三种脉冲序列制备核自旋单重态效率的比较

核自旋单重态的制备和检测在化合物分子的相关分析中具有重要的应用价值和广阔的应用前景.本文以三肽分子AGG（Ala-Gly-Gly）中两个质子构成的一组孤立的自旋耦合体系为研究对象,利用三组基于不同原理的脉冲序列,分别对该体系制备了核自旋单重态;并分别测定和比较了三种方法制备核自旋单重态的效率及其寿命.研究结果表明,对于同一分子的同一自旋耦合体系中的质子,使用不同的脉冲序列制备得到的核自旋单重态的寿命并不会有明显差异,但基于不同脉冲制备核自旋单重态的效率差异相对较大.     

三自旋体系长寿命核自旋单重态的制备

长寿命核自旋单重态的寿命（T_S）可以长于常规的纵向弛豫时间（T₁）,基于这个独特的优势,长寿命核自旋单重态具有较好的应用价值.本文对已有脉冲序列进行了改进,给出了适用于任意三自旋弱耦合体系长寿命核自旋单重态制备的参数计算方法,发现在同一个三自旋体系内核自旋单重态具有多种不同比例系数组合的形式,并以丙烯酸为例制备出了两种长寿命核自旋单重态,实验上观察到不同的核自旋单重态的寿命存在差异,另外我们还探究了温度对丙烯酸核自旋单重态寿命的影响.     

极化等离子体──聚变研究的新设想

在通常的聚变反应装置中,参与核反应的轻核的核自旋是无规分布的.但是,只有那些自旋彼此具有一定取向的轻核才能发生聚变反应.R.M.Kulsrud[1]指出:在D-T反应的托卡马克装置中,有三分之一的氘,氚核是以自旋1/2态彼此碰撞,但它们对聚变反应没有任何贡献.因此,聚变科学家们考虑,向     

14N核四极共振自旋系统自旋-晶格弛豫时间的测量

¹⁴N核四极共振自旋系统的自旋-晶格弛豫是一种双指数弛豫。本文介绍了¹⁴N核四极共振自旋系统的自旋-晶格弛豫时间的3种测量方法,利用可变多面体方法对实验数据进行拟合,获得了¹⁴N核四极共振自旋系统的自旋-晶格弛豫时间T_1s和T₁₁,对有关文献中关于核四极共振弛豫时间的测量的3个观点提出了质疑。     

MEASUREMENT OF HOMONUCLEAR COUPLING CONSTANTS USING TWO-DIMENSIONAL MAXIMUM-QUANTUM CORRELATION NMR SPECTROSCOPY (MAXY-NMR)

偶合常数是一个重要的NMR参数,其数值与分子中化学键的二面角有关,可以为分子结构研究提供很重要的信息.多维NMR谱由于具有较大的化学位移分辨率,因此常常被用来测定同核或异核自旋-自旋偶合常数.本文介绍了利用最高量子相关技术（MAXY）测定同核偶合常数的方法.MAXY是最近发展的一种多维NMR谱编辑技术,可以使不同官能团（CH, CH     

原子核结构的相对论平均场描述

简要评述近几年相对论平均场理论的发展及其在核结构研究中取得的部分进展. 主要内容包括中子晕, 质子晕, 巨晕, 激发态晕等奇特核现象, 超重核结构, 超核结构以及原子核的赝自旋对称性和反核子谱的自旋对称性等.     

￣（14）N核四极共振自旋系统自旋－晶格弛豫时间的测量

￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫是一种双指数弛豫。本文介绍了￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫时间的３种测量方法，利用可变多面体方法对实验数据进行拟合，获得了￣１４Ｎ核四极共振自旋系统的自旋－晶格弛豫时间Ｔ＿１ｓ和Ｔ＿１１，对有关文献中关于核四极共振弛豫时间的测量的３个观点提出了质疑。     

采用BP神经网络研究C-F键核自旋偶合常数

通常理论研究核自旋偶合常数的方法是基于线性模型进行拟合和预测，该方法在拟合和预测中仍有较大误差. 本文在前面工作的基础上，提出了基于非线性模型对C-F键核自旋偶合常数进行研究的观点，采用BP神经网络方法对C-F键核自旋偶合常数的函数关系式进行拟合，并用拟合结果对4种化合物的偶合常数进行预测. 结果表明，采用非线性的BP神经网络方法其训练效果与预测效果均优于线性模型方法；其预测误差对文中的4种化合物不超过0.40%.     

