C-13-H-1 dipolar-assisted rotational resonance in magic-angle spinning NMR

A new C-13-C-13 recoupling mechanism which occurs under magic-angle spinnin g (MAS) is presented. The mechanism can basically be attributed to rotation al resonance (R-2), but the conventional R-2 condition is modified by a rec oupled C-13-H-1 dipolar interaction. The C-13-H-1 recoupling is attained by H-1 rf irradiation fulfilling a rotary-resonance condition. The present me thod does not have the drawbacks associated with rf irradiation on C-13 and is applicable for band-selective recoupling between carbonyl/aromatic carb ons and aliphatic carbons. The C-13-C-13 recoupling mechanism under C-13-H- 1 recoupling is theoretically explained and is experimentally demonstrated using N-acetyl[1,2-C-13] DL-valine and uniformly C-13, N-15-labeled glycyli soleucine. (C) 2001 Elsevier Science B.V. All rights reserved.