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1.
Tiainen M Maaheimo H Niemitz M Soininen P Laatikainen R 《Magnetic resonance in chemistry : MRC》2008,46(2):125-137
The natural abundance 1H-coupled 13C NMR spectra of all proteogenic amino acids were measured in D2O at pH* 1. The accurate 1H,13C spin-spin coupling constants were analyzed using total-line-shape fitting. The obtained spectral parameters can be used to establish a spectral library of amino acid 13C isotopomers. The adaptive spectral library principle is introduced and discussed in this article. The simulated spectra can be applied to quantification of 13C isotopomer mixtures of amino acids and, thus, for exploring metabolic pathways. Also a protocol for amino acid 13C isotopomer metabolomic profiling in 13C labeled glucose feeding experiments is outlined. The approach is suggested to give invaluable information about positional fractional 13C enrichments, which are not easily available by any other method. 相似文献
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The synthesis of [13C6]3,4-diaminobenzoic acid from commercially available [13C6]aniline is described in six steps. Salient features of this route include the preparation of a differentially protected 3,4-diaminobenzonitrile, hydrogen gas free aromatic nitro group reduction with ammonium formate and facile benzimidazole ring closure of the ortho-arylenediamine with triethylorthoformate. This stable-labeled 3,4-diaminobenzoic acid is an ideal [M+6]isotopomer to synthesize complex benzimidazole fragments for mass spectrometry internal assays. 相似文献
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《Magnetic resonance in chemistry : MRC》2003,41(2):107-114
NMR relaxation measurement of perfluorocarbons (PFCs), such as perfluorotributylamine (FTBA), is a convenient method for the determination of oxygen concentrations in tissues and tumors. Previous relaxation studies of FTBA used different 19F NMR assignments causing some confusion. Fluorine‐detected 19F, 13C HMQC and HMBC and selectively 19F‐decoupled 13C NMR provided unequivocal 19F and 13C assignments for FTBA and perfluoropentanoic acid (FPA). Based on those assignments, 13C spin–lattice relaxation time constants (T1) and effective correlation times for FTBA and FPA are reported and discussed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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稻秆木素侧链13C同位素示踪及固体13CNMR分析 总被引:18,自引:0,他引:18
在水稻(Oryza sativa L.)生长过程中,向其茎秆部节间的空腔分别注入在侧链α,β,γ位带有13C标记的松柏醇葡萄糖甙,得到13C标记的稻秆木素,用高分辨率固体核磁13CNMR对其组织进行分析,发现外源性的松柏醇葡萄糖甙并不影响水稻中木素的正常合成.证明了β-O-4,β-β,β-5和β-1结构是稻秆原本木素中的主要结构,另外还有少量的松柏醇和阿魏酸类结构,并证实木素在α位与糖类等组分有共价键形成. 相似文献
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结合非正常油脂(地沟油)的来源(加热植物油和动物油)及反映其不同来源的重要特征指示物,即连接在甘油酯上的十一烷酸和13-甲基十四烷酸,建立了内标法测定油脂中甘油酯上十一烷酸和13-甲基十四烷酸的方法。多维气相色谱-质谱采用不分流进样和选择性切割可以实现在线净化和富集,提高分析的灵敏度和分离度。十一烷酸和13-甲基十四烷酸的方法检出限分别达到0.070、0.006 mg/kg。此外,研究发现绝大多数正常植物油中十一烷酸和13-甲基十四烷酸的含量比非正常油脂中二者的含量低。通过待测油脂中十一烷酸和13-甲基十四烷酸的含量可以在一定程度上推断食用植物油的品质。 相似文献
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Atsushi Asano Masaru Eguchi Takuzo Kurotu 《Journal of Polymer Science.Polymer Physics》1999,37(16):2007-2012
Thermal dehydration process of PMAA was investigated by solid‐state 13C NMR. For heat‐treated PMAA at 150°C, at which the dehydration goes very slowly, we observed three 13C peaks at 172, 178, and 187 ppm in the carboxyl group region. The peak at 172 ppm is due to the intramolecular cyclic anhydrides by comparing the reported value of 13C chemical shift. The peaks at 178 and 187 ppm were assigned to regularly aligned free carboxylic acids and intermolecular acid dimers, respectively, from the 2D‐exchange 13C NMR spectra, 13C chemical shift values and IR spectra. We concluded that by heat‐treatment the rearrangement of intermolecular hydrogen bonding of the carboxylic acids in PMAA occurs firstly to form the regularly aligned acid dimers, and the dimers dissociated to be the regularly aligned free carboxylic acids at high temperatures. The adjacent free carboxyl acids dehydrate with each other, resulting in the formation of intramolecular anhydrides. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2007–2012, 1999 相似文献
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Guaiacol, pyrocatechol and resorcinol, were isolated and quantified as the major products from catalytic pyrolysis of lignin of various origin. The novel procedure utilises formic acid as the hydrogen source in combination with a palladium catalyst and Nafion® SAC-13 as a solid acid catalyst with water as reaction medium. The reaction is conducted at moderate pyrolysis temperature and short reaction time. Several palladium based catalysts and different types of lignin were investigated. The lignins and the model compounds demonstrated various chemical behaviour, under identical reaction conditions; various phenols were formed from the lignins, while the model compounds were hydrodeoxygenated, demethylated and demethoxylated. 相似文献
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Wolfgang Holzer Gernot A. Eller Barbara Datterl Daniela Habicht 《Magnetic resonance in chemistry : MRC》2009,47(7):617-624
