Theoretical investigation on proton transfer mechanism of hydrated melamine

The proton transfer (PT) involved in hydrated melamine has been investigated employing the B3LYP/6-311++G∗∗ basis set level. The energy barriers demonstrate that the water molecules can significantly accelerate the PT involved in melamine. The influence of the water number in the first shell on single PT process is in the order: 0 < 3 < 1 < 2, where the water molecules are those directly participating in the PT process. The side water molecule attached to the water chain can also significantly lower the potential barriers of PT. The influence of the water number in the second shell on single PT process is in the order 0 < 1 < 4 < 2 < 3. Here, the water molecules in the second shell are not involved in the single PT process. The energy barriers of three PT steps are reduced gradually when the reactant is in symmetrical structure initially. The optimal condition for PT in hydrated melamine is the two-water contained first-shell chain with two side water molecules attached to them.