Mechanistic and spectral investigation on the deamination of ammeline and ammelide

Melamine and its metabolites: ammeline, ammelide, and cyanuric acid have attracted great attention as food contaminants. They are added illegally to milk to increase the protein content. Melamine combined with cyanuric acid causes kidney stones, renal toxicity, and kidney failure. The deamination reactions of ammeline and ammelide that producing cyanuric acid are studied both in a vacuum and aqueous solution using the (SMD) solvation model. For both deamination reactions, a two-step mechanism is formed: a nucleophilic addition yielding a tetrahedral intermediate that followed by a 1,3-proton shift to form products. The overall activation energies for deamination of ammeline with 3H(2)O/OH- are 135, 121, 112, and 100 kJ mol(-1) calculated in the vacuum by B3LYP, M06, M06-2X, and APFD combined with the 6-31G(d) basis set, respectively, and 129 kJ mol(-1) calculated at G4MP2 level of theory. In comparison, the deamination reaction of ammelide shows lower energy barriers at all levels of theory (with the lowest values of 61 kJ mol(-1) calculated at APFD/6-31G(d)). In addition, UV, IR, and C-13 NMR spectral studies are performed and compared with the literature values. (C) 2017 Elsevier B.V. All rights reserved.