Crystal Engineering in Nanoporous Matrices

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Titel: Crystal Engineering in Nanoporous Matrices
Autor(en): Graubner, Gitte
Erstgutachter: Prof. Dr. Martin Steinhart
Zweitgutachter: Prof. Dr. Mario Beiner
Zusammenfassung: As former studies reveal, the nanoporous confinement could have influence on polymorphic drug crystallization. However, little attention has been paid to the question how crystallization of the commonly polymorphic drugs in nanoporous matrices influences the drug release. As a consequence, sufficient information about the crystallization conditions and their influence on phase behavior, crystal texture, and stability of polymorphs should be retrieved prior to drug delivery experiments. Drug release should be polymorph-selective and even crystal face-specific. Therefore, the topic of this PhD thesis is the systematic investigation of crystallization parameters (e.g., pore morphology, thermal history, presence or absence of a bulk surface reservoir) and their influence on the nucleation and crystal growth of the two selected model compounds in nanoporous matrices: acetaminophen (ACE) and n-tetracosane. Both are confined to two host-systems: AAO containing aligned cylindrical, isolated pores and CPG containing curved, interconnected pores. The guest materials inside the two model matrices have been investigated with X-ray diffraction (WAXS) and differential scanning calorimetry. In the first part it is shown that the nanopore morphology of the host systems determines into which polymorphic form ACE crystallizes. Moreover, the pore morphology influences the kinetics of solid/solid transitions. In AAO uniformly oriented form III crystals are converted into also uniformly oriented form II crystals by a solid/solid transition. Such a phase transition is kinetically suppressed in CPG membranes due to the curved pore morphology. In the second step, polymorph-specific release experiments with ACE from AAO membranes reveal that the drug dissolution is not exclusively diffusion-limited and can be described by the Korsmeyer-Peppas model. Dissolution of crystalline ACE having rough crystal faces exposed to the environment is nearly as fast as release of amorphous ACE. Encapsulating of ACE in AAO nanopores with a PLLA polymer retard the drug dissolution but does not modify the release kinetics. In the third part of this thesis crystallization of n-tetracosane, a saturated hydrocarbon, in nanoporous matrices was studied. n-Tetracosane shows inside AAO membranes the rotator phase sequence: triclinic−RV−RI−RII−liquid. Further, the long axes of the n-tetracosane molecules are oriented normal to the AAO pore axes. In general, n-tetracosane under confinement shows a more complex phase behavior than the polymeric analogue polyethylene. The presented work expands the available strategies for mesoscopic crystal engineering. The methods might be transferred into other areas of interest such as polymorphism screening or preparation of different types of nanowires with customized optoelectronic or ferroelectric properties.
Schlagworte: acetaminophen; cylindrical nanopores; release kinetic; crystal orientation; n-tetracosane; X-ray diffraction; polymorphic drug; crystallization
Erscheinungsdatum: 12-Feb-2015
Enthalten in den Sammlungen:FB05 - E-Dissertationen

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