Hypercoiling and hydrophobically associating polymers : interfacial synthesis, surface properties and pharmaceutical applications

The objective of the work described was to identify and synthesize a range of biodegradable hypercoiling or hydrophobically associating polymers to mimic natural apoproteins, such as those found in lung surfactant or plasma apolipoproteins. Stirred interfacial polymerization was used to synthesize potentially biodegradable aromatic polyamides (Mw of 12,000-26,000) based on L-Iysine, L-Iysine ethyl ester, L-ornithine and DL-diaminopropionic acid, by reaction with isophthaloyl chloride. A similar technique was used to synthesize aliphatic polyamides based on L-Iysine ethyl ester and either adipoyl chloride or glutaryl chloride resulting in the synthesis of poly(lysine ethyl ester adipamide) [PLETESA] or poly(lysine ethyl ester glutaramide) (Mw of 126,000 and 26,000, respectively). PLETESA was found to be soluble in both polar and non-polar solvents and the hydrophobic/hydrophilic balance could be modified by partial saponification (66-75%) of the ethyl ester side chains. Surface or interfacial tension/pH profiles were used to assess the conformation of both the poly(isophthalamides) and partially saponified PLETESA in aqueous solution. The results demonstrated that a loss of charge from the polymer was accompanied by an initial fall in surface activity, followed by a rise in activity, and ultimately, by polymer precipitation. These observations were explained by a collapse of the polymer chains into non-surface active intramolecular coils, followed by a transition to an amphipathic conformation, and finally to a collapsed hydrophobe. 2-Dimensional NMR analysis of polymer conformation in polar and non-polar solvents revealed intramolecular associations between the hydrophobic groups within partially saponified PLETESA. Unsaponified PLETESA appeared to form a coiled structure in polar solvents where the ethyl ester side chains were contained within the polymer coil. The implications of the secondary structure of PLETESA and potential biomedical applications are discussed.

Increased TG2 expression can result in induction of transforming growth factor β1, causing increased synthesis and deposition of matrix proteins, which can be regulated by nitric oxide

In fibrotic conditions increases in TG2 activity has been linked to an increase in the deposition of extracellular matrix proteins. Using TG2 transfected Swiss 3T3 fibroblasts expressing TG2 under the control of the tetracycline-regulated inducible promoter, we demonstrate that induction of TG2 not only stimulates an increase in collagen and fibronectin deposition but also an increase in the expression of these proteins. Increased TG2 expression in these fibroblasts led to NF-kappaB activation, resulting in the increased expression of transforming growth factor (TGF) beta(1). In addition, cells overexpressing TG2 demonstrated an increase in biologically active TGFbeta(1) in the extracellular environment. A specific site-directed inhibitor of TG abolished the NF-kappaB and TGFbeta1 activation and the subsequent elevation in the synthesis and deposition of extracellular matrix proteins, confirming that this process depends on the induction of transglutaminase activity. Treatment of TG2-induced fibroblasts with nontoxic doses of nitric oxide donor S-nitroso-N-acetylpenicillamine resulted in decreased TG2 activity and apprehension of the inactive enzyme on the cell surface. This was paralleled by a reduction in activation of NF-kappaB and TGFbeta(1) production with a subsequent decrease in collagen expression and deposition. These findings support a role for NO in the regulation of TG2 function in the extracellular environment.

The synthesis, characterisation and electrical conductivity of poly(styrene-co-acetylene)

A novel metathesis catalyst for the polymerisation of acetylene has been developed. The polyacetylene produced by this new catalyst has been characterised by infra-red and NMR spectroscopy. The conductivity of the pristine material has been studied as a function of temperature, pressure and frequency. The effect on the conductivity of doping the material has also been investigated. The new metathesis catalyst has been incorporated into an anionic-to-metathesis transformation reaction. This novel reaction has been used to prepare samples of poly(styrene-co-acetylene). The copolymer has been characterised using U.V./Visible, NMR, infra-red spectroscopy and the surface morphology looked at using scanning electron microscopy. GPC was also used to give some idea of the molecular weights of the materials prepared. The conductivity of the copolymer has been studied as a function of temperature, pressure and frequency. The effect of doping on the conductivity the material has also been investigated. The conductivity results obtained from both materials have been used to try and gain an insight into the mechanism of the conduction processes occurring within the materials. An attempt has also been made to synthesise polyacetylene oligomers (polyenes) by modifying the Ziegler/Natta type catalysts commonly used to synthesise polyacetylene. The polyenes were characterised using U.V./Visible and infra-red spectroscopy together with GPC and GCMS.

