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Surface modification with polymers using living radical polymerisation and click chemistryChen, Gaojian January 2007 (has links)
Thin organic and polymer layers on solid substrates play a key role in many processes aimed at modifying surface properties. Both "grafting to" and "grafting from" methods have been used in this project to modify a variety of surfaces including cellulose, resins and carbon nanotubes (CNT) with functional polymers. Living radical polymerisation and Huisgen [2+3] cycloaddition (often termed "click" reaction) were used to carry out these modifications. Living radical polymerisation was first used to synthesize different α-functional polymers and used for surface modification. For example, Living radical polymerisations of methyl methacrylate and a fluorescent comonomer with 2-bromo- 2-methyl-propionic acid 3-azido-propyl ester and 2-bromo-2-methyl-hept-6-yn-3-one as initiators have been successfully employed for the synthesis of fluorescently tagged azide and alkyne terminated PMMA with molecular weight (Mn) close to that predicted and polydispersity index (PDi) less than 1.20 and good first order kinetics that would be expected for living radical polymerisation. Cotton and organic resin surfaces have been functionalised with alkyne groups using simple condensation with 4-chlorocarbonyl-butyric acid prop-2-ynyl ester. The surfaces have been further modifies using a Huisgen [2+3] cycloaddition (click) reaction of both polymeric and small molecule azides. Different functional azides, namely mono azido-PEG and a new fluorescent hostasol derivative have also been prepared and tested as model substrates for cotton surface modification. This approach is shown to be very general allowing soft and hard surfaces with different geometries to be modified. In particular it is an excellent method to alter the nature of organic resins allowing the incorporation of many different functionalities. The covalent immobilization of a range of carbohydrate derivatives onto resin beads was then carried out. Copper-catalysed Huisgen [2+3] cycloaddition was used to graft mannose-containing azides to complementarily functionalised alkyne surfaces, namely: a) Wang resin or b) "Rasta" particles consisting of a "clickable" alkyne polymer loose outer shell and a Wang resin inner core. For the second approach, Wang resin beads were first converted into immobilized ATRP initiators, and then polymerisation of trimethylsilanyl-protected propargyl methacrylate followed by deprotection with TBAF·3H2O afforded the desired polyalkyne clickable scaffold. An appropriated α-mannopyranoside azide was then clicked onto it, to give a mannose functionalized "Rasta" resin. The binding abilities of these D-mannose-modified particles were then tested using fluorescein labelled Concanavalin A (Con A), a lectin known for its ability of binding certain mannose-containing molecules. Our preliminary results indicated that the novel glycohybrid materials presented in this work are able to efficiently recognize mannose-binding model lectins such as Con A, opening the way for their potential application in affinity chromatography, sensors and other protein recognition/separation fields. Other functional polymers with antibiotic or chiral properties were also grafted from surfaces. Living radical polymerisation of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and a metronidazole monomer (MTD-MA) has been successfully employed for the synthesis of antibiotic metronidazole containing polymers with Mn close to that predicted, narrow polydispersity and good first order kinetics that would be expected for living radical polymerisation. Using the monomers PEGMA and MTD-MA, with preformed immobilized initiator on cotton, surface initiated LRP was carried out to give cotton bearing antibiotic polymers. Surface initiated living radical polymerisation of GMA was then successfully carried out for the synthesis of PGMA containing bead base on Aquagel resin. The hydroxyl groups of the PGMA moiety were then reacted with a single enantiomer (R)-(+)-1- phenylethyl isocyanate (EtPhNCO). This demonstrates a convenient way of immobilise enantiomer moiety onto resin surface and the resulting solid support may be used as chiral stationary phases (CSP) for HPLC chromatography. To modify CNTs with functional polymers not only increase the dispersability of the CNTs, it has also enlarged the application areas of CNT’s due to the polymers' own functional properties. MWCNTs were first converted to a solid support LRP initiator by an esterification reaction and styrene was grafted from MWCNTs through surfaceinitiated LRP, the PSt modified CNTs were then used to form isoporous membranes. Similarly, Poly(amidoamine) (PAMAM) dendrons were covalently attached to MWCNTs and dendron-MWCNT-Ag(0) hybrid materials were made afterwards which occurred via Ag(I) coordination to the PAMAM dendron nitrogen donors, followed by reduction with formaldehyde. Finally, noncovalent method was used to make a thermo-sensitive water soluble CNTs. The homopolymerisations and copolymerisation of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and di(ethylene glycol) methyl ether methacrylate (DEGMA) using a pyrene-containing initiator and a Cu(0)/Me6-Tren catalyst system was investigated. The pyrenefunctionalised polymers synthesised were then used to modify CNTs and thus thermosensitive water-dispersible CNTs were made.
