A library of luminescent cyclometalated gold(III) complexes containing various bis-cyclometalating R-C^N^C ligands derived from 2,6-diphenylpyridine and ancillary alkynyl ligands, [Au(R-C^N^C)(C≡CR’)], has been synthesized. Some of the complexes have been structurally determined by X-ray crystallography. These complexes were found to exhibit intense emission in dichloromethane solution at 298 K, originating from metal-perturbed triplet intraligand (IL) excited states of the R-C^N^C ligand, with substantial charge transfer character from the aryl moiety to the pyridyl ring. In the presence of electron-rich alkynyl ligands, the emission origin could be switched to an alkynyl-to-cyclometalating ligand ligand-to-ligand charge transfer (LLCT) excited state. This class of complexes was also demonstrated to show rich electroluminescence properties as emitters in organic light-emitting devices. In addition, the supramolecular assembly of this class of complexes has also been revealed in gelation studies. N-Heterocyclic carbenes have been incorporated into the gold(III) metal center to prepare a series of luminescent mononuclear and dinuclear gold(III) complexes, [{Au(C^N^C)}n(NHC)](PF6)n and [{Au(tBuC^N^CtBu)}n(NHC)]- (PF6)n (n = 1, 2). The X-ray crystal structures of most of the complexes have been determined. The emissions of these complexes were assigned to originate from the metal-perturbed intraligand excited state of the bis-cyclometalating ligand. One of the C2-bridged dinuclear complexes was found to exhibit two distinct reduction couples, tentatively correlated to the presence of significant intramolecular π-π interaction in the complex. Two novel series of luminescent mononuclear alkynylgold(III) complexes, [Au(C^N)(C≡CR)2] (HC^N = 2-phenylpyridine (Hppy) and derivatives) and [Au(C^N^N)(C≡CR)]PF6 (HC^N^N = 6-phenyl-2,2’-bipyridine and derivatives), have been synthesized. Some of the X-ray crystal structures have been determined. The former class of complexes with bidentate C^N ligands has been observed to show tunable emission spanning across the visible spectrum from 462 to 697 nm. With the exception of [Au(ppy)(C≡C-C6H4-NH2-p)2] which showed a low-energy band originated from a 3LLCT [π(C≡C-C6H4-NH2)→π*(C^N)] excited state, all complexes exhibited vibronic-structured emission bands originated from the intraligand transition of the cyclometalating C^N ligand in dichloromethane solution at 298 K. On the other hand, most of the complexes with the tridentate C^N^N-type ligand have been observed to exhibit vibronic-structured emission bands attributed to the intraligand transition of the C^N^N ligand in low-temperature butyronitrile glass. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Prompted by the successful clinical application of cisplatin in cancer therapy, worldwide efforts have been devoted to develop new metal-based drugs for anticancer treatment. Gold(III) complexes at first received attention as anti-cancer drug candidates because of their square-planar geometry which resembles that of platinum(II) complexes. Subsequent studies revealed that various gold(III) complexes displayed promising anti-cancer activities with different biological mechanisms. Although some achievements have been obtained in the development of anti-cancer gold(III) complexes, challenges including the improvement of bioavailability, stability and selectivity, elucidation of the action mechanisms, and the development of novel delivery approaches of gold(III) complexes to reduce systematic toxicity, remain to be exploited. A panel of anti-cancer complexes [AuIII(R-C^N)(L)]n+ (wherein HC^N is 2-phenylpyridine, L is biguanide or biuret) have been identified and described in Chapter 3. Biguanide or biuret have been employed to improve the solubility of the complexes in aqueous solutions. Meanwhile, the lipophilicity could readily be adjusted by varying the R group to obtain a balance between lipophilicity and aqueous solubility. Among the synthesized complexes, the cationic complexes, [AuIII(butyl-C^N)biguanide]Cl (3.1) and [AuIII(C^N)biguanide]Cl (3.2) are soluble in aqueous solutions with solubility over 5 mg/mL. Besides, introduction of butyl groups to 3.1 and [AuIII(butyl-C^N)biuret] (3.3) resulted in higher cellular uptake of gold, which might enhance their cytotoxic activities (IC50 values: 1.5–17 μM) compared with 3.2 and [AuIII(C^N)biuret] (3.4) (IC50 values: 9.4–47.3 μM). Moreover, 3.1 was also found to induce cell cycle arrest in S-phase and endoplasmic reticulum (ER) damage in human cervical epithelial carcinoma (HeLa) cells, and display significant anti-angiogenic activity at its sub-cytotoxic concentrations. In Chapter 4, a series of gold(III) complexes with dithiocarbamate and 2-phenylpyridine ligands to target deubiquitinases (DUBs), have been designed. These complexes achieved significant inhibition on purified DUBs. Notably, [AuIII(2-(4-nbutylphenyl) pyridyl)(diethyldithiocarbamate)]PF6 (4.1) inhibited both the purified (IC50 values: 46–223 nM) and cell-based DUBs activities with high efficiency. Its interaction with DUB UCHL1 and peptides which are present in several types of DUBs and contain active cysteine residue were confirmed by mass spectrometric analysis. All complexes displayed significant cytotoxicities, and those containing diethyldithiocarbamate ligand displayed specific cytotoxicity on breast cancer cells. Accumulation of a tumor suppressor p53, cell-cycle arrest, and apoptotic cell death were induced in breast cancer cells by 4.1. Besides, 4.1 also showed anti-angiogenic effects. These biological activities might be related with DUBs inhibition. In Chapter 5, a cytotoxic complex [AuIII(C^N^C)(4-dpt)](CF3SO3) (5.1, HC^N^CH = 2,6-diphenylpyridine; 4-dpt = 2,4-diamino-6-(4-pyridyl)-1,3,5-triazine) has been designed to self-assemble into supramolecular polymers (5.1-SP) in acetonitrile. In physiologically relevant solutions, 5.1-SP displayed a sustained-release property of the anti-angiogenic ligand 4-dpt, and in the presence of glutathione (GSH), [AuIII(C^N^C)-GSH] adduct(s) were also gradually released. The supramolecular polymers 5.1-SP also showed selective cytotoxicity toward cancerous cells, and could act as drug-carriers of other cytotoxic agents to achieve sustained-release behavior. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

