https://www.um.edu.mt/library/oar/handle/123456789/77102 2026-04-16T02:03:11Z 2026-04-16T02:03:11Z https://www.um.edu.mt/library/oar/handle/123456789/111252 2023-07-05T07:23:29Z 1999-01-01T00:00:00Z

Title: Interferon-ɑ and sickness behaviour : a study of the dose and time dependency of interferon-ɑ-induced anhedonia and fever Abstract: The use of recombinant human Interferon-ɑ2A for the treatment of more than 14 malignancies and virologic diseases is acknowledged world-wide, in over 40 countries. However, its use has been hampered by the many side effects accompanying its therapy, of which depression and suicidal ideations are the extreme cases. Significant research effort has gone into understanding the neural and molecular mechanisms of action of this cytokine, but to date there exist gaps in our understanding of the underlying fine mechanistic details. The side effects of Interferon-a can be described as typical Sickness Behaviour (a coordinated set of behavioural changes that develop in sick individuals during the course of an infection). A Model of Anhedonia was used as the paradigm within which to test and investigate the dose and time dependency of the effects of recombinant human Interferon-a2A (rHIFN-ɑ2A)· The species-specificity of rHIFN-ɑ2A in rats was also studied within this paradigm. The effects of IFN on temperature were used to monitor the activity of the drug in the rats, while anhedonia (measured as a change in the consumption and preference for 1%, 8% and 32% sucrose solutions) was used to assess the impact of IFN on positive reinforcement. From the results obtained rHIFN-ɑ2A was confirmed to be 100 to 1000 times less potent than rat interferon-ɑA (RIFN-ɑA) in rats. More importantly, new insights into the mechanisms of action of rHIFN-ɑ2A on anhedonia and fever were suggested. However, the whole picture is far from complete and this project just represents a first attempt to improve our knowledge of Interferon neurochemistry. This and future studies could eventually lead to the development of appropriate drugs that dampen the undesirable side effects of Interferon-ɑ therapy, allowing patients to make full use of an otherwise effective therapy. Description: B.SC.(HONS)CHEMISTRY&BIOLOGY

1999-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/101451 2022-09-06T07:20:23Z 1999-01-01T00:00:00Z

Title: Geochemical and mineralogical characterisation of the Lower Globigerina Limestone of the Maltese Islands with special reference to the 'soll' facies Abstract: A detailed geochemical and mineralogical characterisation, supported by petrographical and micro-textural studies, of the Lower Globigerina Limestone was carried out on 109 samples from three cores taken from the largest quarry area of the Maltese islands. In addition, a limited number of samples were obtained from the Middle Globigerina Limestone, the C1 phosphatic nodule bed, the Scutella Bed and the Lower Coralline Limestone. For the Lower Globigerina Limestone, results showed that SiO2, Al2O3, K2O, TiO2 and Fe2O3 increased in concentration within older rocks. These elements also occur in high concentrations in the Middle Globigerina Limestone, within the phosphatic nodule bed and in the "grey" lithofacies located at the base of the Lower Globigerina Limestone. Mineralogical results and petrographical studies in thin section confirmed a progressive increase in insoluble residue down section. There was also a sudden decrease in concentration of the non-carbonate fraction at the Lower Coralline Limestone. Geochemical data for Lower Globigerina Limestone were subjected to statistical analysis, including Principal Component Analysis and Cluster Analysis. This led to a characterisation of the "soll" and "franka" types within this member. The variables SiO2, A1iO3, K2O, TiO2, Fe2O3 were identified as indicators to distinguish between "soll" and "franka" cluster groups. This was confirmed through the subsequent analysis and clustering of additional samples derived from both weathered and non-weathered areas on abandoned quarry faces and from the Hagar Qim prehistoric temples. It was thus found that, for the "soll'' samples under investigation, SiO2 concentrations were> 3.4 ±0.3%, AliO3 > 0.78 ± 0.05%, K2O > 0.13 ±0.01%, TiO2 > 0.06 ±0.002% and Fe2O3 > 0.47 ±0.02%. However, some overlap was found to occur between the "soll" and "franka" stone types for all 5 elements, demarcating another stone type designated as "intermediate". These geochemical differences are also reflected in the mineralogy of the Lower Globigerina Limestone. It was seen that generally the "soil" type contains more quartz (up to 8%) and more phyllosilicates (up to 12%) than the "franka" type. This was reflected as a higher insoluble residue for "soll", of up to 14%. These results were subsequently placed within a geological context. The high concentrations of insoluble residue found at the bottom of the three cores analysed confirmed that the base of the Lower Globigerina Limestone was formed in quite shallow waters where a large amount of fine siliciclastic detrital material was accumulating. In addition, the formation of the "soll" facies probably corresponded to periods of deposition of greater quantities of elastic material or to a slowing down of carbonate sedimentation, where the number and distribution of bioturbations probably also played a determining role. Finally, the appearance of "grey" limestone at the bottom of the Lower Globigerina Limestone member in all 3 cores suggests that shortly after the Lower Globigerina Limestone started to form, a reducing, anaerobic environment occurred, where there was also an increase in the arrival of elastic terrigenous material. This was probably associated with areas of greater depth where the rate of sedimentation, or its duration, also varied, as shown by the varying thickness of this lithofacies in the three different cores. Here, the low energy of the environment led to the accumulation of organic matter and of clay minerals. Description: PH.D.CHEMISTRY