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The nucleation and growth of precipitates in aluminium alloysJacobs, M. H. January 1969 (has links)
The aim of the work described in this dissertation was to gain an improved understanding of the basic factors controlling the nucleation, growth and stability of precipitates in age-hardening alloys. The stimulus for the work was provided by the current use of complex ageing heat treatments for modifying (normally with the object of improving) the mechanical properties of alloys. The research was confined to aluminium-base alloys, but it is believed that many of the ideas and concepts yielded by the work will be equally applicable to other alloy systems. Two aluminium-base alloys were studied in detail: one composition of aluminium-magnesium-silicon alloy and three compositions of aluminium-zinc alloy. The experimental heat treatments were carried out on thin foil samples (~0.01 cm. thickness) and the resulting precipitation was studied by means of thin foil transmission electron microscopy. The low temperature precipitation sequence of aluminium-zinc alloys has been investigated extensively by other workers and their results are reviewed in Chapter 3. During this investigation, some samples of aluminium-zinc, alloy were quenched rapidly to a high ageing temperature arid, under these special ageing conditions, a new type of precipitate was observed. The morphology and crystal structure of this precipitate are described in Chapter 3. Also described in Chapter 3 are the results obtained from an extensive electron diffraction investigation into the crystal structure of the small needle-shaped precipitates which are formed, under suitable ageing conditions, in aluminium-magnesium-silicon alloys. The types of heat treatment that were studied may be broadly classified into two categories: (1) single-step ageing treatments, and (2) two-step ageing treatments. A large number of single-step and two-step ageing treatments were investigated, with the general objective of obtaining a comprehensive idea of the overall response of the two alloys to the heat treatments. These experimental results provided data, for the development of a theoretical model to explain the basic processes affecting the response of both alloys to two-step ageing treatments. It is emphasized that the basis of this model had already been detailed by Dr. D. W. Pashley, F. R. S. to explain the extensive microstructural observations obtained, at T. I. Research Laboratoriesq with an aluminium-magnesium-silicon alloy, during an earlier research programme (the salient points of this model are discussed in Chapter 5 of this dissertation). Many aspects of this model are extended and amplified in Chapters 4 to 7 and it is shown that there is an excellent qualitative agreement between the predictions of the model and the numerous experimental results which have been obtained. This applies not only to the aluminium-magnesium-silicon system but also to the aluminium-zinc system. The model has been particularly successful for aiding the semi-quantitative explanation of the observed marked dependence on heat treatment conditions of the width of grain boundary. precipitate-free zones in aluminium-zinc alloys. A full account of this aspect of the work is presented in Chapter 6. The model also provides a new insight into the basic processes controlling the phenomenon of reversion in aluminium-zinc alloys, and this is described in Chapter 7 together with in account of the experimental results obtained from "reversion" studies with this alloy. Finally, in Chapter 8, the theories and concepts developed in this dissertation are compared and contrasted critically with those of other workers. For brevity, the alloys are denoted throughout this dissertation by their chemical symbols. Except where otherwise state; all alloy compositions are, given in weight per cent.
