High resolution NMR in randomly oriented solids with homonuclear dipolar broadening: Combined multiple pulse NMR and magic angle spinning

Abstract

The first combined multiple pulse-magic angle experiment is reported in which both homonuclear dipole interactions and chemical shift anisotropies are removed to resolve chemically shifted fluorines. The sample selected was KEL-F.(AIP)

Directly and indirectly detected through-bond heteronuclear correlation solid-state NMR spectroscopy under fast MAS

“…Traditionally, high-resolution 1 H experiments were performed by combining rotation and multiple-pulse sequences (CRAMPS) operated under the quasi-static condition s c << s R , where s c = (m c ) À1 describes the cycle time of the pulse sequence which should be short compared to s R = (m R ) À1 , and it is assumed that m c exceeds the strength of the homogeneous broadening to be removed [15,16]. The development of high-field magnets and probes capable of MAS at rates of up to 25 kHz (now regarded as moderate) was followed by the implementation of modified CRAMPS strategies, as thoroughly reviewed by Vega et al [17].…”

Indirectly detected through-bond chemical shift correlation NMR spectroscopy in solids under fast MAS: Studies of organic–inorganic hybrid materials

“…Recent reports have shown the major advantages of using fast MAS in the study of organic-inorganic mesoporous materials [3,4]. Most importantly, MAS at 40 kHz provided a simple and artifact-free way of achieving high 1 H resolution in these materials without the use of multiple-pulse radiofrequency (RF) irradiation and stroboscopic observation (CRAMPS [5]) [3]. Excellent sensitivity per spin, lack of spinning sidebands and the possibility of using low-power decoupling schemes [6] have enabled convenient acquisition of highly resolved 2D 13 C{ 1 H} and 29 Si{ 1 H} heteronuclear correlation (HETCOR) NMR spectra.…”

Enhanced resolution in proton solid-state NMR with very-fast MAS experiments

“…Multi-pulse spin-space narrowing is effective in averaging homo-nuclear dipolar interactions, but does not average broadening resulting from chemical shift anisotropy (CSA % 10-15 ppm). An obvious remedy is to apply the last two strategies simultaneously, which leads to the combined rotation and multiple pulse spectroscopy (CRAMPS) [4]. Almost all CRAMPS sequences use a quasi-static approximation, in which low spinning frequencies (m R = 2-5 kHz) ensure an approximately static sample on the cycle time (s c ) of the rf pulse sequence [5-9].…”