激光等离子体诱导聚甲基硅氧烷的结构重组

将脉冲激光束在惰性气氛中溅射石墨产生的等离子体,与一维链状聚甲基硅氧烷的蒸气束流反应,在产物中通过真空升华和重结晶分离出了两种单晶,经X射线衍射测定为具有(CH3SiO1.5)n(n=8,10)组成的硅氧烷,它们均具有多面体的三维笼状构型。通过色-质联用还检测到其它硅氧烷化合物,其中某些产物已表征为二维多环的构型,反应结果表明,经由激光等离子体的碰撞和能量传递,反应物的链状结构发生解离和进一步反应,经结构重组形成了多种不同组成和构型的产物。     

Identification and evaluation of radiolysis products of irradiated chloramphenicol by HPLC-MS and HPLC-DAD

Summary The radiolysis products of chloramphenicol under γ-radiation sterilization were investigated systematically. Eight main radiolysis products were identified and quantified by HPLC-MS and HPLC-DAD, including two compounds never before reported. The minor radiolysis products were quantified, which shows that they are at concentration levels<threshold for identification. Carbon-carbon rupture reaction and oxidation reaction are proposed as the main radiolysis reactions of chloramphenicol powder. The applicability of γ-sterilization for chloramphenicol products was evaluated quantitatively with qualitative and quantitative data that were compared to the threshold requirements of international regulations for identification. It was concluded that toxicities of the radiolysis products of chloramphenicol produced by γ-radiation sterilization can be neglected, the radiolysis products are safe for human health from the chemical view.     

Identification of Vodkas by Ion Chromatography and Gas Chromatography

Vodka samples from various distilleries were analyzed by ion chromatography in combination with gas chromatography for the identification of alcoholic products. It was shown that vodkas of the same name manufactured at the same distillery exhibited relatively stable anion–cation compositions; therefore, the ionic composition of vodka can serve as an identification feature. The use of methanol, 2-propanol, and 1-propanol concentrations, which were determined by gas chromatography, as identification features of vodka enhances the probability of detecting adulterated alcoholic products.     

天然单萜柠檬烯的微生物转化

天然单萜柠檬烯资源丰富,价格便宜,在日用化工和医药行业已得到重要的应用。近几十年来,以柠檬烯为起始原料的新产品的研究与开发一直受到关注。大量文献报道了微生物能够对柠檬烯进行生物转化,得到系列在化妆品、食品、医药、有机合成等领域有重要应用价值的含氧衍生物。本文系统地综述了柠檬烯的微生物转化菌株和所得到转化产物的结构,分析了微生物对柠檬烯的主要转化途径以及影响微生物转化效率的主要因素。柠檬烯经微生物转化所得到的产物具有区域和立体选择性,并且难以通过人工合成方法得到。对生物转化过程进行系统优化,将有可能实现有用化合物的工业化生产。此外,在转化过程中诱导的高活性酶,尤其是单加氧酶和羟化酶的研究与应用也展现了诱人的前景。     

Characterization of ageing products of ester-based synthetic lubricants by liquid chromatography with electrospray ionization mass spectrometry and by electrospray ionization (tandem) mass spectrometry

Ageing products of a commercial jet engine oil based on pentaerythritol tetraesters which were formed upon operation in an aviation turbine were detected by electrospray ionization mass spectrometry (ESI-MS) and characterized by LC-ESI-MS. The fatty acid composition of these ageing products was investigated by ESI-MS-MS analysis. The ammonium adducts of the newly formed pentaerythritol tetraester degradation products were found to be suitable parent ions for further structure elucidation work. ESI-MS, LC-ESI-MS and ESI-MS-MS proved to be versatile tools to study the chemical composition (distribution of homologues) as well as the mechanism of ageing of ester based lubricants on a molecular level. Due to its high sensitivity, ESI-MS can also be used to characterize and identify trace levels of ester-based lubricants.     

