单晶化学位移张量测量的二维变角相关谱

描述了谱仪的同步控制装置.利用该装置,在MSL-400潜仪上实现了单晶化学位移张量的二维变角相关谱方法测量,获得了典型单晶的DGO (2NH₃⁺CH₂COO^-·2·COOH)的¹³C化学位移张量。     

两位置交换问题魔角旋转核磁共振时域信号的准确解

已知两位置交换分子运动速率对于静态¹³CNMR谱的影响是由一简单代数关系决定,它已成为分析固体中分子运动的常规方法.慢速的魔角旋转可以保留边带,所产生的边带型原则上也可用来分析分子运动,只是缺乏象静态谱那样的简单的关系,以至于在实际应用上是不可行的.本文给出作者所发现的存在分子运动时魔角旋转核磁共振自由诱导衰减信号的解析表达式的理论推导,提供分析固体分子运动的理论谱计算公式.我们选择二甲矾(dimethylsulfone)作为模型化合物,记录其不同温度下¹³CNMR谱,又计算了两个甲基做两位置交换运动的理论谱.理论谱与实验谱定性一致.定量上,边带强度存在一些差别,但边带宽度符合很好.通过理论谱与实验谱的比较,得到交换速率与温度的对应关系.虽然本文限于化学位移各向异性相互作用两位置交换问题,但容易推广到偶极作用多位置交换问题.     

精确测量慢魔角旋转条件下碳氢偶极谱

发展了精确测量二维固体魔角旋转条件下碳氢偶极谱的方法，用以分析固体高分子分子运动，并给出了全同立构聚丙烯的实验谱.     

MOMENT EXPANSIONS OF PROTON DIPOLAR SPINNING-SIDEBAND INTENSITIES IN A 1H MAS NMR SPECTRUM

对于包含分子和分子基团绕至少一个轴高速运动的固体体系，本文推导出其质子核磁共振谱的偶极魔角旋转边带强度的理论计算表达式，建立了用其静态粉末谱的矩的展开的计算方法，计算出旋转边带强度按三十阶矩展开的系数，它可以处理包含高达十五阶边带的谱.     

用多核固体核磁共振研究CsH2PO4 和CsH5(PO4)2的制备

探讨可能用作燃料电池固体酸电解质的化合物CsH₂PO₄ (CDP)和CsH₅(PO₄)₂(CPDP)的制备. CDP和CPDP混合物由摩尔比1∶4的Cs₂CO₃∶H₃PO₄水溶液结晶而成,而CDP和Cs₂HPO₄·1.5H₂O (H-DCHP)混合物依其摩尔比1∶2的水溶液制备. 甲醇清洗能最有效地将CDP从其混合物中分离出来. CDP、CPDP以及H-DCHP的¹³³Cs 和³¹P 魔角旋转谱以及CPDP和H-DCHP的¹H魔角旋转谱均为首次报道,对各化合物的谱峰做了指认. 说明,透过确认合成的电解质以及合成过程所产生的副产物,多核固体核磁共振对于控制固体酸电解质合成的品质是一个非常有用的工具.     

单晶电子顺磁共振研究中零场分裂张量主轴的确定

用电子顺磁共振二维旋转测角器确定量子化轴即零场分裂张量的一个主轴,根据矢量的正交关系计算与量子化轴垂直的主轴平面上的取向二维角组、以便按照计算的二维角组测量电子顺磁共振谱,确认零场分裂张量的另外两个主轴,同时确定了主轴座标系(X,Y,Z)相对实验座标系(x,y,z)的Euler角。以渗Cr³⁺的Na₃(AlMo₆O₂₄H₆)·8H₂O单晶的电子顺磁共振测量作为上述方法的一个应用例子。 关键词：     

质子核磁共振谱的偶极魔角旋转边带强度的矩的展开

对于包含分子和分子基团绕至少一个轴高速运动的固体体系,本文推导出其质子核磁共振谱的偶极魔角旋转边带强度的理论计算表达式,建立了用其静态粉末谱的矩的展开的计算方法,计算出旋转边带强度按三十阶矩展开的系数,它可以处理包含高达十五阶边带的谱     

微量OVARC肽的1H NMR谱线归属

Serpin家族中的卵清蛋白,其反应中心肽段(OVARC,23肽)对应于卵清蛋白序列中343 位至366位残基. 建立在魔角旋转基础之上的Nano探头是一种全新的超微量探头. 本文运用魔角旋转微量检测新技术进行了有关2D NMR实验,完成了卵清蛋白反应中心肽段的¹H NMR 谱线归属.     

