Ion−Molecule Reactions of O,S-Dimethyl Methylphosphonothioate: Evidence for Intramolecular Sulfur Oxidation during VX Perhydrolysis

Elucidating the degradation mechanism of the nerve agent A-234 using various detergents: a theoretical investigation

A-234 (ethyl N-[1-(diethylamino)ethylidene]phosphoramidofluoridate) is one of the highly toxic Novichok nerve agents, and its efficient degradation is of significant importance. The possible degradation mechanisms of A-234 by H2O, H2O2, NH3, and their combinations have been extensively investigated by using density functional theory (DFT) calculations. According to the initial intermolecular interaction and the proton transfer patterns between the detergent and the substrate A-234, the A-234 degradation reaction is classified into three categories, denoted as A, B, and C. In modes A and B, the degradation of A-234 by H2O2, H2O, and NH3 is initiated by the nucleophilic attack of the O or N atom of the detergent on the P atom of A-234, coupled with the proton transfer from the detergent to the O or N atom of A-234, whereas in mode C, the direct interaction of H2N-H with the F-P bond of A-234 triggers ammonolysis through a one-step mechanism with the formation of H-F and N-P bonds. Perhydrolysis and hydrolysis of A-234 can be remarkably promoted by introducing the auxiliary NH3, and the timely formed hydrogen bond network among detergent, auxiliary, and substrate molecules is responsible for the enhancement of degradation efficiency.

Theoretical study of gas-phase detoxication of DMMP and DMPT using ammonia-borane and its analogous compound

The detoxication of DMMP (Dimethyl methylphosphonate) and DMPT (O, S-dimethyl methylphosphonothiolate) via hydrogenation have been investigated computationally employing density functional theory (DFT). In this present study, we aim to explore the direct molecular H₂ assisted as well as ammonia-borane (NH₃BH₃) and 3-methyl-1,2-BN-cyclopentane (denoted as cy-AB) assisted hydrogenation pathways of DMMP and DMPT in order to detoxify them. The detoxication of DMMP has been carried out by successive elimination of two -OMe groups. However, in the case of DMPT, two possibilities have been identified because of two different substituents, -OMe and -SMe. In possibility-I, the elimination of the -OMe group occurs at the beginning, followed by the -SMe group, whereas in possibility-II, the reverse order of elimination occurs for -OMe and -SMe groups. During the detoxication of DMMP using both NH₃BH₃ and cy-AB as the assisting reagents, the first step has been identified as the rate-determining step (RDS) in which the hydrogens attached to the N- and B-centers of NH₃BH₃ are transferred to the O-center of PO and P-center, respectively. In harmony with DMMP detoxication, for DMPT also, analyzing the activation barriers, it can be articulated that for both NH₃BH₃ and cy-AB assisted pathways, both the possibilities are equally feasible as in both the possibilities the common first step is the RDS. Therefore, our computational study is designed to explore the assisting efficiency of NH₃BH₃ and its cyclic analogue for detoxifying the OPCs.

A versatile and recyclable molecularly imprinted polymer as an oxidative catalyst of sulfur derivatives: a new possible method for mustard gas and V nerve agent decontamination

A molecularly imprinted polymer containing a porphyrin unit was developed as a biomimetic heterogenous catalyst for the oxidation of sulfur derivatives. Its catalytic efficiency under mild conditions and its easy recovery represent a great asset for the design of new decontamination tools for yperite and VX.

Synthesis and in vivo antitumor evaluation of an orally active potent phosphonamidate derivative targeting IDO1/IDO2/TDO

Targeting Trp-Kyn pathways has been identified as an attractive approach for the cancer immunotherapies. In this study, a novel phosphonamidate containing compound was designed, synthesized and evaluated for its inhibitory activity against key dioxygenases in Trp-Kyn pathway, including IDO1, IDO2 and TDO. This compound showed potent IDO1 inhibitory activity with an IC₅₀ value of 94 nM in an enzymatic assay and 12.6 nM in HeLa cells. In addition, this compound showed promising IDO2 inhibition and TDO inhibition with IC₅₀ values of 310 nM and 2.6 μM, respectively, in enzyme assay. Based on the promising enzyme inhibitory activity toward IDO/TDO, compound F04 was evaluated of its antitumor effects in two tumor models. Further evaluation of mechanism demonstrated compound F04 with the remarkable capacity of reducing kynurenine level in plasma/TME and restoring anti-tumor immune response. F04 could be further developed as a potential immunotherapeutic agent combined with immune checkpoint inhibitors or chemotherapeutic drugs for cancer treatment.

