Bio-smart materials: kinetics of immobilized enzymes in p(HEMA)/p(pyrrole) hydrogels in amperometric biosensors

Various strategies are being pursued to confer the highly specific molecular recognition properties of bioactive molecules to the transducer action of inherently conductive polymers. We have successfully integrated inherently conductive polypyrrole within electrode-supported, UV cross-linked hydroxyethyl methacrylate (HEMA)-based hydrogels. These electroactive composites were used as matrixes for the physical immobilization of several oxidase enzymes to fabricate clinically important biosensors. Measurements were made of the amperometric responses via H₂O₂ oxidation for each biosensor. Apparent Michaelis constants, K_m(app), for glucose oxidase immobilized in p(HEMA) membranes and in p(HEMA)/p(Pyrrole) composite membranes were 13.8 and 43.7 mM respectively compared to 33 mM in solution. The inclusion of polypyrrole in the hydrogel network increased the thermal stability of the immobilized enzyme at 60°C by 30% and 40% compared to p(HEMA) membranes and solution phase respectively. The composite also yielded larger I_max values (19 μA/cm⁻²) for glucose biosensors compared to similar glucose biosensors fabricated without the conducting polymer (15 μA). K_m(app) values for cholesterol oxidase immobilized in the same composite films were ca. three orders of magnitude higher than the K_m for the soluble enzyme. The polypyrrole component is shown to reduce diffusive transport but to confer thermal stability to these biosensors.     

Čerenkov spectroscopic assay of fission isotopes

This work is a practical application of a previously published procedure for non-destructive, simultaneous determinations of⁹⁰Sr and¹³⁷Cs in aqueous solutions in presence of each other, by a combined use of erenkov counting and -spectrometry. The technique is being used to examine the ion-exchange and retention capacities of three types of zeolites as functions of pH and NaNO₃ concentration. Conclusions are drawn on the usefulness of these procedures and counting techniques in studying the removal of radiostrontium and radiocaesium from aged radioactive waste solutions.Part of this work was presented at the 7th International Zeolite Conference, Tokyo, August 17–22, 1986.     

Interference effects in 157 nm laser ablated cones in polycarbonate and application to spatial coherence measurement

Conical structures formed in 157 nm laser-ablated polycarbonate exhibit a well-defined fringe structure with a period of a few 100 nm surrounding the cone base. Experiments and modelling studies of the interference produced by these micro-conical mirrors are shown to provide a means of measuring the spatial coherence of the highly multi-mode 157 nm laser.     

Determination of photo-oxidation products within photoyellowed bleached wool proteins

Photo-oxidative processes occurring in wool can lead to significant photoyellowing of the fiber. In particular, wool that has been chemically bleached photoyellows more rapidly and to a greater degree than untreated wool. Direct identification of the chromophores responsible for such yellow discoloration in irradiated wool has proven to be elusive for many years. This article describes the characterization and location of yellow photo-oxidation products within the proteins of photoyellowed bleached wool fabric, using advanced protein chemistry techniques. The discolored fabric was enzymatically digested and chromatographed by high-pressure liquid chromatography, with monitoring at 400 nm, to select out fractions containing yellow chromophoric species. Thorough tandem mass spectrometric analysis was then used to sequence peptides and, in turn, to characterize modifications to key amino acid residues that had resulted in yellow chromophore formation. In total, 11 separate yellow chromophoric species were identified, ten derived from tryptophan residues and one from tyrosine. The tryptophan-derived modifications characterized included hydroxytryptophan, N-formylkynurenine, hydroxyformylkynurenine, kynurenine, hydroxykynurenine, carbolines, tryptophandiones and nitrotryptophan. The tyrosine-derived modification of tyrosine to dopa was also identified. The range of photomodifications we observed provides insight into the photo-oxidation pathways occurring within irradiated fibrous proteins leading to the formation of yellow chromophores.     

