Oxygenolysis reaction mechanism of copper-dependent quercetin 2,3-dioxygenase: A density functional theory study

The mechanism of the action of copper-dependent quercetin 2,3-dioxygenase(2,3QD) has been investigated by means of hybrid density functional theory.The 2,3QD enzyme cleaves the O-heterocycle of a quercetin by incorporation of both oxygen atoms into the substrate and releases carbon monoxide.The calculations show that dioxygen attack on the copper complex is energetically favorable.The adduct has a possible near-degeneracy of states between [Cu 2+-(substrate-H +)] and [Cu +-(substrate-H).],and in addition the pyramidalized C 2 atom is ideally suited for forming a dioxygen-bridged structure.In the next step,the C 3-C 4 bond is cleaved and intermediate Int 5 is formed via transition state TS 4.Finally,the O a-O b and C 2-C 3 bonds are cleaved,and CO is released in one concerted transition state(TS 5) with the barrier of 63.25 and 61.91 kJ/mol in the gas phase and protein environments,respectively.On the basis of our proposed reaction mechanism,this is the rate-limiting step of the whole catalytic cycle and is strongly driven by a relatively large exothermicity of 100.86 kJ/mol.Our work provides some valuable fundamental insights into the behavior of this enzyme.     

Analysis of human urine metabolites using SPE and NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopic analysis of metabonome/metabolome has widespread applications in biomedical science researches. However, most of NMR resonances for urinary metabolites remain to be fully assigned. In the present study, human urine samples from two healthy volunteers were pre-treated with C18 solid-phase extraction and the resultant 5 sub-fractions were subjected to one- and two-dimensional NMR studies, including 1H J-Resolved, 1H-1H COSY, 1H-1H TOCSY, 1H-13C HSQC, and HMBC 2D NMR. More than 70 low molecular weight metabolites were identified, and complete assignments of 1H and 13C resonances including many complex coupled spin systems were obtained.     

Subchronic toxicological effects of aquatic nitrobenzene on Medaka and Chinese rare minnow

Based on the simulative exposure experiments of nitrobenzene to two small experimental fishes, Medaka (Oryzias latipes) and Chinese Rare Minnow (Gobiocypris rarus), it was found that nitrobenzene could decrease in a linear way in the static aquatic system. Both fishes could accumulate dose-related levels of nitrobenzene quickly and eliminate the compound rapidly when they were transferred to clean water. The Chinese rare minnow showed more sensitivity to the acute toxicity exposure of nitrobenzene than Medaka. Typical molecular biomarkers in oxidative defense system including superoxide dismu- tase (SOD), catalase (CAT) showed the chemical induced alterations. The changes of acetylcholi- nesterase (AChE) activities indicated that nitrobenzene might affect the normal neural function. Nitro- benzene exposure could also lead to obvious damaging effects on the target organs, such as gill and liver by hitopathological studies.     

Effects of nanoscale quantum dots in male Chinese loaches (<Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>): Estrogenic interference action,toxicokinetics and oxidative stress

Quantum dots (QDs) have more and more attention as a novel example of nanocrystals due to their unique fluorescent characteristics. Recently, the toxicity and the potential environmental effects of QDs have become a research hotspot. In this work, in vivo endocrine disrupting effect, toxicokinetics and oxidative stress of QDs were characterized following the intraperitoneal dosing in Chinese loaches. Vitellogenin (Vtg) levels induced by E2 decreased significantly when administrated with the mixture of QDs and E2, which was consistent with the observations of histopathology in testes. The release of free Cd²⁺ from QDs and the non-specific adsorption of E2 by QDs might be the joint factors contributing to the inhibition of Vtg expression induced by E2 in the male Chinese loaches. In the muscle, bone, intestines, blood and testis, CdSe QDs reached the maximal concentration (C _max) in approximately 1-h postinjection and subsequently presented downtrend with the prolonged time. Whereas, there were even increasing tendencies of CdSe QDs’ concentrations in the liver and kidney. It is educible that CdSe QDs can be persistent at least for 7 days, indicating the overall half-life of CdSe QDs in the fish body is very long. The measurement of hepatic superoxide dismutase (SOD) activity and reduced glutathione (GSH) content indicate that QDs have smaller effects on the antioxidative system of the organisms compared with free Cd²⁺ due to the effective prevention of the release of Cd by PEG coating of QDs. The comprehensive evaluation of QDs’ toxicity in the present study provides an essential and general framework towards more focused research on the elucidation of the biological effects of QDs in vivo.     

