemical Engineering, The University of Melbourne, Melbourne, Victoria 3010, Australia
| | - Adam J Trevitt
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
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13
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Sarkar S, Cheung KPS, Gevorgyan V. C-H functionalization reactions enabled by hydrogen atom transfer to carbon-centered radicals. Chem Sci 2020; 11:12974-12993. [PMID: 34123240 PMCID: PMC8163321 DOI: 10.1039/d0sc04881j] [Citation(s) in RCA: 139] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Accepted: 11/14/2020] [Indexed: 12/12/2022] Open
Abstract
Selective functionalization of ubiquitous unactivated C-H bonds is a continuous quest for synthetic organic chemists. In addition to transition metal catalysis, which typically operates under a two-electron manifold, a recent renaissance in the radical approach relying on the hydrogen atom transfer (HAT) process has led to tremendous growth in the area. Despite several challenges, protocols proceeding via HAT are highly sought after as they allow for relatively easy activation of inert C-H bonds under mild conditions leading to a broader scope and higher functional group tolerance and sometimes complementary reactivity over methods relying on traditional transition metal catalysis. A number of methods operating via heteroatom-based HAT have been extensively reported over the past few years, while methods employing more challenging carbon analogues have been less explored. Recent developments of mild methodologies for generation of various carbon-centered radical species enabled their utilization in the HAT process, which, in turn, led to the development of remote C(sp3)-H functionalization reactions of alcohols, amines, amides and related compounds. This review covers mostly recent advances in C-H functionalization reactions involving the HAT step to carbon-centered radicals.
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Affiliation(s)
- Sumon Sarkar
- Department of Chemistry and Biochemistry, University of Texas at Dallas 800 W Campbell Rd Richardson Texas 75080 USA
| | - Kelvin Pak Shing Cheung
- Department of Chemistry and Biochemistry, University of Texas at Dallas 800 W Campbell Rd Richardson Texas 75080 USA
| | - Vladimir Gevorgyan
- Department of Chemistry and Biochemistry, University of Texas at Dallas 800 W Campbell Rd Richardson Texas 75080 USA
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14
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Nolte TM, Nauser T, Gubler L, Hendriks AJ, Peijnenburg WJGM. Thermochemical unification of molecular descriptors to predict radical hydrogen abstraction with low computational cost. Phys Chem Chem Phys 2020; 22:23215-23225. [PMID: 33029596 DOI: 10.1039/d0cp03750h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chemistry describes transformation of matter with reaction equations and corresponding rate constants. However, accurate rate constants are not always easy to get. Here we focus on radical oxidation reactions. Analysis of over 500 published rate constants of hydroxyl radicals led us to hypothesize that a modified linear free-energy relationship (LFER) could be used to predict rate constants speedily, reliably and accurately. LFERs correlate the Gibbs activation-energy with the Gibbs energy of reaction. We calculated the latter as the sum of one-electron transfer and, if appropriate, proton transfer. We parametrized specific transition state effects to orbital delocalizability and the polarity of the reactant. The calculation time for 500 reactions is less than 8 hours on a standard desktop-PC. Rate constants were also calculated for hydrogen and methyl radicals; these controls show that the predictions are applicable to a broader set of oxidizing radicals. An accuracy of 30-40% (standard deviation) with reference to reported experimental values was found suitable for the screening of complex chemical systems for possibly relevant reactions. In particular, potentially relevant reactions can be singled out and scrutinized in detail when prioritizing chemicals for environmental risk assessment.
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Affiliation(s)
- Tom M Nolte
- Eidgenössische Technische Hochschule (ETH) Zurich, Laboratory of Inorganic Chemistry, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland.
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15
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Ghorbani F, Harry SA, Capilato JN, Pitts CR, Joram J, Peters GN, Tovar JD, Smajlagic I, Siegler MA, Dudding T, Lectka T. Carbonyl-Directed Aliphatic Fluorination: A Special Type of Hydrogen Atom Transfer Beats Out Norrish II. J Am Chem Soc 2020; 142:14710-14724. [PMID: 32786786 DOI: 10.1021/jacs.0c07004] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Recently, our group reported that enone and ketone functional groups, upon photoexcitation, can direct site-selective sp3 C-H fluorination in terpenoid derivatives. How this transformation actually occurred remained mysterious, as a significant number of mechanistic possibilities came to mind. Herein, we report a comprehensive study describing the reaction mechanism through kinetic studies, isotope-labeling experiments, 19F NMR, electrochemical studies, synthetic probes, and computational experiments. To our surprise, the mechanism suggests intermolecular hydrogen atom transfer (HAT) chemistry is at play, rather than classical Norrish hydrogen atom abstraction as initially conceived. What is more, we discovered a unique role for photopromoters such as benzil and related compounds that necessitates their chemical transformation through fluorination in order to be effective. Our findings provide documentation of an unusual form of directed HAT and are of crucial importance for defining the necessary parameters for the development of future methods.
