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    Polymorph Prediction of Organic (Co-) Crystal Structures From a Thermodynamic Perspective.

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    Stephen Chan Thesis final submission.pdf (5.911Mb)
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    Publication date
    2013-05-02
    Author
    Chan, Hin Chung Stephen
    Supervisor
    Leusen, Frank J.J.
    Kendrick, John
    Keyword
    Density Functional Theory
    Computational chemistry
    Force field
    Crystal structure prediction
    Polymorph
    Crystal lattice energy
    Co-crystal structures
    Aspirin derivatives
    Rights
    Creative Commons License
    The University of Bradford theses are licenced under a Creative Commons Licence.
    Institution
    University of Bradford
    Department
    School of Life Sciences
    Awarded
    2012
    
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    Abstract
    A molecule can crystallise in more than one crystal structure, a common phenomenon in organic compounds known as polymorphism. Different polymorphic forms may have significantly different physical properties, and a reliable prediction would be beneficial to the pharmaceutical industry. However, crystal structure prediction (CSP) based on the knowledge of the chemical structure had long been considered impossible. Previous failures of some CSP attempts led to speculation that the thermodynamic calculations in CSP methodologies failed to predict the kinetically favoured structures. Similarly, regarding the stabilities of co-crystals relative to their pure components, the results from lattice energy calculations and full CSP studies were inconclusive. In this thesis, these problems are addressed using the state-of-the-art CSP methodology implemented in the GRACE software. Firstly, it is shown that the low-energy predicted structures of four organic molecules, which have previously been considered difficult for CSP, correspond to their experimental structures. The possible outcomes of crystallisation can be reliably predicted by sufficiently accurate thermodynamic calculations. Then, the polymorphism of 5- chloroaspirin is investigated theoretically. The order of polymorph stability is predicted correctly and the isostructural relationships between a number of predicted structures and the experimental structures of other aspirin derivatives are established. Regarding the stabilities of co-crystals, 99 out of 102 co-crystals and salts of nicotinamide, isonicotinamide and picolinamide reported in the Cambridge Structural Database (CSD) are found to be more stable than their corresponding co-formers. Finally, full CSP studies of two co-crystal systems are conducted to explain why the co-crystals are not easily obtained experimentally.
    URI
    http://hdl.handle.net/10454/5530
    Type
    Thesis
    Qualification name
    PhD
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    Theses

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