Solid-state NMR is a powerful method for the measurement of the structural distribution of insoluble materials such as membrane proteins and amyloid fibrils. In conventional NMR measurements, it is well known that the signal sensitivity due to thermal polarization is very small. Dynamic nuclear polarization (DNP) NMR is a method to enhance the NMR signal intensity by transferring the polarization from the electron spin to the nuclear spin. The organic radicals such as nitroxide radical are widely used in DNP polarizing agents. However, these unpaired electrons are highly chemically reactive. Many DNP polarizing agents are rapidly degraded due to the strongly reducing environment such as in-cell condition.[1] Novel DNP polarizing agents with high reduction resistance are required. Nanometer scale diamond particles have a lot of unpaired electrons derived from surface dangling bond. Some DNP-NMR measurement has been reported that enhanced 13C signal of natural abundance inside diamond and 1H signal of surrounding solvent.[2] These unpaired electrons on nanodiamond are expected to be used as DNP polarizing agent in-cell condition due to their high chemical/physical stability. However, DNP-NMR measurements of biomolecule with nanodiamond-based polarizing agent under magic angle spinning (MAS) condition has not been reported yet.
In this poster presentation, we report on the application of nanodiamond-based polarizing agent for DNP-MAS-NMR on biomolecules such as nanodiamond-conjugated model protein system and amyloid fibril system, to which the nanodiamond is non-covalently attached through a specific molecular interaction. All DNP-MAS-NMR measurements in this study were performed using a home-build closed-circuit helium gas MAS-DNP probe system [3] with a magnetic field of B0 = 16.4 T, MAS νR = 5 kHz, temperature T = 30 K, and a rotor of diameter ϕ = 3.2 mm.