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Inorganic divalent mercury complexes (Hg

Understanding the mechanism of nanosilver-dependent antibacterial activity against microorganisms helps optimize the design and usage of the related nanomaterials. In this study, we prepared four kinds of 10 nm-sized silver nanoparticles (AgNPs) with dictated surface chemistry by capping different ligands, including citrate, mercaptopropionic acid, mercaptohexanoic acid, and mercaptopropionic sulfonic acid. Their surface-dependent chemistry and antibacterial activities were investigated. Owing to the weak bond to surface Ag, short carbon chain, and low silver ion attraction, citrate-coated AgNPs caused the highest silver ion release and the strongest antibacterial activity against Escherichia coli, when compared to the other tested AgNPs. The study on the underlying antibacterial mechanisms indicated that cellular membrane uptake of Ag, NAD+/NADH ratio increase, and intracellular reactive oxygen species (ROS) generation were significantly induced in both AgNP and silver ion exposure groups. The released silver ions from AgNPs inside cells through a Trojan-horse-type mechanism were suggested to interact with respiratory chain proteins on the membrane, interrupt intracellular O2 reduction, and induce ROS production. The further oxidative damages of lipid peroxidation and membrane breakdown caused the lethal effect on E. coli. Altogether, this study demonstrated that AgNPs exerted antibacterial activity through the release of silver ions and the subsequent induction of intracellular ROS generation by interacting with the cell membrane. The findings are helpful in guiding the controllable synthesis through the regulation of surface coating for medical care purpose.

5-methylcytosine (m5C) is a post-transcriptional RNA modification identified in both stable and highly abundant tRNAs and rRNAs, and in mRNAs. However, its regulatory role in mRNA metabolism is still largely unknown. Here, we reveal that m5C modification is enriched in CG-rich regions and in regions immediately downstream of translation initiation sites and has conserved, tissue-specific and dynamic features across mammalian transcriptomes. Moreover, m5C formation in mRNAs is mainly catalyzed by the RNA methyltransferase NSUN2, and m5C is specifically recognized by the mRNA export adaptor ALYREF as shown by in vitro and in vivo studies. NSUN2 modulates ALYREF's nuclear-cytoplasmic shuttling, RNA-binding affinity and associated mRNA export. Dysregulation of ALYREF-mediated mRNA export upon NSUN2 depletion could be restored by reconstitution of wild-type but not methyltransferase-defective NSUN2. Our study provides comprehensive m5C profiles of mammalian transcriptomes and suggests an essential role for m5C modification in mRNA export and post-transcriptional regulation.

Raman-based technologies have proved to be excellent tools for on-site and in-vivo analysis, due to the non-invasive nature of their detection, their capability of providing structure information, their high tolerance to aqueous samples, the ultra-sensitivity of surface-enhanced Raman scattering (SERS) and resonance Raman scattering (RRS), the high spatial resolution of tip-enhanced Raman scattering (TERS), and the ultrashort spectra-acquisition time for coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS). In this review, we highlight the recent success of Raman-based technologies in various applications, including: (1) on-site surface analysis and chemical-reaction monitoring; (2) on-site identification of cultural objects, archeological studies and planetary science; (3) in-vivo analysis of cells and microorganisms; (4) in-vivo diagnosis inside human and animal bodies; (5) in-vivo fast Raman imaging and mapping; (6) the study of SERS processes; and, (7) assessment of nanomaterial safety.

Although progress has been made in some areas, China is struggling to harmonize economic development and environmental protection.

Room-temperature ionic liquids (ILs) are gaining wide recognition as novel solvents in chemistry. Their application in analytical chemistry, especially in separating analytes, is merited because ILs have some unique properties, such as negligible vapor pressure, good thermal stability, tunable viscosity and miscibility with water and organic solvents, as well as good extractability for various organic compounds and metal ions. This review gives a brief overview of the application of ILs in analytical chemistry, including sample preparation, chromatographic/capillary electrophoretic (CE) separation, and detection. (C) 2004 Elsevier Ltd. All rights reserved.

Seafood samples were collected from Dalian, China to study the accumulation and distribution characteristics of short chain chlorinated paraffins (SCCPs) by GC/ECNI-LRMS. Sum of SCCPs (dry weight) were in the range of 77-8 250 ng.g-1, with the lowest value in Scapharca subcrenata and highest concentration in Neptunea cumingi. The concentrations of sum of SCCPs (dry weight) in fish, shrimp/crab and shellfish were in the ranges of 100-3 510, 394-5 440, and 77-8 250 ng.g-1 , respectively. Overall, the C10 and C11 homologues were the most predominant carbon groups of SCCPs in seafood from this area,and a relatively higher proportion of C12-13 was observed in seafood with higher concentrations of sum of SCCPs . With regard to chlorine content, Cl1,, CI8 and CI6 were the major groups. Significant correlations were found among concentrations of different SCCP homologues (except C1, vs. Cl10 ) , which indicated that they might share the same sources and/or have similar accumulation, migration and transformation processes.

