Do solid-to-solid polymorphic transitions in DL-norleucine proceed through nucleation?

JA van den Ende and MMH Smets and DT de Jong and SJT Brugman and B Ensing and PT Tinnemans and H Meekes and HM Cuppen, FARADAY DISCUSSIONS, 179, 421-436 (2015).

DOI: 10.1039/c4fd00214h

DL-Norleucine is a molecular crystal exhibiting two enantiotropic phase transitions. The high temperature alpha <-> gamma transition has been shown to proceed through nucleation and growth Mnyukh et al., J. Phys. Chem. Solids, 1975, 36, 127. We focus on the low temperature beta <-> alpha a transition in a combined computational and experimental study. The temperature dependence of the structural and energetic properties of both polymorphic forms is nearly identical. Molecular dynamics simulations and nudged elastic band calculations of the transition process itself, suggest that the transition is governed by cooperative movements of bilayers over relatively large energy barriers.

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