HETERONUCLEAR MAGNETIZATION-TRANSFER IN RAPIDLY SPINNING SOLIDS

A new multi-pulse sequence is presented for heteronuclear magnetization transfer in solid-state NMR spectroscopy by isotropic mixing in samples undergoing fast magic angle spinning (MAS) at speeds exceeding the breadth of the static spectrum. The sequence has been designed by considering the behaviour of the lowest-order contribution to the average Hamiltonian resulting from a series of short radio-frequency pulses applied at specific times relative to the sample rotation period, an approximation which proves reasonable for the systems studied here at MAS speeds of about 15 kHz. Experiments show that the sequence enables magnetization transfer from protons to carbon-13 by reintroducing a heteronuclear dipolar coupling interaction at spinning speeds where the efficiency of conventional Hartmann-Hahn cross polarization becomes significantly reduced.