Glucose Biosensor Using Glucose Oxidase Immobilized in Polyaniline

A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose with a response time of 2.5–4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for use as a support in optical sensor for clinical application.     

Synthesis,characterization, X-ray structure and preliminary in vitro antitumor activity of the nitrosyl complex fac-[RuCl3(NO)(dppf)], dppf = 1,1′-bis(diphenylphosphine)ferrocene

The reaction of RuCl₃NO · 2H₂O with stoichiometric amount of dppf, 1,1′-bis(diphenylphosphino)ferrocene, afforded the new neutral nitrosyl complex fac-[RuCl₃(NO)(dppf)] which was characterized by spectroscopical, electrochemical and X-ray crystallography techniques as well as elemental analysis. The ν_NO band in the IR spectrum is at 1860 cm⁻¹ (CH₂Cl₂ solution) and in the cyclic voltammogram an irreversible wave was observed at −1.35 V, both are characteristics of a nitrosonium (NO⁺) character for the coordinated NO. Additionally, preliminary in vitro antitumor activity against the MDA-MB-231 breast tumor cell line was carried out for the new complex. The initial results indicated an important activity for fac-[RuCl₃(NO)(dppf)] (IC₅₀ = 10 ± 3 μM ). The complex has a higher cytotoxicity than the precursor complex RuCl₃NO · 2H₂O, the free dppf ligand as well as the reference metallodrug cisplatin.     

57Fe Mössbauer spectroscopic and magnetic studies of R3Fe29-xVx (R=Y,Ce, Nd,Sm, Gd,Tb, and Dy)

Hyperfine Interactions - Mössbauer spectra for Fe atoms in the series of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) compounds were collected at 4.2 K. The ratio of 14.5 T/μB between...     

Enumeration of maps regardless of genus: Geometric approach

We use the conceptual idea of “maps on orbifolds” and the theory of the non-Euclidean crystallographic groups (NEC groups) to enumerate rooted and unrooted maps (both sensed and unsensed) on surfaces regardless of genus. As a consequence we deduce a formula for the number of chiral pairs of maps. The enumeration principle used in this paper is due to Mednykh (2006) [15], it counts the number of conjugacy classes of subgroups in NEC groups which are in one-to-one correspondence with unrooted (sensed or unsensed) maps.     

Influence of the addition of Cr in the microstructure and in the phase transformation temperatures of Cu–Al–Be–Nb–Ni alloys

Journal of Thermal Analysis and Calorimetry - Cu–Al–Be polycrystalline SMAs modified with the addition of inoculants show improved ductility, which accredits them for technological...     

Tunable emission of AgIn5S8 and ZnAgIn5S8 nanocrystals: electrosynthesis,characterization and optical application

Ternary AgIn₅S₈ (AIS) and quaternary ZnAgIn₅S₈-alloy (ZAIS) nanocrystals, stabilized by L-glutathione, were produced by a clean and eco-friendly electrochemical method, eliminating the need of reducing agents. AIS-GSH colloidal solution was obtained by constant current electrolysis (i = 30 mA) in cavity cell. S^2? ions (0.051 mmol) were generated into a graphite powder macroelectrode, reacting in the intermediate compartment of the cell containing Ag⁺/In³⁺ aqueous solution at different ratios (0.5, 0.28, 0.18, and 0.14), and 0.025 mmol/L^?1 glutathione (GSH). ZAIS-GSH NCs were synthesized in the same cavity cell containing the previously prepared AIS-GSH solution. A paired electrolysis (i = 30 mA) was used for simultaneous production of Zn²⁺ and S^2? (Zn⁰ sacrificial anode and graphite powder macroelectrode/S⁰ cathode). The electrochemical method promoted a high reproducibility and efficient luminescence in the preparations of NCs. The sizes of the AIS-GSH and ZAIS-GSH nanoparticles were determined by HRTM (3.4 and 4.0 nm, respectively), and quantum yields reaching 16% (AIS-GSH, Ag⁺/In³⁺ = 0.18). The spectrophotometric characterization showed that Ag⁺/In³⁺ ratio can be used for the tuning of the AIS-GSH nanoparticle emission wavelength, which is associated to electronic defects introduced in the NCs lattice. XRD/EDS analysis of ZAIS-GSH nanoparticles point out to Zn²⁺ ion-exchange into the AIS-GSH lattice. XPS analysis was carried out at different etching levels of the ZAIS nanocrystals surface, making possible to identify the 2p Zn doublet signal, indicating two different Zn²⁺ sites in the alloy structure. Time-resolved spectroscopy measurements/decay curves were carried out to evaluate the effect of silver amount on radioactive and non-radioactive terms. Additionally, the AIS-GSH and ZAIS-GSH photoluminescence and stability were used to produce the active parts of commercial white LEDs, and modulate the colour perception from the respective emission bands.     

