Proton magic angle spinning

H MAS NMR proton magic angle spinning nuclear magnetic resonance (spectroscopy)... 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

Figure 1 Schematic representation of the 13C (or 15N) spin-lattice relaxation times (7"i), spin-spin relaxation (T2), and H spin-lattice relaxation time in the rotating frame (Tlp) for the liquid-like and solid-like domains, as a function of the correlation times of local motions. 13C (or 15N) NMR signals from the solid-like domains undergoing incoherent fluctuation motions with the correlation times of 10 4-10 5 s (indicated by the grey colour) could be lost due to failure of attempted peak-narrowing due to interference of frequency with proton decoupling or magic angle spinning.

Fig. 3 Solid state 31P NMR spectra of fosinopril sodium acquired under single pulse, high-power proton decoupling and various conditions of magic-angle spinning (A) static, (B) 2.5 kHz, (C) 4.0 kHz, (D) 5.0 kHz, and (E) 6.0 kHz. The isotropic chemical shift is designated by an asterisk. (From Ref. 15.)...

In the presence of excess ammonia, the surface complex coexists with its ammonia adduct ](=SiO)2Ta(=NH)(NH2)(NH3)]. NMR studies on the fuUy N-labeled samples have led to unambiguous discrimination between imido, amido and amino resonances of the surface complex and its NH3 adduct, and [=Si- NH2] through the combination of soHd-state magic-angle spinning(MAS), heteronuclear correlation (HETCOR), 2D proton double-quantum (DQ), singlequantum (SQ) correlation, and 2D proton triple quantum (TQ) single quantum... 

Figure 4. The influence of magic angle spinning on the SL cross polarization time constant. In the PlP-cured epoxy the time constant for the nonprotonated carbons increases by about 50% for = 1-3 kHz while those of the protonated carbons are virtually unchanged over this range.

Figure 6. Magic angle spinning, high-power proton decoupling, FT C-13 NMR spectrum of cured, carbon-black-loaded polyisoprene at ambient temperature, FT of normal FID without proton enhancement.

The experimental design was to study both the carbon-13 and proton relaxation as a function of temperature for both polymer and solvent, and to extend these to as high a polymer concentration as the available equipment permitted. Inasmuch as the mechanical properties of polymers can be affected considerably by small amounts of diluents, we would ultimately like to approach the bulk polymer state, where use of strong dipolar decoupling and magic angle spinning are necessary. ... 

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