Design and synthesis of novel hydrogels for biological applications

The aims of this project were:1) the synthesis of a range of new polyether-based vinylic monomers and their incorporation into poly(2-hydroxyethyl methacrylate) (poly(HEMA)) based hydrogel networks, of interest to the contact lens industry.2) the synthesis of a range of alkyltartronic acids, and their derivatives. These molecules may ultimately be used to produce functionalised poly(-hydroxy acids) of potential interest in either drug delivery or surgical suture applications. The novel syntheses of a range of both methoxy poly(ethylene glycol) acrylates (MPEGAs) and poly(ethylene glycol) acrylates (PEGAs) are described. Products were obtained in very good yields. These new polyether-based vinylic monomers were copolymerised with 2-hydroxyethyl methacrylate (HEMA) to produce a range of hydrogels. The equilibrium water contents (EWC) and surface properties of these copolymers containing linear polyethers were examined. It was found that the EWC was enhanced by the presence of the hydrophilic polyether chains.Results suggest that the polyether side chains express themselves at the polymer surface, thus dictating the surface properties of the gels. Consequentially, this leads to an advantageous reduction in the surface adhesion of biological species. A synthesis of a range of alkyltartronic acids is also described. The acids prepared were obtained in very good yields using a novel four-stage synthesis. These acids were modified to give potassium monoethyl alkyltartronates. Although no polyesterification is described in this thesis, these modified alkyltartronic acid derivatives are considered to be potentially excellent starting materials for poly (alkyltartronic acid) synthesis via anhydrocarboxylate or anhydrosulphite cyclic monomers.

Organometallic precursors for pillared clay synthesis

The synthetic hectorite, laponite has been used within the paper industry to produce mildly conducting paper for use in electrographic printing. The aim of this research was to modify laponite in order to improve the electrical conductivity. In a continuation of a previous investigation involving organotin intercalation of laponite, the organotin precursor (p-CH3,OC6H4)4Sn was synthesised and characterised using Mass Spectroscopy, Infrared Spectroscopy and elemental analysis. Results of intercalation with this compound and a range of organobismuth and organoantimony compounds suggested that a halide content within the precursor was necessary for improvement in conductivity to be observed. Organometallic intercalation of a range of organotellurium compounds with laponite provided evidence that a hydrolysis reaction on the clay surface followed by the release of hydrochloric acid was an important first step if a reaction was to occur with the clay. Atomic Absorption Spectroscopy studies have shown that the acid protons underwent exchange with the interlayer sodium ions in the clay to varying degrees. Gas-liquid Chromatography and Infrared Spectroscopy revealed that the carbon-tellurium bond remained intact. Powder X-ray diffraction revealed that there had been no increase in the basal spacing. The a.c. conductivity of the modified clays in the form of pressed discs was studied over a frequency range of 12Hz - 100kHz using two electrode systems, silver paste and stainless steel. The a.c. conductivity consists of two components, ionic and reactive. The conductivity of laponite was increased by intercalation with organometallic compounds. The most impressive increase was gained using the organotellurium precursor (p-CH3OC6H4)2TeCl2. Conductivity investigations using the stainless steel electrode where measurements are made under pressure showed that in the case of laponite, where poor particle-particle contact exists at ambient pressure, there is a two order of magnitude increase in the measured a.c. conductivity. This significant increase was not seen in modified laponites where the particle-particle contact had already been improved upon. Investigations of the clay surface using Scanning Electron Microscopy suggested that the improvement in particle-particle contact is the largest factor in the determination of the conductivity. The other important factor is the nature and the concentration of the interlayer cations. A range of clays were synthesised in order to increase the concentration of sodium interlayer cations. A sol-gel method was employed to carry out these syntheses. A conductivity evaluation showed that increasing the concentration of the sodium cations within the clay led to an increase in the conductivity.

