In molecular transition metal catalyst architectures, ligand design plays a crucial role in enhancing the efficiency of catalytic reactions. Selected ligands can play a bifunctional role in ligand-assisted catalysis, providing first coordination sphere basic sites and facilitating formation of multinuclear species through monomer bridging, as well as through their electronic and steric effects. This research addresses the underutilization of SNS complexes in various catalytic cycles. Our aim is to expand their activity in different cycles, unlocking untapped reactivity. Specifically, we focus on SNS ligands with soft thiolate and hard amido donors, comparing their catalytic performance in diverse coupling reactions. This comparative study provides insights into the suitability of these ligands with different transition metals, contributing to the understanding of ligand-assisted catalysis. Chapter 1 introduces these concepts and outlines the relevant catalytic reactions studied herein. To gain a deeper understanding of the chemistry involved, a comparative analysis of the reactivity differences between transition metal complexes with similar coordination structures is conducted. This investigation is crucial as it provides valuable insights into the design of suitable ligands for transition metal catalysts. Specifically, Chapters 2 and 3 of this thesis delve into a comparison of the reactivity of coordination complexes with identical metal centers and similar ligands, or even the same molecular formula, in catalysis. In the second chapter, we introduce a new cobalt (II) complex bearing an (SNS) amido ligand for the bifunctional hydroboration of carbonyls. Following an unsuccessful attempt to mono-protonate the amido donor in the bis(amido) complex Co(SᴹᵉNSᴹᵉ)₂ (2.1) treatment with 1 equivalent of 1,3-bis(1-adamantyl)imidazolium chloride (IAd•HCl) resulted in the liberation of one protonated ligand, affording CoᴵᴵCl(SᴹᵉNSᴹᵉ)(a-IAd) (2.2) with an "abnormally" coordinated IAd ligand, i.e., specifically bound through C4 instead of C2 of the imidazole ring. Compound 2.2 exhibited excellent catalytic activity in the hydroboration of aldehydes, displaying high substrate tolerance under mild reaction conditions and short reaction times. Stoichiometric reactions of 2.2 with pinacolborane (HBpin) revealed a bifunctional catalyst activation step, generating free SNS-amine, ClBpin and the active cobalt dihydride catalyst. Generation of an analogous catalyst with a normally coordinated IAd ligand showed poor reactivity in the hydroboration of aldehydes and was unable to effect ketone hydroboration. In Chapter 3, two tetranuclear copper(I) complexes bearing thiolate [Cu(SNSᴹᵉ)]₄ (3.1) and amido [Cu(SNSᴹᵉ)]₄ (3.2) SNS ligands are synthesized and their catalytic activity in a base-free azide-alkyne cycloaddition is compared. Complex 3.1 (1 mol%) demonstrated excellent reactivity for performing this 'click' reaction in water, exhibiting a broad substrate scope and enabling the production of various triazole compounds, including bioactive compound 3.16, which holds potential as an anti-cancer drug. DFT calculations suggested a proton shuttle role for the thiolate donor in conversion of the Cu-coordinated terminal alkyne to the key Cu-alkynyl intermediate. On the other hand, complex 3.2 exhibited reactivity similar to copper chloride. This observation was attributed to the basic nature of the amido ligand, which undergoes protonation by the coordinated alkyne C-H bond, with subsequent dissociation of the SNS-amine from the copper. Without a ligand to stabilize the copper in the less stable +1 oxidation state, a disproportionation reaction occurs, leading to catalyst deactivation. Chapter 4 introduces two palladium(II) thiolate complexes: PdI(κ³-SNSᴹᵉ) (4.1) exhibits catalytic activity in promoting the Heck cross-coupling reaction, while Pd(κ²-SNSᴹᵉ)₂ (4.2) affords no coupling product. In concert with triethylamine base, catalyst 4.1 efficiently produces olefin products with excellent yields, even at low catalyst loadings, and exhibits broad substrate tolerance over a 5 h reaction period. In contrast, the limited catalytic activity of 4.2 can be rationalized by proposing the formation of a Pd(N₂S₂) complex through ligand imine coupling at elevated temperatures, a reaction reported previously for Ni and Co analogs. The tetra-coordinated ligand formed through this isomerization occupies critical coordination sites around the metal, thereby preventing oxidative addition of the organohalide substrate, a key step in the Heck reaction mechanism. This work sheds light on the divergent catalytic behaviors of these two intriguing complexes. Finally, in Chapter 5 we assess what has been learned and identify relevant implications for further work.

