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Global concern exists regarding the contamination of food and animal feed with aflatoxin B 1 (AFB 1), which poses a threat to the health of both humans and animals. Previously, we found that a laccase from Bacillus subtilis (Bs CotA) effectively detoxified AFB 1 in a reaction mediated by methyl syringate (MS), although the underlying mechanism has not been determined. Therefore, our primary objective of this study was to explore the detoxification mechanism employed by Bs CotA. First, the enzyme and mediator dependence of AFB 1 transformation were studied using the Bs CotA-MS system, which revealed the importance of MS radical formation during the oxidation process. Aflatoxin Q 1 (AFQ 1) resulting from the direct oxidation of AFB 1 by Bs CotA, was identified using ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results of UPLC-MS/MS and density functional theory calculations indicated that the products included AFQ 1 , AFB 1 -, and AFD 1 -MS-coupled products in the Bs CotA-MS system. The toxicity evaluations revealed that the substances derived from the transformation of AFB 1 through the Bs CotA-MS mechanism exhibited markedly reduced toxicity compared to AFB 1. Finally, we proposed a set of different AFB 1 -transformation pathways generated by the Bs CotA-MS system based on the identified products. These findings greatly enhance the understanding of the AFB 1 -transformation mechanism of the laccase-mediator system. [Display omitted] • AFB 1 can be transformed by Bs CotA both in the presence or absence of a mediator. • AFB 1 was directly converted to AFQ 1 by Bs CotA. • Coupling reactions occurred between AFB 1 and MS radical. • The identified products exhibit lower toxicity levels than AFB 1. [ABSTRACT FROM AUTHOR]

Photocatalysis provides a sustainable way for NOx elimination. However, efficient and safe photocatalytic removal of NOx remain a great challenge due to the limited light-harvesting ability and quick recombination of charge carriers. Herein, holey sulfur-doped g-C 3 N 4 nanosheets (CNN–S) was reported by directly calcining a mixture of hydrolyzed dicyandiamide and thioacetamide. The specific surface area of the pristine g-C 3 N 4 nanosheets (CNN–S0) is 3–4 times higher than bulk g-C 3 N 4 (BCN), and the photocatalytic NO removal rate also increased from 17% (BCN) to 35% (CNN–S0). The effect of sulfur content on the photocatalytic performance was systematic studied, and CNN–S0.5 sample exhibits the highest NO removal rate (53%). The high photoreactivity of S-doped g-C 3 N 4 nanosheets can be attributed to enhanced visible light absorption, increased specific surface area, and effective separation and transfer of photo-generated charges owing to the synergistic effect of the nanosheet structure and sulfur doping. In addition, density functional theory calculations show that the doping of S is also beneficial to the adsorption and activation of the reactants on CN. [Display omitted] • Holey S-doped sheet-like g-C 3 N 4 was prepared by calcining the mixture of hydrolyzed dicyandiamide and thioacetamide. • Doping g-C 3 N 4 nanosheets with S greatly improves the light harvesting ability. • The BET surface area of S-doped g-C 3 N 4 nanosheets is 3 times larger than that of bulk g-C 3 N 4. • S-doped g-C 3 N 4 nanosheets exhibit enhanced photocatalytic activity towards NO oxidation. [ABSTRACT FROM AUTHOR]

Possible mechanisms of copper-catalyzed N–H/C–H activation from N-phenylbenzamidine to 2-phenylbenzimidazole have been investigated using density functional theory (DFT) calculations. In comparison with the C–H activation mechanism, the N–H/C–H activation with a Cu-assisted concerted metalation–deprotonation (CMD) mechanism is found to be more kinetically favorable. Facile occurrence of the studied reactions is supported by the low activation energies of their respective rate-determining steps. A possible alternative mechanism involving a Cu–H agostic transition state is presented, but it is unfavored by the relatively higher activation barriers. [ABSTRACT FROM AUTHOR]

