Electronic structure of alloxan and its dimers: QM/QD simulations and quantum chemical topology analysis.

This study aims to identify the origin of the extra stability of alloxan, a biologically active pyrimidine. To achieve this goal, detailed DFT computations and quantum dynamics simulations have been performed to establish the most stable conformation and the global minimum structure on the alloxan potential energy surface. The effects of the solvent, basis set, and DFT method have been examined to validate the theoretical model adopted throughout the work. Two non-covalent intermolecular dimers of alloxan, the H-bonded and dipolar dimers, have been investigated at the ωB97X-D and M06-2X levels of theory using the triple zeta 6-311++G** to establish their relative stability. Quantum chemical topology features and natural bond orbital analysis (NBO) have been performed to identify and characterize the forces that govern the structures and underlie the extra stability of alloxan.