Validation of the thermodynamic model of inorganic arsenic in non polluted river waters of the Basque country (Spain)

The thermodynamic model of inorganic arsenic was validated by comparing the predicted As(III) concentration with the experimentally determined one in several river waters samples of the Basque Country (Spain) collected in two sampling campaigns: spring and autumn 2000. This model takes into account the acid-base equilibria of As(III) and As(V) together with the redox equilibria between the H₃AsO₃ and H₃AsO₄ species. A correct prediction of As(III) concentration requires the knowledge of the total concentration of arsenic, pH, redox potential (referred to hydrogen electrode), and ionic strength values of the solution. The estimation of the activity coefficients of the arsenic species was performed by means of the Modified Bromley’s Methodology (MBM).In order to perform the experimental As(III) determination, an analytical method was implemented by using an ion exchange separation of As(III)/As(V) on a continuous FIA-IE-HG-AAS system. The total arsenic concentration was determined together with total concentration of the main alkaline or alkaline-earth metals and anions in the natural waters. Temperature compensated measurements of the pH and redox potentials were made in-situ at the sampling sites.For both seasonal campaigns, the agreement between predicted and experimental As(III) is really high for those samples belonging to non polluted river waters.     

催化裂化USY／ZnO／Al2O3脱硫添加剂的高温水热失活

 对USY／ZnO／Al2O3汽油催化裂化脱硫添加剂经高温水热老化处理前后的脱硫性能进行了考察，发现老化后添加剂的脱硫性能大幅度下降．采用XRD和IR等技术对USY／ZnO／Al2O3添加剂在高温和高温水热条件下失活的原因进行了研究．结果表明，在高温下，ZnO可与USY沸石中的铝发生固相反应生成ZnAl2O4尖晶石，从而造成USY晶体结构崩塌，转变成无定形状态．在ZnO含量较高的条件下，ZnO可继续与USY晶体结构崩塌后生成的无定形的硅和铝的氧化物反应，生成Zn2SiO4硅锌矿和ZnAl2O4尖晶石结构．这一方面使添加剂失去了可形成硫化物吸附中心的ZnO，另一方面破坏了硫化物的裂化活性组分USY，从而造成添加剂脱硫性能下降甚至失去脱硫活性．ZnO对USY的破坏作用主要与温度有关．在USY／ZnO／Al2O3体系中，ZnO被ZnO与Al2O3之间形成的锌铝尖晶石膜固定并与USY隔离，单纯的高温条件对添加剂的破坏不显著，而水蒸气可以促进ZnO的移动，有利于ZnO与USY的接触，因此在高温和有水蒸气存 在的条件下添加剂的结构易遭到破坏．     

Asymmetric hetero Diels-Alder as an access to carbacephams.

A short and efficient asymmetric synthesis of the (6R,7S)-7-tert-butoxycarbonylamino-2-ketocarbacepham is described. The key step involves the hetero Diels-Alder reaction of the benzylimine derived from the enantiomer of Garner's aldehyde with Danishefsky's diene.     

Influences of the Hydrophobicity of the Heme-binding Pocket on the Properties and Functions of Cytochrome b_5 Mutants

IntroductionElectrontransferreactionsarethekeystepsinphoto synthesis ,respirationandmanyotherbiochemicalprocess es.1Cytochromeb5isaredoxproteinexistingwidelyinnature ,whichactsasanelectron carrierduringvariouselectrontransferprocessesinthebiologicalsystem .2Cytochromeb5isamembraneproteinwithmolecularweightofapproximately 16kDa ,ofwhichthehydrophobicC terminaldomainanchorscytochromeb5tothemem brane ,andthehydrophilicN terminaldomaincontainshemeprostheticgroupandexhibitsthebiologicalfunctionsof…     

沐浴海绵Spongia zimocca aubspecles irregularia(Lendenfeld)中的含氮化合物

从沐浴海绵Spongia zimocca aubspecles irregularia(Lendenfeld)分离和处理得到3种含氮化合物,通过波谱法鉴定化学结构,化合物1为新的神经酰胺N-2-(1,3-二羟基-十五烷基)-2′,20′-二十一酰胺,2为神经酰胺(E)-N-2-(1,3-二羟基-4-十八烯基)-十六酰胺,3为醋酸胍.     

三维配位聚合物[Zn(HCO2)2(4,4''''-bipy)]∞的合成、晶体结构及性质研究

以ZnO,HCO_2H及4,4'-bipy(摩尔比1∶3∶1.25)溶于H_2O和DMF(体积比13∶1),并在60℃反应,合成了标题化合物[Zn(HCO_2)_2(4,4'-bipy)]_∞,对其进行了元素分析、红外光谱等表征,并测定了晶体结构.该化合物晶体属四方晶系,P4_32_12空间群,a=b=0.79675(5)nm,c=1.7627(2)nm,V=1.1190(3)nm~3,Z=4,Dc=1.850g/cm3,M_r=311.60,F(000)=632,μ=22.07cm-1,最终偏离因子R1=0.0183和wR_2=0.0483.该化合物中Zn原子和两个4,4'-bipy的N原子和四个甲酸根的O原子配位,形成的ZnN_2O_4八面体通过4,4'-bipy和甲酸根桥联,组成一种新颖的3D网络结构.同时,研究了该化合物的热性质和荧光性质.     

Arsenic Speciation Analysis in Solutions Treated with Zeolites

Experiments have been carried out to study the behaviour of organoarsenicals treated with zeolites by means of speciation analysis. IC-ICP-MS was applied to identify and quantify arsenite, arsenate and the following organoarsenicals: monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), trimethylarsine oxide (TMAO), tetramethylarsonium bromide (TMA⁺), arsenobetaine (AsB) and arsenocholine (AsC). Zeolites loaded with ferrous ions did not significantly increase the retention of inorganic arsenic species compared to the native zeolites, while there was a ten-fold removal of arsenate relating to arsenite. The formation of As(V) and DMA in the leachates containing clinoptilolites and mordenites was confirmed in the presence of natural and synthetic zeolites. Arsenobetaine and arsenocholine yielded higher levels of arsenate than the methylated species.     

Hydrothermal Synthesis and Crystal Structure of a Highly Reduced Mixed Molybdenum-vanadium Polyoxometalate with Phosphorus-centered [Ni(phen)3]2H2·[PmoⅤ4MoⅥ4VⅣ6M2M44]5-·4H2O(M=0.78MoⅤ+0.22VⅣ)

Polyoxometalates(POMs0) containing Keggin moieties exhibit a wide variety of compositions and have considerable structrral versatility as well as important magnetic, optical,and catalytic proper-ties[1-6].     

含吡咯烷酮基丙烯酸酯类单体的合成及聚合

轻度交联的聚甲基丙烯酸2-羟乙酯(HEMA)是众所周知的医用水凝胶,即所谓的“Hvdron”。但其吸水率一般在59%(EWC为37%),并不尽人意。近年来,为了提高这类水凝胶的亲水性及生物相容性,常用一些亲水性的烯类单体进行表面改性或通过共聚以达到此目的,N-乙烯基吡咯烷酮是较为常用的这类单体之一。本文合成了含吡咯烷酮基丙烯酸酯类的单体,即丙烯酸2-N-吡咯烷酮基乙酯(PyEA),甲基丙烯酸2-N-吡咯烷酮基乙醋(PyEMA),并研究了这两种单体在甲基丙烯酸二甲氨乙酯(DMAEMA)与过硫酸钾(KPS)所组成的氧化还原引发体系下的聚合。