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Abstract
Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.
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Affiliation(s)
- Dirk Leifert
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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Sowiński MP, Gahlawat S, Lund BA, Warnke AL, Hopmann KH, Lovett JE, Haugland MM. Conformational tuning improves the stability of spirocyclic nitroxides with long paramagnetic relaxation times. Commun Chem 2023; 6:111. [PMID: 37277501 DOI: 10.1038/s42004-023-00912-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 05/24/2023] [Indexed: 06/07/2023] Open
Abstract
Nitroxides are widely used as probes and polarization transfer agents in spectroscopy and imaging. These applications require high stability towards reducing biological environments, as well as beneficial relaxation properties. While the latter is provided by spirocyclic groups on the nitroxide scaffold, such systems are not in themselves robust under reducing conditions. In this work, we introduce a strategy for stability enhancement through conformational tuning, where incorporating additional substituents on the nitroxide ring effects a shift towards highly stable closed spirocyclic conformations, as indicated by X-ray crystallography and density functional theory (DFT) calculations. Closed spirocyclohexyl nitroxides exhibit dramatically improved stability towards reduction by ascorbate, while maintaining long relaxation times in electron paramagnetic resonance (EPR) spectroscopy. These findings have important implications for the future design of new nitroxide-based spin labels and imaging agents.
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Affiliation(s)
- Mateusz P Sowiński
- Department of Chemistry, UiT The Arctic University of Norway, 9037, Tromsø, Norway
| | - Sahil Gahlawat
- Department of Chemistry, UiT The Arctic University of Norway, 9037, Tromsø, Norway
- Hylleraas Center for Quantum Molecular Sciences, UiT The Arctic University of Norway, 9037, Tromsø, Norway
| | - Bjarte A Lund
- Department of Chemistry, UiT The Arctic University of Norway, 9037, Tromsø, Norway
| | - Anna-Luisa Warnke
- Department of Chemistry, UiT The Arctic University of Norway, 9037, Tromsø, Norway
| | - Kathrin H Hopmann
- Department of Chemistry, UiT The Arctic University of Norway, 9037, Tromsø, Norway
| | - Janet E Lovett
- SUPA, School of Physics and Astronomy and BSRC, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
| | - Marius M Haugland
- Department of Chemistry, UiT The Arctic University of Norway, 9037, Tromsø, Norway.
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3
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Grishin DF, Grishin ID. Modern trends in controlled synthesis of functional polymers: fundamental aspects and practical applications. RUSSIAN CHEMICAL REVIEWS 2021. [DOI: 10.1070/rcr4964] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Major trends in controlled radical polymerization (CRP) or reversible-deactivation radical polymerization (RDRP), the most efficient method of synthesis of well-defined homo- and copolymers with specified parameters and properties, are critically analyzed. Recent advances associated with the three classical versions of CRP: nitroxide mediated polymerization, reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization, are considered. Particular attention is paid to the prospects for the application of photoinitiation and photocatalysis in CRP. This approach, which has been intensively explored recently, brings synthetic methods of polymer chemistry closer to the light-induced processes of macromolecular synthesis occurring in living organisms. Examples are given of practical application of CRP techniques to obtain industrially valuable, high-tech polymeric products.
The bibliography includes 429 references.
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Zaytseva EV, Mazhukin DG. Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals. Molecules 2021; 26:677. [PMID: 33525514 PMCID: PMC7865516 DOI: 10.3390/molecules26030677] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 01/19/2021] [Accepted: 01/25/2021] [Indexed: 12/19/2022] Open
Abstract
Spirocyclic nitroxyl radicals (SNRs) are stable paramagnetics bearing spiro-junction at a-, b-, or g-carbon atom of the nitroxide fragment, which is part of the heterocyclic system. Despite the fact that the first representatives of SNRs were obtained about 50 years ago, the methodology of their synthesis and their usage in chemistry and biochemical applications have begun to develop rapidly only in the last two decades. Due to the presence of spiro-function in the SNRs molecules, the latter have increased stability to various reducing agents (including biogenic ones), while the structures of the biradicals (SNBRs) comprises a rigid spiro-fused core that fixes mutual position and orientation of nitroxide moieties that favors their use in dynamic nuclear polarization (DNP) experiments. This first review on SNRs will give a glance at various strategies for the synthesis of spiro-substituted, mono-, and bis-nitroxides on the base of six-membered (piperidine, 1,2,3,4-tetrahydroquinoline, 9,9'(10H,10H')-spirobiacridine, piperazine, and morpholine) or five-membered (2,5-dihydro-1H-pyrrole, pyrrolidine, 2,5-dihydro-1H-imidazole, 4,5-dihydro-1H-imidazole, imidazolidine, and oxazolidine) heterocyclic cores.
