DFT investigation of nitrenium ions derived from metabolism of antitumor 2-(4-aminophenyl)benzothiazoles

Ab initio molecular orbital computation has been performed to study the electronic structure, substituent and solvent effects on the singlet-triplet gaps of a series of nitrenium ions. DFT calculations at the B3LYP/6-311++G** level of theory predict that, the nitrenium ions derived from the metabolism of the antitumor 2-(4-aminophenyl)benzothiazoles exist in the ground singlet state. The preferential stabilization of the singlet state relative to the triplet is due to the transfer of charge density from the phenyl ring to formally electron deficient nitrogen atom. Calculations in solution were carried out using the PCM model. Solvent-solute interaction energies were estimated and reflect a considerable net stabilization of the triplet species at the PCM model. Fourier transform analysis of the internal rotation potential energy function, around the exocyclic bond (C4-N), has been performed for niternium ions studied. The magnitudes and origin of the potential energy barriers have been discussed.