High-resolution heteronuclear correlation spectroscopy based on spatial encoding and coherence transfer in inhomogeneous fields

Two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy has been proven to be a powerful technique for chemical, biological, and medical studies. Heteronuclear single quantum correlation (HSQC) and heteronuclear multiple bond correlation (HMBC) are two frequently used 2D NMR methods. In combination with spatially encoded techniques, a heteronuclear 2D NMR spectrum can be acquired in several seconds and may be applied to monitoring chemical reactions. However, it is difficult to obtain high-resolution NMR spectra in inhomogeneous fields. Inspired by the idea of tracing the difference of precession frequencies between two different spins to yield high-resolution spectra, we propose a method with correlation acquisition option and J-resolved-like acquisition option to ultrafast obtain high-resolution HSQC/HMBC spectra and heteronuclear J-resolved-like spectra in inhomogeneous fields.     

High-resolution 2D NMR spectra in inhomogeneous fields based on intermolecular multiple-quantum coherences with efficient acquisition schemes

High-resolution 2D NMR spectra in inhomogeneous fields can be achieved by the use of intermolecular multiple-quantum coherences and shearing reconstruction of 3D data. However, the long acquisition time of 3D spectral data is generally unbearable for in vivo applications. To overcome this problem, two pulse sequences dubbed as iDH-COSY and iDH-JRES were proposed in this paper. Although 3D acquisition is still required for the new sequences, the high-resolution 2D spectra can be obtained with a relatively short scanning time utilizing the manipulation of indirect evolution period and sparse sampling. The intermolecular multiple-quantum coherence treatment combined with the raising and lowering operators was applied to derive analytical signal expressions for the new sequences. And the experimental observations agree with the theoretical predictions. Our results show that the new sequences possess bright perspective in the applications on in vivo localized NMR spectroscopy.     

基于哈德曼编码的新型高分辨定域谱

核磁共振（NMR）技术作为一种非植入无损伤的检测技术,已经广泛应用于化学、生物和医学等领域.本文基于哈德曼（Hadamard）编码的分子间单量子相干（iSQC）技术提出了一种新的序列,首先从理论上对该序列进行了简要的分析并阐明其原理,然后用套管模型实验和脑模型实验验证该序列在不均匀磁场下准确定域和快速获取高分辨谱的能力.实验表明,该序列在不均匀磁场下可以快速获取高分辨定域谱,同时抑制溶剂峰信号,具备一定的应用价值.     

High-resolution absorptive intermolecular multiple-quantum coherence NMR spectroscopy under inhomogeneous fields

Intermolecular multiple-quantum coherence (iMQC) is capable of improving NMR spectral resolution using a 2D shearing manipulation method. A pulse sequence termed CT-iDH, which combines intermolecular double-quantum filter (iDQF) with a modified constant-time (CT) scheme, is designed to achieve fast acquisition of high-resolution intermolecular zero-quantum coherences (iZQCs) and intermolecular double-quantum coherences (iDQCs) spectra without strong coupling artifacts. Furthermore, double-absorption lineshapes are first realized in 2D intermolecular multi-quantum coherences (iMQCs) spectra under inhomogeneous fields through a combination of iZQC and iDQC signals to double the resolution without loss of sensitivity. Theoretically the spectral linewidth can be further reduced by half compared to original iMQC high-resolution spectra. Several experiments were performed to test the feasibility of the new method and the improvements are evaluated quantitatively. The study suggests potential applications for in vivo spectroscopy.     

不均匀场下空间编码超快速高分辨NMR研究进展

二维核磁共振(2D NMR)的提出和发展,为NMR技术的研究和应用提供了广阔的空间. 然而当样品或磁场本身不均匀时,高分辨的2D NMR谱难以获得. 此外,常规2D NMR实验通常需要长的采样时间. 空间编码超快速采样方法利用空间编码技术,只需单次扫描即可获得2D甚至多维NMR谱,极大地缩短了采样时间. 目前相位补偿、相干转移和分子间多量子相干等技术与空间编码技术相结合,已成功实现不均匀场下超快速获得高分辨NMR谱. 该文对不均匀场下空间编码超快速NMR方法进行了介绍,对其未来发展进行了展望.     

