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1.
脉冲梯度增强技术的初步研究   总被引:2,自引:0,他引:2  
自行研制一套脉冲梯度场系统,配合Bruker公司MSL 300谱仪研究脉冲梯度增强的高分辨核磁共振,研制以PC/286为核心的梯度脉冲波形和幅度可任意调节的梯度场发生器;改装谱仪的1H液体探头、增加梯度场线图.分析了脉冲梯度场产生的涡流磁场的影响;报道了利用自制梯度场系统进行的脉冲梯度增强的高分辨COSY实验.  相似文献   

2.
We demonstrate the first two-dimensional correlation NMR (COSY) spectra obtained at ultra low frequencies (ULF) using the Earth's magnetic field. Using a specially developed spectrometer with multiple audio-frequency pulses under controlled pulse phase, we observe magnetisation transfer arising from heteronuclear J-couplings in trifluoroethanol and para-difluorobenzene. The 2D COSY spectra exhibit all diagonal and off-diagonal multiplets consistent with known J-couplings in these molecules.  相似文献   

3.
核磁共振波谱学自本世纪40年代中期诞生起,已走完了其光辉的50年历程,其间,它已完成了自连续波检测向脉冲傅里叶变换检测的过渡,并在此基础上率先将传统的一维谱的观测拓宽为多维谱的观测,不断提供了其它方法难以提供或无法提供的崭新信息,从而确立了它在分子结构和动力学研究中的独特地位,本文旨在以二维NMR为主,简述被称为现代核磁共振波谱学之核心的多维NMK的概况。  相似文献   

4.
从甘肃产的猫儿屎(Decaisnea Fargesi)植物茎中分离出三个新皂甙.利用二维核磁共振(2DNMR)技术研究确定了它们的化学结构,并对其进行了13C和1H的全归属.  相似文献   

5.
Magnetic field gradients have proven useful in NMR for coherence pathway selection, diffusion studies, and imaging. Recently they have been combined with magic angle spinning to permit high-resolution measurements of semi-solids, where magic angle spinning averages any residual dipolar couplings and local variations in the bulk magnetic susceptibility. Here we show the first examples of coherence pathway selection by gradients in dipolar coupled solids. When the gradient evolution competes with dipolar evolution the experiment design must take into account both the strength of the dipolar couplings and the means to refocus it. Examples of both homonuclear and heteronuclear experiments are shown in which gradients have been used to eliminate the need for phase cycling.  相似文献   

6.
The two dimensional inverse detected heteronuclear correlation experiment HMQC and the homonuclear correlation experiments COSY and ROESY were performed on the natural alkaloid, delphinine enabling complete assignments of the 1H and 13C spectra. The stereochemistry of ring A and B have been determined in solution. The results suggest that the application of direct correlation multipulse NMR techniques allows for unambiguous structural assignment of delphinine.  相似文献   

7.
利用核磁共振氢谱(1H NMR)、碳谱(13C NMR)、同核位移相关谱(1H-1H COSY)、异核单量子相干谱(HSQC)和异核多键相关谱(HMBC)等多种核磁研究方法对抗银屑病药物卡泊三醇的1H、13C信号进行完全归属.  相似文献   

8.
Spin state selective experiments have become very useful tools in solution NMR spectroscopy, particularly in the context of TROSY line narrowing. However, the practical implementation of such pulse sequences is frequently complicated by unexpected instrument behavior. Furthermore, a literal theoretical analysis of sequences published with specific phase settings can fail to rationalize such experiments and can seemingly contradict experimental findings. In this communication, we develop a practical approach to this ostensible paradox. Spin-dynamic design, rationalization, and simulation of NMR pulse sequences, as well as their confident and reliable implementation across current spectrometer hardware platforms, require precise understanding of the underlying nutation axis conventions. While currently often approached empirically, we demonstrate with a simple but general pulse program how to uncover these correspondences a priori in the general case. From this, we deduce a correspondence table between the spin-dynamic phases used in NMR theory and simulation on the one hand and pulse program phases of current commercial spectrometers on the other. As a practical application of these results, we analyze implementations of the original (1)H-(15)N TROSY experiment and illustrate how steady-state magnetization can be predictably, rather than empirically, added to a desired component. We show why and under which circumstances a literal adoption of phases from published sequences can lead to incorrect results. We suggest that pulse sequences should be consistently given with spin-dynamically correct (physical) phases, rather than in spectrometer-specific (software) syntax.  相似文献   

