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Molecules 2017, 22(12), 2238; doi:10.3390/molecules22122238

New Insights into Solid Form Stability and Hydrate Formation: o-Phenanthroline HCl and Neocuproine HCl

1
Institute of Pharmacy, University of Innsbruck, Innrain 52c, 6020 Innsbruck, Austria
2
Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria
*
Author to whom correspondence should be addressed.
Received: 18 November 2017 / Revised: 11 December 2017 / Accepted: 12 December 2017 / Published: 15 December 2017
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Abstract

The moisture- and temperature dependent stabilities and interrelation pathways of the practically relevant solid forms of o-phenanthroline HCl (1) and neocuproine HCl (2) were investigated using thermal analytical techniques (HSM, DSC and TGA) and gravimetric moisture sorption/desorption studies. The experimental stability data were correlated with the structural changes observed upon dehydration and the pairwise interaction and lattice energies calculated. For 1 the monohydrate was identified as the only stable form under conditions of RH typically found during production and storage, but at RH values >80% deliquescence occurs. The second compound, 2, forms an anhydrate and two different hydrates, mono- (2-Hy1) and trihydrate (2-Hy3). The 2-Hy1 structure was solved from SCXRD data and the anhydrate structure derived from a combination of PXRD and CSP. Depending on the environmental conditions (moisture) either 2-Hy1 or 2-Hy3 is the most sable solid form of 2 at RT. The monohydrates 1-Hy1 and 2-Hy1 show a high enthalpic stabilization (≥20 kJ mol−1) relative to the anhydrates. The anhydrates are unstable at ambient conditions and readily transform to the monohydrates even in the presence of traces of moisture. This study demonstrates how the right combination of experiment and theory can unravel the properties and interconversion pathways of solid forms. View Full-Text
Keywords: 1,10-phenanthroline hydrochloride; neocuproine hydrochloride; hydrate; stability; thermal analysis; moisture sorption/desorption analysis; X-ray diffraction; intermolecular energies; crystal structure prediction 1,10-phenanthroline hydrochloride; neocuproine hydrochloride; hydrate; stability; thermal analysis; moisture sorption/desorption analysis; X-ray diffraction; intermolecular energies; crystal structure prediction
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Braun, D.E.; Raabe, K.; Schneeberger, A.; Kahlenberg, V.; Griesser, U.J. New Insights into Solid Form Stability and Hydrate Formation: o-Phenanthroline HCl and Neocuproine HCl. Molecules 2017, 22, 2238.

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