C] Pyruvic Acid*

Increasing the concentration of 13C nuclei in a sample is frequently used in dynamic nuclear polarization (DNP) to raise the resulting nuclear magnetic resonance (NMR) signal. However, the exact relation between polarization and concentration does not seem to be currently known. In order to make some progress in this area, this study looked at the effect of altering the 13C concentration upon the 13C hyperpolarization and spin-lattice relaxation time of [1-13C] pyruvic acid, doped with 15 mM trityl OX063, at 3.35 T and 1.2 K. It was determined that both the 13C polarization and the 13C spin-lattice relaxation time roughly obeyed an inverse exponential equation: both increased asymptotically for sufficiently low concentrations of 13C nuclei. These two observations were discussed in light of spin diffusion and dipole-dipole interactions.