共查询到20条相似文献,搜索用时 31 毫秒
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Abstract 13C nuclear magnetic resonance and 14N nuclear quadrupole resonance spectra of ferroelectric smectic C?liquid crystals and their non-chiral analogues allow for a microscopic determination of the polar and quadrupolar (or bipolar) biasing of rotation around the long molecular axis as well as for a determination of the anisotropy in the fluctuations of this axis. The results show that the microscopic origin of the biquadratic coupling between the polarization and the tilt, which has been recently introduced into the extended Landau model of the SA–S?C transition, is the quadrupolar (or bipolar) rotational bias induced by the anisotropy in the fluctuations of the long molecular axis. The tilt induced anisotropy in the fluctuations is practically identical in chiral and non-chiral smectic C phases. 相似文献
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13C nuclear magnetic resonance and 14N nuclear quadrupole resonance spectra of ferroelectric smectic C*liquid crystals and their non-chiral analogues allow for a microscopic determination of the polar and quadrupolar (or bipolar) biasing of rotation around the long molecular axis as well as for a determination of the anisotropy in the fluctuations of this axis. The results show that the microscopic origin of the biquadratic coupling between the polarization and the tilt, which has been recently introduced into the extended Landau model of the SA-S*C transition, is the quadrupolar (or bipolar) rotational bias induced by the anisotropy in the fluctuations of the long molecular axis. The tilt induced anisotropy in the fluctuations is practically identical in chiral and non-chiral smectic C phases. 相似文献
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Approximate ab-initio calculations of NMR coupling constants are reported, for a number of small molecules. The agreement with experiment is erratic, and is shown to depend critically on the form of the excited state wavefunctions. This suggests that the use of an average energy approximation is far from valid.
Zusammenfassung NMR Kopplungskonstanten werden für eine Anzahl von kleinen Molekülen mitgeteilt, wobei sich keine rechte Übereinstimmung mit dem Experiment ergibt. Es zeigt sich, daß die Werte kritisch von der Form der Wellenfunktion für die angeregten Zustände abhängen. Das läßt vermuten, daß die Verwendung eines mittleren Energienenners nicht zu empfehlen ist.
Résumé Calculs ab-initio approchés des constantes de couplage NMR d'un certain nombre de petites molécules. L'accord avec l'expérience est erratique et dépend d'une façon critique de la forme des fonctions d'onde excitées. Ceci suggère que l'emploi d'une approximation d'«énergie moyenne» est loin d'être valable.相似文献
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Phase transitions in C6H4Cl2 and C6H4I2 were monitored by observing the frequencies and apparent spin-spin relaxation times of the 35Cl and 127I nuclear quadrupole resonances. Decreases in the apparent spin-spin relaxation times were found to accompany the onset of the transitions. 相似文献
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In the production of131I, the presence of a contamination extractable with organic solvents has been detected and its source discovered. The influence
of overheating was established in the preparation of99m
Tc by the extraction method. Finally, details are given of the procedure used for the estimation of199Au present in198Au. 相似文献
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论述了铵梯脲混合炸药中改性硝酸脲和硝酸铵组分含量的一种快速准确的化学分析测定方法。该法在研制和生产铵脲类炸药的过程中,对选择最佳配比,控制生产和质量把关等有着重要的指导作用。同时笔者对测定方法,反应原理,影响因素等作了深入的探讨与研究。 相似文献
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This paper gives complete details of a unique system for Magnetically Recording the Analogue Spectral Signals from an N.Q.R. Spectrometer of the S.R.O./Marginal Oscillator type.This is a very low cost system, but producing a very high order of play-back resolution from recordings, using a normal domestic Cassette or Tape, Reel to Reel Recorder. Spectra can also be transmisted via telephone lines, fibre optic links or radio frequencies.This system has been used now for several years, and due to the design being based mainly om passive components, the order of reliability is extremely high, without any faults being encountered to dete!. 相似文献
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C. Chachaty T. Bredel A. M. Tistchenko J.-P. Caniparoli B. Gallot 《Liquid crystals》2013,40(6-7):815-824