The catalytic dehydrogenation of ammonia borane (NH 3 BH 3 ) with the Ir pincer complex, [Ir(I t Bu′) 2 ] + , has been investigated by density functional theory (DFT). A mechanism has been proposed for dehydrogenation process involving three possible pathways: stepwise B–H/N–H activation, concerted B–H/N–H activation and proton transfer mechanism. The facile occurrence of the studied systems was demonstrated by the activation barriers of the rate-determining steps. It was found that the proton transfer pathway is mostly kinetically favorable with the lowest activation barrier of 28.38 kcal/mol. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ferrocenyl and phenyl groups in cuprous cluster C1 form aromatic microenvironment. • SMP C1 successfully activate inert Ph-Cl in visible-light-driven amination. • SET route for Ph-I/Br and EnT route for Ph-Cl proposed in SMP catalyzed amination. Amination of aryl halides is an important tool in organic synthesis and the activation of inert aryl chlorides is particular difficult. We herein report the first study of aromatic microenvironment modulation of cuprous clusters as single-molecule metallaphotocatalysts (SMPs) for direct phneyl chloride activation in C N coupling reactions. Selenoether L1 was designed to afford aromatic microenvironment with ferrocenyl and phenyl groups. The cuprous cluster [Cu 2 I 2 (L1)] (C1) was proved to be an effective white light-driven SMP , successfully catalyzing the amination of aryl halides with carbazole. This method showed a diverse substrate scopes of aryl halides with electronical and structural variety, affording the highest yield of 63% for 4-chlorobenzonitrile. X-ray crystallographic, in situ electron paramagnetic resonance (EPR) spectroscopic study and density functional theory (DFT) calculations demonstrated that the aromatic microenvironment in C1 promoted the effective intermolecular electron transfer via π-π interactions between SMPs and aryl halides. Interestingly, the mechanism of the amination was dependent on the substrates applied. A single electron transfer (SET) and formation of Cu2+ intermediate was found when Ph-I/Ph-Br were applied, while an energy transfer (EnT) route with Cu3+-intermediate was identified when Ph-Cl substrates were used. [ABSTRACT FROM AUTHOR]

A quantum-chemical mechanistic investigation using density functional theory (DFT) on ammonia-borane dehydrogenation catalyzed by a series of iron bis(phosphinite) pincer complexes is reported. A metal-ligand cooperation mechanism has been proposed, in which the hydrogen atom of B H moves to metal Fe and proton of N H transfers to pincer ipso carbon simultaneously with the lowest activation barriers. DFT calculations and natural bond orbital (NBO) charge analysis suggest that Fe POCOP complex with an electron-donating MeO group at the para position to the ipso carbon exhibits the highest catalytic activity. A plausible explanation of the observed catalytic activities is also given. [ABSTRACT FROM AUTHOR]

Highlights: [•] IR and Raman spectra of the title compound were obtained. [•] Vibrational assignments were made based on the theoretical IR/Raman spectra. [•] The ZE stereoisomer with two viable isopropyl conformers was the most stable. [•] DFT optimized structures agree well with reported X-ray crystal structures. [ABSTRACT FROM AUTHOR]

The mechanism of tandem dimethylamine-borane (NHMe 2 BH 3 , DMAB) dehydrogenation and alkene hydrogenation catalyzed by [Pd(NHC)(PMe 3 )] are investigated by density functional theory (DFT) calculations [NHC = N , N ′-bis(2,6-diisopropylphenyl) imidazole-2-ylidene]. Four possible DMAB dehydrogenation mechanisms have been carefully investigated involving concerted B H/N H activation, sequential B H/N H activation, sequential N H/B H activation, and proton transfer mechanism. DFT studies show that the N H proton transfers to ligated carbene carbon and sequential C H/B H activation is the most kinetically favorable pathway with the lowest activation barrier of 23.8 kcal/mol. For hydrogenation, it was found that a trans -dihydride Pd(II) complex, [Pd(H) 2 (NHC)(PMe 3 )], formed in the dehydrogenation process, serves as an effective catalyst for reduction of trans -stilbene. [ABSTRACT FROM AUTHOR]