334 resultados para ADDUCT
Resumo:
A successful analysis of silver was reported utilizing laser desorption/ionization time-of-flight mass spectrometry (LDI/TOF-MS) in this paper, The silver cluster ions Ag-n(+) and AgnO+ (n=2 similar to 5) were formed during laser desorption/ionization. In the presence of I-, K+ and Na+, the peaks corresponding, to the cluster ions [AgnIn-1](+) (n=2 similar to 6) and the adduct ions [AgI](+), [AgI]Na+ and [AgI]K+ were observed in the positive ion spectrum; the peaks corresponding to [AgnIn+1](-) (n=1 similar to 3) were found in the negative ion spectrum, all of which accompanied by sliver isotope distribution, The formation of silver cluster ions was accomplished through two-stage reaction: the first step was the generation of clusters, which was followed by the processes of photoionization and ion/molecule reaction.
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Ion-molecule reactions of four isomeric cyclopropane derivatives were investigated under chemical ionization(CI) conditions, using methane, acetone and vinyl acetate as reagent gases, The methane positive-ion CI mass spectra of each of two isomer pairs 1,2 and 3,4 are identical, and so are the collision-induced dissociation (CTD) spectra of the protonated molecules of each of the two isomer pairs, The protonation reactions for the isomer pairs 1,2 and 3,4 occurred on the sites of the carboxyl groups and the R groups, respectively, Differences between isomers 1 and 2 are observed in their acetone (A) positive-ion CI mass spectra and in the CID spectra of their adduct ions ([M+H+A](+)), The adduct ions of compounds 2, 3 and 4 with protonated acetone and with protonated acetone dimer are observed in their CI mass spectra, However, only the adduct ions of compound 1 with protonated acetone appear in its CI mass spectrum, The protonated dimers of each of the four compounds are found in their vinyl acetate positive-ion CI mass spectra, and the CID spectra of these dimers for isomers 1 and 2 can also reflect their stereostructural difference. (C) 1998 John Wiley & Sons, Ltd.
Resumo:
Gas phase adduct of endohedral rare-earth fullerenes Nd@C-S2 with the ion system of benzene-[Nd@C-S2-C6H6](+) was observed for the first time by ion-molecular reaction under chemical ionization condition. The possible reaction passageway and molecular structures of this gas phase adduct were discussed and a parallel "reversed umbrella" pi-pi interaction complex of the [C6H6](+) ion reacting with the neutral rare-earth fullerenes Nd@C-S2 was considered to be much reasonable. The experimental result indicated that endohedral rare-earth fullerenes has relatively active reactivity and aromatic properties similar towards benzene molecular ion in gas phase.
Resumo:
A Co(salen)-Nafion modified electrode was prepared by immersing a glassy carbon electrode coated with the Nafion film into the aqueous solution with saturated Co(salen), The modified electrode showed a stable electrochemical reaction of Co(salen) at about 0 V(vs, SCE), The result of XPS indicated the valence of cobalt in Co(salen) changes from +2 before to +3 after Co(salen) enters the Nafion film, It is due to forming axis coordination of cobalt with sulfonic group in Nafion film, It was found that the mode of electron transfer in Co(salen)-Nafion modified electrode was controlled by physical diffusion and electron hopping, It was also found that the modified electrode could catalyze the reduction of O-2 to H2O2. The real catalyst may be the adduct of Co-I(salen) and O-2.
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The axial coordination effect of F- on the redox behavior of (TPP)Co was investigated and spectroeletrochemistry in dichloroethane. It was verified that mono(F-) axial adduct (TPP)Co(II)(F-) could be reduced at 0.1 V(SCE). and bis(F-) axis adduct (TPP)Co(II)(F-)(2) formed with added F- molar ratio>1 could be reduced at the potential <-0.6 V(SCE). The equilibrium between (TPP)Co(II)(F-) and (TPP)Co(II)(F-)(2) was demonstrated.
