Toward an Active and Stable Catalyst for Oxygen Evolution in Acidic Media: Ti‐Stabilized MnO2

Catalysts are required for the oxygen evolution reaction, which are abundant, active, and stable in acid. MnO₂ is a promising candidate material for this purpose. However, it dissolves at high overpotentials. Using first‐principles calculations, a strategy to mitigate this problem by decorating undercoordinated surface sites of MnO₂ with a stable oxide is developed here. TiO₂ stands out as the most promising of the different oxides in the simulations. This prediction is experimentally verified by testing sputter‐deposited thin films of MnO₂ and Ti–MnO₂. A combination of electrochemical measurements, quartz crystal microbalance, inductively coupled plasma mass spectrometry measurements, and X‐ray photoelectron spectroscopy is performed. Small amounts of TiO₂ incorporated into MnO₂ lead to a moderate improvement in stability, with only a small decrease in activity. This study opens up the possibility of engineering surface properties of catalysts so that active and abundant nonprecious metal oxides can be used in acid electrolytes.     

Morphological and quantitative changes in paternal brood‐pouch vasculature during embryonic development in two Syngnathus pipefishes

Vascular corrosion casts of Syngnathus floridae and Syngnathus fuscus brood pouches were examined by scanning electron microscopy. Morphological and quantitative data on the vasculature of the paternal brood pouch during each stage of embryonic development were investigated to explore potential changes during brooding, to consider interspecific differences and to provide structural evidence for previously reported functional roles of the brood pouch. The brood pouches of both species are highly vascularized structures with cup‐like arrangements of brood‐pouch vasculature developing around each embryo shortly after fertilization and breaking down before fry release. The density and size of paternally derived blood vessels in contact with the embryos were found to be consistent for S. fuscus once this structure was established early in development. On the contrary, these vasculature measurements varied with early S. floridae brood stages when the embryo still relied heavily on the yolk sac. Diameter measurements of S. fuscus brood‐pouch blood vessels were also comparatively smaller during these early developmental stages, suggesting that the structural stability and opportunity for greater transport via slower blood flow may contribute to greater paternal allocation. This is the first study to document changes in brood‐pouch vasculature during specific stages of embryonic development, to show regression of this vasculature before fry release and to provide morphological data for two syngnathid species for which information on brood‐pouch physiology is available.     

Understanding and Improving Mechanical Stability in Electrodeposited Cu and Bi for Dynamic Windows Based on Reversible Metal Electrodeposition

Dynamic windows based on reversible metal electrodeposition (RME) can electronically adjust light transmission from ≈70% to <0.1% to improve building aesthetics and energy efficiency by controlling light and heat flow. For RME devices using Cu and Bi, the windows reach “privacy state” (<0.1% transmission) when ≈180 nm of metal is electrodeposited on the transparent conducting electrode. When films with a plated atomic Cu–Bi ratio of ≈2:1 rest in the privacy state, sinusoidal cracks form across the entire film, and the metal delaminates in <1 day. This mechanical failure renders the window unusable as specks of metal are visually unattractive and reduce the dynamic range of the window. The Cu–Bi film is stress free upon deposition, but after 4 h of resting, 38 MPa of tensile stress develops. The tension in Cu–Bi and Cu films combined with the Cu(ClO₄)₂ in the electrolyte results in severe, widespread fractures and delamination due to stress corrosion cracking. In contrast, electrodeposited Bi films have compressive stress, likely due to high self-diffusion and insertion of atoms into grain boundaries while plating, which results in a Bi-based dynamic window with crack-free resting stability that exceeds 9 weeks.     

Angioarchitecture of the venous and capillary system in heart defects induced by retinoic acid in mice

BACKGROUND: Corrosion casting and immunohistochemical staining with anti‐alpha smooth muscle actin and anti‐CD34 was utilized to demonstrate the capillary plexus and venous system in control and malformed mouse hearts. METHODS: Outflow tract malformations (e.g., double outlet right ventricle, transposition of the great arteries, and common truncus arteriosus) were induced in progeny of pregnant mice by retinoic acid administration at day 8.5 of pregnancy. RESULTS: Although control hearts exhibited areas in which capillaries tended to be oriented in parallel arrays, the orientation of capillaries in the respective areas of malformed hearts was chaotic and disorganized. The major branch of a conal vein in control hearts runs usually from the left side of the conus to its right side at the root of the pulmonary trunk and opens to the right atrium below the right auricle; thus, it has a curved course. On the other hand, a conal vein in malformed hearts courses from the left side or from the anterior side of the conus and tends to traverse straight upwards along the dextroposed aorta or along the aortopulmonary groove with its proximal part located outside of the heart. Other cardiac veins in outflow tract malformations are positioned in the same locations as in control hearts. CONCLUSIONS: We postulate that the changed location of the conal vein and disorganized capillary plexus result from malformed morphogenesis of the outflow tract and/or a disturbed regulation of angiogenic growth factor release from the adjacent environment. Birth Defects Research (Part A), 2009. © 2009 Wiley‐Liss, Inc.     

