Resonance assignment heteronuclear multiple

The heteronuclear multiple bond correlation (HMBC) experiment correlates proton nuclei with carbon nuclei that are separated by more than one bond. In Fig. FI. 4.7 the 37CH and 27Ch couplings dominate. Major applications related to anthocyanins include the assignment of resonances of nonprotonated carbon nuclei of the... 

HSQC) or heteronuclear multiple quantum correlation (HMQC). The combined experiments such as 2D HSQC(HMQC)-TOCSY experiments are powerful tools for the assignment of the 13C and 11 resonances belonging to the same sugar residue providing enhanced dispersion of TOCSY correlations in the carbon dimension. More recendy, different carbon multiplicity editing methods, for example, DEPT (distortionless enhanced polarization transfer)-HMQC and E-HSQC, have been developed to reduce the complexity of proton-carbon correlation spectra and to enhance the resolution by narrowing the applied spectral window.11... 

Figure 13(b) shows a JH—15N HSQC spectrum acquired from 0.5 mmol l-1 sample of a 41-residue peptide toxin from the spider Agelena orientalis. The toxin was produced recombinantly and uniformly labeled with 15N. This HSQC spectrum was collected in 30 min, compared with the 12 h required to acquire a natural abundance spectrum from an unlabeled sample of equivalent concentration (see Figure 11). The HSQC, together with the related heteronuclear multiple quantum coherence (HMQC)54 experiment, forms the cornerstone of a wide range of 2D, 3D, and 4D experiments that are designed to facilitate sequence-specific resonance assignment and determination of protein structure. Note that the HSQC technique is the technique of choice for correlation of H and 15N shifts due to generally narrower linewidths in the 15N dimension.55,56 Furthermore, because these and most of the other heteronuclear experiments described below are designed to observe amide protons, the sample must be in H20 (rather than D20). Consequently, a means of suppressing the H20 resonance is required (for details see Section 9.09.2.6).

Ethyl nipecotate contains only one nonprotonated carbon site. Because of this lack of multiple nonprotonated carbon sites, it fails to serve as a useful example for illustrating the power of the 2-D heteronuclear multiple bond correlation (HMBC) experiment in assigning the resonances from nonprotonated C s. As a general rule, a molecule with few nonprotonated carbons will rarely require data from the HMBC experiment. 

Bax A, Davis DG (1985) MLEV-17 Based two-dimensional homonuclear magnetization transfer spectroscopy. J Magn Reson 65 355-360 Bax A, Drobny G (1985) Optimization of two-dimensional homonuclear relayed coherence transfer NMR spectroscopy. J Magn Reson 61 306-320 Bax A, Marion D (1988) Improved resolution and sensitivity in H-detected heteronuclear multiple-bond correlation spectroscopy. J Magn Reson 78 186-191 Bax A, Subramanian S (1986) Sensitivity-enhanced two-dimensional heteronuclear chemical shift correlation NMR spectroscopy. J Magn Reson 67 565-569 Bax A, Summers MF (1986) and Assignments from sensitivity-enhanced detection of heteronuclear multiple bond connectivity by 2D multiple-quantum NMR. J Am Chem Soc 108 2093-2094... 

The proton-decoupled proton spectra allowed a distinction to be made between homo-and heteronuclear spin couplings, and Laurie and coworkers also demonstrated nulling of residual solvent resonances during the 2D /-resolved NMR of uridine in aqueous solution, wrote software for 45° tilting of the 2D spectra, and developed experimental protocols for multiple data-acquisition and processing, and a method for acquisition of the 2D /-resolved spectra in phase-sensitive mode. Lately, the 2D /-resolved technique has been less used, as it yields little evidence for spectral assignments. 

Carbon peak assignments were not available in the earlier reports, and hence, a comprehensive study utilizing H, correlation spectroscopy (COSY), heteronuclear correlation (HETCOR), and heteronuclear multibond correlation (HMBC) nuclear magnetic resonance was undertaken. NMR CDCI3 (5 ppm vs. TMS (multiplicity H s coupling constant assignment)) 7.36 (d IH J5.4 Hz, H-2),... 

Figure 5.16 C-N HSQC-HIVIBC spectrum showing response assignments of 19. The correlation response from the C24 0-methyl group to N-1 is an artefact. The overlap of the H-2 methine and the C24 0-methyl resonances could be recognized in the parent multiplicity-edited H-C HSQC. This type of overlap can give rise to artefact responses in UlC processed heteronuclear correlation data matrices. Reprinted with permission from Martin et al. [27], Copyright 2007 American Chemical Society.

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