Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Dissertation (Ph.D.)--Auburn University, / Abstract. Vita. Includes bibliographic references.

Thesis (Ph. D.)--Syracuse University, 2007. / "Publication number: AAT 3295517."

Thesis (Ph. D.)--University of Oregon, 1999. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 303-350). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9955917.

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 144-157).

Thesis (Ph.D. in Biochemistry, Biomolecular Structure Program) -- University of Colorado Denver, 2007. / Typescript. Includes bibliographical references (leaves 135-146). Online version available via ProQuest Digital Dissertations.

The conformational energy differences have been determined for ethylene glycol, 2- chloroethanol, and 2,2- dichloroethanol in the neat liquid, DMSO, and H20 with Raman spectroscopy. Spectra in the 0-H valence region were utilized to determine the energy difference between interand intramolecularly hydrogen bonded species. It was found that the solvent effect on the relative stabilities of the gauche and trans rotamers of the alcohols differ significantly. The results also indicate that, unlike ethylene glycol, there is significant intramolecular hydrogen bond formation in the halogenated alcohols in the neat liquid phase. Stronger intramolecular hydrogen bond formation was observed in dichloroethanol than in 2-chloroethanol.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeröy / A family of six β-diketone based ligands capable of simultaneously acting as halogen-bond (XB) donors (each of para and meta substituted chloro, bromo and iodo functionalities) and chelating ligands was synthesized. Four ligands were characterized by X-ray diffraction to identify the structural behavior of the ligand itself. The free ligands bearing bromine and iodine show XB interactions (C-X···O) whereas the ligand containing chlorine did not show XB interactions. The corresponding Cu(II) complexes for ligands were also synthesized in different solvents such as acetonitrile, ethyl acetate and nitromethane. Both acetonitrile and ethyl acetate participate in XB interactions with XB donors (Br or I) although nitromethane does not participate in such interaction. Metal-ligand complexes with iodine as XB donor in the para position engage in XB interactions to make extended supramolecular architecture when the solvent is nitromethane. When the XB donor attached in the meta position of the ligand, formation of extended supramolecular architecture was seen even in the presence of a strongly coordinating solvent such as acetonitrile. Two tetra functionalized molecules bearing hydrogen-bond (HB) donors (-OH) and XB donors (-C≡C-I) and one tetra functionalized molecule which has only HB donors (-OH and -C≡C-H) were synthesized. The donor molecules themselves show potential for making HB and XB interactions with the available acceptor sites present in the system. The competition between intermolecular HB and XB was explored by co-crystallizing with suitable nitrogen based acceptors. HB and XB donors showed equal competitiveness toward common acceptors when making HB/ XB interactions. Furthermore, the geometry and relative positioning of the donor sites can, in certain cases, change the balance between the competing interactions by favoring HB interactions. A series of cavitands functionalized with XB donors, HB/XB donors and β-diketone have been synthesized. Binding preferences of XB and HB/XB cavitands towards a series of suitable HB/XB acceptors were studied in solid state and they have confirmed the presence of interactions between donor and acceptors. Cavitands with β-diketone functionality were subjected to binding studies with metal ions in solution as well as in the solid state. Successful metal-ligand complexation in solid state as well as in solution state based on UV/Vis titrations have been confirmed. In order to stabilize chemically unstable energetic compound, pentaerythritol tetranitrocarbamate (PETNC), a co-crystallization approach targeting the acidic protons was employed. A co-crystal, a salt and a solvate were obtained and the acceptors were identified as supramolecular protecting groups leading to reduced chemical reactivity and improved stability of PETNC with minimal reduction of desirable energetic properties. Several potential tetrazole based explosives which are thermal and impact sensitive and solid propellants which are impact sensitive were subjected to co-crystallization experiment to stabilize and enhance their properties. Co-crystals and salts of the explosives were obtained with suitable nitrogen based and oxygen based acceptors. The impact sensitivity and thermal instability of the explosives were improved with the introduction of co-formers. Oxygen based acceptors have shown more favorable explosive property improvements compared to nitrogen based acceptors with significant retention of explosive nature of the parent explosives.