Determination of molecular force field parameters for nitronyl nitroxide derivatives using quantum chemical calculations

The molecular force field plays an important role in molecular design. The force field parameters of small molecules were obtained by applying quantum chemical calculations on a limited number of compounds. However, force field parameters for atypical compounds such as organic radicals have not been obtained yet. In this study, the energy profiles covering conformational changes of nitronyl nitroxide derivatives are calculated using quantum chemical calculations, and the force field parameters are obtained by curve fitting of the energy profiles. For calculating energy curves, we applied the hybrid density functional theory; the atomic charges of the test compounds were calculated based on the restricted electrostatic potential method. As the nitronyl nitroxide derivatives are considered to have great potential applications in biological sciences, the determined parameters are expected to be useful for the molecular design of organic radicals.