Pulse sequence homonuclear

Since the first description of the Hartmann-Hahn transfer in liquids, spectroscopists have been fascinated by this technique. Many theoretical and practical aspects have been thoroughly investigated by several groups. With the development of robust multiple-pulse sequences, homonuclear and heteronuclear Hartmann-Hahn transfer has become one of the most useful experimental building blocks in high-resolution NMR. 

A. Bielecki. A. C. Kolbert and L H. Levitt, Frequency-switched pulse sequences - homonuclear decoupling and dilute spin NMR in solids. Chem. Phys. Lett., 1989, 155, 341-346. 

The ID homonuclear Hartmann-Hahn (HOHAHA) experiment is an excellent way to determine complete coupled spin networks (18). The following pulse sequence is used ... 

The pulse sequence used in homonuclear 2D y-resolved spectroscopy is shown in Fig. 5.18. Let us consider a proton, A, coupled to another proton, X. The 90° pulse bends the magnetization of proton A to the y -axis. During the first half of the evolution period, the two vectors (faster... 

Figure 5.18 (A) Pulse sequence for homonuclear 2D y-resolved spectroscopy. (B) Effect of 90° H and 180° H pulses on an H doublet. (C) In the absence of coupling, the vectors are refocused by the 180° H pulse after t. This serves to remove any field inhomogeneities or chemical shift differences.

Figure 17. Contour plot of the 360MHz homonuclear spin correlation mpa of 10 (2 mg, CDCL, high-field expansion) with no delay inserted in the pulse sequence shown at the top of the figure. Assignments of cross peaks indicating coupled spins in the E-ring are shown with tljie dotted lines. The corresponding region of the one-dimensional H NMR spectra is provided on the abscissa. The 2-D correlation map is composed of 128 x 512 data point spectra, each composed of 16 transients. A 4-s delay was allowed between each pulse sequence (T ) and t was incremented by 554s. Data was acquired with quadrature phase detection in both dimensions, zero filled in the t dimension, and the final 256 x 256 data was symmetrized. Total time of the experiment was 2.31 h (17).

In 2003, Sprang and Bigler have developed a pulse sequence, HMBC-RELAY, subsequently improved in 2004, that yields two simultaneously detected types of long-range correlation spectra.60,61 One spectrum shows all 7ch connectivities while the other shows exclusively 2/ch connectivities. Their method uses homonuclear 3/hh couplings between the protons of adjacent carbons, as already been exploited for the XCORFE... 

Fig. 6 A general pulse sequence (a) for spin diffusion or third-spin assisted mixing for polarization transfer between carbons (as shown) or carbon and nitrogen along with examples of homonuclear mixing elements and illustration of activated parts of H-13C-13C spin systems for PDSD, MIRROR, and PAR (b) (taken from [18] with permission), (c) Example of the application of PDSD for structure determination of the a-spectrin SH3 domain (taken from [133] with permission)...

Fig. 8 Pulse sequence for the measurement of homonuclear correlation spectra with 7 filtering. Narrows bars indicate 7t/2 pulses and broad bars indicate 71 pulses. Experimental conditions employed for a-synuclein fibrils samples static field strength 9.4 T temperature —5 °C spinning frequency 8 kHz T2 filter 100 ms CP contact time 2.5 ms TOBSY mixing time 6 ms. The rf phases can be found in the original figure and caption. (Figure and caption adapted from the Supporting Information of [134]. Copyright (2005) National Academy of Sciences, USA)...

Now consider the pulse sequence in Fig. 10. Each repetition of C spans one rotor period. Between 0 and tr/2, the composite On pulse 90o360igO270o is applied. This composite pulse, which has been commonly referred to as POST, is chosen because it has been shown to compensate for effects of rf inhomogeneity [83], The mirror-image composite pulse is applied between xr/2 and xr. With this particular design of ROCSA, the homonuclear dipole-dipole interaction is considerably suppressed relative to the CSA. 

Fig. 10 ROCSA pulse sequence based on Cn symmetry. The rectangular blocks in black represent jt/2 pulses. The recoupling period (q) comprises k cycles of Cnln. Each complete cycle of Cnln spans n rotor periods (nzR). The rf phase of each Cq subcycle is set equal to 2nq/n, where q is an index running from 0 to n — 1. Within each Cq subcycle, azR and bzR indicate the position and the duration of the POST composite pulse, respectively. We find that the solution (a, b) = (0.0329,0.467) is a favorable choice for the suppression of the homonuclear dipole-dipole interaction. The bracketed and subscripted values indicate the pulse length and rf phase in radians, respectively. (Figure and caption adapted from [158], Copyright [2003], American Institute of Physics)...

NOESY NMR spectroscopy is a homonuclear two-dimensional experiment that identifies proton nuclei that are close to each other in space. If one has already identified proton resonances in one-dimensional NMR spectroscopy or by other methods, it is then possible to determine three dimensional structure through NOESY. For instance, it is possible to determine how large molecules such as proteins fold themselves in three-dimensional space using the NOESY technique. The solution structures thus determined can be compared with solid-state information on the same protein obtained from X-ray crystallographic studies. The pulse sequence for a simple NOESY experiment is shown in Figure 3.23 as adapted from Figure 8.12 of reference 19. 

Fig. 11.6 Pulse sequence for two-dimensional homonuclear chemical-shift correlation experiments. The gray box indicates the mixing sequence, with some examples shown in more detail a RFDR, b RIL, c C7, d DRAWS, e DREAM.

Fig. 11.7 a Pulse sequence for rotational-resonance recoupling of homonuclear spin pairs, b The spinning frequency is matched to the isotropic chemical-shift difference, and one of the resonances is selectively inverted and the polarization exchange measured as a function of the mixing time, c The difference polarization as a function of the mixing can be evaluated to give the dipolar coupling constant. 

Fig. 11.15 Diagram showing the relative proximity of the two ligands Glp and S3P, which form a stable ternary complex with the enzyme EPSP synthase. The distance constraints were obtained from both homonuclear and heteronuclear dipolar couplings obtained using the REDOR and DRAMA pulse sequence, together with a model showing a...

In the pulse sequence for a homonuclear COSY experiment, the first 90° pulse flips the z magnetization into the x direction and into the xy plane. Considering an AX spin system (one in which the nuclei have very different chemical shifts) having two doublets due to spin-spin coupling, the magnetization will include four components processing at different frequencies. During a... 

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