CdSe量子点对雄性泥鳅的毒性效应研究

量子点（Quantum Dots,QDs）,也称纳米微晶体,由于其独特的荧光特性越来越受到研究者的关注.近年来,量子点的生物学毒性效应及其环境影响成为新的研究热点.本文通过活体实验,以雄性泥鳅为模型动物,以腹腔注射为染毒方式,研究了量子点的雌激素干扰效应、毒物动力学行为以及靶器官的氧化应激指标.结果显示,QDs能够显著抑制E2诱导产生的卵黄蛋白原（Vtg）含量,性腺切片的观察结果与其一致.通过游离Cd^2＋和其他几种纳米材料的对比实验,认为量子点对Vtg的抑制表达是游离Cd^2＋和QDs颗粒对E2的非特异性吸附的共同作用结果.毒物动力学结果表明,腹腔注射1h后,肌肉、骨头、肠、血液和性腺中QDs含量达到最大浓度（Cmax）,随后呈降低趋势 而在肝脏和肾脏中,QDs含量呈增加趋势,说明QDs在动物体内的半衰期较长,在体内能够持续存留.通过对靶器官肝脏相关抗氧化酶活性的测定结果发现,量子点由于壳层对Cd^2＋的保护,对抗氧化体系影响较小.本实验对量子点毒性的综合评价为其在活体生物学的应用提供了一定的参考.     

Rapid decolorization of water soluble azo-dyes by nanosized zero-valent iron immobilized on the exchange resin

Nanosized zero-valent iron (NZVI) supported on the cation exchange resin was synthesized and applied to decompose some water soluble azo dyes. The decomposition efficiency for azo dyes was evaluated by using the aqueous suspensions and parked column of this material. Batch experiments indicated that this novel material exhibited excellent degradation ability for 0.05 g·L1 of Acid Orange 7, Acid Orange 8, Acid Orange 10, Sunset Yellow, and Methyl Orange, with decolorization ratio up to 95% in 4 min; pH value was the key factor for degradation and H was one of the reactants; adsorption of azo dyes onto the material existed at the beginning but reduced gradually until disappearing completely. For the packed column system, 58%~90% of azo dyes were decomposed in the 1st circle of solution passing through the column, and the adsorption onto the materials could accelerate the degradation azo dyes with the increasing reaction time. During the degradation process, Fe2 , the product of NZVI, was exchanged to the resin again and could be reduced to Fe0 by KBH4 for reusing. The 10th refreshed NZVI possessed reductive activity up to 90% of the newly systhesized NZVI. Decomposing pollutants in the aqueous solution with columns packed with NZVI immobilized on the cation exchange resin is a promising technology that can solve the reclaiming and refreshing problem of NZVI.     

Progress in the toxicological researches for quantum dots

Quantum dots (QDs) have received more and more attention as a novel example of nanomaterials. Due to their unique fluorescent characteristics,quantum dots have been successfully applied in biotech-nology and medicine applications. Recently,the toxicity and the potential environmental effects of QDs have become a research hotspot. In this paper,toxicological effects of QDs are reviewed,and the prospects and research directions are given based on the analysis of this research field.     

Butyltin compounds in vinegar collected in Beijing: Species distribution and source investigation

Forty-eight vinegar samples including white vinegar,rice vinegar and mature vinegar were collected from several markets in Beijing.Butyltin compounds were determined by headspace solid-phase microextraction coupled with gas chromatography and flame photometric detector after in situ ethylation with sodium tetraethylborate.Butyltin species were detected in sixteen vinegar samples and ranged from 0.012 to 14.10 μg Sn L 1.The detection rate of white vinegar is higher than that of rice vinegar and mature vinegar.Vinegar samples with relatively high butyltin concentration(>1.5 μg Sn L 1) were those stored in plastic bags,indicating that the plastic bag was one of the possible sources of butyltin contamination.This was further confirmed by the leaching experiments of three selected plastic bags,and monobutyltin was detected in the leaching solvents.According to the estimation,the average daily intake of total butyltin compounds through vinegar consumption is about 0.04 ng Sn/kg b.w.,much lower than the Tolerable Daily Intake(TDI) of 100 ng Sn/kg b.w.set by the European Food Safety Authority(EFSA).