Resolution enhancement homonuclear

A new H DQ CRAMPS solid-state NMR experiment incorporating DUMBO homonuclear H dipolar decoupling has been presented. The major resolution enhancement enables DQ peaks corresponding to all 22 close (<3.5 A) proton-proton proximities in the dipeptide AspAla to be observed. In particular, it was shown that the DQ CRAMPS spectrum provides access to the alkyl region of the spectrum and yields a clear assignment of the two CH and two diastereotopic CH2 proton resonances. 

B. Baishya, C.L. Khetrapal, K.K. Dey, Perfect Echo HMQC sensitivity and resolution enhancement by broadband homonuclear decoupling, J. Magn. Reson. 234 (2013) 67-74. 

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... 

In this section, 2D homonuclear and heteronuclear correlation experiments are reviewed. The longer experimental time for a 2D experiment is rewarded by enhancement of resolution achieved by adopting the second dimension. This gives us a chance to get information on both miscibility and polymer-polymer interactions. 

The simplest 2D NMR experiment, which offers enhanced resolution, is the homonuclear /-resolved experiment. ° The experiment is basically a spin-echo sequence, where the echo period is incremented. During this ti period the chemical shift evolution is refocused with a 180° pulse, but homonuclear / couplings are evolved. If we consider a proton H coupled to proton(s) H, the density function of the observed proton magnetization is modulated by these couplings accordingly... 

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... 

As a result of that study, the combination of covariance processing and NUS afforded a decrease in experimental time by a factor of two relative to linear sampling and covariance processing. It even shortened the total acquisition time by a factor of four as compared to conventionally sampled data and FT processing. Again, enhanced resolution and improved sensitivity were observed. The proof of concept was predicted to be amenable to other homonuclear 2D NMR experiments on liquid, aligned or solid samples. 

The apphcation of direct covariance processing to either NMR spectra or mixed time—frequency data matrices was preferentially used for spectral enhancement with respect to resolution. As the resolution of the indirect or incremented dimension is endowed with that of the direct or acquisition dimension, homonuclear spectra were treated almost exclusively. 

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