预浓缩/色谱-质谱测量大气中挥发性有机硫化合物

硫循环是生物地化循环中最复杂的循环之一. 近年来,由于人类活动的影响,大气中硫化物含量急剧增加. 这些硫化物与大气中自由基发生作用,形成SO2、H2SO4和硫酸盐, 导致环境酸化, 酸沉降加剧.硫酸盐气溶胶的形成还改变了大气云层特性,影响大气臭氧含量的垂直分布以及大气热量辐射,对温室效应有一定的贡献[1-3].挥发性有机硫化合物中的甲硫醇(MT),甲硫醚(DMS),二硫化碳(CS2)和二甲二硫(DMDS)还是国家标准控制《恶臭污染物排放标准》中规定的4种恶臭气体,对大气环境质量造成一定的影响.     

超声提取辅助顶空式固相微萃取/气相色谱-质谱法测定塑胶跑道面层中7种挥发性硫化物

建立了一种检测塑胶跑道面层中二甲基硫(DMS)、二硫化碳(CS2)、甲基乙基硫(MES)、二乙基硫(DES)、二甲基二硫(DMDS)、二乙基二硫(DEDS)、二甲基三硫(DMTS)7种挥发性硫化物(VSCs)的超声提取辅助顶空式固相微萃取/气相色谱-质谱(HS-SPME/GC-MS)分析方法.实验优化了顶空固相微萃取的...     

选择离子流动管质谱法测定大蒜酶解液顶空中17种有机硫化合物

采用选择离子流动管质谱(SIFT-MS)法,顶空取样后,以H3O+,NO+或O2+为初始离子,定量分析了17种大蒜酶解液挥发性有机硫化合物。结果表明:有机硫化合物主要为二烯丙基硫醚、甲基烯丙基硫醚、硫代亚磺酸酯和硫醇,其中二烯丙基二硫醚浓度为137 g/m3,二烯丙基三硫醚浓度为13.4 g/m3,甲基烯丙基二硫醚浓度为8.98 g/m3,它们分别占17种有机硫化合物总含量的77.3%,7.58%和5.08%(相对含量);本研究采用顶空取样方法测出大蒜素的浓度为5.63 g/m3,相对含量为3.20%。     

海洋微藻培养液中二甲基硫与二甲基硫丙酸的同步分析

基于水体中二甲基硫(DMS)的固相微萃取-气相色谱-质谱联用分析方法,建立了海洋微藻培养液中DMS、溶解态二甲基硫丙酸(DMSPd)和颗粒态二甲基硫丙酸(DMSPp)的同步测定方法. 结果表明: 本方法在0.01～10.0 μg/L 范围内线性良好, 方法检出限10.6 pg , 加标回收率为(93.1±1.3)%; 相对误差范围小于5%.将4种微藻培养液高速离心,上层和下层溶液分别加固体NaCl后立即测定DMS,加NaOH 溶液反应12 h后测定DMS含量, 根据其数值的差值可得到各微藻培养液中DMS与DMSP的含量.检出结果与文献报道具有相似的结论:甲藻和定鞭藻是DMS(P)的重要生产者.其中颗石藻 (Pleurochrysis carterae)单位细胞DMSPp 的检出含量为(13.8±0.9)pg/cell.     

离子色谱法测定饮用水中的5种卤代乙酸

利用IonPac AS19大容量阴离子交换色谱柱对水中的一氯乙酸、二氯乙酸、三氯乙酸、一溴乙酸、二溴乙酸5种卤代乙酸(HAAs)进行了分离,优化了分离条件.通过控制分离温度实现了二氯乙酸(DCAA)与NO2-的分离;通过梯度洗脱使三氯乙酸(TCAA)与SO42-得到较好、较快的分离;通过中和脱气法解决了在大量CO32-(HCO3-)存在时对实验的干扰.DCAA、TCAA的检出限(以3倍信噪比计)分别达到了2.50 μg/L和3.75 μg/L.5种HAAs在10.0～2 000.0 μg/L线性范围内线性相关系数在0.999以上.     