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Functionalisation of surfaces and interfaces : molecules, particles and crystalsPeruffo, Massimo January 2010 (has links)
This thesis is concerned with understanding and directing the functionalisation of solid surfaces with materials: molecules, nanoparticles and crystals. Both conducting (electrode) and insulating surfaces are of interest. For molecular functionalisation, a sweep potential procedure has been developed to assist the formation of self assembled monolayers (SAMs) of a ruthenium thiolated complex. Electrochemical investigations were employed to characterised the SAM formed on a platinum electrode. Nanoparticles formation explored two distinct routes. First Pd nanoparticles were successfully formed within ultra-thin Nafion films via impregnation and a chemical reduction method. Morphological investigations utilised atomic force microscopy. The electrocatalytic properties of the nanocomposite material were elucidated for the hydrogen oxidation reaction. The methodology used for the preparation of this nanocomposite material shows promise for applications in sensors and fuel cells. Second, the potential-assisted deposition of pre–formed perthiolated-ß-cyclodextrin-capped Pt nanoparticles method is described. Pt nanoparticles (5 nm diameter) were deposited in a controlled fashion on indium tin oxide and highly oriented pyrolytic graphite electrodes. The Pt nanoparticles formed in this way were electrocatalytically active towards hydrogen generation and oxidation. This new approach for the deposition of metal nanoparticles with controlled surface density provides a new tool for the investigation of electrocatalytic processes. A major focus of the second part of the thesis has been the development of methods to study crystal deposition at extreme supersaturation. For this purpose a delivery system for calcium carbonate at high-supersaturation ion has been coupled with a quartz crystal microbalance and in–situ optical microscopy. The dynamics and quantitative evaluation of calcium carbonate deposition onto foreign solid substrates, and the effect of various additives, are described. Ex– situ studies, scanning electron microscopy and microRaman spectroscopy, allowed the morphological characterisation of the phases deposited. The transformation of ACC to calcite has been explored in details. In the study of additives, a significant finding was that citrate concentration shows a nonmonotonic behaviour on the amount of scale deposited. Fast screening of different additives (polymeric and molecular) and a quantitative ranking of their inhibitory properties on calcium carbonate deposition on a gold surface is described. Molecular and polymeric additives showed different inhibitory mechanisms on the scaling process and the technique employed gave a better insight into their mode of action.
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Development and application of evanescent wave cavity ring-down spectroscopy for studies of electrochemical and interfacial processesSchnippering, Mathias January 2009 (has links)
This thesis is concerned with the application of evanescent wave cavity ring-down spectroscopy (EW-CRDS) and evanescent wave broadband cavity enhanced absorption spectroscopy (EW-BB-CEAS) for studies of electrochemical and interfacial processes. These include nanoparticle adsorption/dissolution, polymer nanoparticle formation and surface-bound electrochemical redox reactions. Different experimental setups have been designed to investigate these systems. EW-CRDS is a surface sensitive technique, which allows absorption measurements at solid/liquid and solid/air interfaces. Surface reactions can easily be monitored in real time. A pulsed or modulated laser beam is coupled into an optical cavity which consists of at least one optical element, in which the beam is total internal reflected. At the position of total internal reflection (TIR), an evanescent field is established with the amplitude decaying exponentially with distance from the boundary. The evanescent field can be exploited to investigate the absorbance properties of the liquid phase in the first few hundred nanometres of the solution above the silica surface. These types of instruments have high temporal resolution (up to 2 kHz repetition rate), coupled with high sensitivity (minimum detectable interfacial absorbance per pass: ~80 ppm) which enables the investigation of a variety of processes relating to fundamental questions in the field of physical chemistry and materials science. The aforementioned sensitivity and resolution make EW-CRDS an ideal tool for those investigations, especially if combined with other techniques such as electrochemistry or microfluidic and hydrodynamic techniques. In this thesis, different instrumentational setups will be discussed. EW-BB-CEAS is another example for a TIR based absorption spectroscopic technique and can give additional spectral information about the investigated surface processes by employing broadband light such as supercontinuum radiation. In this case, the amplified light intensity within the optical cavity is measured rather than the light decay. By employing complementary techniques, such as electrochemistry and atomic force microscopy and by fitting experimental data using finite-element modelling, surface processes can not only be described accurately but also kinetic information such as rate constants for the aforementioned systems can be calculated.
