Structure and properties of intermetallic ternary rare earth compounds

The so called material science is an always growing field in modern research. For the development of new materials not only the experimental characterization but also theoretical calculation of the electronic structure plays an important role. A class of compounds that has attracted a great deal of attention in recent years is known as REME compounds. These compounds are often referred to with RE designating rare earth, actinide or an element from group 1 - 4, M representing a late transition metal from groups 8 - 12, and E belonging to groups 13 - 15. There are more than 2000 compounds with 1:1:1 stoichiometry belonging to this class of compounds and they offer a broad variety of different structure types. Although many REME compounds are know to exist, mainly only structure and magnetism has been determined for these compounds. In particular, in the field of electronic and transport properties relatively few efforts have been made. The main focus in this study is on compounds crystallizing in MgAgAs and LiGaGe structure. Both structures can only be found among 18 valence electron compounds. The f electrons are localized and therefor not count as valence electrons. A special focus here was also on the magnetoresistance effects and spintronic properties found among the REME compounds. An examination of the following compounds was made: GdAuE (E = In, Cd, Mg), GdPdSb, GdNiSb, REAuSn (RE = Gd, Er, Tm) and RENiBi (RE = Pr, Sm, Gd - Tm, Lu). The experimental results were compared with theoretic band structure calculations. The first half metallic ferromagnet with LiGaGe structure (GdPdSb) was found. All semiconducting REME compounds with MgAgAs structure show giant magnetoresistance (GMR) at low temperatures. The GMR is related to a metal-insulator transition, and the value of the GMR depends on the value of the spin-orbit coupling. Inhomogeneous DyNiBi samples show a small positive MR at low temperature that depends on the amount of metallic impurities. At higher fields the samples show a negative GMR. Inhomogeneous nonmagnetic LuNiBi samples show no negative GMR, but a large positive MR of 27.5% at room temperature, which is interesting for application.

Perfluorinated compounds in environmental matrices of Lake Victoria Gulf

ABSTRACT One of the major ecological challenges on Lake Victoria resources is the existence of “hot spots”, caused by human waste, urban runoff, and industrial effluents. The lake is tending towards eutrophication which is attributed to the increasing human population in its watershed. A report of the levels of perfluorooctane sulfonate and perfluorooctanoic acid in environmental matrices of Lake Victoria is presented, and the management implication of perfluorinated compounds and similar potential organic pollutants examined. Two widely consumed and economically important fish species namely Lates niloticus (Nile perch) and Oreochromis niloticus (Nile tilapia) were obtained from Winam gulf of Lake Victoria, Kenya, and analysed for perfluorooctane sulfonate and perfluorooctanoic acid in muscles and liver using liquid chromatography coupled with mass spectroscopy. Variability in the concentrations of perfluorooctanoic acid or perfluorooctane sulfonate in river waters (range perfluorooctanoic acid 0.4 – 96.4 ng/L and perfluorooctane sulfonate < 0.4 – 13.2 ng/L) was higher than for Lake waters (range perfluorooctanoic acid 0.4 – 11.7 ng/L and perfluorooctane sulfonate < 0.4 – 2.5 ng/L respectively). Significant correlations were tested between perfluorinated compounds levels in sediments, fish and water. Wastewater treatment plants and other anthropogenic sources have been identified as significant sources or pathways for the introduction of perfluoroalkyl compounds into Lake Victoria ecosystem. In this study, elevated concentrations of perfluorooctanoic acid and perfluorooctane sulfonate was found in two wastewater treatment plants (WWTPs) in Kisumu, City of Kenya. An alternative analytical method to liquid chromatography/ mass spectroscopy for analysis of perfluorocarboxylic acids in abiotic and biotic matrices where high concentrations are expected is also presented. Derivatisation of the acid group to form a suitable alkyl ester provided a suitable compound for mass spectroscopy detection coupled to gas chromatography instrumental analysis. The acid is esterified by an alkyl halide i.e benzyl bromide as the alkylating agent for Perfluorocarboxylic acids quantification. The study also involved degradability measurements of emerging perfluorinated surfactants substitutes. The stability of the substitutes of perfluorinated surfactants was tested by employing advanced oxidation processes, followed by conventional tests, among them an automated method based on the manometric respirometry test and standardized fix bed bioreactor [FBBR] on perfluorobutane sulfonate (PFBS), a fluoroethylene polymer, fluorosurfactant (Zonyl), two fluoraliphaticesters (NOVEC ™ FC4430 and NOVEC ™ FC4432) and 10-(trifluoromethoxy) decane-sulfonate. Most of these emmerging surfactants are well-established in the market and have been used in several applications as alternatives to PFOS and PFOA based surfactants. The results of this study can be used as pioneer information for further studies on the sources, behaviour and fate of PFOA and PFOS and other related compounds in both abiotic and biota compartments of Lake Victoria and other lakes. Further an overview in degradation of emerging perfluorinated compounds substitutes is presented. Contribution in method development especially for acid group based fluorosurfactants is presented. The data obtained in this study can particularly be considered when formulating policies and management measures for preservation and sustainability of Lake Victoria resources.