质子化学位移各向异性的测量

测量质子化学位移各向异性（CSA）有助于表征分子结构与其动力学,但由于¹H-¹H同核偶极耦合相互作用很强及质子各向异性化学位移较小,测量质子化学位移各向异性仍具有巨大挑战,特别是对含有多种质子的生物大分子,如蛋白质.本文简要综述了测量质子化学位移各向异性的方法,包括同核去耦慢速魔角旋转方法、超快魔角旋转方法、对称重耦（RN_n^v）方法、xCSA方法以及量子化学计算方法.我们重点介绍了在高速魔角旋转条件下蛋白质氨基质子化学位移各向异性的测量及它们与氢键长度、蛋白质二级结构之间的关系.     

高分辨魔角旋转核磁共振技术（HR/MAS）在固相合成中的应用

使用微量探头分析了不同树脂、溶剂、温度对¹H NMR线宽的影响，并运用高分辨魔角旋转核磁共振技术跟踪固相载体上羟基氨基酸的糖基化反应. 该研究表明使用高分辨魔角旋转核磁共振探头可以快速、直接鉴定树脂上的产物，是固相合成中重要的分析工具.     

A High-Resolution C 3D CSA-CSA-CSA Correlation Experiment by Means of Magic Angle Turning

It is shown in this paper that a previously reported 90° sample flipping ¹³C 2D CSA-CSA correlation experiment may be carried out alternatively by employing constant slow sample rotation about the magic angle axis and by synchronizing the read pulse to of the rotor cycle. A high-resolution 3D CSA-CSA-CSA correlation experiment based on the magic angle turning technique is reported in which the conventional 90° 2D CSA-CSA powder pattern for each carbon in a system containing a number of inequivalent carbons may be separated according to the isotropic chemical shift value. The technique is demonstrated on 1,2,3-trimethoxybenzene in which all of the overlapping powder patterns that cannot be segregated by the 2D CSA-CSA experiment are resolved successfully by the 3D CSA-CSA-CSA experiment, including even the two methoxy groups (M₁ and M₃) whose isotropic shifts, confirmed by high-speed MAS, are separated by only 1 ppm. A difference of 4 ppm in the principal value component (δ₃₃) between M₁ and M₃ is readily obtained.     

Measurement of 15N chemical shift anisotropy in a protein dissolved in a dilute liquid crystalline medium with the application of magic angle sample spinning

The chemical shifts of nuclei that have chemical shielding anisotropy, such as the 15N amide in a protein, show significant changes in their chemical shifts when the sample is altered from an isotropic state to an aligned state. Such orientation-dependent chemical shift changes provide information on the magnitudes and orientation of the chemical shielding tensors relative to the molecule's alignment frame. Because of the extremely high sensitivity of the chemical shifts to the sample conditions, the changes in chemical shifts induced by adding aligned bicelles do not arise only from the protein alignment but should also include the accumulated effects of environmental changes including protein-bicelle interactions. With the aim of determining accurate 15N chemical shielding tensor values for solution proteins, here we have used magic angle sample spinning (MAS) to observe discriminately the orientation-dependent changes in the 15N chemical shift. The application of MAS to an aligned bicelle solution removes the torque that aligns the bicelles against the magnetic field. Thus, the application of MAS to a protein in a bicelle solution eliminates only the molecular alignment effect, while keeping all other sample conditions the same. The observed chemical shift differences between experiments with and without MAS therefore provide accurate values of the orientation-dependent 15N chemical shifts. From the values for ubiquitin in a 7.5% (w/v) bicelle medium, we determined the 15N chemical shielding anisotropy (CSA) tensor. For this evaluation, we considered uncertainties in measuring the 1H-15N dipolar couplings and the 15N chemical shifts and also structural noise present in the reference X-ray structure, assuming a random distribution of each NH bond vector in a cone with 5 degrees deviation from the original orientation. Taking into account these types of noise, we determined the average 15N CSA tensor for the residues in ubiquitin as Delta sigma=-162.0+/-4.3 ppm, eta=0.18+/-0.02, and beta=18.6+/-0.5 degrees, assuming a 1H-15N bond length of 1.02 A. These tensor values are consistent with those obtained from solid-state NMR experiments.     