NMR spectroscopic studies are undertaken with derivatives of 2‐pyrazinecarboxylic acid. Complete and unambiguous assignment of chemical shifts (1H, 13C, 15N) and coupling constants (1H,1H; 13C,1H; 15N,1H) is achieved by combined application of various 1D and 2D NMR spectroscopic techniques. Unequivocal mapping of 13C,1H spin coupling constants is accomplished by 2D (δ,J) long‐range INEPT spectra with selective excitation. Phenomena such as the tautomerism of 3‐hydroxy‐2‐pyrazinecarboxylic acid are discussed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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运用广义梯度近似(GGA)密度泛函理论的Perdew-Burke-Ernzerh (PBE)方法, 研究了肉桂醛在正二十面体Au13和Pt13团簇上的吸附行为. 通过分析不同吸附模式的吸附能和几何构型发现: 同一金属团簇, 顺式肉桂醛的吸附能强于反式肉桂醛的吸附能. 对于Au13团簇, 肉桂醛的稳定吸附构型为C=C和C=O共吸附模型; 对于Pt13团簇, 肉桂醛的稳定吸附构型为C=O吸附. 比较二者发现, 肉桂醛在Pt13团簇的吸附能力强于Au13团簇.分析Au13和Pt13团簇上肉桂醛最稳定吸附构型的电子结构表明, 电子由肉桂醛原子的2s、2p轨道向金属表面转移, 同时金属部分电子反馈到肉桂醛的反键轨道, 最终肉桂醛稳定吸附于金属团簇. 此外, 肉桂醛在团簇模型上的吸附能大于其在平板模型上的吸附能. 相似文献
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采用直接水热合成和后合成两种方法制备Al-ITQ-13分子筛,用于催化甲醇转化制备烃类化合物。采用XRD、27Al MAS NMR、NH3-TPD、Py-FTIR和SEM等技术对所合成样品进行了表征。结果表明,两种方法制备的Al-ITQ-13结晶度都较高,且晶体形貌为薄片。与ZSM-5相比,Al-ITQ-13在甲醇转化反应中显示出较高的丙烯选择性、较高的丙烯/乙烯产物比以及较好的催化稳定性。同时,由于后合成所得到的SiAl(B)-ITQ-13强酸量减少,其催化性能优于直接合成的SiGeAl-ITQ-13。 相似文献
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《Magnetic resonance in chemistry : MRC》2002,40(7):455-457
Complete assignments of 1H and 13C NMR chemical shifts for newly synthesized benzyl esters of oleanolic, ursolic and crataegolic acid based on DEPT, HSQC, HMBC, COSY, TOCSY, NOE and ROESY experiments are reported. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Cobalt catalyzed hydroformylation-amidocarbonylation of 3-cyanopropene by carbon-13 monoxide and acetamide produced a [1,2-13C2]-labelled mixture of 5-cyano-2-acetamidopentanoic acid and 4-cyano-3-methyl-2-acetamidobutanoic acid (n to b ratio of 7 to 3. 55% yield). Acylase I resolution of this mixture gave the free S-amino acids which could be separated by crystallization. Catalytic reduction of the cyano group of the straight chain acid furnished [1,2-13C2] -S-lysine. HCl. 相似文献
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Volker Spitzer 《Journal of separation science》1995,18(7):413-416
The fatty acids of the total lipids, triglycerides, and the cyanolipid of Paullinia elegans (Sapindaceae) have been analyzed as their methyl esters and 4,4-dimethyloxazoline derivatives by gas chromatography-mass spectrometry. It was shown that the gas chromatographic separation of the oxazoline derivatives was sufficient to ensure the correct identification of the monoenic fatty acid positional isomers. Stereochemistry of the double bonds has been confirmed by infrared and 13C-nuclear magnetic resonance (NMR) spectroscopy. cis-13-Eicosenoic Acid (Paullinic acid) (44.4%) and cis-11-octadecenoic acid (cis-vaccenic acid) (19.8%) were found to be the main components beside other monoenoic acid positional isomers. The cyanolipid of P. elegans was identified as 2,4-dihydroxy-3-methylenebutyronitrile derivative by IR, 1H-NMR, 13C-NMR spectroscopy and was quantified by 1H-NMR spectroscopy (71.4%). 相似文献
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Barakat E. Abu Irmaileh Musa H. Abu Zarga Firas Awwadi Salim F. Haddad 《Natural product research》2015,29(10):893-898
Inula graveolens is a poisonous annual plant of Mediterranean origin. The invasive nature of the plant suggests that it may possess phytotoxic activity. The aim of this study was to assess the ability of I. graveolens to inhibit the growth of different plants in Petri dish and to identify the main bioactive compounds. Bio-guided fractionation of the plant extracts led to the isolation of 2,3,11β,13-tetrahydroaromaticin (THA) and ilicic acid. Both compounds showed selective and significant phytotoxic activity at 25 ppm. Root length of barley, oat, millet, tuberous canary grass and lentils were significantly reduced by 25 ppm of THA, while the root of cauliflower, cress and radish were similarly reduced by ilicic acid at 25 ppm. The structure of each compound was elucidated by using NMR and HR-MS. X-ray crystallography of THA is reported for the first time to confirm the relative stereochemistry of the compound. 相似文献
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M. Zielinski G. Czarnota H. Papiernik-Zielinska 《Journal of Radioanalytical and Nuclear Chemistry》1992,159(2):305-316
The13C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20–80°C. The13C(1) isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40°C. Below this temperature the13C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found inthe decarbonylation of lactic [1-14C] acid. The experimental values of k(12C)/k(13C) ratios of isotopic rate constants for12C and13C are close to, but slightly higher than theoretical13C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C(1)-OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H2O)/(H2SO4) ratio caused the increase of the13C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5°C to 1.0536±0.0008 (at 80.6°C). A discussion of the abnormally high temperature dependence of14C and13C isotope fractionation in this reaction and the discussion of the problem of relative14C/13C kinetic isotope effects is given. 相似文献