The organophosphorous compound tabun is highly neurotoxic because of its irreversible inhibition on acetylcholinesterase (AChE). It is wildly used as a warfare agent in the military. In this work, the aging and reactivation mechanism of tabun-inhibited AChE were studied by using the quantum mechanical / molecular mechanical (QM/MM) method. Geometry optimization of the stationary points were performed at the B3LYP/6–31G(d) level. Single-point energies were computed at the B3LYP/6–311++G(d,p) level. On the basis of the QM/MM results, a conclusion that the C–O bond scission is caused by water attack on the ethoxy group in the aging mechanism can be drawn. The reactivation process initialed by the antidotes CH2NO– or HLÖ-7 consists of three elemental steps, the nucleophilic attack on the P atom by the antidote, the dephosphorylation process, and the decomposition of the antidote–tabun complex. The highest energy barriers of the aging reaction, CH2NO–-induced reactivation, and HLÖ-7-induced reactivation are 19.9, 20.0, and 14.8 kcal/mol (1 cal = 4.184 J), respectively. The relative lower overall energy barrier of HLÖ-7-induced reactivation compared with that of the aging reaction indicates that HLÖ-7 is able to reactivate tabun-inhibited AChE. In addition, whether a newly designed antidote is able to reactivate tabun-inhibited AChE can be examined by the inequation X < 19.9 kcal/mol,where X means the highest energy barrier of the reactivation reaction of the newly designed antidote.

As a common pharmaceutical and personal care product, ibuprofen (IBP) is regarded as an important pollutant in aqueous environments. In this paper, the OH-initiated advanced oxidation processes (AOPs) degradation mechanism and its subsequent reaction mechanism with IBP were studied at the M06-2x/6-311++G(2d, p)//M06-2x/6-31+G(d,p) level. The frontier electron density and bond dissociation energy were analyzed. In addition, profiles of the potential energy surface were constructed, and all the possible pathways were discussed. H-atom abstraction is the most important mechanism. The dominant products were IBAP, 2-[4-(1-hydroxyisobutyl)phenyl]propionic acid, and 1-(4-isobutylphenyl)-1-ethanol, which is in good agreement with the experimental results.

The mechanism for OH radical initiated atmospheric photoxidation reaction of ethyl acetate was carried out by using the density functional theory method. Geometries have been optimized at the B3LYP level with a standard 6-31G(d,p) basis set. The single-point energy calculations have been performed at the MP2/6-31G(d), MP2/6-311++G(d,p), and CCSD(T)/6-31G(d) levels, respectively. All of the possible degradation channels involved in the oxidation of ethyl acetate by OH radicals have been presented and discussed. Among the five possible hydrogen abstraction pathways of the reaction of ethyl acetate with OH radicals, the hydrogen abstractions from the C1-H3 and C2-H5 bonds are the dominant reaction pathways due to the low potential barriers and strong exothermicity. The ␤-ester rearrangement of IM6 is energetically favorable but is not expected to be important. The ␣-ester rearrangement reaction and O 2 direct abstraction from IM17 are the more favorable pathways and are strongly competitive. In addition, the ␣-ester rearrangement reaction is confirmed to be a one-step process. Acetic acid, formic acetic anhydride, acetoxyacetaldehyde, and acetic anhydride are the main products for the reaction of ethyl acetate with OH radicals.

Diethyl phthalate (1,2-benzenedicarboxylic acid diethyl ester, DEP) is one of a group of widely used plasticizers, which can lead to serious environmental problems. Because of manufacturing and application, DEP can be released into the atmosphere where it can undergo transport and chemical transformation. To assess the atmospheric behavior of pollutants, it is critical to know their atmospheric reactions. In this paper, the reaction mechanism and possible oxidation products for the OH-initiated atmospheric reaction of DEP were theoretically investigated by using the density functional theory (DFT) method. The geometries and frequencies of the reactants, intermediates, transition states, and products were calculated at the MPWB1K/6–31+G(d,p) level, and the energetic parameters were further refined by the MPWB1K/6–311+G(3df,2p) method. The present study shows that H abstractions from the CH3 and CH2 groups, as well as OH addition to the benzene ring, are energetically favorable reaction pathways for the reaction of DEP with OH radicals. Detailed degradation products are provided.