Comment on ``Paramagnetic Resonance of Alkyl Nitroxides''

Florin, R. E.

doi:10.1063/1.1711880

Cited by 18 publications

(6 citation statements)

References 5 publications

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“…The average constants a̅ N computed over the last 0.5 or 1 ns of the nitroxide trajectories are summarized in Table , and compared to available experimental data. − Whatever the nitroxide, the root-mean-square deviation concerning the a̅ N mean values ranges between 2.5 and 3.5 G, corresponding to a standard error of the mean of about 0.1 G for the statistical ensembles of 1000 or 2000 structures.…”

Section: Resultsmentioning

confidence: 99%

Further Insights into the Environmental Effects on the Computed Hyperfine Coupling Constants of Nitroxides in Aqueous Solution

et al. 2009

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We investigated the main two factors influencing the mean hyperfine coupling constants of small nitroxide radicals in aqueous solution, i.e., the out-of-plane displacement of their nitrogen atom and the environmental effects (solvent effects), by means of the approach we previously developed and fine-tuned to study the solvation of the dimethyl nitroxide radical. Our methodology efficiently combines classical molecular dynamics based on a polarizable force field at the nanosecond scale and quantum mechanics/molecular mechanics (QM/MM) computations to account for the bulk instantaneous electrostatic environmental effect. Our method has been applied to five small nitroxides, namely methyl nitroxide, ethyl nitroxide, dimethyl nitroxide, di-tert-butyl nitroxide, and PROXYL. The theoretical nitrogen hyperfine coupling constant values for the five nitroxides in solution are in good agreement with experiment (difference of 0.3 G on average). Our approach showed that the solvent shift in nitroxide hyperfine coupling constants is almost constant whatever the nitroxide, and, particularly, whatever the nitroxide NO moiety's accessibility to the solvent. This result contrasts with earlier results derived from 10 ps scale trajectories based on Car-Parrinello molecular dynamics approach. However, we show that if we consider on average these latter results, they are in agreement with our conclusion. We also present an attempt to identify the origin of this result by analyzing the solvent contributions in terms of effects of the nitroxide first hydration shell and of the bulk, and by investigating the relation between these two contributions and the solvent structure at the vicinity of the NO moiety.

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Section: Resultsmentioning

confidence: 99%

Further Insights into the Environmental Effects on the Computed Hyperfine Coupling Constants of Nitroxides in Aqueous Solution

et al. 2009

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“…Furthermore, the few estimates for the three Q values in eqs. [17]- [19] given in Tables I1 and I11 suggest that For personal use only.…”

Section: Q-parameter Values For the Isotropicmentioning

confidence: 99%

“…If the highest value of QN given in method was to choose values of e,,NH and QN Tables I1 and 111, viz., 35 G, is used, the apparand assume the validity of eqs. [17] and [19] Tables I and 11). Acknowledgment…”

Section: Radical (G)mentioning

confidence: 99%

Electron paramagnetic resonance spectroscopic study of nitroxide radicals formed from oximes

Smith¹,

Fox²

1969

Can. J. Chem.

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The addition of hydroxyl radicals to each of the oximes, acetaldoxime, acetoxime, and 2,3-butanedione monoxime, has been studied by mixing titanous chloride, hydrogen peroxide, and the oxime in a n aqueous continuous-flow system. I n each case a p-hydroxy nitroxide (functional structure )c(oH)-NH-0.) is formed. I n confirmation of these results, amino and hydroxymethyl radicals we; e added to the oximes using similar procedures to give in each case the radicals of functional structure >c(NH,)-NH-0. and )C(CH~OH)-NH-o., respectively. Attempts to add methyl radicals, prepared by the reaction betwGen titanous chloride and t-butyl hydroperoxide, to these oximes gave no observable products save the methyl radicals. However, use of titanous chloride and peracetic acid gave results consistent with the addition of hydroxyl radicals. The addition of hydroxyl radicals to the oxime-0-methyl ethers of acetaldehyde and acetone gave radicals of functional structure 'c(oH)-N-0-CH, / (JaNl, ca. 14 G ; a,,0CH3~, ca. 3 G ) which have not previously been identified unambiguously. On the assumption that JQNl = lQHNH = 23 G in all these radicals, pNn has been calculated and used to obtain a value for lQHO H~I of ca. 11 G whlch is within the range of other estimates in the literature.

