Parametric spectrum analysis of 2D NMR signals. Application to in Vivo J spectroscopy

Parametric modeling techniques for spectrum analysis, based on the linear prediction principle, have previously been proposed to process NMR data. In this paper, they are tested on different practical NMR signals, and especially on in vivo 2D NMR spectroscopy data. The linear prediction version of the maximum entropy method, using AR modeling, and the Prony method are outlined with some considerations about the choice of the AR algorithm. Then simulation and experimental results obtained with the Prony method are presented and compared with those obtained with classical 2D Fourier transform processing. The data processed here result from homonuclear 2D J-resolved spectroscopy experiments performed to measure the spin-spin coupling constants between the three phosphorus nuclei of ATP in the rat brain. The parametric techniques (especially the Prony method) applied in both dimensions yield increased resolution and sensitivity and their ability to process limited data allows the total acquisition time to be reduced without loss of resolution. Although the noise may damage the performances, the results obtained here, on in vivo 2D data, are quite encouraging.     

多维核磁共振数据在通用计算机上的处理与三维谱的观测

本文分析、讨论了利用外部通用计算机处理核磁共振数据的方法及程序,包括数据格式转换,一维、二维、三维谱的数据处理,谱图的显示及输出,并以VAX机为例实现了三维谱的观测。文中还详细讨论了编程的原理和一些技术细节。     

二维核磁共振数据处理与显示系统

详细介绍了我们在386微机上建立的二维NMR数据处理与分析系统,该系统采用菜单驱动方式,具有良好的用户界面,可进行标准的常规二维NMR数据处理与分析,数据处理结果可由标准设备输出或者以文件方式存储以便其它应用软件处理,该系统的建立可使通用微计算机成为有效的核磁共振数据处理站。     

Improvement of duty-cycle heating compensation in NMR spin relaxation experiments

To reliably measure NMR relaxation properties of macromolecules is a prerequisite for precise experiments that identify subtle variations in relaxation rates, as required for the determination of rotational diffusion anisotropy, CSA tensor determination, advanced motional modeling or entropy difference estimations. An underlying problem with current NMR relaxation measurement protocols is maintaining constant sample temperature throughout the execution of the relaxation series especially when rapid data acquisition is required. Here, it is proposed to use a combination of a heating compensation and a proton saturation sequence at the beginning of the NMR relaxation pulse scheme. This simple extension allows reproducible, robust and rapid acquisition of NMR spin relaxation data sets. The method is verified with (15)N spin relaxation measurements for human ubiquitin.     

Solid state NMR study of carbon bonding in amorphous hydrogenated carbon films

Carbon bonding environments in hydrogenated amorphous carbon films (a-C:H) deposited from an rf-biased methane plasma onto various substrates have been quantified by application of solid state¹³C NMR. A family of films were prepared by systematically varying the substrate bias voltage. Quantitative data on carbon chemistry in these films is required for modeling the impact of structure on mechanical and optical properties. A variety of NMR acquisition pulse sequences have been investigated to determine the conditions under which quantitative¹³C NMR data can be acquired in this system. The results indicate that data acquisition from this material requires different protocols than for the study of polymeric hydrocarbon films. With proper experimental design, NMR is an excellent technique for structural studies of these materials.     

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.     

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。     

Interlaced Fourier transformation of ultrafast 2D NMR data

A new protocol for processing the data arising in ultrafast 2D NMR is discussed and exemplified, based on the interlaced Fourier transformation. This approach is capable of dealing in a single, combined fashion, with the two mirror-imaged interferograms arising in this kind of experiment as a result of the acquisition of a train of magnetic field gradient echoes. By combining all the acquired data points into a common Fourier processing procedure the spectral width along the direct-acquisition domain becomes effectively doubled, giving the opportunity of employing acquisition gradients that are approximately half as strong as hitherto required. This in turn should lead to an overall enhancement in the signal-to-noise ratio of the experiment of ca. 2, as well as to improvements in the achievable digital resolution. These expectations were tested by carrying out a series of homo- and heteronuclear ultrafast 2D NMR acquisitions, and found systematically fulfilled. The robustness and conditions that allow the interlaced numerical procedure to be implemented in routine analytical applications were explored and are briefly discussed.     

New Approaches to Generalized Two‐Dimensional Correlation Spectroscopy and Its Applications

Abstract

This review is focused on the recent approaches to generalized 2D correlation spectroscopy, a technique widely used for the analysis of spectral data. A brief introduction of generalized 2D correlation spectroscopy is described first. Then the powerful combination of generalized 2D correlation spectroscopy and multivariate chemometircs techniques, such as the data reconstruction by principal component analysis (PCA), eigenvalue manipulation transformation (EMT), and self‐modeling curve resolution (SMCR) analysis are explored. Examples of successful applications of new approaches to generalized 2D correlation spectroscopy are highlighted.     

Nonparametric NMR spectroscopy

The parametric (or model-based) approach to NMR spectroscopy suffers from two general problems: it is sensitive to modeling errors and requires knowledge of the number of resonances present in the compound(s) under analysis. The nonparametric approach has neither of these drawbacks and it may also be computationally simpler than the parametric approach. However, if not applied properly, the nonparametric approach may yield significantly less accurate spectroscopic results than the parametric approach. In this paper we introduce a high-resolution nonparametric methodology for NMR spectroscopy based on the adaptive filter bank approach. The main salient feature of the new approach is that it provides 2D spectra versus both frequency and damping, as opposed to the classical 1D frequency spectra routinely used in NMR spectroscopy. To show the power of our new nonparametric approach we compare its performance with the ultimate performance of the parametric approach. We use both simulated and real NMR signals in our numerical performance study.     