The kinetics of ligand substitution for CO in Co4(CO)10(mu4-PPh2) , 1, have been investigated for the ligands P(OMe)3, P(OEt)3, PPh2H, P(0-i-Pr)3, P(n-Bu)3, PPh3, P(i-Pr)3, and PCy3 over a wide temperature range.

The goal of this research was to develop structurally diverse polyazine-bridged Ru(II),Pt(II) trimetallic and tetrametallic supramolecular complexes and study the impact of component variation on the redox, spectroscopic, and excited state properties that influence photoinduced charged separation and multielectron reduction.  These complexes are active photocatalysts for H2O reduction to H2.  Tetrametallic complexes with the supramolecular architecture [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ (Ru3Pt; TL = phen = 1,10-phenanthroline or Ph2phen = 4,7-diphenyl-1,10-phenanthroline; BL" = dpp = 2,3-bis(2-pyridyl)pyrazine or dpq = 2,3-bis(2-pyridyl)quinoxaline) feature a trimetallic dpp-bridged Ru(II) light absorber coupled to a cis-PtCl2 reactive metal center.  Trimetallic complexes with one less Ru-based light absorbing unit, [{(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+ (Ru2Pt; BL" = dpp or dpq), represent  a new supramolecular architecture that was designed and synthesized to provide less complex systems for excited state analysis.  Both the Ru3Pt and Ru2Pt systems have a remote Ru center separated from the reactive Pt site designed to provide extended 3MLCT lifetimes relative to directly coupled [(TL)2Ru(BL)PtCl2]2+ systems. The building block synthetic method used in constructing supramolecules provides the ability to purify and analyze the properties following each synthetic step, allowing sub-unit variation and structural diversity.  Building a knowledge base about the properties of smaller, less complicated structures is critical in understanding the electrochemistry, spectroscopy, and excited state dynamics of multi-metallic, multi-ligand complexes.  Electrochemical analysis of the [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes suggests a HOMO localized on the terminal Ru centers (E1/2 (RuII/III) = 1.56-1.63 V vs. Ag/AgCl) and a LUMO localized on the remote BL" coordinated to the reactive Pt site, with the energy dictated by the BL" identity (E1/2 = "0.32 or "0.33 V for BL" = dpp or E1/2 = "0.02 or "0.05 V for BL" = dpq).  This provides spatially separated HOMOs and LUMOs which predict lowest-lying charge separated states.  The complexes are robust UV and visible light absorbers due to multiple broad, overlapping ligand centered and metal-to-ligand charge transfer (MLCT) transitions.  The lowest energy 1MLCT absorption is centered around 540-550 nm for the four tetrametallic complexes with high molar absorptivity (31,000-42,000 M"1cm"1).  BL" variation has only a small impact on the electronic absorption spectroscopy, while the TL variation greatly enhances the absorptivity between 350 nm and 500 nm from 29,000 to 42,000 M"1cm"1 for complexes with TL = phen and Ph2phen, respectively.   The tetrametallic [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes exhibit unusual excited state dynamics as well as spatially separated HOMOs and LUMOs. The lowest lying optically populated state is a terminal Ru\'¼-dpp MLCT in all the Ru3Pt and Ru2Pt systems reported herein.  The terminal Ru(dÀ) based HOMO and BL"(À*) based LUMO suggests a lower lying terminal Ru\'BL" CS state in all systems.  Because the lowest lying terminal Ru(dÀ)\'BL"(À*) 3CS (charge separated) state is optically inaccessible, indirect population occurs.  The tetrametallic [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes have similar excited state lifetimes (Ä) of 75-83 ns, and they exhibit quantum yields of emission  ("em) of 7.1 x 10"4 (when BL" = dpp) and 3.2-3.7 x 10"4 (when BL" = dpq).  The lifetimes are shortened and the emission quantum yields are quenched in comparison to the [{(TL)2Ru(dpp)}2Ru(BL")]6+ models which possess the same emissive terminal Ru\'¼-dpp 3MLCT state with Ä = 110 ns and "em = 1.0-1.1 x 10"3.   