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Title: Solubility and phase behaviour of selected pharmaceutical excipients in 2h, 3h-perfluoropentane
Author: Cote, Marie
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2008
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The behaviour of pharmaceutical excipients was studied in 2H, 3H-perfluoropentane (HPFP), a partially fluorinated liquid considered as a highly suitable model propellant for medicinal pressurized metered-dose inhalers (pMDIs) used in drug delivery to the lungs. The additives chosen belonged to three main categories: ethylene oxide oligomers and derivatives, chosen for their wide range of applications in pharmaceutical formulations, their harmlessness and low cost a hydrophobically modified cyclodextrin that shows potential for controlled release via host-guest interactions and some interesting solubility pattern in HPFP a family of tetrahydroxy diesters that act as unprecedented organogelators for mixtures of HPFP and a partially fluorinated alcohol co-solvent. By studying ethylene oxide oligomers and derivatives in HPFP and fully fluorinated analogue PFP, it was found that the solubility of the oligomers could be tuned by varying the nature of their end-group and the polarity of the fluorinated liquids employed. Methyl groups, either placed at the extremities, thus blocking the hydroxyl end-groups of dihydroxyl end-capped polyethylene glycols, or directly added on the polymer backbone, clearly enhanced their solubility. The Lower Critical Solution Temperature initially observed was either displaced or removed via the presence of the additional methyl groups. On the other hand, such phase separation could also be induced by the subsequent addition of PFP it is shown that such behaviours are dominated by end-group/solvent interactions. This study was published in two papers, Journal of Pharmacy and Pharmacology, 2008, 60: p. 593-599 and International Journal of Pharmaceutics, 2008, 362: p. 147-152. As an attractive formulation means, the hydrophobic triacetylated-P-cyclodextrin (TAjJCD) was chosen amongst others for its partial solubility in model propellant HPFP. The observation that various batches of the same chemical entity lead to highly different solubility profiles in HPFP resulted in the full characterisation of two existing polymorphs for this compound. The monitored conversion of one form into the other was achieved, and the amorphous form could be fully recrystallysed into the higher energy form via a limited seeding process. HPFP acted as a discriminator of the two crystalline forms. More details may be found in Journal of Physical Chemistry C, 2008,112: p. 14570-15578. The monitoring of the solubility via solvent properties, as seen in the first part, was also used in the formation of self-assembled supramolecular organogels. The addition of non-solvent HPFP to an initially stable sol composed of a small tetrahydroxy diesters in the fluoroalcohol 1H, 1H-heptafluorobutanol initiated their coming out of solution. However, instead of simply precipitating, the tetrahydroxy diester molecules self-assemble into long cylindrical fibres that form a 3-dimensional network capable of entrapping the fluorinated liquids, leading to a system that is both solid-like macroscopically and liquid-like microscopically. Such gels are thermoreversible and can be obtained at gelator concentrations as low as 0.1 wt%, thus, surface tension and capillary action are thought to be the principal forces behind these structures, along with hydrogen-bonding between the gelators molecules, rather than a specific gelator-solvent interaction. This work is the reference for both Chemical Communications, 2005,31: p. 3998-4000 and a manuscript to be submitted.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available