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     

An operator solution of stochastic games

A class of zero-sum, two-person stochastic games is shown to have a value which can be calculated by transfinite iteration of an operator. The games considered have a countable state space, finite action spaces for each player, and a payoff sufficiently general to include classical stochastic games as well as Blackwell’s infiniteG _δ games of imperfect information. Research supported by National Science Foundation Grants DMS-8801085 and DMS-8911548.     

Unlocking the potential of bile acids in synthesis, supramolecular/materials chemistry and nanoscience

The Maitra group has explored a variety of chemistry with bile acids during the past 15 years and these experiments have covered a wide variety of chemistry-asymmetric synthesis, molecular recognition, ion receptors/sensors, dendrimers, low molecular mass organo and hydrogelators, gel-nanoparticle composites, etc. Some of what excites us in this field is highlighted in this perspective article.     

Structural and rheological properties of aqueous viscoelastic solutions and gels of tripodal cholamide-based self-assembled supramolecules

A tripodal cholic steroid ( TCS+) derivative forms hydrogels in acidic conditions that are studied by the small-angle neutron scattering and rheometry techniques. The self-assembled systems exhibit particular scattering and flow properties unusual in the class of molecular gels. The scattering data show separated form- and structure-factor features with, respectively, a low-Q correlation peak and a large-Q secondary oscillation. A probable aggregation model is deduced involving 3 TCS+ molecules per cross-section of fibrillar aggregates packed in a tail-to-tail fashion. The fibers have monodisperse cross-sections (40 A diameter) and result from a versatile mechanism taking advantage of the free articulation of the three hydrophobic steroid pods ("umbrella-like" packing) around the N+ charge. The N+ charges are distributed at the periphery of the cylinders and give rise to a moderate linear charge density (nu approximately 0.16 e/A). The variation with concentration of the static scattering structure factor peak S(Q) reveals ordering properties typical of 1d polyelectrolytes. The fibers further organize into fractal clusters characterized by their scattering signature at low-Q and also by the exponent of the scaling of the elastic shear modulus with the concentration. It is suggested that the TCS+ polyion fibers extend under shear (or in a concentrated environment) by varying the angle between the pods along the fiber axis. Viscosity overshoots appear at the startup of shear flow experiments. Analogies with the phenomenology observed with DNA solutions are discussed.     

Inorganic-organic hybrid nanoparticles from n-octyl triethoxy silane

Ormosil (organically modified silane) such as n-octyl triethoxy silane has been found to aggregate in the form of normal micelles as well as reverse micelles in which the triethoxy silane moeities are hydrolyzed to form a hydrated silica network while the n-octyl groups are held together through hydrophobic interaction. These nanoparticles are spherical in shape and are nearly monodispersed with an average diameter of below 100 nm. The nanoparticles originating from the micellar aggregate have an hydrophobic core with a layer of the hydrated silica network at the surface. The hydrophobic core can host hydrophobic molecules such as tetraphenyl porphyrin, which is leached out of the particles extremely slowly compared to that in Triton X-100 micelles. The nanoparticles originating from the reverse micelles have a hydrated silica network in the core surrounded by the hydrophobic n-octyl chains on the particle surface. The hydrophilic silica cores of these nanoparticles have been used to encapsulate horseradish peroxidase (HRP) and the enzyme shows its activity and follows Michaelis-Menten kinetics.