新的summing算法的核磁共振实验实现

本文报导了一种新的summing算法的核磁共振实验实现.实验中我们用到了四个量子位的核自旋体系,其中两个量子位构成输入寄存器,另两个量子位构成输出寄存器.最后的实验结果只需通过测量输出寄存器中核自旋的谱线获得.     

核自旋单重态的制备及其转化效率和寿命的影响因素分析

长寿命核自旋单重态（LLS）因具有寿命较长这一特性而具有广泛的应用前景.本文在一个三肽样品（alanylglycylgcine，AGG）的水溶液中，对结构中离手性碳较远的二自旋体系进行核自旋单重态的制备，并探究了样品浓度、温度、射频发射中心位置、自旋体系之间的J耦合常数，以及磁场不均匀性五个因素对LLS的转化效率及其寿命的影响.实验结果表明，核自旋单重态的转化效率和寿命均不受样品浓度以及磁场不均匀性的影响.寿命会随实验温度的升高不断增加，转化效率随温度的下降而减小.射频中心位置在小范围内变化时，核自旋单重态制备所受影响不明显；但当变化较大时，其转化效率与寿命明显减小.同时，核自旋单重态对J耦合的变化则比较敏感，当J值选择不精准时，转化效率及寿命都出现明显降低.     

Adiabatic Mixing in the Liquid State

Adiabatic spin inversion has been used in the liquid state very efficiently for decoupling purposes. Here we show that it can also be adapted for spin mixing experiments, such as the TOCSY and clean TOCSY experiment, and is superior to previously employed mixing sequences. The main advantage of adiabatic mixing sequences over the conventional mixing schemes used in liquid state experiments is an extremely low sensitivity to RF field inhomogeneity and miscalibration of theB₁field strength. The method is evaluated experimentally by comparing results obtained with different mixing schemes in the basic 2D TOCSY experiment. In addition to higher reliability, adiabatic mixing provides a sensitivity improvement of ca. 20% as compared to conventional mixing schemes. This is explained by higher signal losses due to RF inhomogeneity in the experiments employing traditional mixing schemes. More significant sensitivity improvements can be expected in situations where RF homogeneity is traditionally poor, for example, in large volume probes and magnetic resonance imaging experiments.     

J-ONLY-TOCSY: efficient suppression of RDC-induced transfer in homonuclear TOCSY experiments using JESTER-1-derived multiple pulse sequences

The main purpose of homonuclear Hartmann-Hahn or TOCSY experiments is the assignment of spin systems based on efficient coherence transfer via scalar couplings. In partially aligned samples, however, magnetization is also transferred via residual dipolar couplings (RDCs) and therefore through space correlations can be observed in COSY and TOCSY experiments that make the unambiguous assignment of covalently bound spins impossible. In this article, we show that the JESTER-1 multiple pulse sequence, originally designed for broadband heteronuclear isotropic Hartmann-Hahn transfer, efficiently suppresses the homonuclear dipolar coupling Hamiltonian. This suppression can be enhanced even further by variation of the supercycling scheme. The application of the resulting element in homonuclear TOCSY periods results in coherence transfer via J-couplings only. As a consequence, the assignment of scalar coupled spin systems is also possible in partially aligned samples. The bandwidth of coherence transfer for the JESTER-1-derived sequences is comparable to existing TOCSY multiple pulse sequences. Results are demonstrated in theory and experiment.     

Gradient-Enhanced One-Dimensional Proton Chemical-Shift Correlation with Full Sensitivity

High-quality spectra were obtained by implementing pulsed field gradients (PFGs) as part of 1D selective experiments. The use of PFGs for coherence rejection rather than coherence selection ensures that there is no loss of signal and the sensitivity of these experiments is the same as that of their phase-cycled predecessors. The excitation scheme chosen ensures that these experiments are highly resistant to spin–spin relaxation. The following techniques are described: 1D ge-TOCSY, 1D ge-NOESY, 1D ge-TOCSY–TOCSY, 1D ge-NOESY–NOESY, 1D ge-TOCSY–NOESY, and 1D ge-NOESY–TOCSY. Their applications, for the separation of overlapping spin systems, tracing spin-diffusion signals, and extending the transfer of magnetization beyond an individual spin system, are illustrated using oligo- and polysaccharide samples.     

