In this work, we present an extensive investigation of the radiation-induced +NH3−•CH−CO2- glycine radical, using ab initio density functional modeling. The geometry and electron paramagnetic resonance (EPR) characteristics of the radical have been calculated using several model space approaches, including a single molecule approach, cluster models, and periodic calculations. Consecutively, both the calculated structural and spectroscopic properties are compared with experimental values taken from the literature. This comparative study involves the reproduction of the hyperfine coupling constants and the principal directions of the hyperfine tensor. It is found that the accurate calculation of these two features represents a sensitive probe for the accuracy of the proposed methodology to describe the glycine radical. The best overall agreement with experimental EPR parameters is found for a cluster calculation, in which the molecular environment surrounding the radical was explicitly taken into account, not only for the geometry optimization but also for the calculation of the spectroscopic properties. In the case of the +NH3−•CH−CO2- glycine radical, apparently, the magnetic properties are indeed affected by the crystal environment.
Abstract