Hydrogen- and halogen-bond driven supramolecular architectures from small molecules to cavitands, and applications in energetic materials

Doctor of PhilosophyDepartment of ChemistryChrister B. AakeröyA 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

From Laser Speckle to Particle Size Distribution in drying powders: A Physics-Enhanced AutoCorrelation-based Estimator (PEACE)

Extracting quantitative information about highly scattering surfaces from an imaging system is challenging because the phase of the scattered light undergoes multiple folds upon propagation, resulting in complex speckle patterns. One specific application is the drying of wet powders in the pharmaceutical industry, where quantifying the particle size distribution (PSD) is of particular interest. A non-invasive and real-time monitoring probe in the drying process is required, but there is no suitable candidate for this purpose. In this report, we develop a theoretical relationship from the PSD to the speckle image and describe a physics-enhanced autocorrelation-based estimator (PEACE) machine learning algorithm for speckle analysis to measure the PSD of a powder surface. This method solves both the forward and inverse problems together and enjoys increased interpretability, since the machine learning approximator is regularized by the physical law

The Role of Halogen Bonding in Controlling Assembly and Organization of Cu(II)-Acac Based Coordination Complexes

In order to explore the use of non-covalent interactions in the deliberate assembly of metal-supramolecular architectures, a series of β-diketone based ligands capable of simultaneously acting as halogen-bond donors and chelating ligands were synthesized. The three ligands, L1, L2, and L3, carry ethynyl-activated chlorine, bromine, and iodine atoms, respectively and copper(II) complexes of all three ligands were crystallized from different solvents, acetonitrile, ethyl acetate, and nitromethane in order to study specific ligand-solvent interaction. The free ligands L2 and L3, with more polarizable halogen atoms, display C-X⋯O halogen bonds in the solid state, whereas the chloro-analogue (L1) does not engage in halogen bonding. Both acetonitrile and ethyl acetate act as halogen-bond acceptors in Cu(II)-complexes of L2 and L3 whereas nitromethane is present as a ‘space-filling’ guest without participating in any significant intermolecular interactions in Cu(II)-complexes of L2. L3, which is decorated with an iodoethynyl moiety and consistently engages in halogen-bonds with suitable acceptors. This systematic structural analysis allows us to rank the relative importance of a variety of electron-pair donors in these metal complexes

Loop-Configuration for Plug Flow Crystallization Process Development

Continuous crystallization plays a pivotal role in the transition to continuous manufacturing that the pharmaceutical industry is currently undertaking. Alas, the development of a continuous crystallization process using data from continuous operation is prohibitively material-intensive. Given the state of control nature of the continuous formalism, experimental design spaces entail several experiments, in which up to ten residence times are required to assess an experimental condition at steady state. Furthermore, transferring batch kinetics determined from batch experiments to a continuous crystallizer, despite being common practice, adds undesirable uncertainty to the development endeavors due to equipment-dependent mass and heat transfer. In this work, we present a novel configuration of a tubular crystallizer, capable of characterizing a system with a few experiments, curbing the reactor footprint, and abating the development's raw material requirements. A stream of crystallizing material, flowing inside a tubular crystallizer equipped with Kenics static mixers, was fully recirculated, implementing a looped plug flow configuration, and its evolution was monitored in-line continuously by means of in situ Process Analytical Technologies. This allows effective mimicking of long residence times (which correspond to large process volumes) in a short plug flow crystallizer while maintaining plug flow conditions and screening a process from nucleation to equilibrium. Computational fluid dynamics simulations supported the assumption of negligible back mixing and aided the comparison of the mixing with that of a cascade of continuous stirred tank reactors. The use of the novel configuration is showcased for the antisolvent crystallizations of ketoconazole, azithromycin, and glycine. Using this approach, we show reductions in raw material requirements from 50 to 98%, compared with an equivalent standard plug flow crystallizer. Naturally, the configuration can also be employed for manufacturing in a semicontinuous manner