The promoting role of minor amount of water in solvent-free hydrogenation of halogenated nitrobenzenes

This study shows that minor amount of water plays a very important role in solvent-free hydrogenation of halogenated nitrobenzenes. For dried sponge Pd, the reaction cannot occur in the absence of water. For Pd/C catalyst, minor amount of water reduces the induction time, increases the reaction rate and reaction TOFs. Water might enhance the diffusion, adsorption and dissociation of H2 on Pd catalysts.     

Very rapid synthesis of highly efficient and biocompatible Ag2Se QD phytocatalysts using ultrasonic irradiation for aqueous/sustainable reduction of toxic nitroarenes to anilines with excellent yield/selectivity at room temperature

There are many problems associated with the synthesis of nanocatalysts and catalytic reduction of nitroarenes - e.g., high temperatures, costs, long reaction/synthesis process times, the toxicity of chemicals/solvents, undesirable byproducts, the toxic/harmful wastes, low efficiency/selectivity, etc. This study represents an attempt to overcome these challenges. To this purpose, biocompatible and highly efficient Ag₂Se quantum dots (QDs) catalysts with antibacterial activity were synthesized in a very rapid (30 sec, rt), simple, inexpensive, sustainable/green, and one-pot strategy in water using ultrasonic irradiation. Characterization of the QDs was performed using different techniques. UV–Vis absorption and fluorescence spectroscopic studies showed an absorption peak at 480–550 nm and a maximum emission peak around 675 nm, which confirmed the successful synthesis of Ag₂Se QDs via the applied biosynthetic method. Subsequently, catalytic reduction of nitroarenes by them was carried out under safe conditions (H₂O, rt, air atmosphere) in ∼ 60 min with excellent yield and selectivity (>99%). Their catalytic activity in the reduction of various toxic nitroarenes to aminoarenes under green conditions was investigated. Thus, a rapid and safe ultrasound-based method was employed to prepare stable and green Ag₂Se QDs phyto-catalysts with unique properties, including exquisite monodispersity in shape (orthorhombic) and size (∼7 nm), air-stability, and good purity and crystallinity. Importantly, instead of various toxic chemicals, the plant extract obtained by rapid ultrasonic method (10 min, rt) was used as natural reducing, capping, and stabilizing agents. Moreover, antibacterial assays results showed that Ag₂Se-QDs catalysts at low concentrations (ppm) have high activity against all tested bacteria, especially E. coli (MIC:31.25 ppm, MBC:125 ppm) which were significantly different from those of Fig extract (MIC = MBC:500 ppm). The data reflect the role of these bio-synthesized Ag₂Se-QDs catalysts in the development of versatile and very safe catalysts with biomedical properties.     

QSAR Study of Nitrobenzenes’ Toxicity to Tetrahymena Pyriformis Using Semi-empirical Quantum Chemical Methods

1 INTRODUCTION Nitrobenzenes are an important class of industrial chemicals produced with substantial marketing volu-mes and a diverse range of use patterns[1].They are widely used as pesticides,solvents,explosives,dye-stuffs,etc.Most of the nitrobenzenes together with their derivatives are toxic,and they can cause dam-nification of human kidney,liver,eye,skin,blood system and so on[2～4].It is reported that all nitro-benzenes and their metabolites have mutagenicity,which induces the cyto…     

Behaviour of Organic Micropollutants During Groundwater Recharge

Abstract

Pilot plant studies were conducted to investigate the behaviour of organic micropollutants (OM) during artificial ground water recharge of pretreated river Rhine water in the dune areas. The behaviour of the studied OM was mostly affected by biological anaerobic processes. The rate of these processes correlated with the redox potential, which was primarily controlled by the biologically unstabilised organic matter of the recharge aquifer. Under anaerobic conditions (E_h ～ + 150 mV) a substantial or complete transformation of a number of halogenated C₁-C₃ aliphatics, nitro- and chloronitrobenzenes was found at temperatures higher than 5[ddot] C. At lower temperatures a lower degree of the degradation and the formation of some potentially hazardous reaction products (dichloromethane, bromochloromethane, chloroanilines) has been observed. Furthermore the studies revealed a substantial retardation of the transformation rate at low concentration levels of some studied compounds (toluene, dichlorobenzenes, EDTA). Aerobic processes led to a significant elimination of brominated trihalomethanes, some phenoxy pesticides and NTA.     