Trp42 rotamers report reduced flexibility when the inhibitor acetyl-pepstatin is bound to HIV-1 protease

The Q7K/L331/L631 HIV-1 protease mutant was expressed in Escherichia coli and the effect of binding a substrate-analog inhibitor, acetyl-pepstatin, was investigated by fluorescence spectroscopy and molecular dynamics. The dimeric enzyme has four intrinsic tryptophans, located at positions 6 and 42 in each monomer. Fluorescence spectra and acrylamide quenching experiments show two differently accessible Trp populations in the apoenzyme with k(q1) = 6.85 x 10(9) M(-1) s(-1) and k(q2) = 1.88 x 10(9) M(-1) s(-1), that merge into one in the complex with k(q) = 1.78 x 10(9) M(-1) s(-1). 500 ps trajectory analysis of Trp X1/X2 rotameric interconversions suggest a model to account for the observed Trp fluorescence. In the simulations, Trp6/Trp6B rotameric interconversions do not occur on this timescale for both HIV forms. In the apoenzyme simulations, however, both Trp42s and Trp42Bs are flipping between X1/X2 states; in the complexed form, no such interconverions occur. A detailed investigation of the local Trp environments sampled during the molecular dynamics simulation suggests that one of the apoenzyme Trp42B rotameric interconversions would allow indole-quencher contact, such as with nearby Tyr59. This could account for the short lifetime component. The model thus interprets the experimental data on the basis of the conformational fluctuations of Trp42s alone. It suggests that the rotameric interconversions of these Trps, located relatively far from the active site and at the very start of the flap region, becomes restrained when the apoenzyme binds the inhibitor. The model is thus consistent with associating components of the fluorescence decay in HIV-1 protease to ground state conformational heterogeneity.     

Fungal degradation of calcium-, lead- and silicon-bearing minerals

The aim of this study was to examine nutritional influence on the ability of selected filamentous fungi to mediate biogenic weathering of the minerals, apatite, galena and obsidian in order to provide further understanding of the roles of fungi as biogeochemical agents, particularly in relation to the cycling of metals and associated elements found in minerals. The impact of three organic acid producing fungi (Aspergillus niger, Serpula himantioides and Trametes versicolor) on apatite, galena and obsidian was examined in the absence and presence of a carbon and energy source (glucose). Manifestation of fungal weathering included corrosion of mineral surfaces, modification of the mineral substrate through transformation into secondary minerals (i.e. crystal formation) and hyphal penetration of the mineral substrate. Physicochemical interactions of fungal metabolites, e.g. H⁺ and organic acids, with the minerals are thought to be the primary driving forces responsible. All experimental fungi were capable of mineral surface colonization in the absence and presence of glucose but corrosion of the mineral surface and secondary mineral formation were affected by glucose availability. Only S. himantioides and T. versicolor were able to corrode apatite in the absence of glucose but none of the fungi were capable of doing so with the other minerals. In addition, crystal formation with galena was entirely dependent on the availability of glucose. Penetration of the mineral substrates by fungal hyphae occurred but this did not follow any particular pattern. Although the presence of glucose in the media appeared to influence positively the mineral penetrating abilities of the fungi, the results obtained also showed that some geochemical change(s) might occur under nutrient-limited conditions. It was, however, unclear whether the hyphae actively penetrated the minerals or were growing into pre-existing pores or cracks.     

Microbiological influences in 'blue water' copper corrosion

AIMS: To investigate the influence of micro-organisms associated with copper corrosion on 'blue water' corrosion in drinking water. METHODS AND RESULTS: Laboratory rigs comprising of polycarbonate containers attached to annealed copper plumbing tubes were filled with Melbourne drinking water and sterilized by autoclaving. The copper tubes were inoculated with sterile or nonsterile extracts obtained from corroding copper and allowed to stand for 7 days. The extracts were drained and the tubes flushed and filled with sterile water from the rig. The water within the tubes was removed weekly for analysis and the tubes were refilled with freshly aerated water. The tube water sampled was analysed for pH, total copper and the presence of micro-organisms. Sterile rigs and rigs containing nonsterile water, both without tube inoculums, were used as controls. The results demonstrated that tubes inoculated with nonsterile corrosion extracts showed statistically higher copper release compared with the other rigs. Copper release as blue water was only observed after a lag period of 9 weeks. The internal surfaces of tubes releasing copper showed significant amounts of corrosion products and the presence of biofilm. Bacteria isolated from the corroding tubes included Acidovorax spp. and Sphingomonas sp. CONCLUSIONS: The results demonstrate a microbial role in blue water, as corrosion was induced in new copper tubes by exposure to nonsterile copper corrosion products. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential for micro-organisms present in corrosion products to initiate blue water corrosion presents significant implications for the management of corrosion in distribution systems.     

Temperature and pH effects on plant uptake of benzotriazoles by sunflowers in hydroponic culture

This article describes a systematic approach to understanding the effect of environmental variables on plant uptake (phyto-uptake) of organic contaminants. Uptake (and possibly phytotransformation) of xenobiotics is a complex process that may differ from nutrient uptake. A specific group of xenobiotics (benzotriazoles) were studied using sunflowers grown hydroponically with changes of environmental conditions including solution volume, temperature, pH, and mixing. The response of plants to these stimuli was evaluated and compared using physiological changes (biomass production and water uptake) and estimated uptake rates (influx into plants), which define the uptake characteristics for the xenobiotic. Stirring of the hydroponic solution had a significant impact on plant growth and water uptake. Plants were healthier, probably because of a combination of factors such as improved aeration and increase in temperature. Uptake and possibly phytotransformation of benzotriazoles was increased accordingly. Experiments at different temperatures allowed us to estimate an activation energy for the reaction leading to triazole disappearance from the solution. The estimated activation energy was 43 kJ/mol, which indicates that the uptake process is kinetically limited. Culturing plants in triazole-amended hydroponic solutions at different pH values did not strongly affect the biomass production, water uptake, and benzotriazole uptake characteristics. The sunflowers showed an unexpected capacity to buffer the solution pH.