Electrochemical determination of hydrogen peroxide by a nonenzymatic catalytically enhanced silver-iron (iii) oxide/polyoxometalate/reduced graphene oxide modified glassy carbon electrode

The synergism of phosphomolybdic acid hydrate (POM) decorated with silver-iron (III) oxide (Ag-Fe2O3) nanoparticles and anchored on reduced graphene oxide (RGO) have been demonstrated to be effective as a nonenzymatic H2O2 sensor platform. The assembly of the sensor components and their interactions were probed morphologically, spectroscopically and electrochemically. The Ag-Fe2O3/POM/RGO nanocomposite sensor provided an enhanced electroactive surface area, electrical conductivity and sensitivity for hydrogen peroxide compared to an unmodified glassy carbon electrode (GCE) at –0.55 V versus a saturated calomel electrode. The developed sensor amperometric response was linear across the concentration range from 0.3 mM to 3.3 mM (R2 = 0.992) with a detection limit and sensitivity of 0.2 μM and 271 μA·mM‒1·cm−2 respectively. Concomitantly, a short response time of T90 < 5 sec at a signal-to-noise ratio of 4 was achieved. The sensor was shown to determine hydrogen in the presence of interfering species, and exhibited high selectivity with relative standard deviation values less than 4.2%. The results indicate that the use of RGO to anchor and photochemically reduce POM also improved the reduction properties due to the irregular size distribution and catalytic activity of Ag-Fe2O3 stimulated by its adhesion to the distinctive POM/RGO matrix

Unique Properties of Eukaryote-Type Actin and Profilin Horizontally Transferred to Cyanobacteria

A eukaryote-type actin and its binding protein profilin encoded on a genomic island in the cyanobacterium Microcystis aeruginosa PCC 7806 co-localize to form a hollow, spherical enclosure occupying a considerable intracellular space as shown by in vivo fluorescence microscopy. Biochemical and biophysical characterization reveals key differences between these proteins and their eukaryotic homologs. Small-angle X-ray scattering shows that the actin assembles into elongated, filamentous polymers which can be visualized microscopically with fluorescent phalloidin. Whereas rabbit actin forms thin cylindrical filaments about 100 µm in length, cyanobacterial actin polymers resemble a ribbon, arrest polymerization at 5-10 µm and tend to form irregular multi-strand assemblies. While eukaryotic profilin is a specific actin monomer binding protein, cyanobacterial profilin shows the unprecedented property of decorating actin filaments. Electron micrographs show that cyanobacterial profilin stimulates actin filament bundling and stabilizes their lateral alignment into heteropolymeric sheets from which the observed hollow enclosure may be formed. We hypothesize that adaptation to the confined space of a bacterial cell devoid of binding proteins usually regulating actin polymerization in eukaryotes has driven the co-evolution of cyanobacterial actin and profilin, giving rise to an intracellular entity

How Do Spherical Diblock Copolymer Nanoparticles Grow during RAFT Alcoholic Dispersion Polymerization?

A poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) is used for the reversible addition–fragmentation chain transfer (RAFT) alcoholic dispersion polymerization of benzyl methacrylate (BzMA) in ethanol at 70 °C. THF GPC analysis indicated a well-controlled polymerization with molecular weight increasing linearly with conversion. GPC traces also showed high blocking efficiency with no homopolymer contamination apparent and Mw/Mn values below 1.35 in all cases. 1H NMR studies confirmed greater than 98% BzMA conversion for a target PBzMA degree of polymerization (DP) of up to 600. The PBzMA block becomes insoluble as it grows, leading to the in situ formation of sterically stabilized diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA). Fixing the mean DP of the PDMA stabilizer block at 94 units and systematically varying the DP of the PBzMA block enabled a series of spherical nanoparticles of tunable diameter to be obtained. These nanoparticles were characterized by TEM, DLS, MALLS, and SAXS, with mean diameters ranging from 35 to 100 nm. The latter technique was particularly informative: data fits to a spherical micelle model enabled calculation of the core diameter, surface area occupied per copolymer chain, and the mean aggregation number (Nagg). The scaling exponent derived from a double-logarithmic plot of core diameter vs PBzMA DP suggests that the conformation of the PBzMA chains is intermediate between the collapsed and fully extended state. This is in good agreement with 1H NMR studies, which suggest that only 5−13% of the BzMA residues of the core-forming chains are solvated. The Nagg values calculated from SAXS and MALLS are in good agreement and scale approximately linearly with PBzMA DP. This suggests that spherical micelles grow in size not only as a result of the increase in copolymer molecular weight during the PISA synthesis but also by exchange of individual copolymer chains between micelles and/or by sphere–sphere fusion events

Particle Growth Kinetics in Zirconium Sulfate Aqueous Solutions Followed by Dynamic Light Scattering and Analytical Ultracentrifugation - Implications for Thin Film Deposition

Acidic aqueous solutions of Zr(SO4)2 * 4 H2O can be used to deposit nanocrystalline zirconium oxide films on functionalized surfaces. Because zirconium hydrolyzes easily, such solutions are potentially unstable towards colloid formation and precipitation. Particle growth (conditions: 2 or 4 mM Zr(SO4)2, 0.4 or 0.6 N HCl, T = 323, 328, 333, or 343 K) was investigated using dynamic light scattering (DLS, in situ), and analytical ultracentrifugation (AUC, ex situ after quenching to 77 K and re-thawing to 298 K). The AUC measurements revealed three stages of growth (all dimensions given are hydrodynamic radii). 1. Several discrete polynuclear complexes with rh = 0.43 to 2.29 nm coexisted; 2. particle size distribution with single sharp maximum; 3. above rh ≈ 260 nm rapid transition to polydisperse medium with particles up to 100 µm. The DLS measurements revealed a linear increase of the hydrodynamic radii (z-average of particle population) from 5 nm to 1000 - 2500 nm with rates of 0.01 to 0.6 nm*s-1. The rates were proportional to the Zr(SO4)2-concentration, while the increase of the HCl concentration slowed or even inhibited growth. The apparent activation energy for this step was 136 kJ*mol-1. From the induction period before detection of first particles initial growth rates (rh < 5 nm) were calculated to ≈ 1*10-4 to 5*10-3 nm*s-1. Independent of the conditions, the two reaction rates were always proportional to each other, indicating linked rate laws. A 4 mM Zr(SO4)2 in 0.4 N HCl solution exhibited no particle growth at 323 K but complexes of a constant radius (after 6, 12, and 24 h) of 1.16 nm were detected (AUC). Under these conditions, films were deposited, and their thickness increased linearly with time, specifically by 2.1*10-4 nm s-1. This rate corresponds to the initial growth rate in solution. In contrast to films grown from media with significant particle growth, these films showed surfaces free of attached particles, cracks, and holes