Determination of organophosphate pesticides at a carbon nanotube/organophosphorus hydrolase electrochemical biosensor

An amperometric biosensor for oganophosphorus (OP) pesticides based on a carbon nanotube (CNT)-modified transducer and an organophosphorus hydrolase (OPH) biocatalyst is described. A bilayer approach with the OPH layer atop of the CNT film was used for preparing the CNT/OPH biosensor. The CNT layer leads to a greatly improved anodic detection of the enzymatically generated p-nitrophenol product, including higher sensitivity and stability. The sensor performance was optimized with respect to the surface modification and operating conditions. Under the optimal conditions the biosensor was used to measure as low as 0.15 μM paraoxon and 0.8 μM methyl parathion with sensitivities of 25 and 6 nA/μM, respectively.     

Stochastic Navier-Stokes equations

We construct a solution to stochastic Navier-Stokes equations in dimension n4 with the feedback in both the external forces and a general infinite-dimensional noise. The solution is unique and adapted to the Brownian filtration in the 2-dimensional case with periodic boundary conditions or, when there is no feedback in the noise, for the Dirichlet boundary condition. The paper uses the methods of nonstandard analysis.The research of this author was supported by an SERC Grant.     

Dynamics of theD-dimensional FRW-cosmological models within the superstring-generated gravity model

We study the dynamics of the generalizedD-dimensional (D = 1+3+d) Friedman-Robertson-Walker (FRW) cosmological models in the framework of an extended gravity theory obtained by adding the Gauss-Bonnet term to the standard Einstein-Hilbert action. In our discussion we extensively use methods of dynamical systems. We consider models filled in with a perfect fluid obeying the equation of statep=(–1) and vacuum but non-flat models. We present a detailed analysis of the ten dimensional model and in particular we study the vacuum case. Several phase portraits show how the evolution of this model depends on the parameter.     

Mobility and non-separability

A mobility phenomenon is typical for a large class of non-linear evolutions. It is shown that the mobility can be responsible for a malignant form of quantum mechanical non separability of two correlated systems. An explicit example based on Weinberg's non linear quantum mechanics is considered. We show that in such a theory a transfer of information without a transfer of energy is possible and discuss physical roots of this phenomenon. In Polchinski's approach this effect is not present.1 Permanent address: Laboratory of Dielectrics and Organic Semiconductors, Technical University of Gdask, Gdask, Poland.     

Formation of the surface charge on silica in mixed solvents

At sufficiently high concentrations of methanol and of alkali salts in aqueous silica dispersions, the negative -potentials of the particles are decreased. This effect is more pronounced with lithium than with other alkali cations, and it is independent on the anion. The NMR spectra indicate lithium adsorption on silica from mixed solvents, but not in the absence of alcohol.Supported by a contract with the XMX Corporation, Burlington, Massachusetts, USA     

The first tetranuclear vanadium(V) peroxo complex: Preparation, vibrational spectra and X-ray crystal structure of K6[V4O4(O2)8(PO4)]·9H2O

The vanadium(V) peroxo phosphato complex K₇[V₄O₄(O₂)₈(PO₄)]·9H₂O has been obtained from the KVO₃---KH₂PO₄---KOH---H₂O₂---H₂O---C₂H₅OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V₂O₂(O)₂)₂(μ-η¹ : η²-O₂)₂] units are connected by the μ₄-PO₄ group.     

Syntheses with organoboranes. IX. Vinyl- and 1-alkenyldichloroboranes as ethylene and 1-alkene equivalents for the Diels–Alder reaction

Vinyl- and 1-alkenyldichloroboranes were used as dienophiles for the Diels–Alder reaction with representative aliphatic and cyclic 1,3-dienes. The organoborane adducts were transformed into the corresponding olefins either by protonolysis or by oxidation–mesylation–reduction. Direct protonolysis of the adducts gave in most cases mixtures of olefins whereas the reduction of mesylates with lithium triethylborohydride produced pure olefins in good yields.     

The dimeric and tetrameric octarepeat fragments of prion protein behave differently to its monomeric unit

Potentiometric and spectroscopic data have shown that octarepeat dimer and tetramer are much more effective ligands for Cu(II) ions than simple octapeptide. Thus, the whole N-terminal segment of prion protein due to cooperative effects, could be more effective in binding of Cu(II) than simple peptides containing a His residue. The gain of the Cu(II) binding by longer octarepeat peptides derives from the involvement of up to four imidazoles in the coordination of the first Cu(II) ion. This type of binding increases the order of the peptide structure, which allows successive metal ions for easier coordination.     

