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1.
The CP/MAS 13C NMR spectra of crystalline L-leucine and DL-leucine at 7 T are compared with previously reported spectra at lower field strengths. An increasing dominance of chemical shift effects over residual 14N-13C dipolar interactions is observed on the C alpha and C beta splittings with increasing field strength. A new structure is observed in the 25 ppm region of both samples. The spectra in this region were assigned by application of the depolarisation-repolarisation method. The assignment showed differences in the ordering of peaks between solid state and liquid state chemical shifts. 相似文献
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13C CP MAS NMR and GIAO-CHF calculations of coumarins 总被引:1,自引:0,他引:1
13C cross-polarization magic-angle spinning NMR spectra were recorded for a series of solid coumarins. Ab initio calculations of shielding constants were performed with the use of GIAO-CHF method. The combined CPMAS NMR and theoretical approach was successful in characterizing solid-state conformations of coumarins; a relationship sigma (ppm) = -1.032 xdelta + 205.28 (R(2) = 0.9845) can be used to obtain structural information for coumarins, for which solid-state NMR or crystal structure data are not available. 相似文献
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Hisashi Honda Shinshin Kyo Yousuke Akaho Satoshi Takamizawa Hiromitsu Terao 《Hyperfine Interactions》2010,197(1-3):275-285
H/D isotope effects onto 79Br NQR frequencies of piperidinium p-bromobenzoate were studied by deuterium substitution of hydrogen atoms which form two kinds of N–H?O type hydrogen bonds, and the isotope shift of ca. 100 kHz were detected for a whole observed temperature range. In addition, 1H MAS NMR spectra measurements of piperidinium and pyrrolidinium p-bromobenzoate were carried out and little isotope changes of NMR line shape were detected. In order to reveal effects of molecular arrangements into the obtained isotope shift of NQR frequencies, single-crystal X-ray measurement of piperidinium p-bromobenzoate-d2 and density-functional-theory calculation were carried out. Our estimation showed the dihedral-angle change between piperidine and benzene ring contributes to isotope shift rather than those of N–H lengths by deuterium substitution. 相似文献
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《Journal of Magnetic Resonance (1969)》1992,96(3):574-581
A new, simple, and inexpensive technique is presented for monitoring high-resolution solid-state NMR of 13C at temperatures ranging between 85 and 450 K. In this procedure, the reaction conditions are controlled by preparing samples at 77 K in 5 mm NMR tubes, while attached to a vacuum system. The NMR tubes are prefitted with a rotor for spinning. After preparation, the samples are sealed, transferred to the double-resonance MAS NMR probe, and analyzed, all while the sample temperature is maintained as low as 85 K. The spinning rates vary from 3.0 kHz at 85 K to 5.2 kHz at 300 K using nitrogen drive gas. Probe design and performance, sample-preparation procedure, and details of the low-temperature experiment are described. In general, the technique may be applied in studies of low-temperature reaction mechanisms and kinetics. 13C CP/MAS spectra of ethylene adsorbed on silica-supported ruthenium catalyst are presented to illustrate its performance and possible application. 相似文献
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Previous H2 permeation tests showed a degradation of H2 permeation flux with time. To understand the cause of degradation and develop a solution, the stability of $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ and $ {\text{SrZr}}_{{0.2}} {\text{Ce}}_{{0.7}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ samples were studied under dry and wet H2 atmospheres. Total conductivity of $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ increased with time in dry H2. The X-ray diffraction pattern of $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ after dry hydrogen atmosphere heat treatments show CeO2 peaks indicating that $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ decomposes under dry H2 atmospheres; scanning electron microscopy and energy dispersive X-ray spectroscopy analyses prove that decomposition proceeded along the grain boundaries. $ {\text{SrZr}}_{{0.2}} {\text{Ce}}_{{0.7}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ was investigated and demonstrated greater stability under dry hydrogen atmospheres. However, Zr substitution results in a tradeoff with electrical properties. 相似文献
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He Yang Yankun Xiong Zhouwei Xie Lijun Jin Yang Li Juan Yang Haoquan Hu 《Proceedings of the Combustion Institute》2021,38(3):4161-4170
