The Isocyanoarene Motif in Organometallic Crystal Engineering and New Azulene-Based Organometallics

Isocyanides (:CN-R) and their metal complexes play an important role in many areas including synthetic organic chemistry, catalysis, diagnostic medicine, as well as surface, polymer, and materials sciences. The rich chemistry of isocyanides stems from the tunability of the molecular and electronic structure through variations of the substituent R. Isocyanides represent a rather versatile class of ligands and can accommodate metal ions in both high and low oxidation states upon complexation. Isocyanoarene derivatives have been shown to be effective in the design of charge transport materials (e.g., molecular wires). In addition, di- and other polyisocyanoarenes have been employed as building blocks in the coordination chemistry of polynuclear organometallics. In the past decade, Barybin et al. have developed the chemistry of electron-rich compounds and materials that incorporate isocyanoarene ligands featuring nonbenzenoid aromatic azulenyl and η5-cyclopendadienyl substituents. In this Dissertation, isocyanide-terminated benzenoid and nonbenzenoid arenes as well as the organometallic complexes thereof are discussed. Chapter I constitutes a review of recent developments in the chemistry of isocyanoarenes as ligands in low-valent organometallics. Particular emphases are placed on (1) isocyanometalates (isocyanide complexes of metals in negative oxidation states), (2) low-coordinate complexes of extremely bulky isocyanoarenes, and (3) the chemistry of nonbenzenoid isocyanoarenes. The first part of Chapter II is dedicated to the chemistry of an unusual supramolecular charge-transfer ensemble ([Cp2Co]2[{(OC)5V}2(μ-CNC6Me4NC)])∞ (Cp = cyclopentadienyl) held together via synergistic π-stacking and contact-ion interactions. This three-dimensional, porous framework features channels capable of housing linear molecules such as acetonitrile, carbon dioxide, etc., and offers new opportunities in organometallic crystal engineering. The second part of Chapter II describes preliminary studies on the interaction of the novel 2-isocyano-1,3-dimethylazulene ligand with sub-valent metal ions (e.g., Co(I-) and Fe(II-)). Chapter III of this Dissertation describes the syntheses and coordination chemistry of the polar, linear 2-isocyano-1,3-diethoxycarbonyl-2',6-biazulene ligand and related species. Detailed electrochemical and spectroscopic studies of these novel ligands and their low-valent homoleptic complexes shed light on electron delocalization between the azulenic/biazulenic π-systems and electron-rich metal ions mediated by the isocyanide junction. In Chapter IV, synthetic studies toward a family of azulene-based metal-organic frameworks are described. Two-dimensional, rectangular metal-organic frameworks were formed by bridging {Cp*ClIr(III)} corner fragments (Cp* = pentamethylcyclopentadienyl) with either asymmetric 2,6-diisocyanoazulenic or symmetric 2,2'-diisocyano-6,6'-biazulenic ditopic edge units. 16-Electron metal carbonyl units, namely [Cr(CO)5], were employed as end caps to control orientation of the molecular dipole of 2,6-diisocyano-1,3-diethoxycarbonylazulene within tetrametallic molecular frameworks

Reducing Crop Production Cost

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Synthesis and evaluation of troponoids as a new class of antibiotics

Novel antibiotics are urgently needed. The troponoids [tropones, tropolones, and α-hydroxytropolones (α-HT)] can have anti-bacterial activity. We synthesized or purchased 92 troponoids and evaluated their antibacterial activities against Staphylococcus aureus, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa. Preliminary hits were assessed for minimum inhibitory concentrations (MIC80) and cytotoxicity (CC50) against human hepatoma cells. Sixteen troponoids inhibited S. aureus/E. coli/A. baumannii growth by ≥80% growth at 50 values >50 μM. Two selected tropolones (63 and 285) inhibited 18 methicillin-resistant S. aureus (MRSA) strains with similar MIC80 values as against a reference strain. Two selected thiotropolones (284 and 363) inhibited multidrug-resistant (MDR) E. coli with MIC80 ≤30 μM. One α-HT (261) inhibited MDR-A. baumannii with MIC80 ≤30 μM. This study opens new avenues for development of novel troponoid antibiotics to address the critical need to combat MDR bacterial infections

