Nuclear magnetic resonance second-order spectra

We present a solid-state nuclear magnetic resonance (NMR) experiment that allows the observation of a high-resolution two-dimensional heteronuclear correlation (2D HETCOR) spectrum between aluminum and phosphorous in aluminophosphate molecular sieve VPI-5. The experiment uses multiple quantum magic angle spinning (MQMAS) spectroscopy to remove the second order quadrupolar broadening in Al nuclei. The magnetization is then transferred to spin-1/2 nuclei of P via cross polarization (CP) to produce for the first time isotropic resolution in both dimensions. 

Figure 9 (A) Typical line shape of an observed quadrupolar nucleus S, showing the second-order quadrupole shift AcTqs, and the relative position of the centre-of-gravity with respect to the isotropic chemical shift ajso- (B) Al solid-state MAS NMR spectrum of Sr8(AI02)i2-Se2 at 78.15 MHz (7.05 T). Asterisks denote sidebands. Reproduced with permission of Elsevier Science Publishers from Weller MT, Brenchley ME, Apperley DC and Davies NA (1994) Correlations between aI magic-angle spinning nuclear magnetic resonance spectra and the coordination geometry of framework alumlnates. Solid State Nuclear Magnetic Resonance Z 103-106.

The nuclear Overhauser effect is used to measure distances between nuclei. It is a relaxation effect that, like a chemical reaction, is incoherent in nature as opposed to the scalar coupling that is coherent and is detected as a frequency splitting of resonances in the spectrum. Relaxation can be best viewed at as the flow of population between different states as it would occur in a chemical reaction where one molecule is transformed, e.g., by a reaction of zero-order into a second molecule. The same is true for the NOE where magnetization of spin A by a zero-order reaction is transferred to mag-... 

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