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Affiliation(s)
- Fereshte Ghorbani
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Stefan Andrew Harry
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Joseph N Capilato
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Cody Ross Pitts
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Jacob Joram
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Garvin N Peters
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - John D Tovar
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Ivor Smajlagic
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
| | - Maxime A Siegler
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
| | - Travis Dudding
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1, Canada
| | - Thomas Lectka
- Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, United States
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16
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Kang J, Hwang HS, Soni VK, Cho EJ. Direct C(sp3)–N Radical Coupling: Photocatalytic C–H Functionalization by Unconventional Intermolecular Hydrogen Atom Transfer to Aryl Radical. Org Lett 2020; 22:6112-6116. [DOI: 10.1021/acs.orglett.0c02179] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jihee Kang
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Ho Seong Hwang
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Vineet Kumar Soni
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Eun Jin Cho
- Department of Chemistry, Chung-Ang University, Seoul 06974, Republic of Korea
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17
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Ding D, Jiang H, Ma X, Nash JJ, Kenttämaa HI. Effects of the Distance between Radical Sites on the Reactivities of Aromatic Biradicals. J Org Chem 2020; 85:8415-8428. [PMID: 32482062 DOI: 10.1021/acs.joc.0c00658] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Coupling of the radical sites in isomeric benzynes is known to hinder their radical reactivity. In order to determine how far apart the radical sites must be for them not to interact, the gas-phase reactivity of several isomeric protonated (iso)quinoline- and acridine-based biradicals was examined. All the (iso)quinolinium-based biradicals were found to react slower than the related monoradicals with similar vertical electron affinities (i.e., similar polar effects). In sharp contrast, the acridinium-based biradicals, most with the radical sites farther apart than in the (iso)quinolinium-based systems, showed greater reactivities than the relevant monoradicals with similar vertical electron affinities. The greater distances between the two radical sites in these biradicals lead to very little or no spin-spin coupling, and no suppression of radical reactivity was observed. Therefore, the radical sites can still interact if they are located on adjacent benzene rings and only after being separated further than that does no coupling occur. The most reactive radical site of each biradical was experimentally determined to be the one predicted to be more reactive based on the monoradical reactivity data. Therefore, the calculated vertical electron affinities of relevant monoradicals can be used to predict which radical site is most reactive in the biradicals.
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Affiliation(s)
- Duanchen Ding
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Hanning Jiang
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Xin Ma
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - John J Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
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18
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Kelly PD, Bright CC, Blanksby SJ, da Silva G, Trevitt AJ. Molecular Weight Growth in the Gas-Phase Reactions of Dehydroanilinium Radical Cations with Propene. J Phys Chem A 2019; 123:8881-8892. [DOI: 10.1021/acs.jpca.9b04088] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Patrick D. Kelly
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong 2522, Australia
| | - Cameron C. Bright
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong 2522, Australia
| | - Stephen J. Blanksby
- Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology, Brisbane 4001, Australia
| | - Gabriel da Silva
- Department of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne 3010, Victoria, Australia
| | - Adam J. Trevitt
- School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong 2522, Australia
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19
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Kotha RR, Yerabolu R, Ding D, Szalwinski L, Ma X, Wittrig A, Kong J, Nash JJ, Kenttämaa HI. Spin–Spin Coupling Between Two
meta
‐Benzyne Moieties In a Quinolinium Tetraradical Cation Increases Their Reactivities. Chemistry 2019; 25:4472-4477. [PMID: 30648302 DOI: 10.1002/chem.201806096] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 01/12/2019] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Duanchen Ding
- Department of Chemistry Purdue University West Lafayette IN 47907 USA
| | - Lucas Szalwinski
- Department of Chemistry Purdue University West Lafayette IN 47907 USA
