Kinetic mechanism and effects of molecular structure on thermal hazards of azo compounds

In this paper, the kinetic mechanism of AIBN, AMBN, and ABVN was proposed, and the effect of molecular structure on their thermal hazards based on the kinetic mechanism was investigated. Calculated by non-isothermal DSC datum, the kinetic mechanism of AIBN, AMBN, and ABVN is revealed by the linear relationship between the integrated form of mechanical function and reaction time. The results indicate that the thermal decomposition process is controlled by the Johnson-Mehl-Avrami equation. Based on the determination of kinetic mechanism function, the reaction rate constants at various heating rates are directly calculated, and the intercept of the best fitting straight line of reaction rate constants with heating rate is approximately equal to the reaction rate constant under isothermal conditions. Besides, theoretical values obtained by multiplying kinetic mechanism function by reaction rate are well consistent with the experimental values, suggesting that the kinetic mechanism obtained is credible. Bond Dissociation Energies (BDE) calculated by quantum chemical equations are employed to evaluate the thermodynamics stability of AIBN, AMBN, and ABVN. Depending on similar molecular structures, the influence of differentiated group structure on the thermodynamic stability represented by BDE and heat release and the kinetic stability characterized by reaction rate constant were revealed. Finally, the results demonstrate that the thermal hazard increases as the volume of substituent group and molecular weight.     

用超滤法处理洗毛污水

本文就聚砜中空纤维超滤法处理洗毛污水进行了研究，首先考查了不同截留分子量的超滤膜对超滤性能的影响，发现截留分子量为３万的膜超滤性能较佳；然后考查了压力、温度、浓度及流速等操作参数对超滤性能的影响；污水经过超滤后，脂、总固体及ＣＯＤ去除率分别在９８％、８０％和９５％以上．     

络合滴定－阳极溶出伏安法测定腐植酸与金属络合物的稳定常数

以金属离子络合滴定－阳极溶出伏安法（ＡＳＶ法）测定得出湘江底泥、灵石风化煤和德都泥炭３种腐植酸分别与Ｐｂ、Ｃｄ的络合稳定常数、络合容量和分子量３个参数．并探讨了可能的误差来源及消除方法。     

菌丝体表面分子印迹壳聚糖吸附剂对Cr3+的吸附性能研究

菌丝体表面分子印迹吸附剂所保留的印迹对过渡金属离子有着良好的吸附作用,以Cr3 作为吸附离子,系统研究了该吸附剂的吸附特性和影响因素.结果表明:吸附剂对Cr3 的饱和吸附容量可达60 mg/g;其吸附行为满足Langmuir方程式.初始浓度为200 mg/L时,最佳吸附pH在3～4,吸附容量可达到50 mg/g左右,离子强度对吸附没有影响,用0.5 mol/L硝酸或硫酸解吸Cr3 ,解吸率在90%以上.     

Molecular ecological networks reveal the spatial-temporal variation of microbial communities in drinking water distribution systems

Microbial activity and regrowth in drinking water distribution systems is a major concern for water service companies. However, previous studies have focused on the microbial composition and diversity of the drinking water distribution systems(DWDSs), with little discussion on microbial molecular ecological networks(MENs) in different water supply networks.MEN analysis explores the potential microbial interaction and the impact of environmental stress, to explain the characteristics of microbial...     

Relating Cd2 + binding by humic acids to molecular weight: A modeling and spectroscopic study

Molecular weight(Mw) is a fundamental property of humic acids(HAs), which considerably affect the mobility and speciation of heavy metals in the environment. In this study, soil humic acid(HA) extracted from Jinyun Mountain, Chongqing was ultra-filtered into four fractions according to the molecular weight, and their properties were characterized.Complexation of cadmium was investigated by titration experiments. For the first time,Langmuir and non-ideal competitive adsorption-Donna(NICA-Donnan) models combined with fluorescence excitation-emission matrix(EEM) quenching were employed to elucidate the binding characteristics of individual Mw fractions of HA. The results showed that the concentration of acidic functional groups decreased with increasing Mw, especially the phenolic groups. The humification degree and aliphaticity increased with increasing Mw as indicated by elemental composition analysis and FT-IR spectra. The binding capacity of Cd~(2+) to Mw fractions of HA followed the order UF1( 5 kDa) UF2(5–10 kDa) UF4( 30 kDa) UF3(10–30 kDa). Moreover, the distribution of cadmium speciation indicated that the phenolic groups were responsible for the variations in binding of Cd~(2+) among different Mw fractions. The results of fluorescence quenching illustrated that the binding capacity of Cd~(2+) to Mw fractions was controlled by the content of functional groups, while the binding affinity was largely influenced by structural factors. The results provide a better understanding of the roles that different HA Mw fractions play in heavy metal binding,which has important implications in the control of heavy metal migration and bio-toxicity.     

