CDS&E: Combining Nuclear Magnetic Resonance and Neutron Scattering for Determining Macromolecular and Liquid Structure: Towards Development of the Novel NMR-PNS Technique

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Michael Kotlarchyk and colleagues George Thurston, and Pratik Dholabhai at Rochester Institute of Technology are laying the groundwork for development of a powerful next-generation technique to probe structures and dynamics of molecules, molecular assemblies, and solutions. The targeted technique, based on a combination of Nuclear Magnetic Resonance (NMR) and Polarized Neutron Scattering (PNS), has the potential to revolutionize the detailed, molecular-scale information available for a broad variety of materials, including liquid mixtures, catalysts, nanomaterials, and biological macromolecules.

The information to be gained is crucial for predicting and rationalizing many processes of industrial, medical, and societal importance. The PIs are actively engaged in programs seeking to enhance STEM engagement by students from underrepresented groups, for involvement in interdisciplinary state-of-the-art research.

The project focuses on calculational modeling as a foundation for future development of experimental methods. The team is extending the quantum-mechanical density-operator treatment of NMR-PNS to treat spin relaxation, spin coupling, and the incorporation of nuclei with any quantum spin. This will enable the prediction and simulation of PNS cross sections and signal-to-noise ratios for hyperpolarized molecules in solution and for molecules prepared via specialized NMR protocols.

Molecular dynamics simulations of molecules hyperpolarized in solution via Signal Amplification by Reversible Exchange (SABRE) are being undertaken to permit quantitative evaluations of site-site spatial correlations in solution, which are essential for predicting the PNS signal and for a rigorous statistical analysis of PNS signal-to-noise. NMR protocols that apply selective pulse-shaping and sequencing to hyperpolarized molecules will be designed and simulated, thereby enabling use of the correlation functions to evaluate the resulting polarized neutron scattering cross-sections.

Finally, complete statistical analyses of putative NMR-PNS protocols for SABRE-hyperpolarized molecules will be performed. The simulated scattering signals will inform the design of effective NMR-PNS instrumentation and experiments, including sample environment, beamline, and detector parameters. The ultimate aim is to determine structure factors between atomic pairs selected via NMR spin-manipulation, from sub-angstrom to micron length scales, thereby giving valuable information about molecular conformations and relative orientations in solution.

The SABRE-PNS methods to be developed are important stepping-stones toward full NMR-PNS and will be valuable in their own right.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.