Decomposition of triazole and 3-nitrotriazole upon low-energy electron attachment

Compounds based on nitrotriazole have been studied for their application as potential radiosensitizers for the treatment of tumors and as energetic materials. In the former application, the initial reduction of the compounds may serve as a mechanism which leads to the formation of tumor-active species. In this study, we investigated the fundamental properties of anion formation in isolated 3-nitro-1,2,4-triazole (3NTR) molecules upon attachment of low-energy electrons. The resulting product anions formed were detected via mass spectrometry. Quantum chemical calculations were performed to study the dissociation pathways and to derive the threshold energies. We also studied the attachment of electrons to the native 1H-1,2,4-triazole (TR) molecule, revealing the influence of the nitro group on anion formation. Comparing the results for these two systems, we computationally observed a considerable more stable parent anion for 3NTR, which results in significantly more effective degradation of the molecule at lower electron energies. Although characteristic fragmentation reactions in the presence of the nitro group were observed (like formation of NO₂^- or the release of an OH radical), the main dissociation channel for the 3NTR anion turned out to be the direct dissociation of a hydrogen radical by a single bond cleavage, which we also observed for TR as the main channel. Thus, the triazole ring shows a pronounced stability against electron attachment-induced cleavage compared, for example, to the imidazole ring, which is found in common nitroimidazolic radiosensitizers.