Thesis (MSc.(Pharmacology)--Faculty of Health Sciences)-University of Pretoria, 2008. / Includes bibliographical references.

M.Sc. (Chemistry) / Please refer to full text to view abstract

Although known since the 1930s, organogold chemistry has been dormant until recently, primarily due to preconceptions about the inertness of gold in transformations. However, this last decade has witnessed the emergence of a Golden Age with the development of a wealth of reports on gold in a plethora of reactions. In recent years, the drive for more atom- and step-economical and environmentally friendly reactions has become a field of intense research. In our on-going research on well-defined transition metal complexes bearing NHC ligands, our group recently discovered a new gold(I) hydroxide complex [Au(OH)(IPr)] (1a) that can be easily synthesised from the chloride precursor [AuCl(IPr)] (1b). A preliminary survey of the reactivity of this gold synthon has demonstrated interesting reactivity that holds great potential in bond activation reactions and the development of useful synthetic methods. Simplistically, this gold hydroxide complex can be seen as a strong Brønsted base. This thesis is dedicated to an in-depth examination of the reactivity of this complex in base-free bond activation reactions. Two themes predominate in the following chapters: the first part demonstrates the activity of gold(I) hydroxide as a bond activation agent to readily and efficiently access organogold complexes while the second part studies the reactivity of this compound in decarboxylation processes with carboxylic acids. Chapter 2 and 3 were dedicated to the development of new synthetic routes to access organogold complexes via base-free transmetalation reactions with organoborons and silanes using 1a. The combination of experimental and computational studies allowed identification and isolation of key intermediates in these reactions. Chapter 4 can be seen as a transition between the development of novel methodologies to synthesise aryl and heteroarylgold complexes and the first steps of gold hydroxide 1a as mediator in decarboxylation reaction. As a result, a novel mode of reactivity for gold was discovered and the synthetic route developed constitutes one of the greenest procedures to prepare organogold complexes with the generation of water and CO₂ as only side products. Chapter 5 and 6 venture further into the exploration of 1a in decarboxylation reactions and detail the development of a catalytic process for the protodecarboxylation reaction and subsequent mechanistic investigations of this reaction through stoichiometric experiments and kinetic and computational studies.

In order to gain insights into the electronic interactions between metallic gold and self-assembled monolayers composed of π-conjugated thiols, a series of thiol-containing molecules based on a stilbene backbone were synthesized and assembled on gold surface. The resulted monolayers were characterized with a variety of surface-sensitive techniques and the electronic properties of the obtained surfaces were studied with the use of ultraviolet photoelectron spectroscopy. Work-function changes and alignment of the molecular energy levels with respect to the Fermi level of the metal were investigated and important insights regarding the electronic properties of the metal / organic interfaces were obtained. Another aspect of interactions between organic dyes and metallic gold was studied in the context of spectroscopic properties of systems incorporating gold nanoparticles with organic fluorophores covalently attached to the nanoparticle surface. Ultrafast dynamics of the excited-state deactivation of the organic fluorophores attached to the surface of gold nanoparticles were studied with the use of a fs transient absorption technique. It was found that the close proximity of a gold nanoparticle had a profound impact on the excited-state lifetime of the studied organic fluorophore. The influence of the structure of the studied systems on the excited-state deactivation dynamics of the organic fluorophores was described.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

M.Sc. (Chemistry) / Please refer to full text to view abstract

M.Sc. / Please refer to full text to view abstract.