Homonuclear COSY spectra

Fig. 2.8 Sequence procedures to obtain magnitude and phase sensitive homonuclear COSY spectra.

Figure 33 Schematic homonuclear COSY spectrum with diagonal... 

Fig. 2.43 a. Contour plot of the homonuclear COSY spectrum (HOMCOR) of rhizobactin (42) revealing the coupling connectivities of the four separate units that compose the molecule plus an impurity b contour plot of the heteronuclear COSY (HECTOR) showing carbon and proton assign-... 

The DQF (double-quantum filtered)-COSY spectrum of an isoprenyl coumarin along with H-NMR data are shown. Determine the H/ H homonuclear interactions in the DQF-COSY spectrum. 

The HMQC spectrum, H-NMR chemical shift assignments, and C-NMR data of vasicinone are shown. Consider the homonuclear correlations obtained from the COSY spectrum in Problem 5.14, and then determine the carbon framework of the spin systems. 

The DQ filter destroys all terms from the homonuclear front end except for the one with both operators Ia and Ib in the x-y plane the second term — 2IaIb c s. This term will become the diagonal and the crosspeak in the DQF-COSY spectrum. To understand its fate we will express it in terms of pure ZQC and DQC... 

In a homonuclear hydrogen COSY spectrum the signals along the diagonal reflect the normal H spectrum. It is the... 

Figure 4 Homonuclear 2D spectra of the 8mer peptide EWTLYWR in 90 % H2O, 10 % D2O. (a) Representation of coherence transfer pathways for COSY (soiid arrows), TOCSY (dotted arrows) and NOESY (dashed arrows) experiments, (b) Section of COSY spectrum displaying the backbone H -H -correlations, additionaiiy the side-chain H -H -correlations of R8 is visible in the upper right-hand corner. The H -H -correlation of El cannot be detected because of soivent-exchange broadening of the N-terminal amino group, (c) Section of TOCSY spectrum that displays the correlations of the backbone with all protons within the amino acid side chain, (d) Section of ROESY spectrum that displays correlations between backbone H -H intraresidual as well as to the neighboring (i-1) amino acid. The cross peaks to the (i-1) amino acid have higher intensities. Thus, a "sequential walk" is possible (arrows) that allows identification of the position of amino acids within the peptide chain. Additionally the H of El can be assigned (first arrow on the left).

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. 

In Check it 2.3.12 a homonuclear COSY magnitude calculation spectrum [2.34] is converted into its various phase sensitive analogues. Fig. 2.8 shows the phase incrementation and loop commands necessary for this conversion. Table 3.5 in chapter 3 lists the recommended processing parameters to use for the different types of experiment. The gradient based Echo/Antiecho COSY experiment is discussed further in section... 

In a homonuclear decoupling experiment a particular multiplet is irradiated suppressing the coupling interaction between the irradiated nucleus and its coupling partners. A comparison of the standard coupled ID spectrum and the selectively homonuclear decoupled spectrum reveals which nuclei are coupled. Whether a homonuclear decoupling experiment or a 2D homonuclear COSY experiment would be the best solution for multiplet analysis in a one-dimensional spectrum depends very much on the nature of the problem under investigation. If a large number of multiplets need to be irradiated then a two-dimension approach may be preferable. 

Spin pinging [5.86] has been proposed as a method of using rectangular pulses in 2D homonuclear COSY experiments for tailored excitation. Using spin pinging it would be possible to select regions of overlapping multiplets which are not defined sufficiently in a standard 2D COSY spectrum because of the restricted number of data points. Probably... 

Two-dimensional homonuclear correlation spectroscopy (COSY) is well established for the study of liquids [24,25] and has recently been shown to be effective with solid samples [8,26-38], many of which are of catalytic interest [30,37]. The COSY spectrum contains diagona] peaks and off-diagonal cross-peaks. The cross-peaks arise because of coherence transfer between spins, and they indicate that the resonances at the relevant shift positions on the two axes are coupled. In the solid state, the necessary coherence transfer may occur through dipolar or scalar interactions. Experiments based on scalar couplings have been more popular, because in favorable circumstances they allow the spectroscopist to establish unambiguously the atomic connectivities within molecules in solid samples [8,27-38] including complex zeolitic frameworks [8,30-37]. 

The homonuclear correlation spectrum (COSY) in Figure 5 helps... 

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