The use of N-heterocyclic carbenes (NHCs) as ligands in catalysis is one of the most significant developments in modern catalysis and organometallic chemistry. One way to extend the scope of NHC ligand tuning is by means of annulation of carbocyclic and heterocyclic rings to the NHC backbone. The bis(imino)acenaphthene-supported N-heterocyclic carbene [IPr(BIAN)] has been synthesized and can be regarded as originating from the fusion of a naphthalene ring to an NHC. Several metal complexes of IPr(BIAN), including those incorporating copper(I), silver(I), gold(I), or iridium(I) have been synthesized and characterized, including single-crystal X-ray diffraction studies. The doncity of IPr(BIAN) was investigated using the Tolmen Electronic Parameter (TEP) method. A TEP value of 2042 cm-1 was calculated for the IPr(BIAN) ligand using the Ir(CO)2Cl complex which indicates that IPr(BIAN) is a relatively strong electron donating NHC ligand. The well-behaved redox chemistry of the BIAN ligand class rendered IPr(BIAN) an excellent candidate for exploration of the relationship between ligand charge and carbene donicity. The electrochemical reduction of IPr(BIAN) was studied by cyclic voltammetry (CV) in a THF solution and a reversible reduction wave was detected at - 1.79 V vs SCE. Spectroelectrochemical IR studies were also undertaken to further characterize the nature of the reduced state. IPr(BIAN) was found to be a stronger electron donating ligand in the reduced state in comparison with the neutral state of the ligand. IPr(BIAN) was also chemically reduced using potassium graphite and the resulting radical anion was studied by electron paramagnetic resonance (EPR) techniques. An isotropic EPR signal was observed at a g value of 2.0112. Due to the known antimicrobial activities of silver and gold NHCs, the activities of the silver and gold complexes of IPr(BIAN) and the imidazolium salts of several BIAN ligands were investigated using the minimum inhibitory concentration test. The silver(I) and gold(I) complexes of IPr(BIAN) were found to be moderately active. The most active compounds were found to be the imidazolium salts, with MIC values ranging between < 0.6 μg/mL and 78 μg/mL for the diisopropylphenyl(BIAN) and the mesityl(BIAN) imidazolium chlorides against S. aureas, B. subtilis, E. coli, and P. aeruginosa. The preparation of nanofibers impregnated with IPr(BIAN)AuCl by the process of electrospinning was also explored. The antimicrobial activities of the resulting nanofiber mats were determined on the basis of the inhibition zone test, and a localized antimicrobial activity was observed for the Gram-positive bacteria M. leuteus. / text

Saccharopolyspora spinosa is a rare actinomycete that synthesizes the secondary metabolite spinosyn A, which is an active ingredient in several important commercial insecticides. Spinosyn aglycone formation occurs via a type I polyketide synthase. After release of the polyketide chain from the synthase, various tailoring enzymes modify the aglycone core. These unique enzyme transformations result in unusual structural characteristics found in spinosyn A. The enzymes SpnG, SpnP, SpnF and SpnL each perform a key reaction during post-PKS processing. The work presented in this dissertation focuses on the structural determination and analysis of SpnG, SpnP, SpnF and SpnL. SpnG, which naturally catalyzes the 9-OH rhamnosylation of spinosyn, is capable of adding diverse sugars to the spinosyn aglycone from TDP-hexoses, such as TDP-glucose. However, the substitution of UDP-glucose for TDP-glucose as the donor substrate is known to result in a >60,000-fold reduction in k [subscript cat]. The structure of SpnG at 1.65 Å resolution, the 1.86 Å resolution structure of SpnG bound to TDP, and the 1.70 Å resolution structure of SpnG bound to AGL were determined. The SpnG-TDP complex reveals how SpnG employs N202 to discriminate between TDP- and UDP-sugars. The SpnG-AGL complex shows that SpnG binds the acceptor substrate primarily through hydrophobic interactions and implicates H13 as the potential catalytic base. A model for how rhamnose binds in the active site was constructed to elucidate which features enable SpnG to transfer diverse hexoses. SpnP transfers forosamine from a TDP-D-forosamine donor substrate to a spinosyn pseudoaglycone acceptor substrate. The structures of SpnP and its complex with TDP were determined to 2.50 Å and 3.15 Å resolution, respectively. SpnP possesses a structural feature that has only been previously observed in a related glycosyltransferase, which employs an auxiliary protein that aids in its catalysis. This unique feature may be a used as a predictive motif of glycosyltransferases that interact with an auxiliary protein. SpnF and SpnL are two novel S-adenosyl-L-methionine dependent cyclases. Structural data was utilized in order to gain insight into the unusual cycloaddition catalyzed by the putative Diels-Alderase and Rauhut-Currierase, SpnF and SpnL, respectively. Together these structures provide valuable insights into the unusual mechanisms involved in spinosyn biosynthesis. / text

