Dynamic nuclear polarization enhancement of ¹³C in glucose using electrical discharge induced radicals as polarizing agents

The creation of radicals via electrical discharge is a unique approach capable of facilitating dynamic nuclear polarization (DNP) in solids without the need to co-dissolve them with exogenous polarization agents. This method has previously been shown to generate high proton polarization in a variety of organic and inorganic solid compounds. In this work, we extend the scope of applicability for these so-called electrical discharge-induced radicals (EDIRs), by showing their use in DNP of ¹³C nuclei of glucose. We achieved significant NMR signal enhancement in low temperature solid-state DNP experiments. This enhancement was further improved by the use of a frequency modulated microwave pump instead of conventional DNP with single-frequency microwaves. We demonstrated successful dissolution DNP experiments with such hyperpolarized solid glucose, achieving ¹³C polarization levels of up to ∼0.6% in the resulting solution (∼0.95% at the exit of the polarizer). This is to be compared with the ∼6% polarization levels achieved with a trityl radical mixed with glucose in a frozen aqueous solution using the same DNP setup and experimental conditions. It is concluded that the use of EDIRs can serve as a suitable polarizing approach for metabolic MRI using glucose, avoiding the need to employ diluted solutions and eliminating the filtration stage of the polarizing agents.