正己烷溶液中4一氯联苯的紫外光降解研究

研究了正己烷溶液中4一氯联苯的紫外光降解反应。首次讨论了正己烷溶液中多氯联苯的特征紫外吸收和光反应中氯的形成的研究，光降解的主要反应途径为一级反应的脱氯。分子中C-Cl键断裂形成联苯自由基，该自由基从溶剂分子上脱去氢形成联苯，在光照下联苯继续降解最终生成脂肪烃。联苯的紫外光降解实验进一步证明了这种机理。     

Regio- and diastereoselective reductive coupling of vinylepoxides catalyzed by titanocene chloride

[reaction: see text] The Ti(III)-catalyzed reaction of a series of vinylepoxides leads, with regio- and E-diastereoselectivity control, to good-to-excellent yields of the corresponding homocoupling products. This homocoupling reaction, which involves a new C-C bond-forming method, takes place via a S(N)2' process between an allyltitanium species and the starting vinylepoxide. The process can be used for the rapid and efficient formation of highly valuable intermediates for organic synthesis, as well as new interesting homologues of natural products.     

Cyclobutenes by platinum-catalyzed cycloisomerization reactions of enynes

1,6-Enynes bearing (electron-rich) aryl substituents on their alkyne moiety rearrange to cyclobutene derivatives in the presence of catalytic amounts of PtCl2 in toluene. The reaction is significantly accelerated when performed under an atmosphere of CO (1 atm), most likely by increasing the electrophilicity of the metal template by temporary coordination to this pi-acidic ligand. This transformation allows the build up of considerable strain in the products as witnessed by the productive formation of tricyclic skeletons, such as 7 or 9. Moreover, these products provide evidence for the mechanistic scenario of platinum-catalyzed cycloisomerization reactions previously proposed, which are thought to proceed via organo-platinum species that mimic the reactivity of metal-complexed "nonclassical" carbocations.     

PGC-MS鉴别乙烯-辛烯共聚物

乙烯-辛烯共聚物与聚乙烯性能、价格差别很大,但无鉴别二者的检验方法。我们采用裂解气相色谱一质谱(PGC-MS)方法研究这两种聚合物的热裂解产物的组成,发现两者裂解产物的成分相同,均为不同碳数的烷烃、烯烃化合物;但含量有区别,主要区别在辛烯。乙烯-辛烯共聚物裂解产物中辛烯(C8)的相对含量明显高于聚乙烯,C8峰可作为鉴别乙烯-辛烯共聚物的特征峰,据此建立了鉴别两种聚合物的方法,并在进出口商品检验中得到很好的应用。     

A synthetic approach to seven-membered lactones by the microbial transformation of ynones having a trifluoromethyl group

Studies on the microbial transformations of a number of ynones bearing a trifluoromethyl group prepared by the reaction of ethyl trifluoroacetate with a variety of lithium alkynates, have been undertaken. The major products were the corresponding carbinols but microbial carbon-carbon bond degradation and formation occurred also, which proceeded to novel fluorinated seven-membered lactones as significant products.     

Measurement of the abrasion of radioactive teeth by dentifrices

The purpose of this study is to assess the dentifrice abrasivity of both commercially available products and test products. The assessment of abrasivity was carried out by the measurement of 32P released from tooth by using radioactive dentifrice abrasion (RDA) method. In dentine, RDA values, which show the polishing ability for dentine, were 65-100 with dentifrices with normal cleaning power and 106-182 with those with high cleaning power, respectively. On the other hand, REA values which show the polishing ability for enamel were 12-405 with both market products and test products. The difference of the REA values according to the dentifrices appears to be largely influenced by the difference of polishing agents of each dentifrice. It is concluded that RDA method is usefull for assessing of dentifrice abrasivity. However, particular attention should be given to the abrasion of dentine.     

