Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments?

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments?

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments?

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments?

Is Experimental Evidence Sufficient Enough To Account for the Stabilization Effect of Bisnitroxide on the Fate of NMP Experiments

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

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

Supplemental material for Collision-induced dissociation of stable nitroxides: A combined tandem mass spectrometry and computational study of TEMPO^• and SG1^•

Supplemental Material for Collision-induced dissociation of stable nitroxides: A combined tandem mass spectrometry and computational study of TEMPO• and SG1• by Anouk Gaudel-Siri, Cathie Marchal, Vincent Ledentu, Didier Gigmes, Didier Siri and Laurence Charles in European Journal of Mass Spectrometry</p

Structure and Spectromagnetic Properties of the Superoxide Radical Adduct of DMPO in Water: Elucidation by Theoretical Investigations

In the field of spin trapping chemistry, the design of more efficient radical traps can be assisted by the development of theoretical methods able to give a quantitative evaluation of the electron paramagnetic resonance (EPR) spectrum features of the spin-adduct radical, even before initiating the experimental work. The superoxide radical adduct of the 5,5-dimethyl-1-pyrroline-N-oxide nitrone (DMPO−OOH) has been reported in a huge number of papers devoted to the study of the oxidative stress. Here, we present for the first time the theoretical study of DMPO−OOH in an explicit water solution, based on the combined QM/MM//MD protocol we recently proposed, featuring a full coupling between the solute and all the explicit water molecules. Our results show that the DMPO−OOH EPR spectrum, whose interpretation is still debated, can be explained in the light of two sites in chemical exchange, in agreement with the most recent experimental data. Moreover, we demonstrate that each site consists of an equilibrium between the two main 5-membered ring conformations of DMPO−OOH. We provide also an analysis of the solvent contribution to the hyperfine coupling constants (hcc’s) as well as an exhaustive study of the possible relationship between the hcc’s and the main structural characteristics of DMPO−OOH. Our QM/MM//MD protocol appears thus to be an accurate theoretical tool allowing the investigation of the magnetic properties of large nitroxide spin adducts in complex environments

Structure and Spectromagnetic Properties of the Superoxide Radical Adduct of DMPO in Water: Elucidation by Theoretical Investigations

In the field of spin trapping chemistry, the design of more efficient radical traps can be assisted by the development of theoretical methods able to give a quantitative evaluation of the electron paramagnetic resonance (EPR) spectrum features of the spin-adduct radical, even before initiating the experimental work. The superoxide radical adduct of the 5,5-dimethyl-1-pyrroline-N-oxide nitrone (DMPO−OOH) has been reported in a huge number of papers devoted to the study of the oxidative stress. Here, we present for the first time the theoretical study of DMPO−OOH in an explicit water solution, based on the combined QM/MM//MD protocol we recently proposed, featuring a full coupling between the solute and all the explicit water molecules. Our results show that the DMPO−OOH EPR spectrum, whose interpretation is still debated, can be explained in the light of two sites in chemical exchange, in agreement with the most recent experimental data. Moreover, we demonstrate that each site consists of an equilibrium between the two main 5-membered ring conformations of DMPO−OOH. We provide also an analysis of the solvent contribution to the hyperfine coupling constants (hcc’s) as well as an exhaustive study of the possible relationship between the hcc’s and the main structural characteristics of DMPO−OOH. Our QM/MM//MD protocol appears thus to be an accurate theoretical tool allowing the investigation of the magnetic properties of large nitroxide spin adducts in complex environments

Intramolecular Hydrogen Bond in Alkoxyamines. Influence on the C–ON Bond Homolysis

The C–ON bond homolysis in alkoxyamines can be influenced by the presence of an intramolecular hydrogen bond (IHB) between the alkyl and the nitroxyl fragments, which leads to an 8-fold decrease in the homolysis rate constant kd. When the IHB is disrupted by the solvent or by substitution of the hydrogen involved in the IHB by a protecting group (OMe, OAc, OBz, OBn, or OTBDMS), a higher homolysis rate constant kd is observed, as expected from the correlations developed by Marque (Bertin, D.; Gigmes, D.; Marque, S.; Tordo, P. Macromolecules 2005, 38, 2638−2650). Results were confirmed by DFT calculations at the B3LYP/6-31G­(d,p) level

Structure and Spectromagnetic Properties of the Superoxide Radical Adduct of DMPO in Water: Elucidation by Theoretical Investigations

In the field of spin trapping chemistry, the design of more efficient radical traps can be assisted by the development of theoretical methods able to give a quantitative evaluation of the electron paramagnetic resonance (EPR) spectrum features of the spin-adduct radical, even before initiating the experimental work. The superoxide radical adduct of the 5,5-dimethyl-1-pyrroline-N-oxide nitrone (DMPO−OOH) has been reported in a huge number of papers devoted to the study of the oxidative stress. Here, we present for the first time the theoretical study of DMPO−OOH in an explicit water solution, based on the combined QM/MM//MD protocol we recently proposed, featuring a full coupling between the solute and all the explicit water molecules. Our results show that the DMPO−OOH EPR spectrum, whose interpretation is still debated, can be explained in the light of two sites in chemical exchange, in agreement with the most recent experimental data. Moreover, we demonstrate that each site consists of an equilibrium between the two main 5-membered ring conformations of DMPO−OOH. We provide also an analysis of the solvent contribution to the hyperfine coupling constants (hcc’s) as well as an exhaustive study of the possible relationship between the hcc’s and the main structural characteristics of DMPO−OOH. Our QM/MM//MD protocol appears thus to be an accurate theoretical tool allowing the investigation of the magnetic properties of large nitroxide spin adducts in complex environments