Dehydration mechanism of a small molecular solid: 5-nitrouracil hydrate

Okoth, Maurice O., Vrcelj, Ranko M., Sheen, David B. and Sherwood, John N. (2013) Dehydration mechanism of a small molecular solid: 5-nitrouracil hydrate. CrystEngComm, 15 (40). p. 8202. ISSN 1466-8033

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Previous studies of the dehydration of 5-nitrouracil (5NU) have resulted in it being classified as a ‘‘channel
hydrate’’ in which dehydration proceeds principally by the exit of the water molecules along channels in
the structure. We have re-examined this proposal and found that in fact there are no continuous channels
in the 5NU structure that would contribute to such a mechanism. Product water molecules would be
immediately trapped in unlinked voids in the crystal structure and would require some additional
mechanism to break loose from the crystal. Through a detailed structural analysis of the macro and micro
structure of the 5NU as it dehydrates, we have developed a model for the dehydration process based on
the observed development of structural defects in the 5NU crystal and the basic crystallography of the
material. The model was tested against standard kinetic measurements and found to present a satisfactory
account of kinetic observations, thus defining the mechanism. Overall, the study shows the necessity of
complementing standard kinetic studies with a parallel macro and micro examination of the dehydrating
material when evaluating the mechanisms of dehydration and decomposition processes.

Keywords:Dehydration, 5-Nitrouracil
Subjects:F Physical Sciences > F190 Chemistry not elsewhere classified
F Physical Sciences > F151 Pharmaceutical Chemistry
F Physical Sciences > F130 Structural Chemistry
Divisions:College of Science > School of Pharmacy
ID Code:16730
Deposited On:18 Feb 2015 14:35

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