利用差异衍生同步分析醛糖和酮糖

建立了一种可同时对醛、酮糖进行精确定性和定量分析的方法。以肌醇作为内标，用80％乙醇超声提取，利用醋酸酐和HMDS＋TMCS（1：3）进行差异衍生，在EI源下用SIM模式进行GC／MS分析。结果表明：11种标准单糖在1—4mg／L范围内线性良好；仪器检出限：醛糖在8．15—22．4μg／L之间；酮糖为2．32μg／L和3．47μg/L；高、中、低3个量的平均回收率在73．0％-95．7％，相对标准偏差在3．1％-10．0％。对枸杞游离单糖进行测定，各单糖含量分别在0．26—368．6mg／g。该方法弥补了以前单糖分析中的缺陷，对既含有醛糖又含有酮糖的样品可同时进行精确的定性定量分析。     

2H Chemical-shift resolution and dipolar2H-1H,2H-15N correlations in solid-state MAS NMR spectroscopy for structure determination and distance measurements in hydrogen-bonded systems

In solid-state NMR, deuteron (²H) spectroscopy can be performed in full analogy to¹H spectroscopy, including²H chemical-shift resolution and²H-X dipolar correlation schemes, when the NMR experiments are conducted in a “rotor-synchronized” fashion under fast magic-angle spinning. Here, 2H-X NMR experiments of this type, including²H-¹⁵N and²H-¹H chemical-shift correlations and distance measurements, are introduced and demonstrated on cytosine monohydrate, whose acidic protons can readily be replaced by deuterons by recrystallization from D₂O. In this way,²H NMR spectroscopy provides information complementary to¹H NMR data, which is particularly useful for studying hydrogen bonds in supra- or biomolecular systems. Electronic supplementary material Supplementary material is available in the online versionof this article atand is accessible for authorized users.     

Theoretical investigation of 1,4-dioxane complexes with water in the <Emphasis Type="Italic">chair</Emphasis> conformation by semiempiric MNDO/PM3 method

The structure and relative stability of 1,4-dioxane-water, (Diox)_n·(H₂O )_m (n = 1, 2, m = 1–6), molecular complexes have been calculated by semiempirical MNDO/PM3 method. A considerable variety of (Diox)_n·(H₂O )_m isomeric structures was stated. The mean energy of O_Diox…H_W-O_W hydrogen bond in (Diox)_n·(H₂O)_m complexes formed by 1,4-dioxane molecules in the chair conformation amounts to ?2.293 ± 0.210 kcal/mol with the average bond length 2.797 0.015 Å.     

Cyclic Conjugation Energy Effects in Polycyclic π-Electron Systems

Summary. The fact that cyclic arrangements of double bonds have a dramatic effect on the behavior of conjugated organic molecules is known since the 19th century. The fact that in monocyclic conjugated systems the size of the cycle and the number of -electrons involved is decisive for their stability (aromaticity) or lack of stability (antiaromaticity) is known since the 1930s. In polycyclic -electron systems several cyclic effects are present simultaneously and their separation became possible only recently. A molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic -electron systems can be estimated. This method is briefly outlined and illustrated by pertinent examples. An exhaustive bibliography of the topic considered is given.     

DFT investigation of sites of protonation of antitumor of 2‐(4‐aminophenyl)benzazoles in the gas phase and in solution

The proton affinity on each of the possible sites in the antitumor 2‐(4‐aminophenyl)benzazoles has been calculated at the B3LYP/6‐311G** level of theory in the gas phase and in solution. The N₃‐site of protonation is found to be strongly favored over the NH₂‐site for the studied compounds both in gas phase and in solution. The stability of N₃‐protonated species is explained by the resonance interaction of the NH₂‐group with the heterocyclic ring. The potential energy surface (PES) for the protonation process was studied at the density functional theory (DFT)/B3LYP/6‐311++G** level of theory. Solvent effects on the PES were also examined using two models: Onsager self‐consistent field and polarizable continuum model (PCM). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Phenol methylation over CrPO4 and CrPO4?AlPO4 catalysts

The vapor-phase catalytic alkylation of phenol with methanol and dimethyl carbonate on a series of differently prepared CrPO₄ (Cr/P=1) and CrPO₄-AlPO₄ (CrAIP) catalysts, has been studied at different temperatures (473–673 K). The reaction is first order in phenol, giving a mixture of O- and C-alkylated products (C-alkylation taking place preferentially at theortho-position). Moreover, dimethyl carbonate is a better methylating agent than methanol.     

