Three trityl-OX063 samples-(1) 10 mM trityl in the glycerol-d8:D2O:H2O :: 6:3:1 glassing matrix, (2) 20 mM trityl in glycerol-d8:D2O:H2O :: 6:3:1, and (3) 10 mM trityl in glycerol-d8:H2O :: 6:4were prepared for the DNP experiments. All the samples were thoroughly degassed by storing the matrix material inside fluorinated ethylene propylene (FEP) vials in an argon atmosphere inside a glove box for more than a week. During the storage period, FEP allows oxygen molecules to diffuse out of the solutions through the FEP tubes, while remaining impermeable to liquids such as glycerol and water. In addition, the samples were transferred inside FEP tubes (3 mm OD, 2 mm ID, 30 mm long, ̴ 70 µL volume) and sealed by welding the tube to itself inside of the glove box in order to minimize oxygen contamination. The long nuclear 𝑇 $. at 70K reported below confirms that the samples were well degassed.