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tert-Butylstyrene in Ziegler-Natta polymerisationsTheaker, Giles William January 2010 (has links)
Chapter One introduces Ziegler-Natta polymerisation through mechanisms of polymerisation encompassing activation, propagation and termination of a polymer. The mechanisms of monomer insertion and their effects on polymer microstructure are shown. Several important catalysts of different design (metallocenes, half-sandwich complexes and post-metallocenes) are shown. Chapter Two focuses on ethene/styrene and ethene/tert-butylstyrene copolymerisations using commercially available metallocene catalysts, with the goal of increasing styrenic co-monomer incorporation without sacrificing productivity. Terpolymers of the above systems with hexene are briefly discussed. Chapter Three looks at ethene/tert-butylstyrene copolymerisations using post-metallocene catalysts, focusing specifically on zirconium based salicylaldimine species. The dramatic effects of modified styrenic monomers on these catalysts is shown. Chapter Four shows how zirconium based salicylaldimine catalysts and similar species can be activated so as to homopolymerize tert-butylstyrene in the presence of H2 and other monomers. A mechanistic explanation of the effects is postulated. The effects of ligand modification are explored, leading to the discovery of the active species involved in the above homopolymerisations. Chapter Five covers experimental details relating to the above chapters, including synthesis of precursors, ligands, precatalysts and polymerisation methodologies.
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Modelling techniques for the study of molecular self-organisationFortuna, Sara January 2010 (has links)
In this thesis we develop computational techniques for modelling molecular selforganisation. After a short review of the current nanotechnological applications of molecular self-assembly and the main problems encountered in modelling the selforganised behaviour of chemical systems, we introduce a set of methods, from both chemistry and complexity science, for the prediction of self-assembled structures, with particular focus on Monte Carlo (MC) based methods. We apply the MC method to two systems of experimental interest. First we model the silica nanoparticles on the surface of spherical polystyrene latex droplets, synthesised by the S. Bon Group at the University of Warwick, as a set of soft spheres on a spherical surface, to study their packing patterns as a function of the broadening of the nanoparticle size distribution. Then we develop a hexagonal lattice model for the study of the two-dimensional self-organisation of planar molecules capable of complementary interactions, to study their phase diagrams as a function of the strength of their complementary interactions and bonding motif. In both cases, the phases are characterised using a number of order parameters. We show that these simplified models are able to reproduce the experimental observations. We then develop an Agent Based (AB) algorithm, traditionally used for the study of complex systems, for the modelling of molecular self-organisation. In this algorithm, an agent is identified with a stable portion of the system under investigation. The agents can then evolve following a set of rules which include elements of adaptation (new configurations induce new types of moves) and learning (past successful choices are repeated), in order to drive the system towards its lowest energy configuration. We first apply the method to the study of the packing of a set of idealised shapes, then we extend it to the study of a realistic system. The latter is achieved by linking the AB algorithm to an available molecular mechanics code, in order to calculate the interaction energies of atomistic models. In both cases we compare the AB result with that of MC based methods, showing that for all the systems studied, the AB method consistently finds significantly lower energy minima than the MC algorithms in less computing time. Finally, we show how the AB algorithm can be used as a part of the protocol to calculate the phase diagram of a rigid organic molecule (1,4-benzene-dicarboxylic acid or TPA) with less computational effort than standard techniques.
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The synthesis and ring-opening polymerisation of novel cyclic esters from malic acidPounder, Ryan J. January 2010 (has links)
