Ab Initio Molecular Dynamics Simulations and g-Tensor Calculations of Aqueous Benzosemiquinone Radical Anion:  Effects of Regular and “T-Stacked” Hydrogen Bonds

Asher, James R.; Doltsinis, Nikos L.; Kaupp, Martin

doi:10.1021/ja0485053

Cited by 58 publications

(66 citation statements)

References 43 publications

(127 reference statements)

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“…Such an effect is in agreement with calculations by O'Malley [11] who used a cluster model to describe H-bond donation at site O2. Similar redistribution of spin density has been found for the phenoxyl radical in aqueous solution [14] and semiquinones [18]. When considering the spin localization on the three different sites O1+C1, O2+C2 and O3+C3, we notice a small spin transfer in going from vacuum to solution.…”

Section: Methodssupporting

confidence: 81%

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Ab initio molecular dynamics study of ascorbic acid in aqueous solution

et al. 2007

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Section: Methodssupporting

confidence: 81%

“…It is not clear to what extent this effect is reflected in the molecular spin density. This question has been recently addressed in an ab initio molecular dynamics (MD) study of the benzoquinone radical anion in aqueous solution [18].…”

Section: Introductionmentioning

confidence: 99%

Ab initio molecular dynamics study of ascorbic acid in aqueous solution

et al. 2007

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“…However, for smaller water shells than used here, calculations with fully converged solute-solvent clusters have been presented. 50 In Ref. 22, it has been shown that the simpler LDA can be used for the frozen part, and that it is advantageous to calculate the frozen density from a superposition of molecular densities.…”

Section: Validation Of the Solvent Modelmentioning

confidence: 99%

Modeling solvent effects on electron-spin-resonance hyperfine couplings by frozen-density embedding

Neugebauer

Louwerse

Belanzoni

et al. 2005

The Journal of Chemical Physics

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In this study, we investigate the performance of the frozen-density embedding scheme within density-functional theory ͓J. Phys. Chem. 97, 8050 ͑1993͔͒ to model the solvent effects on the electron-spin-resonance hyperfine coupling constants ͑hfcc's͒ of the H 2 NO molecule. The hfcc's for this molecule depend critically on the out-of-plane bending angle of the NO bond from the molecular plane. Therefore, solvent effects can have an influence on both the electronic structure for a given configuration of solute and solvent molecules and on the probability for different solute ͑plus solvent͒ structures compared to the gas phase. For an accurate modeling of dynamic effects in solution, we employ the Car-Parrinello molecular-dynamics ͑CPMD͒ approach. A first-principles-based Monte Carlo scheme is used for the gas-phase simulation, in order to avoid problems in the thermal equilibration for this small molecule. Calculations of small H 2 NO-water clusters show that microsolvation effects of water molecules due to hydrogen bonding can be reproduced by frozen-density embedding calculations. Even simple sum-of-molecular-densities approaches for the frozen density lead to good results. This allows us to include also bulk solvent effects by performing frozen-density calculations with many explicit water molecules for snapshots from the CPMD simulation. The electronic effect of the solvent at a given structure is reproduced by the frozen-density embedding. Dynamic structural effects in solution are found to be similar to the gas phase. But the small differences in the average structures still induce significant changes in the computed shifts due to the strong dependence of the hyperfine coupling constants on the out-of-plane bending angle.

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“…[24] These observations most likely indicate that H-bonding induces a redistribution of the electron spin density, as demonstrated earlier by Lucarini et al [26] Interestingly, the relatively large Dg iso shift of 0.0003-0.0004 between the signal of the non-hydrogen-bonded NMe2 LC (g = 2.0046) and that of NHOH LC (g = 2.0043) or NHMe LC (g = 2.0042) is consistent with the latter two radicals being H-bonded phenoxyl radicals. Indeed, theoretical [27][28][29][30] and experimental studies [6,7,[31][32][33] have indicated that hydrogen bonding to a phenoxyl (or Tyr) radical results in a considerable lowering of the g x value but leaves g y and g z essentially unaffected. Thus, assuming that g y and g z are the same for all RR' LC, a Dg x shift of 0.0012-0.0016 (3Dg iso ) is obtained.…”

mentioning

confidence: 99%

Persistent Hydrogen‐Bonded and Non‐Hydrogen‐Bonded Phenoxyl Radicals

Wanke¹,

Bénisvy

Kuznetsov³

et al. 2011

Chemistry A European J

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The production of stable phenoxyl radicals is undoubtedly a synthetic chemical challenge. Yet it is a useful way to gain information on the properties of the biological tyrosyl radicals. Recently, several persistent phenoxyl radicals have been reported, but only limited synthetic variations could be achieved. Herein, we show that the amide-o-substituted phenoxyl radical (i.e. with a salicylamide backbone) can be synthesised in a stable manner, thereby permitting easy synthetic modifications to be made through the amide bond. To study the effect of H-bonding on the properties of the phenolate/phenoxyl radical redox couple, simple H-bonded and non-H-bonded o,p-tBu-protected salicylamidate compounds have been prepared. Their redox properties were examined by cyclic voltammetry and showed a fully reversible one-electron oxidation process to the corresponding phenoxyl radical species. Remarkably, the redox potential appears to be correlated, at least partially, with H-bond strength, as relatively large differences (ca. 300 mV) in the redox potential between H-bonded and non-H-bonded phenolate salts are observed. The corresponding phenoxyl radicals produced electrochemically are persistent at room temperature for at least an hour; their UV/Vis and EPR characterisation is consistent with that of phenoxyl radicals, which makes them excellent models of biological tyrosyl radicals. The analyses of the experimental data coupled with theoretical calculations indicate that both the deviation from planarity of the amide function and intramolecular H-bonding influence the oxidation potential of the phenolate. The latter H-bonding effect appears to be predominantly exerted on the phenolate and not (or only a little) on the phenoxyl radical. Thus, in these systems the H-bonding energy involved in the phenoxyl radical appears to be relatively small.

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Ab Initio Molecular Dynamics Simulations and g-Tensor Calculations of Aqueous Benzosemiquinone Radical Anion: Effects of Regular and “T-Stacked” Hydrogen Bonds

Cited by 58 publications

References 43 publications

Ab initio molecular dynamics study of ascorbic acid in aqueous solution

Ab initio molecular dynamics study of ascorbic acid in aqueous solution

Modeling solvent effects on electron-spin-resonance hyperfine couplings by frozen-density embedding

Persistent Hydrogen‐Bonded and Non‐Hydrogen‐Bonded Phenoxyl Radicals

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