Theoretical study of two-dimensional COSY experiments for S = 7/2 spins: application to (59)Co in the tetrahedral cluster HFeCo(3)(CO)(11)PPh(2)H

The first investigation and analysis of (59)Co 2D NMR homonuclear chemical shift correlation spectra are reported for the tetrahedral mixed-metal cluster HFeCo(3)(CO)(11)PPh(2)H. For this cluster in solution, the (59)Co 2D COSY and DQF COSY NMR spectra prove the existence of a scalar coupling between (59)Co nuclei. In order to obtain a value of this coupling, the 2D COSY and DQF COSY NMR spectra for a three-spin 7/2 AX(2) system have been simulated by numerical density matrix calculations. The comparison between experimental and theoretical 2D NMR spectra gives a spin-coupling constant |(1)J((59)Co - (59)Co)| = (115 +/- 20) Hz for this cluster. Experimental measurements of T(1) and of the line widths for cobalt 59 as well as theoretical (59)Co 1D NMR spectra are reported and support our findings.     

3D imaging with a single-sided sensor: an open tomograph

An open tomograph to image volume regions near the surface of large objects is described. The central achievement in getting such a tomograph to work is the design of a fast two-dimensional pure phase encoding imaging method to produce a cross-sectional image in the presence of highly inhomogeneous fields. The method takes advantage of the multi-echo acquisition in a Carr-Purcell-Meiboom-Gill (CPMG)-like sequence to significantly reduce the experimental time to obtain a 2D image or to spatially resolve relaxation times across the sensitive volume in a single imaging experiment. Depending on T(2) the imaging time can be reduced by a factor of up to two orders of magnitude compared to the one needed by the single-echo imaging technique. The complete echo train decay has been also used to produce T(2) contrast in the images and to spatially resolve the T(2) distribution of an inhomogeneous object, showing that variations of structural properties like the cross-link density of rubber samples can be distinguished by this method. The sequence has been implemented on a single-sided sensor equipped with an optimized magnet geometry and a suitable gradient coil system that provides two perpendicular pulsed gradient fields. The static magnetic field defines flat planes of constant frequency parallel to the surface of the scanner that can be selected by retuning the probe frequency to achieve slice selection into the object. Combining the slice selection obtained under the presence of the static gradient of the open magnet with the two perpendicular pulsed gradient fields, 3D spatial resolution is obtained.     

二维接力-HOHAHA和NOE差谱法测定甙类化合物的结构

该文提出一种新的二维接力-HOHAHA实验方法.研究结果表明,该方法可用于从高度重迭的谱图中分离出各个糖体的¹H NMR信号,并且与NOE差谱实验相结合可以用于测定甙类化合物中糖体间和糖体与甙元间的连接位置.本方法以¹H NMR为基础,故其灵敏度比以¹³C NMR为基础的甙化位移方法高得多.     

Combination of (13)C-(13)C COSY and DARR (COCODARR) in solid-state NMR

In this work, we describe a new 2D (13)C-(13)C correlation experiment in solids, in which (13)C-(13)C J-correlation (COSY) and dipolar correlation (DARR) are recorded at the same time. The sequence is similar to COCONOSY in the liquid-state NMR, in which (1)H-(1)H COSY and NOESY spectra are obtained in a single experiment. The combined COSY and DARR experiment facilitates assignment of (13)C signals in solids.     

Reduced data acquisition time in multi-dimensional NMR spectroscopy using multiple-coil probes

A new hardware-based approach is presented to reduce data acquisition times in multi-dimensional NMR spectroscopy using a multiple-coil probe. Using a four-coil setup, two-dimensional COSY and TOCSY spectra were acquired in one-quarter the time of conventional spectra by simultaneous acquisition of different effective t1 evolution times for each coil. Data processing consists of simple phase-shifting and intensity normalization of the individual data sets, and results in spectra almost identical to those acquired in a conventional manner. This method can potentially be integrated with other new data acquisition and processing schemes for further increases in data acquisition speed.     

