Hydration of DNA bases and compounds containing small rings - A model for interactions of the ricin toxin A-chain. A theoretical ab initio study

Ab initio quantum chemical calculations were performed for four neutral gas phase adenine and four pterin tautomers along with guanine and formycin bases. The water complexes of the lowest energy tautomers of these bases have been studied to mimic their interaction with the ricin toxin A chain (RTA). The water molecules create a full first hydration shell around the bases. Full geometry optimizations without any constraints on the planarity of these hydrated complexes were carried out at the HF/6-31G(d,p) level. Single point calculations were also performed at the correlated MP2/6-31G(d,p)//HF/6-31G(d,p) level of theory. Hydration energies were corrected for the basis set superposition error. Hydration energies of adenine and formycin are predicted to be lower (in magnitude) than those for the pterin and guanine. Due to these properties, two pterin tautomers can be considered as potentially useful inhibitors of RTA.