The alpha-to-beta conformational transition of Alzheimer's Abeta-(1-42) peptide in aqueous media is reversible: a step by step conformational analysis suggests the location of beta conformation seeding

Current views of the role of beta-amyloid (Abeta) peptide fibrils range from regarding them as the cause of Alzheimer's pathology to having a protective function. In the last few years, it has also been suggested that soluble oligomers might be the most important toxic species. In all cases, the study of the conformational properties of Abeta peptides in soluble form constitutes a basic approach to the design of molecules with "antiamyloid" activity. We have experimentally investigated the conformational path that can lead the Abeta-(1-42) peptide from the native state, which is represented by an alpha helix embedded in the membrane, to the final state in the amyloid fibrils, which is characterized by beta-sheet structures. The conformational steps were monitored by using CD and NMR spectroscopy in media of varying polarities. This was achieved by changing the composition of water and hexafluoroisopropanol (HFIP). In the presence of HFIP, beta conformations can be observed in solutions that have very high water content (up to 99 % water; v/v). These can be turned back to alpha helices simply by adding the appropriate amount of HFIP. The transition of Abeta-(1-42) from alpha to beta conformations occurs when the amount of water is higher than 80 % (v/v). The NMR structure solved in HFIP/H2O with high water content showed that, on going from very apolar to polar environments, the long N-terminal helix is essentially retained, whereas the shorter C-terminal helix is lost. The complete conformational path was investigated in detail with the aid of molecular-dynamics simulations in explicit solvent, which led to the localization of residues that might seed beta conformations. The structures obtained might help to find regions that are more affected by environmental conditions in vivo. This could in turn aid the design of molecules able to inhibit fibril deposition or revert oligomerization processes.     

Influence of strontium for calcium substitution in bioactive glasses on degradation,ion release and apatite formation

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO₂–P₂O₅–CaO–Na₂O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions.     

Methane decomposition over Co thin layer supported catalysts to produce hydrogen for fuel cell

Co/Al₂O₃/Silica Cloth Thin Layer Catalysts (CoAS) for Catalytic Decomposition of Natural Gas (CDNG) were investigated using a new Multilayer Catalytic Reactor (MCR). The influence of Co loading and reaction temperature was evaluated. Irrespective of Co loading, initial CH₄ conversion rises with T_R, while for lifetime and carbon capacity (C/Ni, number of CH₄ molecules decomposed for Ni atom until complete deactivation) it is not possible to find a direct relationship with other operating parameters or catalyst characteristics. However, Co loading significantly affects the catalytic activity: Co loading as high as 20 wt.% ensures both long lifetime and high H₂ productivity. On the contrary of what occurs using Ni-based catalysts and irrespective of reaction temperature investigated, filamentous coke forms with a “base” reaction mechanism and Co catalyst can be regenerated in oxygen without any problem, thus allowing to realize a dual-step process for the production of “CO_x-free” hydrogen stream.     

Effect of austenitising conditions on the impact properties of an alloyed austempered ductile iron of initially pearlitic matrix structure

This study sets out to investigate the effect of austenitising conditions on the microstructure and impact properties of an austempered ductile iron containing Copper and Nickel and having an initially fully pearlitic structure. Un-notched Izod impact test specimens were solution treated in the range 850–1000 °C for durations between 15 and 360 min. and then austempered at 360 °C for 180 min.

It was shown that increasing the austenitising temperature increases the amount of carbon taken in solution by the original austenite. This reduces the driving force controlling the transformation of the austenite to the ausferrite product, ferrite and austenite. As a result, the retained austenite volume in the final microstructure increases but simultaneously its stability falls. This places an upper limit on the austenitising temperature and the amount of retained austenite permissible. On the other hand, for optimum properties, the austenitising temperature and time must be high and long enough respectively to ensure complete austenitisation.

It was also shown that generally, in irons with an initially pearlitic structure, the impact properties increase steadily to a maximum value as the austenitising time increases to about 180 min. and remain constant as the soaking period extends further. Optimum properties are obtained following austenitising between 850 and 900 °C for durations of 120 to 180 min. and correspond to heat treatment cycles which saturate the initial austenite with carbon.     

Competition of several carbonation reactions in concrete: A parametric study

Carbonation caused by atmospheric carbon dioxide is one of the major physicochemical processes which can compromise the service life of reinforced concrete structures. While the bulk of the carbonation reaction is that of calcium hydroxide, other constituents of the porous matrix can also carbonate and compete with calcium hydroxide for carbon dioxide. Particularly the carbonation of calcium–silicate hydrates and unhydrated constituents are neglected by most authors in carbonation prediction models. In this paper, a mathematical model of carbonation is extended to include additional carbonation and hydration reactions. The competition of the several reactions and their effect on the carbonation depth is investigated by dimensional analysis and numerical simulations. A parameter study emphasises that multiple internal reaction layers appear. Their position and speed essentially depend on the strength of the different reactions. It is also observed that, for a wide range of parameters, the effect of some of the additional reactions on the carbonation depth is small. In particular, a comparison with data from laboratory experiments justifies the neglect of the carbonation of the unhydrated constituents in prediction models.     

