Theoretical Study Of The Hydrated Cyanuric Acid Proton Transfer Mechanism

On the basis of the reliable B3LYP/6-311++G** basis set level, the solubility, stability, and proton transfer mechanism of cyanuric acid are disscussed in this work. The main purpose is to investigate the effect of the water molecule on cyanuric acid system.First, in order to resolve the above problems, many coupling modes of cyanuric acid with water molecule are designed. Two most stable cyanuric acid isomers (keto and enolic form) are chosen to investigate the tautomeric process of cyanuric acid. In fact, the tautomeric process of cyanuric acid is an intramolecular proton transfer reaction. In this work we design and optimize a lot of coupling modes for hydrated cyanuric acid system. Based on the same level, the water-assisted proton transfer processes of cyanuric acid are explored. Results reveal that water molecules hold an assisting effect on the proton transfer process. The first water molecule adding to cyanuric acid monomer donates the strongest assisting effect compared with the subsequent water molecules. But the assisting effect is not always enhanced with the number of water molecules increased. Two water molecules in the hydrated systems are proved to be the optimal number in assisting the proton transfer. Analysis also reveals that two-shell structure is in favor of proton transfer. The formation of the water cluster with two water molecules in the second shell is the most favorable for proton transfer. Detailed structural parameters and energy changes are discussed for different proton transfer processes.To further explore the proton transfer mechanism of cyanuric acid, the effect of another cyanuric acid molecule is also considered, so the cyanuric acid dimer is also investigated in our work. Results illustrates that the second cyanuric acid molecule can make the system more stable. Using the same method, we design the coupling modes of the dimer of cyanuric acid with water molecule and optimize them. Compared with cyanuric acid monomer, the effect of water molecule to the dimer of cyanuric acid molecule is similar. There are some low-barrier hydrogen bonds in the dimer of cyanuric acid system. The water molecules can also assist the proton transfer process of low-barrier hydrogen bonds.