| | - Xin Ma
- Department of Chemistry Purdue University West Lafayette IN 47907 USA
| | - Ashley Wittrig
- ExxonMobil Research & Engineering Company Annandale NJ 08801 USA
| | - John Kong
- Department of Chemistry Purdue University West Lafayette IN 47907 USA
| | - John J. Nash
- Department of Chemistry Purdue University West Lafayette IN 47907 USA
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20
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Gao J, Jankiewicz BJ, Sheng H, Kirkpatrick L, Ma X, Nash JJ, Kenttämaa HI. Substituent Effects on the Reactivity of the 2,4,6-Tridehydropyridinium Cation, an Aromatic σ,σ,σ-Triradical. European J Org Chem 2018; 2018:6582-6589. [PMID: 31692928 PMCID: PMC6830858 DOI: 10.1002/ejoc.201801249] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Indexed: 11/06/2022]
Abstract
2,4,6-Tridehydropyridinium cation (7) undergoes three consecutive atom or atom group abstractions from reagent molecules in the gas phase. By placing a π-electron-donating hydroxyl group between two radical sites, their reactivity can be quenched by enhancing their through-space coupling via a favorable resonance structure. Indeed, 3-hydroxy-2,4,6-tridehydropyridinium cation (8) abstracts only one atom or group of atoms from reagents. On the other hand, an electron-withdrawing cyano group between two of the radical sites (9) destabilizes the analogous resonance structure and diminishes through-space coupling between the radical sites, resulting in abstraction of three atoms, just like 7. However, the cyano-substituent also increases acidity to the point that 9 reacts pre-dominantly via proton transfer instead of undergoing radical reactions. Therefore, acidic triradicals may undergo nonradical, barrierless proton transfer reactions faster than radical reactions, which are usually accompanied by barriers. Examination of the analogous cyano-substituted mono-and biradicals revealed behavior similar to that of the corresponding unsubstituted species, with the exception of substantially greater reactivities due to their greater (calculated) vertical electron affinities. Finally, the 3-cyano-2,6-didehydropyridinium cation with a singlet ground state (S-T splitting: -11.9 kcal mol-1) was found to react exclusively from the lowest-energy triplet state by fast proton transfer reactions.
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Affiliation(s)
- Jinshan Gao
- Department of Chemistry and Biochemistry, Center for Quantitative Obesity Research, Montclair State University, 1 Normal Avenue, Montclair, NJ 07043, USA
| | | | | | | | - Xin Ma
- Department of Chemistry, Purdue University,West Lafayette, IN 47907, USA
| | - John J Nash
- Department of Chemistry, Purdue University,West Lafayette, IN 47907, USA
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University,West Lafayette, IN 47907, USA
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21
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Nolte TM, Peijnenburg WJGM. Use of quantum-chemical descriptors to analyse reaction rate constants between organic chemicals and superoxide/hydroperoxyl (O2•−/HO2•). Free Radic Res 2018; 52:1118-1131. [DOI: 10.1080/10715762.2018.1529867] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- Tom M. Nolte
- Department of Environmental Science, Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, the Netherlands
- Laboratory of Inorganic Chemistry, Eidgenossische Technische Hochschule (ETH) Zurich, Zurich, Switzerland
| | - Willie J. G. M. Peijnenburg
- National Institute of Public Health and the Environment, Bilthoven, The Netherlands
- Institute of Environmental Sciences (CML), Leiden University, Leiden, The Netherlands
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22
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Sheng H, Ma X, Lei HR, Milton J, Tang W, Jin C, Gao J, Wittrig AM, Archibold EF, Nash JJ, Kenttämaa HI. Polar Effects Control the Gas-Phase Reactivity of para-Benzyne Analogs. Chemphyschem 2018; 19:2839-2842. [PMID: 30203923 DOI: 10.1002/cphc.201800646] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Indexed: 11/05/2022]
Abstract
We report herein a gas-phase reactivity study on a para-benzyne cation and its three cyano-substituted, isomeric derivatives performed using a dual-linear quadrupole ion trap mass spectrometer. All four biradicals were found to undergo primary and secondary radical reactions analogous to those observed for the related monoradicals, indicating the presence of two reactive radical sites. The reactivity of all biradicals is substantially lower than that of the related monoradicals, as expected based on the singlet ground states of the biradicals. The cyano-substituted biradicals show substantially greater reactivity than the analogous unsubstituted biradical. The greater reactivity is rationalized by the substantially greater (calculated) electron affinity of the radical sites of the cyano-substituted biradicals, which results in stabilization of their transition states through polar effects. This finding is in contrast to the long-standing thinking that the magnitude of the singlet-triplet splitting controls the reactivity of para-benzynes.