Synthesis and evaluation of novel ligands for quantum dot stabilisation and polymerisation studies

This thesis describes the design and synthesis of a variety of functionalised phosphine oxides and sulfides, based on the structure of trioctylphosphine oxide, synthesised for the purpose of surface modification of quantum dots. The ability of the ligands to modify the surface chemistry via displacement of the original hexadecylamine capping layer of quantum dots was evaluated. Finally the surface modified quantum dots were investigated for enhancement in their inherent properties and improved compatibility with the various applications for which they were initially designed. Upon the commencement of research involving quantum dots it became apparent that more information on their behaviour and interaction with the environment was required. The limits of the inherent stability of hexadecylamine capped quantum dots were investigated by exposure to a number of different environments. The effect upon the stability of the quantum dots was monitored by changes in the photoluminescence ability of their cores. Subtle differences between different batches of quantum dots were observed and the necessity to account for these in future applications noted. Lastly the displacement of the original hexadecylamine coating with the "designer" functionalised ligands was evaluated to produce a set of conditions that would result in the best possible surface modification. A general procedure was elucidated however it was discovered that each displacement still required slight adjustment by consideration of the other factors such as the difference in ligand structure and the individuality of the various batches of quantum dots. This thesis also describes a procedure for the addition of a protective layer to the surface of quantum dots by cross-linking the functionalised ligands bound to the surface via an acyclic diene metathesis polymerisation. A detailed description of the problems encountered in the analysis of these materials combined with the use of novel techniques such as diffusion ordered spectroscopy is provided as a means to overcome the limitations encountered. Finally a demonstration of the superior stability, upon exposure to a range of aggressive environments of these protected materials compared with those before cross-linking provided physical proof of the cross-linking process and the advantages of the cross-linking modification. Finally this thesis includes the presentation of initial work into the production of luminescent nanocrystal encoded resin beads for the specific use in solid phase combinatorial chemistry. Demonstration of the successful covalent incorporation of quantum dots into the polymeric matrices of non-functionalised and functionalised resin beads is described. Finally by preliminary work to address and overcome the possible limitations that may be encountered in the production and general employment of these materials in combinatorial techniques is given.

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

The surface environment and structural evolution of silica supported phosphotungstic acid (H3PW12O40) catalysts have been investigated as a function of acid loading. H3PW12O40 clusters are deposited intact upon the silica surface, adopting a Stranksi-Krastanov growth mode forming a two-dimensional adlayer which saturates at 45wt% acid. Intimate contact with the silica support perturbs the local chemical environment of three tungstate centres, which become inequivalent with those in the remaining cluster, suggesting an adsorption mode involving three terminal W==O groups. Above the monolayer, H3PW12O40 clusters form three-dimensional crystallites with physico-chemical properties indistinguishable from those in the bulk heteropoly acid. These H3PW12O40/SiO2 materials are efficient for the solventless isomerisation of α-pinene under mild reaction conditions. Activity scales directly with the number of accessible perturbed tungstate sites at the silica interface; these are the active species.

Palmitate promotes monocyte atherogenicity via de novo ceramide synthesis

Elevated plasma free fatty acids (FAs) are associated with increased risk of cardiovascular disease. This study investigates the effects of the saturated FA palmitate and unsaturated FA oleate on monocyte phenotype and function. Incubation of human U937 and THP-1 monocytes with palmitate for 24h increased cell surface expression of integrin CD11b and scavenger receptor CD36 in a concentration-dependent manner with some decrease in mitochondrial reducing capacity at high concentration (300µM). Monocytes incubated with palmitate, but not oleate, showed increased uptake of oxidized LDL and increased adhesion to rat aortic endothelium, particularly at bifurcations. The palmitate-induced increase in CD11b and CD36 expression was associated with increased cellular C16 ceramide and sphingomyelin, loss of reduced glutathione, and increased reactive oxygen species (ROS). Increased monocyte surface CD11b and CD36 was inhibited by fumonisin B1, an inhibitor of de novo ceramide synthesis, but not by the superoxide dismutase mimetic MnTBap. In contrast, MnTBap prevented the mitochondrial ROS increase and metabolic inhibition due to 300µM palmitate. This study demonstrates that in viable monocytes, palmitate but not oleate increases expression of surface CD11b and CD36. Palmitate increases monocyte adhesion to the aortic wall and promotes uptake of oxidized LDL and this involves de novo ceramide synthesis.

