Harriott Nowell
Single Crystal Diffraction
Harriott Nowell is beamline scientist on the small molecule single crystal diffraction beamline, I19. Her background spans a range of areas within small molecule crystallography, including: crystal structure prediction and the calculation of hypothetical polymorphs, solution of crystal structures from powder diffraction data, and the study of complex systems using single crystal diffraction data. Email: Harriott Nowell
Tel: +44 (0) 1235 778507
Beamline I19: Single Crystal Diffraction
Key Research Interests
Parametric structural studies; structural studies of framework materials; Rietveld refinement and the use of restraints; polymorphism; crystal structure prediction and crystal structure solution from powder diffraction data.
Current Research Interests
I have recently been involved in performing parametric structural studies on single crystal samples, to investigate the benefits of this approach for the efficient study of framework structure under changing environmental parameters. Initial results show promise for allowing detailed understanding of progressive structural changes over a wide and steadily changing temperature range providing the possibility, for example, to study the evolving behaviour of a guest species within a framework. There is interest in optimising the approach for these studies and extending the work to different materials.
Crystal structure solution from powder diffraction data is sometimes necessary when a single crystal of sufficient quality is not available. Peak overlap in a powder diffraction pattern means that information is lost and makes crystal structure solution from powder data less straightforward. A number of studies, including studies of challenging flexible molecules, have allowed the development of approaches to the problem. A restrained Rietveld refinement typically follows crystal structure solution from powder diffraction data in order to achieve the best possible structural model; and my research has involved investigating the use of restraints in the refinement of molecular structures from powder diffraction data.
Crystal structure prediction and the computation of hypothetical molecular crystal structures is a challenging task. It is, however, a challenge in which there is considerable interest. In the pharmaceutical industry, for example, it is important that polymorphism of a drug molecule is understood as early as possible. My research focussed on crystal structure prediction for challenging, flexible, molecules with a range of competing hydrogen bond motifs. One successful project involved a "blind" crystal structure prediction of piracetam; searches were performed using a series of rigid conformers, and the resulting crystal structures were evaluated using the sum of lattice energy and an intramolecular energy penalty to account for the deviation of the conformation from the gas phase optimised conformer. In this case the predicted structure that ranked in first place matched the experimental crystal structure of the novel form IV of piracetam that had been independently solved by an experimental team during the early stages of the theoretical study.
Selected Publications
- "Blind crystal structure prediction of a novel second polymorph of 1-hydroxy-7-azabenzotriazole. ", H. Nowell, C. S. Frampton, J. Waite & S. L. Price, (2006) Acta Crystallogr. B62, 642-650.
- "Validation of a search technique for crystal structure prediction of flexible molecules by application to piracetam.", H. Nowell & S. L. Price, (2005) Acta Crystallogr. B61, 558-568.
- "X-ray and Neutron Powder Diffraction Studies of the Crystal Structure of Vitamin K3", H. Nowell & J. P. Attfield, (2004) New J. Chem. 3, 406-411.
- "The use of restraints in Rietveld refinement of molecular compounds; a case study using the crystal structure determination of tryptamine free base.", Nowell, H., Attfield, J. P. & Cole, J. C. (2002). Acta Crystallogr. B58, 835-840.
- "Methyl group librations in sterically hindered dimethylnaphthalene molecules: neutron diffraction studies of 1, 8-dimethylnaphthalene between 50 and 200K.", Wilson, C. C. & Nowell, H. (2000) New J. Chem. 24, 1063-1066.