ABSTRACT
The acetylation mechanisms of several selected typical substrates from experiments, including arylamines and arylhydrazines, are investigated with the density functional theory in this paper. The results indicate that all the transition states are characterized by a four-membered ring structure, and hydralazine (HDZ) is the most potent substrate. The bioactivity for all the compounds is increased in a sequence of PABA ≈ 4-AS < 4-MA < 5-AS ≈ INH < HDZ. The conjunction effect and the delocalization of the lone pairs of N atom play a key role in the reaction. All the results are consistent with the experimental data.
ABSTRACT
A theoretical study for the water-assisted mechanism in one-carbon unit transfer reaction catalyzed by glycinamide ribonucleotide transformylase (GAR Tfase) is investigated in which the proton transfers in an indirect way and the energy barrier for each transition state has been lowered about 80-100 kJ/mol when compared with the corresponding one in a no-water-involved mechanism. There are two possible pathways in each mechanism: one is concerted and the other is stepwise. Our results have verified the presumption from experiments that one water molecule can assist to achieve the whole reaction. Because the addition of this water molecule in the transition states can relax the strong strain in the unstable system and greatly lowered the energy barrier. The water-assisted paths are preferable to the no-water-involved ones and the bulk solvent effect of water is also discussed.
