Asymmetric Amination of Unstrained C(sp3)-C(sp3) Bonds.

The asymmetric functionalization of unstrained C(sp3)-C(sp3) bonds could be a powerful strategy to stereoselectively reconstruct the backbone of an organic compound, but such reactions are rare. Although allylic substitutions have been used frequently to construct C-C bonds by the cleavage of more reactive C-X bonds (X is usually an O atom of an ester) by transition metals, the reverse process that involves the replacement of a C-C bond with a C-heteroatom bond is rare and generally considered thermodynamically unfavorable. We show that an unstrained, inert allylic C-C σ bond can be converted to a C-N bond stereoselectively via a designed solubility-control strategy, which makes the thermodynamically unfavorable process possible. The C-C bond amination occurs with a range of amine nucleophiles and cleaves multiple classes of alkyl C-C bonds in good yields with high enantioselectivity. A novel resolution strategy is also reported that transforms racemic allylic amines to the corresponding optically active allylic amine by the sequential conversion of a C-N bond to a C-C bond and back to a C-N bond. Mechanistic studies show that formation of the C-N bond is the rate-limiting step and is driven by the low solubility of the salt formed from the cleaved alkyl group in a nonpolar solvent.

Asymmetric Substitution by Alkynyl Copper Driven Dearomatization and Rearomatization.

Catalytic asymmetric transformations by dearomatization have developed into a widely applicable synthetic strategy, but heavily relied on the use of arenes bearing a heteroatom. In this case, the dearomatization is facilitated by the involvement of a p-orbital electron of the heteroatom. Different from the conventional substrate-dependent model, here we demonstrate that the activation by a d-orbital electron of the transition-metal center can serve as a driving force for dearomatization, and is applied to the development of a novel asymmetric alkynyl copper facilitated remote substitution reaction. A newly modified PyBox chiral ligand enables the construction of valuable diarylmethyl and triarylmethyl skeletons in high enantioselectivities. An unexpected tandem process involving sequential remote substitution/cyclization/1,5-H shift leads to the formation of the enantioenriched C-N axis. A gram-scale reaction and various downstream transformations highlight the robustness of this method and the potential transformations of the products. Preliminary mechanistic studies reveal a mononuclear Cu-catalyzed remote substitution process.

Polycyclic aromatic hydrocarbons in street dust from different functional areas in Chengdu, China: seasonal variation and health risk assessment.

This is the first investigation that identified seasonal variation, possible sources and health risk of 16 PAHs in street dust sampled park area (PA), educational area (EA), commercial area (CA), residential area (RA), and traffic area (TA) of Chengdu, one of the new first-tier cities in China. The total PAHs (∑16PAHs) concentrations of averaging over two seasons varied from 2.15 to 10.6 mg/kg with a median value of 4.61 mg/kg and in winter (5.48 ± 1.52 mg/kg) were significantly higher than that in summer (4.04 ± 0.91 mg/kg). The highest ∑16PAHs concentration was found in TA (median 6.74 mg/kg). Statistical analysis results indicated that mixture sources of petroleum combustion and combustion of biomass and coal seem to be the primary source of the PAHs in street dust. Carcinogenic risk by incremental lifetime cancer risk (ILCR) model for PAHs in street dust indicates an acceptable potential cancer risk for residents. The same sequences of cancer risk to be observed for both children and adults among different functional areas: TA > CA > EA > RA > PA. The results provided advice for habitants in Chengdu to encourage outdoor activities in parks and residential areas and minimize traffic areas and commercial areas.

Using fly larvae to convert food waste for growing Oujiang color common carps: health risk assessment of polycyclic aromatic hydrocarbons.

The present study used Chrysomya megacephala larvae (CML) to transform food waste into safe and high-quality fish feed to substitute fish meal as a source of protein for growing Oujiang color common carps followed by a human health risk assessment of polycyclic aromatic hydrocarbons (PAHs). The results showed the ∑PAH concentration in the CML fed with food waste ranged from 50 to 370 µg kg-1, and the most abundant PAH compound in the CML was BaP, contributing 59-84% of ∑PAHs. The Pearson correlation analysis results indicated no correlation between the ∑PAH concentrations and the culture substrate ratio (p > 0.05). Concentrations of BaP in the CML decreased with the increase of breeding density (p < 0.01). The residues as organic fertilizers have no potential ecological risk for PAHs. The biotransformed larva meal was used to partially or completely replace the fish meal as supplementary protein in the experimental feeds (T0, 0%; T50, 50%; T100, 100%). No significant difference (p < 0.05) of survival rate, lipid, and protein content in Oujiang color common carp was noted among T0, T50, and T100 fish feeds. Concentrations of ∑PAHs in Oujiang color common carp fed with the CML fish feeds all met the food safety standards in the European Union (EU). Furthermore, the consumption of Oujiang color common carps fed with the CML feed does not pose any health risks of PAHs for humans.

