Multiple-quantum relaxation in the magic-angle-spinning NMR of [formula omitted] spin pairs

Abstract

We determine the decay rate constants of zero-, double- and single-quantum coherence for 13 C spin pairs in magic-angle-spinning solid-state NMR. The double-quantum coherence is excited by a C7 pulse sequence and converted into zero-quantum coherence by a frequency-selective pair of π/2 pulses. The zero-quantum coherence is reconverted into observable magnetization by a second pair of π/2 pulses followed by a second C7 sequence. In a magnetically dilute system where the 13 C– 13 C distance is 0.296 nm, the relaxation rate constants are consistent with a model of uncorrelated random fields at the two labeled 13 C sites. In a fully-labelled system with a short 13 C– 13 C distance of 0.153 nm, the measured rate constants are inconsistent with the uncorrelated random field model.