EUROISMAR 2019

Specific Cross-Relaxation Enhancement by Active Motions under DNP (SCREAM-DNP) is a method which relies on direct polarization transfer in solid-state DNP at typical DNP temperatures.^[1] The mechanism is based on cross relaxation between ¹H and ¹³C. It is generated by the internal dynamics of methyl groups resulting in negative enhancement and inverted ¹³C MAS NMR signal in a direct DNP experiment.^[2] Furthermore, this effect can be suppressed by ¹H saturation. Through mathematical subtraction, we can exclusively observe magnetization which was generated by cross relaxation. Therefore, the use of methyl groups as a specific promotor for polarization transfer opens new applications in DNP.
In this work, we show the application of SCREAM-DNP on a tetracycline-binding RNA aptamer. Here, CH₃ groups were introduced into the biomolecular complex by non-covalent interaction between the aptamer and its highly specific ligand. Thereby, we use tetracycline which carries three CH₃-groups as a source of cross-relaxation enhancement for complex formation studies. Moreover, we can influence the reorientation dynamics of methyl groups to a significant degree by changing the temperature, resulting in an increase of cross-relaxation efficiency. In conclusion, SCREAM-DNP is a promising method for different applications, especially in site-specific DNP-studies.
^[1] Aladin et al., Angew. Chem. Int. Ed. 2019, 58, 4863.
^[2] Daube et al., J. Am. Chem. Soc. 2016, 138, 16572.