Dipolar Order Mediated <sup>1</sup>H→<sup>13</sup>C Cross-Polarization for Dissolution-Dynamic Nuclear Polarization

Abstract

<p><strong>Abstract.</strong> 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 <sup>13</sup>C spins in small molecules, enhancing their sensitivity by up to four orders of magnitude. This is usually performed by direct <sup>13</sup>C polarization, which is straightforward but often takes more than an hour. Alternatively, indirect <sup>1</sup>H polarization followed by <sup>1</sup>H→<sup>13</sup>C 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 <sup>1</sup>H→<sup>13</sup>C polarization transfer process by using alternative schemes with: (i) less rf-power; (ii) less overall rf-energy; (iii) simple rf-pulse shapes; and (iv) no synchronized <sup>1</sup>H and <sup>13</sup>C rf-irradiation. An experimental demonstration of such a simple <sup>1</sup>H→<sup>13</sup>C polarization transfer technique is presented for the case of [1-<sup>13</sup>C]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 <sup>13</sup>C polarization of ~ 8.7 % after ~ 10 minutes of microwave irradiation and a single polarization transfer step.</p>

A cryogen-free, semi-automated apparatus for bullet-dynamic nuclear polarization with improved resolution

“…The rapid-melt DNP (Sharma et al, 2015) avoids the dissolution altogether and is also readily combined with NMR on a chip (van Meerten et al, 2018;de Vries et al, 2019). The throughput of a DNP polarizer can be increased by parallel polarization of multiple samples (Batel et al, 2012;Cheng et al, 2020) or by employing 1 H DNP in combination with cross-polarization (Jannin et al, 2012) or via adiabatic demagnetization (Jacquinot et al, 1974;Elliott et al, 2020).…”

Boosting Dissolution-Dynamic Nuclear Polarization by Multiple-Step Dipolar Order Mediated 1H->13C Cross-Polarization

“…We have recently demonstrated the use in a DNP context of an alternative rf-pulse sequence to CP which is of low-power, does not require synchronized B1-matched spin-locking rf-fields and can ultimately overcome all previous limitations [22]. In such cases, the transfer of spin polarization is mediated by an intermediary reservoir of nuclear dipolar spin order [23][24][25][26][27][28][29][30][31][32][33], and even though the exact mechanism underlying the polarization transfer is yet to be fully understood, the rf-pulse sequence has consequently been termed dipolar order mediated crosspolarization (dCP).…”