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X-ray Diffraction and Solid-State NMR Investigation of the Single-Crystal to Single-Crystal Dehydration of Thiamine Hydrochloride Monohydrate
journal contribution
posted on 2003-08-15, 00:00 authored by Ruth L. Te, Ulrich J. Griesser, Kenneth R. Morris, Stephen R. Byrn, Joseph G. StowellThe dehydration of a thiamine hydrochloride (vitamin B1) hydrate, commonly referred to as the
monohydrate, was investigated by solid-state NMR (SSNMR) and X-ray diffraction (XRD) techniques. The hydrate
can be classified as a nonstoichiometric solvate since the water content depends on the water vapor pressure of the
surrounding atmosphere and essentially maintains the three-dimensional molecular arrangement upon dehydration.
Thus, we were able to determine the crystal structures of both the hydrate and the isomorphic desolvate with one
single crystal. The loss of water leads to a shrinkage of the unit cell volume of about 5% and to a slight increase in
the free volume. This is also accompanied by an increase in molecular motion as is demonstrated by SSNMR 1H and
13C T1 measurements. The largest change in T1 was observed for the carbons of the hydroxyethyl functional group
that is hydrogen bonded to the water molecules in the hydrate. This investigation confirms that an increase in free
volume results in an increase in molecular mobility and demonstrates the impact of molecular interactions on the
mobility of specific molecular entities.