PNNL

Abstract

We report the first computational study of the chromophores responsible for the chromogenic effect of aromatic neurotoxicants containing a 1,2-diacetyl moiety in their oxidation metabolites. A series of ab initio electronic strucure calculations were performed on two representative aromatic compounds, 1,2-diecetylbenzene (1,2-DAB) and 1,2-diacetyl tetramethyltetralin (1,2-DATT), the metabolites of the widely used neurotoxic aromatic hydrocarbon solvents 1,2-diethylbenzene (1,2-DEB) and acetyl ethyl tetramethyl tetralin (AETT), and products of possible reactions which could lead to chromogenic effects. The electronic excitation energies determined by three different computational approaches are all consistent with each other. The calculated results are consistent with the conclusion/prediction that the chromogenic effects of 1,2-DAB (or 1,2-DEB) and 1,2-DATT (or AETT) are due to the ninhydrin-like reactions, rather than the formation of pyrrole-like compounds. Our pKa calculations further indicate that the chromophore, i.e. the product of the ninhydrin-like reaction, showing the blue color is deprotonated in nuetral aqueous solution, whereas the corresponding protonated strucure has a different color and its chromogenic contribution could be significant in solution at lower pH. In acidic solutions, the protonated structure could be dominant and the chromophore could show a different color.