Selective heteronuclear J-resolved

Figure 7.6. The proton-detected selective heteronuclear J-resolved spectrum of adenosine 73. The HI proton has been selectively inverted and the doublet splittings in f record its long-range couplings to C8 and C2 (reproduced with permission from reference [6]).

Figure 7.4. Heteronuclear J-resolved sequences for the measurement of long-range proton-carbon coupling constants (a) semi-selective, (b) selective and (c) selective with proton observation (see text).

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. 

H coupling in carbohydrates by selective 2D heteronuclear J-resolved n.m.r. spectroscopy has been demonstrated for heteronuclear couplings to H-1 of methyl o<-D-glucopyranoside, which are... 

M. Liu, R.D. Farrant, J.M. GUlam, J.K. Nicholson, J.C. Lindon, Selective inverse-detected long-range heteronuclear J-resolved NMR spectroscopy and its application to the measurement of Jqh> J- Magn. Reson. B 109 (1995) 275—283. 

M.J. Gidley and S.M. Bociek, Selective 2D-heteronuclear J-resolved NMR spectroscopy, J. Chem. Soc., Chem. Commun., 220(1985). 

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. "... 

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. 

Figure 5.45. (A) The selective spin-flip method for recording heteronuclear 2D J-resolved spectra in which the signals are modulated by long-range coupling constants. The pulse sequence is shown above while its effect on the magnetization vectors is shown below it. The selective 180° pulse results in elimination of the large one-bond coupling constants, Jch ( ) j -Methylcellobioside with the torsional angles (j) and ij/ indicated.

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... 

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