R. R. Ernst

Investigation of exchange processes by two‐dimensional NMR spectroscopy

A new general technique for the investigation of exchange processes in molecular systems is proposed and demonstrated. Applications comprise the study of chemical exchange, of magnetization transfer by inter‐ and intramolecular relaxation in liquids, and of spin diffusion and cross‐relaxation processes in solids.

Two‐dimensional spectroscopy. Application to nuclear magnetic resonance

The possibilities for the extension of spectroscopy to two dimensions are discussed. Applications to nuclear magnetic resonance are described. The basic theory of two‐dimensional spectroscopy is developed. Numerous possible applications are mentioned and some of them treated in detail, including the elucidation of energy level diagrams, the observation of multiple quantum transitions, and the recording of high‐resolution spectra in inhomogenous magnetic fields. Experimental results are presented for some simple spin systems.

Improved spectral resolution in COSY 1H NMR spectra of proteins via double quantum filtering

A double quantum filter is inserted into a two-dimensional correlated (COSY) 1H NMR experiment to obtain phase-sensitive spectra in which both cross peak and diagonal peak multiplets have anti-phase fine structure, and in which the cross peaks and the major contribution to the diagonal peaks have absorption lineshapes in both dimensions. The elimination of the dispersive character of the diagonal peaks in phase-sensitive, double quantum-filtered COSY spectra allows identification of cross peaks lying immediately adjacent to the diagonal, which represents a significant improvement over the conventional COSY experiment.

A TWO-DIMENSIONAL NUCLEAR OVERHAUSER ENHANCEMENT (2D NOE) EXPERIMENT FOR THE ELUCIDATION OF COMPLETE PROTON-PROTON CROSS-RELAXATION NETWORKS IN BIOLOGICAL MACROMOLECULES

Abstract The recently developed technique of two-dimensional (2D) cross-relaxation spectroscopy is utilized for systematic measurements of selective nuclear Overhauser enhancements (NOE) in the high resolution 1H nuclear magnetic resonance (NMR) spectra of biological macromolecules in solution. Compared to conventional one-dimensional NOE studies, the 2D NOE experiment has the principal advantage that it avoids detrimental effects arising from the limited selectivity of preirradiation in crowded spectral regions. Furthermore, it yields with a single instrument setting a complete network of NOEs between all the protons in the macromolecule. The resulting information on intramolecular proton-proton distances provides a new avenue for studies of the spatial structures of biopolymers.

Elucidation of cross relaxation in liquids by two-dimensional N.M.R. spectroscopy

Two-dimensional N.M.R. spectroscopy is applied to the elucidation of cross relaxation pathways in liquids. The theory underlying two dimensional studies of cross relaxation and of transient nuclear Overhauser effects is developed. The influence of the correlation time of the molecular random process is investigated. It is found that in the limit of short correlation times (extreme narrowing limit) weak negative cross-peaks are observed. However, for long correlation times (spin diffusion limit) strong positive cross-peaks can be obtained. The technique appears particularly promising for the study of cross relaxation in macromolecules. Examples of intra- and intermolecular cross relaxation in the extreme narrowing limit are presented.

Application of Fourier Transform Spectroscopy to Magnetic Resonance

The application of a new Fourier transform technique to magnetic resonance spectroscopy is explored. The method consists of applying a sequence of short rf pulses to the sample to be investigated and Fourier‐transforming the response of the system. The main advantages of this technique compared with the usual spectral sweep method are the much shorter time required to record a spectrum and the higher inherent sensitivity. It is shown theoretically and experimentally that it is possible to enhance the sensitivity of high resolution proton magnetic resonance spectroscopy in a restricted time up to a factor of ten or more. The time necessary to achieve the same sensitivity is a factor of 100 shorter than with conventional methods. The enhancement of the sensitivity is essentially given by the square root of the ratio of line width to total width of the spectrum. The method is of particular advantage for complicated high resolution spectra with much fine structure.

Two-dimensional chemical exchange and cross-relaxation spectroscopy of coupled nuclear spins

Abstract The features of two-dimensional cross-relaxation and chemical exchange spectroscopy of coupled spins are investigated theoretically and by experiment. It is shown that spin-spin couplings can lead to J cross-peaks in analogy to cross-peaks in two-dimensional autocorrelated spectroscopy. They reflect a coherent magnetization transfer in contrast to the incoherent processes responsible for cross-relaxation and for chemical exchange. Possibilities of selectively suppressing J cross-peaks are discussed.

Experimental techniques of two-dimensional correlated spectroscopy

Abstract Two-dimensional (2D) homonuclear correlated spectra manifest connectivities between spin-coupled nuclei and can thus provide assignments of individual spin systems in complex 1 H NMR spectra. Two experimental techniques discussed in this paper, spin-echo correlated spectroscopy and foldover-corrected correlated spectroscopy, are particularly suitable versions for handling the large data matrices encountered in work with biological macromolecules. This paper explains the fundamental aspects of these two techniques and the relations with the conventional 2D correlated spectroscopy technique.

Indirect detection of magnetic resonance by heteronuclear two-dimensional spectroscopy

A method is disclosed for highly sensitive indirect detection of nuclear magnetic resonance of nuclei having a low gyromagnetic ratio using pulse techniques. The method employs a coherent transfer of transverse magnetization from the nuclei of interest to nuclei of high gyromagnetic ratio for which the free induction decay, S (t2), is observed as a function of the length of the time interval, t1, between imposition of transverse magnetization upon the nuclei of interest and transfer of magnetization to the observed nuclei. Contribution to the observed resonances not arising from the transferred transverse magnetization is eliminated and the resulting function S (t1, t2) is double Fourier transformed to the frequency domain and displayed as a two dimensional plot for resolving the multiplet spectral structure of the spectra of the nuclei having such low gyromagnetic ratio.

Analysis of networks of coupled spins by multiple quantum N.M.R.

It is shown that multiple quantum N.M.R. allows straightforward identification of networks of scalar coupled spins. The information obtained is particularly useful for the identification of magnetic equivalence when multiplet splittings are not fully resolved. The interpretation of multiple quantum spectra is based on a set of simple selection rules which restrict coherence transfer between multiple quantum and single quantum transitions.