Microsolvation effects on the reactivity of oxy-nucleophiles: the case of gas-phase SN2 reactions of YO-(CH3OH) n=1,2 towards CH3Cl

The modified G4(MP2) method was applied to explore microsolvation effects on the reactivity of four solvated normal oxy-nucleophiles YO^-(CH₃OH) _n=1,2 (Y = CH₃, C₂H₅, FC₂H₄, ClC₂H₄), and five α-oxy-nucleophiles YO^-(CH₃OH) _n=1,2 (Y = HO, CH₃O, F, Cl, Br), in gas-phase S_N2 reactions towards the substrate CH₃Cl. Based on a Brønsted-type plot, our calculations reveal that the overall activation barriers of five microsolvated α-oxy-nucleophiles are obviously smaller than the prediction from the correlation line constructed by four normal microsolvated ones to different degrees, and clearly demonstrate the existence of an α-effect in the presence of one or two methanol molecule(s). Moreover, it was found that the α-effect of the mono-methanol microsolvated α-nucleophile is stronger than that of the monohydrated α-nucleophile. However, the α-effect of YO^-(CH₃OH)₂ becomes weaker for Y = HO and CH₃O, whereas it becomes stronger for Y = F, Cl, Br than that of YO^-(H₂O)₂, which can be explained by analyses of the activation strain model in the two cases. It was also found that the rationale about the low ionization energy of α-nucleophile inducing the α-effect was not widely significant. Graphical abstract Variation of alpha-effect in the gas-phase S_N2 reaction with the microsolvation.

The α-effect and competing mechanisms: the gas-phase reactions of microsolvated anions with methyl formate

The enhanced reactivity of α-nucleophiles, which contain an electron lone pair adjacent to the reactive site, has been demonstrated in solution and in the gas phase and, recently, for the gas-phase S(N)2 reactions of the microsolvated HOO(-)(H2O) ion with methyl chloride. In the present work, we continue to explore the significance of microsolvation on the α-effect as we compare the gas-phase reactivity of the microsolvated α-nucleophile HOO(-)(H2O) with that of microsolvated normal alkoxy nucleophiles, RO(-)(H2O), in reactions with methyl formate, where three competing reactions are possible. The results reveal enhanced reactivity of HOO(-)(H2O) towards methyl formate, and clearly demonstrate the presence of an overall α-effect for the reactions of the microsolvated α-nucleophile. The association of the nucleophiles with a single water molecule significantly lowers the degree of proton abstraction and increases the S(N)2 and B(AC)2 reactivity compared with the unsolvated analogs. HOO(-)(H2O) reacts with methyl formate exclusively via the B(AC)2 channel. While microsolvation lowers the overall reaction efficiency, it enhances the B(AC)2 reaction efficiency for all anions compared with the unsolvated analogs. This may be explained by participation of the solvent water molecule in the B(AC)2 reaction in a way that continuously stabilizes the negative charge throughout the reaction.

