Radio-frequency Driven Dipolar Recoupling (RFDR) is an NMR technique that has been developed to measure couplings between 13C nuclei in the solid state. The goal of this and related techniques to observe and quantify dipolar couplings is to provide a foundation for structural connectivity studies of proteins. Based on observed couplings between nuclei, it is possible to infer local structure and to quantify distances since the dipolar coupling has a strong dependence on internuclear distance. It would be advantageous to apply this technique to 1H nuclei since they have a higher gyro-magnetic ratio. The consequently stronger couplings would be easier to observe and measure. Thus, we have initiated studies in this direction. Unfortunately, the high natural abundance of 1H nuclei makes it difficult to obtain high-quality highly resolved 1H spectra in the solid-state. The large and abundant dipole couplings broaden the spectra. To counteract this problem we use spin dilution of 1H by 2H(deuterium). With sufficient dilution, well-resolved spectra are observed. Combining these two techniques, we have demonstrated in a model peptide the feasability of observing dipolar coupling and magnetization exchange via RFDR between 1H nuclei. We believe this technique may prove to be of great advantage in the structural studies of peptides not amenable to study via crystallography or solution NMR.
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