The RNase a superfamily: Generation of diversity and innate host defense

Summary The Ribonuclease A superfamily includes an extensive network of distinct and divergent gene lineages. Although all ribonucleases of this superfamily share invariant structural and catalytic elements and some degree of enzymatic activity, the primary sequences have diverged significantly, ostensibly to promote novel function. We will review the literature on the evolution and biology of the RNase A ribonuclease lineages that have been characterized specifically as involved in host defense including: (1) RNases 2 and RNases 3, also known as the eosinophil ribonucleases, which are rapidly-evolving cationic proteins released from eosinophilic leukocytes, (2) RNase 7, an anti-pathogen ribonuclease identified in human skin, and (3) RNase 5, also known as angiogenin, another rapidly-evolving ribonuclease known to promote blood vessel growth with recently-discovered antibacterial activity. Interestingly, some of the characterized anti-pathogen activities do not depend on ribonuclease activity per se. We discuss the ways in which the anti-pathogen activities characterized in vitro might translate into experimental confirmation in vivo. We will also consider the possibility that other ribonucleases, such as the dimeric bovine seminal ribonuclease and the frog oocyte ribonucleases, may have host defense functions and therapeutic value that remain to be explored. (190 words)     

Hydroformylation by Pt-Sn compounds from N-heterocyclic stannylenes

[(Me(2)Si{NAr}(2))-κ(2)N,N']Sn, reacts with PtCl(2)(L(2)) and [PtCl(μ-Cl)(L)](2) to afford products containing Pt-Sn bonds. In the absence of supporting ligands L, coordination of the stannylene and rearrangement to a structurally unique PtSn(2)N(2)Si metallacycle occurs. The hydroformylation activity of a representative Pt-Sn compound is investigated.     

Analysis of heuristics for finding a maximum weight planar subgraph

The problem of identifying a planar subgraph of maximum total weight in an edge-weighted graph has application to the layout of facilities in a production system and elsewhere in industrial engineering.This problem is NP-hard, and so we confine our attention to polynomial-time heuristics. In this paper we analyse the performance of some heuristics for this problem.     

Uptake of radionuclides on antimony silicate

The uptake of fission products ¹³⁷Cs, ⁸⁵Sr, ⁵⁷Co, onto an antimony silicate, and its Na, K, Ca ion-exchanged forms have been studied. Distribution coefficients have been determined as a function of the concentrations of sodium, potassium and calcium nitrate solutions (0.01, 0.1 and 1M). Plots of log distribution coefficients against concentrations enabled the elucidation of exchange mechanisms in some cases. Potassium had the least, and calcium the most effect on isotope uptake when present as macro ions. The presence of sodium promoted hydrolysis that also affected the exchange selectivity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Volumes Spanned by Random Points in the Hypercube

Consider the hypercube [0, 1]ⁿ in Rⁿ. This has 2ⁿ vertices and volume 1. Pick N = N(n) vertices independently at random, form their convex hull, and let V_n be its expected volume. How large should N(n) be to pick up significant volume? Let k=2/√≈1.213, and let ? > 0. We shall show that, as n→∞, V_n→0 if N(n)?(k??)ⁿ →1 if N(n) ? (k + ?)ⁿ. A similar result holds for sampling uniformly from within the hypercube, with constant .     

Čerenkov spectroscopic assay of fission isotopes

A erenkov counting technique is presented for the radioassay of¹⁰⁶Ru in aqueous solutions containing nitrate, nitric acid, chloride as well as inactive ruthenium nitrosyl complex carrier. The counting efficiency was found to be a function of colour quenching by these substances in the UV and visible range. Measurements made on a three-channel automatic liquid scintillation spectrometer indicated that the counting efficiency can be calculated by use of the experimentally determined channel ratio of a quenched sample, without prior knowledge of the quencher concentration. The technique can be useful during studies on the removal of¹⁰⁶Ru from nuclear waste solutions. Special settings of discriminator windows enable radioassays in presence of weak -emitters such as¹³⁷Cs. The possibility of determining¹⁰⁶Ru in presence of⁹⁰(Sr/Y) was also investigated.