Effect of ultra-micro powder Dendrobium officinale on the molecular diversity of intestinal bacteria in mice with spleen-deficiency constipation北大核心CSCD

This research aimed to study the effect of ultra-micro powder Dendrobium officinale on the molecular diversity of intestinal bacteria in mice with spleen-deficiency constipation, in order to provide scientific basis for ultra-micro D. officinale therapy. The mice with spleen-deficiency constipation in treatment groups were respectively given the traditional decoction of D. officinale and 50% dose ultra-micro powder D. officinale. The metagenome DNA of intestinal flora was extracted from intestinal contents. Then ARDRA analysis was made after PCR by universal primer of bacteria. The results showed that OTUs, Shannon index and Brillouin index were the same between the normal group and the 50% dose ultra-micro powder group, and between the model group and the traditional decoction group, but greater in the former two groups than the latter ones. The similarity coefficient (0.500 0) was bigger between the 50% dose ultra-micro powder group and the normal group than between the model group and the traditional decoction group, which was 0.181 8. Both cluster analysis and principal components analysis showed that the molecular diversity of intestinal microbiotia in mice of 50% dose ultra-micro powder group was the closest to that in the normal group. The results showed that the weakened molecular diversity of intestinal bacteria in mice with spleen-deficiency constipation can be regulated by the two kinds of D. officinale treatments to different extent. The efficacy of 50% dose ultra-micro powder D. officinale is better than the traditional decoction.     

Review on the study of mercury/silver ions-pyrimidine base pairs in DNA duplexes and their application in detection technology北大核心CSCD

Nucleic acids and their analogues are getting more and more attention. Metal-mediated base pairs as a kind of simple and functionalized nucleic acids in special positions have widened the scope of application of functional nucleic acids and their analogues. In this type of base pairs, the representative is the interaction between metal ions and pyrimidine bases, especially the research on thymine-Hg2+-thymine (T-Hg2+-T) and cytosine-Ag+-cytosine (C-Ag+-C) base pairs. This review summarizes the structure and mechanism of metal-mediate pyrimidine base pairs as well as the application in the biochemical analysis. It explores the mode and ratio of coordination between metal ions and base pairs, the effects on the stability of DNA helical structure, the related crystal structure and the three-dimensional configuration information in the DNA helix. The analytical application mainly includes various probes of metal ions, small molecules, protein and the detection of single nucleotide polymorphism. Among them the most widely used metal ions detection, and its combination with spectrum technology, visualization and amplification technology greatly promoted the rapid development of sensitive detection technology. In further studies, it is necessary to reveal the mechanism of interaction between T-Hg2+-T and C-Ag+-C, and more attention should be paid to combining of T-Hg2+-T and C-Ag+-C base pairs with other new technologies. The scope of practical application should also be further extended.     

Molecular diversity of arbuscular mycorrhizal fungi at a large-scale antimony mining area in southern China

Arbuscular mycorrhizal fungi(AMF) have great potential for assisting heavy metal hyperaccumulators in the remediation of contaminated soils. However, little information is available about the community composition of AMF under natural conditions in soils contaminated by antimony(Sb). The objective of this study was to investigate the characteristics of AMF molecular diversity, and to explore the effects of Sb content and soil properties on the AMF community structure in an Sb mining area. Four Sb mine spoils and one adjacent reference area were selected from around the Xikuangshan mine in southern China. The association of AMF molecular diversity and community composition with the rhizosphere soils of the dominant plant species was studied by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis(PCR-DGGE). Results from all five studied sites showed that the diversity of AMF decreased with increasing Sb concentration. Principal component analysis(PCA) indicated that the AMF community structure was markedly different among these groups. Further redundancy analysis(RDA) showed that Sb contamination was the dominating factor influencing the AMF community structure in the Sb mine area. However, the multivariate analysis showed that, apart from the soil Sb content, extractable nitrogen content and organic matter content also attributed to AMF sequence distribution type. Some AMF sequences were only found in the highly contaminated area and these might be ideal candidates for improving phytoremediation efficiency in Sb mining regions. Gene sequencing analysis revealed that most species were affiliated with Glomus, suggesting that Glomus was the dominant AMF genus in the studied Sb mining area.     

Alteration of acetylcholinesterase activity in Semele solida (MOLLUSCA: SEMELIDAE) as a biochemical response to coastal anthropogenic impact

Acetylcholinesterase (AChE) activity was analyzed as a molecular marker indicative of exposure to organophosphorus pesticide residues in individuals of the endemic clam species Semele solida in selected coastal locations of Chile's VIII Region. AChE activity was assayed in clams from (i) Penco Beach near the mouth of the Andalién River (Concepción Bay), (ii) Lenga Beach, near the mouth of the Lenga Estuary (San Vicente Bay), and (iii) Coliumo Beach, near the mouth of the Coliumo Estuary (Coliumo Bay). We also analyzed variations in protein content of clam hemolymph, and variability in the activity of AChE in relation to the sizes of the individual clams sampled. Collection of the clams was done using routine methods, during the spring of 2005, the period during which the use of pesticides is typically intensified in the surrounding forestry and agriculture. The results showed no significant correlation of AChE activity with either the size of the clam, or with the concentration of proteins in the hemolymph. The lowest AChE activity was observed in clams from mouth of the Andalién River (187.5 ± 34.9 Umin^?1) which was significantly less than that measured in specimens collected near the mouth of the Coliumo Estuary and the mouth of the Lenga Estuary. A very close relation was observed between the degree of anthropogenic inputs, ocean dynamics, and alterations in AChE activity in S. solida. This clam appears to be a useful indicator species, and AChE activity a sensitive marker for the presence of xenobiotics.