Synthesis and characterization of dual-functionalized core-shell fluorescent microspheres for bioconjugation and cellular delivery

The efficient transport of micron-sized beads into cells, via a non-endocytosis mediated mechanism, has only recently been described. As such there is considerable scope for optimization and exploitation of this procedure to enable imaging and sensing applications to be realized. Herein, we report the design, synthesis and characterization of fluorescent microsphere-based cellular delivery agents that can also carry biological cargoes. These core-shell polymer microspheres possess two distinct chemical environments; the core is hydrophobic and can be labeled with fluorescent dye, to permit visual tracking of the microsphere during and after cellular delivery, whilst the outer shell renders the external surfaces of the microspheres hydrophilic, thus facilitating both bioconjugation and cellular compatibility. Cross-linked core particles were prepared in a dispersion polymerization reaction employing styrene, divinylbenzene and a thiol-functionalized co-monomer. These core particles were then shelled in a seeded emulsion polymerization reaction, employing styrene, divinylbenzene and methacrylic acid, to generate orthogonally functionalized core-shell microspheres which were internally labeled via the core thiol moieties through reaction with a thiol reactive dye (DY630-maleimide). Following internal labeling, bioconjugation of green fluorescent protein (GFP) to their carboxyl-functionalized surfaces was successfully accomplished using standard coupling protocols. The resultant dual-labeled microspheres were visualized by both of the fully resolvable fluorescence emissions of their cores (DY630) and shells (GFP). In vitro cellular uptake of these microspheres by HeLa cells was demonstrated conventionally by fluorescence-based flow cytometry, whilst MTT assays demonstrated that 92% of HeLa cells remained viable after uptake. Due to their size and surface functionalities, these far-red-labeled microspheres are ideal candidates for in vitro, cellular delivery of proteins, as described in the accompanying paper.

Synthesis, characterisation and applications of diamond materials

This thesis presented a detailed research work on diamond materials. Chapter 1 is an overall introduction of the thesis. In the Chapter 2, the literature review on the physical, chemical, optical, mechanical, as well as other properties of diamond materials are summarised. Followed by this chapter, several advanced diamond growth and characterisation techniques used in experimental work are also introduced. Then, the successful installation and applications of chemical vapour deposition system was demonstrated in Chapter 4. Diamond growth on a variety of different substrates has been investigated such as on silicon, diamond-like carbon or silica fibres. In Chapter 5, the single crystalline diamond substrate was used as the substrate to perform femtosecond laser inscription. The results proved the potentially feasibility of this technique, which could be utilised in fabricating future biochemistry microfluidic channels on diamond substrates. In Chapter 6, the hydrogen-terminated nanodiamond powder was studied using impedance spectroscopy. Its intrinsic electrical properties and its thermal stability were presented and analysed in details. As the first PhD student within Nanoscience Research Group at Aston, my initial research work was focused on the installation and testing of the microwave plasma enhanced chemical vapour deposition system (MPECVD), which will be beneficial to all the future researchers in the group. The fundamental of the on MPECVD system will be introduced in details. After optimisation of the growth parameters, the uniform diamond deposition has been achieved with a good surface coverage and uniformity. Furthermore, one of the most significant contributions of this work is the successful pattern inscription on diamond substrates by femtosecond laser system. Previous research of femtosecond laser inscription on diamond was simple lines or dots, with little characterisation techniques were used. In my research work, the femtosecond laser has been successfully used to inscribe patterns on diamond substrate and fully characterisation techniques, e.g. by SEM, Raman, XPS, as well as AFM, have been carried out. After the femtosecond laser inscription, the depth of microfluidic channels on diamond film has been found to be 300~400 nm, with a graphitic layer thickness of 165~190 nm. Another important outcome of this work is the first time to characterise the electrical properties of hydrogenterminated nanodiamond with impedance spectroscopy. Based on the experimental evaluation and mathematic fitting, the resistance of hydrogen-terminated nanodiamond reduced to 0.25 MO, which were four orders of magnitude lower than untreated nanodiamond. Meanwhile, a theoretical equivalent circuit has been proposed to fit the results. Furthermore, the hydrogenterminated nanodiamond samples were annealed at different temperature to study its thermal stability. The XPS and FTIR results indicate that hydrogen-terminated nanodiamond will start to oxidize over 100ºC and the C-H bonds can survive up to 400ºC. This research work reports the fundamental electrical properties of hydrogen-terminated nanodiamond, which can be used in future applications in physical or chemical area.