A method for quantitatively characterizing the carbon skeletal structure of coal by variable contact time experiment using high-resolution CP/MAS 13C solid-state NMR spectroscopy is proposed in this paper. The initial polarization transfer intensity from protons directly bonded with carbons, instead of dipolar-dephasing techniques which had to run on a lower frequency NMR spectrometer (100.02 MHz for proton), was used to divide the bridgehead and protonated aromatic carbons, making all the NMR data in this paper obtained on a high frequency NMR spectrometer (500.12 MHz for proton). On this basis, the fractions of different carbons in coal were further divided by the initial polarization transfer intensity from spin diffusion of protons unbonded with carbons. The structure of Naomaohu coal, a subbituminous coal from China, was measured. The change of polarization transfer with contact time was analyzed quantitatively. The fractions of aromatic, aliphatic, carboxyl and carbonyl carbons, and corrective aromaticity are 0.61, 0.39, 0.1 and 0.51, respectively. The fractions of protonated and bridgehead aromatic carbons are 0.22 and 0.09, respectively. These results agreed with literatures, and bond concentration calculated by the carbon skeletal structure distribution of coal was reasonable. 相似文献
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Single-crystal X-ray diffraction and 13C solid state NMR spectroscopy were used to characterize the structure and dynamics of the p-xylene clathrate of Dianin's compound. In contrast to conclusions obtained from single-crystal 2H NMR and modelling, the diffraction results suggest there is a single (symmetry disordered) guest site without any significant distortion of the host framework. A single xylene guest statistically disordered over six overlapping equivalent positions can account for the 13C NMR spectrum at room temperature. The high crystal-lographic symmetry arises from space averaging. At high temperatures the 13C spectrum is consistent with the onset of dynamic processes that result in higher effective symmetry. 相似文献
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Man Ken CHEUNG 《波谱学杂志》2002,19(1):82-82
High-resolution 13C spectra of solid polymers are often acquired with cross polarization with magic angle spinning (CP/MAS) to take advantage of the abunda
ntly available protons in the polymer chains. The sequence for transferring mag
netization from 1H to13C using Hartmann-Hahn spin locking in the rotating frame is now a standard in commercial solidstate NMR spectrometers. 相似文献
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The 13C CP/MAS NMR spectrum of [(n-C3H7)4N][Cd(SCN)3], 1, indicates the presence of three non-equivalent thiocyanate ligands, in agreement with the results of a recent single-crystal X-ray diffraction study. Examination of the 13C MAS line shapes allows direct measurement of the indirect spin-spin coupling constants, 1J(14N, 13C) = 16 +/- 1 Hz and 2J(111/113Cd, 13C) = 75 +/- 5 Hz, for the unique N-bonded thiocyanate ligand. This is the first reported measurement of 1J(14N, 13C) and 2J(111/113Cd, 13C) in the solid state. Possible reasons for the failure to observe 1J(14N, 13C) values in previous high-resolution 13C CP/MAS NMR studies are summarized. 相似文献
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Christopher A. Rice Kevin C. Gross Glen P. Perram 《Applied physics. B, Lasers and optics》2013,111(2):173-182
A tunable diode laser absorption spectroscopy (TDLAS) device fiber coupled to a pair of 12.5 in. telescopes was used to study atmospheric propagation for open path lengths of 100–1,000 meters. More than 50 rotational lines in the molecular oxygen A-band O2 $ {\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} $ transition near 760 nm were observed. Temperatures were determined from the Boltzmann rotational distribution to within 1.3 % (less than ±2 K). Oxygen concentration was obtained from the integrated spectral area of the absorption features to within 1.6 % (less than ±0.04 × 1018 molecules/cm3). Pressure was determined independently from the pressure-broadened Voigt lineshapes to within 10 %. A fourier transform interferometer (FTIR) was also used to observe the absorption spectra at 1 cm?1 resolution. The TDLAS approach achieves a minimum observable absorbance of 0.2 %, whereas the FTIR instrument is almost 20 times less sensitive. Applications include atmospheric characterization for high energy laser propagation and validation of monocular passive raging. 相似文献