The work in this thesis is directed towards the preparation of cyclic ester monomers using malic acid as a renewable resource. Their subsequent controlled ring-opening polymerisation (ROP) to yield functionalised poly(ester)s is studied and application in micellar self-assembly reported. Chapter 1 reviews the many synthetic strategies that have been employed in the preparation of functional glycolides, lactides, ε-caprolactones, δ-valerolactones and β-propiolactones. Their subsequent polymerisation and applications are also discussed. Chapter 2 describes the improved synthesis of 3-(S)- [(benzyloxycarbonyl)methyl]- and 3,6-(S)-[di(benzyloxycarbonyl)methyl]-1,4- dioxane-2,5-diones, BMD and malide respectively, from L-malic acid. Controlled organocatalytic ROP of BMD realised functional poly(glycolic acid-co-benzyl α- malate)s (PBMD) with the choice of initiator proving important in determining the resulting molecular weight. Successful hydrogenolysis of these poly(glycolic acid-co-benzyl α-malate)s yielded hydrophilic poly(glycolic acid-co-α-malic acid)s (PGMA) with subsequent degradation studies in H2O observing complete degradation after six days. In Chapter 3, the synthesis of 5-(S)- and 5-(R)-[(benzyloxycarbonyl)methyl]-1,3- dioxolane-2,4-dione (L-malOCA and D-malOCA respectively) from L- and Dmalic acid respectively is reported. ROP of malOCA with a range of pyridine based catalysts enabled the synthesis of functional poly(benzyl α-malate)s (PBMA). Mechanistic studies revealed the formation of several side products that were eliminated via judicious choice of catalyst and column chromatography. Subsequent hydrogenolysis realised hydrophilic poly(α-malic acid)s (PMA) with degradation studies in H2O observing complete degradation after 10 days. Chapter 4 reports the synthesis of novel amphiphilic PEO-b-PBMA block copolymers by the ROP of L-malOCA or D-malOCA from PEO macroinitiators with subsequent self-assembly realising polymeric micelles. Variation in both size dimensions and stability of the micelles through changes in both the hydrophobic and hydrophilic block lengths and their relative ratios was demonstrated. The self-assembly of an equimolar mixture of homochiral PEO-b- P(L-BMA) and PEO-b-P(D-BMA) resulted in the formation of stereocomplexed polymeric micelles. Chapter 5 provides a summary of the findings in chapters 2 – 4 with chapter 6 providing the corresponding experimental data.
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Reducing catalyst loadings in radical cyclisation reactions and investigating atropisomerism in enamidesWilson, Paul January 2010 (has links)
The bulk of the work presented in this thesis represents an evolution of copper-mediated atom transfer radical cyclisation. Chapter 1 provides introduction to radical cyclisation methods and applications and is followed by the shortest results chapter that discusses the outcome of 1,4-dimethylpiperazine mediated radical cyclisation of monobromoacetamides. Cyclisation was possible but competing reduction and elimination pathways are prevalent when less reactive substrates are used. Chapters 3 and 4 focus on the evolution of copper-mediated atom transfer radical cyclisation. A number of additives were screened in the hope of achieving catalyst regeneration which would allow catalyst loadings to be reduced without loss of efficiency and negate the need for an inert atmosphere throughout the reaction. In chapter 3, AIBN was found to be the optimum additive and efficient cyclisation was possible using copper (I) (Cu(TPA)Br) and copper (II) (Cu(TPA)Br2) complexes (1 mol%) in DCM and toluene (at 50 and 110 oC respectively) suggesting AIBN could activate and reactivate the catalyst in situ. In chapter 4 an alternative, highly efficient process was developed using copper (II) in the presence of potassium borohydride in MeOH. Reaction times were significantly reduced (10-30 min) and reactions were performed at room temperature even at decreased catalyst loadings (0.1 mol%). The mechanism for the process is likely to differ from that of conventional atom transfer radical cyclisation. UV analysis of the catalyst complex and the reactions progress, compared to literature data, suggest the active catalyst could be a copper borohydride (CuBH4) complex. Finally chapter 5 compiles a structural analysis of a variety of enamides to determine the feasibility of chiral induction during 5-endo trig radical cyclisation. A number of N-cycloalkenyl and N-cyclohexenyl enamides, which share an axis of chirality about the N-C(cycloalkenyl) bond, were analysed by variable temperature NMR to determine the rate and barrier of rotation of the chiral axis. Although none of the enamides studied had barriers great enough to achieve chiral induction it was recognised that the barrier to rotation could be significantly increased if tetrasubstituted enamides were accessible. Tetrasubstituted enamides were prepared and their barriers were determined by chiral HPLC, with barriers predicted to be great enough for chiral induction. Cyclisation was attempted but to no avail with unexpected oxidation products being obtained. Despite this, a more comprehensive understanding of the enamide structure has paved the way for potential chiral induction in 5-endo trig radical cyclisation.
