Selective Heteronuclear Resolved Experiment

The selective heteronuclear /-resolved experiment (Bax, 1984) is used to determine heteronuclear long-range coupling constants via a selecdve n pulse that causes splitting of all carbon signals coupled to that proton. 

Selective excitation of a resolved resonance followed by homonuclear or heteronuclear Hartmann-Hahn transfer can also be advantageous in the preparation period of two-dimensional experiments. For example, two-dimensional COSY, NOESY, TOCSY, and two-dimensional /-resolved subspectra of individual spin systems can be acquired based on this principle (Homans, 1990 Sklenaf and Feigon, 1990 Nuzillard and Massiot, 1991 Gardner and Coleman, 1994). In selective two-dimensional experiments like soft COSY (Briischweiler et al., 1987 Cavanagh et al., 1987),... 

Heteronuclear coupling constants (1,b7c,h) are most commonly measured from heteronuclear 2D experiments. The 3/c H couplings can be easily extracted from /-resolved spectra as well as from f or F2 proton coupled HSQC spectra. The undesired evolution of "/CH during q can be eliminated with use of an appropriate bilinear rotation decoupling (BIRD) pulse, such as BIRDd,x in. /-resolved spectroscopy35 and 111RD in Fi-coupled HSQC.36 Spin-state selective excitation techniques, S3E and S3CT37 38 (spin-state-selective coherence transfer), can also be used for the measurement of... 

To improve the sensitivity the selective J-resolved pulse sequence may be combined with a refocused INEPT polarization transfer experiment. In contrast to the original heteronuclear J-resolved experiment the first excitation pulse is executed on the F2 channel with the spin-echo sequence sandwiched between two incremental delay. Coupling evolves during the second incremental delay before the refocused INEPT unit creates in-phase coherence for the nuclei which are coupled to the selected proton nucleus allowing decoupling on the F2 channel during data acquisition. 

A survey of literature gave over 20 papers where 2D NMR experiments was successfully applied in quantification of complex samples. The selection of the used experiments was also quite diverse all typical 2D homo- and heteronuclear correlation experiments were among them. Many of the authors also compared the 2D NMR results against ID NMR quantification or quantification with other analytical technique. In overall, 2D NMR quantification offered a better linearity and accuracy in these comparisons due to better resolved peaks. Additionally, the approach often facilitated analysis of minor components that were not distinguishable from ID NMR spectra. The main part of the papers that demonstrated 2D NMR quantification focused on the analysis of natural products like animal and plant metabolites. Some articles were also found where quantitative 2D NMR was applied to quality control in food industry, and on characterization of the products of oil industry. The following sections give a short summary of the quantitative 2D NMR on the aforementioned topics. 

Figure 5.15 (A) Pulse sequence designed for the combination of polarization transfer and selective flip of attached protons. The long-range couplings are suppressed, and only one-bond heteronuclear couplings are observed in this experiment. (B) (a) Quartet of nitromethane obtained by using the basic pulse sequence of the heteronuclear 2D /-resolved experiment, (b) The same quartet, but with misset delays, which results in spurious peaks, (c) Quartet obtained by the combination of INEPT with spin manipulation. Peak intensification is due to the polarization transfer effect, (d) Effect of missetting of pulse widths in (c). (Reprinted from ]. Magn. Reson. 58, V. Rutar, 132, copyright (1984), with permission from Academic Press, Inc.)...

There are several types of heteronuclear 2D J-resolved experiments (i) the gated decoupler method, (ii) the spin-flip method, (iii) the selective spin-flip method, (iv) the semi-selective spin-flip method, and (v) the use of polarization transfer, e.g., INEPT. In all these experiments, the pulse sequence results in the generation of spin echoes which are modulated during the evolution period by coupling frequencies. 

DEPT to enhance the signal of some other experiment in the sections devoted to those experiments (e.g. heteronuclear correlations, INADEQUATE, DQF COSY, 7-resolved spectra). Similarly, an INEPT experiment can be made selective in a number of ways some are discussed in Section VI.C.l on selective experiments. 

Meissner A, Duus JO, S0rensen OW (1997) Integration of spin-state-selective excitation into 2D NMR correlation experiments with the heteronuclear ZQ/2Q pi rotations for Jxh resolved E.COSY-type measurements of heteronuclear coupling constants in proteins. J Biomol NMR 10 89-94... 

In addition to the importance of parameter selection on F skew, the ACCORD-HMBC experiment has also been shown to exhibit strong coupling artifact responses similar to those observed in heteronuclear 2D J-resolved spectra. - Finally, the triplet character of responses in the second frequency domain superimposed over the Fi skew was mathematically accounted for by Zangger and Armitage in their development of the ACCORD-HMQC experiment. "... 

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