9.
用脉冲梯度切核磁共振测量固态样品中的扩散遇到很多困难,对于一个不用内锁的电磁体系统,观测到脉冲场梯度过后涡流造成样品处的磁场强度的强烈振荡.提出了一个用该系统测量凝胶聚合物中锂离子扩散可获得较好结果的脉冲序列.  相似文献   

10.
By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (F(p/r) and G(p/r)), magic pulsed field gradient (MPFG) ratios for the prepare (G(p)/F(p)) and the read (G(r)/F(r)) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the tau-intervals between the pi and pi/2 rf pulses, these two MPFG ratios coincide to eta=G(p/r)/F(p/r)=1-8/[1+(1/3)(delta/tau)(2)]. Since the width of the pulsed field gradients (delta) is bounded by 0< or =delta< or =tau, eta can only be in the range of 5< or =-eta< or =7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.  相似文献   

11.
Methodology for the study of dynamics in heteronuclear systems in the laboratory frame was described in the previous paper [1]. Now the methodology for the study of molecular dynamics in the solid state heteronuclear systems in the rotating frame is presented. The solid state NMR off-resonance experiments were carried out on a homemade pulse spectrometer operating at the frequency of 30.2 MHz for protons. This spectrometer includes a specially designed probe which contains two independently tuned and electrically isolated coils installed in the coaxial position on the dewar. A unique probe design allows working at three slightly differing frequencies off and on resonance for protons and at the frequency of 28.411 MHz for fluorine nuclei with complete absence of their electrical interference. The probe allows simultaneously creating rf magnetic fields at off-resonance frequencies within the range of 30.2–30.6 MHz and at the frequency of 28.411 MHz. Presented heteronuclear cross-relaxation off-resonance experiments in the rotating frame provide information about molecular dynamics.  相似文献   

12.
More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation of NMR imaging techniques. The algorithm uses the solution of the Bloch equations at each point of a simulated object. The direction of every elementary magnetic moment is computed at each instant, and stored in an array giving the global signal to be processed, whatever the pulse and gradient sequence. To test the validity of this program, we have simulated some well-known experimental results. Some applications are presented which contribute to the understanding of image distortions and to techniques such as selective radio-frequency pulse or oscillating gradients. This program can be used to unravel physical and technological causes of image distortions, to have a "microscopic" look at any parameter of an experiment, and to study the contrast given by various NMR imaging techniques as a function of the three NMR parameters, i.e., the hydrogen nuclei density rho and the relaxation times T1 and T2.  相似文献   

13.
We demonstrate that cogwheel phase cycling, which was previously only used in solid state NMR, can be applied to optimize the efficiency of commonly used pulse sequences in multiple resonance liquid-state biomolecular NMR. In favorable cases the required minimum number of scans can be reduced by more than 80% as compared to a corresponding sequence with nested phase cycles. Since cogwheel phase cycling procedures can be designed for a range of scan numbers, and can be combined with pulsed field gradients, the total experiment time can be adjusted closely to the required signal-to-noise ratio with minimal overhead. Examples are shown for 3D-TROSY-HNCO, 3D-TROSY-HNCACO, and 3D-HACACO experiments on diamagnetic and paramagnetic proteins.  相似文献   