1999-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/101267 2022-08-31T09:27:33Z 2013-01-01T00:00:00Z

Title: Polymers and related systems exhibiting anomalous mechanical behaviour Abstract: Recent research has led to the prediction, discovery and/or synthesis of various materials which exhibit negative Poisson's ratio. Such materials are termed 'auxetic' and exhibit the unusual property of expanding when uniaxially stretched and getting thinner when compressed, thus contrasting with conventional materials which show the opposite behaviour. Considerable advances have been made in research involving auxetic polymers at the molecular level, both from the theoretical and synthetic aspects. The work presented in this thesis reports studies on two classes of polymers, poly(phenylacetylene) networked polymers and potentially auxetic liquid crystalline polymers (LCPs), with the aim of further understanding their behaviour at the molecular level and also to develop novel molecular-level system exhibiting negative Poisson's ratio. Monte-Carlo based sorption simulations have been performed to study the effect of foreign solvent or gas molecules on the mechanical properties of reflexyne (auxetic) and flexyne (non-auxetic) poly(phenylacetylene) networked polymers. Simulations indicate that, while the Poisson's ratio remains more or less constant in the presence of gas of solvent foreign molecules, the stiffness of the networked polymer is significantly affected, particularly by large numbers of solvent molecules which are accommodated within the systems. For example, the Young's modulus of 1,4-reflexyne decreased in the direction perpendicular to the plane of the network, a property which is explained by the fact that the solvent molecules were accommodated in between the layers, thus effectively increasing the inter-layer separation of the material without imparting additional stiffness characteristics. On the other hand, the pores of 2,8-reflexyne and 1,4-flexyne were large enough to accommodate the molecules, whose presence significantly increased the Young's modulus of the networked polymers, something which may be attributed to the densification of the system resulting from increased interaction between the layers. Such results have important implications in the eventuality of the synthesis of such networks in the future and also on possibly tailoring the properties of such polymers through the variation of sorbate concentration. Novel poly(phenylacetylene) systems which are meant to mimic the behaviour of known auxetic macrostructures were also proposed, modelled and discussed. In particular, a novel poly(phenylacetylene) system based on the macromodel designed by Bezazi et al. [Bezazi 2005] was studied. A series of such systems, termed bezaflexynes, have been modelled and studied via static mechanical simulations, which show that these molecularlevel systems behave in a rather versatile manner which is dissimilar to the model on which they are based, particularly due to significant out-of-plane bending of the acetylene Vl chains. This structural behaviour inhibit most of the systems from exhibiting auxetic behaviour, particularly in the case of beza-1,3-flexynes. On the other hand, most beza-1,2- flexynes exhibit a negative Poisson's ratio, a property which is possibly promoted by the 1,2-substitution of the benzene rings. In addition to these systems, the study on poly(phenylacetylene) networked polymers has also been extended to the design of novel systems based on the same chemistry and inspired by Grima's polytriangles-n-yne systems [Grima 2000a]. These novel systems, termed (n1,n2,n3)-polytriangles-Type II systems are also characterised by significant out-of-plane bending, but still exhibit a negative Poisson's ratio in most modelled systems, a property arising through the 'rotating triangles' deformation mechanism, which is not dissimilar to