Abstract A thermotropic ionic lamellar phase from non-stoichiometric pyridinium octyl-phosphates has been investigated by multinuclear N.M.R. and X-ray diffraction. At room temperature and above, this phase is formed for pyridine to octylphosphoric acid molar ratios from 0.2 to 0.8.2H and 13C relaxation experiments show that the pyridinium ion undergoes a very anisotropic motion with Dzz > Dxx ? Dyy, z and x being the perpendicular direction to the ring and the c 2 symmetry axis, respectively. The order parameters given by the 2H quadrupolar splittings and the 13C chemical shift anisotropy (CSA) are Szz = 0.13, Syy = -0.08 and Sxx = -0.05, showing that the pyridinium ring is preferentially oriented parallel to the lamellar plane. The 31P CSA and the C1-P dipolar splitting yield Szz = 0.33 and Sxx ? Syy for the octylphosphate anion. The order parameters of alkyl C-H bonds have been obtained from the J resolved two-dimensional 13C N.M.R. spectra of oriented samples. Two limiting conformational models have been considered to calculate the S CH. One of them is reasonably consistent with the structure derived from X-ray experiments and has been used to calculate the dipolar 31P relaxation. Taking into account the CSA contribution, the relaxation measurements performed at 36, 121 and 202 MHz show that the octylphosphate anion undergoes a quasi-axial reorientation about the long molecular axis x with D∥/D⊥ = 4 and D⊥ ? 107 rad/s at 300 K. 相似文献
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Dr. Hidetoshi Noda Yasuko Asada Dr. Tatsuro Maruyama Dr. Naoki Takizawa Dr. Nobuo N. Noda Prof. Dr. Masakatsu Shibasaki Dr. Naoya Kumagai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(17):4299-4304
A new scaffold for producing efficient organic fluorescent materials was identified: 2,5-diamino-4,6-diarylpyrimidine featuring a C4N4 elemental composition. Single-step installation of two aryl groups at the 4,6-positions of the pyrimidine core delivered fluorescent organic materials in a modular fashion. A range of fluorescent compounds with distinct absorption/emission properties was readily accessed by changing the aromatic attachments. A generally high absorption coefficient and quantum yield were observed, including C4N4 derivatives that could fluoresce even in the solid state. The two amino groups at the 2,5-positions of the pyrimidine were essential for intense fluorescence with a large Stokes shift, which was corroborated by structural relaxation to a p-iminoquinone-like structure in the excited state. Besides live-cell imaging capabilities, fluorescent labeling of a protein involved in autophagy elucidated a new protein–protein interaction, supporting potential utility in bioimaging applications. 相似文献
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The dependence of the proton N.M.R. absorption spectrum on nematic director configuration and molecular self-diffusion in nematic submicrondroplets is analysed. The lineshape is evaluated numerically for radial and bipolar director configuration. The motional averaging is taken into account by means of a numerical simulation of the molecular diffusion which induces slow molecular reorientations due to non-uniform orientational ordering in the droplet. This diffusion process strongly affects the absorption spectra of the radial configuration, whereas spectra of the bipolar configuration are only slightly influenced. The possibility of determinating the submicrometre nematic droplet structures using the proton N.M.R. lineshape is discussed. 相似文献
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The dependence of the proton N.M.R. absorption spectrum on nematic director configuration and molecular self-diffusion in nematic submicrondroplets is analysed. The lineshape is evaluated numerically for radial and bipolar director configuration. The motional averaging is taken into account by means of a numerical simulation of the molecular diffusion which induces slow molecular reorientations due to non-uniform orientational ordering in the droplet. This diffusion process strongly affects the absorption spectra of the radial configuration, whereas spectra of the bipolar configuration are only slightly influenced. The possibility of determinating the submicrometre nematic droplet structures using the proton N.M.R. lineshape is discussed. 相似文献
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The isomers of the nitrogen-substituted fullerenes (azafullerenes) C19N, C59N, C69N, and C75N are examined using all-electron Gaussian atomic orbital basis density functional theory, to determine the doublet radical geometries and hyperfine coupling constants. We find that the inaccuracy of previously calculated hyperfine coupling constants of C59N resulted from a poor treatment of the geometry optimization. We find that UB3LYP minimization of the radical geometry in the 6-31G basis, followed by single-point evaluation of the hyperfine constants in which an expanded basis is used on the atomic sites of interest, forms an efficient compromise between computational cost and accuracy with respect to experimental hyperfine constants. Using this approach, we assign the hyperfine signals observed in experiments on the C69N radical by calculating the hyperfine coupling constants for all five of the isomers and examine the electron spin density distribution. Finally, we present predicted hyperfine coupling constants for the isomers of C19N and C75N for use in the interpretation of future experiments. 相似文献