An investigation of the chemistry of silver in biological systems, and the development of silver-containing materials for use as antibacterial agents

The antibacterial properties of silver have been known for centuries; however, the threat of antibiotic resistant bacteria has led to renewed focus on the noble metal. Silver is now commonly included in a range of household and medical items to imbue them with bactericidal properties. Despite this, the chemical fate of the metal in mammalian or bacterial biological systems, is poorly understood. Through a metallomics approach, using techniques like X-ray absorption spectroscopy (XAS), and size-exclusion chromatography hyphenated inductively coupled plasma mass spectrometry (SEC-ICP-MS), results are presented that advance our understanding of the chemistry of these interactions. In bacterial systems, endogenous and exogenous silver ions were found to be predominantly coordinated by thiolate species, likely cysteine residues. Silver in broth was found to be associated exclusively with moderately size species (~30 kDa). Conversely, in S. aureus and E. coli, silver was bound by a range of species, ranging from 20-30 kDa, to >1220 kDa. Silver was also nonuniformly associated with copper-bound species, suggesting possible cellular processing of the noble metal as nutrient copper. Colocation of Ag with Cu could also provide insight into the cellular distribution of silver, as copper is predominantly found in the extracytoplasmic space of bacteria as it is a strictly regulated nutrient due to potential toxicity. Exposure of human whole blood to 2 mM AgNO3 resulted in lysis of red blood cells (RBCs), regardless of the isotonicity of the added solution. Despite this, within five minutes ~90% of silver ions were localised in the RBCs. Inside the RBCs Ag+ interacted predominantly with haemoglobin and no low molecular weight complexes (e.g. glutathione). Linear combination fitting of Ag K-edge XANES of the RBC fraction from a sample of human whole blood treated with AgNO3 indicated ~53% of the experimental spectrum could be described by a silver-haemoglobin model with the remaining percent explained by a silver-cysteine model. In isolated plasma the speciation of silver was found to strongly resemble that of solid silver chloride. Conversely, the speciation of silver in the plasma fraction from whole blood was found to have no contribution from the same AgCl model spectrum. The dominant binder of silver in human plasma was human serum albumin as well as higher molecular weight species. Finally, the pore environment of UiO-66 was tailored for use as an antibacterial agent. In. general, inclusion of sulfur-containing functionality in the framework resulted in increased silver ion uptake (relative to the parent material). While sulfhydryl-decorated pores were found to take up significantly more silver, the material did not release significant concentrations of Ag+. Allyl and alkyl thioethers were found to both increase silver uptake and control release. The silver-loaded materials were successfully embedded into polymer matrices; extending applicability as antibacterial hybrid coatings and providing further control over silver release. Ag XAS revealed that, when loaded with silver ions, the unfunctionalised UiO-66 partially reduced Ag(I) to Ag(0) in the absence of an added reductant. All silver-loaded UiO-66 derivatives embedded in polymer matrices were found to have antibacterial activity against S. aureus and E. coli.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202

Geosciences / Identifying Spatio-Temporal Landslide Hotspots on North Island, New Zealand, by Analyzing Historical and Recent Aerial Photography

Accurate mapping of landslides and the reliable identification of areas most affected by landslides are essential for advancing the understanding of landslide erosion processes. Remote sensing data provides a valuable source of information on the spatial distribution and location of landslides. In this paper we present an approach for identifying landslide-prone “hotspots” and their spatio-temporal variability by analyzing historical and recent aerial photography from five different dates, ranging from 1944 to 2011, for a study site near the town of Pahiatua, southeastern North Island, New Zealand. Landslide hotspots are identified from the distribution of semi-automatically detected landslides using object-based image analysis (OBIA), and compared to hotspots derived from manually mapped landslides. When comparing the overlapping areas of the semi-automatically and manually mapped landslides the accuracy values of the OBIA results range between 46% and 61% for the producers accuracy and between 44% and 77% for the users accuracy. When evaluating whether a manually digitized landslide polygon is only intersected to some extent by any semi-automatically mapped landslide, we observe that for the natural-color images the landslide detection rate is 83% for 2011 and 93% for 2005; for the panchromatic images the values are slightly lower (67% for 1997, 74% for 1979, and 72% for 1944). A comparison of the derived landslide hotspot maps shows that the distribution of the manually identified landslides and those mapped with OBIA is very similar for all periods; though the results also reveal that mapping landslide tails generally requires visual interpretation. Information on the spatio-temporal evolution of landslide hotspots can be useful for the development of location-specific, beneficial intervention measures and for assessing landscape dynamics.FFG-ASAP-847970(VLID)165265