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Affiliation(s)
- Huaming Sheng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Xin Ma
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Hao-Ran Lei
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Jacob Milton
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Weijuan Tang
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Chunfen Jin
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Jinshan Gao
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Ashley M Wittrig
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Enada F Archibold
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - John J Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
| | - Hilkka I Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907, USA
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23
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Vinueza NR, Jankiewicz BJ, Gallardo VA, Nash JJ, Kenttämaa HI. Effects of hydrogen bonding on the gas-phase reactivity of didehydroisoquinolinium cation isomers. Phys Chem Chem Phys 2018; 20:21567-21572. [PMID: 30094447 DOI: 10.1039/c8cp03350a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two previously unreported isomeric biradicals with a 1,4-radical topology, the 1,5-didehydroisoquinolinium cation and the 4,8-didehydroisoquinolinium cation, and an additional, previously reported isomer, the 4,5-didehydroisoquinolinium cation, were studied to examine the importance of the exact location of the radical sites on their reactivities in the gas phase. The experimental results suggest that hydrogen bonding in the transition state enhances the reactivity of the 1,5-didehydroisoquinolinium cation towards tetrahydrofuran but not towards allyl iodide, dimethyl disulfide or tert-butyl isocyanide. The observation of no such enhancement of reactivity towards tetrahydrofuran for the 4,8-didehydroisoquinolinium and 4,5-didehydroisoquinolinium cations supports this hypothesis as these two biradicals are not able to engage in hydrogen bonding in their transition states for hydrogen atom abstraction from tetrahydrofuran. Quantum chemical transition state calculations indicate that abstraction of a hydrogen atom from tetrahydrofuran by the 1,5-didehydroisoquinolinium cation occurs at the C-1 radical site and that the transition state is stabilized by hydrogen bonding.
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Affiliation(s)
- Nelson R Vinueza
- Purdue University, Department of Chemistry, 560 Oval Drive, West Lafayette, IN 47907, USA.
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24
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Zhao S, Eriksson LA, Zhang RB. Theoretical Insights on the Inefficiency of RNA Oxidative Damage under Aerobic Conditions. J Phys Chem A 2017; 122:431-438. [PMID: 29206039 DOI: 10.1021/acs.jpca.7b10711] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Oxidative damage to RNA has been linked to change or loss of RNA function and development of many human age-related diseases. However, knowledge on the nature of RNA oxidative damage is relatively limited. In this study, oxidative damage to RNA is investigated under anaerobic and aerobic conditions by exploring the properties and reactions of 5-hydroxyl-2'-uridin-6-yl and its peroxyl diastereoisomers in the RNA strand, respectively. Selective addition of OH to the nucleic base from the 5'-end is studied at the molecular level for the first time, explaining the large number of the 5S-isomer available for further reactions. Our results provide clear evidence that the efficiency of C2'-H2' bond activation in the peroxyl isomers is lower than in the carbon radical species. An exception is observed for the isomer cis-(5S,6R)-A1, whose internucleotidyl H2'-abstraction barrier is far smaller than that in the corresponding C6-yl radical. However, analysis of the equilibrium species distribution reveals that the amount of cis-(5S,6R)-A1 is very small among the peroxyl diastereoisomers, and hence the resulting products from direct strand scission should be a less important component in RNA oxidative damage. The species with maximum distribution is the cis-(5S,6R)-B1 isomer, which is derived from cis-(5S,6R)-A1 and has a moderate intranucleotidyl H2'-abstraction barrier. More importantly, the reaction is mildly exothermic. These results show that the main fraction of the intranucleotidyl H2'-abstraction intermediates can be formed from the cis-(5S,6R)-B1 isomer. The absolute reduction potentials, the hydrogen atom binding energies, and the key structural parameters of the C6-peroxyl species are used to understand the diverse reactivity of the cis-(5S,6R) diastereoisomers toward the C2'-H2' bonds activation. The present study shows that in addition to the selectivity of the OH radical addition, there is a strong correlation between the conformation of the modified uracil base and its reactivity in RNA oxidative damage.
