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No description available.

No description available.

No description available.

No abstract available. / Thesis (M.Sc.Eng.)-University of Durban-Westville, 2000.

Recently established as an excellent activator for π-systems, efforts made in gold chemistry have increased enormously, resulting in a new ‘Gold Rush’ in chemistry. This thesis is a small contribution to it. There are two main aspects dominating the following chapters: gold catalysts bearing N-heterocyclic carbenes (NHCs) as supporting ligand, and H₂O assisted catalysis. The initial motivation for the presented work was to specifically demonstrate the potential of [(NHC)AuCl] as suitable catalysts for both known and new organic transformations and to establish these commercially available catalysts in gold chemistry, a field currently dominated by phosphine bearing gold complexes. Water mediated catalysis became the next repeatingly occurring aspect of this thesis by pursuing this initial aim and finding water as a useful solvent or agent, respectively. Various useful applications for gold-NHC complexes are presented, starting with the Meyer-Schuster rearrangement of propargylic alcohols as a continuation of the work realized with propargylic acetates by the Nolan group in early investigations on gold catalysts. Next, a study on alkyne hydration is presented with focus on low catalysts loadings to establish gold catalysts as a powerful choice for such a highly relevant reaction. The catalytic system is then advantageously adapted to a silver-free variation, still active at low catalyst loadings and with further mechanistic insight. Inspired by gold activation of alkynes, a gap of reactivity in gold catalysis is closed by a successful demonstration of nitrile hydration, a functionality previously thought to be inert towards gold activation. In this context, formation and role of dinuclear hydroxy-bridged gold complexes is investigated highlighting these complexes as a possible resting state of gold complexes in the presence of water. Next, the formation of furanones via alkoxylation/lactonization of propargylic propiolates is presented, an observation initially made when exploring the scope of the Meyer-Schuster rearrangement. The dissertation finally closes with the gold-catalyzed formation of amides, this time however achieved from aldoximes reacting via dehydration/hydration mechanism.

<p>Cationic gold(I) complexes containing phosphine and N-heterocyclic carbene based ligands are a powerful catalysts for the hydrofunctionalization of C-C multiple bonds with carbon and heteroatom based nucleophiles as well as the cycloisomerization of enynes and related &#960;-systems. Mechanisms involving outer sphere, nucleophilic attack an activated gold &#960;-complex are typically invoked for both hydrofunctionalizations and cycloisomerizations, however, direct experimental evidence for these mechanisms remain limited.</p><p>Gold(I) catalyzed allene racemization is an important background reaction in the hydrofunctionalization of 1,3 disubstituted allenes. It can compromise chirality transfer or be exploited to realized stereoconvergent synthesis of allylic alcohols and amines. The kinetics of the racemization of aromatic 1,3-disubstituted allenes catalyzed by gold(I) phosphine complexes has been investigated. The rate of racemization displayed first order dependence on allene and gold concentration. Kinetic analysis gold(I) catalyzed racemization of allenes as a function of allene and phosphine donor ability established a depletion of electron density on the terminal allene carbons and an accumulation of electron density on the phosphine ligand in the rate-limiting transition state.</p><p>Investigation of the mechanism of gold(I) catalyzed hydrofunctionalization of allenes with alcohols, carbamates, and anilines established a variable catalyst resting state depending on the equilibrium binding affinities of the nucleophile and the relative concentrations of allene and nucleophile that are employed. Reversible C-X bond formation may explain the difference in regioselectivity observed for hydroalkoxylation and hydroamination with carbamates. Additionally, in situ analysis of the hydrofunctionalization of enatiopure 1,3-disubstituted allenes for enatiopurity of the allene and product ruled out trapping of an achiral &#951;1-intermediate and established concomitant allene racemization as the cause of loss of enatiopurity.</p><p>Finally we report the two gold(I) carbene complexes not stabilized by &#960;-conjugated heteroatoms. First, we report the hydride abstraction from a neutral gold cycloheptatrienyl complex that was isolated and characterized in solution and by single crystal X-ray diffraction. This complex represents the first example of a gold carbenoid complex that lacks conjugated heteroatom stabilization. Second we report the synthesis of the first gold(I) vinylidene via hydride abstraction from a gold (disilyl)ethylacetylide complex to form a cationic &#946;,&#946;-disilacyclopentyl vinylidene complex. The C1 and C2 carbon atoms of the vinylidene complex underwent facile interconversion presumably through the gold &#960;-disilacyclohexyne.</p> / Dissertation