Behavioral and Antennal Responses of Tribolium confusum to Varronia globosa Essential Oil and Its Main Constituents: Perspective for Their Use as Repellent

Essential oils of aromatic plants represent an alternative to classical pest control with synthetic chemicals. They are especially promising for the alternative control of stored product pest insects. Here, we tested behavioral and electrophysiological responses of the stored product pest Tribolium confusum, to the essential oil of a Brazilian indigenous plant, Varronia globosa, collected in the Caatinga ecosystem. We analyzed the essential oil by GC-MS, tested the effects of the entire oil and its major components on the behavior of individual beetles in a four-way olfactometer, and investigated responses to these stimuli in electroantennogram recordings (EAG). We could identify 25 constituents in the essential oil of V. globosa, with anethole, caryophyllene and spathulenole as main components. The oil and its main component anethole had repellent effects already at low doses, whereas caryophyllene had only a repellent effect at a high dose. In addition, the essential oil abolished the attractive effect of the T. confusum aggregation pheromone. EAG recordings revealed dose-dependent responses to the individual components and increasing responses to the blend and even more to the entire oil. Our study reveals the potential of anethole and the essential oil of V. globosa in the management of stored product pests.     

Synthesis, Raman, X-ray diffraction, and density functional studies of antimony(III) heterotetracycles displaying intramolecular transannular interactions O → Sb

A set of compounds of general formula [{S(C₆H₃S)₂O}SbHal] [Hal = Cl (1), Br (2), I (3)] has been synthesized and studied by Raman and NMR spectroscopy as well as quantum chemical DFT calculations. X-ray diffraction studies of compound 2 revealed that the oxygen atom participates as donor and the antimony atom plays the role of acceptor, adopting a Ψ-distorted trigonal bi-pyramidal geometry, where the eight-membered central ring displays a boat–boat conformation. Furthermore, a series of DFT calculations was performed on compounds 1–3 as well as calculations on the non-synthesized heterotetracyclic systems [{S(C₆H₃S)₂O}SbF] (4a) and the cation [{S(C₆H₃S)₂O}Sb]⁺ (5a). The theoretic study at DFT level indicates as the electronegativity increases at exocyclic substituent along the set of compounds, the interaction is stronger. Moreover, the topological analysis of electronic density showed the existence of critical points along the O → Sb direction which prompted us to suggest the existence of a dative bond.     

Exploiting ion-pair formation for the enhancement of electroanalytical determination of pyridoxine (B6) onto polyurethane-graphite electrodes

The present study reports some aspects of ion-pair formation between pyridoxine and dodecyl sulphate under suitable conditions of pH, and its application with analytical purposes. Electrochemical behavior of the analite onto a graphite-polyurethane electrode was assessed by both cyclic and square-wave voltammetries under different conditions (pH from 1.2 to 13.0, with and without surfactant), aiming to study its mechanisms and to define best parameters for such determination exploiting the association of electroanalytical variables and ion-pair formation; besides these, electrochemical impedance spectroscopy was also applied to evaluate ion-pair formation and its influence on interfacial fenomena. Best conditions were reach by square-wave voltammetry in pH 4.2 acetate buffer sweeping from + 0.7 to + 1.2 V (vs. Ag|AgCl_sat) in pulses of 50 mV amplitude and 10 mV step, in a frequency of 10 Hz. The concentration of sodium dodecyl sulphate was optimized being the optimal value a constant submicelar concentration of 3 mmol L^-1. Under such conditions a linear dynamic range from 2 to 18 μmol L^-1 was observed, providing faster, more selective and sensitive system. Interference studies were also carried out showing no relevant influence of thiamine, riboflavine and nicotinamide over the analysis of pyridoxine. The system was successfully applied to commercial parenteral samples containing thiamine and pyridoxine as purchased, without further treatment.