Multidimensional NMR spectra

Includes basic interpretation, 30 valuable tables of data, and a concise introduction to multidimensional NMR spectra from an interpretational point of view. 

Highly sophisticated pulse sequences have been developed for the extraction of the desired information from ID and multidimensional NMR spectra [172]. The same techniques can be used for high-resolution 1-NMR, s-NMR and NQR. Pulse experiments are commonly used for the measurement of relaxation times [173], for the study of diffusion processes [174] and for the investigation of chemical reactions [175]. Davies et al. [176] have described naming and proposed reporting of common NMR pulse sequences (IUPAC task group). An overview of pulse sequence experiments has been given [177],... 

Two-dimensional and multidimensional NMR spectra. Proteins have such complex NMR spectra that, except for small regions at the upheld and downfield... 

The assignments are made through a battery of techniques to identify the through-bond and through-space interactions. Multidimensional NMR spectra are taken in which the sample is irradiated by two radio frequency fields in... 

The other general way of resolving powder patterns from different chemical sites is to generate multidimensional NMR spectra in which the desired powder patterns (or magic-angle spinning sideband patterns) are resolved in one dimension, separated according to (for instance) isotropic chemical shift in another dimension. These techniques are discussed below in the relevant section for each type of nuclear spin interaction. 

Multidimensional NMR spectra are not restricted to cases where the separate frequency axes encode signals from different nuclear types. Indeed, much of the early work on the development of 2D NMR was performed on cases where both axes involved chemipal shifts. The main value in such spectra comes from the information content in cross peaks between pairs of protons. In COSY-type spectra (COSY = Correlation SpectroscopY) cross peaks occur only between protons that are scalar coupled (i.e., within 2 or 3 bonds) to each other, whereas in NOESY (NOE Spectroscopy) spectra cross peaks occur for protons that are physically close in space (<5 A apart). A combination of these two types of 2D spectra may be used to assign the NMR signals of small proteins and provides sufficient information on internuclear distances to calculate three-dimensional structures. Figure 12.3 includes a panel showing the COSY spectrum of cyclosporin and highlights the relationships between ID H-NMR spectra and corresponding 2D homonuclear (COSY) and heteronuclear (HSQC) spectra. 

Many other pulse-sequence techniques besides COSY can be used to produce multidimensional NMR spectra. It will suffice here to simply list the acronyms of some of the better known methods EXSY (exchange spectroscopy), NOESY (nuclear Overhauser effect spectroscopy), TOCS Y (total correlation spectroscopy), ROESY (rotational nuclear Overhauser effect spectroscopy). The nuclear Overhauser effect (NOE) refers to a change in intensity of one NMR peak when another peak is irradiated. 

Bernstein, R., et al., Computer-Assisted Assignment of Multidimensional NMR Spectra of Proteins Application to 3D NOESY-HMQC and TOCSY-HMQC Spectra, J. Biomol. NMR, 3, 245, 1993. 

With the dissemination of multinuclear multidimensional NMR experiments, the automated NMR resonance assignment became feasible and indispensable, simultaneously.23,35,41,99 Typically, 10-20 individual multidimensional NMR spectra are measured for a large protein. The NMR-derived information quality definitely relies on the resonance assignment. The precious assignment has been based on and assessed by the sequential NOE continuity on the peptide sequence and consistency with the amino acid spin... 

In this review we will focus on applications of FT to processing of non-uniformly (sparsely) data sets devoted to the reconstruction of high-resolution multidimensional NMR spectra. 

Fig. 19 Experimental example of ultra-high resolution multidimensional NMR spectra obtained by the proposed technique 174 intra-residual resonance from 89 h 4D HNCACO- H -coupled experiment acquired for 5-79 fragment of bovine Ca -loaded Calbindin protein. Depicted cross-sections of 4D cube 50 x 450 x 40 x 100 Hz surrounding the peak allow determination of coupling constants from resolved 4D E.COSY pattern. JcaHa = 135.9 Hz, Jhnhci = 5.8 Hz, = —5.0 Hz, Jnhhcx = —10 Hz with numerical resolution of 0.4 Hz/point, 1.7 Hz/point, 0.2 Hz/point, and 0.7 Hz/point in dimensions F], F2, F3, and F4, respectively. Reprinted with permission from [80]...

Frydman L, Scherf T, Lupulescu A (2002) The acquisition of multidimensional NMR spectra within a single scan. Proc Natl Acad Sci USA 99(25) 15858-15862... 

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