Nitroxides: 170 Years of History

Likhtenshtein, Gertz I.

doi:10.1007/978-3-030-34822-9_1

Cited by 4 publications

(10 citation statements)

References 73 publications

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“…11 These advantages contribute to their use as spin labels and spin probes for material and biochemical studies. 11,12 Electron paramagnetic resonance (EPR) spectroscopy is a crucial tool for obtaining valuable information about the electron distribution of open-shell molecules. Spin labeling allows one to study the electronic properties of even a diamagnetic molecule with EPR spectroscopy.…”

Section: ■ Introductionmentioning

confidence: 99%

Unraveling the Isotropic Hyperfine Coupling Constants of Nitroxide Radicals via Molecular Electrostatic Potential Analysis

Thamleena,

Mathew,

Sajith

2024

J. Phys. Chem. A

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Nitroxide radicals have wide and promising applications as organic magnetic materials. Modulating the isotropic hyperfine coupling constants (HFCCs) of these radicals through proper structural design is an effective strategy for their application as spin probes and spin labels. In the present work, density functional theory calculations were carried out to develop a robust descriptor based on the molecular electrostatic potential for nitrogen HFCCs of nitroxide radicals. Forty nitroxide radicals from five distinct classes, namely, derivatives of cyclic, acyclic, imino, nitronyl, and benzimidazole nitronyl nitroxides, were selected, and the molecular electrostatic potential (MESP) at the nitrogen atom (V N ) of the NO moiety was calculated. The V N values efficiently capture the electronic changes associated with the steric and electronic nature of these systems. A significant correlation between V N values and the experimental HFCCs of nitrogen nuclei demonstrates the applicability of V N as a simple and efficient descriptor for monitoring HFCCs. Furthermore, a good correlation between V N and experimental nitrogen HFCCs for each class of nitroxide radicals indicates the use of V N in the evaluation of the magnetic nature of the nitroxide radicals. The findings in this work are expected to facilitate the design of novel nitroxide radicals with desirable magnetic properties based on MESP topology analysis.

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Section: ■ Introductionmentioning

confidence: 99%

Unraveling the Isotropic Hyperfine Coupling Constants of Nitroxide Radicals via Molecular Electrostatic Potential Analysis

Thamleena,

Mathew,

Sajith

2024

J. Phys. Chem. A

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“…It has been theoretically and experimentally clarified that 1,3-phenylene-bridges serve as a robust ferromagnetic coupler in the context of the spin-polarization mechanism or topological rule [4,5,[11][12][13][14][15][16][17][18][19]. Triphenylmethyls and diphenylcarbenes are the most popular paramagnetic centers in this research field, but heteroatomic ones can also be utilized as a spin source [17][18][19][20][21][22]. Nitroxides or aminoxyls are persistent radicals and are available for various aspects in chemistry, physics, and biology [20][21][22][23] thanks to the stability achieved through the resonance of the following canonical formulas: R 1 -N(-O • )-R 2 ←→R 1 -N +• (-O -)-R 2 .…”

Section: Introductionmentioning

confidence: 99%

“…Triphenylmethyls and diphenylcarbenes are the most popular paramagnetic centers in this research field, but heteroatomic ones can also be utilized as a spin source [17][18][19][20][21][22]. Nitroxides or aminoxyls are persistent radicals and are available for various aspects in chemistry, physics, and biology [20][21][22][23] thanks to the stability achieved through the resonance of the following canonical formulas: R 1 -N(-O • )-R 2 ←→R 1 -N +• (-O -)-R 2 . The non-bonding molecular orbital (NBMO) belongs to a π* symmetry and has comparable contributions from N and O atomic orbitals.…”

Section: Introductionmentioning

confidence: 99%

A Triplet/Singlet Ground-State Switch via the Steric Inhibition of Conjugation in 4,6-Bis(trifluoromethyl)-1,3-phenylene Bisnitroxide

Haga,

Ishida

2023

Molecules

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Ground triplet 4,6-bis(trifluoromethyl)-1,3-phenylene bis(tert-butyl nitroxide) (TF2PBN) reacted with [Y(hfac)3(H2O)2] (hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate), affording a doubly hydrogen-bonded adduct [Y(hfac)3(H2O)2(TF2PBN)]. The biradical was recovered from the adduct through recrystallization. Crystallographic analysis indicates that the torsion angles (|θ| ≤ 90°) between the benzene ring and nitroxide groups were 74.9 and 84.8° in the adduct, which are larger than those of the starting material TF2PBN. Steric congestion due to o-trifluoromethyl groups gives rise to the reduction of π-conjugation. Two hydrogen bonds enhance this deformation. Susceptometry of the adduct indicates a ground singlet with 2J/kB = −128(2) K, where 2J corresponds to the singlet–triplet gap. The observed magneto-structure relation is qualitatively consistent with Rajca’s pioneering work. A density functional theory calculation at the UB3LYP/6-311+G(2d,p) level using the atomic coordinates determined provided a result of 2J/kB = −162.3 K for the adduct, whilst the corresponding calculation on intact TF2PBN provided +87.2 K. After a comparison among a few known compounds, the 2J vs. |θ| plot shows a negative slope with a critical torsion of 65(3)°. The ferro- and antiferromagnetic coupling contributions are balanced in TF2PBN, being responsible for ground-state interconversion by means of small structural perturbation like hydrogen bonds.

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“…Only in the last decade, many monographs, book chapters, and reviews were published regarding the physicochemical features of these radicals, methods of their synthesis, and their various applications [ 2 , 3 , 4 , 5 ] in synthetic organic chemistry (as oxidants) [ 6 ], the creation of functional materials [ 7 , 8 , 9 , 10 ], and polymer chemistry [ 11 ], including their role as agents in nitroxide-mediated radical polymerization [ 12 , 13 , 14 ], as unique molecular spin probes [ 15 ] and indispensable spin labels [ 16 , 17 ], and antioxidants and potential therapeutic agents for biological research and medicine [ 18 , 19 , 20 ].…”

Section: Introductionmentioning

confidence: 99%

Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals

Zaytseva

Mazhukin

2021

Molecules

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Spirocyclic nitroxyl radicals (SNRs) are stable paramagnetics bearing spiro-junction at α-, β-, or γ-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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Nitroxides: 170 Years of History

Cited by 4 publications

References 73 publications

Unraveling the Isotropic Hyperfine Coupling Constants of Nitroxide Radicals via Molecular Electrostatic Potential Analysis

Unraveling the Isotropic Hyperfine Coupling Constants of Nitroxide Radicals via Molecular Electrostatic Potential Analysis

A Triplet/Singlet Ground-State Switch via the Steric Inhibition of Conjugation in 4,6-Bis(trifluoromethyl)-1,3-phenylene Bisnitroxide

Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals

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