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.
Houriez
Céline
C
UMR 6264 Laboratoire Chimie Provence, Faculté des Sciences de Saint-Jérome Case 521, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France.
Ferré
Nicolas
N
Siri
Didier
D
Tordo
Paul
P
Masella
Michel
M
D003198:Computer Simulation; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D006860:Hydrogen Bonding; D008962:Models, Theoretical; D015394:Molecular Structure; D013113:Spin Labels; D013481:Superoxides / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D003497:Cyclic N-Oxides; D013113:Spin Labels; D014867:Water; D013481:Superoxides; C017245:5,5-dimethyl-1-pyrroline-1-oxide