Hybrid Polarizing Solids with Extended Pore Diameters for Dissolution Dynamic Nuclear Polarization

Abstract

Dissolution dynamic nuclear polarization (dDNP) has emerged as a powerful technique to address the inherent sensitivity limitations in nuclear magnetic resonance imaging and spectroscopy. The technique relies on the use of stable paramagnetic polarizing agents that act as a source of hyperpolarization but unfortunately, their presence contaminates the sample and significantly enhances paramagnetic relaxation of the hyperpolarized solutions. In the last decade, novel sample formulations have been proposed to combat this issue, including silica-based hybrid polarizing solids (HYPSO), which have enabled the production of contamination-free hyperpolarization. Herein, a new generation of polarizing solids with pore diameters increased from 4 up to 28 nm is presented. Compared to the previously described HYPSOs with smaller pore sizes of 4 nm, larger pores ultimately achieve the ambitious contradictory goals of 1) providing rapid and high solid-state polarization and improving cross-polarization efficiency, while 2) decreasing hyperpolarization losses upon melting, transfer, and filtration, and 3) reducing the overall concentration of the polarizing agent by a factor of 2. These HYPSO materials can be used in virtually any existing dDNP settings without modification, apart from the sole addition of an in-line commercial filter to retain the HYPSO powder upon dissolution and transfer.