CRAMPS Combined Rotational and Multiple

CRAMPS combined rotation and multiple pulse spectroscopy... 

In general, multiple pulse techniques sufficiently average the dipolar interactions, compress the chemical shift scale, but they do not affect heteronuclear dipolar interactions and the chemical shift anisotropy. A combination of both multiple pulse techniques and magic angle spinning, so-called CRAMPS (Combined Rotational And Multiple Pulse Spectroscopy) is found to yield satisfactory results in the solid state H NMR of solids 186). The limitations of all these techniques, from the analytical point of view, arises from the relatively small chemical shift range (about 10 ppm) as compared with some other frequently studied nuclei. However, high resolution H NMR of solids is useful in studies of molecular dynamics. 

Besides 29Si-NMR, that distinguishes between siloxane bridges, single and double silanols, especially H-NMR-CRAMPS (Combined Rotation and Multiple Pulse Spectroscopy) is a very powerful tool. This technique allows to differentiate the Si-OH and (after hydrolysis) the Ti-OH species, yielding thereby useful information on the structure of the surface groups3. Due to spectral overlap, this distinction is very difficult to observe by infrared spectroscopy. 

CRAMPS Combined Rotation and Multiple Pulse Spectroscopy... 

MAS is normally applied concurrently with the dipole line-narrowing methods in order to eliminate the effects of CSA and provide true high resolution NMR spectra in the solid phase. For heteronuclear systems the combined method is usually referred to by the initials CP-MAS, and for homonuclear systems the acronym CRAMPS (combined rotation and multiple pulse spectroscopy) has been coined. 

In order to obtain optimum line narrowing and improved sensitivity in a solid-state NMR spectrum of a zeolitic material, the experimental techniques discussed in this chapter may be applied in combination, as, e.g., CP/MAS, DD/MAS, CP/DOR or CRAMPS (Combined rotation and multiple pulse spectroscopy). The rotor synchronization technique provides... 

Although NMR is probably the most widely used NMR technique in chemical applications, it has only been used sparingly in studies of humic substances. Much of the literature in which this technique is used was published prior to 1987 and is well covered in the review by Wilson.(5) Use of NMR is mostly limited to solutions, and it is thus necessary to dissolve humic substances in aqueous solutions. Of course, one must reduce the amount of H s from solvent molecules by use of deuterated water, but it is often difficult to reduce these background signals to negligible amounts. Wilson(5) described the application of water suppression techniques which have been necessary to obtain H NMR spectra of humic isolates from soil. In the case of solid-state NMR of whole soils and humic substances, the development of a new technique called CRAMPS (combined rotation and multiple pulse spectroscopy) has not received the attention it has in the field of coal science, primarily because of the lack of resolution. Thus, recent applications of either solution or solids NMR has been very limited in humic substance science since Wilson s(5) review. 

Another method to remove the anisotropy of spin interactions and to obtain high resolution spectra of solids is by multiple-pulse sequences. The combination of multiple-pulse sequences and MAS (CRAMPS combined rotational and multiple-pulse spectroscopy) is used to obtain highly resolved proton spectra. 

---