Discerning the degenerate transitions of scalar coupled H NMR spectra: Correlation and resolved techniques at higher quantum

The blend of spin topological filtering and the spin state selective detection of single quantum transitions by the two dimensional multiple quantum-single quantum correlation and higher quantum resolved techniques have been employed for simplifying the complexity of scalar coupled ¹H NMR spectra. The conventional two dimensional COSY and TOCSY experiments, though identify the coupled spin networks, fail to differentiate them due to severe overlap of transitions. Non-selective excitation of homonuclear higher quantum of protons results in filtering of spin systems irrespective of their spin topologies. The spin state selection by passive ¹⁹F spins provides fewer transitions in each cross section of the single quantum dimension simplifying the analyses of the complex spectra. The degenerate single quantum transitions are further discerned by spin selective double and/or triple quantum resolved experiments that mimic simultaneous heteronuclear and selective homonuclear decoupling in the higher quantum dimension. The techniques aided the determination of precise values of spectral parameters and relative signs of the couplings.     

Determining the relative sign and size of scalar and residual dipolar couplings in homonuclear two-spin systems

Based on the sign and amplitude of TOCSY transfer functions, it is possible to determine the relative sign and size of scalar and residual dipolar couplings in homonuclear spin systems consisting of two spins 1/2. The efficiency of different mixing sequences and different transfer functions is examined both theoretically and experimentally.     

大叶吊兰甙A和B的NMR化学位移全归属

应用2D NMR实验技术进一步研究确定了从百合科植物大叶吊兰中分离到的两个新的C-27甾体皂甙类化合物,大叶吊兰甙(chloromaloside)A和B的化学结构,并对其¹H和¹³C NMR信号进行了全归属.     

Gradient- and Sensitivity-Enhanced TOCSY Experiments

A pulsed field gradient version of the sensitivity-enhanced 2D TOCSY experiment is proposed which yields high-quality spectra with improved sensitivity and a minimum of two scans pert₁increment. For rapid acquisition of 1D TOCSY spectra, the 1D DPFGSE–TOCSY experiment was modified to include phase-encoded multiple-selective excitation followed by a simple spectral editing. Combination of these two building blocks is used in a sensitivity-enhanced 2D analog of the 3D TOCSY–TOCSY experiment which provides an efficient tool for resolving severely overlapped signals of oligomers in short experimental time.     

铁磁体中缺陷对自旋波的影响

本文提出了一个处理磁性杂质或其他缺陷在磁性晶体中对自旋波频谱的影响的一般理论方法,并特别着重讨论了局域模自旋波。以一维线性格子为例进行计算的结果显示出:一个代位磁性杂质,可能产生不只一个高于连续带顶的局域模。其产生的条件和其能级位置均通过J′S′/JS和J′/J表达出来,这里S′和S各为杂质原子和基质原子的自旋量子数,J′和J各为杂质与近邻之间和一般近邻之间的交换作用系数。高度集中的应变和间隙原子如致使邻近处的交换作用增大,也导致局域模的出现。我们也考虑了磁偶极矩相互作用的影响,证明其并不破坏这些局域模的     

用新近发展的1H NMR技术研究腐殖酸

将一些新近发展起来的¹H NMR技术用于溶在不同溶剂(D₂O,NaOH/D₂O及DMSO-d₆)中的腐殖酸样品的研究,这包括全相关谱方法(TOCSY),扩散谱方法和最大量子谱方法(MAXY).DMSO溶液的TOCSY谱中4与8之间的相关峰表明在腐殖酸中可能包含有不溶于水的多肽,扩散谱指出在碱性条件下,一些小分子脱离了腐殖酸聚合体,而MAXY谱编辑方法则使得一些细致的归属成为可能.