Two-dimensional high-resolution NMR spectra in matched B(0) and B(1) field gradients

In a recent publication we presented a method to obtain highly resolved NMR spectra in the presence of an inhomogeneous B(0) field with the help of a matched RF gradient. If RF gradient pulses are combined with "ideal" 90 degrees pulses to form inhomogeneous z rotation pulses, the line broadening caused by the B(0) gradient can be refocused, while the full chemical shift information is maintained. This approach is of potential use for NMR spectroscopy in an inhomogeneous magnetic field produced by an "ex-situ" surface spectrometer. In this contribution, we extend this method toward two-dimensional spectroscopy with high resolution in one or both dimensions. Line narrowing in the indirect dimension can be achieved by two types of nutation echoes, thus leading to depth-sensitive NMR spectra with full chemical shift information. If the nutation echo in the indirect dimension is combined with a stroboscopic acquisition using inhomogeneous z-rotation pulses, highly resolved two-dimensional correlation spectra can be obtained in matched field gradients. Finally, we demonstrate that an INEPT coherence transfer from proton to carbon spins is possible in inhomogeneous B(0) fields. Thus, it is possible to obtain one-dimensional (13)C NMR spectra with increased sensitivity and two-dimensional HETCOR spectra in the presence of B(0) gradients of 0.4 mT/cm. These schemes may be of some value for ex-situ NMR analysis of materials and biological systems.     

不均匀场下基于分子间双量子相干核磁共振技术的果肉检测

核磁共振（NMR）谱图可在不破坏生物样品的状态下提供组织成分组成及其含量的信息,已被广泛应用于生物、医学和食品检测等领域.NMR谱图分辨率越高,提供的与组织成分相关的信息越丰富、越准确,也越有利于未知成分的定性和定量分析.传统的高分辨NMR谱图通常要在均匀磁场下采集.但在实际应用中,均匀的磁场较难获得.这就使得我们采集的NMR谱图的分辨率,以及由此获得的生物组织成分组成和含量等信息的准确性受到影响.源于远程偶极相互作用的分子间双量子相干（iDQC）技术对磁场均匀度不敏感,可在不均匀场下获得高分辨率NMR谱图.本文采用基于iDQC技术的IDEAL-Ⅱ序列对甲基丙烯酸丁酯、蕃茄和西瓜三种样品进行了NMR实验,结果证明基于iDQC技术在不均匀场下获得水果的高分辨NMR谱图是可行的,这对食品科学以及食品检测具有积极的意义.     

Quantitative comparison between a multiecho sequence and a single-echo sequence for susceptibility-weighted phase imaging

The aim of this study was to investigate the benefits arising from the use of a multiecho sequence for susceptibility-weighted phase imaging using a quantitative comparison with a standard single-echo acquisition. Four healthy adult volunteers were imaged on a clinical 3-T system using a protocol comprising two different three-dimensional susceptibility-weighted gradient-echo sequences: a standard single-echo sequence and a multiecho sequence. Both sequences were repeated twice in order to evaluate the local noise contribution by a subtraction of the two acquisitions. For the multiecho sequence, the phase information from each echo was independently unwrapped, and the background field contribution was removed using either homodyne filtering or the projection onto dipole fields method. The phase information from all echoes was then combined using a weighted linear regression. R2 maps were also calculated from the multiecho acquisitions. The noise standard deviation in the reconstructed phase images was evaluated for six manually segmented regions of interest (frontal white matter, posterior white matter, globus pallidus, putamen, caudate nucleus and lateral ventricle). The use of the multiecho sequence for susceptibility-weighted phase imaging led to a reduction of the noise standard deviation for all subjects and all regions of interest investigated in comparison to the reference single-echo acquisition. On average, the noise reduction ranged from 18.4% for the globus pallidus to 47.9% for the lateral ventricle. In addition, the amount of noise reduction was found to be strongly inversely correlated to the estimated R2 value (R=-0.92). In conclusion, the use of a multiecho sequence is an effective way to decrease the noise contribution in susceptibility-weighted phase images, while preserving both contrast and acquisition time. The proposed approach additionally permits the calculation of R2 maps.     

