Nafion® Coated Electropolymerised Flavanone-based pH Sensor

This work summarizes the electrochemical response of flavanone carbon composite electrodes in comparison with Nafion®-coated flavanone carbon composite electrodes, for use as voltammetric pH sensors in both buffered and low-buffered media. Square wave voltammetric measurements suggest the peak potential achieved from the electrochemical polymerization after the electron-proton oxidation responds with accuracy to buffered pH solutions for both coated and non-coated electrodes, with a potential shift of 55.1 mV and 54.6 mV per pH unit respectively. However, a considerable improvement in stability, accuracy and sensitivity is provided by the proton-transfer Nafion® layer in CO₂ bubbled sea water. Furthermore, Nafion®-coated flavanone carbon composite electrodes predicted a pH of 8.04 for the commercial seawater, which is in excellent agreement with the measured pH 8.05 value.     

Anaerobic Respiration on Self-Doped Conjugated Polyelectrolytes: Impact of Chemical Structure

We probe anaerobic respiration of bacteria in the presence of conjugated polyelectrolytes (CPEs). Three different CPEs were used to probe how structural variations impact biocurrent generation from Shewanella oneidensis MR-1. For the self-doped anionic CPE only, absorption spectroscopy shows that the addition of S. oneidensis MR-1 leads to the disappearance of the polaron (radical cation) band at >900 nm and an increase in the band at 735 nm due to the neutral species, consistent with electron transfer from microbe to polymer. Microbial three-electrode electrochemical cells (M3Cs) show an increase in the current generated by S. oneidensis MR-1 with addition of the self-doped CPE relative to other CPEs and controls. These experiments combined with in situ cyclic voltammetry suggest that the doped CPE facilitates electron transport to electrodes and reveal structure–function relationships relevant to developing materials for biotic/abiotic interfaces.     

Manganese Tetraboride,MnB4: High‐Temperature Crystal Structure,p–n Transition, 55Mn NMR Spectroscopy,Solid Solutions,and Mechanical Properties

The structural and electronic properties of MnB₄ were studied by high‐temperature powder X‐ray diffraction and measurements of the conductivity and Seebeck coefficient on spark‐plasma‐sintered samples. A transition from the room‐temperature monoclinic structure (space group P2₁/c) to a high‐temperature orthorhombic structure (space group Pnnm) was observed at about 650 K. The material remained semiconducting after the transition, but its behavior changed from p‐type to n‐type. ⁵⁵Mn NMR measurements revealed an isotropic chemical shift of ?1315 ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr_1?xMn_xB₄ (two phases in space groups Pnnm and P2₁/c) were synthesized for the first time. In addition, nanoindentation studies yielded values of (496±26) and (25.3±1.7) GPa for the Young’s modulus and hardness, respectively, compared to values of 530 and 37 GPa obtained by DFT calculations.     

Convexity without convex combinations

Separation theorems play a central role in the theory of Functional Inequalities. The importance of Convex Geometry has led to the study of convexity structures induced by Beckenbach families. The aim of the present note is to replace recent investigations into the context of an axiomatic setting, for which Beckenbach structures serve as models. Besides the alternative approach, some new results (whose classical correspondences are well-known in Convex Geometry) are also presented.     

Quantification of Antioxidant Properties in Popular Leaf and Bottled Tea by High-performance Liquid Chromatography (HPLC), Spectrophotometry,and Voltammetry

Polyphenols in plants such as tea may offer many health benefits. The leaf and bottled teas available on the market today are advertised with a strong emphasis on their antioxidant properties. In this study, we have quantified the total polyphenol, flavonoid, and theaflavin concentrations by simple colorimetric methods, measured the reactivity of polyphenols using direct and indirect oxidation methods, and identified specific polyphenols present using high-performance liquid chromatography in a variety of commercially available teas. We find that, per given volume, freshly brewed teas are richer in polyphenols and reactivity by a factor five or more compared to bottled teas. Within the brewed and bottled categories, white and green teas are richer in antioxidants than oolong and black teas although the differences are less than a factor of two. We also find that the presence of additives causes changes in antioxidant properties such as an enhancement in Cranberry Orange tea and a reduction in Earl Grey tea. Since we verified our results using several overlapping techniques, we are able to evaluate the analytical tools commonly used in antioxidant studies. We find that the Folin–Ciocalteu method of quantifying polyphenols is a good indicator of the relative antioxidant reactivity of teas.     

The effect of irregularity on the dielectric dispersion characteristics of spherical cellular suspension

The dielectric dispersion characteristics of cellular suspensions are fundamentally determined based on the analogy to composite dielectric materials when periodically and discrete arrangement of cells is assumed. However, under native physiological conditions, when flocculation and clamping events usually occur, those assumptions are usually not valid. In the framework of this study, an examination of irregularity effect on the dispersion characteristics of spherical cellular suspensions is presented. Here, the permittivity spectra of the suspensions have been determined by both measurements of living K562 cell suspensions and finite numerical simulations. Based on the measured and simulated spectra, the dispersion characteristics of the suspensions, for several destinies and arrangements of cells, have been quantitatively analyzed using the Havriliak–Negami empirical formula. Generally, a strong correlation between the low dispersion characteristics was observed as the concentration and density of the cells was increased. In addition, all characteristics found to be significantly deviated in comparison to the characteristics of a periodically arrayed suspension. However, when low-dense arrangement was assumed, the correlation found to be much lower when all characteristics found to be less perturbated. Based on a simple model of interacting cells, it is suggested that those deviations are related to intercellular interactions between adjacent cells.     

Core‐shell particles with glycopolymer shell and polynucleoside core via RAFT: From micelles to rods

Amphiphilic block copolymers were synthesized via the reversible addition fragmentation chain transfer (RAFT) copolymerisation of 2‐methacrylamido glucopyranose (MAG) and 5′‐O‐methacryloyl uridine (MAU). Homopolymerisations of both monomers using (4‐cyanopentanoic acid)‐4‐dithiobenzoate (CPADB) proceeded with pseudo first order kinetics in a living fashion, displaying linear evolution of molecular weight with conversion and low PDIs. A bimodal molecular weight distribution was observed for PMAU at low conversions courtesy of hybrid behavior between living and conventional free radical polymerization. This effect was more pronounced when a PMAG macroRAFT agent was chain extended with MAU, however, in both cases, good control was attained once the main RAFT equilibrium was established. A stability study on PMAU found that its hydrolysis is diffusion controlled, and is accelerated at physiological pH compared with neutral conditions. Self‐assembly of four block copolymers with increasing hydrophobic (PMAU) block lengths produced micelles, which demonstrated an increased tendency to form rods as the PMAU block length increased. Interestingly, none of the block copolymers were surface‐active. An initial assessment of PMAU's ability to bind the nucleoside adenosine through base pairing was highly promising, with DSC measurements indicating that adenosine is fully miscible in the PMAU matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1706–1723, 2009