Design, Synthesis and Characterization of N-Containing Organic Compounds

The needed of new intermediates/products for screening in the fields of drug discovery and material science is the driving force behind the development of new methodologies and technologies. Organic scaffolds are privileged targets for this scouting. Among them a priority place must be attributed to those including nitrogen functionalities in their scaffolds. It comes out that new methodologies, allowing the introduction of the nitrogen atom for the synthesis of an established target or for the curiosity driven researches, will always be welcome. The target of this PhD Thesis’ work is framed within this goal. Accordingly, Chapter 1 reports the preparation of new N-Heteroarylmethyl 3-carboxy-5-hydroxy piperidine scaffold, as potential and selective α-glucosidase inhibitors. The proposed reversible uncompetitive mechanism of inhibition makes them attractive as interesting candidate for drug development. Chapter 2 is more environmentally method-driven research. Eco-friendly studies on the synthesis of enantiomerically pure 1,4-dihydropyridines using “solid” ammonia (magnesium nitride) is reported via classical Hantzch method. Chapter 3 and Chapter 4 may be targeted as the core of the Thesis’s research work. Chapter 3 reports the studies addressed to the synthesis of N-containing heterocycles by using N-trialkylsilylimine/hetero-Diels–Alder (HAD) approach. New eco-friendly methodology as MAOS (Microwave Assisted Organic Synthesis) has been used as witness of our interest to a sustainable chemistry. Theoretical calculations were adopted to fully clarify the reaction mechanism. Chapter 4 is dedicated to picture the most recent studies performed on the application of N-Metallo-ketene imines (metallo= Si, Sn, Al), relatively new intermediates which are becoming very popular, in the preparation of highly functionalized N-containing derivatives, accordingly to the Thesis’ target. Derivatives obtained are designed in such a way that they could be of interest in the field of drug and new material chemistry.

