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991.
研究二维光学薄膜SnO2:TiO2在乙醇、丙酮、氨蒸汽中的气敏反射光谱,发现它与厚膜(膜厚20μm)的气敏反射光谱有明显的差异,它的反射光强在气体浓度较低时随气体浓度增加而增强,气体浓度较高时则现象相反,并且它的反射峰会发生位移。利用不同气体的反射峰的气敏特性,可制成有气体选择性的气敏光纤传感器。 相似文献
992.
The modification of the triple helical structure in aqueous gelatin solutions by changing pH and adding alkyl sulphates at 298 K and after rechilling the solution to 283 K was investigated by CD-measurement. At 298 K the triple helical content at the IEP of the gelatin has its maximum value. It is only weakly affected by adding sodium dodecyl sulphate (SDDS) at concentrations <10–4 M/dm3. The unfolding of the triple helix affected by pH and SDDS is reversible by rechilling the solution. The triple helical content of gelatin solutions decreases at SDDS concentrations higher than 10–4 M/dm3. In all cases the decrease of the amount of triple helical structure is connected with an increase of the cis-configuration in single chains and leads to chain reversals. At sufficiently high SDDS concentrations-sheets are formed. These changes are thermally irreversible. Sodium decyl sulphate (SDS) has a more minor influence than SDDS except in the range of the c.m.c. of SDS. At sufficiently high SDS concentrations,-turns appear. 相似文献
993.
NMR spectroscopy plays an important part in the determination of the structures of organic compounds. The parameters of importance here are the chemical shifts of the 1H and 13C nuclei and the spin-spin interactions both between 1H nuclei and between 1H and 13C nuclei. Couplings between 13C nuclei were almost completely neglected until a few years ago, since they were extremely difficult to observe because of the low natural abundance of 13C. However, it is these couplings which afford information directly on the carbon-carbon connectivities in the molecule. It is now possible to use a special NMR pulse sequence to make these couplings more readily visible: the result of using this sequence is a 13C-NMR spectrum from which the carbon skeleton concerned can be directly read off. Two-dimensional spectra in particular are very easy to evaluate. The pulse sequence involved, which bears the somewhat puzzling name INADEQUATE, produces double-quantum coherences from which the NMR signals of the coupled carbon nuclei can be obtained. In this article the principle of double-quantum coherence is described and a number of examples for the application of the INADEQUATE pulse sequences to problems in synthetic organic chemistry, biosynthesis and natural products chemistry are presented; in addition, the possibility of applying the INADEQUATE method to other nuclei is considered. 相似文献
994.
Silvia Stumpf Gudrun Goretzki Kerstin Gloe Karsten Gloe Wilhelm Seichte Edwin Weber Jan W. Bats 《Journal of inclusion phenomena and macrocyclic chemistry》2003,45(3-4):225-233
The di- and tetra-allyl ethers of tert-butylcalix[4]arene 1 and 2 have been prepared by alkylation of tert-butylcalix[4]arene with allyl bromide and K2CO3 using different reaction times. Solution 1H NMR measurement of the di-allyl ether 1 and X-ray crystal structures of the complexes of 1 with chloroform (1a) or methanol (1b) indicate the cone conformation of 1 in which intramolecular hydrogen bonding can be maximized. The crystalline state conformers 1a and 1b are distorted in different grades depending on the solvent. While methanol is incorporated in the macrocycle, chloroform molecules do not occupy the cage. The solution 1H NMR spectra of tetra-allyl ether 2 show the co-existence of the cone and partial cone conformation. The partial cone conformer of 2 was investigated by X-ray crystallography. In this compound hydrogen bonding is not existent. The conformer distribution is likely affected by steric and template effects. 相似文献
995.
通过实验阐明了同步荧光光谱与普通荧光光谱之间的关系,在此基础上讨论了溶剂散射光对同步荧光分析的影响以及同步荧光分析的灵敏度。 相似文献
996.
基于荧光激发光谱和发射光谱对波长呈高斯分布的设定,本文推导出固定波长同步荧光光谱峰峰值位置、相对强度和半峰宽度等3个主要光谱参数的理论计算式。所提出的计算式应用于若干荧光物质光谱参数的计算,并和实测值、文献计算值作了对照。结果表明,和文献计算方法相比,本法与所研究物质的实际光谱参数较为接近,可为固定波长同步荧光光谱参数的理论计算提供一有效方法。 相似文献
997.
998.
The enolate anion of chlorophyll b (Chl b) has been synthesized under deoxygenated conditions and its electronic structure characterized for the first time by 1H NMR and electronic absorption spectroscopy. The formation of the enolate anion caused a marked perturbation to the 18 π-electron [18]diazaannulene aromatic pathway of Chl b. This perturbation appeared as noticeable upfield shifts, exceeding 1 ppm, for the meso-CH protons of the Chl b enolate anion. Nevertheless, the enolate anion remained diatropic, maintaining aromaticity in its delocalized macrocycle. 相似文献
999.
G. G. Danagulyan G. A. Panosyan L. G. Sahakyan 《Chemistry of Heterocyclic Compounds》2007,43(8):996-1000
The interaction of the iodomethylates of pyrimidinyl-2-acetic acid derivatives with monosubstituted hydrazines, in addition
to the products of a Kost-Sagitullin rearrangement, leads also to N-substituted triazoles. The structure of the triazoles
was demonstrated by NOESY NMR experiments. The structure of the reaction products was determined on the basis of the response
observed in the spectra between the methyl group protons of the triazole ring and the spatially close proton of the substituent
in position 1 and a conclusion was drawn on the direction of the primary attack of nucleophile in the recyclization process
of the pyrimidinium salts into a 1,2,4-triazole.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1175–1179, August, 2007. 相似文献
1000.
Quantum chemical calculations at mPW1PW91 level, with full geometry optimization, using the 6-31g(d) basis set, and GIAO (gauge including atomic orbitals) 13C NMR chemical shifts using the 6-31g(d,p) basis set, are here utilized as a support to define the configurational features of the natural product passifloricin A, whose previously proposed relative configuration has been recently shown, by synthetic studies, to be incorrect. This study suggests that the relative stereostructure for passifloricin A corresponds to the δ-lactone of the (5R,7R,9S,11R)-tetrahydroxyhexacos-2-enoic acid. 相似文献