This thesis investigates the synthesis and activation of highly monodisperse Au25(SR)18 - clusters and bimetallic clusters (AuAg and AuPd) protected with various stabilizers for reduction and hydrogenation catalytic reactions. The first chapter is the introduction chapter, which summarizes the literature involving monolayer protected Au clusters, atomically precise Au clusters, bimetallic clusters, X-ray absorption spectroscopy, research objectives, and organization and scope. The second chapter describes the synthesis of Au25(SR)18 - clusters protected with various thiolate stabilizers for nitrophenol reduction catalysis using NaBH4 as a reducing agent. This chapter also describes the stability of these clusters under reaction conditions using UV-Vis spectroscopy and MALDI mass spectrometry. The third chapter details the synthesis of carboxylic acid-protected Au25 clusters using a NaBH4 purification strategy. Here, the knowledge obtained in the second chapter regarding the exceptional stability of Au25(SR)18 - clusters in the presence of NaBH4 was used to isolate carboxylic acid protected Au25 clusters from a polydisperse reaction mixture. The fourth chapter describes the synthesis and activation of mesoporous carbon supported Au25(SR)18 - clusters for nitrophenol reduction catalysis. Here, thermal removal of thiolate stabilizers led to the enhancement in the catalytic activity at low calcination temperatures; however, at higher calcination temperatures activity dropped as particle sintering was observed. Activation of these clusters on mesoporous carbon support was followed by TEM and X-ray absorption spectroscopy. The fifth chapter describes the thermal and chemical removal of thiolate stabilizers from supported Au25(SC8H9)18 - clusters. Here, the removal of thiolate stabilizers and subsequent growth of Au25 clusters was followed by TEM and EXAFS spectroscopy. The sixth and seventh chapters describe the synthesis of AuPd and AuAg bimetallic clusters using Au25(SR)18 - clusters as precursors and their characterization using UV-Vis spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy. Here, AuPd bimetallic clusters were thermally and chemically treated, which resulted in the formation of AuPd bimetallic nanoparticles with segregated Pd atoms on the surface. AuPd bimetallic nanoparticles were used for the selective hydrogenation catalysis of allyl alcohol. The last chapter of this thesis includes final conclusions and possible avenues for future work.

This thesis is based on theoretical studies of the molecular and electronic structure of solvated ions and molecules. Very detailed information of the system can be obtained from theoretical calculations, but a realistic model is dependent on an accurate computational method. Accurate calculations of core level electronic spectra, and evaluation of the modeling against experiments, are central parts of this work. The main tools used for characterization of the systems are high-level quantum chemistry and molecular dynamics simulations.  Molecular components in solutions are involved in many key processes converting sunlight into chemical or electrical energy. Transition metal complexes, with their pronounced absorption in the visible light region of the electromagnetic spectrum, are core components in various energy conversion applications, and the iodide/triiodide redox couple is a commonly used electrolyte. The local structure of the electronic valence in transition metal complexes and the details of the solvation mechanisms of electrolyte solutions are investigated through the combination of computational modeling and core level spectroscopy. The studies of model systems show that interactions between the solute and solvent are important for the electronic structure, and knowledge of the details in model systems studied can be relevant for energy conversion applications. Furthermore, high-level quantum chemistry has been applied for interpreting time-resolved spectra, where the electronic structure of a metal complex is followed during a photoinduced chemical reaction in solution. With advanced modeling in combination with recent experimental developments, more complex problems than previously addressed can be dissected. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 8: Manuscript.</p>

