Construction of an amperometric pyruvate oxidase enzyme electrode for determination of pyruvate and phosphate

In this study an amperometric biosensor based on pyruvate oxidase was developed for the determination of pyruvate and phosphate. For construction of the biosensor pyruvate oxidase was immobilized with gelatin and insolubilized in film by forming cross-linked bonds with glutaraldehyde. The film was fixed on a YSI type dissolved oxygen (DO) probe, covered with a teflon membrane which is high-sensitive for oxygen. The working principle of the biosensor depends on detection of consumed DO concentration related to pyruvate concentration which is used in enzymatic reaction catalyzed by pyruvate oxidase. The biosensor response shows a linearity with pyruvate concentration between 0.0025 and 0.05 μM and also response time of the biosensor is 3 min. In the optimization studies of the biosensor the most suitable enzyme activity was found as 2.5 U/cm² for pyruvate oxidase, and also phosphate buffer (pH 7.0; 50 mM) and 35 °C were established as providing the optimum working conditions. In the characterization studies of the biosensor some parameters such as reproducibility, substrate specificity, operational stability, determination of phosphate, and interference effects of some compounds on the pyruvate determination were investigated. Finally, the concentration of pyruvate was determined by using spectrophotometric method and the results obtained were compared to results obtained by the biosensor.     

Estimating average precision when judgments are incomplete

We consider the problem of evaluating retrieval systems with incomplete relevance judgments. Recently, Buckley and Voorhees showed that standard measures of retrieval performance are not robust to incomplete judgments, and they proposed a new measure, bpref, that is much more robust to incomplete judgments. Although bpref is highly correlated with average precision when the judgments are effectively complete, the value of bpref deviates from average precision and from its own value as the judgment set degrades, especially at very low levels of assessment. In this work, we propose three new evaluation measures induced AP, subcollection AP, and inferred AP that are equivalent to average precision when the relevance judgments are complete and that are statistical estimates of average precision when relevance judgments are a random subset of complete judgments. We consider natural scenarios which yield highly incomplete judgments such as random judgment sets or very shallow depth pools. We compare and contrast the robustness of the three measures proposed in this work with bpref for both of these scenarios. Through the use of TREC data, we demonstrate that these measures are more robust to incomplete relevance judgments than bpref, both in terms of how well the measures estimate average precision (as measured with complete relevance judgments) and how well they estimate themselves (as measured with complete relevance judgments). Finally, since inferred AP is the most accurate approximation to average precision and the most robust measure in the presence of incomplete judgments, we provide a detailed analysis of this measure, both in terms of its behavior in theory and its implementation in practice. We gratefully acknowledge the support provided by NSF grants CCF-0418390 and IIS-0534482.     

Influence of ruthenium alkylidene complexes bearing tricyclohexylphosphine or 3-bromopyridine ligand on the properties of fluorine containing polymers

The catalytic performance of ruthenium alkylidene complexes bearing tricyclohexylphosphine or 3-bromopyridine ligand in the ring opening metathesis polymerization (ROMP) of fluorine containing monomers, exo-N-4-fluorophenyl-7-oxanorbornene-5,6-dicarboximide (FPhONDI) and exo-N-4-fluorophenyl-norbornene-5,6-dicarboximide (FPhNDI) was investigated. Pure monomers were subjected to ROMP with RuCl₂(PCy₃)₂(CHPh) (I), RuCl₂(PCy₃)(H₂IMes)(CHPh) (II), RuCl₂(3-Br-py)₂(PCy₃)(CHPh) (III) and RuCl₂(3-Br-py)₂(H₂IMes)(CHPh) (IV). The polymers were fully characterized using NMR, DSC, SEM and GPC. Catalysts I–IV displayed significant ROMP activity, allowing for the synthesis of the corresponding polymers with polydispersity indices (PDIs) in the range of 1.4–4.0. High molecular weight polymers (Mw up to 4.95 x10⁵) were prepared in yields up to 90 %, depending on the initiator and monomer used.     

Palladium nanoparticles supported on chemically derived graphene: An efficient and reusable catalyst for the dehydrogenation of ammonia borane

Chemically derived graphene (CDG) was prepared by hydrazine hydrate reduction of graphene oxide and used as support for palladium nanoparticles (Pd NPs) generated ex situ with controllable particle size and dispersion. The Pd NPs supported on CDG were well characterized by using a combination of advance analytical techniques and employed as catalyst in the dehydrogenation and hydrolysis of ammonia borane (AB) in organic solvents and aqueous solutions, respectively. Monodisperse Pd NPs of 4.5 nm were prepared from the reduction of palladium(II) acetylacetonate by tert-butylamine borane in the presence of oleylamine. They were readily impregnated on CDG which has BET surface area of 500 m² g⁻¹. Pd NPs retain their particle size dispersion and stability when supported on chemically derived graphene. The resulting materials are highly active and stable catalyst for the dehydrogenation and hydrolysis of AB. In addition to their high activity and stability, these Pd NPs are also reusable catalyst in both dehydrogenation and hydrolysis of AB preserving 85% and 95% of initial activity after 5th and 10th runs, respectively.     

COD Fractionation in Wastewater Characterization—The State of the Art

Wastewater characterization is now regarded as an indispensable step yielding all the necessary information for a reliable modelling and design of biological treatment processes. It should mainly include fractionation of the chemical oxygen demand (COD), and assessment of significant kinetic and stoichiometric coefficients. COD fractionation involves identification of inert and biodegradable COD together with readily biodegradable and slowly biodegradable fractions. Experimental methods developed or selected for the assessment of COD fractions should be compatible with the mathematical models defining biological treatment and should yield consistent and reliable values. A critical review of available experimental methodology is provided and values of significant COD components determined in this work and reported in the literature, for different types of domestic and industrial wastewaters are outlined. © 1997 SCI.     

Synthesis and properties of oxalic acid-doped polyaniline

Conductive polyaniline was synthesized in aqueous 1.0M oxalic acid containing 0.1 M aniline by electrochemical and chemical oxidation and characterized by conductivity, solubility, ultraviolet and infrared spectroscopy, and cyclic voltammetry. The solubility experiments showed that the solubility of oxalic acid-doped polyaniline in dimethylsulfoxide and dimethylformaide increased to a certain extent. The soluble part of the polyaniline was free from impurities such as quinones. Cyclic voltammetric studies in oxalic acid medium revealed that aniline exhibited a similar behaviour to that in H₂SO₄ and the polymerization rate was much slower than that in H₂SO₄.