Proton-enhanced NMR of dilute spins in solids

Abstract

The NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled. The gain. in power sensitivity as compared with conventional observation of the rare spins approaches N/ (I + l)'Y/IN s S (S + I}'Y/, or '" 10 3 for S = 13C, 1= IH in organic solids. The transfer of polarization is accomplished by any of a number of double resonance methods. High-frequency resolution of the S-spin signal is obtained by decoupling of the abundant spins. The experimental requirements of the technique are discussed and a brief comparison of its sensitivity with other procedures is made. Representative applications and experimental results are mentioned.

Orientational order of Australian spider silks as determined by solid‐state NMR

“…Proton ramp CP 35 was used for 13 C and 15 N excitation. The 50 kHz 1 H excitation pulse was followed by 1 ms Hartmann-Hahn match and 40 kHz TPPM proton decoupling was applied during acquisition.…”

Uniform-sign cross-peak double-quantum-filtered correlation spectroscopy

“…The refocusing delay s is set to an integral number of rotor periods to rigorously refocus the chemical shift interaction, and maximum signal intensity is obtained in 2-spin systems for s ¼ 1=4J IS . Although shown with a p=2 preparation pulse, cross-polarization [36] is appropriate in many cases. Pure phase spectra can be obtained using the method of States [37].…”

SIMPSON: A general simulation program for solid-state NMR spectroscopy

“…This may be the case for desired as well as undesired terms of the Hamiltonian implying that accurate determination of structural parameters from the desired terms as well as evaluation of the multiple-pulse building blocks providing suppression of undesired terms very often depend on the ability to numerically simulate the spin dynamics of the actual NMR experiment. This applies, for example, to the solid-state NMR experiments for which dipolar recoupling (e.g, rotational resonance [16,17], REDOR [18], DRAMA [19], DRAWS [20], RFDR [21], RIL [22], HORROR [23], BABA [24], C7 [25,26], RF-DRCP [27]), multiple-pulse homo-or heteronuclear decoupling (e.g., BR-24 [28], FSLG [29], MSHOT-3 [30], TPPM [31]), cross-polarization [32,33], QCPMG-MAS [34], or MQ-MAS [35] pulse sequences are indispensable building blocks. Thus, considering the very large number of advanced experiments already available, the large number of possible combinations between these, and the rapidly increasing number of new experimental procedures presented every year there is a substantial need for a general and consistent simulation tool to support experiment design, user-specific method implementation, and evaluation of spectral data.…”