Diffusion ordered spectroscopy is a powerful technique for investigating the solution phase properties of molecules, and has found particular application in the pseudo-separation of complex mixtures. This separation is hampered by both resonance overlap and accidental similarity of observed diffusion coefficients. Techniques such as multiexponential fitting and numerical inversion has a role to play in these analyses, however, are not straightforward to apply in a robust manner. Recently work by the groups of Calderelli, Hoffman, and Morris, amoungst others, have demonstrated that modification of the solvent system by the use of chromatography stationary phases can improve resolution in the diffusion domain.

We are interested in the applications and development of chromatograhic NMR methods, particularly, in relation to its application to assembling and aggregating systems. Some of our recent work is described below.

Size Exclusion Chromatographic NMR 

Diffusion NMR methods effectly allow separation based on molecular size. Similar outcomes can be achieved using size exclusion or gel permeation chromatographies. We have recently investigated the combination of the two by performing diffusion NMR measurements in the presence of a size exclusion stationary phase. We clearly observe changes in diffusion coefficient for a range of polymer molecular weight reference standards, providing their moleclar weights fall within the fractionation range of the SEC phases. 

We have demonstrated the application of these methods to the aggregating system sunset yellow, observing a partitioning of the aggregates between the pores of the SEC phase and the free solution. We have also shown a link between this partitioning and the pore size. 

More recently, we have investigating applicatios of the SEC-DOSY method to polymer mixtures and other more complex solutions.

Current efforts are focused on understanding the diffusion modification processes involved in in-situ SEC-DOSY experiments.

Key Publications