Química

Synthesis, crystal structure, magnetism and spectroelectrochemistry of [Co 2 (tidf)(ClO 4 ) 2 (H 2 O) 2 ] (tidf = a Robson type macrocyclic ligand obtained on condensation of 2,6-diformyl-4-methylphenol and 1,3diaminopropane) are reported. The title compound crystallizes in the monoclinic space group P2(1)/c with a Co-Co distance of 3.099 Å and each metal center shows a different geometry around it. Magnetism as a function of the temperature is consistent with antiferromagnetism with an exchange and axial splitting parameters J and D estimated at À10.3 cm À1 and 8.74 cm À1 , respectively.

The morphological structures that permit Oryzophagus oryzae aquatic activities and swimming behavior were studied and compared with various weevils and other relevant species. The use of scanning electron microscopy facilitated the recognition of three different hydrofuge scales and sensilla. Based on the microscopic observations of behavior, morphological evidence, and comparisons with other curculionid species, it was supported that the gas exchange in O. oryzae adults relies on a subelytral air store maintained by hydrofuge scales and a ribbed margin on the adult elytra. The plastron structure is identical to Lissorhoptrus oryzophilus supporting the application of similar control measures for both species.

Polypyrrole (PPy) is the conducting polymer most widely employed in electrochemical sensors for ammonia detection in the last decade. Although sensors have been described in depth in the literature, the mechanism of ammonia detection by polypyrrole is still a matter of controversy. The differential electrochemical mass spectrometry (DEMS) technique, together with UV-Vis spectroscopy, gives direct and conclusive evidence with respect to the ammonia oxidation products formed in NaOH solution (pH = 10) at polyrrole or N-methyl polypyrrole film sensors polarized at 0.35 V (Ag/AgCl). Monitoring of the different possible ammonia oxidation products by on-line DEMS measurements indicates that only NO is formed and that other species such as N 2 or N 2 O are absent. UV-Vis absorption spectroscopy also showed that ionic products such as nitrate or nitrite are not formed.

The present paper describes the utilization of nickel hydroxide modified electrodes toward the catalytic oxidation of carbohydrates (glucose, fructose, lactose and sucrose) and their utilization as electrochemical sensor. The modified electrodes were employed as a detector in flow injection analysis for individual carbohydrate detection, and to an ionic column chromatography system for multi-analyte samples aiming a prior separation step. Kinetic studies were performed on a rotating disk electrode (RDE) in order to determine both the heterogeneous rate constant and number of electrons transferred for each carbohydrate. Many advantages were found for the proposed system including fast and easy handling of the electrode modification, low cost procedure, a wide range of linearity (0.5-50 ppm), low detection limits (ppb level) and high sensitivities.

The electrocatalytic oxidation of glycine by doped nickel hydroxide modified electrodes and their use as sensors are described. The electrode modification was carried out by a simple electrochemical coprecipitation and its electrochemical properties were investigated. The modified electrode presented activity for glycine oxidation after applying a potential required to form NiOOH (∼0.45 V vs Ag/AgCl). In these conditions a sensitivity of 0.92 A mmol −1 L and a linear response range from 0.1 up to 1.2 mmol L −1 were achieved in the electrolytic solutions at pH 12.6. Limits of detection and quantification were found to be 30 and 110 mol L −1 , respectively. Kinetic studies performed with rotating disk electrode (RDE) and by chronoamperometry allowed to determine the heterogeneous rate constant of 4.3 × 10 2 mol −1 L s −1 , suggesting that NiOOH is a good electrocatalyst for glycine oxidation. NiOOH activity to oxidize other amino acids was also investigated.

Research and development of conductive nanomaterials based on biocompatible matrices has been greatly rising in the past decade since synergistic properties can be achieved by combining metallic nanoparticles and natural/ conductive polymers. Poly(3,4-ethylenedioxythiophene) (PEDOT) is known to be an intrinsically conductive polymer, difficult to handle in aqueous medium. Therefore, in this work, we present a physical-chemical perspective in the development of novel aqueous dispersible nanocomposites of gold nanoparticles (AuNPs) and PEDOT, obtained through a one-pot synthesis, using the biopolymer gum acacia (GA) as stabilizer. A thorough kinetic study was carried out and correlated with microscopy analyses, evidencing that the concentration of GA influences the AuNP size by affecting their nucleation and growth stages. A quantitative detailing using kinetic models is shown, which to the best of our knowledge is the first report relating mechanism and rate constants with size contr...