Simultaneous determination of hydrogen as its iodine equivalent and of nitrogen by a volumetric method

Summary The method developed for simultaneous determination of hydrogen (by means of an equivalent amount of iodine) and of nitrogen by a volumetric method, is based on a flash combustion technique in a stream of CO₂ (100 ml/min) with controlled addition of O₂ (20%). Hydrogen is determined by conversion of water into hydrogen chloride on anhydrous magnesium chloride heated at 600–650° C, and reaction of the hydrogen chloride with Ag₂OI₂ at 220° C to yield iodine, which is collected on silver and weighed. The precision of the determination of hydrogen is excellent, the standard deviation being 0.008–0.017% abs., about a tenth of that obtained by the classical methods. The error in the determination of hydrogen was ±0.006% abs.

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Gleichzeitige Bestimmung von Wasserstoff als dessen Jodäquivalent und von Stickstoff auf volumetrischem Wege

Zusammenfassung Die entwickelte Methode zur gleichzeitigen Bestimmung von Wasserstoff in Form seines Jodäquivalents und von Stickstoff auf gasvolumetrischem Wege beruht auf der Entflammungsmineralisation im CO₂-Strom (100 cm³/min) mit kontrolliertem Zusatz von O₂ (20%). Der Gasstrom wird zusätzlich über P₂O₅ getrocknet. Die dem Wasserstoff äquivalente Jodmenge wird an metallischem Silber gebunden und gravimetrisch bestimmt, wobei Wasser bei 600–650° C mit Magnesiumchlorid in Chlorwasserstoff übergeführt wird, der nachfolgend bei 220° C mit Ag₂Oj₂ zu Jod umgesetzt wird. Für Verbindungen, die neben C, H, N und O auch Br, Cl, P und S enthalten, werden Wasserstoffresultate mit hoher Präzision erzielt:s _H beträgt 0,008 bis 0,017% absolut und ist etwa 10mal kleiner als bei den üblichen, klassischen Methoden. Die Genauigkeit der Wasserstoffbestimmung entspricht einem mittleren Fehler=±0,006% absolut. Die Resultate für den Wasserstoff und Stickstoff verlangen eine Blindwertkorrektur.

     

Hydrodynamics of interaction of particles (including cells) with surfaces

The study of the phenomena related to the motion of particles flowing in the proximity of the wall is pursued for purely cognitive reason as well as for some important practical purposes in various fields of technology, biology and medicine.When small spherical rigid particles move in the direction parallel to the surface their velocity is smaller than that of the fluid and depends on the ratio of the distance from the wall to the particle radius. The velocity of a particle falling down in a vertical cylinder is maximal in an eccentric position. A sphere in contact with the wall remains stationary. Translational velocity of spherical rigid particles the dimension of which are comparable to that of the tube is only slightly dependent of their lateral position. The differences in the flow parameters of deformable particles in comparison with rigid ones depend on the particle and fluid viscosity coefficient. When the particles move perpendicularly toward the wall, their velocity decreases as the particle approaches the surface. The change of particle velocity is inversely proportional to the gap.There are several theories explaining the influence of the channel diameter on the suspension viscosity (sigma phenomenon); a modern approach is based on the analysis of rheological properties of suspensions. The explanations of the Fahraeus effect (i.e. the fact that the concentration of particles flowing in a tube linking two containers are smaller than that in the containers) are based on non-uniform particle distribution in a transverse cross section and on the differences of velocities of particles and medium. The deviation of the velocity profile of a suspension of rigid particles flowing through a tube from the parabolic shape (blunting) does not depend on the flow velocity; as concerns deformable particles, however, this effect is the smaller the greater is the flow velocity.When the Reynolds number for particles is greater than 10^-3, there appears a component of particle velocity perpendicular to the streamline direction.This phenomenon is the cause of the lateral migration of particles. Neutrally buoyant rigid particles migrate to a certain concentrical region situated between the tube axis and the wall (tubular pinch region). Deformable neutrally buoyant particles migrate towards the tube axis, and deformable non-neutrally buoyant particles may move either toward the tube axis or toward the wall.In the research on the influence of the flow delimiting surface on the motion of particles in suspension a considerable progress has recently been made.However, the phenomena in this field are extremely complex. At present, two main types of approach may be distinguished. On a microscopic level direct interactions between particles and surfaces are analyzed. A macroscopic approach consists in treating particle suspension as fluid, and overall influence of the surface on its properties are studied. A comprehensive theory linking these two levels has not yet emerged.