Homonuclear coherent magnetization transfer

Fig. 7.2.31 Filters for homonuclear coherent magnetization transfer. All filters start from and end with longitudinal magnetization, (a) Selective excitation and reconversion of coherences with a nonselective mixing period, (b) Realization of a nonselective mixing period in a z filter via longitudinal magnetization, (c) Nonselective excitation and reconversion of coherences with a selective mixing period, (d) Realization of a selective mixing period by a multi-quantum filter, (e) Selective exchange of transverse magnetization within the multiplets of coupled homonuclear spin pairs by a homonuclear version of the INEPT method.

The properties of homonuclear coherence and magnetization transfer under CW irradiation have been discussed in detail in the literature (Bax and Davis, 1985a Bazzo and Boyd, 1987 Bax, 1988a, b Listerud and Drobny, 1989 Glaser and Drobny, 1989, 1991 Chandrakumar et al., 1990 Elbayed and Canet, 1990). 

The step from 2D homonuclear correlation spectroscopy to 2D heteronuclear con elation spectroscopy is relatively straight forward but there is one important point to consider relating to the evolution of the antiphase coherence for magnetization transfer. Irrespective of whether direct or indirect detection is used, the delay times for optimum... 

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... 

In the relayed coherence transfer experiment the first step is an initial homonuclear magnetization transfer (i.e., from proton A to proton B). The coherence is then relayed to a third nucleus, which may be a proton (homonuclear relay) or a different nucleus (e.g., heteronuclear relay). Recently, another variation of the relay experiment has been reported which involves transfer of coherence to a heteronuclear spin as the first step ( H-X heteronuclear shift correlation). The coherence is then relayed to a third nucleus, a proton (X- H coherence transfer), which is the nucleus observed. ... 

Figure 1.45 Coherence transfer pathways in 2D NMR experiments. (A) Pathways in homonuclear 2D correlation spectroscopy. The first 90° pulse excites singlequantum coherence of order p= . The second mixing pulse of angle /3 converts the coherence into detectable magnetization (p= —1). (Bra) Coherence transfer pathways in NOESY/2D exchange spectroscopy (B b) relayed COSY (B c) doublequantum spectroscopy (B d) 2D COSY with double-quantum filter (t = 0). The pathways shown in (B a,b, and d) involve a fixed mixing interval (t ). (Reprinted from G. Bodenhausen et al, J. Magn. Resonance, 58, 370, copyright 1984, Rights and Permission Department, Academic Press Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887.)...

Both homonuclear and heteronuclear versions of relayed nOe experiments are known. The homonuclear relayed NOESY experiment involves both an incoherent transfer of magnetization between two spins H and H/ that are not coupled but close in space, and a coherent transfer of magnetization between two spins H(and H that are /-coupled together. The magnetization pathway may be depicted as... 

A first pulse create.s transverse magnetization components (coherences) which evolve in the evolution period tl (DO in the schemes) with their characteristic precession frequencies (chemical shift and homonuclear J-coupling). The effect of the second (mixing) pulse is that information from one nucleus that evolves in tl is transferred to another (J-coupled) nucleus, the magentization components of which evolve and are detected in t2. Therefore, the nuclei carry information that relates not only to their own chemical shifts and coupling constants but also the corresponding information about the other, coupled spins. 

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