The Limits and Opportunities of Regional Solidarity: Exploring Refugee Resettlement in Brazil and Chile

This paper explores the implementation and experience of refugee resettlement in Brazil and Chile by focusing on the main limits and opportunities of regional ‘solidarity’, the principle on which the programme is based. By analysing how the notion of solidarity is understood in the context of resettlement in Latin America, I review the programme at two levels. First, at the regional level, I focus on the programmes in both Brazil and Chile, to assess resettlement as an instrument of international cooperation and responsibility sharing. At the local level, I look at refugees’ residency status and access to rights. I focus here on the resettlement of Colombian and Palestinian refugees in both countries. Exploring resettlement through the lens of solidarity, allows us to understand the nuances and multiple dimensions of resettlement. This is timely, as countries of the Southern Cone of Latin America are identified as ‘emerging resettlement countries’ and expected to increase their resettlement intake. The findings discussed in this paper show that resettlement should aim for a complementary understanding of solidarity in order to improve the quality of the programme, as well as expanding its scope and capacity

Permanent embryo arrest: molecular and cellular concepts

Developmental arrest is one of the mechanisms responsible for the elevated levels of embryo demise during the first week of in vitro development. Approximately 10–15% of IVF embryos permanently arrest in mitosis at the 2- to 4-cell cleavage stage showing no indication of apoptosis. Reactive oxygen species (ROS) are implicated in this process and must be controlled in order to optimize embryo production. A stress sensor that can provide a key understanding of permanent cell cycle arrest and link ROS with cellular signaling pathway(s) is p66Shc, an adaptor protein for apoptotic-response to oxidative stress. Deletion of the p66Shc gene in mice results in extended lifespan, which is linked to their enhanced resistance to oxidative stress and reduced levels of apoptosis. p66Shc has been shown to generate mitochondrial H2O2 to trigger apoptosis, but may also serve as an integration point for many signaling pathways that affect mitochondrial function. We have detected elevated levels of p66Shc and ROS within arrested embryos and believe that p66Shc plays a central role in regulating permanent embryo arrest. In this paper, we review the cellular and molecular aspects of permanent embryo arrest and speculate on the mechanism(s) and etiology of this method of embryo demise

A process-based model of conifer forest structure and function with special emphasis on leaf lifespan

We describe the University of Sheffield Conifer Model (USCM), a process-based approach for simulating conifer forest carbon, nitrogen, and water fluxes by up-scaling widely applicable relationships between leaf lifespan and function. The USCM is designed to predict and analyze the biogeochemistry and biophysics of conifer forests that dominated the ice-free high-latitude regions under the high pCO2 “greenhouse” world 290–50 Myr ago. It will be of use in future research investigating controls on the contrasting distribution of ancient evergreen and deciduous forests between hemispheres, and their differential feedbacks on polar climate through the exchange of energy and materials with the atmosphere. Emphasis is placed on leaf lifespan because this trait can be determined from the anatomical characteristics of fossil conifer woods and influences a range of ecosystem processes. Extensive testing of simulated net primary production and partitioning, leaf area index, evapotranspiration, nitrogen uptake, and land surface energy partitioning showed close agreement with observations from sites across a wide climatic gradient. This indicates the generic utility of our model, and adequate representation of the key processes involved in forest function using only information on leaf lifespan, climate, and soils

Self-oscillation

Physicists are very familiar with forced and parametric resonance, but usually not with self-oscillation, a property of certain dynamical systems that gives rise to a great variety of vibrations, both useful and destructive. In a self-oscillator, the driving force is controlled by the oscillation itself so that it acts in phase with the velocity, causing a negative damping that feeds energy into the vibration: no external rate needs to be adjusted to the resonant frequency. The famous collapse of the Tacoma Narrows bridge in 1940, often attributed by introductory physics texts to forced resonance, was actually a self-oscillation, as was the swaying of the London Millennium Footbridge in 2000. Clocks are self-oscillators, as are bowed and wind musical instruments. The heart is a "relaxation oscillator," i.e., a non-sinusoidal self-oscillator whose period is determined by sudden, nonlinear switching at thresholds. We review the general criterion that determines whether a linear system can self-oscillate. We then describe the limiting cycles of the simplest nonlinear self-oscillators, as well as the ability of two or more coupled self-oscillators to become spontaneously synchronized ("entrained"). We characterize the operation of motors as self-oscillation and prove a theorem about their limit efficiency, of which Carnot's theorem for heat engines appears as a special case. We briefly discuss how self-oscillation applies to servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business cycle, among other applications. Our emphasis throughout is on the energetics of self-oscillation, often neglected by the literature on nonlinear dynamical systems.Comment: 68 pages, 33 figures. v4: Typos fixed and other minor adjustments. To appear in Physics Report