Resumo:
The DCI MS of C-60 with the reactions of gaseous cyclohexane and cyclohexene have been studied. Several kinds reactions of C-60 have been observed. The results show that the gasphase C-60 has very active chemical properties. The adduct ions of [C60C4H7](+) and [C60C5H7](+) may be formed by [2+4] cycloaddition where one of double bonds of C-60 acted as a dienophilic unit.
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Gas phase ion-molecular reactions of C-60 with the ion system of CS2 have been studied in the ion source of mass spectrometer. It was found for the first time that the sulfuric derivative of C-60-C60S+ was the main ions in the ion source, they did not react with C-60 to form adduct ions due to their highly saturated structures. According to the dynamic analysis, the product ion came from the reaction of C-60 with the fragment ion S+. The adduct ion may have the structure of epsulfide that is advantageous in energy.
Resumo:
In chemical ionization mass spectrometry (CIMS) gas phase C-60(+) or C-60 can react with fragment ions from three chloromethane and four multichloroethane molecular ions via ion-molecule reactions. A dozen of gas-phase adduct ions of C-60 are observed, and most of them contain chlorine atoms. The results of the comparison and analysis show that the relative intensities of adductions are not directly proportional to the corresponding fragment ions in the MS of reagents,which implies that some fragment ions containing radicals are more reactive with C-60(+) or C-60. This indicates that the alkene-like C-60(+) or C-60 can act as a radical sponge in addition reactions.
Resumo:
Gas phase reactions of C-60 and C-70 with the ion system of acetone under chemical ionization conditions have been studied. C-60 and C-70 can react with acetyl and oxonium ions, which come from self-chemical ionization of acetone, to form adduct ions. In addition, C-60 and C-70 can accept protons to produce protonated ions. C-70 is more active in the above reactions than C-60 because of its stronger gas-phase basicity. A sigma-bond between C-60 and an acyl carbon atom can be formed to produce stable acetylated C-60 ions. The above results may be relevant to the acetylation reactions of C-60 in the condensed phase.
Resumo:
Gas-phase ion-molecular reactions of C-60 and C-70 with the ion system of acetone have been studied in this paper. The ions of protoned and acetylized C-60 and C-70 were formed by the reactions of C-60 and C-70 with some ions which existed in the ion system when mass spectrometer worked on chemical ionization conditions. The reactivity of C-70 is greater than that of C-60. Results of quantum chemical calculation for the adduct ions showed a sigma bond between the acyl carbon atom and C-60 may be Formed. These results will provide some valuable informations on the condense-phase acetylization of C-60.
Resumo:
Rare earth chlorides were used to catalyze the synthesis of 2-butoxy-3, 4-dihydro-2H-pyran using equimolar acrolein and vinyl butyl either. The cycloadduct is unstable which undergoes catalytic ring opening oligomerization. The way to stabilize the cyclo adduct has been studied, thus high yields of 90-95% were obtained.
Resumo:
