共查询到20条相似文献,搜索用时 15 毫秒
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固体核磁共振(NMR)中双交叉极化(DCP)是用于膜蛋白信号指认的多维异核相关实验的基本技术模块.DCP的效率在很大程度上决定了多维异核相关实验的效率.本文分析了3种典型的膜环境中的膜蛋白(AQPZ、DAGK和EV71 2B)的DCP效率及其影响因素.结果显示,在相同的实验条件下,3种蛋白样品的DCP效率存在明显差异:其中AQPZ的DCP效率最高(31%),DAGK的效率次之(23%),EV71 2B的效率最低(14%).通过测量它们在旋转坐标下的自旋-晶格弛豫时间(T1ρ)和偶极耦合常数(DHN),发现膜蛋白的运动会明显缩短T1ρ,但对DHN的影响较小.在实验的基础上,建立了T1ρ与DCP效率相关的模型,并基于DCP动力学的定量分析,证明了运动导致的T1ρ缩短是降低DCP效率的主要原因.因此,可以通过定量分析未知样品的T1ρ来预测其DCP的最优效率,为DCP实验的优化提供依据. 相似文献
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近年来,固体核磁共振被广泛应用于膜蛋白、纤维化蛋白等体系的结构和功能研究.在固体核磁共振实验中,快速魔角旋转或高功率射频场照射等实验条件将导致样品发热.生物样品发热能导致严重的后果,例如样品温度的快速升高,信号分辨率、信噪比的降低,发热严重时甚至导致样品的不可逆损坏.近年来,人们对样品发热问题进行了一些研究,发现通过优化样品制备条件或固体核磁共振实验条件,以及改进探头设计等手段,可以在一定程度上减轻样品发热.该文主要综述了生物固体核磁共振研究中导致样品发热的原因和减轻样品发热的方法. 相似文献
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在低场脉冲核磁共振实验中为了增大射频激励的带宽,通常采用的方法是提高射频激励磁场的场强. 针对共振区域中静磁场的不均匀性,本文提出了根据共振区域中的静磁场分布设计射频线圈以提高射频激励带宽,并用目标场方法实现了这一构想. 相似文献
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《Journal of Magnetic Resonance, Series A》1993,101(3):277-284
This work has two objectives. First, heteronuclear editing was considered, with particular aim at proton-detected NMR spectroscopy of rare nuclei. The second aspect refers to localized heteronuclear NMR spectroscopy, implying the editing option. The common basis of both techniques is J cross polarization (or coherent rotating-frame polarization transfer). In the presence of magnetic field gradients this process is slice selective and is introduced as a principle for localized liquid-state NMR, particularly of heteronuclear spins. Heteronuclear editing of NMR lines is performed by the aid of a cyclic cross-polarization pathway. Both methods can be combined to a technique for localized proton-detected NMR spectroscopy of rare nuclei. Test experiments demonstrating the slice selectivity of the transfer process and the efficiency of the cyclic cross-polarization editing procedure are reported. Applications to localized homo- or heteronuclear spectroscopy and imaging are discussed. 相似文献
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Kay Saalwchter Robert Graf Hans W. Spiess 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(2):398
An in-depth account of the effects of homonuclear couplings and multiple heteronuclear couplings is given for a recently published technique for 1H–13C dipolar correlation in solids under very fast MAS, where the heteronuclear dipolar coupling is recoupled by means of REDOR π-pulse trains. The method bears similarities to well-known solution-state NMR techniques, which form the framework of a heteronuclear multiple-quantum experiment. The so-called recoupled polarization-transfer (REPT) technique is versatile in that rotor-synchronized 1H–13C shift correlation spectra can be recorded. In addition, weak heteronuclear dipolar coupling constants can be extracted by means of spinning sideband analysis in the indirect dimension of the experiment. These sidebands are generated by rotor encoding of the reconversion Hamiltonian. We present generalized variants of the initially described heteronuclear multiple-quantum correlation (HMQC) experiment, which are better suited for certain applications. Using these techniques, measurements on model compounds with 13C in natural abundance, as well as simulations, confirm the very weak effect of 1H–1H homonuclear couplings on the spectra recorded with spinning frequencies of 25–30 kHz. The effect of remote heteronuclear couplings on the spinning-sideband patterns of CHn groups is discussed, and 13C spectral editing of rigid organic solids is shown to be practicable with these techniques. 相似文献
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Laurent Delevoye Christian Fernandez Cludia M. Morais Jean-Paul Amoureux Valrie Montouillout Joo Rocha 《Solid state nuclear magnetic resonance》2002,22(4):306-512
27Al decoupling has been used to remove residual J-coupling interactions between31 P and 27Al in microporous aluminophosphates AlPO4-14 and AlPO4-40. In combination with 1H high-power decoupling, 27Al adapted decoupling yields 31P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO4-14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27Al dimension and double-resonance decoupling in the 31P acquisition domain. 相似文献
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Fang Tian Riqiang Fu Timothy A. Cross 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,139(2):377
While 15N solid-state NMR has proven to be very advantageous for the development of structural biological methods, 13C spectroscopy has increased sensitivity and spectral dispersion. However, large natural abundance signals and homonuclear dipolar interactions pose significant problems. Here we have used a pair of 13C-labeled sites in a lipid-solubilized polypeptide to show the selective polarization can be used in combination with spin diffusion to achieve simplified spectra. Both unoriented and oriented samples have been used, with the latter providing a well-resolved homonuclear dipolar splitting. 相似文献
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Fast acquisition of multi-dimensional spectra in solid-state NMR enabled by ultra-fast MAS 总被引:1,自引:1,他引:0
Sgolne Laage Joseph R. Sachleben Stefan Steuernagel Roberta Pierattelli Guido Pintacuda Lyndon Emsley 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,196(2):133-141
