Quantitative evaluation of the aqueous dihydronitroxide nitrogen hyperfine coupling constant from QM/MM//MD computations

A sequential molecular dynamics + hybrid quantum mechanical/molecular mechanical (QM/MM//MD) approach is presented and applied to the determination of the nitrogen hyperfine coupling constant in the dihydronitroxide radical solvated in water. The model relies on a sophisticated polarizable force-field featuring a many-body hydrogen bond potential, whose parameters have been carefully fitted to QM calculations with special attention paid to the nitrogen out-of-plane angle. It involves also an electronic embedding of the QM subsystem thanks to the ElectroStatic Potential Fitted (ESPF) operator method which is shown to be superior to continuum methods like the polarizable continuum method when anisotropic electrostatic interactions take place between the QM subsystem and its classical surroundings.