Research Areas

Structure and dynamics in organic solids 

Solid-state NMR is often an invaluable complement to diffraction-based methods for the characterisation of crystalline solids. This is particularly important for pharmaceutical systems, where the solid forms (polymorphs) and transformations between them must be fully understood. ¹³C NMR spectra readily distinguish between different solid forms, including amorphous forms lacking long-range ordering. We have a strong track record of collaboration with various pharmaceutical companies (e.g. AstraZeneca, GlaxoSmithKline, Sanofi-Aventis) for developing methods for characterising structure and dynamics in molecular organic solids. Current systems of interest include a range of solvate materials, looking in particular at the changes associated with desolvation, using a combination of ¹³C NMR to follow overall structural changes and ²H NMR to probe the solvent and its dynamics.

Structure and dynamics in inorganic systems 

In joint work with the group of Prof. John Evans, we apply solid-state NMR of the study of inorganic framework materials. Characterisation of the structure of these materials by (powder) diffraction techniques alone is difficult, but combining the local information on structure and dynamics from multi-nuclear NMR (e.g. ¹⁷O, ³¹P, ¹⁸³W) with the long-range structural information from diffraction studies, provide a much fuller understanding of these complex materials. Past projects have used ¹⁷O NMR to study the dynamics of oxygen motion in ZrW₂O₈: solid-state NMR is only technique that allows to both quantify the dynamics and identify its chemical nature. We are currently exploring how solid-state NMR, powder XRD and first principles calculations can be fully integrated to solve increasingly complex structural problems.

Molecular dynamics as a bridge between NMR and molecular behaviour 

NMR is a sensitive and versatile technique for investigating dynamics in the solid state, capable of observing motion over a wide range of time scales. But although NMR experiments can measure parameters such as rates and energy barriers, they cannot tell us directly about the physical process involved. Molecular dynamics can help us connect the results from solid-state NMR to the underlying processes. 

Recent developments such as metadynamics, parallel tempering and potential softening have improved the ability of MD to sample rare events that would usually occur on long time scales (> ns). This should also allow us to investigate processes occurring on the timescales that can be typically explored using NMR. 

Theoretical development 

There are some important questions in solid-state NMR that are still unresolved e.g. what resolution can we hope to achieve in ¹H NMR of solids? Very fast sample spinning (spin rates >60 kHz) allows us to obtain a modest resolution from this highly important nucleus. Our understanding of ¹H NMR decoupling in the ¹³C NMR of solids is correspondingly poor. Unfortunately, a corresponding theoretical description is very difficult: the dynamics of multiply interacting magnetic nuclei are complex and often intractable. We are developing novel simulation techniques which allow us to simulate what happens in real solids. We are combining these “first principles” numerical simulation with careful experimentation to address fundamental problems in solid-state NMR.