The binding of sodium and calcium ions to single and multiple poly-G decamer strands has been modelled by conducting a series of molecular dynamics simulations. Implications for metal mediated ...inter-strand interactions and gel assembly have been explored by systematically introducing up to three strands into each of these simulations. A particular emphasis has been placed on revealing intrinsic binding modes by an unbiased initial positioning of the metal ions. The results have revealed binding modes that provide a rationale for the observed gelling of alginate by calcium rather than sodium ions. A number of junction zones involving calcium ions have been identified that result in chain aggregation. This includes a distinctive perpendicular motif that appears to be ubiquitous in previously reported AFM images of open 3-D alginate networks. The coordination geometries of the metal ions have been characterised and the metal-mediated junctions between associated strands are described in detail.
•Alginates with high M content foul (bind to) hydrophobic membranes at low and neutral pH.•M has been shown by quantum chemical calculations to be to be uniquely amphiphilic.•A hydrophobic patch on M ...allows alginate polymers containing M to bind to a hydrophobic surface.•The mechanism of alginate binding to a hydrophobic membrane (polypropylene) has been demonstrated by MD simulations.•The hydrophobic patch of M is essential for the functioning of the enzyme mannuronan C-5 epimerase AlgE4.
Ostensibly hydrophilic alginates are known to foul hydrophobic membranes, under various conditions. Here, controlled experiments have been conducted at high and low pH on the fouling of a polypropylene membrane by alginate and the results suggest that the observed fouling is due to an intrinsic property of the alginate. Thus quantum chemical calculations on the M and G monomers of alginate reveal that M adopts an equilibrium geometry that is hydrophilic on one face and hydrophobic on the other, i.e. is potentially amphiphilic. Molecular dynamics simulations on short alginate chains of different sequences interacting with a modelled polypropylene surface, show that this characteristic is carried over to the polymer and results in hydrophobic patches along the chain that facilitate attractive interactions with the polypropylene surface. This concept is buttressed by an analysis of the binding characteristics of a previously reported X-ray structure of the mannuronan C-5 epimerase AlgE4 enzyme.
•PVDF membranes are influenced by conditions of polymer dissolution.•Dope sonication improves PVDF membrane properties.•PVDF membranes properties were correlated to porosity/pore size.•Porosity/pore ...size are adjustable by dissolution conditions.•Dissolution effects relate to unfolding and entanglements of the molecular chains.
Poly (vinylidene fluoride) (PVDF) is an important membrane forming material for water treatment. Earlier works have shown that major morphological changes can be achieved when PVDF is dissolved under different conditions with practical applications in membrane distillation and protein attachment. However, no previous report has discussed the effects of dissolution conditions on the performance of PVDF under ultrafiltration, which is one of the most important applications of the polymer. In this work, four different PVDF ultrafiltration membranes were produced from dopes dissolved either by stirring at 24°C, 90°C, 120°C or by sonication. It is shown that dope sonication results in membrane with enhanced thermal and mechanical stability, improved permeate flux during oil emulsion filtration and high flux recovery of ∼63% after cleaning. As a comparison, flux recovery of only ∼26% was obtained for the membrane produced from dope dissolved at 24°C. The outstanding performance of the dope-sonicated membrane was linked to its slightly lower porosity, narrow distribution of small pores and relatively smooth skin layer. Performance parameters for all membranes showed good correlation to porosity suggesting a tool for membrane design achievable by simple variation in the mode of polymer dissolution. The polymer dissolution effect was related to the degree of unfolding of the polymer molecular chains and their entanglements.
•Different sequences have different implications for Ca2+-mediated chain aggregation.•Intrastrand Ca2+–carboxylate crosslinks in poly-M and GM causes chain distortions.•Intrastrand Ca2+ crosslink ...distortions influence interchain aggregation.•Ca2+-mediated poly-GM aggregates are less stable than poly-G and poly-M.•Identified motifs consistent with reported AFM imaging of 3-D gel network.
Whilst the involvement of poly-G sequences in the formation of metal-mediated alginate gels has been previously studied in some detail, investigations into the role of poly-M and poly-GM sequences has been relatively neglected. In this regard, the binding of sodium and calcium ions to poly-M and poly-GM decamers, and their influence on chain aggregation, has been modelled by conducting a series of molecular dynamics simulations. This work complements a previous analogous study carried out for the poly-G decamer, whereby up to three strands are systematically introduced into each simulation. As in the previous study, this method allows intrinsic binding modes and interchain structural motifs to be revealed, that are consistent with those observed in available AFM images of consolidated 3-D networks. It is apparent from these studies that different sequences have different structural implications for metal-mediated chain association.