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Affiliation(s)
| | - Dmitrii G. Mazhukin
- Novosibirsk Institute of Organic Chemistry, Siberian Branch of Russian Academy of Sciences (SB RAS), Academician Lavrentiev Ave. 9, 630090 Novosibirsk, Russia;
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Design and synthesis of trivalent Tn glycoconjugate polymers by nitroxide-mediated polymerization. Tetrahedron 2019. [DOI: 10.1016/j.tet.2019.130776] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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6
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Efficiency of low-molecular-weight and high-molecular-weight alkoxyamines in the synthesis of polystyrene. Russ Chem Bull 2019. [DOI: 10.1007/s11172-019-2597-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Székely A, Klussmann M. Molecular Radical Chain Initiators for Ambient‐ to Low‐Temperature Applications. Chem Asian J 2018; 14:105-115. [DOI: 10.1002/asia.201801636] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Indexed: 01/14/2023]
Affiliation(s)
- Anna Székely
- Max Planck Institut für Kohlenforschung Kaiser-Wilhelm-Platz 2 45470 Mülheim an der Ruhr Germany
| | - Martin Klussmann
- Max Planck Institut für Kohlenforschung Kaiser-Wilhelm-Platz 2 45470 Mülheim an der Ruhr Germany
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Kreutzer J, Yagci Y. Metal Free Reversible-Deactivation Radical Polymerizations: Advances, Challenges, and Opportunities. Polymers (Basel) 2017; 10:E35. [PMID: 30966069 PMCID: PMC6415071 DOI: 10.3390/polym10010035] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Revised: 12/06/2017] [Accepted: 12/07/2017] [Indexed: 12/21/2022] Open
Abstract
A considerable amount of the worldwide industrial production of synthetic polymers is currently based on radical polymerization methods. The steadily increasing demand on high performance plastics and tailored polymers which serve specialized applications is driven by the development of new techniques to enable control of polymerization reactions on a molecular level. Contrary to conventional radical polymerization, reversible-deactivation radical polymerization (RDRP) techniques provide the possibility to prepare polymers with well-defined structures and functionalities. The review provides a comprehensive summary over the development of the three most important RDRP methods, which are nitroxide mediated radical polymerization, atom transfer radical polymerization and reversible addition fragmentation chain transfer polymerization. The focus thereby is set on the newest developments in transition metal free systems, which allow using these techniques for biological or biomedical applications. After each section selected examples from materials synthesis and application to biomedical materials are summarized.
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Affiliation(s)
- Johannes Kreutzer
- Department of Chemistry, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey.
| | - Yusuf Yagci
- Department of Chemistry, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey.
- Center of Excellence for Advanced Materials Research (CEAMR) and Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia.
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Gryn’ova G, Smith LM, Coote ML. Computational design of pH-switchable control agents for nitroxide mediated polymerization. Phys Chem Chem Phys 2017; 19:22678-22683. [DOI: 10.1039/c7cp04337f] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In the present work we use accurate quantum chemistry to evaluate several known and novel nitroxides bearing acid–base groups as pH-switchable control agents for room temperature NMP.
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Affiliation(s)
- Ganna Gryn’ova
- ARC Centre of Excellence for Electromaterials Science
- Research School of Chemistry
- Australian National University
- Canberra ACT 2601
- Australia
| | - Leesa M. Smith
- ARC Centre of Excellence for Electromaterials Science
- Research School of Chemistry
- Australian National University
- Canberra ACT 2601
- Australia
| | - Michelle L. Coote
- ARC Centre of Excellence for Electromaterials Science
- Research School of Chemistry
- Australian National University
- Canberra ACT 2601
- Australia
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10
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Jing Y, Tesch M, Wang L, Daniliuc CG, Studer A. Synthesis of a bulky nitroxide and its application in the nitroxide-mediated radical polymerization. Tetrahedron 2016. [DOI: 10.1016/j.tet.2016.04.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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11
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Ballard N, Aguirre M, Simula A, Agirre A, Leiza JR, Asua JM, van Es S. New Class of Alkoxyamines for Efficient Controlled Homopolymerization of Methacrylates. ACS Macro Lett 2016; 5:1019-1022. [PMID: 35614638 DOI: 10.1021/acsmacrolett.6b00547] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Despite significant efforts, the design of alkoxyamines for polymerization of methacrylic monomers in a well-controlled fashion with good retention of the active chain ends remains a challenge. Herein, the facile synthesis of several alkoxyamines, which are capable of achieving this long sought-after goal, is reported. Controlled homopolymerization of methyl methacrylate is achieved as determined by a linear increase in molecular weight with conversion and first-order rate plots for various alkoxyamine concentrations. The versatility of the alkoxyamines is further exemplified by the ability to control the homopolymerization of styrene and by synthesis of a block copolymer of a second methacrylate in an efficient chain extension process.