In marked contrast to the large number of Ru polyazine systems studied, both monometallic and supramolecular complexes, the lowest lying 3MLCT state of the Ru3Pt complexes is not populated with unit efficiency due to 3CS state population from the emissive terminal Ru(dÀ)\'dpp(À*) 3CT state and a higher energy 3MLCT state, likely the central Ru(dÀ)\'BL"(À*) 3CT state.  The degree of population of this state is strongly dependent on the LUMO energy or driving force for population.  Stabilization of the BL" = dpq(À*) compared to higher energy dpp(À*) provides a larger driving force for intramolecular electron transfer to populate the 3CS state, resulting in ca. 40 % and 95 % population of the emissive state when BL" = dpq and dpp, respectively.  This suggests ca. 60 % and 5 % indirect population of the non-emissive 3CS state via a higher-lying 3MLCT state and the terminal Ru\'dpp 3MLCT emissive state when BL" = dpq and dpp, respectively.  These complexes violate Kasha\'s rule, an unusual occurrence for Ru(II) polyazine complexes, as the emissive state is not populated with unit efficiency.  Instead, the degree of population of the emissive state is dependent on the excitation wavelength. The Ru3Pt complexes are active photocatalysts for H2O reduction to H2.  In the presence of light and the sacrificial electron donor, DMA (N,N-dimethylaniline), the tetrametallic complexes collect electrons on the ligand À* orbitals of the central Ru to serve as photoinitiated electron collectors.  The photocatalytic activity in H2 production is drastically impacted by BL" identity, consistent with the enhanced driving force for charge separation to move electrons toward the cis-PtCl2 moiety.  After photolysis for 10 h, 15 ± 1 ¼mol (66 ± 4 TON) and 4 ± 1 ¼mol (18 ± 1 TON) of H2 were produced using [{(phen)2Ru(dpp)}2Ru(dpq)PtCl2]6+ and [{(phen)2Ru(dpp)}2Ru(dpp)PtCl2]6+, respectively.  Varying TL to Ph2phen serves to enhance light absorptivity and subsequently increase H2 production to 21 ± 1 ¼mol (94 ± 6 TON) and 5 ± 1 ¼mol (23 ± 2 TON) using [{(Ph2phen)2Ru(dpp)}2Ru(dpq)PtCl2]6+ and [{(Ph2phen)2Ru(dpp)}2Ru(dpp)PtCl2]6+, respectively.  The identity of BL" greatly influences the ability to direct the flow of charge through the supramolecular architecture impacting photocatalysis, while the identity of TL serves to fine tune the light absorbing and excited state properties. Due to the complicated excited state properties imparted by the large number of MLCT transitions in the [{(TL)2Ru(dpp)}2Ru(BL")PtCl2]6+ complexes, the analogous [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+ complexes were designed and a synthetic scheme developed.  The trimetallics possess similar electronic absorption spectroscopy with fewer terminal metal-based transitions due to removal of one (TL)2RuII(dpp) sub-unit and allow for distinguishable spectroscopic shifts resulting from perturbation of specific sub-units and the related molecular orbitals.  The trimetallic complexes exhibit similar redox properties with the HOMO localized on the terminal Ru and the LUMO localized on the remote BL", providing a low lying 3CS state.  Similar degrees of emission quenching are observed with the trimetallic complexes and their [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")]4+ models as was observed in the tetrametallic complexes.  The values of Ä and "em measured for [(Ph2phen)2Ru(dpp)Ru(bpy)(dpp)PtCl2]4+ were 90 ns and 1.1 x 10"3, respectively, and these values were 100 ns and 5.2 x 10"4 for [(Ph2phen)2Ru(dpp)Ru(bpy)(dpq)PtCl2]4+.  Similar to the Ru3Pt systems, the lifetimes are shortened and the emission is quenched compared to the [(Ph2phen)2"Ru(dpp)Ru(bpy)(BL")]4+ models (Ä = 120 ns and "em = 1.50 x 10"3, regardless of BL" identity).  These values provide ca. 98 % and 45 % population of the emissive state in the Ru2Pt systems for BL" = dpp and dpq, respectively, suggesting ca. 2 % and 55 % population of the non-emissive 3CS state for BL" = dpp and dpq, respectively.  