Mismatched Hartmann-Hahn Conditions Cause Proton-Mediated Intermolecular Magnetization Transfer between Dilute Low-Spin Nuclei in NMR of Static Solids

摘要

Since the discovery of cross polarization (CP), magnetization transfer under the Hartmann-Harm matching conditions remains the most popular means of both enhancing the sensitivity of dilute spins (e.g., ~(15)N and ~(13)C) and probing their interactions with the surrounding protons in NMR of biological solids. The proton network can also be used to probe the couplings between dilute spins themselves. For instance, proton-driven spin diffusion represents a means of using the proton bath to induce the spin flips between chemically different dilute spin sites. While the dilute spin exchange experirnent can be successfully applied in static solids to induce the correlations between spins separated by less than 3.5 A, the mixing times to correlate more distant spins would become longer than 10 s, which would also result in additional loss in sensitivity due to relaxation.