Heusler compounds as thermoelectric materials

Heusler compounds as thermoelectric materialsrnrnThis work reports on Heusler and Half Heusler compounds and their thermoelectric properties. Several compounds were synthesized and their resistivity, Seebeck coefficient, thermal conductivity, and the figure of merit were determined. The results are presented in the following chapters.rnrnIn chapter 3 Co was substituted with Ni and Fe in the series TiCo1-x(Fe0.5Ni0.5)xSb. The substitution lead to a reduced loss of Sb during the synthesis. Further the Seebeck coefficient was increased and the thermal conductivity was reduced. These observations can be used to significantly improve the quality of TiCoSb based compounds in thermoelectric applications. rnrnIn chapter 4 the series TiCo1-xNixSnxSb1-x was investigated. Ni was substituted with Co and Sn with Sb. Especially for high Ni concentrations the figure of merit was enhanced compared to unsubstituted TiCoSb. This enhancement is based on the strong reduction of the thermal conductivity. The found values are among the lowest that have been determined up to date for Heusler compounds. rnrnIn chapter 5 Li containing Heusler compounds were theoretically and experimentally investigated. Li containing Heusler compounds are of special interest because the Li atoms scatter phonons efficiently. Therefore the thermal conductivity is decreased. The thermoelectric properties and especially the thermal conductivity are investigated in this chapter.rnrnIn chapter 6 several substitutions of TiCoSb were investigated. In the series TiCo1+xSb additional Co was introduced into the vacancies of the compound and the effect on the thermoelectric properties was measured. In the series TiCo1-xCuxSb Co was substituted with Cu. No significant enhancement of the ZT value were observed. In the series TiCoSb1-xBix Sb was substituted by Bi. The thermoelectric properties were significantly enhanced for small Bi concentrations. The Seebeck coefficient was increased and the resistivity was reduced at the same time. This unusual phenomenon is explained by band structure calculations.rnrnIn chapter 7 the material class of half metallic ferromagnets was investigated as a new materialclass for thermoelectric applications. The 26 valence electron compounds Co2TiSi, Co2TiGe, and Co2TiSn were used as model systems. The transport properties were determined theoretically. Then the properties were measured and compared to the calculated ones. The calculated values are in good agreement with the experimentally determined ones. The observed Seebeck coefficient has a big value and is nearly constant above the Curie temperature. This makes the materials appealing for the use as materials in thermocouples.rn

Polysulfurated aromatic compounds: preparation and photophysical properties

The aim of this thesis was the synthesis and photophysical characterization of some new polysulfurated aromatic compounds: this class of molecules can offer intriguing properties, potentially useful for the construction of new materials for optoelectronic devices. Two main families of compounds have been synthesized: the first is represented by a series of small molecular asterisks, with peripheral aromatic units, showing luminescence in solid phase or in highly rigid conditions. All compounds with peripheral substituents display an AIE behavior (Aggregation Induced Emission) with radiative deactivation of the triplet states. Taking inspiration from these smaller asterisks, a larger molecule with the same geometry has been designed, decorated with terpyridyl moieties as the outermost units: this compound shows great affinity for the coordination of several transition metal ions, changing luminescence properties after the interaction with zinc ions. With the same intentions, a tetrasulfurated pyrene-core molecule with terpyridyl external units has been synthesized and isolated: this ligand exhibits good coordination capabilities towards transition metal ions, giving rise to luminescent nanoaggregates upon addition of zinc(II), characterized by DLS and AFM microscopy. In addition a NIR emission is recorded after coordination of neodymium(III), showing evidence of an intramolecular energy transfer process.

Phenotype and genotype characterization of Monilinia spp. isolates and preformed antifungal compounds in peach peel fruit at different developmental stages

The brown rot fungi belong to a group of fungal pathogens that causes considerable damage to cultivated fruits trees, particularly stone fruits and apples in the temperate regions of the World and during the postharvest with an important economic impact. In particular in Italy, it is important to monitor the Monilinia population to control economic losses associated to the peach and nectarine market. This motivates the research steps presented in this dissertation on Monilinia Italian isolates. The Monilinia species collected from stone fruits have been identified using molecular analysis based on specific primers. The relevant role of M. fructicola was confirmed and, for the first time, it was found also on apple fruits. To avoid the development of resistant strains and implement valid treatment strategies, the understanding of the fruit natural resistance during different developmental stages and the assessment of the Monilinia sensitivity/resistance to fungicides are required. The relationship between the inhibition spots and the phenolic compounds in peach fruit peel was highlighted in this research. Three methods were used to assess isolate resistance/sensitivity, the amended medium, the Spiral Gradient Endpoint Method (SGD) and the Alamar Blue method. The PCR was used to find possible mutation points in the b-tubulin gene that is responsible for fungicide resistance. Interestingly, no mutation points were observed in resistant M. laxa isolates, suggesting that the resistance could be stimulated by environmental factors. This lead to the study of the effect of the temperature on the resistance and the preliminary results of in vitro tests showed that maximum inhibition was observed at 30°C.