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Residual dipolar coupling between carbons and 14N nuclei in the 13C CPMAS NMR spectrum of solid imidazole is studied. Calculations of expected splittings with a previously reported equation leads to the complete assignment of the solid state carbon chemical shifts. Additionally, information is provided on the location of 14N electric field gradient axes at the N-H site. 相似文献
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Yuriy G. Kolyagin Irina I. Ivanova Yuri A. Pirogov 《Solid state nuclear magnetic resonance》2009,35(2):104-112
The early stages of methane, ethane and propane conversion were studied by in situ 1H and 13C MAS NMR techniques over fully exchanged Zn2+/MFI catalyst obtained by the reaction with zinc vapour. The in situ techniques revealed strong interaction of alkanes with Zn2+ cations evidenced by significant shift of the corresponding NMR lines. Besides that, the formation of methyl zinc, ethyl zinc and n-propyl zinc species along with bridging and silanol surface OH-groups was detected already at the ambient temperature. These results pointed to dissociative adsorption of alkanes over (ZO)–Zn2+–(OZ) and (ZO)–Zn2+–(OSi) active sites of the catalyst. The dissociative adsorption was shown to be a dead-end surface reaction in the case of methane starting reactant, while in the case of ethane and propane, it appeared to be responsible for the initiation of the catalytic cycle leading to alkenes and dihydrogen formation and regeneration of zinc containing catalytic sites. 相似文献
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Freita JC Emmerich FG Cernicchiaro GR Sampaio LC Bonagamba TJ 《Solid state nuclear magnetic resonance》2001,20(1-2):61-73
13C high-resolution solid-state nuclear magnetic resonance (NMR) was employed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut, peat, and PVC). For heat treatment temperatures (HTTs) above about 600 C, all materials presented 13C NMR spectra composed of a unique resonance line associated with carbon atoms in aromatic planes. With increasing HTT a continuous broadening of this resonance and a diamagnetic shift in its central frequency were verified for all samples. The evolution of the magnitude and anisotropy of the magnetic susceptibility of the heat-treated carbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite, for which the magnetic susceptibility effect is also present and is much more pronounced. 相似文献
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Jakobsen HJ Daugaard P Hald E Rice D Kupce E Ellis PD 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(1):152-154
The design of a broadband 4-mm magic-angle spinning (MAS) X-(1)H/(19)F double resonance probe for cross-polarization (CP)/MAS NMR studies at 21.15 T ((1)H at 900 MHz) is described. The high-frequency (1)H/(19)F channel employs a new and efficient transmission line tuning design. The first (13)C CP/MAS NMR spectra recorded at 21.15 T have been obtained with this probe and exhibit the best S/N per milligram sample of hexamethylbenzene achieved so far for a 4-mm rotor. 相似文献
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Werner-Zwanziger U Lis G Mastalerz M Schimmelmann A 《Solid state nuclear magnetic resonance》2005,27(1-2):140-148
Thermal maturity of oil and gas source rocks is typically quantified in terms of vitrinite reflectance, which is based on optical properties of terrestrial woody remains. This study evaluates 13C CP/MAS NMR parameters in kerogen (i.e., the insoluble fraction of organic matter in sediments and sedimentary rocks) as proxies for thermal maturity in marine-derived source rocks where terrestrially derived vitrinite is often absent or sparse. In a suite of samples from the New Albany Shale (Middle Devonian to the Early Mississippian, Illinois Basin) the abundance of aromatic carbon in kerogen determined by 13C CP/MAS NMR correlates linearly well with vitrinite reflectance. 相似文献
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V. S. Zuev A. V. Kanaev L. D. Mikheev D. B. Stavrovskii 《Journal of Russian Laser Research》1982,3(4):287-302
The operating principle of a photodissociation XeF laser (λ?350 nm) is discussed. A laser operating on the gas mixture XeF2:N2(SF6):Ar pumped by radiation from an open high-current discharge is described. The maximum lasing duration is 5 μsec, the maximum output energy is 0.15 J. The vibrational structure of the XeF-molecule transition B2Σ1/2 + ? X2Σ1/2 +, observed in absorption, luminescence, and stimulated emission, is investlgated. The vibrational quantum and the anharmonicity in the upper and lower states are measured: ωe ' = 308.7 cm-1, ωe 'xe ' = 1.44 cm-1, ωe '' = 225.7 cm-1, ωe ''xe '' = 11.0 cm-1. The difference between the equilibrium internuclear distances of the XeF molecule is determined for the excited (B) and ground (X) states, namely re ' - re '' = 0.33 +- 0.01 Å. 相似文献