Homonuclear correlation experiments for quadrupolar nuclei, spinning away from the magic angle

We present a set of homonuclear correlation experiments for half-integer quadrupolar spins in solids. In all these exchange-type experiments, the dipolar interaction is retained during the mixing time by spinning the sample at angles other than the “regular magic angle” (54.7°). The second-order quadrupolar interaction is averaged by different strategies for the different experiments. The multiple-quantum off magic angle spinning (MQOMAS) exchange experiment is essentially a regular MQMAS experiment where the quadrupolar interaction is averaged by combining magic angle spinning with a multiple- to single-quantum correlation scheme. The sample is spun at the magic angle at all times except during the mixing time which is added to establish homonuclear correlation. In the multiple-quantum P₄ magic angle spinning (MQP₄MAS) exchange experiment, the sample is spun at one of the angles at which the fourth-order Legendre polynomial vanishes (P₄ magic angle), the remaining second-order quadrupolar interaction now governed by a second-rank tensor is refocussed by the multiple to single-quantum correlation scheme. In the dynamic angle spinning (DAS) exchange experiment, the second-order quadrupolar interaction is averaged by correlating the evolution from two complementary angles. These experiments are demonstrated and compared, in view of their specific advantages and disadvantages, for ²³Na in the model compound Na₂SO₃.     

基于核磁共振的统计全相关谱在大鼠肾脏组织中的应用

生物组织是基于NMR的代谢组学研究的主要对象之一，广泛应用于分子病理学、毒理学、生物医学等众多领域. 但是，为了保证测定的准确，组织的NMR实验往往需要在较低的温度下和较短时间内完成，以防止由于组织内酶的降解和扩散而导致的某些代谢物质的分析信息被破坏. 统计全相关谱(Statistical Total Correlation Spectroscopy, STOCSY)是依靠一维谱来实现二维谱的一些功能的方法，不需要额外的实验时间，已经被广泛应用于代谢组学研究中. 本文采用STOCSY方法，通过对一系列¹H高分辨魔角旋转谱的统计分析和计算，得到了肾脏组织的准二维相关谱，其中共振峰之间的相关较为准确的反应了物质之间的耦合信息，为物质的归属提供了帮助.     

固态交叉极化魔角旋转NMR中的极化转移

在普通有机固体中,直接键合的S和I自旋之间的偶极相互作用强于SI_n基团和其它质子之间的I-I耦合。因此,SI_n子系统中的相互作用支配了交叉极化过程中的自旋动力学,在这一新概念的指引下,样品魔角旋转时极化转移的理论和技术有了飞跃发展,特别是,各种新技术涌现出来,以提高高速魔角旋转时极化转移的效率。这些新技术的共同特点是仅调制射频辐射的位相或幅度,而保持高速度的魔角旋转不变。一系列谱编辑方法也已发展起来,它能依据相连质子的个数,产生碳的4个子谱,即C,CH,CH₂和CH₃子谱,这个技术已被用于一组煤样,在煤的CPMAS谱中,4种类型的碳谱是完全互相交迭在一起的,该技术的应用,已取得了令人鼓舞的成果。     

Hydrogen bonding effects on the (15)N and (1)H shielding tensors in nucleic acid base pairs