14.
核磁共振(NMR)异核单量子相干(HSQC)实验因具有较高的灵敏度和分辨率而被广泛用于液体大分子化合物的结构鉴定和研究.然而由于HSQC脉冲的复杂性,需要严格控制实验参数和实验条件才能得到高质量的谱图.本文基于量子力学原理对HSQC实验进行数学建模,通过理论推导、数值计算求解自旋1/2的IS双核体系在每个脉冲节点作用后的密度矩阵,然后结合二维NMR信号采样方法,使用计算机程序完成了该体系HSQC谱图的模拟,同时,还实现了乙醇分子的HSQC谱图模拟. HSQC实验的成功模拟基于对复杂演化过程的精确计算,可用于预测谱图以及实验参数改变对NMR谱图的影响,指导高质量HSQC实验谱图的采集.  相似文献   

15.
A new PGSE NMR experiment, designed to measure molecular diffusion coefficients in systems with nonvanishing static dipolar coupling, is described. The fast static dipolar dephasing of the single-quantum (13)C coherences is removed by multiple-pulse heteronuclear decoupling. The resulting slow dephasing of the (13)C coherences allows for inserting appropriate gradient pulses into the pulse sequence. The presence of the large magnetic field gradient reduces the efficiency of the decoupling sequences which is compensated for by introducing a scheme of sequential slice selection across the sample. The method is demonstrated by (19)F-decoupled (13)C PGSE NMR experiments in a lyotropic nematic and lamellar liquid crystal.  相似文献   

16.
17.
四维NMR谱     
尽管3DNMR谱的分辨率有所提高,但解释较大的三维异核NMR谱时,仍存在含糊性。因此,人们希望通过增加维数进一步提高分辨率,在最近几年中出现了4DNMR谱,4DNMR谱常常是说明2DNMR谱的方法,4DNMR实验可简单地看作是由三个2DNMR实验所组成,新的4DNMR技术仍在不断地发展,已有许多将4DNMR谱应用于蛋白质及核酸研究的报道。  相似文献   

18.
Exact numerical simulations of NMR experiments are often required for the development of new techniques and for the extraction of structural and dynamic information from the spectra. Simulations of solid-state magic angle spinning (MAS) experiments can be particularly demanding both computationally and in terms of the programming required to carry them out, even if special simulation software is used. We recently developed a number of approaches that dramatically improve the efficiency and allow a high degree of automation of these computations. In the present paper, we describe SPINEVOLUTION, a highly optimized computer program that implements the new methodology. The algorithms used in the program will be described separately. Although particularly efficient for the simulation of experiments with complex pulse sequences and multi-spin systems in solids, SPINEVOLUTION is a versatile and easy to use tool for the simulation and optimization of virtually any NMR experiment. The performance of SPINEVOLUTION was compared with that of another recently developed NMR simulation package, SIMPSON. Benchmarked on a series of examples, SPINEVOLUTION was consistently found to be orders of magnitude faster. At the time of publication, the program is available gratis for non-commercial use.  相似文献   

19.
A custom-written Common Gateway Interface (CGI) program for remote control of an NMR spectrometer using a World Wide Web browser has been described. The program, running on a UNIX workstation, uses multiple processes to handle concurrent tasks of interacting with the user and with the spectrometer. The program's parent process communicates with the browser and sends out commands to the spectrometer; the child process is mainly responsible for data acquisition. Communication between the processes is via the shared memory mechanism. The WWW pages that have been developed for the system make use of the frames feature of web browsers. The CGI program provides an intuitive user interface to the NMR spectrometer, making, in effect, a complex system an easy-to-use Web appliance.  相似文献   

20.
The application of common two-dimensional NMR correlation experiments to gaseous analytes for structural elucidation is reported. Standard sequences such as COSY, HSQC, and HMBC are readily applied to volatile hydrocarbons and fluorocarbons. In experiments using (19)F or (13)C as the observed nucleus, it is possible to take advantage of efficient spin-rotation relaxation to perform common experiments swiftly (a (19)F COSY acquired in 6s is shown) or to render insensitive experiments possible on a practical timescale (e.g. a gas phase INADEQUATE at natural isotopic abundance in 14h). NOE-based experiments were not successful on the gaseous systems studied.  相似文献   

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