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.     

基于WATERGATE的双溶剂峰抑制方法

WATERGATE（W3/W5）是NMR实验中使用较为广泛的溶剂峰抑制方法,但该方法通常仅能对一个溶剂信号进行有效抑制. 本文对WATERGATE的脉冲序列进行修饰、优化,发展了两种新的双溶剂峰抑制方法. 实验结果表明,经过修饰、优化后的WATERGATE,实验的设立非常简单,不需要复杂的优化过程就能够对双（多）溶剂峰进行有效抑制, 可用于常规1D & 2D NMR 实验、HPLC NMR实验,以及天然产物粗提取物的分析中.     

基于近似l0范数最小化的NMR波谱稀疏重建算法

在核磁共振（NMR）波谱中,过长的数据采集时间会使很多化学以及分子生物学领域的高分辨率多维谱应用难以实现. 传统的解决办法是使用随机非均匀采样代替奈奎斯特采样,但这样会使谱图质量受损. 压缩传感的出现为此提供了更好的解决办法,合适的压缩传感重建算法可以通过很少的随机非均匀采样将谱图高质量的重建出来. 该文先介绍了一种可用于谱图重建的压缩传感重建算法,名为“平滑l₀范数最小化法”,然后针对该算法对采样噪声鲁棒性较差的缺点进行了改进. 通过将改进后的算法与原算法在一维实数域信号以及NMR波谱信号重建实验中进行对比后表明,改进后的算法对噪声的鲁棒性明显提高,并能获得更好的重建性能.     

Dual processing of two-dimensional exchange data in magic angle spinning NMR of solids.

We discuss procedures for processing data in rotor-synchronized two-dimensional magic angle spinning (2D MAS) NMR exchange measurements for both structural and dynamical studies. We show, both mathematically and experimentally, that there are two distinct data processing procedures that lead to 2D MAS exchange spectra with purely absorptive crosspeaks. One procedure is that described previously by Hagemeyer, Schmidt-Rohr, and Spiess (HSS). The other procedure is related, but different, and leads to crosspeak intensities given by the formulae of Herzfeld, Roberts, and Griffin (HRG). In 2D MAS exchange experiments on doubly (13)C-labeled l-alanylglycylglycine, we demonstrate that the HSS and HRG crosspeak intensities can be extracted separately from the same data set and contain independent information. Processing and analysis of 2D MAS exchange data with both the HSS and the HRG procedures may enhance utilization of the information content of 2D MAS exchange measurements.     

三维NMR谱

３ＤＮＭＲ谱是２ＤＮＭＲ谱附加一个时间周期扩展而成，３ＤＮＭＲ共振峰的重叠降低，并且灵敏度与常规的２ＤＮＯＥＳＹ实验大体相当，采集３ＤＮＭＲ数据组所需时间太长，因此迄今为止，该方法的实际应用只局限于那些浓度相当高的样品。尽管目前还十分费时，但很可能３ＤＮＭＲ不久即可成为常规的ＮＭＲ技术。     

Model-Free Analysis of Mixtures by NMR Using Blind Source Separation

The concept of blind source separation is described and examples of its use in 1D and 2D NMR spectroscopy are presented. The goal of this data processing method is to extract the spectra of components molecules when only mixtures are available.     

129Xe NMR study of Xe adsorption on multiwall carbon nanotubes

¹²⁹Xe NMR spectroscopy has been used to study the adsorption of Xe on multi-wall carbon nanotubes (MWCNT). The results obtained have shown the ¹²⁹Xe NMR ability to probe the intercrystalline (aggregate) and the inner porosity of CNT. In particular, the effects on porosity of tubes openings by hydrogen exposure and of ball milling were examined. Dramatic changes observed in the ¹²⁹Xe NMR spectra after moderate ball milling of MWCNTs were attributed to the destruction of the initial intercrystalline pore structure and to the Xe access inside the nanotubes. To examine the exchange dynamics the mixture of as-made and milled MWCNTs was studied with one- and two-dimensional (1D and 2D) ¹²⁹Xe NMR. The exchange between the interior of milled nanotubes and the aggregate pores of as-made MWCNTs was fast on the NMR acquisition time scale. The Xenon exchange between the interior of the as-made MWCNTs and the large aggregate pores occurred on a longer time scale of 10 ms, as was established by 2D ¹²⁹Xe NMR exchange spectroscopy. Variable temperature ¹²⁹Xe NMR data were also discussed and analyzed in terms of the fast exchange approximation.     

Planar microcoil-based microfluidic NMR probes

Microfabricated small-volume NMR probes consisting of electroplated planar microcoils integrated on a glass substrate with etched microfluidic channels are fabricated and tested. 1H NMR spectra are acquired at 300 MHz with three different probes having observed sample volumes of respectively 30, 120, and 470 nL. The achieved sensitivity enables acquisition of an 1H spectrum of 160 microg sucrose in D2O, corresponding to a proof-of-concept for on-chip NMR spectroscopy. Increase of mass-sensitivity with coil diameter reduction is demonstrated experimentally for planar microcoils. Models that enable quantitative prediction of the signal-to-noise ratio and of the influence of microfluidic channel geometry on spectral resolution are presented and successfully compared to the experimental data. The main factor presently limiting sensitivity for high-resolution applications is identified as being probe-induced static magnetic field distortions. Finally, based on the presented model and measured data, future performance of planar microcoil-based microfluidic NMR probes is extrapolated and discussed.