The epidemiology and cost of falls requiring hospitalisation in children in Western Australia: a study using linked administrative data

OBJECTIVE: The aim of this study was to examine the epidemiology and health system cost of children's falls resulting in hospitalisation in 2003 in Western Australia. METHODS: The Injury Cost Database was used to identify children who were admitted to hospital with a falls related injury. Adjusted incidence rate ratios (IRR) of hospitalisation were modelled using Poisson regression. In-patient hospital costs were assigned using the published DRG costs for Western Australia. These costs were then extrapolated to health system costs based on previously published relative proportions. RESULTS: When adjusted for other covariates in the model males had a 53% higher incidence of falls requiring hospitalisation compared with females. Aboriginal children had a 36% higher incidence compared with their non-Aboriginal counterparts, and the incidence of falls reduced with increasing age. The total cost of in-patient hospitalisation associated with children's falls in Western Australia was A$4,554,000 with an average cost of A$1876 per case. In children aged 0-4 years and 10-14 years the highest cost resulted from falls on the flat (slips and trips). However, in children aged 5-9 years injuries resulting from falls from playground equipment resulted in both the highest cost group (A$539,000) and the highest cost per case (A$1917). The total cost to the health system of children's falls in Western Australia in 2003 were estimated to be A$21.5 million, with the total cost to the community estimated at A$108.5 million. CONCLUSION: Children's falls impose a considerable burden and cost to both the health care system and the community. This study has provided information on where the burden of risk and the majority of costs lie, namely males, Aboriginal children and for children aged 5-9 years, unlike their younger and older peers, playground equipment.     

Variation in the carotenoid composition of acerola and its processed products

Acerola is now commercially produced and processed in Brazil. Known for its very high vitamin C content, this fruit is also a good source of β‐carotene. The present study was carried out to verify variation in the carotenoid composition along the food chain. Neoxanthin, violaxanthin, lutein, β‐cryptoxanthin, α‐carotene and β‐carotene were found in the acerola fruit. β‐Carotene predominated with mean concentrations of 12.4 and 38.1 µg g^?1 in the ripe fruit, 8.8 and 30.1 µg g^?1 in the peeled ripe fruit and 5.4 and 12.0 µg g^?1 in the partially ripe fruit of an undefined variety taken from home gardens and the commercial cultivar Olivier, respectively. Aside from β‐carotene, β‐cryptoxanthin increased significantly in both garden and commercial fruits and violaxanthin in the latter fruits during ripening. Peeling reduced β‐carotene in both garden and commercial lots, violaxanthin decreased in the commercial fruits, and the other carotenoids remained virtually unchanged. Four brands of frozen pulp and three brands of processed juice had variable and markedly lower carotenoid levels than those of the fresh fruit, indicating that the processing should be improved. Copyright © 2006 Society of Chemical Industry     

Photoelectrocatalytic determination of NADH in a flow injection system with electropolymerized methylene blue

It was firstly described that a glassy carbon electrode electropolymerized with methylene blue shows an efficient photoelectrocatalytic activity towards NADH oxidation in a phosphate buffer solution (pH 7.0). In order to perform the photoelectrocatalytic determination of NADH in a flow injection analysis (FIA) system, a home-made flow electrochemical cell with a suitable transparent window for the irradiation of the electrode surface was constructed. The currents obtained from the photoamperometric measurements in the FIA system at optimum conditions (flow rate of carrier solution, 1.3 mL min⁻¹; transmission tubing length, 10 cm; injection volume, 100 μL; and constant applied potential, +150 mV vs. Ag/AgCl) were linearly dependent on the NADH concentration and linear calibration curves were obtained in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁴ M. The detection limit was found to be 4.0 × 10⁻⁸ M for photoamperometric determination of NADH.     

Kinetics of para-nitrophenol and chemical oxygen demand removal from synthetic wastewater in an anaerobic migrating blanket reactor

A laboratory scale anaerobic migrating blanket reactor (AMBR) was operated at different HRTs (1-10.38 days) in order to determine the para-nitrophenol (p-NP) and COD removal kinetic constants. The reactor was fed with 40 mg L(-1)p-NP and 3000 mg L(-1) glucose-COD. Modified Stover-Kincannon and Grau second-order kinetic models were applied to the experimental data. The predicted p-NP and COD concentrations were calculated using the kinetic constants. It was found that these data were in better agreement with the observed ones in the modified Stover-Kincannon compared to Grau second-order model. The kinetic constants calculated according to Stover-Kincannon model are as follows: the saturation value constant (K(B)) and maximum utilization rate constants (R(max)) were found as 31.55 g CODL(-1)day(-1), 29.49 g CODL(-1)day(-1) for COD removal and 0.428 g p-NPL(-1)day(-1), 0.407 g p-NPL(-1)day(-1) for p-NP removal, respectively (R(2)=1). The values of (a) and (b) were found to be 0.096 day and 1.071 (dimensionless) with high correlation coefficients of R(2)=0.85 for COD removal. Kinetic constants for specific gas production rate were evaluated using modified Stover-Kincannon, Van der Meer and Heerrtjes and Chen and Hasminoto models. It was shown that Stover-Kincannon model is more appropriate for calculating the effluent COD, p-NP concentrations in AMBR compared to the other models. The maximum specific biogas production rate, G(max), and proportionality constant, G(B), were found to be 1666.7 mL L(-1) day(-1) and 2.83 (dimensionless), respectively in modified Stover-Kincannon gas model. The bacteria had low Haldane inhibition constants (K(ID)=14 and 23 mg L(-1)) for p-NP concentrations higher than 40 mg L(-1) while the half velocity constant (K(s)) increased from 10 to 60 and 118 mg L(-1) with increasing p-NP concentrations from 40 to 85 and 125 mg L(-1).