Heteronuclear correlation decoupling

Recently, the two-dimensional 13C H heteronuclear correlation (HETCOR) NMR method, using the frequency-switched Lee-Goldberg (FSLG) H decoupling sequence55 at high MAS rates, has been developed, in order to provide intermolecular and spatial distance information. The HETCOR spectrum often has multiple proton cross peaks for each carbon, and these cross peaks can be extremely helpful for assigning the spectrum. Thus, this method can be used to characterize the structure of polymers in solids.55 71... 

Heteronuclear correlation (HETCOR) spectroscopy is a standard two-dimensional NMR technique. The resolution of 31P 1H CPMAS spectra is generally not sufficient to unequivocally detect the HP042 ions and the apatitic OH- ions in bone or dentin samples.15 In this regard, the breakthrough came from the first application of 31P 1H HETCOR to HAp and bone samples,24 where the correlation peak at 0.2 and 3 ppm of the 1H and 31P dimensions, respectively, has been established as the spectral marker of apatitic OH- ions. To enhance the spectral resolution in the XH dimension, 1H homonuclear decoupling was employed during the fi... 

It is also possible through selective heteronuclear singlefrequency decoupling to correlate bonded carbons and protons (HETCOR, Heteronuclear Correlated Spectroscopy) as an alternative to identify all directly bonded and longdistance carbon-proton pairs in a molecule. 

The proton-decoupled 13C NMR spectrum of pergolide mesylate indicates the presence of twenty carbons, which are further identified as four non-protonated carbons, six methine carbons, and ten methyl and methylene carbons via a Distortionless Enhancement by Polarization Transfer (DEPT) spectrum. The eight aromatic and olefinic carbon resonances in the 134 ppm to 106 ppm region have chemical shifts consistent with an indole structure (2). The H NMR spectrum contains four aromatic proton resonances, from 6.88 to 7.22 ppm, whose chemical shifts are also indicative of an indole-type structure. The assignment of these carbon and proton resonances were confirmed with IH correlation spectroscopy (CDSY) and 3C-1H heteronuclear correlation spectroscopy (HETCORR). The UV spectrum also indicates the presence of an indole chromophore. 

In a 2D heteronuclear correlation (HETCOR) experiment, the h and t2 periods correspond to the evolution of SQC of two different nuclei, e. g., and A number of different HETCOR experiments have been proposed which differ with respect to, e. g., the means by which coherence transfer is achieved, the type of coherence which evolves during h, as well as the application of homonuclear decoupling sequences. 

Indirect covariance processing as depicted in Fig. 5.IB is another type of single spectmm manipulation. Here, a heteronuclear correlation spectmm is transformed into a correlation spectmm of the indirect dimension of the original data. In the current example, a H—C HSQC—TOCSY spectmm is converted into a C—C correlation spectmm, containing only correlations of carbon atoms that share the connectivity information of their attached protons. Quaternary carbons thus remain unobserved due to the principle of the H-C HSQC—TOCSY. While the direct covariance processing leads to an increase in resolution, the indirect covariance processing results in a formal decrease. Yet, the reduction of signals under retention of the information content in the case of the latter transformation compensates for the decrease in dimensionafity. It is also possible to use the indirect covariance procedure on homonuclear spectra to obtain homo-decoupled... 

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