Salnikov, Evgeniy Sergeevich, Fabien Aussenac, Sebastian Abel, Armin Purea, Paul Tordo, Olivier Ouari, and Burkhard Bechinger. “Dynamic Nuclear Polarization / Solid-State NMR of Membranes. Thermal Effects and Sample Geometry.” Solid State Nuclear Magnetic Resonance 100 (August 2019): 70–76.
https://doi.org/10.1016/j.ssnmr.2019.03.004.
Whereas specially designed dinitroxide biradicals, reconstitution protocols, oriented sample geometries and NMR probes have helped to much increase the DNP enhancement factors of membrane samples they still lag considerably behind those obtained from glasses made of protein solutions. Here we show that not only the MAS rotor material but also the distribution of the membrane samples within the NMR rotor have a pronounced effect on the DNP efficiency. These observations are rationalized with the cooling efficiency and the internal properties of the sample, monitored by their T1 relaxation, microwave on versus off signal intensities and DNP enhancement. The data are suggestive that for membranes the speed of cooling has a pronounced effect on membrane phase transitions and concomitantly the distribution of biradicals within the sample.