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Affiliation(s)
- Shuang Zhao
- School of Chemistry and Chemical Engineering, Beijing Institute of Technology , South Street No. 5, Zhongguancun, Haidian District, Beijing 100081, China
| | - Leif A Eriksson
- Department of Chemistry and Molecular Biology, University of Gothenburg , Box 462, 405 30 Göteborg, Sweden
| | - Ru-Bo Zhang
- School of Chemistry and Chemical Engineering, Beijing Institute of Technology , South Street No. 5, Zhongguancun, Haidian District, Beijing 100081, China
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25
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Vinueza NR, Jankiewicz BJ, Gallardo VA, LaFavers GZ, DeSutter D, Nash JJ, Kenttämaa HI. Reactivity Controlling Factors for an Aromatic Carbon-Centered σ,σ,σ-Triradical: The 4,5,8-Tridehydroisoquinolinium Ion. Chemistry 2015; 22:809-15. [DOI: 10.1002/chem.201502502] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Revised: 09/27/2015] [Indexed: 11/07/2022]
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26
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Wittrig AM, Archibold EF, Sheng H, Nash JJ, Kenttämaa HI. Polar Effects Control the Gas-phase Reactivity of Charged para-Benzyne Analogs. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2015; 377:39-43. [PMID: 25838787 PMCID: PMC4378589 DOI: 10.1016/j.ijms.2014.04.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The gas-phase reactivity of charged para-benzynes is entirely unexplored as they and/or their precursors tend to undergo ring-opening upon their generation. We report here a gas-phase reactivity study of two such benzynes, the 2,5-didehydropyridinium and 5,8-didehydroisoquinolinium cations, generated in a modified dual-linear quadrupole ion trap (DLQIT) mass spectrometer. Both biradicals were found to form diagnostic products with organic molecules, indicating the presence of two radical sites. As opposed to earlier predictions that the singlet-triplet (S-T) splitting controls the radical reactivity of such species, the 2,5-didehydropyridinium cation reacts much faster in spite of its larger S-T splitting. Calculated vertical electron affinities of the radical sites of the para-benzynes, a parameter related to the polarity of the transition states of their reactions, appears to be the most important reactivity controlling factor.
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Affiliation(s)
- Ashley M. Wittrig
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - Enada F. Archibold
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - Huaming Sheng
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - John J. Nash
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
| | - Hilkka I. Kenttämaa
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907 (USA)
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27
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Gao J, Jankiewicz BJ, Reece J, Sheng H, Cramer CJ, Nash JJ, Kenttämaa HI. On the factors that control the reactivity of meta-benzynes. Chem Sci 2014. [DOI: 10.1039/c4sc00194j] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The key reactivity controlling parameters of meta-benzynes have been identified and demonstrated to have a major influence on their reactivity.
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Affiliation(s)
- Jinshan Gao
- Department of Chemistry
- Purdue University
- West Lafayette, USA
| | | | - Jennifer Reece
- Department of Chemistry
- Purdue University
- West Lafayette, USA
| | - Huaming Sheng
- Department of Chemistry
- Purdue University
- West Lafayette, USA
| | - Christopher J. Cramer
- Department of Chemistry
- Chemical Theory Center and Supercomputing Institute
- University of Minnesota
- Minneapolis, USA
| | - John J. Nash
- Department of Chemistry
- Purdue University
- West Lafayette, USA
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28
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Williams PE, Jankiewicz BJ, Yang L, Kenttämaa HI. Properties and reactivity of gaseous distonic radical ions with aryl radical sites. Chem Rev 2013; 113:6949-85. [PMID: 23987564 PMCID: PMC3889672 DOI: 10.1021/cr400121w] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Peggy E. Williams
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47906
| | | | - Linan Yang
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47906
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29
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Assessment of theoretical methods for the study of hydrogen abstraction kinetics of global warming gas species during their degradation and byproduct formation (IUPAC Technical Report). PURE APPL CHEM 2013. [DOI: 10.1351/pac-rep-10-02-38] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Global climate change is a major concern as it leads to an increase in the
average temperature of the earth’s atmosphere. The existence and
persistence of some gaseous species in the atmosphere contribute to global
warming. Experimental techniques are used to study the kinetics and degradation
of global warming gases. However, quantum mechanical methods are also useful for
the kinetic and radiative forcing study of global warming species and can
precede experimental investigations. Research has also been targeted to develop
more adapted procedures using ab initio and density functional theory (DFT)
methods. This report provides a global perspective, in simplified manner, of the
theoretical studies of the degradation of gas species in the atmosphere with an
emphasis on the hydrogen abstraction kinetics of global warming gas species
during their degradation and byproduct formation. En route, the results obtained
from these studies are analysed and compared with experimental data where
available. Our analyses indicate that the theoretical predictions are in
agreement with experimental findings but the predicted parameters are dependent
on the method being used. Theoretical methods are used to predict the
thermodynamic parameters of reactions, and, with relevance to this report, the
global warming potential (GWP) index can also be calculated. This report can be
useful for future investigations involving global warming gaseous species while
providing suggestions on how computations can fill in data gaps when
experimental data are unavailable.