海洋微生物拥有丰富多样的次生代谢途径,其中海洋生物内生真菌次生代谢产物研究日益受到天然产物化学界的重视。本论文以菌丝体生物量、发酵产物重量、抗菌与细胞毒活性、薄层色谱分析结果以及高效液相色谱分析结果等为评价依据对采自青岛沿海的13株海藻内生真菌在四种液体培养基上的静置发酵产物进行了综合评价,并从中选择了黑曲霉Aspergillus niger EN-13(分离自褐藻囊藻Colpomenia sinuosa)和杂色曲霉A. versicolor EN-7(分离自褐藻鼠尾藻Sargassum thunbergii)两株真菌进行了30升规模发酵(分别采用GPYM培养基和PDB培养)和化学成分的研究,对分离得到的大部分化合物进行了初步的生物活性筛选。 发酵提取物采用常规的硅胶柱层析、反相硅胶柱层析,凝胶Sephadex LH-20柱层析、制备薄层层析、半制备高效液相色谱以及重结晶等分离手段,得到单体化合物。利用各种现代波谱技术(IR、UV、EI-MS、FAB-MS、HR-ESI-MS、1H-NMR、13C-NMR、DEPT、1H-1H COSY、HSQC、HMBC等)并结合化学方法从两种菌株发酵提取物中鉴定了55个化合物的结构。其中从菌株A. niger EN-13分离鉴定了31个化合物,发现9个新化合物,包括2个鞘酯类化合物(AN-1~2)、3个萘并-γ-吡喃酮类化合物(AN-3~5)、3个苯乙基取代的α-吡喃酮类化合物(AN-17, AN-19~20)和1个甾体Diels-Alder加成产物(AN-21),另有1个新的天然环二肽(AN-27)被分离鉴定;从菌株A. versicolor EN-7分离鉴定了24个化合物,发现2个新化合物,为蒽醌AV-12与AV-17,另外,从前一菌株(A. niger EN-13)中鉴定的2个新鞘酯类化合物(AN-1~2)在A. versicolor EN-7中也被再次分离到。 对大部分单体化合物进行了抗菌活性、DPPH自由基清除活性和细胞毒活性测试。结果显示新化合物AN-1、AN-5和AN-20具有弱或中等强度的抑制白色念珠菌生长的活性,AN-4、AN-5、AN-21显示了弱或中等强度的抑制黑曲霉生长的活性,AV-12、AV-17显示了弱的抑制大肠杆菌生长的活性。在DPPH自由基清除活性筛选中,AN-5显示了中等强度的活性,其EC50为109.3 mM,与阳性对照BHT相近(EC50为81.8 mM)。其它部分已知化合物在抗菌和DPPH自由基清除活性的筛选中也显示了弱或中等强度的活性。在针对人肝癌细胞株SMMC-7721和人肺腺癌细胞株A549的体外细胞毒活性筛选中,所测样品均未显示显著活性。
Resumo:
Metallocene based polyethylenes were prepared by SMOPEC's "metallocene adduct" technology in a gas phase fluidized bed model reactor. The C-13-NMR spectra of ethylene/1-butene (S-34) and ethylene/1-hexene(S-43) copolymers were studied in a manner analogous to that established by Hsieh and Cheng. The comonomer sequence distributions of copolymer samples were obtained. The results show that these metallocene based copolymers contain a small amount of butene and hexene, and the EE and EEE sequences are dominant.
Resumo:
A microchip electrophoresis method coupled with laser-induced fluorescence (LIF) detection was established for simultaneous determination of two kinds of intracellular signaling molecules (reactive oxygen species, ROS, and reduced glutathione, GSH) related to apoptosis and oxidative stress. As the probe dihydrorhodamine-123 (DHR123) can be converted intracellularly by ROS to the fluorescent rhodamine-123 (Rh123), and the probe naphthalene-2,3-dicarboxaldehyde (NDA) can react quickly with GSH to produce a fluorescent adduct, rapid determination of Rh-123 and GSH was achieved on a glass microchip within 27 s using a 20 mm borate buffer (pH 9.2). The established method was tested to measure the intracellular ROS and GSH levels in acute promyelocytic leukemia (APL)-derived NB4 cells. An elevation of intracellular ROS and depletion of GSH were observed in apoptotic N134 cells induced by arsenic trioxide (AS(2)O(3)) at low concentration (1-2 mu m). Buthionine sulfoximine (BSO), in combination with AS(2)O(3) enhanced the decrease of reduced GSH to a great extent. The combined treatment of AS(2)O(3) and hydrogen peroxide (H2O2) led to an inverse relationship between the concentrations of ROS and GSH obtained, showing the proposed method can readily evaluate the generation of ROS, which occurs simultaneously with the consumption of the inherent antioxidant.
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Measures of prevention and control against polycyclic aromatic hydrocarbons (PAHs) focus on an official food control, a code of best practice to reduce PAHs levels by controlling industry and in the development of a chemopreventive strategy. Regulation (EU) 835/2011 establishes maximum levels of PAHs for each food group. In addition, Regulations (EU) 333/2007 and 836/2011 set up the methods of sampling and analysis for its official control. Scientific studies prove that the chemopreventive strategy is effective against these genotoxic compounds effects. Most chemopreventive compounds studied with proven protective effects against PAHs are found in fruit and vegetables.