Jeener spectrum

A useful technique is to use broad-band decoupling in the co dimension. The pulse sequence shown in Figure 5.64 is used to achieve this. The fully coupled spectrum appears on one axis while the fully decoupled spectrum appears on the other axis. This method has the advantage that the chemical shifts of the individual protons can be read from the singlets on one axis and the proton-proton couplings can be easily identified. The Jeener spectrum of a tricyclodecane derivative is shown in Figure 5.65. The spectrum above the... 

The second development that has revolutionized the practice of NMR was the introduction of multidimensional spectroscopy. This was initialized by Jeener [2], who showed that, by introducing a second pulse and varying the time between them, a second time-axis could be constructed. A double Fourier transformation yields the familiar two-dimensional spectrum, nowadays known by everyone as the COSY spectrum. Ernst, already involved in the development of FT-NMR, showed that the concept was more generally applicable [3], and paved... 

The next milestone, in the history of NMR [Frel], was the extension of the NMR spectrum to more than one frequency coordinate. It is called multi-dimensional spectroscopy and is a form of nonlinear spectroscopy. The technique was introduced by Jean Jeener in 1971 [Jeel] with two-dimensional (2D) NMR. It was subsequently explored systematically by the research group of Richard Ernst [Em 1 ] who also introduced Fourier imaging [Kuml]. Today such techniques are valuable tools, for instance, in the structure elucidation of biological macromolecules in solution in competition with X-ray analysis of crystallized molecules as well as in solid state NMR of polymers (cf. Fig. 3.2.7) [Sch2]. 

One of the first steps in a conventional assault on a complex assignment problem in proton NMR is to run a series of homonuclear double resonance experiments. Not only can this establish which multiplets have a mutual J coupling, but it can reveal hidden resonances obscured by overlap, through their couplings to less crowded parts of the spectrum. Since a separate experiment is needed for each multiplet, this approach can be quite time-consuming. Similar information can however be obtained more efficiently by 2D NMR methods indeed, this was the purpose of the first 2D NMR experiment, proposed by Jeener in 1971. 

Figure 10. Homonuclear correlation 2D spectrum for viomycin in D2O, obtained using the Jeener two-pulse sequence with the added phase cycling scheme [13] to allow frequency discrimination in both dimensions, recorded on an XL-200 using a data matrix of 256x256 complex points. Solvent saturation was again used to suppress the residual HDD signal. Spurious signals near f2 = 3.1 and 4.5 ppm have been removed in order not to obscure cross peaks.

FOCSY Spectra. Another modification of the Jeener 2D-shift correlated spectroscopy which finds limited application in some special cases is known as Foldover Corrected Correlated Spectroscopy (FOCSY). The COSY spectrum is modified by software amendments to correct folding errors along the axis, and the chemical shifts of the normal spectrum appear on a horizontal line at coj = 0, so that the 2D contour plot resembles the SECSY spectrum. Again no reduction in data matrix size is achieved unless the largest chemical shift difference between coupled nuclei is smaller than half of the spectral width. 

The corresponding perturbation of the zero point energy may be studied by comparing the whole frequency spectrum of the pure isotopes to that of the mixed system (Prigogine, Bingen and Jeener [1954], Prigogine and Jeener [1954]). 

Another relaxation technique that is likely to see much utilization for structural studies in the future is the two-dimensional (2D) NOE experiment. The basic experiment has been largely developed in Ernst s lab with applications to proteins illustrated in Wutti ch s k. The pulse sequence [ n/2) -ti- n/2 -ZM ( /2)%-h-] generates a 2D spectrum following the two Fourier transforms. The intenrity of a peak in fte 2D-NOE spectrum arising from interaction of nucleus k with nucleus 1 is (Jeener et al., 1979 Macura and Ernst, 1980)... 

In order to demonstrate the methodology for generating a two-dimensional NMR spectrum, the homonuclear, /-correlated experiment first proposed by Jeener will be described. This experiment has been named COSY for... 

A two-dimensional experiment has been described for correlating the chemical shifts of nuclei undergoing chemical exchange (Jeener ef al., 1979 Macura et al., 1981). The pulse sequence for generating a homonuclear correlated exchange spectrum is shown in Fig. 20. At the end of the... 

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