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30
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Prendergast MB, Cooper PA, Kirk BB, Silva GD, Blanksby SJ, Trevitt AJ. Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations. Phys Chem Chem Phys 2013; 15:20577-84. [DOI: 10.1039/c3cp53690d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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31
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Affiliation(s)
- Sandra Osburn
- Department of Chemistry and Biochemistry and Center for Biochemical and Biophysical Studies, Northern Illinois University, DeKalb, Illinois 60115, USA
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32
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Jankiewicz BJ, Gao J, Reece JN, Vinueza NR, Narra P, Nash JJ, Kenttämaa HI. Substituent effects on the nonradical reactivity of 4-dehydropyridinium cation. J Phys Chem A 2012; 116:3089-93. [PMID: 22352890 DOI: 10.1021/jp2101557] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Recent studies have shown that the reactivity of the 4-dehydropyridinium cation significantly differs from the reactivities of its isomers toward tetrahydrofuran. While only hydrogen atom abstraction was observed for the 2- and 3-dehydropyridinium cations, nonradical reactions were observed for the 4-isomer. In order to learn more about these reactions, the gas-phase reactivities of the 4-dehydropyridinium cation and several of its derivatives toward tetrahydrofuran were investigated in a Fourier transform ion electron resonance mass spectrometer. Both radical and nonradical reactions were observed for most of these positively charged radicals. The major parameter determining whether nonradical reactions occur was found to be the electron affinity of the radicals--only those with relatively high electron affinities underwent nonradical reactions. The reactivities of the monoradicals are also affected by hydrogen bonding and steric effects.
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Affiliation(s)
- Bartłomiej J Jankiewicz
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2038, USA
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Widjaja F, Jin Z, Nash JJ, Kenttämaa HI. Direct comparison of solution and gas-phase reactions of the three distonic isomers of the pyridine radical cation with methanol. J Am Chem Soc 2012; 134:2085-93. [PMID: 22148169 DOI: 10.1021/ja207899j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
To directly compare the reactivity of positively charged carbon-centered aromatic σ-radicals toward methanol in solution and in the gas phase, the 2-, 3-, and 4-dehydropyridinium cations (distonic isomers of the pyridine radical cation) were generated by ultraviolet photolysis of the corresponding iodo precursors in a mixture of water and methanol at varying pH. The reaction mixtures were analyzed by using liquid chromatography/mass spectrometry. Hydrogen atom abstraction was the only reaction observed for the 3- and 4-dehydropyridinium cations (and pyridines) in solution. This also was the major reaction observed earlier in the gas phase. Depending on the pH, the hydrogen atom can be abstracted from different molecules (i.e., methanol or water) and from different sites (in methanol) by the 3- and 4-dehydropyridinium cations/pyridines in solution. In the pH range 1-4, the methyl group of methanol is the main hydrogen atom donor site for both 3- and 4-dehydropyridinium cations (just like in the gas phase). At higher pH, the hydroxyl groups of water and methanol also act as hydrogen atom donors. This finding is rationalized by a greater abundance of the unprotonated radicals that preferentially abstract hydrogen atoms from the polar hydroxyl groups. The percentage yield of hydrogen atom abstraction by these radicals was found to increase with lowering the pH in the pH range 1.0-3.2. This pH effect is rationalized by polar effects: the lower the pH, the greater the fraction of protonated (more polar) radicals in the solution. This finding is consistent with previous results obtained in the gas phase and suggests that gas-phase studies can be used to predict solution reactivity, but only as long as the same reactive species is studied in both experiments. This was found not to be the case for the 2-iodopyridinium cation. Photolysis of this precursor in solution resulted in the formation of two major addition products, 2-hydroxy- and 2-methoxypyridinium cations, in addition to the hydrogen atom abstraction product. These addition products were not observed in the earlier gas-phase studies on 2-dehydropyridinium cation. Their observation in solution is explained by the formation of another reactive intermediate, the 2-pyridylcation, upon photolysis of 2-iodopyridinium cation (and 2-iodopyridine). The same intermediate was observed in the gas phase but it was removed before examining the reactions of the desired radical, 2-dehydropyridinium cation (which cannot be done in solution).
