Hydrated Melamine Proton Transfer Mechanism In Theoretical Research

Recently, the frequent occurrence of renal failure caused by melamine has attracted more and more attention. Melamine is commonly used in industrial production and food production to increase the apparent protein content. In fact, melamine is harmless, while when it is combined with cyanuric acid (CA) through H-bonds in 1:1 ratio, the insoluble crystal sediment comes into being eventually and damages renal tubules, leading to renal failure ultimately.Hydrogen bond plays a key role in determining the configurations, properties, and functions of biomolecules. As a major contributor to the architecture of many molecules, particularly biomolecules, the studies of hydrogen bonds are of great importance. Two types of H-bonds, N-H…O and O-H…N, are formed between melamine and water. Therefore, water molecules are prone to form a series of hydrogen compounds with melamine molecules.Previous studies have found that the energy barrier of the proton transfer (PT) is greatly reduced with assistant of the water chain. Recently, the coupled models between water and biomolecules and the function of water chain as a protective or assistant unit in PT process have been an active area of investigation. Unfortunately, the studies on this area about melamine have not been reported up to now. Therefore, the focus of this investigation is placed on the PT mechanism of melamine and the corresponding hydrates. It is believed that the resolution of these questions plays a vital role in both chemical and biological.In this paper, B3LYP density functional theory method is performed at the 6-311++G** level in order to investigate the PT mechanism involved in hydrated melamine. The comparison of energy barriers demonstrates 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.