Barbituric acid derivative supramolecular assembly as a matrix for oxygen-sensitive photodriven formation of superoxide and carbon-centered radicals

Abstract

Supramolecular system of native barbituric acid and its 1,3-dimethyl derivative with melamine was studied using continuous-wave Q-band EPR spectroscopy. For separation of EPR signals, a special mathematical method was developed and applied. One axial symmetry signal and three singlet signals were detected and interpreted as belonging to superoxide radical and C-centered radicals, correspondingly. Radical activity of the system and predominance of specific radical centers were found to depend on compounds ratio, pH and light irradiation as well as samples storage time and oxygen presence. Quantum chemical calculations were performed to propose the localization of C-centered radicals in both supramolecular systems.