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Affiliation(s)
- Fanny Widjaja
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
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Pates GO, Guler L, Nash JJ, Kenttämaa HI. Reactivity and selectivity of charged phenyl radicals toward amino acids in a Fourier transform ion cyclotron resonance mass spectrometer. J Am Chem Soc 2011; 133:9331-42. [PMID: 21612203 PMCID: PMC3131205 DOI: 10.1021/ja111280t] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The reactivity of 10 charged phenyl radicals toward several amino acids was examined in the gas phase in a dual-cell Fourier transform ion cyclotron resonance mass spectrometer. All radicals abstract a hydrogen atom from the amino acids, as expected. The most electrophilic radicals (with the greatest calculated vertical electron affinities (EA) at the radical site) also react with these amino acids via NH(2) abstraction (a nonradical nucleophilic addition-elimination reaction). Both the radical (hydrogen atom abstraction) and nonradical (NH(2) abstraction) reaction efficiencies were found to increase with the electrophilicity (EA) of the radical. However, NH(2) abstraction is more strongly influenced by EA. In contrast to an earlier report, the ionization energies of the amino acids do not appear to play a general reactivity-controlling role. Studies using several partially deuterium-labeled amino acids revealed that abstraction of a hydrogen atom from the α-carbon is only preferred for glycine; for the other amino acids, a hydrogen atom is preferentially abstracted from the side chain. The electrophilicity of the radicals does not appear to have a major influence on the site from which the hydrogen atom is abstracted. Hence, the regioselectivity of hydrogen atom abstraction appears to be independent of the structure of the radical but dependent on the structure of the amino acid. Surprisingly, abstraction of two hydrogen atoms was observed for the N-(3-nitro-5-dehydrophenyl)pyridinium radical, indicating that substituents on the radical not only influence the EA of the radical but also can be involved in the reaction. In disagreement with an earlier report, proline was found to display several unprecedented reaction pathways that likely do not proceed via a radical mechanism but rather by a nucleophilic addition-elimination mechanism. Both NH(2) and (15)NH(2) groups were abstracted from lysine labeled with (15)N on the side chain, indicating that NH(2) abstraction occurs both from the amino terminus and from the side chain. Quantum chemical calculations were employed to obtain insights into some of the reaction mechanisms.
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Affiliation(s)
- George O. Pates
- Department of Chemistry, Purdue University, West Lafayette, IN 47907
| | - Leonard Guler
- Department of Chemistry, Purdue University, West Lafayette, IN 47907
| | - John J. Nash
- Department of Chemistry, Purdue University, West Lafayette, IN 47907
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Adeuya A, Nash JJ, Kenttämaa HI. Influence of hydrogen bonding on hydrogen-atom abstraction reactions of dehydropyridinium cations in the gas phase. J Phys Chem A 2010; 114:12851-7. [PMID: 21080694 PMCID: PMC3014263 DOI: 10.1021/jp107254k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The reactions of several substituted, positively charged dehydropyridinium cations with cyclohexane, methanol, and tetrahydrofuran have been examined in a Fourier-transform ion cyclotron resonance mass spectrometer. All of the charged monoradicals react with the neutral reagents exclusively via hydrogen atom abstraction. For cyclohexane, there is a good correlation between the reaction efficiencies and the calculated electron affinities at the radical sites; that is, the greater the electron affinity of the charged monoradical at the radical site, the faster the reaction. The reaction efficiencies with methanol and tetrahydrofuran, however, do not correlate with the calculated electron affinities. Density functional theory (DFT) calculations indicate that for these reagents a stabilizing hydrogen bonding interaction exists in the hydrogen atom abstraction transition states for some of the charged monoradicals but not for others. At both the MPW1K and G3MP2B3 levels of theory, there is a good correlation between the calculated activation enthalpies and the observed reaction efficiencies, although the G3MP2B3 method provides a slightly better correlation than the MPW1K method. The extent of enhancement in the reaction efficiencies caused by the hydrogen bonding interactions parallels the calculated hydrogen bond lengths in the transition states.
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Affiliation(s)
| | - John J. Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
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Boyarskii VP, Sangaranarayanan MV, Khaibulova TS, Boyarskaya IA. Reduction of mono- and dichlorobiphenyls with sodium-naphthalene complex. RUSS J GEN CHEM+ 2010. [DOI: 10.1134/s1070363210040201] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Adeuya A, Price JM, Jankiewicz BJ, Nash JJ, Kenttämaa HI. Gas-phase reactivity of protonated 2-, 3-, and 4-dehydropyridine radicals toward organic reagents. J Phys Chem A 2009; 113:13663-74. [PMID: 19902945 PMCID: PMC2804851 DOI: 10.1021/jp901380y] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
To explore the effects of the electronic nature of charged phenyl radicals on their reactivity, reactions of the three distonic isomers of n-dehydropyridinium cation (n = 2, 3, or 4) have been investigated in the gas phase by using Fourier-transform ion cyclotron resonance mass spectrometry. All three isomers react with cyclohexane, methanol, ethanol, and 1-pentanol exclusively via hydrogen atom abstraction and with allyl iodide mainly via iodine atom abstraction, with a reaction efficiency ordering of 2 > 3 > 4. The observed reactivity ordering correlates well with the calculated vertical electron affinities of the charged radicals (i.e., the higher the vertical electron affinity, the faster the reaction). Charged radicals 2 and 3 also react with tetrahydrofuran exclusively via hydrogen atom abstraction, but the reaction of 4 with tetrahydrofuran yields products arising from nonradical reactivity. The unusual reactivity of 4 is likely to result from the contribution of an ionized carbene-type resonance structure that facilitates nucleophilic addition to the most electrophilic carbon atom (C-4) in this charged radical. The influence of such a resonance structure on the reactivity of 2 is not obvious, and this may be due to stabilizing hydrogen-bonding interactions in the transition states for this molecule. Charged radicals 2 and 3 abstract a hydrogen atom from the substituent in both phenol and toluene, but 4 abstracts a hydrogen atom from the phenyl ring, a reaction that is unprecedented for phenyl radicals. Charged radical 4 reacts with tert-butyl isocyanide mainly by hydrogen cyanide (HCN) abstraction, whereas CN abstraction is the principal reaction for 2 and 3. The different reactivity observed for 4 (as compared to 2 and 3) is likely to result from different charge and spin distributions of the reaction intermediates for these charged radicals.