The advantages offered by ultra-fast (>60 kHz) magic angle spinning (MAS) rotation for the study of biological samples, notably containing paramagnetic centers are explored.It is shown that optimal conditions for performing solid-state 13C NMR under 60 kHz MAS are obtained with low-power CW 1H decoupling, as well as after a low-power 1H,13C cross-polarization step at a double-quantum matching condition. Acquisition with low-power decoupling highlights the existence of rotational decoupling sidebands. The sideband intensities and the existence of first and second rotary conditions are explained in the framework of the Floquet–van Vleck theory.As a result, optimal 13C spectra of the oxidized, paramagnetic form of human copper zinc superoxide dismutase (SOD) can be obtained employing rf-fields which do not exceed 40 kHz during the whole experiment. This enables the removal of unwanted heating which can lead to deterioration of the sample. Furthermore, combined with the short 1H T1s, this allows the repetition rate of the experiments to be shortened from 3 s to 500 ms, thus compensating for the sensitivity loss due to the smaller sample volume in a 1.3 mm rotor. The result is that 2D 13C–13C correlation could be acquired in about 24 h on less than 1 mg of SOD sample. 相似文献
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The solid-state phase transitions of CuBr, CuI and NaNbO3 can be readily observed using 63Cu and 23Na high-temperature magic-angle spinning nuclear magnetic resonance spectroscopy. Temperature has large, linear effects on the peak maximum of 63Cu in each solid phase of CuBr and CuI, and there is large jump in shift across each phase transition. The 23Na MAS NMR peak intensities and the line widths in NaNbO3 also clearly show its high-temperature transition to the cubic phase. These data can be used to calibrate high-temperature MAS NMR probes up to 913 K, which is two hundred degrees higher than the commonly-used temperature calibration based on the chemical shift of 207Pb in Pb(NO3)2. 相似文献
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The cross gain modulation, the cross phase modulation and their recovery time in the SOAs with the various lengths were experimentally investigated. It was found that these values strongly depended on the device length. 相似文献
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Sren L. Poulsen Vanessa Kocaba Gwenn Le Saoût Hans J. Jakobsen Karen L. Scrivener Jrgen Skibsted 《Solid state nuclear magnetic resonance》2009,36(1):32-44
The applicability, reliability, and repeatability of 29Si MAS NMR for determination of the quantities of alite (Ca3SiO5) and belite (Ca2SiO4) in anhydrous Portland cement was investigated in detail for 11 commercial Portland cements and the results compared with phase quantifications based on powder X-ray diffraction combined with Rietveld analysis and with Taylor–Bogue calculations. The effects from paramagnetic ions (Fe3+) on the spinning sideband intensities, originating from dipolar couplings between 29Si and the spins of the paramagnetic electrons, were considered and analyzed in spectra recorded at four magnetic fields (4.7–14.1 T) and this has led to an improved quantification of alite and belite from 29Si MAS NMR spectra recorded at “high” spinning speeds of νR=12.0–13.0 kHz using 4 or 5 mm rotors. Furthermore, the impact of Fe3+ ions on the spin-lattice relaxation was studied by inversion-recovery experiments and it was found that the relaxation is overwhelmingly dominated by the Fe3+ ions incorporated as guest-ions in alite and belite rather than the Fe3+ sites present in the intimately mixed ferrite phase (Ca2AlxFe2−xO5). 相似文献
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A protocol using (207)Pb NMR of solid lead nitrate was developed to determine the temperature of magic-angle spinning (MAS) NMR probes over a range of nominal set temperatures and spinning speeds. Using BioMAS and FastMAS probes with typical sample spinning rates of 8 and 35 kHz, respectively, empirical equations were devised to predict the respective sample temperatures. These procedures provide a straightforward recipe for temperature calibration of any MAS probe. 相似文献
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Shunkang Liu 《International Journal of Infrared and Millimeter Waves》1999,20(10):1749-1755
A computation technique for gain, efficiency and output power in broadband millimeter wave helix TWTs from their dimensions is described. The computed results by modeling are good agreement with experimental measurements. It is shown that the method is fast and useful accuracy. It can be used as engineering design for MMW TWTs. 相似文献
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Lloyd Lumata Matthew Merritt Craig Malloy A. Dean Sherry Zoltan Kovacs 《Applied magnetic resonance》2012,43(1-2):69-79
The yttrium complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(1′-13C-acetic acid) [13C]DOTA was synthesized. Fast dissolution dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) studies revealed that the 89Y, 13C, and 15N nuclei present in the complex could be co-polarized at the same optimum microwave irradiation frequency. The liquid-state spin–lattice relaxation time T 1 of these nuclei were found to be reasonably long to preserve some or most of the DNP-enhanced polarization after dissolution. The hyperpolarized 13C and 89Y NMR signals were optimized in different glassing mixtures. The overall results are discussed in light of the thermal mixing model of DNP. 相似文献
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Z. F. Zhang L. Z. Xiao H. B. Liu F. Deng X. Li T. L. An V. Anferov S. Anferova 《Applied magnetic resonance》2013,44(7):849-857
Three-dimensional (3-D) nuclear magnetic resonance (NMR) experiments reflect material structure, such as physical array of porous media and chemical compositions of complex fluids. However, a huge database is acquired in multi-dimensional NMR and obstructs the extraction of this information in a proper manner. In this paper, a new fast 3-D Laplace inversion procedure is introduced which contains a specially designed 3-D pulse sequence to acquire the data responding to interesting NMR properties simultaneously and efficient data-processing algorithm referring this pulse sequence. A 3-D NMR experiment in low-field on water-saturated synthetic porous sample is presented to demonstrate the validity of the designed 3-D inverse Laplace algorithm. 相似文献