Triplet dynamic nuclear polarization of pyruvate supramolecular chemistry

Dynamic nuclear polarization (DNP) significantly improves the sensitivity of magnetic resonance imaging, and its most important medical application is cancer diagnosis via hyperpolarized 13 C-labeled pyruvate. Unlike cryogenic DNP, triplet-DNP uses photoexcited triplet electrons under mild conditions. However, triplet-DNP of pyruvate has not been observed because of incompatibility of the hydrophobic polarizing agent with hydrophilic pyruvate. This work demonstrates that supramolecular complexation with β-cyclodextrin can disperse 4,4′-(pentacene-6,13-diyl)dibenzoate (NaPDBA), a pentacene derivative with hydrophilic substituents, even in the presence of high sodium pyruvate concentrations. The polarization of photoexcited triplet electron spins in NaPDBA was transferred to the 13 C spins of sodium pyruvate via triplet-DNP of 1 H spins in water and 1 H-to- 13 C cross-polarization. This provides an important step toward the widespread use of ultra-sensitive MRI for cancer diagnosis. Formation of supramolecular complexes with cyclodextrins improves the dispersibility of pentacene derivatives in polar matrices, resulting in the first triplet dynamic nuclear polarization of an important bioprobe, pyruvate.