The α-effect exhibited in gas-phase S(N)2@N and S(N)2@C reactions

In order to explore the existence of α-effect in gas-phase S(N)2@N reactions, and to compare its similarity and difference with its counterpart in S(N)2@C reactions, we have carried out a theoretical study on the reactivity of six α-oxy-Nus (FO(-), ClO(-), BrO(-), HOO(-), HSO(-), H2NO(-)) in the S(N)2 reactions toward NR2Cl (R = H, Me) and RCl (R = Me, i-Pr) using the G2(+)M theory. An enhanced reactivity induced by the α-atom is found in all examined systems. The magnitude of the α-effect in the reactions of NR2Cl (R = H, Me) is generally smaller than that in the corresponding S(N)2 reaction, but their variation trend with the identity of α-atom is very similar. The origin of the α-effect of the S(N)2@N reactions is discussed in terms of activation strain analysis and thermodynamic analysis, indicating that the α-effect in the S(N)2@N reactions largely arises from transition state stabilization, and the "hyper-reactivity" of these α-Nus is also accompanied by an enhanced thermodynamic stability of products from the n(N) → σ*(O-Y) negative hyperconjugation. Meanwhile, it is found that the reactivity of oxy-Nus in the S(N)2 reactions toward NMe2Cl is lower than toward i-PrCl, which is different from previous experiments, that is, the S(N)2 reactions of NH2Cl is more facile than MeCl.

Gas chromatographic-ion trap mass spectrometric analysis of volatile organic compounds by ion-molecule reactions using the electron-deficient reagent ion CCl3(+)

When using tetrachloromethane as the reagent gas in gas chromatography-ion trap mass spectrometry equipped with hybrid ionization source, the cation CCl(3)(+) was generated in high abundance and further gas-phase experiments showed that such an electron-deficient reagent ion CCl(3)(+) could undergo interesting ion-molecule reactions with various volatile organic compounds, which not only present some informative gas-phase reactions, but also facilitate qualitative analysis of diverse volatile compounds by providing unique mass spectral data that are characteristic of particular chemical structures. The ion-molecule reactions of the reagent ion CCl(3)(+) with different types of compounds were studied, and results showed that such reactions could give rise to structurally diagnostic ions, such as [M+CCl(3) - HCl](+) for aromatic hydrocarbons, [M - OH](+) for saturated cyclic ether, ketone, and alcoholic compounds, [M - H](+) ion for monoterpenes, M(·+) for sesquiterpenes, [M - CH(3)CO](+) for esters, as well as the further fragment ions. The mechanisms of ion-molecule reactions of aromatic hydrocarbons, aliphatic ketones and alcoholic compounds with the reagent ion CCl(3)(+) were investigated and proposed according to the information provided by MS/MS experiments and theoretical calculations. Then, this method was applied to study volatile organic compounds in Dendranthema indicum var. aromaticum and 20 compounds, including monoterpenes and their oxygen-containing derivatives, aromatic hydrocarbon and sesquiterpenes were identified using such ion-molecule reactions. This study offers a perspective and an alternative tool for the analysis and identification of various volatile compounds.

Rapid monitoring of sulfur mustard degradation in solution by headspace solid-phase microextraction sampling and gas chromatography mass spectrometry

A method using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography/mass spectrometry (GC/MS) analysis has been developed to gain insight into the degradation of the chemical warfare agent sulfur mustard in solution. Specifically, the described approach simplifies the sample preparation for GC/MS analysis to provide a rapid determination of changes in sulfur mustard abundance. These results were found to be consistent with those obtained using liquid-liquid extraction (LLE) GC/MS. The utility of the described approach was further demonstrated by the investigation of the degradation process in a complex matrix with surfactant added to assist solvation of sulfur mustard. A more rapid reduction in sulfur mustard abundance was observed using the HS-SPME approach with surfactant present and was similar to results from LLE experiments. Significantly, this study demonstrates that HS-SPME can simplify the sample preparation for GC/MS analysis to monitor changes in sulfur mustard abundance in solution more rapidly, and with less solvent and reagent usage than LLE.

Enhanced reactivity of RC[triple bond]CZ- (R = H and Cl; Z = O, S, and Se) and the influence of leaving group on the alpha-effect in the E2 reactions

The enhanced reactivity exhibited by six pseudo-alpha-bases, RC[triple bond]CZ(-) (R = H and Cl; Z = O, S, and Se) in gas-phase E2 reactions with ethyl chloride was examined at the G2(+) level. It is found that anomalous reactivity is observed despite the fact that these chalcogen bases do not possess adjacent lone-pair electrons. The influence of the halide leaving groups on the alpha-effect and the origin of the alpha-effect in the E2 reactions of ethyl halides are investigated and discussed.