This supports the use of this new Ru2Pt motif as models to study the excited state dynamics.  A substantial difference was observed between the excitation and absorption spectra for [(Ph2phen)2Ru(dpp)Ru(bpy)(dpq)PtCl2]4+, consistent with non-unity population of the emissive 3MLCT excited state. The simplified electronic absorption spectroscopy allowed the use of nanosecond transient absorption (TA) spectroscopy to analyze the excited state, and strong evidence of violation of Kasha\'s rule through partial population of the terminal Ru(À)\'BL"(À*) 3CS state (Ä = 25 ns)  in addition to the emissive terminal Ru(dÀ)\'dpp(À*) 3MLCT state (Ä = 120 ns) was observed through excitation-based emission spectroscopy and time-resolved TA spectroscopy. The synthesis, electrochemistry, electronic absorption spectroscopy, and steady-state and time-resolved emission spectroscopy for the [2Ru(BL")PtCl2]6+ and [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+ complexes as well as photocatalytic H2 production with [2Ru(BL")PtCl2]6+ and transient absorption spectroscopy of [(Ph2phen)2Ru(dpp)Ru(bpy)(BL")PtCl2]4+, are reported herein.  The work discussed within this dissertation provides in depth knowledge about the effects of component modification on the excited state dynamics and photocatalytic activity of structurally diverse Ru3Pt and Ru2Pt supramolecular complexes that is important in developing photochemical molecular devices.  Unusual excited state dynamics make it clear that much remains to be uncovered about structure-property relationship in these complex mixed-metal, mixed-ligand supramolecular motifs.  These supramolecular motifs also have applications in photodynamic therapy drug development and are currently under investigation by members of the Brewer research group. / Ph. D.

Low affinity Fcg receptor III (FcgRIII, CD16) triggers a variety of cellular events upon binding to the Fc portion of IgG. A real-time flow cytometry method was developed to measure the affinity and kinetics of such low affinity receptor/ligand interactions, which was shown as an easily operated yet powerful tool. Results revealed an unusual temperature dependence of reverse rate of CD16aTM dissociating from IgG. Except for a few studies using mammalian cell CD16s, most kinetics analyses use purified aglycosylated extracellular portion of the molecules, making it impossible to assess the importance of the receptor anchor and glycosylation on ligand binding. We used a micropipette adhesion frequency assay to demonstrate that the anchor length affects the forward rate and affinity of CD16s for IgG in a species specific manner, most likely through conformational changes. Receptor glycosylation dramatically reduced ligand binding by 100 folds. T cell receptor (TCR) is arguably the most important receptor in the adaptive human immune system. Together with coreceptor CD4 or CD8, TCR can discriminate different antigen peptides complexed with major histocompatibility complex (MHC) molecule (pMHC), which differ by as few as only one amino acid, and trigger different T cell responses. When T cell signaling was suppressed, TCR had similar affinity and kinetics for agonist and antagonist pMHC whose binding to CD8 was undetectable. TCR on activated T cell had a higher affinity for pMHCs, suggesting that TCRs organize themselves differently on activated T cells than on naïve T cells. In the absence of inhibitors for signaling, TCR binds agonist pMHC with several orders of magnitude higher affinity than antagonist pMHC. In addition, engagement of TCR by pMHC signals an upregulation of CD8 binding to pMHC, which is much stronger than the TCR-pMHC binding. The transition from weak TCR binding to the strong CD8 binding takes place around 0.75 second after TCR in contact with pMHC and can be reduced by several inhibitors of tyrosine and lipid phosphorylation, membrane rafts, and actin cytoskeleton. These results provide new insights to understanding T cell discrimination.

