Spin probe-enhanced NMR to decode surface properties for materials function Seminar

Among the most promising prospect for dynamic nuclear polarization (DNP) is to transform NMR—offering atomistic details, but usually averaged over the entire sample—into a surface-sensitive and selective tool. We suggest that the success of this premise will hinge on two key factors, namely to achieve dramatic NMR signal enhancements and to do so while employing site-selective spin label or localized spin probes to molecular regions or materials domains of interest. Recent innovation in instrument development, mechanistic understanding, experimental design and applications for solid and solution state DNP will be presented. Two types of surfaces will be discussed: biomolecular surfaces interfacing the hydration water network and catalysts surfaces interfacing the solute/solvent.

First, solution-state Overhauser DNP of local hydration water near nitroxide spin label is exploited to extract the translational diffusive correlation time of surface water moving with 10s and 100s of picosecond correlation times, via dramatic and selective enhancement of water within 5-10 Angstrom of the spin label. The key point to be made is that surface water diffusivity reflects on surface properties and whose stability and landscape directly modulates molecular interactions, including adsorption, binding events, protein activation to signaling.

Second, a solid-state DNP instrument at 7 Tesla, powered by a widely tunable (193-201 GHz) solid-state microwave source, via quasi optics transmission, and thus capable of coherent EPR manipulation, will be presented. Crucially, this setup and the operating condition of 4-40 K yields competitive enhancement with generic mono-nitroxide radicals, instead of designer biradicals, offering an unprecedented opportunity to selectively characterize heterogeneous surfaces, as showcased with 27Al DNP of SBA-15 alumino-silicate catalysts. Crucially, the surface property of the catalyst support may be equally critical as the catalyst itself—a major objective that stands a chance to be tackled by surface-sensitive DNP approaches.

All welcome to attend