We have shown previously that hydroxyl radicals (HO • ) can be produced by H 2 O 2 and halogenated quinones, independent of transition metal ions; however, the underlying molecular mechanism is still unclear. In the present study, using the electron spin resonance secondary radical spin-trapping method, we found that tetrachloro-1,4-benzoquinone (TCBQ), but not its corresponding semiquinone anion radical, the tetrachlorosemiquinone anion radical (TCSQ •− ), is essential for HO • production. The major reaction product between TCBQ and H 2 O 2 was identified by electrospray ionization quadrupole time-of-flight mass spectrometry to be the ionic form of trichlorohydroxy-1,4-benzoquinone (TrCBQ-OH), and H 2 O 2 was found to be the source and origin of the oxygen atom inserted into the reaction product TrCBQ-OH. On the basis of these data, we propose that HO • production by H 2 O 2 and TCBQ is not through a semiquinone-dependent organic Fenton reaction but rather through the following mechanism: a nucleophilic attack of H 2 O 2 to TCBQ, forming a trichlorohydroperoxyl-1,4-benzoquinone (TrCBQ-OOH) intermediate, which decomposes homolytically to produce HO • . This represents a mechanism of HO • production that does not require redox-active transition metal ions.

The use of technical HCH (1, 2, 3, 4, 5, 6-hexachlorocyclohexane), DDT (dichlorodiphenyltrichloroethane) and lindane in Heilongjiang River Basin (HRB) of China was studied. Between 1952 and 1984 the total usage in the HRB was 108900 t for technical HCH, and 4900 t for DDT, respectively, and the use of DDT due to dicofol application in the HRB was 220 t from 1984 to 2003. The usage of lindane in HRB was 109 t from 1991 to 2000. The results show that the highest technical HCH use (41800 t) in HRB was on maize, accounting for 38.3% of the total usage on all crops, followed by the use on wheat (28000 t, 25.7%) and on soybean (26600 t, 24.4%). The highest DDT use (2300 t) was on soybean, accounting for 46.8% of the total usage on all crops, followed by the use on maize (1500 t, 31.3%) and on sorghum (600 t, 13.2%). The major use of lindane was mainly on wheat. Gridded usage inventories of these three OCPs (organochlorine pesticides), in HRB with a 1/6 degrees latitude by 1/4 degrees longitude resolution have been created by using different gridded cropland as surrogates. Some soil samples have also been collected in HRB. Data of usage and soil concentrations of sigma HCH in HRB match quite well to those in Shanghai region, and much higher soil concentration of sigma DDT in Shanghai region could be due to much heavier dicofol use in this region.

A comprehensive method for the determination of methylmercury by capillary gas chromatography (GC) on-line coupled with atomic fluorescence spectrometry (AFS) was developed. The hyphenation system was carefully designed and the operation conditions such as injector temperature, carrier gas flow rate, make-up gas flow rate and argon flow rate were optimized in detail. The absolute detection limits (3sigma) were 0.005 ng of Hg for both methylmercury (MMC) and ethylmercury (EMC). The relative standard deviations (RSD, n = 5) for MMC and EMC at 10 ng x mL(-1) of Hg levels were 2.5% and 1.3%, respectively. The method was evaluated by analyzing a certified reference material (DORM-2), and the MMC concentration determined was in good agreement with the certified value. In addition, the recoveries of MMC in two sediment samples were 70% and 77%, respectively. The proposed method was accurate, sensitive and suitable for the determination of MMC in biological and sediment samples.

Butyltins in surface water, sediments and biota samples from Taihu Lake were determined. The results show that butyltins content in most of the surface water samples is under the limit of the detection; five out of ten sediment samples are measured detectable butyltins. Monobutyltin (MBT) was the main species with the concentrations ranging from below the detection limits to 0.95 ng/g; while all biota samples were detected relatively higher butyltin concentrations with a range of 27.05 - 181.23 ng/g due to the obvious bioaccumulation. Tributyltin (TBT) was the main composition that occupied almost 70% of the total butyltins. The antifouling paints applied on the aquatic cultural box and boats was the possible main source of butyltin compounds in Taihu Lake.

Base on the previous work in laboratory, a novel polyaniline doped with polydimethylsiloxane coating was developed on a stainless steel wire for solid phase microextraction(SPME) by electroplating method. This electroplating method not only has advantages of ease preparation and simple equipments required, but also increases the lifetime of the SPME fiber. The composite fiber (polyaniline/ polydimethylsiloxane(PANI/PDMS)) was evaluated by analyzing n-tridecane, n-tetradecane and n-pentadecane in aqueous sample. The new fiber coating showed comprehensive abilities to extract alkanes compounds. The relative standard deviations were found to be 6.8%-10.33%.

The concentration and speciation of six heavy metals in sediments of eight sampling sites of Haihe River were investigated. The metals, namely Cd, Cu, Co, Ni, Mn and Pb were considered. By using sequential extraction (SE), the total metals were divided into five fractions: exchangeable, carbonate bound, iron/manganese oxide bound, sulfides and organic matter fraction and residual fraction. A multivariate statistical approach (principal component analysis, PCA) was used to evaluate the contamination of heavy metals by the total levels and chemical forms, respectively. The results showed that the total metals concentration (TMC) could not provide sufficient and accurate information because the mobility, bioavailability and toxicity of metals depend not only on their total concentration but also on the physicochemical form in which they occur.

