Determination of solubility product of mercurous acetate at various ionic strengths in aqueous medium

The conditionals (K-ps) and thermodynamics (K-ps(o)) solubility products of mercurous acetate have been determined, in aqueous solution, at 25 degrees C and ionic strength (I) comprised between 0.300 and 3.000 mol/L (NaClO4). The investigation was carried out potentiometrically by using a second class electrodes which responds to acetate ions. The values obtained for [pK(ps) (I)] were: 9.49+/-0.08 (0.000); 9.51+/-0.08 (0.300); 9.53+/-0.08 (0.500); 9.54+/-0.08 (0.700); 9.55+/-0.09 (0.900), 9.57+/-0.09 (1.200); 9.59+/-0.10(1.500); 9.61+/-0.10 (1.800); 9.63+/-0.10 (2.100); 9.65+/-0.11 (2.400); 9.67+/-0.11 (2.700) e 9.69+/-0.12 (3.000).

Semi-selective culture medium for Curtobacterium flaccumfaciens pv. flaccumfaciens isolation from bean seeds

Curtobacterium wilt has become an important disease of beans in several localities in the country. Its causal agent, Curtobacterium flaccumfacciens pv. flaccumfaciens (Cff), survives and is disseminated through seeds. To date, few studies have been conducted with the objective of developing an effective and low-cost culture medium to isolate this bacterium from bean seeds, for health analysis purposes. Usually, the culture media employed for coryneform bacteria isolation contain specific carbon sources and antimicrobial products not available in the Brazilian market. A culture medium known as MSCFF was developed (peptone - 5 g, meat extract - 3 g, sucrose - 5 g, agar 15 g, skim milk powder* - 5 g. Congo red* - 0.05 g-, chlorothalonil* - 0.01 g, thiophanate methyl* - 0.01 g, nalidixic acid* - 0.01 g, nitrofurantoin* - 0.01 g. oxacillin* 0.001 g, sodium azide* - 0.001 g and distilled water q.s. 1L; *added after autoclaving the basal medium), which has the ability to inhibit growth of a large amount of saprophytic bacteria, but with low supressivity to Cff isolates. The MSCFF medium was highly effective for Cff isolation from naturally infected bean seeds and could be used for routine detection of this bacterium in bean seeds.

TiO2 films organofunctionalized with 2-aminothiazole ligand and adsorbed Pd(II) ions applied in the photocatalytic degradation of phenol in an aqueous medium

This paper describes the preparation of thin titanium films via sol-gel route and their subsequent chemical modification by anchoring with 2-aminothiazole ligand and Pd(II) ion sorption, aiming to maximize the photocatalytic activity. The material was characterized by diffuse reflectance infrared Fourier transform spectroscopy, ultraviolet and visible spectrometry, X-ray diffractometry, and scanning electronic microscopy. The amount of palladium adsorbed on the film's surface, determined by graphite furnace atomic absorption spectrometry, showed a value of 2.69 x 10(16) atoms CM-2. The photocatalytic tests indicated that the functionalization with 2-aminothiazole and the adsorption of palladium (II) were determinants in the semiconductor's enhanced photocatalytic activity. (c) 2007 Elsevier B.V. All rights reserved.

Photo luminescence: A probe for short, medium and long-range self-organization order in ZrTiO4 oxide

Photoluminescent disordered ZrTiO4 powders were obtained by the polymeric precursor soft-chemical method. This oxide system (ordered and disordered) was characterized by photoluminescence, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry and UV vis absorption experiments. The UV absorption tail formation in the disordered oxides was related to the diminution of optical band gap. In the disordered phase, this oxide displayed broad band photoluminescence caused by change in coordination number of titanium and zirconium with oxygen atoms. The gap decreased from 3.09 eV in crystalline oxide to 2.16 eV in disordered oxide. The crystalline oxide presented an orthorhombic alpha-PbO2-type structure in which Zr4+ and Ti4+ were randomly distributed in octahedral coordination polyhedra with oxygen atoms. The amorphous-crystalline transition occurred at almost 700 degrees C, at which point the photoluminescence vanished. The Raman peak at close to 80-200 cm(-1) indicated the presence of locally ordered Ti-O-n and Zr-O-n polyhedra in disordered photoluminescent oxides. (c) 2006 Elsevier B.V. All rights reserved.

Resonance in positron-helium scattering at medium energy

A narrow S-wave resonance has been found in the positron-helium system at about 30 eV, using the close-coupling approach, in excitation and rearrangement cross sections to He(1s2s), He(1s2p), Ps(1s) and Ps(2s) states by employing different combinations of the following basis functions: He(1s1s), He(1s2s), He(1s2p), Ps(1s) and Ps(2s), where Ps stands for the positronium atom.