The results of systematic ab initio calculations of (15)N and (1)H chemical shielding tensors in the GC base pair as a function of hydrogen bond length are presented for the first time. The hydrogen bond length characterized by the distance r(N...N) between purine N1 and pyrimidine N3 was varied between 2.57 and 3.50 A and the chemical shift tensors were calculated by the sum-over-states density functional perturbation theory. It is shown that the hydrogen bond length has a strong effect on the chemical shielding tensor of both imino proton and nitrogen, on their orientation, and, as a consequence, on the relaxation properties of both nuclei. For a nitrogen nucleus not involved in hydrogen bonding, the shielding tensor is nearly axially symmetric and almost collinear with the bond vector. As the length of the hydrogen bond decreases, the least shielding component sigma(11) deflects from the N-H vector and the shielding tensor becomes increasingly asymmetric. The significance of the presented results for the analysis of relaxation data and the efficiency of TROSY effects together with a summary of the relevant shielding parameters are presented and discussed.     

Chemical shift anisotropy amplification

A new NMR experiment which allows a measurement of the chemical shift anisotropy (CSA) tensor under magic angle spinning (MAS) is described. This correlates a fast MAS spectrum in the omega2 dimension with a sideband pattern in omega1 in which the intensities mimic those for a sample spinning at a fraction of the rate omega r/N, and these sidebands result from an amplification by a factor N of the modulation caused by the CSA. Standard methods can be used to extract the principal tensor components from the omega1 sideband patterns, and the nature of the experiment is such that the use of a large number of t1 increments can be avoided without compromising the resolution of different chemical sites. The new experiment is useful for accurately measuring narrow shift anisotropies.     

Orientational analysis of the Achilles tendon and enthesis using an ultrashort echo time spectroscopic imaging sequence

Tendons and entheses are magnetic resonance (MR) “invisible” when imaged with conventional clinical pulse sequences. When the highly ordered, collagen-rich fibers in tendons and entheses are placed at the magic angle, dipolar interactions are decreased and their T2s are often considerably increased. The bulk magnetic susceptibility of tendons and entheses also varies with orientation to B₀, leading to a direction-dependent resonance frequency shift. Ultrashort echo time (UTE) sequences with a minimum TE of 8 μs provide high signal from both tendons and entheses. The combination of a UTE sequence with an interleaved undersampled variable TE acquisition scheme provides a new approach for fast spectroscopic imaging of short T2 tissues. This UTE spectroscopic imaging (UTESI) technique provides quantitative information including T2?, chemical shift and resonance frequency shift due to bulk susceptibility effect. In this article, the orientational effects on tendons and entheses were investigated using a UTESI sequence on a clinical 3-T scanner. T2? was found to increase fivefold for tendons and twofold for entheses due to the magic angle effect. A resonance frequency shift up to 1.2 ppm was observed for both tendons and entheses due to the bulk susceptibility effect when their orientation was changed from 0° to 90° relative to B₀.     

Obtaining molecular and structural information from 13C-14N systems with 13C FIREMAT experiments

The effect of dipolar coupling to 14N on 13C FIREMAT (five pi replicated magic angle turning) experiments is investigated. A method is developed for fitting the 13C FIREMAT FID employing the full theory to extract the 13C-14N dipolar and 13C chemical shift tensor information. The analysis requires prior knowledge of the electric field gradient (EFG) tensor at the 14N nucleus. In order to validate the method the analysis is done for the amino acids alpha-glycine, gamma-glycine, l-alanine, l-asparagine, and l-histidine on FIREMAT FIDs recorded at 13C frequencies of 50 and 100 MHz. The dipolar and chemical shift data obtained with this analysis are in very good agreement with the previous single-crystal 13C NMR results and neutron diffraction data on alpha-glycine, l-alanine, and l-asparagine. The values for gamma-glycine and l-histidine obtained with this new method are reported for the first time. The uncertainties in the EFG tensor on the resultant 13C chemical shift and dipolar tensor values are assessed.