Improved decoupling during symmetry-based C9-TOBSY sequences

Spin diffusion type polarization transfer among heteronuclei e.g. 13C or 15N plays an important role in many solid state NMR experiments for structure determination of proteins. In such experiments chemical shift compensation is provided by the proton bath (‘proton driven’) which can be improved by radio frequency irradiation of the protons. Here we address the problem that the polarization transfer rates depend not only on the intermolecular distance but also on the chemical shift difference of the two spins. We introduce rf modulation schemes that allow eliminating the chemical shift dependence to a large extent over a predefined range. At the same time the rate constants are maximized.