General research interests: solid-state NMR spectroscopy
of low-frequency quadrupolar nuclei, halogen bonding,
double-rotation NMR, biomolecular NMR spectroscopy, solid-state
NMR of inorganic and bioinorganic systems, mechanochemistry,
interpretation and quantum chemical calculation of NMR
The long-term goal of our research program is to produce novel and impactful chemical insight into the structure and properties of chemical compounds and materials by furthering our understanding of the connection between these properties and various solid-state nuclear magnetic resonance (SSNMR) observables. More specifically, the information gained through the measurement and computation of chemical shifts (CS), quadrupolar couplings, and J couplings affords direct insight into chemical bonding, molecular and electronic structure, and the crystal structure itself.
A few areas of current interest are outlined briefly below. Please also refer to my ‘publications’ page for additional topics of interest.
1. Solid-State NMR Studies of Halogen Bonds and other
Halogen bonding (RX…YZ) is a non-covalent interaction between an electron donor (Y) and the electrophilic polar region of a halogen X. It is responsible for many novel effects in the structures and properties of diverse systems including supramolecules and biological molecules. We have published a series of articles describing our studies of the halogen bond with multinuclear SSNMR. Historically, NMR has played a key role in the understanding of hydrogen bonding. We are now carrying out the research required to understand the area of halogen bonding and other sigma-hole interactions, such as tetrel bonding, via NMR. Our experimental data are interpreted using DFT approaches and revealed a unified NMR description of halogen bonds and hydrogen bonds.
2. 2. Novel Effects and Applications in the Solid-State NMR Spectroscopy of Quadrupolar Nuclei
Standard interpretation of NMR spectra of quadrupolar nuclei (spin > 1/2), which comprise 70 % of all elements, relies on second-order perturbation theory. We discovered in 127I and 185/187Re NMR spectra higher-order quadrupolar effects which affect the interpretation of the spectra. We also demonstrated experimentally that J coupling can be observed between magnetically equivalent quadrupolar nuclei. This has provided a new and unambiguous probe of crystal structure and symmetry. This discovery has also provided a novel window into the electronic structure and reactivity of compounds featuring quadrupolar spin pairs. We are currently applying these methods to study metal-organic frameworks as well as the nature of metal-metal bonding in solids.
3. NMR Crystallography and Polymorphism
NMR crystallography employs NMR data to refine or solve crystal structures. This hot area of research has been focussed on the interpretation of 1H and 13C chemical shifts. Our contributions have recognized that the majority of the elements in materials are quadrupolar, and that special experimental and analytical methods are required to use their NMR spectra to their full potential. We have developed a sophisticated experimental/computational protocol whereby structural models of solids are refined jointly against experimental quadrupolar couplings and a DFT-optimized energy term. The models are then further cross-validated against experimental chemical shifts. Related work on the structures of pharmaceuticals, polymorphs, and solvates has generated interest from the pharmaceutical industry. We are currently exploring novel methods to identify and detect polymorphs via in-situ NMR.