Intermolecular interactions in hydrates of 4-methylpiperidine and 4-chloropiperidine – a structural and computational study

The highest hydrates of 4-methylpiperidine and 4-chloropiperidine are trihydrates, which are very similar but not isostructural and contain water layers of the L4(6)5(7)6(8) type.

t-Butanol Enables Dual Functionality of Mannitol: A Cryoprotectant in Frozen Systems and Bulking Agent in Freeze-Dried Formulations

The effect of tertiary butyl alcohol (TBA) as a cosolvent on the phase behavior of mannitol in frozen and freeze-dried systems was characterized using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD; laboratory and synchrotron sources). Solutions of mannitol (2 and 5% w/w) in TBA-water systems of different compositions (5 to 30% w/w TBA) were characterized, both during cooling and warming using DSC and XRD. At and below the TBA-water eutectic composition (22.5% w/w TBA), mannitol crystallization was completely inhibited in the frozen state, while it crystallized as anhydrous δ-mannitol in the final lyophile. The presence of mannitol did not affect the phase behavior of TBA. The ability of mannitol to serve as a cryoprotectant in frozen solutions, and as a bulking agent in final lyophile was evaluated using human serum albumin (HSA) as a model protein. When HSA in a TBA (5% w/w)-water solution containing mannitol (2% w/w) was freeze-thawed or freeze-dried, there was no evidence of HSA aggregation. Thus, when TBA was used as a cosolvent, mannitol exhibited dual functionality, serving as a cryoprotectant in frozen solutions and as a bulking agent in the final lyophile.

Deciphering the hydrogen-bonding scheme in the crystal structure of triphenylmethanol: a tribute to George Ferguson and co-workers

The crystal structure of triphenylmethanol, C19H16O, has been redetermined using data collected at 295 and 153 K, and is compared to the model published by Ferguson et al. over 25 years ago [Ferguson et al. (1992). Acta Cryst. C48, 1272-1275] and that published by Serrano-González et al., using neutron and X-ray diffraction data [Serrano-González et al. (1999). J. Phys. Chem. B, 103, 6215-6223]. As predicted by these authors, the hydroxy groups are involved in weak intermolecular hydrogen bonds in the crystal, forming tetrahedral tetramers based on the two independent molecules in the asymmetric unit, one of which is placed on the threefold symmetry axis of the R-3 space group. However, the reliable determination of the hydroxy H-atom positions is difficult to achieve, for two reasons. Firstly, a positional disorder affects the full asymmetric unit, which is split over two sets of positions, with occupancy factors of ca 0.74 and 0.26. Secondly, all hydroxy H atoms are further disordered, either by symmetry, or through a positional disorder in the case of parts placed in general positions. We show that the correct description of the hydrogen-bonding scheme is possible only if diffraction data are collected at low temperature. The prochiral character of the hydrogen-bonded tetrameric supramolecular clusters leads to enantiomorphic three-dimensional graphs in each tetramer. The crystal is thus a racemic mixture of supS and supR motifs, consistent with the centrosymmetric nature of the R-3 space group.

Discrepancy between thermodynamic and kinetic stabilities of thetert-butanol hydrates and its implication for obtaining pharmaceutical powders by freeze-drying

The substitution of sublimed “H1 + Ih” for “H2 + Ih” leads to both a reduction of primary drying time and a significant increase in specific surface area of the trehalose freeze-dried cakes.