The extreme polar morphology that has been observed for crystals of the stable form of a steroid is explained by a molecular dynamics simulations approach. The habit modification is caused by surface-solvent interactions, which affect the growth rate of the polar faces differently. The same effect was observed for the metastable polymorphic form. Depending on the solvent, the nature of the difference is mainly caused by the hydrogen bond interactions or the electrostatic part of the interactions.
We present in-situ observations of the epitaxial nucleation of the metastable polymorph of a steroid
on specific faces of the stable form in different solutions using optical microscopy. The polar morphology of the
crystals allows for the determination of the specific face where the epitaxial nucleation takes place. The observations
prove that there is a different barrier for 2D epitaxial nucleation of the metastable polymorph on the opposite polar
faces. In-situ Raman measurements are used to confirm the structure of the epitaxially growing crystals. The
metastable zone width and the role of the solvent in this process are discussed. The relatively large lifetime of the
metastable polymorph in ethanol solutions is exploited to determine the solubility curves of the bulk phases of both
polymorphs. The relation between the solubility of the two polymorphs in different solvents and the polymorphic
transformation rate is discussed.
This paper investigated the pharmacokinetics and biotransformation of mirtazapine in healthy human volunteers. The results showed that the area under the plasma drug concentration-time curve (AUC) of mirtazapine in human plasma appeared to be three times higher than the AUC of demethylmirtazapine. As mirtazapine is marketed as a racemic mixture and both enantiomers possess pharmacological properties essential for the overall activity of the racemate, the pharmacokinetics of mirtazapine were examined and appeared to be enantioselective. The R(-)-enantiomer showed the longest elimination half-life from plasma. This was ascribed to the preferred formation of a quaternary ammonium glucuronide of the R(-)-enantiomer. This glucuronide may be deconjugated, leading to a further circulation of the parent compound, thus causing a prolongation in the elimination half-life. The S(+)-enantiomer was preferentially metabolised into an 8-hydroxy glucuronide. Other metabolic transformation pathways found for mirtazapine were demethylation and N-oxidation. Mirtazapine was extensively metabolised and almost completely excreted in the urine (over 80%) and faeces within a few days after oral administration.
The reactions of radioactive chlorine atoms recoiling from two nuclear processes, "Cl(n, 2n)"'"a and "Cl(n, 7)"CI have been studied in different liquid halobenzenes. The ratio "Q-for-Cl vs.^'Cl-for-H yield for C^HjCl is dose-dependent, indicative for radiation-enhanced ^' Cl-for-Cl exchange. The Cl-for-Cl replacement yield is lowered on the addition of Ij, but much more for "CI than for It is suggested that the precursors to the exchange is a charge-transfer 7r-complex, rather than a a-complex. The fraction of the * Cl-for-Cl replacement yield not affected by Ij is ascribed to direct hot one-step processes. The behaviour of m-Cj H4 Clj is different to the extent that -as measured for 34 mQ _ thermal exchange seems to take place. Also, isomeric dichlorobenzenes irradiated in a mixture show differences among each other in exchange behaviour. Part of the unidentified products is attributed to an excited jr-complex subject to ring-opening and/or fragmentation. The ""'Cl vs."Cl isotope effect is not due to external radiation and is discussed in terms of differences in the recoil energy distribution and the life-time of lower levels of nuclear excitation.
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