Single-scan 2D DOSY NMR spectroscopy

Spatial encoding is a particular kind of spin manipulation that enables the acquisition of multidimensional NMR spectra within a single scan. This encoding has been shown to possess a general applicability and to enable the completion of arbitrary nD NMR acquisitions within a single transient. The present study explores its potential towards the acquisition of 2D DOSY spectra, where the indirect dimension is meant to encode molecular displacements rather than a coherent spin evolution. We find that in its simplest form this extension shows similarities with methods that have been recently discussed for the single-scan acquisition of this kind of traces; still, a number of advantageous features are also evidenced by the “ultrafast” modality hereby introduced. The principles underlying the operation of this new single-scan 2D DOSY approach are discussed, its use is illustrated with a variety of sequences and of samples, the limitations of this new experiment are noted, and potential extensions of the methodology are mentioned.     

黄花远志黄花皂甙D的二维核磁共振谱研究

用一维、二维波谱技术研究了从中药黄花远志根中分离出一种含六个糖的三萜皂甙,黄花皂甙D,确定了皂甙的双糖链结构以及甙元与糖基、糖基与糖基间的连接位置,并对其一维谱进行了归属.     

用2D NMR及NOE差谱研究一个新的紫杉烷二萜化合物

采用多种二维核磁共振技术及NOE差谱来研究一个新的紫杉烷二萜化合物的结构,确定了3个乙酰基和一个丙酰基的取代位置,解决了大部分立体化学问题,对大多数¹³C及¹H的化学位移给予准确归属.     

Fast high-resolution nuclear magnetic resonance spectroscopy through indirect zero-quantum coherence detection in inhomogeneous fields

In many cases, high-resolution nuclear magnetic resonance （NMR） spectra are virtually impossible to obtain by con- ventional nuclear magnetic resonance methods because of inhomogeneity of magnetic field and inherent heterogeneity of sample. Although conventional intramolecular zero-quantum coherence （ZQC） can be used to obtain high-resolution spectrum in inhomogeneous field, the acquisition takes rather long time. In this paper, a spatially encoded intramolecular ZQC technique is proposed to fast acquire high-resolution NMR spectrum in inhomogeneous field. For the first time, the gradient-driven decoding technique is employed to selectively acquire intramolecular ZQC signals. Theoretical analyses and experimental observations demonstrate that high-resolution NMR spectral information can be retrieved within several scans even when the field inhomogeneity is severe enough to erase most spectral information. This work provides a new way to enhance the acquisition efficiency of high-resolution intramolecular ZQC spectroscopy in inhomogeneous fields.     

雪胆双糖的NMR碳氢化学位移完全解析

从圆果雪胆的块茎中分离出一个结构新颖的双糖-雪胆双糖（amabiose），应用DEPT 、¹H-¹H COSY, HMQC 等NMR多种核磁技术，对其结构进行研究，再经X-ray单晶衍射实验确证其化学结构是一分子葡萄糖和一分子雪胆糖缩合而得，本文报道了雪胆双糖的NMR碳氢化学位移完全解析.     

天然结晶辣椒碱的NMR谱研究

用一维¹H NMR谱、¹H-¹H COSY谱和一维¹³C NMR谱、DEPT谱研究辣椒碱分子和二氢辣椒碱分子及其混合物,得到¹H和¹³C的化学位移,采用¹H NMR谱测定天然辣椒碱中辣椒碱和二氢辣椒碱的相对含量.     

3'(,3")-(二)甲酰基(二)苯并冠醚的2D NMR研究

测定了3'(,3")-(二)甲酰基(二)苯并冠醚(1~7)的¹H、¹³C谱,首次结合¹H-¹H COSY、¹³C-¹H COSY、COLOC二维谱对这些化合物的¹H、¹³C化学位移进行了归属。用NOESY谱确定了合成产物冠4、冠5的结构,并对溶液中的构象异构体及其溶剂影响进行了初探。作者以冠1~8的¹H、¹³C谱的归属为参照,提出了正确归属冠醚醚环上次甲基¹H、¹³C化学位移的一般规则。