Extension of the AMBER Force Field for Nitroxide Radicals and Combined QM/MM/PCM Approach to the Accurate Determination of EPR Parameters of DMPO-H in Solution

A computational strategy that combines both time-dependent
and time-independent approaches is exploited to accurately model molecular
dynamics and solvent effects on the isotropic hyperfine coupling constants of
the DMPO-H nitroxide. Our recent general force field for nitroxides derived
from AMBER ff99SB is further extended to systems involving hydrogen atoms
in ?-positions with respect to NO-moiety. The resulting force-field has been
employed in a series of classical molecular dynamics simulations, comparing the
computed EPR parameters from selected molecular configurations to the
corresponding experimental data in different solvents. The effect of vibrational
averaging on the spectroscopic parameters is also taken into account, by secondorder
vibrational perturbation theory involving semidiagonal third energy
derivatives together first and second property derivatives.