MDM2, murine double minute 2, is a RING type-E3 ligase protein and also an oncogene. MDM2 plays a critical role in determining the steady levels and activity of p53 in cells using two mechanisms. The N-terminal domain of MDM2 binds to the transactivation domain of p53 and inhibits its transcriptional activity. The RING domain of MDM2 plays a role in the ubiquitination (and degradation) of p53. Several proteins are responsible for the ubiquitination mechanism including the ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2) and ubiquitin ligase (E3). Since the E2-E3 interaction is essential for ubiquitination, the protein-protein recognition site is a potential drug target. Two different MDM2 RING constructs were expressed and purified: MDM2RING (residues 386-491) and MDM2RING△C (residues 386-478). Both constructs were characterised using dynamic light scattering, size exclusion chromatography, mass spectrometry, NMR and electron microscopy. E3 ligase activity in vitro was also studied. Taken together these results showed that the MDM2RING construct formed a concentration-dependent oligomeric structure. In contrast, the MDM2RING△C construct formed a dimer at all concentrations. Both MDM2RING and MDM2RING △ C retain E3 ligase activity. However, the MDM2RING△C construct is less active. Full length E2 enzyme UbcH5a was also purified. Various biophysical techniques were used to study its interaction with MDM2 as well as with potential small molecule inhibitors as in principle, small molecules which disrupt the interaction between MDM2 and UbcH5a, could prevent/promote ubiquitination of p53. The dimerisation of MDM2 is important for its E3 activity and the C8-binding site potentially provides a second druggable site. In this work, peptide 9, which has the same sequence as the C-terminus of MDMX (an MDM2 homologue) was found to inhibit MDM2 E3 activity. Various biological techniques including NMR, fluorescence anisotropy, and electrospray mass spectrometry were used to investigate the interaction between two inhibitory peptides and MDM2. A major part of project involved virtual screening (VS) to search for small molecules which can affect MDM2-dependent ubiquitination. Three potential targets were considered: (1) the C8-binding site of MDM2; (2) the UbcH5a-binding site of MDM2; and (3) the MDM2-binding site of UbcH5a. Several small molecules were identified using our virtual screening database-mining and docking programs that were shown to affect MDM2-dependent ubiquitination of p53. In terms of understanding the complex biochemical mechanism of MDM2 this work provides two interesting and functionally relevant observations: (i) the MDM2 RING△C construct is a dimer as this would not be expected form the existing studies, and has less E3 ligase activity than MDM2RING; (ii) small molecules that bind MDM2 on the E2 binding site enhanced E3 ligase activity. One model to explain these observations is that binding of small molecule activators family to the RING induces a change in the conformation of the Cterminal tail residues which may enhance E2 binding.

The glycine receptor (GlyR) is a ligand-gated ion channel member of the Cys-loop receptor superfamily, responsible for inhibitory neurotransmission in the brain and spinal cord. Zinc is a potent allosteric modulator of GlyR function, enhancing GlyR activity at low nM to 10[mu]M concentrations while inhibiting GlyR activity at higher concentrations. We investigated sources of contaminating zinc, identifying low nM levels of zinc in ultrapure H₂O, powdered reagents used in the preparation of common electrophysiological buffers, and in polystyrene pipets. These low levels of zinc were capable of enhancing GlyR function. These findings suggest that without checking for this effect using a zinc-chelator such as tricine, one cannot assume that responses elicited by glycine applied alone are not necessarily also partially due to some level of allosteric modulation by zinc. Taurine-activated GlyR may have a role in the rewarding effects of drugs of abuse. Zinc is found at GlyR-potentiating concentrations throughout the nervous system, so we examined the combinatorial effects of zinc with drugs of abuse on taurine-activated GlyR to mimic in vivo conditions. Whole cell recordings revealed that zinc potentiation of saturating taurine-generated currents decreased further potentiation by drugs of abuse, indicating no synergistic