Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of ¹³C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ∼170,000 over thermal equilibrium. The signal of the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. Hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.

Alkali and alkaline earth metals (AAEMs) naturally occurring in most lignocellulosic biomass have strong catalytic reactivity during biomass depolymerization. Considering the fact that only a small amount of AAEMs can dramatically change the thermal pathway of each biomass component, an in-depth understanding of the effect of AAEMs on pyrolysis kinetics is necessary to develop the catalytic and thermal routes for effective lignin depolymerization. This work investigated the pyrolysis kinetics of Na and Mg metal-infused lignin using a distributed activation energy model (DAEM) to analyze experimental pyrolysis data. We also performed computational modeling of lignin decomposition using density functional theory (DFT) and Bader's atoms-in-molecules (AIM) analysis to understand the bond properties and calculate the bond length of the aryl–ether linkage in the lignin model dimer and the stabilized energy level in the presence of Na and Mg. Quantum mechanical calculation allowed us to understand how the metal ions interact at the molecular level with the lignin structure. Along with computational studies, kinetic parameters including the distribution curve of the activation energy, f(E), and the activation energy dependent frequency factor, k₀, were obtained. The peak of the f(E) curve was centered at 180 kJ mol⁻¹ for the control lignin, which increased up to 208 kJ mol⁻¹ with the infusion of Mg but decreased to 145 kJ mol⁻¹ with Na treatment. DFT calculations on lignin model compounds identified the most stable metal–lignin complex, in which metals can bind the O(C_β) and O(methoxy) forming a stable half-sandwich structure. Although Mg has a stronger catalytic effect elongating the dissociating bond, C_β–O, the Mg–lignin complex dramatically reduces the stabilized energy, which brings strong recalcitrance to lignin decomposition. These results provide both kinetic parameter level and molecular level understanding of the effect of AAEMs on lignin pyrolysis, allowing the development of more useful pyrolysis models.

¹²⁹ Xe–cucurbit[6]uril NMR signals were blocked via rotaxanes until chemically activated. This platform is customizable for a broad range of applications.