Chemistry and synthesis of 3(2H)-furanones and 4,5-dihydro analogues: mechanistic investigations and stereochemical control

The subject matter of this thesis relates to the chemistry of the five-membered oxygen heterocycles – 3(2H)-furanones and their 4, 5-dihydro analogues. Chapter one of the thesis is a review of the relevant chemistry of the compounds: their synthesis and key transformations. In chapter two, new research on 3(2H)-furanones is outlined in two parts. The first describes an investigation into the cyclisation of α'-trialkylsilyloxyenone adducts with arenesulfenyl and selenenyl chlorides into the corresponding sulfur and selenium substituted 3(2H)-furanones without the involvement of a Lewis acid catalyst. The study, largely involving in situ NMR techniques, identified key features associated with the formation and reaction of the chlorosulfide and chloroselenide intermediates, including operation of the Thorpe-Ingold effect. The knowledge gained in this study was applied (the second part) to the synthesis of vinyl substituted furanone systems from α'-trialkylsilyloxydienones where choice of the reaction conditions and electrophilic reagent was a key feature. An important difference in the behaviour of arenesulfenyl and selenenyl halides towards conjugated dienes emerged from this work. This phase of the research concluded with a new synthesis of geiparvarin, a natural product possessing anti-tumour properties.

Micronutrient intakes and the role of nutritional supplements in the diets of Irish adults and pre-school children

To investigate micronutrient intakes and the role of nutritional supplements in the diets of Irish adults aged 18-64 years and pre-school children aged 1-4 years. Analysis is based on data from the National Adult Nutrition Survey (NANS) (n=1274) and the National Pre-School Nutrition Survey (NPNS) (n=500). Food and beverage intakes and nutritional supplement use were recorded using 4-day food records. Nutrients were estimated using WISP© which is based on McCance and Widdowson’s The Composition of Foods, 6thEd and the Irish Food Composition Database. “Meats”, “milk/yoghurt”, “breads”, “fruit/fruit juices” and “breakfast cereals” made important contributions to the intakes of a number of micronutrients. Micronutrient intakes were generally adequate, with the exception of iron (in adult females and 1 year olds) and vitamin D (in all population groups). For iron, zinc, copper and vitamin B6, up to 2% of adults had intakes that exceeded the upper limit (UL). Small proportions of children had intakes of zinc (11%), copper (2%), retinol (4%) and folic acid (5%) exceeding the UL. Nutritional supplements (predominantly multivitamin and/or mineral preparations) were consumed by 28% of adults and 20% of pre-school children. Among users, supplements were effective in reducing the % with inadequate intakes for vitamins A and D (both population groups) and iron (adult females only). Supplement users had a lower prevalence of inadequate intakes for vitamin A and iron compared to non-users. In adults only, users had a lower prevalence of inadequate intakes for magnesium, calcium and zinc, and displayed better compliance with dietary recommendations and lifestyle characteristics compared with non-users. There is poor compliance among women of childbearing age for the recommendation to take a supplement containing 400µg/day of folic acid. These findings are important for the development of nutrition policies and future recommendations for adults and pre-school children in Ireland and the EU.

Synthesis, functionalisation and characterisation of germanium nanocrystals & their applications

In the last two decades, semiconductor nanocrystals have been the focus of intense research due to their size dependant optical and electrical properties. Much is now known about how to control their size, shape, composition and surface chemistry, allowing fine control of their photophysical and electronic properties. However, genuine concerns have been raised regarding the heavy metal content of these materials, which is toxic even at relatively low concentrations and may limit their wide scale use. These concerns have driven the development of heavy metal free alternatives. In recent years, germanium nanocrystals (Ge NCs) have emerged as environmentally friendlier alternatives to II-VI and IV-VI semiconductor materials as they are nontoxic, biocompatible and electrochemically stable. This thesis reports the synthesis and characterisation of Ge NCs and their application as fluorescence probes for the detection of metal ions. A room-temperature method for the synthesis of size monodisperse Ge NCs within inverse micelles is reported, with well-defined core diameters that may be tuned from 3.5 to 4.5 nm. The Ge NCs are chemically passivated with amine ligands, minimising surface oxidation while rendering the NCs dispersible in a range of polar solvents. Regulation of the Ge NCs size is achieved by variation of the ammonium salts used to form the micelles. A maximum quantum yield of 20% is shown for the nanocrystals, and a transition from primarily blue to green emission is observed as the NC diameter increases from 3.5 to 4.5 nm. A polydisperse sample with a mixed emission profile is prepared and separated by centrifugation into individual sized NCs which each showed blue and green emission only, with total suppression of other emission colours. A new, efficient one step synthesis of Ge NCs with in situ passivation and straightforward purification steps is also reported. Ge NCs are formed by co-reduction of a mixture of GeCl4 and n-butyltrichlorogermane; the latter is used both as a capping ligand and a germanium source. The surface-bound layer of butyl chains both chemically passivates and stabilises the Ge NCs. Optical spectroscopy confirmed that these NCs are in the strong quantum confinement regime, with significant involvement of surface species in exciton recombination processes. The PL QY is determined to be 37 %, one of the highest values reported for organically terminated Ge NCs. A synthetic method is developed to produce size monodisperse Ge NCs with modified surface chemistries bearing carboxylic acid, acetate, amine and epoxy functional groups. The effect of these different surface terminations on the optical properties of the NCs is also studied. Comparison of the emission properties of these Ge NCs showed that the wavelength position of the PL maxima could be moved from the UV to the blue/green by choice of the appropriate surface group. We also report the application of water-soluble Ge NCs as a fluorescent sensing platform for the fast, highly selective and sensitive detection of Fe3+ ions. The luminescence quenching mechanism is confirmed by lifetime and absorbance spectroscopies, while the applicability of this assay for detection of Fe3+ in real water samples is investigated and found to satisfy the US Environmental Protection Agency requirements for Fe3+ levels in drinkable water supplies.