Analyte-receptor binding kinetics for different types of biosensors

A fractal analysis is presented for analyte-receptor binding kinetics for different types of biosensor applications. Data taken from the literature may be modeled using a single-fractal analysis, a single- and a dual-fractal analysis, or a dual-fractal analysis. The latter two methods represent a change in the binding mechanism as the reaction progresses on the surface. Predictive relationships developed for the binding rate coefficient as a function of the analyte concentration are of particular value since they provide a means by which the binding rate coefficients may be manipulated. Relationships are presented for the binding rate coefficients as a function of the fractal dimension D _f or the degree of heterogeneity that exists on the surface. When analyte-receptor binding is involved, an increase in the heterogeneity on the surface (increase in D _f ) leads to an increase in the binding rate coefficient. It is suggested that an increase in the degree of heterogeneity on the surface leads to an increase in the turbulence on the surface owing to the irregularities on the surface. This turbulence promotes mixing, minimizes diffusional limitations, and leads subsequently to an increase in the binding rate coefficient. The binding rate coefficient is rather sensitive to the degree of heterogeneity, D _f , that exists on the biosensor surface. For example, the order of dependence on D _f1 is 7.25 for the binding rate coefficient k ₁ for the binding of a Fab fragment of an antiparaquat monoclonal antibody in solution to an antigen in the form of a paraquat analog immobilized on a sensor surface. The predictive relationships presented for the binding rate coefficient and the fractal dimension as a function of the analyte concentration in solution provide further physical insights into the binding reactions on the surface, and should assist in enhancing biosensor performance. In general, the technique is applicable to other reactions occurring on different types of surfaces, such as cell-surface reactions.     

Preparation and characterisation of magnesium sulphate heptahydrate from Kimberlite tailings

Weathered Kimberlite tailings of Panna Diamond Mines were characterised by DTA and XRD techniques. The XRD pattern shows the presence of serpentine, quartz, calcite, hematite, magnetite and anatase phases. DTA curve indicates first endothermic peak at 125C due to dehydration of the mineral and second endo peak at 670C due to dehydroxylation of serpentine closely followed by an exothermic peak at 810C associated with the formation of forsterite. XRD and DTA studies of sulphuric acid leach residue of the Kimberlite shows the disappearance of serpentine phase with the appearance of CaSO₄·2H₂O phase. The product MgSO₄·7H₂O obtained after purification and crystallisation. From the optical emission spectroscopic analysis, the product was found to contain Ca, Fe and SiO₂ as trace impurities.

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Zusammenfassung Mittels DTA und Röntgendiffraktion wurden verwitterte Kimberlit-AbgÄnge aus Diamantbergwerken in Panna charakterisiert. Das Röntgendiagramm zeigt die Gegenwart von Serpentin-, Quarz-, Kalzit-, HÄmatit-, Magnetit- und Anatas-Phasen. Die DTA-Kurve zeigt einen ersten endothermen Peak bei 125C (Dehydratation des Minerales) und einen zweiten endothermen Peak bei 670C (Dehydroxylierung von Serpentin), eng gefolgt von einem exothermen Peak bei 810C (Bildung von Forsterit). Röntgendiffraktionsund DTA-Untersuchungen an einem schwefelsauren Extraktionsauszug von Kimberlit zeigen das Verschwinden der Serpentin-Phase, aber das zusÄtzliche Auftreten einer CaSO₄·2H₂O-Phase. Nach Reinigung und Kristallisation wurde MgSO₄·7H₂O als Produkt erhalten, dessen optische emissionsspektroskopische Untersuchung in Spuren Verunreinigungen mit Ca, Fe und SiO₂ zeigten.

     

Boric acid: an efficient and environmentally benign catalyst for transesterification of ethyl acetoacetate

An efficient and environmentally benign boric acid catalyzed protocol for the transesterification of ethyl acetoacetate with a variety of primary and secondary alcohols in good to excellent yields is described. The versatility of this transformation is demonstrated with problematic substrates such as propargyl alcohol and allyl alcohol, which are known to undergo Carroll rearrangement during transesterification.     

On path correlation and PERT bias

Most studies of project time estimation assume that (a) activity times are mutually independent random variables; many also assume that (b) path completion times are mutually independent. In this paper, we subject the impact of both these assumptions to close scrutiny. Using tools from multivariate analysis, we make a theoretical study of the direction of the error in the classical PERT method of estimating mean project completion time when correlation is ignored. We also investigate the effect of activity dependence on the normality of path length via simulation.     

Synthesis and characterization of sulfonated‐fluorinated,hydrophilic‐hydrophobic multiblock copolymers for proton exchange membranes

Hydrophilic/hydrophobic block copolymers as proton exchange membranes (PEMs) has become an emerging area of research in recent years. These copolymers were obtained through moderate temperature (～ 100 °C) coupling reactions, which minimize the ether‐ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The hydrophilic blocks were based on the nucleophilic step polymerization of 3,3′‐disulfonated, 4,4′‐dichlorodiphenyl sulfone with an excess 4,4′‐biphenol to afford phenoxide endgroups. The hydrophobic (fluorinated) blocks were largely based on decafluoro biphenyl (excess) and various bisphenols. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure‐property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to the ionic proton conducting channels formed through the self‐assembly of the sulfonated blocks. The nano‐phase separated morphologies of the copolymer membranes were studied and confirmed by atomic force microscopy. Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state‐of‐the‐art PEM, Nafion, were achieved. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1038–1051, 2009     

Stability and dynamical properties of material flow systems on random networks

The theory of complex networks and of disordered systems is used to study the stability and dynamical properties of a simple model of material flow networks defined on random graphs. In particular we address instabilities that are characteristic of flow networks in economic, ecological and biological systems. Based on results from random matrix theory, we work out the phase diagram of such systems defined on extensively connected random graphs, and study in detail how the choice of control policies and the network structure affects stability. We also present results for more complex topologies of the underlying graph, focussing on finitely connected Erdös-Réyni graphs, Small-World Networks and Barabási-Albert scale-free networks. Results indicate that variability of input-output matrix elements, and random structures of the underlying graph tend to make the system less stable, while fast price dynamics or strong responsiveness to stock accumulation promote stability.     

Supersimple theories

We prove elimination of hyperimaginaries in supersimple theories. This means that if an equivalence relation on the set of realisations of a complete type (in a supersimple theory) is defined by a possibly infinite conjunction of first order formulas, then it is the intersection of definable equivalence relations.