effects on efficacy when receptors are saturated with taurine as may be seen during synaptic events in vivo. Finally, we utilized phage display to identify novel peptide modulators of the GlyR. We tested 26 peptides against [alpha1beta] GlyRs, identifying peptides with various levels of activity on GlyR function. We demonstrated that these modulators were zinc-dependent, as their effects on GlyR activity were abolished in the presence of the zinc-chelating agent tricine. Together, these data indicate the importance of accounting for the effects of zinc when studying the function of the GlyR, as even low levels of zinc that can be found as contaminants in labware and buffers can affect GlyR function and responses to various allosteric modulators, including drugs of abuse. / text

An increasing number of proteins with unknown function have their three-dimensional structure solved at high resolution. This situation, largely due to structural genomics initiatives, has been stimulating the development of automated structure-based function prediction methods. Knowledge of residues important for function – and more particularly – for binding can help automated prediction of function in different ways. The properties of a binding site such as its shape or amino acid composition can provide clues on the ligand that may bind to it. Also, having information on functionally important regions in similar proteins can refine the process of annotation transfer between homologues. Experimental results indicate that functional residues often have an unfavourable contribution to the stability of the folded state of a protein. This observation is the underlying principle of several computational methods for predicting the location of functional sites in protein structures. These methods search protein structures for destabilising residues, with the assumption that these are likely to be important for function. We have developed a method to detect clusters of destabilising residues which are in close spatial proximity within a protein structure. Individual residue contributions to protein stability are evaluated using detailed atomic models and an energy function based on fundamental physico-chemical principles. Our overall aim in this work was to evaluate the overlap between these clusters of destabilising residues and known binding sites in proteins. Unfortunately, reliable benchmark datasets of known binding sites in proteins are sorely lacking. Therefore, we have undertaken a comprehensive approach to define binding sites unambiguously from structural data. We have rigorously identified seven issues which should be considered when constructing datasets of binding sites to validate prediction methods, and we present the construction of two new datasets in which these problems are handled. In this regard, our work constitute a major improvement over previous studies in the field. Our first dataset consists of 70 proteins with binding sites for diverse types of ligands (e.g. nucleic acids, metal ions) and was constructed using all available data, including literature curation. The second dataset contains 192 proteins with binding sites for small ligands and polysaccharides, does not require literature curation, and can therefore be automatically updated. We have used our dataset of 70 proteins to evaluate the overlap between destabilising regions and binding sites (the second dataset of 192 proteins was not used for that evaluation as it constitutes a later improvement). The overlap is on average limited but significantly larger than random. The extent of the overlap varies with the type of bound ligand. Significant overlap is obtained for most polysaccharide- and small ligand-binding sites, whereas no overlap is observed for nucleic acid-binding sites. These differences are rationalised in terms of the geometry and energetics of the binding sites. Although destabilising regions, as detected in this work, can in general not be used to predict all types of binding sites in protein structures, they can provide useful information, particularly on the location of binding sites for polysaccharides and small ligands. In addition, our datasets of binding sites in proteins should help other researchers to derive and validate new function prediction methods. We also hope that the criteria which we use to define binding sites may be useful in setting future standards in other analyses.

