High-order multiple quantum excitation in 13C nuclear magnetic resonance spectroscopy of organic solids

Excitation and detection of high-order multiple quantum (MQ) coherences among ${}^{13}\mathrm{C}$ nuclear spins in singly-${}^{\mathrm{13}}\mathrm{C}$ -labeled organic solids is demonstrated experimentally. MQ signals involving at least ten quanta of spin angular momentum are observed in nuclear magnetic resonance (NMR) measurements on polycrystalline L-methionine-methyl-${}^{13}\mathrm{C}$ and L-alanine-${\text{1-}}^{13}\mathrm{C},$ using a time-reversible multiple pulse excitation sequence modified specifically for experiments on systems with weak homonuclear dipole–dipole couplings and strong inhomogeneous interactions such as anisotropic chemical shifts. The feasibility of high-order MQ excitation and detection in ${}^{\mathrm{13}}\mathrm{C}$ -labeled organic solids promises to expand significantly the range of applications of MQ NMR as a structural tool, to include such systems as ${}^{\mathrm{13}}\mathrm{C}$ -labeled synthetic polymers and biopolymers.