the mechanism shown by Grima' s polytriangles-n-yne systems. A comparative analysis of these novel systems indicates that the polytriangles seem to have the better auxetic characteristics. Also studied were potentially auxetic LCPs based on the concepts proposed by Griffin et al., which are meant to achieve auxetic behaviour through nano-scale rotations of laterally attached nano-rods. The simulations performed in this thesis, which were meant to complement the experimental work by Griffin et al., have elucidated how the system behaves at the molecular level when stress is applied along the direction of the main chain. Static and molecular dynamics simulations have shown that such LCP systems are anisotropic and are indeed likely to exhibit an expansion in at least one direction orthogonal to the stretching main chain direction (negative Poisson's ratio). This direction where the lateral expansion occurs depends on the plane in which the laterally attached rods rotate, which lies at the heart of the deformation mechanism that the polymer undergoes when uniaxially stretched. Simulations have also shown that para-connected phenyl-based laterally attached rods experience significant bending during rotation, something which inhibits the system from showing its full auxetic potential. The anisotropic nature of the Poisson's ratio as well as the bending of the rods had not been looked into before and may have important implications on future testing and use of these highly promising auxetic materials. A solution to the problem of bending rods is proposed through the design of novel quinoid type rods which show a significantly more rigid character and impart enhanced auxetic properties on the LCP system. This resulted in the design of a new generation of potentially auxetic LCPs based on Griffin's concept, which are likely to exhibit better auxetic characteristics. Given the enhanced properties of LCPs incorporating quinoid-based rod types, as well as the interesting results found on the poly(phenylacetylene) systems, it is hoped that future synthesis of molecular-level auxetic polymers will steer towards this direction. Description: PH.D.CHEMISTRY

2013-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/100887 2022-08-25T08:15:17Z 1974-01-01T00:00:00Z

Title: The orobanche grenata germination factor Abstract: The major part of this account is concerned with the development of a purification technique for the D. crenata germination factor, present in the root systems of the field bean, Vicia fabae Various thin layer chromatographic systems were investigated for their efficiency as regards separation and for their effect on the biological activity of the material recovered after separation. The most satisfactory of these was a silica gel layer eluted with ethyl acetate, but this was, later, shown to cause serious losses of germination activity. Various solvent extraction and partition systems were investigated as were several forms of column chromatography. The procedure finally adopted for the isolation of the stimulant, in an essentially pure form, involved the successive application of solvent extraction, column chromatography on polyamide, counter-current-distribution, thin layer chromatography and high pressure liquid chromatography. Some instrumental data was obtained on the fractions obtained from the last named system above and a tentative structure for the active germination stimulant is proposed. Later sections describe the results of applying the techniques mentioned above to the extracts of the root systems of Phassolus vulgaris and of Pisum sativum. Though fractions of pure material were obtained and some of these proved biologically active in the germination of D. crenata, too little material was obtained to enable more than tentative ideas concerning the chemical nature of these compounds. Description: PH.D.CHEMISTRY

1974-01-01T00:00:00Z