Engineering a polyketide with a longer chain by insertion of an extra module into the erythromycin-producing polyketide synthase

BACKGROUND: Modular polyketide synthases catalyse the biosynthesis of medically useful natural products by stepwise chain assembly, with each module of enzyme activities catalysing a separate cycle of polyketide chain extension. Domain swapping between polyketide synthases leads to hybrid multienzymes that yield novel polyketides in a more or less predictable way. No experiments have so far been reported which attempt to enlarge a polyketide synthase by interpolating additional modules. RESULTS: We describe here the construction of tetraketide synthases in which an entire extension module from the rapamycin-producing polyketide synthase is covalently spliced between the first two extension modules of the erythromycin-producing polyketide synthase (DEBS). The extended polyketide synthases thus formed are found to catalyse the synthesis of specific tetraketide products containing an appropriate extra ketide unit. Co-expression in Saccharopolyspora erythraea of the extended DEBS multienzyme with multienzymes DEBS 2 and DEBS 3 leads to the formation, as expected, of novel octaketide macrolactones. In each case the predicted products are accompanied by significant amounts of unextended products, corresponding to those of the unaltered DEBS PKS. We refer to this newly observed phenomenon as 'skipping'. CONCLUSIONS: The strategy exemplified here shows far-reaching possibilities for combinatorial engineering of polyketide natural products, as well as revealing the ability of modular polyketide synthases to 'skip' extension modules. The results also provide additional insight into the three-dimensional arrangement of modules within these giant synthases.     

改进的低温固相法制备钙钛矿型KTaO3

采用改进的固相法, 以K2CO3和氢氧化钽为原料, 通过添加KF, 在相对低温下制备了单一钙钛矿结构的KTaO3. KF的加入抑制了烧绿石相的生成, 通过水洗可脱除KF. 使用X射线衍射仪(XRD), 扫描电子显微镜(SEM)和紫外-可见(UV-Vis)漫散射光谱仪对不同温度下制备的产物进行了表征. 结果表明, 各个温度下制备的产物均是由粒径在10~30 nm范围内的粒子聚集成的大颗粒; 500, 600和800℃制备的产物带隙分别为3.68, 3.63和3.54 eV. 进一步考察其它碱金属卤化物对产物结构的影响发现, LiF, NaF和KF的作用相同; 当添加碱金属氯化物时, 主要产物分别是钽酸锂、 钽酸钠和烧绿石结构的钽酸钾.     

Removal of 3'-phosphate group by bacterial alkaline phosphatase improves oligonucleotide sequence coverage of RNase digestion products analyzed by collision-induced dissociation mass spectrometry

RNase mapping by nucleobase-specific endonucleases combined with liquid chromatography/tandem mass spectrometry (LC/MS/MS) is a powerful analytical method for characterizing ribonucleic acids (RNAs). Endonuclease digestion of RNA yields products that contain a 3'-terminal phosphate group. MS/MS via collision-induced dissociation (CID) of these digestion products on a linear ion trap generates fragmentation pathways that include the loss of phosphoric acid (-H(3)PO(4); -98 u), which does not provide information about the sequence of the digestion products and can reduce ion abundance from other pathways that provide sequence information. Here we investigate the use of bacterial alkaline phosphatase (BAP) after RNase digestion to remove the 3'-terminal phosphate from all RNase digestion products prior to LC/MS/MS analysis. RNase digestion products lacking the 3'-phosphate were found to produce CID spectra with more consistent, high-abundance c- and y-type fragment ions as well as significantly more a-Base and w-type ions than digestion products retaining the 3'-phosphate. In this manner, RNase mapping with LC/MS/MS can provide more complete RNA sequence information from fragment ions of higher abundance that are easier to interpret and identify.     

