Proton-Detected, Long-Range

Ipsenol Proton-Detected, Long Range 1H—13C Heteronuclear Correlation HMBC... 

Proton-Detected, Long-Range H—,3C Heteronuclear Correlation HMBC 263... 

Proton-Detected, Long-Range H—13C Heteronudear Correlation HMBC 265... 

The first proton-detected long-range heteronuclear shift correlation experiment to be developed was the HMBC experiment reported in 1986 by Bax and Summers." The pulse sequence for the experiment is shown in Fig. 5. The experiment is quite simple in constitution, utilizing only a total of five pulses. Following the first proton pulse, a fixed delay, A, is in.serted, optimized as a function of ( Jch)- The phase of the following 90° C or X-pulse is alternated 0202 while the receiver phase is alternated 0022. This pulse operator is referred... 

Ramos A, Varani G (1998) A new method to detect long-range protein-RNA contacts NMR detection of electron-proton relaxation induced by nitroxide spin-labeled RNA. J Am Chem Soc 120(42) 10992-10993... 

Two-dimensional C//correlations such as C//COSY or HC HMQC and HSQC provide the Jqh connectivities, and thereby apply only to those C atoms which are linked to H and not to non-protonated C atoms. Modifications of these techniques, also applicable to quaternary C atoms, are those which are adjusted to the smaller Jqh and Jqh couplings (2-25 Hz, Tables 2.8 and 2.9) Experiments that probe these couplings include the CH COLOC (correlation via long range couplings) with carbon-13 detection (Fig. 2.16) and HC HMBC (heteronuclear multiple bond coherence) with the much more sensitive proton detection (Fig. 2.17)... 

CH COLOC Correlation via long-range CH coupling, detects CH connectivities through two or three (more in a few cases) bonds in the CH COSY format, permits localisation of carbon nuclei two or three bonds apart from an individual proton... 

Fiffire 5.38 Pulse sequence for delayed COSY—a modification of the COSY experiment. The fixed delays at the end of the evolution period t and before the acquisition period <2 allow the detection of long-range couplings between protons. 

This is a variation of the proton-detected shift-correlation experiment via long-range couplings proposed by Bax and Summers (Bax and Summers, 1986), with the difference that the first C pulse is substituted by a frequency selective pulse (Fig. 7.14) (Bermel et al., 1989 Kessler et al., 1989b,1990). This significantly increases resolution in the F dimension. For example, this can be used to remove the overlap between the cross-peaks of the carbonyl resonances of peptide bonds in proteins that all occur within a... 

In 2003, Sprang and Bigler have developed a pulse sequence, HMBC-RELAY, subsequently improved in 2004, that yields two simultaneously detected types of long-range correlation spectra.60,61 One spectrum shows all 7ch connectivities while the other shows exclusively 2/ch connectivities. Their method uses homonuclear 3/hh couplings between the protons of adjacent carbons, as already been exploited for the XCORFE... 

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