Alkali- and nitrate-free synthesis of highly active Mg-Al hydrotalcite-coated alumina for FAME production

Mg-Al hydrotalcite coatings have been grown on alumina via a novel alkali- and nitrate-free impregnation route and subsequent calcination and hydrothermal treatment. The resulting Mg-HT/AlO catalysts significantly outperform conventional bulk hydrotalcites prepared via co-precipitation in the transesterification of C-C triglycerides for fatty acid methyl ester (FAME) production, with rate enhancements increasing with alkyl chain length. This promotion is attributed to improved accessibility of bulky triglycerides to active surface base sites over the higher area alumina support compared to conventional hydrotalcites wherein many active sites are confined within the micropores. © 2014 The Royal Society of Chemistry.

Rational design of heterogeneous catalysts for biodiesel synthesis

Dwindling oil reserves and growing concerns over carbon dioxide emissions and associated climate change are driving the utilisation of renewable feedstocks as alternative, sustainable fuel sources. Catalysis has a rich history of facilitating energy efficient, selective molecular transformations, and contributes to 90% of current chemical manufacturing processes. In a post-petroleum era, catalysis will be pivotal in overcoming the scientific and engineering barriers to economically feasible bio-fuels. This perspective highlights some recent developments in heterogeneous catalysts for the synthesis of biodiesel from renewable resources, derived from plant and aquatic oil sources. Particular attention will be paid to the importance of catalyst pore architecture, surface polarity and acid and base properties, in meeting the challenge of transforming highly polar and viscous bio-based reactants. © 2012 The Royal Society of Chemistry.

Hierarchical macroporous-mesoporous SBA-15 sulfonic acid catalysts for biodiesel synthesis

Hierarchical macroporous-mesoporous SBA-15 silicas have been synthesised via dual-templating routes employing liquid crystalline surfactants and polystyrene beads. These offer high surface areas and well-defined, interconnecting macro- and mesopore networks with respective narrow size distributions around 300 nm and 3-5 nm for polystyrene:tetraethoxysilane ratios ≥2:1. Subsequent functionalisation with propylsulfonic acid yields the first organized, macro-mesoporous solid acid catalyst. The enhanced mass transport properties of these new bi-modal solid acid architectures confer significant rate enhancements in the transesterification of bulky glyceryl trioctanoate, and esterification of long chain palmitic acid, over pure mesoporous analogues. This paves the way to the wider application of hierarchical catalysts in biofuel synthesis and biomass conversion. © 2010 The Royal Society of Chemistry.

The application of calcined natural dolomitic rock as a solid base catalyst in triglyceride transesterification for biodiesel synthesis

Natural dolomitic rock has been investigated in the transesterification of C and C triglycerides and olive oil with a view to determining its viability as a solid base catalyst for use in biodiesel synthesis. XRD reveals that the dolomitic rock comprised 77% dolomite and 23% magnesian calcite. The generation of basic sites requires calcination at 900 °C, which increases the surface area and transforms the mineral into MgO nanocrystallites dispersed over CaO particles. Calcined dolomitic rock exhibits high activity towards the liquid phase transesterification of glyceryl tributyrate and trioctanoate, and even olive oil, with methanol for biodiesel production. © The Royal Society of Chemistry 2008.

Structure-sensitive biodiesel synthesis over MgO nanocrystals

Size-controlled MgO nanocrystals were synthesised via a simple sol-gel method and their bulk and surface properties characterised by powder XRD, HRTEM and XPS. Small, cubic MgO single crystals, generated by low temperature processing, expose weakly basic (100) surfaces. High temperature annealing transforms these into large, stepped cuboidal nanoparticles of periclase MgO which terminate in more basic (110) and (111) surfaces. The size dependent evolution of surface electronic structure correlates directly with the associated catalytic activity of these MgO nanocrystals towards glyceryl tributyrate transesterification, revealing a pronounced structural preference for (110) and (111) facets. © 2009 The Royal Society of Chemistry.