Recoupling of Heteronuclear Dipolar Interactions with Rotational-Echo Double-Resonance at High Magic-Angle Spinning Frequencies
✍ Scribed by Christopher P Jaroniec; Brett A Tounge; Chad M Rienstra; Judith Herzfeld; Robert G Griffin
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 120 KB
- Volume
- 146
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Heteronuclear dipolar recoupling with rotational-echo doubleresonance (REDOR) is investigated in the rapid magic-angle spinning regime, where radiofrequency irradiation occupies a significant fraction of the rotor period (10 -60%). We demonstrate, in two model 13 C-15 N spin systems, [1-13 C, 15 N] and [2-13 C, 15 N]glycine, that REDOR ⌬S/S 0 curves acquired at high MAS rates and relatively low recoupling fields are nearly identical to the ⌬S/S 0 curve expected for REDOR with ideal ␦-function pulses. The only noticeable effect of the finite pulse length on the recoupling is a minor scaling of the dipolar oscillation frequency. Experimental results are explained using both numerical calculations and average Hamiltonian theory, which is used to derive analytical expressions for evolution under REDOR recoupling sequences with different pulse phasing schemes. For xy-4 and extensions thereof, finite pulses scale only the dipolar oscillation frequency by a well-defined factor. For other phasing schemes (e.g., xx-4 and xx -4) both the frequency and amplitude of the oscillation are expected to change.