A comprehensive method for simultaneous determination of methylmercury (MeHg) and ethylmercury (EtHg) in rice by capillary gas chromatography (GC) coupled on-line with atomic fluorescence spectrometry was developed. The experimental conditions, including the pyrolyzer temperature and flow rates of the make-up gas and sheath gas, were optimized in detail. The absolute detection limits (3sigma) were 0.005 ng as Hg for both MeHg and EtHg. The relative standard deviation values (n=5) for 10 ng Hg/mL of MeHg and EtHg were 2.5 and 1.3%, respectively. The method was evaluated by analyzing 2 certified reference materials (DORM-2 and GBW08508), and the determined values of MeHg and total mercury concentrations were in good agreement with the certified values. In addition, the recoveries of MeHg and EtHg spiked into a rice sample collected from Jiangsu province in China were 86 and 77%, respectively. The proposed method was applied to analysis of MeHg and EtHg in 25 rice samples cultivated in 15 provinces of China. In all samples, MeHg was detectable and no EtHg was found. The MeHg contents in rice samples ranged from 1.9 to 10.5 ng/g, accounting for 7-44% of the total mercury measured.

The wide occurrence of estrogenic compounds 4-tert-octylphenol, 4-nonylphenol, bisphenol A in surface water of Guanting Reservoir was successfully determined. The target compounds in water samples were preconcentrated by liquid-liquid extraction with dichloromethane, derivatized by trifluoroacetic anhydride, and quantified by gas chromatography-mass spectrometry(GC-MS) with selected ion monitoring (SIM). In the selected seven sampling sites (S1-S7), the concentration of NP in sample S7 was significantly higher than the other in reservoir. The status of pollution in S3 and S7 were much more serious. The concentrations of OP, NP and BPA were in the range of 44.5-48.8, 221.6-349.6 and 30.2-82.7 ng/L, respectively. The pollutants were mainly inputted from the upper river and released from sediments in Guanting Reservoir.

A method was developed to determine the concentration of methyl tert-butyl ether(MTBE) in gasoline, diesel and heating oil by gas chromatography(GC) with mass spectrometry(GC-MS) or flame ionization detection (FID). The diluted gasoline was directly injected into the GC, and the complete separation of MTBE from co-eluting hydrocarbons was not required. GC/MS or GC/FID method can be used to analyze MTBE in different concentration range and have good consistency.

A possible butyltin contamination source in wine was studied in this paper. Agglomerated cork stoppers, which were produced in Portugal, Spain, and Italy, used in wine bottles were examined. The domestic cork products, cork granules, and mucus used for cork products were also analyzed. The levels of mono- and dibutyltin compounds in corks were found in the range from0.0024 to 3.3 and from0.0029 to 6.7 microg of Sn/g, respectively. A low level of tributyltin contamination was also found in 2 of 31 tested samples. The presence of butyltin compounds in agglomerated cork stoppers was confirmed by GC-MS. Experimental results indicated that all overseas agglomerated cork stoppers studied contained mono- and/or dibutyltins. Butyltins were not detected in cork granules, mucus, most of the natural cork stoppers, and domestic agglomerated cork products. The concentrations of mono- and dibutyltins increased with the time in a 30-day experiment, showing that butyltin compounds can leach from agglomerated cork to the wine. When the butyltin concentrations in wine samples were compared with their levels in the corresponding agglomerated cork stoppers, a correlation was found. The potential harm of such food contamination was evaluated by the toxic research of butyltin compounds using Daphnia sp. as the experimental model.

An on-line method capable of the separation of arsenic species was developed for the speciation of arsenite As(III), arsenate As(V), monomethylarsenic (MMA) and dimethylarsenic acid (DMA) in biological samples. The method is based on the combination of high-performance liquid chromatograph (HPLC) for separation, UV photo oxidation for sample digestion and hydride generation atomic fluorescence spectrometry (HGAFS) for sensitive detection. The best separation results were obtained with an anion-exchange AS11 column protected by an AG11 guard column, and gradient elution with NaH2PO4 and water as mobile phase. The on-line UV photo oxidation with 1.5% K2S2O8 in 0.2 mol L(-1) NaOH in an 8 m PTFE coil for 40 s ensures the digestion of organoarsenic compounds. Detection limits for the four species were in the range of 0.11-0.15 ng (20 microL injected). Procedures were validated by analysis of the certified reference materials GBW09103 freeze-dried human urine and the results were in good agreement with the certified values of total arsenic concentration. The method has been successfully applied to speciation studies of blood arsenic species with no need of sample pretreatment. Speciation of arsenic in blood samples collected from two patients after the ingestion of realgar-containing drug reveals slight increase of arsenite and DMA, resulting from the digestion of realgar.