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After reviewing the literature on factors influencing zinc availability in soils, it was decided to investigate further aspects of the well documented zinc/phosphate interaction for the soil/maize system and to study the migration and transformations of inorganic and organic (sludge) fertilizer zinc in soils. A conventional pot experiment with maize to look at zinc/phosphate interaction, with thorough mixing of added fertilizer, indicated that phosphate could alleviate zinc toxicity effects, but did not show whether this was a soil or plant effect. A subsequent experiment in which soils treated with zinc and phosphate fertilizers were spatially separated by nylon net provided evidence that the interaction occurred, at least in part, in plant roots. This suggests limited benefit in the field for separate placement. Under field conditions, it is unrealistic to expect the same degree of soil mixing as used in typical pot experiments. Therefore an experiment with <SUP>65</SUP>Zn was used to study the vertical movement of surface-applied inorganic zinc fertilizer. The same experiment was also used to study the changes in distribution of added zinc between a range of soil fractions (exchangeable, organic, manganese oxide, iron oxide and residual) at three soil pH values. Uptake was higher at lower pH, corresponding to greater amounts of zinc being retained on exchange sites. However, much of the added zinc was found in the manganese oxide fraction especially at higher pH. Zinc mobility during the experiment was almost negligible. Subsequently the soils left at the end of this experiment were incubated for 6 months and then used for a further pot experiment, to gain insight into residual zinc fertilizer effects. This showed a reduction in exchangeable zinc and plant uptake, with increases in zinc associated with organic matter and iron oxides.

Sepsis is the major cause of mortality on intensive care units (ICU) with ~36,000 deaths annually in the UK. Sepsis is a systemic, dysregulated activation of the innate immune system in response to an infection characterised by excessive inflammatory mediator production and oxidative stress. Mitochondrial dysfunction is implicated in sepsis-­‐induced organ dysfunction and death. Zinc is an essential micronutrient with a multitude of biological functions, including anti-­‐inflammatory and antioxidant properties. A relationship has been established between zinc deficiency and severity of sepsis, in which zinc deficiency negatively influences the processes of sepsis leading to organ damage and ultimately death. This study investigated the effect of zinc on sepsis-­‐related mechanisms to evaluate its importance for sepsis pathophysiology. The relationship between zinc levels and sepsis-­‐related molecular mechanisms were investigated in an endothelial cell culture model of sepsis and in blood samples obtained from patients on ICU with and without sepsis. The in vitro study showed no evidence of zinc as an antioxidant or anti-­‐inflammatory agent in endothelial cells exposed to lipopolysaccharide and peptidoglycan, however mitochondrial baseline function was increased in a zinc concentration-­‐dependent manner. Plasma zinc levels were far below normal in all patients and patients with sepsis had lower levels compared to non-­‐infected patients, possibly because they were overall more severely ill. No clear correlations could be established between plasma zinc and markers of inflammation, oxidative stress or disease severity. The lack of anti-inflammatory and antioxidant properties of zinc in the endothelial sepsis model, and the lack of clear correlations between zinc and markers of disease severity, inflammation and oxidative stress in the clinical study, challenges the concept of the importance of zinc in the pathophysiology of sepsis. The prolonged reduction of plasma zinc in all ICU patients prompts to consideration of zinc supplementation to replenish plasma levels and assure sufficient availability to maintain tissue functions.

Cette étude propose un procédé d'ignifugation en masse du PET basé sur l'incorporation de retardateur de flamme phosphoré (OP950) et de nanoparticules (LDH, MWNT, OMPOSS). Si les LDH synthétisés entrainent la dégradation du PET, les MWNT et les OMPOSS apportent une amélioration des propriétés feu. Un effet de synergie est observé lors de l'incorporation simultanée d'OP950 (source d'intumescence) et d'OMPOSS. Cet effet est attribué à des phénomènes physiques tels que la sublimation des OMPOSS. L'étude de la dégradation des différents composants du mélange a révélé la formation d'espèces à base de phosphates ou de silice qui ne réagissent pas entre elles ou avec le polymère. L'amélioration des propriétés feu est donc due à la formation de composés phosphorés jouant le rôle de barrière entre la flamme et le polymère, et de silice issue de la dégradation de l'OMPOSS améliorant la résistance du char. L'émission de composés gazeux contribuerait également au développement de l'intumescence. La faisabilité du filage de la formulation intumescente a été étudiée et des fibres élaborées, malgré la faible dispersion des additifs au sein de la matrice polymère. Un masterbatch a été conçu industriellement à partir de cette étude par des partenaires industriels. Les non-tissés fabriqués montrent une résistance au feu améliorée comparée au polyester seul et passent de nombreux tests métier. Ce masterbatch est actuellement commercialisé / This study proposes to f1ame retard PET by the incorporation of a phosphorous based fia me retardant (OP950) and nanoparticles (LDH, MWNT, OMPOSS). Whereas the synthesized LDH lead to the degradation of PET, MWNT and OMPOSS bring an improvement in the f1ame retarding properties. A synergistic effect is observed when OMPOSS are added simultaneously with OP950 (bringing intumescence). This effect is due to physical phenomena such as the sublimation of the POSS. The study of the degradation of the different components of the blend revealed the formation of phosphate based species or silica, that do not react with each other or with the polymer. The improvement of the fire properties is then attributed to the formation of phosphorous components acting as a barrier between the polymer and the f1ame. It is proposed that silica reinforce the mechanical properties of the char, and that the gaseous components act as blowing agent. The feasibility of the spinning has been studied and fibres elaborated in spite of the poor dispersion of the additives into the polymer matrix. A masterbatch has been industrially prOOuced from this study by industrial partner. The non-wovens manufactured with those fibres show goOO fire retarding properties. They pass a number of normalized tests. This masterbatch is now commercialized.