[Remediation Potential of Taraxacum kok-saghyz Rodin on Lead and Cadmium Contaminated Farmland Soil].

Taraxacum kok-saghyz Rodin (TSK) is an energy plant that can be used as a raw material for natural rubber. The aim of this study was to examine the remediation potential of TSK to lead (Pb)- and cadmium (Cd)-contaminated farmland soil. In this study, a pot experiment was conducted, and the "Soil Environmental Quality and Agricultural Land Soil Pollution Risk Control Standard (GB 15618-2018)" was used as reference. We set up four different concentrations of Pb and Cd pollution treatment to study the characteristics of the accumulation and tolerance of TSK to Pb and Cd. The results showed that as the content of Pb and Cd in the soil increased, the chlorophyll content and biomass of TSK gradually decreased, and the SOD, POD, and CAT enzyme activities gradually increased. The BCF and TF of Cd were between 1.20 and 1.50, indicating that TSK presented some characteristics of a Cd hyperaccumulator. The BCF and TF of Pb were between 0.71 and 1.11. Thus, TSK was a good Pb enrichment plant and possessed the potential to repair soil with ω(Pb) below 400 mg·kg-1. The accumulation of Pb and Cd gradually increased, and the maximum accumulation of Cd and Pb in the shoots was 9.832 µg·plant-1 and 1091.185 µg·plant-1, respectively. However, in lower concentrations of Pb- and Cd-contaminated soil, the removal rate was greater, and the remediation efficiency was better. Overall, using TSK to repair Pb- and Cd-contaminated farmland soil has good application prospects and economic value.

Bioaccumulation and health risk assessments of trace elements in housefly (Musca domestica L.) larvae fed with food wastes.

This study aimed to use food waste to culture housefly larvae, which serve as the major source of protein in fish feeds, to evaluate copper (Cu), zinc (Zn), iron (Fe), nickel (Ni), cadmium (Cd), and chromium (Cr) bioaccumulation and trophic transfer in the food chain. In addition, the potential health risk to humans of exposure to these metal elements via dietary intake of tilapia fed with housefly larvae feeds was also evaluated. The results showed the bioavailability of trace elements in dish waste to housefly larvae was lower than that in staple food waste. Trace element concentrations in housefly larvae fed with food waste met the animal feed standards in China and the European Union (EU). The highest concentrations of Cu, Zn, Ni, Cr, and Cd in residue did not exceed the limits specified for fertilizer in China, Canada, and Germany. The tilapia fed with dried housefly larvae presented a greater final weight and protein content than those fed with commercial feed and fresh housefly larvae (p<0.05). The Cu, Cr, and Cd concentrations in tilapia fed with commercial feed were higher than in those fed with commercial housefly larvae or dried housefly larvae (p<0.05). The highest bioaccumulation of Cu, Zn, and Ni was found in tilapia fed with fresh housefly larvae feed. The results of the health risk assessment showed that the tilapia fed with the housefly larvae feed pellets or fresh housefly larvae were safe for consumption from the perspective of trace elements.

Occurrence and distribution of phthalate esters in freshwater aquaculture fish ponds in Pearl River Delta, China.

The concentrations, congener profiles and spatial distribution of 13 phthalate esters (PAEs) in the freshwater fish ponds in the Pearl River Delta (PRD) region were investigated in water and sediment samples collect from 22 sites during Jul. 2016-Sept. 2017. The di-2-ethylhexyl phthalate (DEHP) was the predominant compounds in both water and sediment samples, accounting for 70.1% and 66.1% of ∑PAEs, respectively. The DEHP concentrations in the water samples collected from the sites of Zhongshan (35.7 µg/L), Jingmen (17.3 µg/L) and Nanhai (14.2 µg/L) were higher than that collected from other sampling sites (p <0.05), and exceed the Chinese environmental quality standards for surface water (DEHP, 8.00 µg/L). The concentrations of ΣPAEs (mean and median were 11.8 mg/kg dw and 7.95 mg/kg dw) in sediment was higher than that in sediment of river and estuary in the PRD region (p <0.05). The median concentrations of DEHP and di-n-butyl phthalate (DBP) exceeded recommend environmental risk limit (ERL) that posed a potential risk to the aquaculture fish pond environment in the PRD.

Characteristics and health risk assessment of heavy metals exposure via household dust from urban area in Chengdu, China.

To investigate the characteristics of heavy metals (Cr, Cd, Pb, Zn, Cu and Ni) in household dust in urban household environment of Chengdu, China, 90 household dust samples were collected from 6 districts of the city. The information of houses and residents were also recorded during dust sampling to identify the correlations between heavy metals in household dust and the house attributes. And also the principal component analysis and cluster analysis for sources and impactor factors. The concentrations of Pb (123mg·kg-1), Zn (675mg·kg-1), Cu (190mg·kg-1), Cr (82.7mg·kg-1), Cd (2.37mg·kg-1) and Ni (52.6mg·kg-1) in household dust are in low or moderate levels when compare with that from other counties or areas. The heavy metals of household dust samples from Chengdu is higher concentrations than that in the street dust from Chengdu, except for Cr. Statistical analysis result showed traffic sources and corrosion of alloys are important factors contributing to the rise concentrations of heavy metals in household dust. In addition, there is negative correlation (p<0.05) between the heavy metals concentrations and floor levels. The ingestion is the important pathway for Pb, Zn, Cu and Ni via household dust exposure to the residents, and the dermal contact was identified as a main route for Cr and Cd in household dust exposure to the residents. There are minor non-carcinogenic and carcinogenic risks from the heavy metals in household dust for the residents in Chengdu.