Endocrine disruptors and obesity: a current review on environmental obesogens

Obesity represents an important public health concern because it substantially increases the risk of multiple chronic diseases and thereby contributing to a decline in both quality of life and life expectancy. Besides unhealthy diet, physical inactivity and genetic susceptibility, environmental pollutants also contribute to the rising prevalence of obesity epidemic. An environmental obesogen is defined as a chemical that can alter lipid homeostasis to promote adipogenesis and lipid accumulation whereas an endocrine disrupting chemical (EDC) is defined as a synthetic chemical that can interfere with the endocrine function and cause adverse health effects. Many obesogens are EDCs that interfere with normal endocrine regulation of metabolism, adipose tissue development and maintenance, appetite, weight, and energy balance. An expanding body of scientific evidence from animal and epidemiological studies has begun to provide links between exposure to EDCs and obesity. Despite the significance of environmental obesogens in the pathogenesis of metabolic diseases, the contribution of synthetic chemical exposure to obesity epidemic remains largely unrecognised. Hence, the purpose of this review is to provide a current update on the evidences from animal and human studies on the role of fourteen environmental obesogens in obesity, a comprehensive view of the mechanisms of action of obesogens and current green and sustainable chemistry strategies to overcome chemical exposure to prevent obesity. Designing of safer version of obesogens through green chemistry approaches requires a collaborative undertaking to evaluate the toxicity of endocrine disruptors using appropriate experimental methods, which will help in developing a new generation of inherently safer chemicals

Late Quaternary evolution of Matakana Island, Bay of Plenty, New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Geography at Massey University

Matakana Island consists of two main parts - an area of mainly Pleistocene materials to the southwest and a c.24 km long Holocene barrier to the northeast. Together with the tombolo systems of Bowentown Heads and Mount Maunganui, Matakana Island encloses the c.200 km2 Tauranga Harbour. This study establishes the late Quaternary geomorphological history of Matakana Island, focussing primarily on the evolution of the Holocene barrier. The barrier consists largely of relict foredunes, with relict parabolic dunes, lakes/wetland areas, washover deposits and estuarine flats also present. A detailed geomorphological map provides a foundation for palaeoenvironmental reconstructions. The landform information is supplemented with details of the sedimentology, tephrochronology, pedology, archaeology and palynology of the barrier in order to identify and describe past environmental changes. The Pleistocene part of the island contains remnants of at least three late Pleistocene terraces, mantled by thick beds of tephra and ignimbrite. The lowest terrace, which retains some coastal landforms, originated as a relict foredune plain which probably formed during the Last Interglacial maximum (c. 125 000 years ago). The older, higher terraces are likely to have originated during earlier interglacial periods. The barrier consists primarily of moderately well sorted to well sorted medium to fine sand. The dominance of quartz, feldspar and hypersthene indicate that much of the sediment was originally derived from the active Taupo Volcanic Zone. Following the end of the Postglacial Marine Transgression c.7 000 cal BP, deposits of these materials on the continental shelf were reworked and transported shoreward to form the Holocene barrier. Barrier formation commenced by around c.6 000 cal BP. The barrier initially formed in at least two separate parts, separated by a tidal inlet at present-day Blue Gum Bay. The entrance migrated southeastward as the barrier prograded and was closed off c.3 750 cal BP. Following the closure of the entrance, foredunes became larger and more irregular, suggesting a major change to the coastal sediment budget. Progradation rates, calculated from shoreline ages determined by airfall tephra deposits, radiocarbon ages and sea-rafted pumice deposits, generally decreased with time, from about 0.46 metres/year initially to about 0.18 metres/year over the last c.650 years. Significant erosion of the southeastern end of the barrier culminated shortly after the Kaharoa eruption (c.650 cal BP), at which time the barrier was approximately 83 percent of its present length. Subsequently, both ends of the barrier extended rapidly. The coarse texture of sand comprising the barrier ends and anomalously old radiocarbon ages of incorporated shells suggests that, as the entrances narrowed, sediment from adjacent ebb-tidal deltas was reworked to form the barrier ends. The barrier also underwent considerable change following the first arrival of humans on Matakana Island sometime after the Kaharoa eruption. Widespread vegetation clearance and soil disturbance are likely to have contributed to dune instability. Matakana Island appears to have developed in a similar fashion to many Holocene barrier systems of southeastern Australia in terms of a predominant shelf sediment source, onshore sediment transport following the end of the Postglacial Marine Transgression and decreasing progradation rates through time