Linear silver clusters in aqueous solution (clusterites): radiation-induced chemical synthesis and properties

The formation and properties of the products of the radiation-induced chemical reduction of silver ions in aqueous solutions containing sodium polyacrylate were investigated. The absorption spectra of these species exhibit a band at 290 mn and a band in the visible region. The latter shifts from 470 nm to -800 nm with time or after the addition of silver ions. The species obtained (clusterites) arc linear silver clusters bound to the carboxyl groups of the ion exchanger. The red shift of the visible band is due to the increase in their size. The mechanism of the formation and the structure of the clusterites are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1429–1435, June, 1996.     

中孔分子筛SO42-/Zr-MCM-41催化裂解聚丙烯反应研究

采用水热合成法制备了不同硅锆比的中孔分子筛Zr-MCM-41,用强酸性基团SO42-对其进行修饰,制得SO42-/Zr-MCM-41中孔分子筛.采用XRD、FT-IR、NH3-TPD及氮气吸附脱附等技术对其结构和酸强度进行表征.通过改变硅锆比、负载不同的酸性基团对Zr-MCM-41的酸性进行调变,并将其用于催化聚丙烯(PP)的裂解反应,结果表明S i/Zr=40的SO42-/Zr-MCM-41具有较好的催化裂解活性.另外,与热裂解以及HZSM-5和Zr-MCM-41为催化剂时PP的裂解反应结果进行了比较,结果证明SO42-/Zr-MCM-41不仅具有较高的裂解转化率,而且具有较高的液体产物收率,适宜于空间位阻较大的PP的催化裂解反应.     

Chemische Ionisations-Massenspektrometrie von Organophosphors?ureinsecticiden mit verschiedenen Reaktantgasen

Zusammenfassung Chemische Ionisations-Massen-spektren (CI-MS) wurden mit einer Kopplung Dünnfilmcapillar-Gas-Chromatographie-Massenspektrometrie von 23 Organophosphorsäurepesticiden mit Isobutan als Reaktantgas gemessen. Alle Substanzen zeigten im CI-MS ein intensives Ion bei M + 1. Die CI-MS der einzelnen Substanzen werden diskutiert und mit Elektronenstoß-MS und CI-MS, die mit Methan oder Methanol als Reaktantgas erhalten wurden, verglichen. Die MS werden beim Übergang von Elektronenstoßionisation zu CI mit den Reaktantgasen Methan, Isobutan und Methanol in dieser Reihenfolge einfacher. Mit Methanol wird nur noch das M + 1-Ion gefunden. Für die praktische Rückstandsanalyse wird Isobutan als Reaktantgas vorgeschlagen.

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Chemical ionization mass spectrometry of organophosphorus pesticides with various reagent gases

Summary Chemical ionization mass spectra (CI-MS) of 23 organophosphorus pesticides with isobutane as reagent gas were obtained by a combination of open tubular column gas chromatography-mass spectrometry. All substances show intense M + 1 ions in the CI-MS. The CI-MS of the individual substances obtained with isobutane were discussed and compared with their electron impact mass spectra (EI-MS) and CI-MS obtained with methane or methanol as reagent gases. The spectra became simpler applying CI-MS instead of EI-MS. In CI-MS the extent of fragmentation decreased changing the reagent gas from methane to isobutane and methanol. With methanol, usually only the M + 1 ion was observed in the spectra. For routine residue analysis, isobutane as reagent gas is recommended.