原位衍生分散液相微萃取-气相色谱/质谱快速检测饮用水中的痕量三氯生

建立了原位衍生分散液相微萃取-气相色谱/质谱检测饮用水中痕量三氯生的方法.将含有30.0 μL氯苯(萃取剂)和50.0 μL乙酸酐(衍生试剂)的0.5 mL丙酮(分散剂)作为萃取体系,快速注入到5.0 mL含有K2CO3(0.5%, m/V)的水溶液中.在5000 r/min下离心2 min后,得到(10±0.5) μL沉积相(氯苯),取底部沉积相1.0 μL进行气相色谱/质谱联用仪分析.方法的线性范围为0.05～50 μg/L(r=0.9994),检出限为0.01 μg/L;相对标准偏差2.0%(n=5).利用本方法检测了饮用水中的三氯生,平均加标回收率分别为92.1%和98.4%,结果满意.     

固相萃取-反相高效液相色谱法测定水中的邻苯二甲酸酯

建立了固相萃取-反相高效液相色谱法检测水中3种邻苯二甲酸酯类物质邻苯二甲酸二甲酯、邻苯二甲酸二(2-乙基己基)酯、邻苯二甲酸二正辛酯的方法. 考察了固相萃取柱、洗脱溶剂、洗脱体积、上样速度以及洗脱速度对萃取效率的影响. 通过综合分析, 选定SupelcleanLC-18 SPE Tube固相萃取柱, 甲醇为洗脱剂, 洗脱体积2 mL, 上样速度为4 mL/min, 洗脱速度为1 mL/min. 在此萃取条件下, 萃取回收率在83.4%～121.2%之间. 邻苯二甲酸二甲酯、邻苯二甲酸二(2-乙基己基)酯、邻苯二甲酸二正辛酯质量浓度在2～100 mg/L之间均为线性. 经萃取后, 方法的最低检出限分别为邻苯二甲酸二甲酯0.06 μg/L, 邻苯二甲酸二(2-乙基己基)酯0.16 μg/L, 邻苯二甲酸二正辛酯0.08 μg/L. 方法的精密度在10%～15%之间. 应用该方法测定自来水中酞酸酯类化合物的含量, 加标回收率为83.6%～110.2%.     

离子色谱-氢化物发生原子荧光光谱联用技术在砷形态分析中的应用

建立了离子色谱-氢化物发生原子荧光光谱联用分离4种常见有毒砷化合物的方法. 二者通过内径0.25 mm的PEEK管直接相连. 实验对影响分离度和测定灵敏度的参数进行了优化. 在优化条件下, 质量浓度均为50 μg/L的4种砷化合物混合标准溶液平行7次进样, 得到DMA、 As(Ⅲ)、 MMA和As(Ⅴ)的色谱峰面积的相对标准偏差(RSD)为2.8～3.0%. 250 μL进样的线性范围为5～1000 μg/L, 检出限为0.8～1.2 μg/L (三倍基线噪音峰高). 用建立的方法测定了砷处理后的水稻木质部伤流液中的砷量, 4种砷化合物的加标回收率为89%～105%. 该装置接口简单, 方法分离度好, 灵敏度高, 可用于实际样品中痕量砷化合物的形态分析.     

2-亚磷酸二乙酯基杂环烯酮缩胺类化合物的合成

用廉价易得原料Mn(OAc)2-KMnO4体系代替昂贵的Mn(OAc)3催化二甲缩硫醚(1)与亚磷酸二乙酯反应获得结构新颖的2-亚磷酸二乙酯基缩硫醚化合物2a～2d.然后,化合物2a～2d与二胺类化合物3反应以较高产率合成了一系列2-亚磷酸二乙酯基杂环烯酮缩胺(4).     