Piscivorous species like the Little Penguin (Eudyptula minor) are particularly at risk of being negatively impacted by pollution due to their heightened exposure through aquatic food chains. ...Therefore, determining the concentration of heavy metals in the fish prey of seabirds is an essential component of assessing such risk. In this study, we report on arsenic, cadmium, mercury, lead and selenium concentrations in three fish species, which are known to comprise a substantial part of the diet of Little Penguins at the urban colony of St Kilda, Melbourne, Australia. Metal concentrations in the fish sampled were generally within the expected limits, however, arsenic and mercury were higher than reported elsewhere. Anchovy (Engraulis australis) and sandy sprat (Hyperlophus vittatus) contained higher Hg concentrations than pilchard (Sardinops sagax), while sandy sprat and pilchard contained more selenium. We present these findings together with metal concentrations in Little Penguin blood and faeces, sampled within weeks of the fish collection. Mercury concentrations were highest in the blood, while faeces and fish prey species contained similar concentrations of arsenic and lead, suggesting faeces as a primary route of detoxification for these elements. We also investigated paired blood - faecal samples and found a correlation for selenium only. Preliminary data from stable isotope ratios in penguin blood indicate that changes in penguin blood mercury concentrations cannot be explained by trophic changes in their diet alone, suggesting a variation of bioavailable Hg within this semi-enclosed bay.
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•Little Penguins prey contained elevated concentrations of arsenic and mercury.•Mercury was highest in blood, while faeces contained highest concentrations of lead and arsenic.•Only selenium was correlated between blood and faeces of paired samples.•Diet-adjusted mercury concentrations were unable to explain temporal variations.
Metals and metalloids in prey, blood and faeces of a resident urban high trophic feeder are presented together with paired blood - faecal sample correlations and stable isotope ratios.
Little Penguins (Eudyptula minor) are high-trophic coastal feeders and are effective indicators of bioavailable pollutants in their foraging zones. Here, we present concentrations of metals and ...metalloids in blood of 157 Little Penguins, collected over three years and during three distinct seasons (breeding, moulting and non-breeding) at two locations: the urban St Kilda colony and the semi-rural colony at Phillip Island, Victoria, Australia. Penguin metal concentrations were foremostly influenced by location (St Kilda>Phillip Island for non-essential elements) and differed among years and seasons at both locations, reflecting differences in seasonal metal bioaccumulation or seasonal exposure through prey. Mean blood mercury concentrations showed an increasing annual trend and a negative correlation with flipper length at St Kilda. Notably, this study is the first to report on blood metal concentrations during the different stages of moult, showing the mechanism of non-essential metal mobilisation and detoxification.
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•Metals and metalloids measured in penguin blood over three years.•Arsenic, mercury and lead significantly higher at urban colony•Mercury showed increasing annual trend at urban colony.•Penguin flippers shorter at urban colony and correlate with mercury.•Within-moult variations show metal mobilisation and detoxification.
Monitoring trace metal and metalloid concentrations in marine animals is important for their conservation and could also reliably reflect pollution levels in their marine ecosystems. Concentrations ...vary across tissue types, with implications for reliable monitoring. We sampled blood and moulted feathers of the Little Penguin (Eudyptula minor) from three distinct colonies, which are subject to varying levels of anthropogenic impact. Non-essential trace metal and metalloid concentrations in Little Penguins were clearly linked to the level of industrialisation adjacent to the respective foraging zones. This trend was more distinct in blood than in moulted feathers, although we found a clear correlation between blood and feathers for mercury, lead and iron. This study represents the first reported examination of trace metals and metalloids in the blood of any penguin species and demonstrates that this high trophic feeder is an effective bioindicator of coastal pollution.
•Trace metals measured in blood and feathers.•Arsenic, Mercury and Lead significantly higher at urban colony.•Correlations found between trace metals in feathers and blood.•Little Penguins are suitable bioindicators for coastal metal pollution.
This study confirms the suitability of the Little Penguin as a bioindicator of coastal metal pollution in coastal areas using non-destructive sampling methods.
Helium and water gas plasma were used to modify the surface morphology and chemistry of commercial thin film composite membranes. Such surface treatment is a convenient tool to alter performance of ...the membranes and subsequently reduce interactions with contaminants in solution. Plasma reactions such as etching and re-deposition resulted in surface functionalization and texturation which were correlated with membrane flux and salt rejection changes. Investigations conducted using atomic force microscopy revealed morphology alterations which were apparent as either smoother surfaces or rougher surfaces. While the smoothing was attributed to a re-deposition of polymer material, which originated most likely from vaporization of surface polymer, the roughening was a result from balanced plasma surface reactions. The beneficial etching can occur under certain conditions when helium is used in conjunction with low excitation power, which resulted in flux enhancements up to 66% (i.e. from 30L.m−2.h−1 to 50L.m−2.h−1) with 98% rejection. The hydrophilicity was dramatically increased from 46.6° to as low as 8.9° after 5min of helium plasma duration. The impact that plasma treatments have on the nascent structure was discussed in order to highlight its application as a convenient tool to functionalize the surface of thin film composite membranes.
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