High-pressure polymorphism in amino acids

Abstract

Pressure up to 10 GPa is a powerful method for studying polymorphism in organic crystal structures, and this review surveys work carried out on high-pressure polymorphism in amino acids. High-pressure polymorphs have been established crystallographically for glycine, alanine, serine, cysteine and leucine. Phase transitions can be driven by the avoidance of very short intermolecular contacts or by promotion of a more stable molecular conformation. Experimental methods are also briefly surveyed, along with three methods that have proved very helpful in the analysis of high-pressure polymorphs, namely the PIXEL method for calculation of intermolecular energies, topological analysis with Voronoi–Dirichlet partitioning and Hirshfeld surfaces for gaining a graphical overview of intermolecular interactions.

Keywords:

• high-pressure
• polymorphism
• amino acids

Acknowledgements

Our work on amino acids has developed over the course of some eight years, and would not have been possible without the insight, support and encouragement of numerous colleagues. In particular, we would like to thank David Allan (Diamond), Alice Dawson, Patricia Lozano-Casal, Francesca Fabbiani, Russell Johnstone, Konstantin Kamenev, Carole Morrison, Iain Oswald, Colin Pulham, Lindsay Sawyer and Peter Tasker (all University of Edinburgh). Beyond Edinburgh we have collaborated closely with Vladislav Blatov (Samara), Stewart Clark (Durham), Graeme Day (Cambridge), Angelo Gavezzotti (Milan), Sam Motherwell, Elna Pidcock (both CCDC), Josh McKinnon and Mark Spackman (Western Australia). It is also a pleasure to acknowledge our valuable collaborations with instrument scientists John Warren and Alistair Lennie at Daresbury Laboratory and Bill Marshall at ISIS, and software developers David Watkin and Richard Cooper [CRYSTALS ( 128 )], Alan Coehlo [TOPAS-Academic ( 187 )] and Michael Ruf (Bruker-Nonius software). We also thank Dr Javier Sanchez-Benitez and Mr Somchai Tancharakorn for their help with some of the figures. Finally we thank The University of Edinburgh, EPSRC, CCDC and CCRLC/STFC for funding, and the referees of this review for their helpful comments.

Subject Index

• absorption correction 151

• α-alanine 164

• β-alanine 164, 172

• L-asparagine monohydrate 172

• beryllium 147, 148

• beryllium-free DACs 148

• boehler--Almax 148

• coordination sequence 154, 163

• L-cysteine 152, 164, 166, 167, 172, 173

• data processing 150

• data reduction 150

• diamond anvil cell (DAC) 147

• dipeptides 173

• fingerprint plot 158, 170, 171

• glycine 164, 173, 174

• α-glycine 164, 165, 173

• β-glycine 164

• γ-glycine 164

• δ-glycine 164

• ε-glycine 164, 172

• glycine: Phase nomenclature 164

• glycyl-glycine 173

• Hirshfeld surface 143, 153, 155, 156, 157, 158, 170, 175

• hydrostatic media 149, 152

• integration 150

• intermolecular energy 153

• L-leucine 170, 171, 173

• Paris-Edinburgh cell 152

• PIXEL method 143, 153, 169

• powder diffraction 146, 152, 162, 164, 167, 169, 172, 173

• pressure measurement 149

• ruby fluorescence 149

• DL-serine 172, 173

• L-serine 152, 168, 169, 170, 171, 172, 173

• single crystal diffraction 149, 170, 171, 172, 173, 174, 175

• synchrotron 150, 152

• L-threonine 172, 173

• topology 153, 154, 163, 164

• DL-valine 146, 172, 173

• Voronoi-Dirichlet polyhedra 154