Superior Performance of a MoS2‐RGO Composite and a Borocarbonitride in the Electrochemical Detection of Dopamine,Uric Acid and Adenine

A MoS₂‐RGO composite and borocarbonitride (BC₅N) have been used as electrodes to selectively detect dopamine and uric acid in the presence of ascorbic acid. Both the electrodes show excellent eletrocatalytic activity towards the detection of dopamine, the detection limits being 0.55 μM and 2.1 μM in the case of MoS₂‐RGO and BCN respectively. MoS₂‐RGO shows a linear range of current over the 1–110 μM concentrations of dopamine, while BCN shows over the 2.3–20 μM range. BCN also exhibits satisfactory performance in the oxidation of uric acid with a detection limit of 3.8 μM and the linear range from 4 to 40 μM. The MoS₂‐RGO has also been used to detect adenine as well.     

Unusual structural effects on the chemical degradation of steroid sidechains

17-Chlorosteroids from template-directed halogenation can be converted to 17(20) olefins with DBU or DBN. The dependence of this reaction on base-structure and reaction conditions suggests geometric control by liquid packing effects related to those operating in liquid crystals.     

Finitely additive stochastic games with Borel measurable payoffs

We prove that a two-person, zero-sum stochastic game with arbitrary state and action spaces, a finitely additive law of motion and a bounded Borel measurable payoff has a value. Received December 1996/Final version November 1997     

Characterization of the interaction of poly(ethylene oxide) with nanosize fumed silica: Surface effects on crystallization

Poly(ethylene oxide) (PEO) of 4600 molar mass (PEO‐4600) was crystallized from methanol in the presence of hydrophilic fumed silicas (A380, A200, and OX50) with nominal surface areas of 380, 200, and 50 m²/g and a hydrophobic fumed silica (R812s) modified with methyl groups. The composites were characterized by thermogravimetric analysis and differential scanning calorimetry. The inhibition of crystallization and the tendency for chain reorganization after melting were in the order of A380 > A200 > OX50 > R812s, respectively, that is, both were least for the hydrophobic silica and increased with increasing specific surface area for the hydrophilic silica. The interaction of PEO with the silica increased in the melt state as compared with the solution‐cast samples, resulting in enhanced suppression of crystallization. The following took place at a high silica content: (1) crystallization occurred at crystallization temperatures [T_c < T_c (bulk)], suggesting that the silica inhibited crystallization; (2) crystallites with melt temperatures [T_m < T_m (bulk)] were observed, indictive of smaller and/or less perfect crystals; and (3) melt entropies [ΔS_m (surface) < ΔS_m (bulk)] suggested that the interaction of surface silanols, Si_sOH, with PEO decreased both the melt entropy and crystallite size/perfection. Crystallinity was observed in solution‐cast composites when there were greater than ～0.03 PEO molecules/nm² for native and ～0.01 PEO molecules/nm² for methylated fumed silica, similar to reported plateau equilibrium adsorption values from methanol. These results were consistent with a model in which PEO interacted more strongly with native fumed silica as compared with hydrophobically modified silica because of hydrogen bonding of the ether oxygens of PEO with the acidic silanols, preventing chain mobility and crystallization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1978–1993, 2003     

Borel hierarchies in infinite products of Polish spaces

Let H be a product of countably infinite number of copies of an uncountable Polish space X. Let Σ_ξ be the class of Borel sets of additive class ξ for the product of copies of the discrete topology on X (the Polish topology on X), and let . We prove in the Lévy-Solovay model that

Continuous-flow potentiometric determination of horseradish peroxidase with a fluoride-selective electrode

A continuous-flow system is reported for the determination of horseradish peroxidase (HRP) with a fluoride-selective electrode. Reaction conditions are optimized for the HRP-catalysed oxidation of p-fluoroaniline (0.104 M) with hydrogen peroxide (4.0 mM) as the oxidant in 0.16 M acetate buffer at pH 4.6. HRP is determined in the concentration range 0.016–0.12 U ml^?1 in the flow system at a sampling rate of 24 h^?1. Interfering effects caused by known HRP inhibitors, including metal ions, cyanide and sulphide, are reported for the range 1 μM–1 mM. Applications of the system for determination of the enzyme in turnip extract and milk are described.     

Organophosphorus acid interferences in flame atomic absorption spectrometry

The interference of the organophosphorus acids, 1-hydroxyethane-1,1-bisphosphonic acid, aminotris(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid) and hexamethylenediaminetetrakis(methylenephosphonic acid) on the determination of eighteen metal ions by flame atomic absorption spectrometry is reported. Comparisons with the effect of orthophosphoric acid reveal similarities and distinct differences in their interfering effects. In the air/acetylen flame, depressive interferences are attributed to the formation of phosphates, M₃(PO₄)₂, or hydroxynpatite-like compounds, M₅(OH)(PO₄)₃, in the flame aerosol particles for Mg, Ca, Sr, Ba, Mn, Co and Ni. Iron(III) and chromium(III) appear to form stable oxide phosphates, M₂O₃?MPO₄ or M₃O₄?MPO₄. Evidence for the formation of stable molybdenum carbides, MoC and MoC₂, is also presented. In the nitrous oxide/acetylene flame, serious interferences perssisted only for molybdenum but were eliminated by the addition of sodium sulphate.     

A new bile acid-derived lariat-ether: Design, synthesis and cation binding properties

A newchola lariat ether (1, a 21-crown-6) was constructed fromreadily available precursors. The association constant of compound1 with alkali metal picrates was measured using Cram’s extraction protocol. Evidence is presented for the involvement of the 3-methoxy group for the complexation. Energy minimised structures show that the A-ring gets slightly distorted upon metal ion binding. Dedicated to Professor C N R Rao on his 70th birthday