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Affiliation(s)
- Nicholas Ballard
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
| | - Miren Aguirre
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
| | - Alexandre Simula
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
| | - Amaia Agirre
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
| | - Jose R. Leiza
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
| | - José M. Asua
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
| | - Steven van Es
- POLYMAT
and Kimika Aplikatua Saila, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, 20018 Donostia/San Sebastián, Spain
- Dispoltec BV, P.O. Box 331, 6160 AH Geleen, The Netherlands
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Ballard N, Mecerreyes D, Asua JM. Redox Active Compounds in Controlled Radical Polymerization and Dye-Sensitized Solar Cells: Mutual Solutions to Disparate Problems. Chemistry 2015; 21:18516-27. [PMID: 26449200 DOI: 10.1002/chem.201503098] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Controlled radical polymerization (CRP) and dye-sensitized solar cells (DSSCs) are two fields of research that at an initial glance appear to have little in common. However, despite their obvious differences, both in application and in scientific nature, a closer look reveals a striking similarity between many of the compounds widely used as control agents in radical polymerization and as redox couples in dye-sensitized solar cells. Herein, we review the various redox active compounds used and examine the characteristics that give them the ability to perform this dual function. In addition we explore the advances in the understanding of the structural features that enhance their activity in both CRP and DSSCs. It is hoped that such a comparison will be conducive to improving process performance in both fields.
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Affiliation(s)
- Nicholas Ballard
- POLYMAT and Departamento de Química Aplicada, Facultad de Ciencias Químicas, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, Donostia-San Sebastián, 20018 (Spain).
| | - David Mecerreyes
- POLYMAT and Departamento de Química Aplicada, Facultad de Ciencias Químicas, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, Donostia-San Sebastián, 20018 (Spain)
| | - José M Asua
- POLYMAT and Departamento de Química Aplicada, Facultad de Ciencias Químicas, University of the Basque Country UPV/EHU, Joxe Mari Korta Zentroa, Tolosa Hiribidea 72, Donostia-San Sebastián, 20018 (Spain)
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Zaremski MY. Kinetic features of pseudoliving radical polymerization under conditions of reversible inhibition by nitroxide radicals. POLYMER SCIENCE SERIES C 2015. [DOI: 10.1134/s1811238215010099] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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Payne KA, Nesvadba P, Debling J, Cunningham MF, Hutchinson RA. Nitroxide-Mediated Polymerization at Elevated Temperatures. ACS Macro Lett 2015; 4:280-283. [PMID: 35596337 DOI: 10.1021/acsmacrolett.5b00054] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A new alkoxyamine based on a highly thermally stable nitroxide is used for the controlled polymerization of styrene and butyl acrylate at temperatures up to 200 °C. High monomer conversions are reached in a few minutes with a linear increase in polymer chain-length with conversion, a final dispersity (Đ) of ∼1.2, and successful chain-extension of the resulting material. The alkoxyamine concentration was altered to target various chain lengths, with autopolymerization dictating the polymerization rate of styrene regardless of alkoxyamine concentration. Controlled polymerization of methacrylate monomers and acrylic acid was successful with the addition of styrene. The new material opens the possibility to increase the range of specialty products made for applications in coatings, inks, overprint varnishes, and adhesives.
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Affiliation(s)
- Kevin A. Payne
- Department
of Chemical Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada
| | | | - Jon Debling
- BASF Corp., 1609 Biddle Avenue, Wyandotte, Michigan 48192, United States
| | - Michael F. Cunningham
- Department
of Chemical Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada
| | - Robin A. Hutchinson
- Department
of Chemical Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada
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