High pressure strongly
favors the highest-density polymorph Z of
active pharmaceutical ingredient 2-(2,6-xylidino)-5,6-dihydro-4H-1,3-thiazine hydrochloride (xylazine hydrochloride, XylHCl)
up to about 0.1 GPa only, but still higher pressure destabilizes this
structure. Above 0.1 GPa, XylHCl preferentially crystallizes as solvates
with CH2Cl2, CHCl3, or (CH3)2CHOH depending on the solvent used. However, when XylHCl·H2O is dissolved in any of these solvents, the high-pressure
crystallizations yield the hydrate XylHCl·H2O only.
The single crystals of the CH2Cl2, CHCl3, and (CH3)2CHOH solvates could be grown
in situ in a diamond anvil cell, which allowed their structure determination
from the single-crystal diffraction data. At 0.4 GPa the XylHCl·H2O hydrate undergoes a pressure-induced phase transition doubling
the unit cell dimensions.
Cyclodextrin (CD) has been used to prepare biocompatible and nontoxic metal-organic frameworks (MOFs) suitable for biomedical applications as drug carriers. In this study, γ-CD/K-based MOF (γ-CD-MOF-1-α) was synthesized and its stability in various solvents was explored by single-crystal X-ray diffractometry (SCXRD) and powder X-ray diffractometry (PXRD). As a result of solvent-induced phase transformations, two novel crystalline phases of γ-CD-MOF-1 were discovered. The newly formed ε- and δ-phases crystallize in orthorhombic and tetragonal symmetry, respectively. In ε-phase, toluene was determined as a guest molecule by SCXRD. Interactions between γ-cyclodextrin and solvent molecules in ε-phase were evaluated using Hirshfeld surface analysis. The thermal stability of the new crystal forms of γ-CD-MOF-1 was analyzed by differential scanning calorimetry and thermogravimetric analysis.
In this work, the hydration of Xylazine hydrochloride polymorphic forms A, Z and M was monitored by gravimetry. A solid state kinetic model of hydration was defined, and rate constants were calculated for different temperatures and humidity conditions. Activation energy values were obtained from the Arrhenius plots of the rate constants in the coordinates ln k -T -1 .
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