A concise synthesis of substituted stilbenes and styrenes from propargylic phosphonium salts by a cobalt-catalyzed Diels-Alder/Wittig olefination reaction sequence

The cobalt(I)-catalyzed Diels-Alder reaction of propargylic phosphonium salts and longer chained alkyne-functionalized phosphonium salts with 1,3-dienes led to dihydroaromatic phosphonium salt intermediates which were directly used in a one-pot Wittig-type olefination reaction with aldehydes. Subsequent oxidation led to styrene- and stilbene-type products under formation of three new carbon-carbon bonds in a single synthetical step starting from three variable starting materials. The E/Z stereoselectivities of the products revealed that the dihydroaromatic phosphonium ylides behave as semistabilized ylides giving predominantly the E-configured products. The application of unsymmetrical 1,3-dienes as well as internal phosphonium functionalized alkynes is also described.     

Characterization of stress degradation products of amodiaquine dihydrochloride by liquid chromatography with high‐resolution mass spectrometry and prediction of their properties by using ADMET Predictor™

The degradation behavior of amodiaquine dihydrochloride, an antimalarial drug, was investigated in solution as well as solid states. The drug was subjected to hydrolytic, photolytic, oxidative, and thermal stress conditions, according to International Conference on Harmonization guideline Q1A(R2). It showed extensive hydrolysis in acidic, alkaline, and neutral solutions both with and without light, while it proved to be stable to thermal and oxidative conditions. In total, six degradation products were formed, which were separated on a C8 column, employing a gradient reversed‐phase high‐performance liquid chromatography method in which acetonitrile and 10 mM ammonium formate (pH 3.0) were used in the mobile phase. To characterize the degradation products, mass fragmentation behavior of the drug was established by direct infusion of solution to quadrupole time‐of‐flight and multiple‐stage mass spectrometry systems. Liquid chromatography with high‐resolution mass spectrometry studies were subsequently carried out on the stressed samples using the same gradient high‐performance liquid chromatography method employed for the separation of the degradation products. Hydrogen/deuterium exchange studies were additionally conducted to determine the number of labile hydrogen atoms. The degradation pathway of the drug was delineated, justified by mechanistic explanation. Lastly, ADMET Predictor™ software was employed to predict relevant physicochemical and toxicity data for the degradation products.     

Production and characterization of the biofuels obtained by thermal cracking and thermal catalytic cracking of vegetable oils

The thermal cracking and the thermal catalytic cracking of soybean oil were evaluated for the production of biofuels as an alternative to fossil fuels. The catalyst proposed for the cracking reaction was bauxite, a high-acidity and low-cost catalyst. The chromatographic profile of the biofuels obtained by cracking showed hydrocarbon compounds such as alkanes, alkenes and aromatics, as well as some oxygenated compounds such as carboxylic acids, ketones and alcohols. The products generated by the thermal catalytic cracking process showed better results than the thermal cracking products because of the low quantity of acids present. The catalyst used was thus shown to act in the secondary cracking process, in which the fatty acids decompose and generate hydrocarbons.     

基于热重红外联用分析的PE、PS、PVC热解机理研究

利用TGA-FTIR联用技术考察了PE、PS、PVC三种典型塑料的热解特性。结果表明,热稳定性从弱到强依次为PVC、PS、PE。PE热解反应过程为典型的一段式反应,红外光谱分析结果表明,PE热解过程为无规则断链形式,生成产物成分复杂,且随热解过程而改变,开始以饱和烃基团为主,中后期以烯烃基团为主,同时有少量炔烃;PS热解过程同样为一段式反应,红外光谱显示主要热解产物为苯乙烯单体,说明热解过程主要是苯乙烯的解聚过程;PVC热解过程较为复杂,主要分为脱氯阶段和共轭多烯重构阶段,红外光谱结果表明,产物中有芳香族化合物。脱氯过程和共轭多烯重构、环化过程在时间和空间上有重合,给二噁英类污染物的生成制造了可能。     

TEA法测定NO2的反应机理研究

应用FABMS、NMR、IR、HPLC和紫外吸收光谱研究了室温下三乙醇胺与较高浓度NO₂(2.48%)的反应情况,证明反应产物为三乙醇胺硝酸盐和三乙醇胺亚硝酸盐,提出了可能的反应机理,为TEA法监测空气中NO₂的浓度提供了依据.