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeröy / Four different methods; molecular electrostatic potentials (MEPs), hydrogen-bond energies (HBE), hydrogen-bond propensities (HBP) and hydrogen-bond coordination (HBC) were used for mapping out the structural landscape of twelve pyrazole and twelve thiazole based molecules. In seven out of eight crystal structures obtained in pyrazoles, a combination of HBE and HBP predicted the experimentally observed synthons correctly. In all eight crystal structures obtained in thiazoles, the synthons were predicted correctly using all four methods. A series of co-crystallizations between twelve pyrazole with twenty carboxylic acids (240 experiments), and twelve thiazole with twenty carboxylic acids (240 experiments) were carried out to build an experimental library that could be used for evaluating the ability of electrostatics, energies, propensities and molecular complementarity methods to rationalize the observed intermolecular interactions. The results suggested that a combination of electrostatics and molecular complementarity are essential for identifying the predominant molecular recognition events in the pyrazole based study, and methods such as MEPs, HBE, and HBP all predicted the observed synthons in co-crystals of the thiazole-based molecules. In order to examine competition between hydrogen and halogen bonds, and to synthesize ternary co-crystals, four thiazole based molecules were co-crystallized with 15 hydrogen-bond donors and one halogen bond donor resulting in new co-crystals in 44 out of 60 experiments, and the crystal structures of two ternary co-crystals were obtained. A series of eight unactivated and activated amide functionalized molecules were synthesized to establish a supramolecular halogen-bond hierarchy. The positive electrostatic potential on the halogen atoms was enhanced through an sp-hybridized carbon and electron-withdrawing fluoro group(s) next to amide group. Tetraflourinated and iodoethynyl based molecules were identified as the most effective halogen-bond donors and were therefore least successful for co-crystal synthesis. In order to predict crystallizability of 83 drug-like molecules a molecule, logistic regression approach was employed using molecular descriptors such as molecular weight, rotatable bond, surface area, heteroatom, melting temperature, glass transition temperature, and molecular shape/volume. Four different models were developed, and the success rate was above 85% (using experimental DSC data for the crystallization classification). Finally, the solid-form landscape of urea was explored using full interaction maps (FIMs), and data from the CSD to develop optimum protocols for synthesizing co-crystals of this compound. As a result, 49 of 60 attempted reactions produced new co-crystals. Moreover, the goal of reducing solubility and lowering hygroscopicity of the parent compound was achieved, which, in turn, offers new opportunities for a slow-release fertilizer with limited hygroscopicity thereby reducing many current problems of transport, handling, and storage of urea.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / A methodology for estimating hydrogen-bond preferences and binding affinities in solution, based on molecular electrostatic potential surfaces (MEPS), is presented using tritopic hydrogen bond acceptor and a series of aromatic carboxylic acids. The plot of calculated MEPS values against experimentally determined binding constants produces a goodness-of-fit of over 0.93 and a similar positive correlation is obtained between MEPS values and binding enthalpies. A series of tritopic N-heterocyclic compounds were synthesized and subjected to systematic co-crystallizations with selected multi-topic aliphatic and aromatic carboxylic acids to determine if ditopic and tritopic donors formulate assemblies with desired stoichiometries. The co-crystals formed contained the COOHᐧᐧᐧBzim synthon, and we observe vacant sites on the acceptor molecules. A series of co-crystallizations between tritopic N-heterocyclic compounds and perfluoroiodoarenes were carried to map out structural landscapes. At least one potential binding site on the acceptor is left vacant on all the four structures obtained. The absence of halogen bonds to all sites can be ascribed primarily due to deactivation of the σ-hole on the iodo-arene donors and partially due to steric hindrance. Four nonsteroidal anti-inflammatory (NSAID) drugs were chosen due to the presence of the COOH moiety, to establish if aqueous solubility can be modulated by systematic solubility measurements of the complex. Two different solids were obtained with a 1:1 and 1:3 stoichiometry. The solubility of the 1:1 co-crystal decreased by 12-fold compared to pure aspirin (3mg/mL at 20 °C) indicating that co-crystals can offer promising new solid forms of pharmaceutically relevant compounds. A series of hydrogen- and halogen bonding Tröger’s base derivatives were synthesized using aromatic N-heterocycles and the iodoethynyl functionality, followed by a series of co-crystallization between aliphatic dicarboxylic acids and symmetric ditopic acceptors. The results suggest that reducing the number of binding sites from three to two facilitates the formation of co-crystals with the desired stoichiometry. The results indicate that directed assembly can be achieved more easily when the molecular building blocks are conformationally rigid.