The present paper outlines the methods used to reduce the interference signal caused by ascorbic and uric acids on an ammonia amperometric sensor in aqueous solutions. The sensor was prepared by electrochemical deposition of poly(pyrrole), doped with dodecylbenzenesulfonic anions (DBS), onto platinum substrates. Poly(pyrrole) films were coated with different membranes, aiming to find different ways to diminish the interference response

The present paper describes the physical-chemical characterization and electrochemical behavior of a new nanomaterial formed by the addition of cadmium and cobalt atoms into the structure of nickel hydroxide nanoparticles, these ones synthesized by an easy sonochemical method. Particles of about 5 nm diameter were obtained and characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction and Raman spectroscopy. Different nickel hydroxide nanoparticles were immobilized onto transparent conducting substrates by using electrostatic layer-by-layer providing thin films at the nanoscale and the electrochemical behavior was investigated. The formation of a mixed hydroxide was corroborated by observation of very interesting properties as redox potential shifting to less positive potentials and high stability when submitted to long electrochemical cycling or high times of ultrasonic synthesis, suggesting practical applications.

P olycrystalline boron doped diamond (pBDD) attracts much interest as an electrode material for electroanalysis, 1,2 due to its very wide potential window in aqueous electrolytes, 3À5 low background currents, 6,7 and resistance to fouling. 8À10 As such, pBDD has been used to detect a wide range of electrochemically active species, from metal ions and inorganics such as lead 11 and sulfides, 12 to organics, including chlorophenols, 13,14 glucose, 15 polyamides, 16 and serotonin. 10 pBDD is also resistant to corrosion under both acidic and alkaline conditions, as well as at extreme positive and negative applied potentials, and is stable at high temperatures and pressures. Typically, macrosized pBDD electrodes (g1 mm) have been employed for electroanalytical measurements in quiescent solutions 19,20 but to improve sensitivity there has been a push toward miniaturization through the development and application of pBDD-based microelectrodes 4,21À24 and microarrays. 25À28 Alternatively, hydrodynamic techniques can be used to enhance the voltammetric signal. To-date, there have been relatively few hydrodynamic studies employing pBDD electrodes. These include, the analysis of dopamine 29 and nicotinamide adenine dinucleotide 30 using pBDD rotating disk electrodes and the detection of chlorophenol, 31 with BDD channel flow electrodes. 32 pBDD disk microelectrodes have also been used as detectors in capillary electrophoresis and flow injection analysis. 33À35 A major challenge in the use of pBDD as an electrode material for hydrodynamic (flow) studies is how to encapsulate the electrode in an insulating support structure to produce a coplanar structure. Recession or protrusion of the electrode surface from the surrounding insulator can significantly affect the flow hydrodynamics and complicate the mass transport characteristics. It is also desirable that the encapsulating insulating material does not limit the wide range of applications, e.g., chemical stability in aggressive environments and at elevated temperatures and pressure, etc. facilitated by the use of BDD as an electrode.

IN ELECTROCATALYSIS, ELECTROCHROMISM AND SECONDARY BATTERIES. The present review paper describes the main features of nickel hydroxide modified electrodes covering its structural and electrochemical behavior and the newest advances promoted by nanostructured architectures. Important aspects such as synthetic procedures and characterization techniques such as X-Ray diffraction, Raman and Infrared spectroscopy, Electronic Microscopy and many others are detailed herein. The most important aspect concerning nickel hydroxide is related to its great versatility covering different fields in electrochemical-based devices such as batteries, electrocatalytic systems and electrochromic electrodes, the fundamental issues of these devices are also commented. Finally, some of the newest advances achieved in each field by the incorporation of nanomaterials will be shown.