Opening up the periodic table for solid-state NMR spectroscopy with fast magic angle spinning and proton detection

Abstract

Nuclear Magnetic Resonance (NMR) is a widely used technique to analyze the structure of organic, inorganic and biological molecules. However, NMR suffers from an intrinsically poor sensitivity. In liquid-state NMR, 1H (or proton) detection of low gyromagnetic ratio is a widely used approach to enhance the sensitivity of NMR experiments. In solid-state NMR, rotors containing the analyte are spun at the ‘magic angle’ to average anisotropic nuclear spin interactions that typically broaden NMR spectra and improve sensitivity. Recent technological advancements have permitted fast magic angle spinning greater than 30 kHz in frequency that helps narrow 1H NMR linewidths and enable 1H detection. However, 1H detection in solid-state NMR is mainly limited to common spin-1/2 isotopes such as 13C, 15N, 29Si and 31P. Whereas, over 75% of the periodic table consists of unreceptive nuclei that are under-studied using NMR due to the lack of sensitive approaches. This dissertation demonstrates the development and application of 1H detection techniques for unreceptive nuclei such as half-integer quadrupolar nuclei, low gyromagnetic ratio nuclei and heavy spin-1/2 nuclei that suffer from low sensitivity due to high chemical shift anisotropy. The methods developed here are applied on small organic molecules with implications in pharmaceuticals, inorganic materials and on organometallic compounds that are relevant in catalysis. The improved sensitivity obtained with the techniques proposed here is expected to open up the periodic table and new materials containing these elements for analysis using solid-state NMR.