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

A new 13C–13C recoupling mechanism which occurs under magic-angle spinning (MAS) is presented. The mechanism can basically be attributed to rotational resonance (R2), but the conventional R2 condition is modified by a recoupled 13C–1H dipolar interaction. The 13C–1H recoupling is attained by 1H rf irradiation fulfilling a rotary-resonance condition. The present method does not have the drawbacks associated with rf irradiation on 13C and is applicable for band-selective recoupling between carbonyl/aromatic carbons and aliphatic carbons. The 13C–13C recoupling mechanism under 13C–1H recoupling is theoretically explained and is experimentally demonstrated using N-acetyl[1,2-13C] dl-valine and uniformly 13C, 15N-labeled glycylisoleucine.