Multiplicities from HMQC/HSQC

D one-bond correlation (with spectrum editing) HMQC or HSQC (with editing) Carbon assignments transposed from proton assignments. Proton spectrum dispersed by C shifts. Carbon multiplicities from edited HSQC (faster than above ID approach). 

There are two approaches to pulse sequence classification depending on the user s occupation. For the chemist who has to solve a structural question or characterize a new compound it is the spectra obtained from the pulse sequence that is of primary importance. The NMR spectroscopist is usually more concerned with the pulse sequence structure and choice of experimental parameters and whether a particular pulse sequence can be improved or modified to solve a specific problem. These two different approaches lead to confusion in pulse sequence nomenclature such that names are often a combination of the purpose of the experiment and the sequence layout. For example the commonly used acronyms HMQC, HSQC and HMBC imply a consistent abbreviation system yet HMQC and HSQC describe the coherence state during the evolution time whilst HMBC denotes an experiment to correlate nuclei using multiple bond heteronuclear scalar coupling. 

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).

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