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81.
82.
Ling-Tian Tang Yu Wei Yi Wang Shao-Wen Hu Xin-Qi Liu Tai-Wei Chu Xiang-Yun Wang 《Journal of Molecular Structure》2004,686(1-3):25-30
The formation of charge-transfer (CT) complexes between N-methyl-6,7-methylenedioxy-tetrahydro-4-isoquinolone (MMDTIQ, the model molecule of alkaloids) and iodine monochloride has been studied with the density functional B3LYP method. The competition for ICl between n-donor(s) and π-donor in the same molecule has been compared for the first time. The results indicate that the electron-donating ability of various donor sites decreases in the following order: amino nitrogen>carbonyl oxygen>etheric oxygen≈aromatic ring. Complexes with a stoichiometry of 1:1 to 1:5 (MMDTIQ–ICl) might form. Among complexes with a given stoichiometry, the one in which the phenyl ring is involved in the binding is always the least stable. According to these results, in order to ensure an alkaloid iodinated, the amount of ICl should be far beyond that of alkaloids and a low polar solvent should be used, which is quite in agreement with our recent experimental results. 相似文献
83.
(+)-Xyloketal D was prepared in a one-pot multistep domino reaction by heating optically active 5-hydroxy-4-methyl-3-methylenepentan-2-one (R) in toluene with 2,4-dihydroxyacetophenone. The absolute configuration of the natural product was confirmed by preparation of the starting enone from a lactone of established absolute configuration. 相似文献
84.
近年来有不少报道从事于生理活性Drimane类倍半萜的合成,较多采用了分子间Diels-Alder反应来建立Drimane的骨架。本文首次采用内分子Diels-Alder反应作为关键反应合成了Drimane类化合物。同时还在引入了手性诱导基团后,首次完成了从无手性的原料化合物β-紫罗兰酮至光学活性(-)-drimenin1的不对称合成。 相似文献
85.
Five new fused-hexacyclic alkaloids, daphniglaucins D (1), E (2), F (3), G (4), and H (5), and two new yuzurimine-type alkaloids, daphniglaucins J (6) and K (7), have been isolated from the leaves of Daphniphyllum glaucescens, and the structures and relative stereochemistry were elucidated on the basis of spectroscopic data and chemical means. 相似文献
86.
Herein, we report the first use of chiral alkaloid brucine to synthesize novel porphyrin-brucine conjugate capable of acting as a gelator of methanol and acetonitrile at extremely low level of concentration. The synthesis, characterization and spectral properties of gelator based on a novel structural motif, quaternized alkaloid conjugates, are described. Different spectroscopic methods (1H NMR spectroscopy, Raman and infrared spectroscopy, and spectroscopy of electronic and vibrational circular dichroism) were used for characterization of the prepared organogel. The aggregation of the gelator studied by UV-vis spectroscopy and electronic circular dichroism showed the formation of chiral J-aggregates in water and water-methanol (1:1) mixture. A new methodology for the determination of functional groups involved in gel formation based on vibrational circular dichroism is presented. 相似文献
87.
Three non-specific methods for the extraction of total petroleum hydrocarbons (TPH) from soil into organic solvent were compared.
The techniques used for sample preparation were Soxhlet extraction, closed-vessel microwave-assisted extraction, and CEN shake
extraction. The total concentrations of extracted compounds in the boiling point range of C10–C40 were determined by gas chromatography
with flame ionization detection. The best recovery (99%) and repeatability (±3%) from standard oil mixtures were obtained
with microwave-assisted extraction. However, the different extraction methods exhibited different behaviour when spiked soil
samples were extracted. The best repeatability was obtained with CEN shake extraction (±6%) but the repeatability values for
Soxhlet and microwave-assisted methods were quite high (>20%). However, the larger uncertainties of the latter extraction
methods does not necessarily limit the applicability of these methods to the determination of petroleum hydrocarbons in soil,
as in the assessment of soil contamination the expanded uncertainty of the result is usually not limited by analytical uncertainty,
but rather by the uncertainty of the primary sampling stage. However, distinctive variation found in the chromatographic profiles
illustrates that discretion should be obeyed when chromatograms obtained after application of different extraction methods
on petroleum contaminated samples are to be used in the fingerprinting or age dating studies. Otherwise, misleading conclusions
concerning the age of spillage could be drawn. 相似文献
88.
在束-气条件下,通过检测产物的化学发光,研究了亚稳电子激发态He(23S)原子与CH3Cl、CH3I传能反应.采用参比反应的方法,测得了由上述反应产生的主要碎片CH(A2△)、CH(B2∑-)、CH(C2∑+)和H*形成速率常数.通过对测得的CH(A2△-X2∏r)和CH(B2∑--X2∏r)色散谱进行计算机模拟,获得了初生态的CH(A2△,v=0-2)和CH(B2∑-,v=0态)的振动-转动布居,实验结果表明,CH(A2△,v=0)态的转动布居是呈双Boltzman分布的,并且反应的可资用能大部分将转变成产物的平动能.根据实验结果和反应阈能的分析,本文对He(23S)与CH3Cl/CH3I传能反应机理进行了探讨。 相似文献
89.
A free standing film of polyaniline as large as 18 cm×18cm×0.002 cm can be obtained by evaporation of a solution of the chemically synthesized base in NMP. Its structure was examined by the elemental analysis, IR, U.V.-visible spectra, XPS, DSC, SEM and X-ray scattering and its conducting behavior as well as electrochemical properties were studied. Results show that the composition, structure of main chain, physical properties of the free standing film of polyanilme is similar to that of the powder. However, some differences in its electronic structure, conductivity at room temperature and potential of redox couple between the flee standing film and powder are observed, which may be due to cross-linking of the film of polyaniline. 相似文献
90.
An investigation of electronic structure in some neurotransmitter drugs has been made using the CNDO/2 semi-empirical molecular orbital method.The electronic structure has been conveniently characterized by the electronic parameters nett atomic population (NAP) and bond index (BI). A variation of these electronic parameters with respect to conformation has been studied and has been found unlikely to exceed 0.1 e in most. cases. Further, the useful extent to which the electronic parameters of some commonly occurring functional groups may be regarded as conformationally invariant has been demonstrated. Also presented are (i) a discussion on the intramolecular close-approach of functional groups — the interaction between terminal —COO? and ?NH3+ groups of α-ω anaino acids is explicitly considered; (ii) an enquiry into the extension of ‘standard’ (idealized) geometry models in the elucidation of electronic structure.The implication of the results and observations presented here are briefly discussed with reference to classical and quantum structure-activity studies of drug molecules. 相似文献