The observable properties of galaxy groups, and especially the thermal and chemical properties of the intragroup medium (IGrM), provide important constraints on the different feedback processes associated with massive galaxy formation and evolution. In this {work}, we present a detailed analysis of the global properties of simulated galaxy groups with X-ray temperatures in the range $0.5 - 2$ keV over the redshift range $0 \leq z \leq 3$. The groups are drawn from a cosmological smoothed particle hydrodynamics simulation that includes a well-constrained prescription for momentum-driven, galactic outflows powered by stars and supernovae but no explicit treatment of AGN feedback. Our aims are (a) to establish a baseline against which we will compare future models; (b) to identify model successes that are genuinely due to stellar/supernovae-powered outflows; and (c) to pinpoint mismatches that not only signal the need for AGN feedback but also constrain the nature of this feedback. We find that even without AGN feedback, our simulation successfully reproduces the observed present-day group properties such as the IGrM mass fraction, the various X-ray luminosity-temperature-entropy scaling relations, as well as both the mass-weighted and the emission-weighted IGrM iron and silicon abundance versus IGrM temperature relationships, for all but the most massive groups. We also show that these trends evolve self-similarly for $z < 1$, in agreement with the observations. In contrast to the usual expectations, we do not see any evidence of the IGrM undergoing catastrophic cooling. And yet, the $z=0$ group stellar mass is a factor of $\sim 2$ too high. Probing further, we find that the latter is due to the build-up of cold gas in the massive galaxies {\it before} they are incorporated inside groups. This not only indicates that another feedback mechanism must activate as soon as the galaxies achieve $M_*\approx$ a few $\times 10^{10}\;\rm{M_{\odot}}$ but that this feedback mechanism must be powerful enough to expel a significant fraction of the halo gas component from the galactic halos. ``Maintenance-mode" AGN feedback of the kind observed in galaxy clusters will not do. At the same time, we find that stellar/supernovae-powered winds are essential for understanding the metal abundances in the IGrM and these results are expected to be relatively insensitive to the addition of AGN feedback. We further examine the detailed distribution of the metals within the groups and their origin. We find that our simulated abundance profiles fit the observational data pretty well except that in the innermost regions, there appears to have an excess of metals in the IGrM, which is attributed to the overproduction of stars in the central galaxies. The fractional contribution of the different types of galaxies varies with radial distances from the group center. While the enrichment in the core regions of the groups is dominated by the central and satellite galaxies, the external galaxies become more important contributors to the metals at $r\simgreat R_{500}$. The IGrM at the groups' outskirts is enriched at comparatively higher redshifts, and by relatively less massive galaxies. / Graduate

The purpose of this study was to investigate the effects of two perturbations, the application of an external magnetic field and randomised chemical pressure through Ti4+/Sn4+ substitution, on the dynamic spin ice state in Pr2Sn2O7. We show through magnetometry, heat capacity and powder neutron diffraction that the dynamic spin ice state in Pr2Sn2O7 is extremely fragile, requiring an external field of approximately 0.5 T to induce a transition into a long range ordered antiferromagnetic state, in accordance with the recorded behaviour of other spin ice materials. Similarly, the dynamic spin ice state in Pr2Sn2O7 only required a doping percentage of less than 2.5% to induce a transition away from the spin ice state. But instead of the predicted spin glass state, Pr2Sn2O7 assumes a cluster-type magnetic structure with extremely weak intercluster antiferromagnetic interactions, a magnetic structure that persists even to the highest doping level of 30%. The results of this thesis reveals that careful attention must be taken when selecting and placing the tetravalent cation in the 16c Wyckoff site in the pyrochlore structure, if one desires to have a spin ice state. / October 2015