A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the Degree of Master of Science in Medicine (Pharmacy), Johannesburg / This thesis presents a multifaceted approach which comprehensively describes the design of novel drug delivery polymeric complexes through the application of innovative crosslinking reactions. These reactions have been built on the statistical and mathematical principles governing the technique of Design of Experiments. At the outset, pertinent aspects covering the importance of rate-controlled drug delivery in achieving superior therapeutics is presented. In addition, the fundamental mechanisms which regulate the complex behaviour of polymeric materials are outlined, placing emphasis on the mathematical models which demonstrate the critical need to be able to synchronize the processes of matrix hydration, relaxation, disentanglement, erosion and dissolution. Initially, the Plackett-Burman Design was evaluated to develop a crosslinked polymeric oilisphere device for the in vitro site-specific delivery of Mentha piperita oil. This design proved to be highly successful in rapidly identifying the appropriate release rate-modifying variables through the application of stepwise regression optimization and Artificial Neural Networks. / IT2018

Zinc is now firmly established as an essential trace element in the human body. Whilst it has many key structural and catalytic fixed roles, it is also found in 'mobile' pools in many essential organs and organelles that are readily chelatable. The presence and trafficking of these zinc pools are thought to contribute in some form to many human disease states associated with these organs, for example, Type 2 diabetes in the pancreas, some forms of cancer in the prostate, and even ischemic stroke, epilepsy and Alzheimer's disease. The exact role however, remains largely unknown and this is due to our current limitations with the methods in which we monitor the movement of this important element in our body. This thesis presents our efforts to develop novel Zn2+ selective chemosensors that can meet contemporary criteria for successful and simple imaging. Many efforts are being made to develop simple fluorescent molecular probes to monitor the trafficking and progress of Zn2+ through these cells and organs in real time via these chelatable 'mobile' pools. Chapter 1 will outline some successful efforts towards these and discuss their relevance and mechanisms of action, as well as outlining 'click'-chemistry and its role in chemosensing to date. Chapter 2 describes a novel 'click'-chemistry approach designed to aid with the simple construction of novel zinc-chelating probes in a facile and high yielding manner. This methodology was taken forward to the synthesis of 6 novel Zn2+-selective small molecule fluorescent probes that incorporate a cell organelle targeting motif in their structure. These are described in Chapter 3, and their successful testing both in-vitro and in-cellulo in murine pancreatic islet cells is presented and discussed. Finally, Chapter 4 discusses the development of some modified fluorescent [2]rotaxanes as molecularly interlocked architectures capable of binding and sensing metals, and will specifically focus on how small structural changes led to vast differences in their fluorescence properties, ultimately resulting in a Zn2+-selective [2]rotaxane in organic media.

Bacterial infection and colonisation of polymeric biomaterials represents a major problem that is on the rise within the health care industry. Bacterial attachment and biofilm formation on medical polymers is often the cause of addition discomfort, pain and in the worse case scenario sepsis and even mortality. This, in combination to the overuse of antibiotics and evolution of resistant bacterial stains, means there is a need for a more intelligent approach in the prevention of biofilm formation and bacterial infection. In this work, the antimicrobial properties of metals (in particular silver and zinc) was utilized and incorporated into polymeric biomaterial to render them antimicrobial. Several methods of functionalising polymers with antimicrobial metals were assessed. The materials developed throughout this work were designed to respond to changes in environmental as a result of infection. These changes include differences in pH and temperature all of which are altered in response to infection. This smart design allows for the reduction of unnecessary release of antimicrobial, and will reduce the likelihood of toxicity and resistance. Polymer modifications in this research include modifications made during polymer synthesis, i.e. reaction with additional antimicrobial monomer. In this case, pH responsive zinc containing crosslinker molecule was designed to crosslink into any polymeric material. Post synthesis modifications were also investigated, and include the ‘grafting to’ and ‘grafting from’ of polymers which could then be functionalised with antimicrobial metals. This work demonstrated methods to modify non-woven polypropylene. A system, for the ‘grafting from’ approach to give a pH responsive release of antimicrobial metals from a polymer brush was investigated. Secondly a ‘grafting to’ approach to give a temperature responsive release of metals was investigated. Finally, several zinc compounds were synthesised and assessed for there ability to graft via plasma assisted grafting. The results presented in this work demonstrate novel ways of incorporating antimicrobial metal functionality into polymeric biomaterials and their antimicrobial efficacy.