Magic angle-spinning spectra

Figure 8 500 MHz H NMR magic angle spinning spectra of prostatic tissue from humans with malignant prostate cancer sampled by transurethral radical prostatectomy (TURP) (A), or needle biopsies (B, C) contrasted with that of a benign prostatic hyperplasia (BPH) patient sampled via radical prostatectomy (D). Spectrum (C) is different, as the needle has sampled a different region of the prostate. The spectrum of the prostate tissue from the BPH patient (D) displays higher levels of citrate but lower lipid levels relative to spectra (A) and (C) from the malignant cancer patients. (See Tomlins AM, Foxall PJD, Lindon JC, Lynch MJ, Spraul M, Everett JR, and Nicholson JK (1998). Analytical Communications 35 113-115).

Modem solid-state NMR involves the use of very short radio-frequency pulses (of variable duration from 1 to 200 ms) and can be complemented with real-time Fourier transform analysis and multiple scan capability. Standard NMR enhancements nowadays, such as scalar (low power, ca. 4 kHz) and dipolar (about 45 kHz) decoupling, magic angle spinning, spectra of multiple elemental isotopes beyond... 

Fig. 7 Magic Angle Spinning spectra of Cd(CN)2.QHi2 (top), Cd(CN)2 (middle), and Cd(CN)2.2/3H20.Bu 0H (bottom) at 39.93 MHz [41,45] a=CdC4, b=CdC N, c=CdC2N2 d=CdCN3, e=CdN4, and g=Cd02N4 (octahedral). Spinning sidebands are indicated by asterisks.

Harris RK and Olivieri AC (1992) Quadrupole effects transferred to spin- magic-angle spinning spectra of solids. Progress in Nuclear Magnetic Resonance Spectroscopy 24 435—456. 

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 18. 31P-NMR spectrum of polycrystalline phosphorus pentachloride with magic angle spinning. The two lines arise from the differently shielded PClf and PCl6 ions of which the solid is composed.

Figure 8.3 Illustration of HR-MAS techniques applied to a resin-bound trisaccharide (a) static XH spectrum of the solvent swollen sample (b) XH spectrum with magic-angle spinning at 3.5 kHz (c) H spectrum with MAS and spin echo pulse sequence.

Figure 1. Three stages of resolution in a C-I3 spectrum of a cured epoxy. The top spectrum is obtained under conditions appropriate to a liquid-state spectrometer no dipolar decoupling and no magic angle spinning. Dipolar decoupling at 60 kHz is used for the middle spectrum and to that is added magic angle rotation at 2.2 kHz for the bottom figure.

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.

Figure 2. 50.33 MHz 13C NMR spectrum of lime cutin, obtained with cross polarization (contact time 1.5 ms, repetition rate 1.0 s), magic-angle spinning (5.0 kHz), and dipolar decoupling (762/211 = 48 kHz). This spectrum was the result of 6000 accumulations and was processed with a digital line broadening of 20 Hz. Chemical-shift assignments are summarized in Table I. Reproduced from Ref. 7 of the American Chemical Society.

Solid-state C variable-amplitude cross polarization magic-angle spinning (VACP/MAS) nuclear magnetic resonance (NMR) spectra were acquired for the sorbitol samples. Proton decoupling was achieved by a two-pulse phase modulation (TPPM) sequence. Identical C spectra were measured for the y-form sorbitol samples, and a representative spectrum is shown in Figure 9. 

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