Bread owes its appeal to its aerated structure which directly relies on the bubbles entrained into the dough during mixing. If the bubble size distribution (BSD) in the dough can be determined at the end of mixing, then the resulting loaf quality could be predicted before bread is fully manufactured. However, non-invasively monitoring the structure of a fragile opaque soft solid such as dough is challenging. This thesis addressed the challenge by determining dough’s BSD and its evolution using ultrasound and X-ray microtomography. Using a resonant scattering model and the frequency dependence of the ultrasonic parameters measured in the dough, the change in the BSD in dough (made without yeast) with time as a result of disproportionation was determined. At 30 min after mixing, the median radius (R0) of the lognormal BSD was 6.5 microns. Converting the BSD to the radius dependence of bubble volume fraction (BVF(R)), R0V (the median radius of BVF(R)) was 66.4 microns and increased 18 % in the succeeding 90 min. In order to validate the bubble sizes determined ultrasonically, X-rays from a synchrotron source were utilized to examine dough’s microstructure. Large numbers of very small bubbles were discovered and it was apparent that lognormality did not describe the BSDs. Nevertheless, lognormal characterization of the BVF(R) was appropriate. At 30 min after mixing R0V of the BVF(R) was 32.5 microns and it increased by 20 % in the succeeding 90 min, supporting the ultrasonic quantification of bubble volume changes due to disproportionation. Changes in the mode, median and mean of the BVF(R) with time after mixing had the same trend for ultrasound and for X-ray microtomography. The time evolution of the mode of the BVF(R) obtained by ultrasound and X-ray microtomography matched very well; both increasing linearly as a function of time. Ultrasonic assessments of bubble sizes and their changes with time are very encouraging, but the ultrasonic model should use distribution functions that precisely define the empirical data, perhaps not making ‘pre-assumptions’ of lognormality for the BSD data. / February 2015

Long-lived trees preserve a record of environmental conditions during their lifetime in the pattern of yearly xylem widths and in changing wood density within and among the increments. Crossdated earlywood, latewood, and total ring widths, and minimum earlywood and maximum latewood densities, from three sites in the mountains of Maine, are analyzed visually and statistically to evaluate their relationships to one another and to external, environmental factors which affect the ring width and density through internal, physiological processes. Maximum density values show highest levels of similarity within and among the three site chronologies, thus implying a good degree of sensitivity to climate; minimum density values, however, showed lowest sensitivity to climate. Two biologically reasonable hypotheses concerning climate--tree growth interactions are proposed: (1) that maximum density is related to spring temperatures prior to its formation; and (2) that maximum density is related to summer water relations as the latewood forms. With the help of response function analysis, simple correlation, and multiple linear regression, these two hypotheses are tested: (1) maxmum density as a single predictor explains up to 37% of spring temperature variance; with earlywood widths at one site, 47% of spring temperature variance is explained; (2) maximum density as a single predictor explains up to 45% of summer temperature variance, 11% of summer precipitation variance, and 23% of the variance of Thornthwaite water deficit values; with total ring widths at one site, 22% of the variance of summer stream runoff is explained. Regression equations were applied to the 201- to 310-year tree-ring records to form reconstructions of these past climatic events. Independent verification testing of the reconstructions strongly validates the relationship between maximum density and spring temperature; the relationship to summer water relations is not as strongly verified, but results encourage further testin of this relationship. Results from this study may be applied both to (1) an increased understanding of relationship of climate to the formation of wood density; and (2) further development of dendroclimatology in mesic regions such as northeastern North America.

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