The bonding in a series of ligand-bridged metal dimer complexes has been characterized by He(I) and He(II) photoelectron spectroscopy and approximate molecular orbital calculations. Bridging ligands such as carbonyl, nitrosyl, methylene and pyrazolyl in the complexes [CpFe(NO)]₂, [Cp*Fe(NO)]₂, [CpRu(NO)]₂, [Cp*Co(CO)]₂, [CpFe(CO)₂]₂, [Cp*Fe(CO)₂]₂, [CpFe(CO)]₂-μCO-μCH₂, [Cp*Fe(CO)]₂-μCO-μCH₂, [CpFe(NO)]₂- μCh₂, [CpRu(NO)]₂-μCH₂, [CpCo(CO)]₂-μCH₂, [CpRh(CO)]₂-μCH₂, [Ir(pyrazolyl)(CO)₂]₂, [Ir(3-methylpyrazolyl)(CO)₂]₂ and [Ir(3,5-dimethylpyrazolyl)(CO)₂]₂ are investigated and their effects upon metal-metal interactions are surveyed. Due to the presence of two d⁷ or d⁸ late metal atoms per molecule, these complexes display many overlapping ionization bands in a narrow valence ionization region. Attention has been given to modelling the photoelectron single ionization with asymmetric and symmetric Gaussians. The overlapping ionizations are successfully represented in terms of the model bandshapes. Thermodynamic relationships between bond dissociation and photoelectron ionization energies are also investigated. With relationships of this type, trends in bond energies may be correlated with ionization energies. Ligand inductive and bonding effects as well as small changes in molecular geometry cause shifts in the metal-based ionizations, which aid chemical understanding and interpretation of the molecular orbital picture. By comparing a series of related metal dimers, the assignment of related ionizations in the photoelectron spectra becomes apparent. Changes in ligand π accepting ability and changes in metal and formal oxidation states are also probed. Addition information is provided by vibrational fine structure in Cp₂Os, [CpFe(NO)]₂, and [Cp*Co(CO)]₂ and spin-orbit splitting in Cp₂Os. The metal-ligand backbonding combinations are found to be the most stable interactions and are responsible for the stability of the metal dimers. Metal-metal interactions are found to be relatively unimportant. Ligands with stronger π accepting abilities allow for more stabilized supported metal dimer complexes.

This thesis details the attempt to design and synthesis a range of ligands and organocatalysts based on a common backbone design. Initial results were promising with a number of ligands being generated from our common C2-symmetric backbone. Unfortunately none of the molecules synthesises gave promising results in test reactions. Variations on the initial design also failed to give any encouraging results. More positively, work on phosphorus-nitrogen (P,N) ligands was successful, with a number of different ligands being synthesised and metal complexes prepared. Pleasingly we were able to obtain X-ray crystallography of one of these complexes indicating that the ligand was complexed to the metal via the phosphorus moiety. Work using the Buchwald-Hartwig reaction for coupling aryl bromides to both 1,2,3,4-tetrahydroisoquinoline and 1,2,3,4-tetrahydroquinoline was successful, with methodology being developed which we believe can be applied to the synthesis of Ancistrocladinium A. In particular the coupling between 1,2,3,4-tetrahydroisoquinoline and 1-bromonaphthalene afforded us the full carbon skeleton of the ring system of the natural product in one step, from which we were able to generate the iminium salt. We also investigated an alternative route for the synthesis of Ancistrocladinium A achieving atropoisomerism. Experimental data is provided in chapter three, and all X-ray crystallography structures reported in chapter two are provided in the appendix.

Organic cation transporters (OCTs) play a pivotal role in the absorption, tissue distribution, and excretion of a diverse array of substances, and currently the nature of the biochemical interactions between substrate and OCTs are unknown. Therefore, identifying which amino acid residues are critical for OCT-substrate interactions is of central importance to understanding and predicting interactions between drugs and OCTs. A three-dimensional (3-D) homology model of human OCT3 was generated using the crystal structure of a high affinity phosphate transporter from Piriformospora indica (PiPT) as template, and putative binding pocket for the prototypical hOCT3 ligand 1-methyl-4-phenylpyridinium (MPP+) was identified through docking studies. Five residues, Phe36, Val40, Trp358, Glu451 and Asp478, were identified as potentially mediating hOCT3-MPP+ interactions, and confirmed through in vitro studies. Additionally, 3-D homology modeling of the functional hOCT3 mutant Val40Leu, and all non-functional hOCT3 mutants, indicated changes in binding pocket architecture consistent with weakening of ligand-transporter interactions. Docking of structurally divergent hOCT3 substrates indicated binding interactions in the same general region as that identified for MPP+, albeit with mostly unique residues. Interspecies differences were explored by generating 3-D homology models for rat and murine Oct3. Results from docking studies using compounds exhibiting vastly different binding affinities (Km or IC50) towards the OCT3/Oct3 orthologs were consistent with varying strength in ligand-transporter binding pocket interactions. Finally, a series of novel compounds exhibiting anti-depressant-like activity was screened for OCT interaction in vitro, and demonstrated significant inhibitory effects on OCTs for many of the compounds.