新型1,2,4-三唑硫醚取代乙酰胺类化合物的合成及抗菌活性

以3, 4, 5-三甲氧苯甲酸为原料,将具有优良生物活性的1,2,4-三唑与酰胺结构有机结合,通过酯化、肼解、环化、醚化、水解、缩合等反应合成1, 2, 4-三唑硫醚乙酰胺类化合物6a-6m,其结构经1H NMR,13C NMR,MS和元素分析进行了结构确证。初步生物活性测试表明：化合物浓度在50 μg/mL时,化合物6a-6m对猕猴桃软腐病中的葡萄座腔菌、拟茎点霉菌（Phomopsis sp.）和灰霉菌（B. cinerea）表现一定的抑制活性,其中化合物6k和6l对葡萄座腔菌、拟茎点霉菌和灰霉菌的抑制活性在83.4%至91.3 %;化合物6k对葡萄座腔菌和拟茎点霉菌的EC50值为46.6 μg/mL和30.8 μg/mL,均优于对照药剂嘧霉胺(57.6 μg/mL 和 32.1 μg/mL)。以上生物活性表明,1, 2, 4-三唑硫醚乙酰胺类化合物具有较好的抑菌活性,为进一步开发高活性化合物奠定一定基础。     

Generation and detection of levuglandins and isolevuglandins in vitro and in vivo

Levuglandins (LGs) and isolevuglandins (isoLGs), formed by rearrangement of endoperoxide intermediates generated through the cyclooxygenase and free radical induced oxidation of polyunsaturated fatty acids (PUFAs), are extraordinarily reactive, forming covalent adducts incorporating protein lysyl ε-amino groups. Because they accumulate, these adducts provide a dosimeter of oxidative injury. This review provides an updated and comprehensive overview of the generation of LG/isoLG in vitro and in vivo and the detection methods for the adducts of LG/isoLG and biological molecules in vivo.     

Femtosecond electron-transfer reactions in mono- and polynucleotides and in DNA

Quenching of redox active, intercalating dyes by guanine bases in DNA can occur on a femtosecond time scale both in DNA and in nucleotide complexes. Notwithstanding the ultrafast rate coefficients, we find that a classical, nonadiabatic Marcus model for electron transfer explains the experimental observations, which allows us to estimate the electronic coupling (330 cm(-1)) and reorganization (8070 cm(-1)) energies involved for thionine-[poly(dG-dC)](2) complexes. Making the simplifying assumption that other charged, pi-stacked DNA intercalators also have approximately these same values, the electron-transfer rate coefficients as a function of the driving force, DeltaG, are derived for similar molecules. The rate of electron transfer is found to be independent of the speed of molecular reorientation. Electron transfer to the thionine singlet excited state from DNA obtained from calf thymus, salmon testes, and the bacterium, micrococcus luteus (lysodeikticus) containing different fractions of G-C pairs, has also been studied. Using a Monte Carlo model for electron transfer in DNA and allowing for reaction of the dye with the nearest 10 bases in the chain, the distance dependence scaling parameter, beta, is found to be 0.8 +/- 0.1 A(-1). The model also predicts the redox potential for guanine dimers, and we find this to be close to the value for isolated guanine bases. Additionally, we find that the pyrimidine bases are barriers to efficient electron transfer within the superexchange limit, and we also infer from this model that the electrons do not cross between strands on the picosecond time scale; that is, the electronic coupling occurs predominantly through the pi-stack and is not increased substantially by the presence of hydrogen bonding within the duplex. We conclude that long-range electron transfer in DNA is not exceptionally fast as would be expected if DNA behaved as a "molecular wire" but nor is it as slow as is seen in proteins, which do not benefit from pi-stacking.     

