Boosting dissolution-dynamic nuclear polarization by multiple-step dipolar order mediated 1H→13C cross-polarization

Dissolution-dynamic nuclear polarization can be boosted by employing multiple-contact cross-polarization techniques to transfer polarization from 1H to 13C spins. The method is efficient and significantly reduces po-larization build-up times, however, it involves high-power radiofrequency pulses in a superfluid helium envi-ronment which limit its implementation and applicability and prevent a significant scaling-up of the sample size. We propose to overcome this limitation by a stepwise transfer of polarization using a low-energy and low-peak power radiofrequency pulse sequence where the 1H -> 13C polarization transfer is mediated by a dipolar spin order reservoir. An experimental demonstration is presented for [1-13C]sodium acetate. A solid-state 13C polarization of-43.5% was achieved using this method with a build-up time constant of-5.1 minutes, leading to a-27.5% 13C polarization in the liquid-state after sample dissolution. The low-power multiple-step polarization transfer efficiency achieved with respect to the most advanced and highest-power multiple-contact cross-polarization approach was found to be-0.69.