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Modelling of the interaction between peptides and graphitic surfacesTomasio, Susana de Miranda January 2010 (has links)
The aim of this thesis is to understand the interactions of peptides with graphitic surfaces such as carbon nanotubes and graphite, in order to help establish guiding principles for the design of peptide sequences with controllable affinity to graphitic surfaces. Atomistic molecular dynamics (MD) simulations with our extended polarisable AMOEBAPRO force-field, which includes parameters for graphitic surfaces is used throughout. The peptide sequences studied were identified by phage-display experiments for their strong affinity to CNTs, and are rich in tryptophan and histidine residues [94]. The importance of the tryptophan residues on the binding affinity to CNTs is investigated by mutating each tryptophan by either tyrosine and phenylalanine. In addition, the effect of the surface curvature on the binding affinity is also explored. It is found that sequences containing tryptophan residues have more affinity to graphitic surfaces than those containing tyrosine or phenylalanine. Furthermore, it is suggested that these peptide sequences were selected for interfacial shape, since in the case of graphite, a compromise between having all the aromatic residues close to the surface and also allowing the non-aromatic residues to approach the surface is found. Following this study, the interaction of peptide sequences with CNTs is again studied, but this time with the aim to investigate the order of the residues, on the binding affinity to CNTs. The influence of the peptide sequence on the binding affinity to CNTs is studied by scrambling the sequence (HWKHPWGAWDTL). This study suggests that binding affinity is strongly dependent on the order of the content of the peptide sequences and gives some useful insights to the identification of principles that may help in the design of peptide sequences with controllable binding affinity to CNTs. For instance, it is found that strong binding may be due to the presence of isolated pairs of tryptophans, while weaker binding may be due to the presence of two tryptophan residues intercalated by another residue. The interactions of water with graphitic surfaces – CNTs, fullerenes and graphite – are also considered and it is found that the water structuring at the interface is weak and that there are no more than tree layers of structured water on the graphitic surfaces. Finally, the effect of the presence of OH defects on CNTs on the binding affinity to peptides is investigated. The results show that the binding affinity is not significantly affected by the presence of OH defects, but a general increase in the peptide mobility is noticed, giving insights for the applications of real CNTs with peptides. The work described in this thesis helps to understand what are the key residues involved in the interaction with CNTs, why do these key residues bind better to CNTs and provide insights on the mechanisms of peptided binding to CNTs, by demonstrating the role of peptide conformation.
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Self-assembly and bioinorganic chemistry of optically pure helical complexesHowson, Suzanne E. January 2011 (has links)
Chapter 1 introduces the concept of helicates and the importance of chirality in these complexes. The different literature methods used to synthesise optically pure helicates are reviewed and their advantages and disadvantages discussed. Finally, a new approach towards synthesising diastereomerically pure helicatelike complexes is considered. Chapter 2 describes the syntheses of optically and diastereomerically pure factris( diimine) monometallic complexes of Fe(II) with d.r. > 200:1. The origins of this unprecedented stereo- and chemical selectivity are investigated via computational and structural studies, and compared with analogous complexes of other 3d metals (ZnII, CoII, CoIII). The reactivity of the optically and stereochemically pure Fe(II) complexes towards e.g. copper(I)-catalysed Huisgen 1,3-dipolar cycloaddition ‘click’ reactions is investigated. Recently published Cu(II) complexes of the same ligand by Min et al. are also discussed. Chapter 3 focuses on extending the chemistry described in Chapter 2 to design ligands capable of forming helicate-like structures. The resulting Fe(II) and Zn(II) bimetallic triple stranded complexes are diastereomerically pure with d.r. > 200:1. A detailed structural study is described based on a single crystal X-ray structure. The ability to add substituents to the pyridine rings successfully allows useful functionalities to be incorporated on the periphery of the structure. Chapter 4 describes the synthesis of a second family of diastereomerically pure helicate-like complexes. Useful functionalities are easily incorporated on the periphery of the structure via the use of different (R)-2-phenylglycinol derived amines in a one-pot synthesis. The reactivity of the alkyne hexa-functionalised Fe(II) complex towards copper(I)-catalysed Huisgen 1,3-dipolar cycloaddition reactions is also investigated. Chapter 5 focuses on the synthesis and biological applications of water soluble helicate-like bimetallic complexes. Specifically, experiments probing the binding of these complexes to DNA and DNA structural motifs are described. The antimicrobial activity of the complexes against the Gram-negative bacterium E. coli and the Gram-positive bacterium S. aureus (MRSA252) is also investigated. Chapter 6 details the experimental procedures used to carry out the work in this thesis.
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