Supercomputing and supercomputers for science and engineering in general and for chemistry and biosciences in particular

We start by pointing out relationships between production of information, global simulation, and supercomputing, thus placing our research activities in today's society context. Then we detail the evolution in hardware and software for 1CAP, our experimental supercomputer, which we claim to be especially well suited for supercomputing in science and engineering. A preliminary discussion of 1CAP/3090 (our latest experimental effort) is included. Many examples from different disciplines are provided to verify our assertions. We “prove” our point by presenting an example of global supercomputing. Starting with 3 nuclei and 10 electrons, building up to a single water molecule, then to a few hundred, we learn, for example, about Raman, infrared, and neutron scattering; we then move up to a few hundred thousand molecules to analyze particle flow and obstructions; finally we experiment, but only preliminarily, with a few million particles to learn more on nonequilibrium dynamics as in the Rayleigh-Benard systems. In this way, quantum mechanics is overlapped with statistical mechanics and expanded into microdynamics. The entire paper is finally reanalyzed from a different perspective, presenting rather systematically, even if most briefly, our ideas on “modern” computational chemistry, where quantum mechanics is as much needed as fluid dynamics and graphics. In this section the main computational techniques are analyzed in terms of computer programs and their associated flow diagrams to solve the basic equations using parallel supercomputers.     

Carbon chains and rings in the laboratory and in space

Seventy-seven reactive organic molecules of astrophysical interest have been identified in a supersonic molecular beam, 73 in the radio band by Fourier-transform microwave spectroscopy, four in the optical by laser cavity ringdown spectroscopy. Most are linear carbon chains, but six consist of carbon chains attached to the compact, highly polar C3 ring, and two are rhomboidal cyclic configurations of SiC3. The laboratory astrophysics of the radio molecules is complete for the time being, in the sense that essentially all the rotational transitions of current interest to radio astronomy (including hyperfine structure when present) can now be calculated to a small fraction of 1 km s(-1) in equivalent radial velocity; six of the radio molecules have already been detected in space on the basis of the present data. The FTM spectrometer employed in this work is far from fundamental limits of sensitivity, so many more molecules can probably be found by refinements of present techniques. The density of reactive molecules in our supersonic beam is generally high by the standards of laser spectroscopy, and many of the radio molecules probably have detectable optical transitions which we are attempting to find, largely motivated by the long-standing problem of the diffuse interstellar bands. Our most interesting result to date is the detection of a fairly strong molecular band at 443 nm in a benzene discharge, in exact coincidence with the strongest and best known interstellar band. Isotopic shifts measured with partially and totally deuterated benzene suggest that the carrier of the laboratory band is a hydrocarbon molecule with the elemental formula CnH5, with n most likely in the range 3-6.     

钙与人体及临床

钙是宏量元素，是人体中含量较高的元素之一，体内99％的钙构成骨骼和牙齿以及维持骨骼结构，1％的钙调节人体重要生理功能。钙的含量过高或过低都与许多疾病有关，只有保持一种平衡状态，才能使机体处于正常环境。     

Structure Formation and Molecular Mobility in Water and in Aqueous Solutions

The study of the structure of water and of aqueous solutions has recently received new impetus from the efforts at commercial desalineation of sea water and from developments in molecular biology. The current view that, apart from single molecules, water contains only one type of structural element, namely “flickering” network structures with tetrahedrally hydrogen-bonded water molecules (two-states model) is proving inadequate in the interpretation of new experimental data and in the calculation of thermodynamic functions. After a critical discussion of the basis of this model and of the concept of hydrogen bonds, a second kind of structural element, i.e. a third state, is suggested: small aggregates of molecules containing mainly non-tetrahedral hydrogen bonds as well as some tetrahedral ones, and packed more densely than allowed by the lattice-like structure. These aggregates – dimers to hexamers – can be regarded as the primary products of disruption of the network structures, and displace the latter as structural components in water with increasing temperature or concentration of solutes. This “combined” model allows a consistent interpretation of the properties of water and of the various effects of dissolved substances.     

Electrostatic interactions in cations and their importance in biology and chemistry

Electrostatic effects exert strongly stabilizing influences on cations, in many cases controlling the conformational preferences of these cations. The lowest energy conformers are ones where the positive charge is brought closest to substituents bearing partial negative charges. These conformational biases, along with stereoelectronic effects, can control the stereoselectivity of reactions involving carbocationic intermediates.