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Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) has enabled promising applications in spectroscopy and imaging, but remains poorly widespread due to experimental complexity. Broad democratization of dDNP could be realized by remote preparation and distribution of hyperpolarized samples from dedicated facilities. Here we show the synthesis of hyperpolarizing polymers (HYPOPs) that can generate radical- and contaminant-free hyperpolarized samples within minutes with lifetimes exceeding hours in the solid state. HYPOPs feature tunable macroporous porosity, with porous volumes up to 80% and concentration of nitroxide radicals grafted in the bulk matrix up to 285 μmol g −1 . Analytes can be efficiently impregnated as aqueous/alcoholic solutions and hyperpolarized up to P ( 13 C) = 25% within 8 min, through the combination of 1 H spin diffusion and 1 H →  13 C cross polarization. Solutions of 13 C-analytes of biological interest hyperpolarized in HYPOPs display a very long solid-state 13 C relaxation times of 5.7 h at 3.8 K, thus prefiguring transportation over long distances. Hyperpolarization by dissolution dynamic nuclear polarization has brought highly sensitive magnetic resonance to reality but there still remains severe limitations. Here the authors show an approach relying on the generation of hyperpolarizing polymers that bear a dual function.

Magnetic resonance imaging and spectroscopy often suffer from a low intrinsic sensitivity, which can in some cases be circumvented by the use of hyperpolarization techniques. Dissolution-dynamic nuclear polarization offers a way of hyperpolarizing 13C spins in small molecules, enhancing their sensitivity by up to 4 orders of magnitude. This is usually performed by direct 13C polarization, which is straightforward but often takes more than an hour. Alternatively, indirect1H polarization followed by 1H→13C polarization transfer can be implemented, which is more efficient and faster but is technically very challenging and hardly implemented in practice. Here we propose to remove the main roadblocks of the 1H→13C polarization transfer process by using alternative schemes with the following: (i) less rf (radiofrequency) power; (ii) less overall rf energy; (iii) simple rf-pulse shapes; and (iv) no synchronized 1H and13C rf irradiation. An experimental demonstration of such a simple1H→13C polarization transfer technique is presented for the case of [1-13C]sodium acetate, and is compared with the most sophisticated cross-polarization schemes. A polarization transfer efficiency of ∼0.43 with respect to cross-polarization was realized, which resulted in a 13C polarization of ∼8.7 % after∼10 min of microwave irradiation and a single polarization transfer step.

Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) has enabled promising applications in spectroscopy and imaging, but remains poorly widespread due to experimental complexity. Broad democratization of dDNP could be realized by remote preparation and distribution of hyperpolarized samples from dedicated facilities. Here we show the synthesis of hyperpolarizing polymers (HYPOPs) that can generate radical- and contaminant-free hyperpolarized samples within minutes with lifetimes exceeding hours in the solid state. HYPOPs feature tunable macroporous porosity, with porous volumes up to 80% and concentration of nitroxide radicals grafted in the bulk matrix up to 285 μmol g ⁻¹ . Analytes can be efficiently impregnated as aqueous/alcoholic solutions and hyperpolarized up to P( ¹³ C) = 25% within 8 min, through the combination of¹ H spin diffusion and¹ H →¹³ C cross polarization. Solutions of¹³ C-analytes of biological interest hyperpolarized in HYPOPs display a very long solid-state¹³ C relaxation times of 5.7 h at 3.8 K, thus prefiguring transportation over long distances.

Dissolution dynamic nuclear polarization (dDNP) is a method of choice for preparing hyperpolarized 13C metabolites such as [1-13C]-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 of13C spins reaching polarizations of >50% in ~1-2 hours. Alternatively, 1H spins are polarized before transferring their polarization to 13C spins using cross-polarization (CP), reaching similar polarization levels as direct DNP in only ~20 min. However, it relies on more complex instrumentation, requiring highly skilled personnel. Here, we explore an alternative route using 1H dDNP followed by an inline adiabatic magnetic field inversion in the liquid state during the transfer. 1H 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 1H→13C 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 anti-level crossing. We report liquid-state 13C polarization up to ~17% for [3-13C]-pyruvate and 13C-formate. The instrumentation needed to perform this experiment in addition to a conventional dDNP polarizer is simple and readily assembled.

Magnetic resonance imaging and spectroscopy often suffer from a low intrinsic sensitivity, which can in some cases be circumvented by the use of hyperpolarization techniques. Dissolution-dynamic nuclear polarization offers a way of hyperpolarizing 13C spins in small molecules, enhancing their sensitivity by up to 4 orders of magnitude. This is usually performed by direct 13C polarization, which is straightforward but often takes more than an hour. Alternatively, indirect 1H polarization followed by 1H→13C polarization transfer can be implemented, which is more efficient and faster but is technically very challenging and hardly implemented in practice. Here we propose to remove the main roadblocks of the 1H→13C polarization transfer process by using alternative schemes with the following: (i) less rf (radiofrequency) power; (ii) less overall rf energy; (iii) simple rf-pulse shapes; and (iv) no synchronized 1H and 13C rf irradiation. An experimental demonstration of such a simple 1H→13C polarization transfer technique is presented for the case of [1-13C]sodium acetate, and is compared with the most sophisticated cross-polarization schemes. A polarization transfer efficiency of ∼0.43 with respect to cross-polarization was realized, which resulted in a 13C polarization of ∼8.7 % after ∼10 min of microwave irradiation and a single polarization transfer step.