Lee-Goldburg experiment

Recently, Vega and co-workers have presented a phase-modulated Lee-Goldburg experiment (PMLG) experiment, in which only the phase of a series of adjacent pulses is changed, i.e., a i remains constant.76 77 In an ingenious reinterpretation of the LG concept, the zero-order term in the average Hamiltonian can be shown to vanish when the modulation of the pulse phase described by... 

E. Vinogradov, P.K. Madhu, S. Vega, High-resolution proton sohd-state NMR spectroscopy by phase-modulated Lee-Goldburg experiment, Chem. Phys. Lett. 

In the solid, dynamics occurring within the kHz frequency scale can be examined by line-shape analysis of 2H or 13C (or 15N) NMR spectra by respective quadrupolar and CSA interactions, isotropic peaks16,59-62 or dipolar couplings based on dipolar chemical shift correlation experiments.63-65 In the former, tyrosine or phenylalanine dynamics of Leu-enkephalin are examined at frequencies of 103-104 Hz by 2H NMR of deuterated samples and at 1.3 x 102 Hz by 13C CPMAS, respectively.60-62 In the latter, dipolar interactions between the 1H-1H and 1H-13C (or 3H-15N) pairs are determined by a 2D-MAS SLF technique such as wide-line separation (WISE)63 and dipolar chemical shift separation (DIP-SHIFT)64,65 or Lee-Goldburg CP (LGCP) NMR,66 respectively. In the WISE experiment, the XH wide-line spectrum of the blend polymers consists of a rather featureless superposition of components with different dipolar widths which can be separated in the second frequency dimension and related to structural units according to their 13C chemical shifts.63... 

Frequency-switched Lee-Goldburg (FSLG) 13C-1H heteronuclear correlation (HETCOR) experiments... 

Figure 13 Pulse sequence for the solid-state 31P—1H frequency-switched Lee-Goldburg (FSLG) experiment. Proton-proton homonuclear decoupling was performed by using the FSLG decoupling sequence. Quadrature detection in Wi was achieved by using the TPPI method. During the acquisition period, TPPM heteronuclear decoupling was applied.

Fig. 5. (A) Vector picture describing the relationship between the rf field strength and offset frequency in off-resonance experiments such as LGCP and PISEMA. (B) A simple pulse sequence (called LGCP or FFLGCP) to set-up the Lee-Goldburg condition. As explained in the text, this sequence can be used to determine the S-spin-lock field strength that matches ileff./for the effective spin exchange between / and S spins.

Fig. 18. Proton-detected ID PISEMA spectra of a powder sample of A-acetyl- A-D,L-valine obtained using the pulse sequence shown in Fig. 17 under static condition. The experiments were performed with a H Lee-Goldburg spin-lock RF power of...

A new 3D experiment that allows direct probing of proton spin-diffusion process between resolved proton spectra obtained under Lee-Goldburg homo-nuclear decoupling has been reported. It is anticipated that this class of experiments will soon be used to study poorly crystalline hybrid materials as well as finely divided or porous inorganic materials. 

Fig. 4.6. Spin-diffusion spectrum (or TOSSY spectrum) of uniformly labeled calcium acetate monohydrate. Intramolecular as well as intermolecular cross-peaks are detected. The mixing time in the presence of a RIL mixing sequence with Lee-Goldburg proton decoupling was 20 ms. 512 ti experiments were performed with 16 scans each. Contour levels are shown for constant intervals between 2 and 15% of the maximal signal intensity. The signals marked by a star are assigned to a second crystal form present as a contamination. (Figure adapted from Ref. [2]).

Using Lee—Goldburg based decoupling methods, a FWHMH of 150—170 Hz has been reported for the aliphatic resonances in L-alanine [106] this is demonstrated in Fig. 9.22c, where, for comparison, the (a) static and (b) MAS (vk = 30 kHz) spectra are also shown. Lesage et al. have further shown that the frontiers of high-resolution H solid-state NMR can be pushed back yet further using the constant-time (CT) GRAMPS experiment [106] a FWHMH as low as 60 Hz can be obtained for the aliphatic resonances in L-alanine (see Fig. 9.22d). 

Thin-film amorphous hydrogenated boron carbide (BxC Hy) from an orthocarborane precursor was studied by solid state NMR. Using Lee-Goldburg cross-polarization and heteronuclear recoupling experiments are used to confirm atomic connectivities which allowed a model to be proposed for this. 

V. Ladizhansky, S. Vega, Polarization transfer dynamics in Lee-Goldburg cross polarization nuclear magnetic resonance experiments on rotating sohds, J. Chem. Phys. 112 (2000) 7158-7168. 

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