Region surrounding the Central Bohemian Plutonic Complex represents one of the most important gold bearing zones in the Czech Republic. Several types of gold deposits dominated by hydrothermal quartz gangue were explored here and distinguished: the Intrusion related gold deposits ("Petráčkova hora" and "Mokrsko") and the orogenic gold deposits ("Jílové u Prahy" and "Kasejovice" ). Deposits "Libčice u Nového Knína" and "Roudný u Vlašimi" are partially similar to the orogenic gold type, but are different from other orogenic type deposits in the region. All together 38 samples from these five deposits were analyzed with laser ablation technique (LA- ICP-MS) to produce 228 measurements. Selected samples were selected to represent both main quartz gangue carrying the Au ore and latter weakly mineralized quartz gangue. Samples representing hydrothermal quartz gangue with no direct relation to Au-ore deposits were also collected in order to compare chemical composition of both quartz types originating from the same area. Main concern of this work was in-situ analysis of chemical composition of different generations of quartz gangue and statistical comparison of differences within individual deposits as well as comparing the examined deposits themselves. Total 65 isotopes were measured, trace element...

>Magister Scientiae - MSc / Cancer is one of the leading causes of death, worldwide. Mortality tolls are estimated to reach approximately 13.1 million in 2030. These statistics suggest that current therapeutic strategies are not effective. This is partly due to the fact that the drugs used in the treatment of cancer lack selectivity and specificity, which lead to undesirable side effects and reduced drug efficacy. There is therefore a need for alternative therapeutic approaches. In view of this, the therapeutic goal of chemotherapy has shifted towards targeted drug delivery systems, which have been successfully demonstrated using nanotechnology. The nano-based drug delivery vehicles that specifically target diseased cells are appealing as they could reduce drug toxicity towards healthy tissues and be more effective at lower dosages. The main aim of this study was to develop gold nanorods (AuNRs) capable of inducing cell death in cancer cells specifically. Selectivity of the AuNRs (denoted as AGK) for cancer cells was achieved by conjugating the AuNRs to a peptide (Adipose Homing Peptide or AHP) that has high affinity and specificity for a cell surface receptor (prohibitin or PHB) that is expressed on some cancer cells. Cell death was achieved through conjugating the AuNRs to a pro-apoptotic peptide, D(KLAKLAK)2. Spherical AuNPs (AuNSs) conjugated with AHP and D(KLAKLAK)2, capable of selectively inducing apoptosis in cancer cells that express PHB, was previously reported. However, in this study the AuNSs were replaced with AuNRs. AuNRs has the ability to absorb light in the near infrared (NIR) light spectrum and converts this light energy into heat. This property of AuNRs has been used in several studies to demonstrate the application of AuNRs for the treatment of cancer using photothermal therapy (PTT). Consequently, the AuNRs described in this study can also be used for PTT. These AuNRs can induce cell death through the target specific delivery of the pro-apoptotic peptide D(KLAKLAK)2 as well as through PTT. The study showed that three human cancer cell lines (PC-3, Caco-2 and U-87) express PHB. The cytotoxicity testing of AGK AuNPs on PC-3 cells showed that these AuNRs could induce apoptosis in these cells without exposure to a NIR light source. The study also shows that AuNRs conjugated with the targeting peptide only (denoted as AG) can induce cell death in Caco-2 through PTT. This study demonstrates the potential of the AuNRs described in this study for application in the targeted elimination of cancer cells through the selective induction of PTT and apoptosis.