Photopolymerization is considered an attractive alternative in many industries to traditional polymerization processes. The advantages of photopolymerization over other types of polymerization include elimination of heat sources, faster cure times, and reduction in the use of volatile organic solvents. Despite these environmental and cost-saving advantages, photopolymerizations have several limitations. Light attenuation can be a problem for systems containing pigments or fillers. The radiation source penetrates only to a shallow depth beneath the surface, limiting the thickness of strongly pigmented or filled coatings and films. Photopolymerization is also generally limited to systems with simple geometries that can be uniformly illuminated. Coatings on three-dimensional substrates, or other systems with complex geometries, are difficult to uniformly cure. These problems can be solved by "shadow cure," which is defined as the reactive diffusion of photoinitiated active centers into regions of a polymer that are unilluminated. In this contribution, the generation and subsequent spatial and temporal evolution of the active center concentrations during illumination are analyzed using the differential equations that govern the light intensity gradient and photoinitiator concentration gradient for polychromatic illumination. Reactive diffusion of the active centers during the post-illumination period is shown to result in cure of unilluminated regions. A kinetic analysis is performed by coupling the active center concentration profiles with the propagation rate equation, yielding predicted cure times for a variety of applications. This analysis is used for the evaluation of cationic shadow cure in pigmented photopolymerization systems, and systems with complex geometries. The extensive characterization of cationic systems is then applied to free-radical photopolymerization to examine the potential of shadow cure for active centers with much shorter lifetimes. An example of a free-radical photopolymerization system is characterized in which the dimensional scales are small enough to utilize the short lifetimes of the active centers. The results presented for both free-radical and cationic shadow cure indicate that the reactive diffusion of photoinitiated active centers may be used for effective cure in unilluminated regions of a photopolymer. This research will potentially allow photopolymerization to be applied in industries where it has never before been utilized.

xiv, 82 p., ill. (some col.) / Cellular processes are carried out by proteins, which often utilize conformational changes for function. In theory, conformational changes can be harnessed to promote, prevent or monitor cellular processes. Such changes in protein active centers require perturbations through interactions with other proteins, small molecules or through energy input into the system, for example light. The work presented incorporates rational design and crystallographic elucidation of two-state conformational changes in two proteins, green fluorescent protein (GFP) and malate synthase (MS). GFP indicators were previously developed to quantitate the thiol/disulfide redox status within cells. Cysteine residues were introduced in close proximity on the surface of GFP and allow the formation of a disulfide bond. The indicators provide a fluorescent readout of the ambient thiol/disulfide equilibrium, however thermodynamic studies showed the resulting thiol/disulfide to be unusually stable (-287 mV) in comparison to the cellular redox buffer glutathione (-240 mV). In order to produce a family of redox indicators suitable for use in less reducing environments, amino acids were inserted near the introduced cysteine pair in order to destabilize the disulfide. The resulting family of redox indicators, termed roGFP-iX, exhibit midpoint potentials in the more desirable range of -229 to -246 mV. Crystallographic analysis indicates that roGFP-iX indicators undergo much larger two-state conformational changes than the original indicators. Surprisingly, a cis-peptide was discovered between the cysteine and the inserted residue which in combination with the conformational changes helps to explain the reduced stability of the disulfide. Malate synthase is an important virulence factor for certain microbes and carries out the Claisen condensation between glyoxylate and acctyl-CoA to produce malate. Crystal structures of Mycobacterium tuberculosis and Escherichia coli malate synthase isoform G had previously been determined with substrates or products bound. To determine the conformational changes necessary for substrate binding and product release, crystal structures of Escherichia coli malate synthase isoform A were determined in both the apo and acetyl-CoA/inhibitor bound forms. The crystallographic models revealed two-state conformational changes in the part of the active-site loop necessary for substrate binding, which has important implications for drug design. This dissertation includes my unpublished co-authored materials. / Adviser: S. James Remington

<p dir="ltr">The field of nanoclusters includes a broad range of sizes and structures that influence both their physical and chemical properties. Scientists use several techniques, such as atom-by-atom substitution, to synthesize atomically precise nanoclusters, and ligand shell mixing to protect nanoclusters from unwanted side reactions, while controlling their reactivity and solubility. These combined techniques can provide stable products, but isomers and structural analogs often remain in the product mixture, complicating the structural characterization of individual nanoclusters. Leading structural characterization techniques in nanocluster research are often limited in their ability to examine both the structure of the metal core and ligand shell in sufficient detail. The primary aim of this research is to systematically characterize the structures and chemical properties of several types of transition metal oxide nanoclusters of interest to applications in energy production, catalysis, and magnetic resonance imaging, without requiring purification. Specifically, this work focuses on 1) Polyoxovanadates (POV) with a mixture of methoxy, ethoxy, and ether ligands, 2) Fe- and W-substituted POV alkoxides, and 3) Octanuclear iron oxide clusters substituted with In atoms. Mass spectrometry techniques enable the structural characterization of individual clusters from multicomponent mixtures without interference. Specifically, we use ion mobility spectrometry to explore how surface ligands affect the metal core in mixed-ligand POV alkoxide species. We examine structure-specific fragments to identify the positions of ligands and heteroatoms within the metal core of mixed-ligand species and W and Fe-substituted POV methoxides. Additionally, we use ion soft-landing to purify W-substituted POV methoxide anions on surfaces for characterization using cyclic voltammetry and infrared spectroscopy. We discovered unique characteristics of each nanocluster including the position of heteroatoms, ligands shell mobilities, structures and collisional cross sections, and provided first insights into the redox properties of W-substituted POV alkoxide. These results highlight the growing influence of mass spectrometry in the field of nanocluster characterization and design.</p>