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Affiliation(s)
| | | | | | - John J. Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
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Li S, Fu M, Habicht SC, Pates GO, Nash JJ, Kenttämaa HI. Phenyl radical-induced damage to dipeptides. J Org Chem 2009; 74:7724-32. [PMID: 19772324 PMCID: PMC2790419 DOI: 10.1021/jo901470f] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Laser-induced acoustic desorption (LIAD) incorporated with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) has been utilized to investigate phenyl radical-induced damage to dipeptides in the gas phase. On the basis of the product branching ratios measured for the reactions of two different positively charged phenyl radicals with 17 different dipeptides, the overall order of susceptibility to attack of the different sites in the dipeptides was determined to be heteroaromatic side chain approximately = S atom in SCH(3) group > H atom in SH group > H atom in CH group > aromatic side chain > S atom in SH group > NH(2) in side chain > N-terminal NH(2) > COOH in side chain approximately = C-terminal COOH. The amino acid sequence also influences the selectivity of these reactions. As expected, the ability of a phenyl radical to damage dipeptides increases as the electrophilicity of the phenyl radical increases.
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Affiliation(s)
| | - Mingkun Fu
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
| | - Steven C. Habicht
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
| | - George O. Pates
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
| | - John J. Nash
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
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Ly T, Julian RR. Tracking radical migration in large hydrogen deficient peptides with covalent labels: facile movement does not equal indiscriminate fragmentation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2009; 20:1148-1158. [PMID: 19286394 DOI: 10.1016/j.jasms.2009.02.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2008] [Revised: 01/29/2009] [Accepted: 02/05/2009] [Indexed: 05/27/2023]
Abstract
Photodissociation of iodo-tyrosine modified peptides yields localized radicals on the tyrosine side chain, which can be further dissociated by collisional activation. We have performed extensive experiments on model peptides, RGYALG, RGYG, and their derivatives, to elucidate the mechanisms underlying backbone fragmentation at tyrosine. Neither acetylation nor deuteration of the tyrosyl phenolic hydrogen significantly affects backbone fragmentation. However, deuterium migration from the tyrosyl beta carbon is concomitant with cleavage at tyrosine. Substitution of tyrosine with 4-hydroxyphenylglycine, which does not have beta hydrogens, results in almost complete elimination of backbone fragmentation at tyrosine. These results suggest that a radical situated on the beta carbon is required for a-type fragmentation in hydrogen-deficient radical peptides. Replacement of the alphaH of the residue adjacent to tyrosine with methyl groups results in significant diminution of backbone fragmentation. The initial radical abstracts an alphaH from the adjacent amino acid, which is poised to "rebound" and abstract the betaH of tyrosine through a six-membered transition-state. Subsequent beta-scission leads to the observed a-type backbone fragment. These results from deuterated peptides clearly reveal that radical migration in peptides can occur and that multiple migrations are not infrequent. Counterintuitively, close examination of all experimental results reveals that the probability for fragmentation at a particular residue is well correlated with thermodynamic radical stability. A-type fragmentation therefore appears to be most likely when favorable thermodynamics are combined with the relevant kinetic control. These results are consistent with ab initio calculations, which demonstrate that barriers to migration are significantly smaller in magnitude than probable dissociation thresholds.
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Affiliation(s)
- Tony Ly
- Department of Chemistry, University of California, Riverside, California 92521, USA
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Moore BN, Blanksby SJ, Julian RR. Ion–molecule reactions reveal facile radical migration in peptides. Chem Commun (Camb) 2009:5015-7. [DOI: 10.1039/b907833a] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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