Pollution characteristics and risk assessment of human exposure to oral bioaccessibility of heavy metals via urban street dusts from different functional areas in Chengdu, China.

Urban street dusts were collected in commercial area (CA), traffic area (TA), educational area (EA), residential area (RA) and parks area (PA) of Chengdu, China, to investigate the concentrations of heavy metals (Pb, Zn, Cu, Ni, Cd and Cr), and analyzed to evaluated possible sources and health risk assessment. The average concentrations (mg/kg) of Pb (82.3), Zn (296), Cu (100), Cd (1.66) and Cr (84.3) in urban street dusts were all higher than the local soil background values. The concentrations of heavy metals in each functional area could be classified as follows: CA>TA>RA>EA>PA. Principal component analysis and Cluster analysis showed mainly derived from the mixed sources of nature and traffic (51.7%). The results of health risk assessment showed no non-carcinogenic and carcinogenic risks of the metals for inhabitants. However, higher concentrations and oral bioaccessibility of the heavy metals in the dusts from CA and TA, indicating there was more health risks to the inhabitants in than that in other functional areas.

Research on Root Responses to Pb and Zn Combined Stress of Carex putuoshan.

Pb hyper-accumulated Carex putuoshan was taken as experimental material and subjected to combined stress of Pb and Zn. The differential expression of proteins in their roots were analyzed by Proteomic Approach. The protein that was directly involved in the cellular defense under the Pb and Zn combined stress was separated, and expression of those genes was analyzed with Carex Evergold as control. The results were obtained by MALDI-TOF/MS analysis. After applying Pb and Zn combined stress, the expression of 9 protein spots (including 7 different proteins, 2 identical proteins, 1 unknown protein) in Carex putuoshan root was found to be significantly up-regulated. Five proteins were obtained from the 9 proteins related to carbohydrate metabolism, including malate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, frutose-1,6-bisphosphate aldolase, enolase, and 6- phosphogluconate dehydrogenase. Two proteins were related to protein biosynthesis, including isoflavone reductase and phytochelatin synthase (PCS). From these proteins, the most important protein is PCS, which is a key enzyme in the synthesis of phytochelatins (PCs) and plays an important role in chelation. It is directly involved in cellular defense under Pb and Zn stress. After Pb and Zn combined stress, the CpPCS in Carex putuoshan was cloned. The full length of cDNA is 1461 bps, and it encodes 486 amino acids with molecular weight of 53.86 kD and pI value of 6.12. Two typical phytochelatin synthase subfamily domains constitute CpPCS protein, which includes three adjacent Cys-Cys elements in the C-terminal region. Phylogenetic analysis of PCS proteins from different species showed that it had the closest relationship with the Oryza sativa and Triticum aestivum. Real-time quantitative PCR analysis indicated that CpPCS and CePCS (Carex Evergold) genes were expressed in the root. The CpPCS and CePCS genes were up-regulated by Pb and Zn treatments. The expression of CpPCS was higher than that of CePCS under the same condition. The study found that CpPCS expression was increased by Pb and Zn stress in the Carex putuoshan enrichment process of Pb, which lead to high expression of PCS protein. CpPCS improved the accumulation ability and resistance of Carex putuoshan to heavy metals with the expression level of glucose metabolism related proteins increasing after Pb and Zn stress.

Dynamic features of a laser-induced cavitation bubble near a solid boundary.

This paper deals with detailed features of bubble dynamics near a solid boundary. The cavitation bubble was created by using a Q-switched Nd: YAG laser pulse and observed using a high-speed camera (up to 100,000 frames per second). A hydrophone system was employed to monitor the acoustic signals generated by the transient pressure impulses and estimate the bubble oscillation periods. Experimental observations were carried out for bubbles with various maximum expanded radius Rmax (between 1.0mm and 1.6mm) and stand-off distances, ds (defined as the distance between the solid boundary and the bubble center at inception) of 0.4≤γ≤3.0, and γ=ds/Rmax. The existence of a solid boundary created asymmetry in the flow field and forced the bubble to collapse non-spherically, which finally brought forth the jet impact phenomenon. The dimensionless first and second oscillation periods were dependent on γ. A series of expansion and collapse of the bubble with cascading loss of energy were observed after the bubble had been generated. This study revealed that most bubbles lost about two-thirds of the total energy from the first maximum expansion to the second maximum expansion.