Rapid and Simple 13 C-Hyperpolarization by 1 H Dissolution Dynamic Nuclear Polarization Followed by an Inline Magnetic Field Inversion.

Dissolution dynamic nuclear polarization (dDNP) is a method of choice for preparing hyperpolarized 13 C metabolites such as 1- 13 C-pyruvate used for in vivo applications, including the real-time monitoring of cancer cell metabolism in human patients. The approach consists of transferring the high polarization of electron spins to nuclear spins via microwave irradiation at low temperatures (1.0-1.5 K) and moderate magnetic fields (3.3-7 T). The solid sample is then dissolved and transferred to an NMR spectrometer or MRI scanner for detection in the liquid state. Common dDNP protocols use direct hyperpolarization of 13 C spins reaching polarizations of >50% in ∼1-2 h. Alternatively, 1 H spins are polarized before transferring their polarization to 13 C spins using cross-polarization, reaching polarization levels similar to those of direct DNP in only ∼20 min. However, it relies on more complex instrumentation, requiring highly skilled personnel. Here, we explore an alternative route using 1 H dDNP followed by inline adiabatic magnetic field inversion in the liquid state during the transfer. 1 H polarizations of >70% in the solid state are obtained in ∼5-10 min. As the hyperpolarized sample travels from the dDNP polarizer to the NMR spectrometer, it goes through a field inversion chamber, which causes the 1 H → 13 C polarization transfer. This transfer is made possible by the J -coupling between the heteronuclei, which mixes the Zeeman states at zero-field and causes an antilevel crossing. We report liquid-state 13 C polarization up to ∼17% for 3- 13 C-pyruvate and 13 C-formate. The instrumentation needed to perform this experiment in addition to a conventional dDNP polarizer is simple and readily assembled.