Solvation Dependences of Isotropic Hyperfine Interaction Constants and out-of-Plane Distortions of ortho-Substituted Nitrobenzene Radical Anions

For a number of ortho-substituted nitrobenzene radical anions (RAs) generated in DMF and its binary mixtures with water, it is shown that for radical anions with a substituent of minor effective volume in one ortho position to the nitro group, the dependences of the isotropic hyperfine interaction (ihfi) constants on the mole fraction of water are S-like and dictated by the medium composition and the concerted out-of-plane rotational and pyramidal distortions of the nitro group of the radical anion. The S-like shape of the solvation dependences of the ihfi constants is dictated by the dominant rotational distortions of the nitro group. For most radical anions with two ortho substituents or with one ortho substituent with a large effective volume, the S-like dependences are not observed, and the values of the nitrogen ihfi constants depend on the dominant pyramidal distortion of the nitro group. For the 2-tert-butylnitrobenzene radical anion in water, the nitrogen ihfi constant is a_N=25.62 G, which is typical of nitroaliphatic radical anions. This effect is explained based on the pyramidal structure of the nitro group in the case of its large rotation angles.     

葫［7］环联脲作为毛细管电泳分离介质的研究

以葫［7］环联脲(CB［7］)作为毛细管电泳添加剂,成功地分离了6种硝基苯类化合物。考察了pH值对电渗流的影响,初步评价了其基本的电泳性能,结果表明在所考察的pH值范围内(pH 2~6.5),葫［7］环联脲是质子化的,且吸附到毛细管内壁上,这使得毛细管内壁带上正电荷,电渗流反向;初步考察了葫［7］环联脲的浓度对分离的影响,证明了用葫［7］环联脲作为添加剂可完全分离对硝基乙苯、对硝基甲苯、对氯硝基苯、间二硝基苯、2,4-二硝基氯苯和硝基苯这6种物质,最佳的缓冲液为10 mmol/L Na2HPO4（用盐     

In‐situ cryocrystallization of 1,2‐dimethyl‐3‐nitrobenzene and 2,4‐dimethyl‐1‐nitrobenzene

The crystal structures of 1,2‐dimethyl‐3‐nitrobenzene, C₈H₉NO₂, and 2,4‐dimethyl‐1‐nitrobenzene, C₈H₉NO₂, which are liquids at room temperature, have been obtained through in‐situ cryocrystallization. Weak C—H...O and also π–π interactions are present in both crystal structures.     

SAR Models for Futile Metabolism: One-Electron Reduction of Quinones,Phenols and Nitrobenzenes

Abstract

Benzoquinones, naphthoquinones and aziridinylbenzoquinones, can be reduced by flavoproteins to semiquinones that react with molecular oxygen to form superoxide anion with the subsequent regeneration of the parent compounds. This redox cycling, a form of futile metabolism, produces reactive oxygen species and depletes the reducing equivalents of cells without concomitant energy production. The ability of a toxicant to redox cycle is related to its one-electron reduction potential, and this study attempted to estimate reduction potential from structure using semi-empirical quantum chemical models for a diverse set of chemicals. The results of this study suggest that one-electron reduction potentials, within structural classes of benzoquinones, naphthoquinones, phenols and nitrobenzenes, can be estimated from local and global electronic indices that are related to delocalization. Smaller absolute charge on the carbonyl carbon in the quinone moiety correlated with more positive one-electron reduction potentials of 1,4-benzoquinones, naphthoquinones and two-electron reduction potentials of aziridinylbenzoquinones. The energy of frontier orbitals of the quinones, phenols and nitrobenzenes also co-varied with reduction potential. More positive reduction potentials of 1,4-benzoquinones, 1,4-naphthoquinones and phenols were correlated with more negative values of E_HOMO, while more negative values of E_LUMO were correlated with more positive potentials of nitrobenzenes and aziridinylbenzoquinones. Delocalization of electron density also correlated with reduction potentials within individual classes.