Do the fragments from decomposed ZIF-8 greatly affect some of the intramolecular proton-transfer of thymine? A quantum chemical study.

The intramolecular proton-transfer processes of thymine were investigated by the density functional theory method. It is shown that the mutation from keto (T) to enol (T') form is affected by zeolitic imidazolate framework-8 (ZIF-8) fragments such as single 2-methylimidazole neutral crystals (M), and negatively charged 2-methylimidazole ligands (M). Results show that with the number () of water (w) molecules that assist proton-transfer increasing from 1 to 4, the order of the tautomeric energy barriers (in kcal mol) is T-2w (16.3) < T-1w (17.6) < T-3w (17.8) < T-4w (20.5). In the presence of M, the order of energy barrier is MT-2w (16.6) < MT-1w (17.7) < MT-3w (18.9) < MT-4w (20.8). M has a catalysis effect on the energy barrier and the order is MT-2w (14.4) < MT-3w (15.2) < MT-1w (16.3) < MT-4w (16.8). The attachment of the M fragment slightly promotes the proton-transfer processes in some instances. The characterization of the proton-transfer processes is helpful to understand the genotoxicity of ZIF-8 during drug delivery applications.