Synthesis of novel first-row transition metal-N-heterocyclic carbene complexes and synthesis of N-heterocyclic carbene-functionalized linkers for metal organic frameworks

1 online resource (xv, 165 pages) : illustrations (some colour), charts, graphsIncludes abstract and appendices.Includes bibliographical references (pages 85-101).Although N-heterocyclic carbene ligands are highly versatile and powerful ligands in transition metal catalysis, complexes of N-heterocyclic carbenes with 3d metals are uncommon and frequently unstable. In order to explore the reactivity of some 3d metal-N-heterocyclic carbene complexes, two tridentate NCN pincer ligands were prepared: 1,3-bis(2- pyridylmethyl)imidazolium chloride and 1,3-bis(2-pyridylmethyl)benzimidazolium chloride. These ligands were coordinated to copper(II) and nickel(II) salts in air to yield a variety of 3d metal-N-heterocyclic carbene complexes. The counterion to the metal cation appears to have a significant influence on the coordination mode of the ligands and geometry around the metal centres. Synthesis of the novel metal complexes, as well as possible applications, are described herein. Carbon dioxide is the primary contributor to climate change. As such, materials that can capture and fix carbon dioxide are important tools to limit climate change. One highly effective class of material for gas adsorption is metal-organic frameworks. In an effort to prepare a metal-organic framework with superior carbon dioxide capture and fixation capabilities, a series of linkers with N-heterocyclic carbene moieties were designed, of which two were successfully prepared. Thus far, efforts to prepare a metal-organic framework based on either of the two linkers have been unsuccessful

The Evolution of Massive YSOs in the LMC: Part I. Identification and Spectral Classification

We present and categorize Spitzer IRS spectra of 294 objects in the Large Magellanic Cloud (LMC) to create the largest and most complete catalog of massive young stellar object (YSO) spectra in the LMC. Target sources were identified from infrared photometry and multi-wavelength images indicative of young, massive stars highly enshrouded in their natal gas and dust clouds. Our sample primarily consists of 277 objects we identify as having spectral features indicative of embedded YSOs. The remaining sources are comprised of 7 C-rich evolved sources, 8 sources dominated by broad silicate emission, and 1 source with multiple broad emission features. Those with YSO-like spectra show a range of spectral features including polycyclic aromatic hydrocarbon emission, deep silicate absorption, fine-structure lines, and ice absorption features. Based upon the relative strengths of these features, we have classified the YSO candidates into several distinct categories using the widely-used statistical procedure known as principal component analysis. We propose that these categories represent a spectrum of evolutionary stages during massive YSO formation. We conclude that massive pre-main sequence stars spend a majority of their massive, embedded lives emitting in the UV. Half of the sources in our study have features typical of compact HII regions, suggesting that massive YSOs can create a detectable compact HII region half-way through the formation time present in our sample. This study also provides a check on commonly used source-selection procedures including the use of photometry to identify YSOs. We determine a high success rate (>95%) of identifying objects with YSO-like spectra can be achieved through careful use of infrared CMDs, SEDs, and image inspections.Comment: Accepted to The Astrophysical Journa

Genomic characterization of coagulase-negative staphylococci including methicillin-resistant Staphylococcus sciuri causing bovine mastitis

Methicillin-resistant coagulase-negative staphylococci (MRCoNS) have recently emerged as a significant cause of bovine mastitis worldwide. Here we describe the isolation of MRCoNS from cases of bovine mastitis from a single dairy farm in Australia. Fourteen CoNS isolates were identified as MRCoNS on the basis of having an oxacillin MIC of =0.5 µg/mL. The isolates were speciated as S. chromogenes (n = 1) S. fleurettii (n = 1), S. haemolyticus (n = 2), S. sciuri (n = 5), S. simulans (n = 1) S. succinus (n = 2) and S. xylosus (n = 2). Five of the isolates (S. fleuretti, S. haemolyticus S. sciuri and two S. succinus) were mecA-positive. We also detected a previously described S. sciuri mecA homolog in four oxacillin-resistant S. sciuri isolates. The remainder of the putative MRCoNS did not contain any mecA-related resistance determinants in their genomes. Comparative genomic analysis of three previously published S. sciuri isolates, from humans, a squirrel and a cereal crop (rice), and a representative isolate from our study demonstrated clustering and a high degree of genetic homogeneity (>95%), suggesting S. sciuri has low host specificity. In conclusion, CoNS, in particular S. sciuri, may act as a reservoir for SCCmec elements that can easily be spread between different host species by direct cross-infection