The hydrogen evolution reaction on codeposited Ni-hydrogen storage intermetallic particles in alkaline medium

The hydrogen evolution reaction (HER) was studied on Ni-LaNi5 and Ni-MmNi(3.4)Co(0.8)Al(0.8) electrode materials in 1 mol dm(-3) NaOH solution. The steady-state polarization curves and electrochemical impedance spectroscopy experimental data showed a pronounced improvement in HER kinetics when these electrode materials were used. The electrochemical results are in accordance with the Volmer-Heyrovsky mechanism. The kinetic results indicate a more effective improvement in the Heyrovsky step, suggesting an electrocatalytic synergistic effect of the hyper-electronic character of the Ni and the hypo-electronic character of the rare-earth element on the electrode surface. (C) 2000 International Association for Hydrogen Energy. Published by Elsevier B.V. Ltd. All rights reserved.

Spectrophotometric determination of formaldehyde with chromotropic acid in phosphoric acid medium assisted by microwave oven

In the present study. a spectrophotometric method for the determination of formaldehyde by using chromotropic acid was devised. in which the use of potentially hazardous and corrosive concentrated sulfuric acid was eliminated and advantageously C replaced by a mixture of H, concentrated H3PO4 and H2O2. The reaction between formaldehyde and chromotropic acid (CA) in a cone phosphoric acid medium was accelerate by irradiating the mixture with microwave energy for 35 s (1100 W), producing a violetred compound (lambda(max)=570 nm). Beer's Law is obeyed in a concentration range of 0.8-4.8 mg 1(-1) of formaldehyde with a good correlation coefficient (r = 0.9968). The proposed method was applied in the analysis of formaldehyde in commercial disinfectants. Recoveries were within 98.0-100.4%, with standard deviations ranging from 0.03 to 0.13%. (C) 2003 Elsevier B.V All rights reserved.

Investigation of the systems silica and silica containing chromium in alcohol medium

The purpose of this work is to obtain micrometer sized spherical particles of silica and silica-chromium from sodium silicate. Spherical particles were prepared by sol-gel method from hydrolysis to polycondensation of aqueous sodium silicate in alcohol medium. Chromium was added to the system for some samples. Compositions and morphologies were achieved by changing the precipitation agent. X-ray diffractometry, electrophoretic mobility, infrared spectroscopy and scanning electron microscopies were carried out on these particles to identify phases, determine particle mobility, morphology, particle sizes, shapes and order at short distance. Non-crystalline silica particles with spherical shapes and micrometric size were obtained. The surface potentials of the silica particles differed from that of the silica-chromium particles. (C) 1999 Elsevier B.V. B.V. All rights reserved.

pH at the micellar interface: Synthesis of pH probes derived from salicylic acid, acid-base dissociation in sodium dodecyl sulfate micelles, and Poisson-Boltzmann simulation

The study of the H+ concentration at the micellar interface is a convenient system for modeling the distribution of H+ at interfaces. We have synthesized salicylic acid derivatives to analyze the proton dissociation of both the carboxylic and phenol groups of' the probes, determining spectrophotometrically the apparent pK(a)'s (pK(ap)) in sodium dodecyl Sulfate, SDS, micelles with and without added salt. The synthesized probes were 2-hydroxy-5-(2-trimethylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumacetyl)benzoate- 2-hydroxy-5-(2-dimethylhexadecylammoniumhexanoyl)benzoate-, 2-hydroxy-5-(2-diniethylhexadecylammoniumundecanoyl)betizoate; 2-hydroxy-5-acetylbenzoic acids and 2-hydroxy-5-dodecanoylbenzoic acid. Upon incorporation into SDS micelles the pK(ap)'s of both carboxylic and phenol groups increased by ca. 3 pH units and NaCl addition caused a decrease in the probe-incorporated pKap. The experimental results were fitted with a cell model Poisson-Boltzmann (P-B) equation taking in consideration the effect of salt on the aggregation number of SDS and using the distance of' the dissociating group as a parameter. The conformations of the probes were analyzed theoretically using two dielectric constants, e.g., 2 and 78. Both the P-B analysis and conformation calculations can be interpreted by assuming that the acid groups dissociate very close to, or at, the interface. Our results are consistent with the assumption that the intrinsic pK(a)'s of both carboxylic and phenol groups of the salicylic acid probes used here can be taken as those in water. Using this assumption the micellar and salt effects on the pKap's of the (trialkylammonium)benzoate probes were described accurately using a cell model P-B analysis. (c) 2005 Elsevier B.V. All rights reserved.

Curtobacterium flaccumfaciens pv. Flaccumfaciens detection in bean seeds using a semi-selective culture medium

The bacterial wilt caused by Curtobacterium flaccumfaciens pv. flaccumfaciens is currently considered one of the most important bacterial bean disease in Brazil. One of the most effective control methods against this disease is the use of healthy seeds. However, no methods are known that could be routinely used to detect this bacterium in bean seeds under Brazilian condition. The aim of this work was to evaluate qualitative and quantitative detection methods for Curtobacterium flaccumfaciens pv. flaccumfaciens in naturally-infected bean seeds, and the detection of this pathogen in thirty bean seed samples, by sowing onto a semi- selective culture medium the leachate obtained from soaked bean seeds. Both the qualitative and quantitative methods were effective for detecting the presence of the bacteria in the seeds samples analysed. The qualitative method proved more practical for rotine use; of the thirty bean seed samples analyzed by this method, fifty percent were infected with Curtobacterium flaccumfaciens pv. flaccumfaciens.