“Nanoscale Zippers” in the Crystalline Solid. Structural Variations in the Giant Magnetocaloric Material Gd5Si1.5Ge2.5

Single-crystal X-ray diffraction coupled with TEM and SAD investigations demonstrate that Gd5Si1.5Ge2.5 exists as two distinct structural phases at room temperature:  the orthorhombic Sm5Ge4-type and the monoclinic Gd5Si2Ge2-type. This phenomenon occurs from the “nanoscale zippers” involving (Si, Ge) dimers that form or break bonds between the fundamental building units

Comparing crop growth and carbon budgets simulated across AmeriFlux agricultural sites using the Community Land Model (CLM)

Improvement of process-based crop models is needed to achieve high fidelity forecasts of regional energy, water, and carbon exchanges. However, most state-of-the-art Land Surface Models (LSMs) assessed in the fifth phase of the Coupled Model Inter-comparison project (CMIP5) simulated crops as unmanaged C3 or C4 grasses. This study evaluated the crop-enabled version of one of the most widely used LSMs, the Community Land Model (CLM4- Crop), for simulating corn and soybean agro-ecosystems at relatively long-time scales (up to 11 years) using 54 site-years of data. We found that CLM4-Crop had a biased phenology during the early growing season and that carbon emissions from corn and soybean were underestimated. The model adopts universal physiological parameters for all crop types neglecting the fact that different crops have different specific leaf area, leaf nitrogen content and vcmax25, etc. As a result, model performance varied considerably according to crop type. Overall, the energy and carbon exchange of corn systems were better simulated than soybean systems. Long-term simulations at multiple sites showed that gross primary production (GPP) was consistently over-estimated at soybean sites leading to very large short and long-term biases. A modified model, CLM4-CropM’, with optimized phenology and calibrated crop physiological parameters yielded significantly better simulations of gross primary production (GPP), ecosystem respiration (ER) and leaf area index (LAI) at both short (hourly) and long-term (annual to decadal) timescales for both soybean and corn

Epidemic Wave Dynamics Attributable to Urban Community Structure: A Theoretical Characterization of Disease Transmission in a Large Network.

BACKGROUND: Multiple waves of transmission during infectious disease epidemics represent a major public health challenge, but the ecological and behavioral drivers of epidemic resurgence are poorly understood. In theory, community structure—aggregation into highly intraconnected and loosely interconnected social groups—within human populations may lead to punctuated outbreaks as diseases progress from one community to the next. However, this explanation has been largely overlooked in favor of temporal shifts in environmental conditions and human behavior and because of the difficulties associated with estimating large-scale contact patterns. OBJECTIVE: The aim was to characterize naturally arising patterns of human contact that are capable of producing simulated epidemics with multiple wave structures. METHODS: We used an extensive dataset of proximal physical contacts between users of a public Wi-Fi Internet system to evaluate the epidemiological implications of an empirical urban contact network. We characterized the modularity (community structure) of the network and then estimated epidemic dynamics under a percolation-based model of infectious disease spread on the network. We classified simulated epidemics as multiwave using a novel metric and we identified network structures that were critical to the network's ability to produce multiwave epidemics. RESULTS: We identified robust community structure in a large, empirical urban contact network from which multiwave epidemics may emerge naturally. This pattern was fueled by a special kind of insularity in which locally popular individuals were not the ones forging contacts with more distant social groups. CONCLUSIONS: Our results suggest that ordinary contact patterns can produce multiwave epidemics at the scale of a single urban area without the temporal shifts that are usually assumed to be responsible. Understanding the role of community structure in epidemic dynamics allows officials to anticipate epidemic resurgence without having to forecast future changes in hosts, pathogens, or the environment