MEASUREMENT OF INTERNUCLEAR DISTANCES BY SWITCHED ANGLE SPINNING NMR

Dipolar switched angle spinning, an NMR technique due to Terao et al. [Terao, T.; Miura H.; Saika, A, J. Chem. Phys. 1986, 85, 3816], has be en used to measure C-13-C-13 distances in the solid state. The experim ent involves rotation of the sample at two different angles during dif ferent periods of a two-dimensional experiment. An evolution period wi th off-magic-angle spinning and chemical shift refocusing, followed by detection of the signal under magic angle spinning, yields scaled Pak e patterns in omega(1), correlated with their isotropic shifts in omeg a(2) allowing the high-resolution measurement of dipolar couplings. We demonstrate this experiment on samples of doubly C-13 labeled zinc ac etate and a 14 amino acid peptide, in which we show that under optimal conditions distances of up to 5 Angstrom may be measured.