Hyperpolarization of Long-Lived States of Protons in Aliphatic Chains by Bullet Dynamic Nuclear Polarization, Revealed on the Fly by Spin-Lock-Induced Crossing.

It is shown that proton spins highly polarized by dynamic nuclear polarization (DNP) retain substantial polarization upon the rapid transfer of frozen bullets from a polarizer to an NMR spectrometer. After injection in solution, the resulting hyperpolarization in aliphatic chains comprises population imbalances between singlet and triplet states of geminal protons and combinations thereof. These hyperpolarized long-lived states (LLSs) can be reconverted into observable transverse magnetization by polychromatic spin-lock-induced crossing (poly-SLIC). This reconversion can be achieved simultaneously in several molecules. Consecutive partial reconversion steps can be carried out to determine the lifetimes on the fly in a single experiment. The enhancement factors of hyperpolarized LLS-derived signals in our experiments are at least 2 orders of magnitude. These methods extend applications of bullet-DNP to protons in molecules containing short aliphatic chains and may be useful for drug screening.