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“…In many cases, the solvent effect on the electronic structure of the nitroxide radical was studied by ESR experiment. [2][3][4]14,25 Symons et al showed a high correlation between the n-π* excitation energy and a N and suggested that the solvent effects on these two quantities originated in the same cause. 14 In our previous theoretical works, [20][21][22] the hfcc's of the N atom of DMNO were evaluated by using the MC/MO method, and the difference in the hydrogen-bonding or non-hydrogen-bonding solvents was reproduced well.…”

Section: Introductionmentioning

confidence: 99%

“…Nitroxide radicals are very popular radicals in various research areas. − ESR spectra of dimethyl nitroxide (DMNO), (CH 3 ) 2 NO, have been observed in H 2 O and CHCl 3 ; , the hyperfine coupling constant (hfcc) of the N atom ( a N ) is larger in H 2 O than in CHCl 3 . Di- tert -butyl nitroxide (DTBN), ((CH 3 ) 3 C) 2 NO, is a stable radical, and its a N value has been determined in various solvents. ,,,− The a N value of DTBN is larger in polar solvents.…”

Section: Introductionmentioning

confidence: 99%

MC/MO Study of the Solvent Effect on the Excitation Energies of the (CH₃)₂NO Radical in Hydrogen-Bonding and Non-Hydrogen-Bonding Solvents

2001

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A combination of Monte Carlo (MC) simulation and ab initio molecular orbital (MO) calculation was applied to dimethyl nitroxide (DMNO) in H 2 O, CH 3 OH, CH 3 CN, and (CH 3 ) 2 CO solutions, and the solvent effect on the electronic structure and n-π* and π-π* excitation energies was analyzed. The solution structures were generated by MC simulations, and the ROHF-SCI calculation with the MIDI-4 basis set was carried out for each solution structure. The electronic structure and excitation energies in the four solutions were obtained by averaging the 100 solution structures for each solution. Solvent effect was calculated by the point charge model and supermolecule model. In the point charge model, all solvent molecules were approximated by point charges at atomic nuclei, while in the supermolecule model the solute molecule and some of the solvent molecules were treated as a supermolecule surrounded by other solvent molecules approximated by point charges. The calculated n-π* excitation energy increased (blue shift) in the four solvents as compared to that in the gas phase. The magnitude of the solvent effect reflects the dielectric constant of the solvent. The calculated E n-π * value in CH 3 OH was larger than that in CH 3 CN, whose dielectric constant is larger than that of CH 3 OH. This is due to the hydrogen-bonding ability of CH 3 OH and agrees well with experiment. The π-π* excitation energy was predicted to decrease in the four solvents, although the red shift was overestimated. The solvent effect was well elucidated by using the Mulliken charges of DMNO in the ground state and the excited states and the electrostatic potential generated by the solvent molecules.

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Comment on ``Paramagnetic Resonance of Alkyl Nitroxides''

Cited by 18 publications

References 5 publications

Further Insights into the Environmental Effects on the Computed Hyperfine Coupling Constants of Nitroxides in Aqueous Solution

Further Insights into the Environmental Effects on the Computed Hyperfine Coupling Constants of Nitroxides in Aqueous Solution

Electron paramagnetic resonance spectroscopic study of nitroxide radicals formed from oximes

MC/MO Study of the Solvent Effect on the Excitation Energies of the (CH₃)₂NO Radical in Hydrogen-Bonding and Non-Hydrogen-Bonding Solvents

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Comment on ``Paramagnetic Resonance of Alkyl Nitroxides''

Cited by 18 publications

References 5 publications

Further Insights into the Environmental Effects on the Computed Hyperfine Coupling Constants of Nitroxides in Aqueous Solution

Further Insights into the Environmental Effects on the Computed Hyperfine Coupling Constants of Nitroxides in Aqueous Solution

Electron paramagnetic resonance spectroscopic study of nitroxide radicals formed from oximes

MC/MO Study of the Solvent Effect on the Excitation Energies of the (CH3)2NO Radical in Hydrogen-Bonding and Non-Hydrogen-Bonding Solvents

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MC/MO Study of the Solvent Effect on the Excitation Energies of the (CH₃)₂NO Radical in Hydrogen-Bonding and Non-Hydrogen-Bonding Solvents