Examination of stress-induced transformations within multicomponent pharmaceutical crystals
University of Cambridge
Doctor of Philosophy (PhD)
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Schneider Rauber, G. (2018). Examination of stress-induced transformations within multicomponent pharmaceutical crystals (Doctoral thesis). https://doi.org/10.17863/CAM.30357
Crystal engineering has advanced the strategies of design and synthesis of organic solids with the main focus being on improving the properties of the developed materials. Research in this area has a significant impact on large-scale manufacturing as industrial processes may give rise, at various stages, to stress-induced transformations and product modification. This thesis investigates the solid-state properties at play in the case of the surface and structural reorganization which results from the stress within a crystal during the drying of labile multicomponent organic solids. Chapter 1 introduces various concepts in solid-state chemistry and explores their application in the manufacture of solid pharmaceuticals. The significance of stress-induced transformations during the drying process is illustrated by reactions associated with crystal decomposition processes such as dehydration, desolvation and sublimation. The chapter also introduces carbamazepine (CBZ) multicomponent materials as models for the studies of stress-induced transformations. Chapter 2 presents the experimental section of the work and describes the materials, methods and equipment used for the study. Chapter 3 presents the analysis of the various crystal structures of CBZ. The crystal forms are classified with an emphasis on a comparison of intermolecular interactions, coformer arrangement, crystal packing and the geometric parameters of slip/cleavage planes within the crystals. Chapter 4 details the experimental methods for preparation of the samples. Cooling solution crystallization was the standard method which has been selected, and crystal habit and surface variations have been studied as a function of the solution concentration and the crystallization environment. Attention is given, in particular, to the preparation of carbamazepine dihydrate and the specific cocrystals carbamazepine cocrystals formed with benzoquinone and oxalic acid. Chapter 5 is devoted to the dehydration of carbamazepine dihydrate for samples prepared and examined in approximate 1-gram laboratory scale quantities. It explores the effect of vacuum, temperature, humidity and seeding on the surface and bulk properties of the products. Chapter 6 presents the solid-state characterization results obtained for samples crystallized at a much larger scale (ca. kilogram quantities) with a particular emphasis placed on their mechanical properties. It explores the comparison of large scaled batches with laboratory scale samples in order to obtain a greater understanding of how small-scale laboratory studies may be extrapolated to more commercial processes. Chapter 7 present results on the stress-induced transformations of carbamazepine solvates and cocrystals. It details the effect of thermal decomposition on the surface and bulk properties of the products, possible seeding effects, and the interconversion between carbamazepine dihydrate and carbamazepine benzoquinone cocrystal. Chapter 8 combines the research findings concerning the structural analyses of the materials in the context of current literature. Limitations related to the use of carbamazepine as a model and to the experimental set-up are also explored. In the final chapter conclusions are presented which correlate observations made on the crystallization and decomposition of multicomponent materials operating at small-scale to effects appropriate to manufacturing of pharmaceuticals at large scale.
Stress-induced transformations, Multicomponent pharmaceutical materials, Carbamazepine, Dehydration, Desolvation, Drying, Particle breakage
CAPES - Coordenação de Aperfeiçoamento de Nível Superior (Science Without Borders Program, Brazil, CsF BEX 9530/13-4), COT - Cambridge Overseas Trust (United Kingdom) and AbbVie Inc. (Chicago, Illinois, USA).
This record's DOI: https://doi.org/10.17863/CAM.30357
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