Temperature (over) compensation in an oscillatory surface reaction

Biological rhythms are regulated by homeostatic mechanisms that assure that physiological clocks function reliably independent of temperature changes in the environment. Temperature compensation, the independence of the oscillatory period on temperature, is known to play a central role in many biological rhythms, but it is rather rare in chemical oscillators. We study the influence of temperature on the oscillatory dynamics during the catalytic oxidation of formic acid on a polycrystalline platinum electrode. The experiments are performed at five temperatures from 5 to 25 degrees C, and the oscillations are studied under galvanostatic control. Under oscillatory conditions, only non-Arrhenius behavior is observed. Overcompensation with temperature coefficient (q(10), defined as the ratio between the rate constants at temperature T + 10 degrees C and at T) < I is found in most cases, except that temperature compensation with q(10) approximate to I predominates at high applied currents. The behavior of the period and the amplitude result from a complex interplay between temperature and applied current or, equivalently, the distance from thermodynamic equilibrium. High, positive apparent activation energies were obtained under voltammetric, nonoscillatory conditions, which implies that the non-Arrhenius behavior observed under oscillatory conditions results from the interplay among reaction steps rather than, from a weak temperature dependence of the individual steps.

Pendimethalin determination in natural water, baby food and river sediment samples using electroanalytical methods

This work describes the electroanalytical determination of pendimethalin herbicide levels in natural waters, river sediment and baby food samples, based on the electro-reduction of herbicide on the hanging mercury drop electrode using square wave voltammetry (SWV). A number of experimental and voltammetric conditions were evaluated and the best responses were achieved in Britton-Robinson buffer solutions at pH 8.0, using a frequency of 500 s(-1). a scan increment of 10 mV and a square wave amplitude of 50 mV. Under these conditions, the pendimethalin is reduced in an irreversible process, with two reduction peaks at -0.60 V and -0.71 V. using a Ag/AgCl reference system. Analytical curves were constructed and the detection limit values were calculated to be 7.79 mu g L(-1) and 4.88 mu g L(-1), for peak 1 and peak 2, respectively. The precision and accuracy were determinate as a function of experimental repeatability and reproducibility, which showed standard relative deviation values that were lower than 2% for both voltammetric peaks. The applicability of the proposed methodology was evaluated in natural water, river sediments and baby food samples. The calculated recovery efficiencies demonstrate that the proposed methodology is suitable for determining any contamination by pendimethalin in these samples. Additionally, adsorption isotherms were used to evaluate information about the behavior of pendimethalin in river sediment samples. (C) 2010 Elsevier B.V. All rights reserved.

A simple and sensitive detection of diquat herbicide using a dental amalgam electrode A comparison using the chromatographic technique

This paper describes the use of a dental amalgam electrode (DAE) to evaluate the electrochemical behaviour and to develop an electroanalytical procedure for determination of diquat herbicide in natural water and potato samples. The work was based on the square wave voltammetry responses of diquat, which presented two well-defined and reversible reduction peaks, at -0.56 V (peak 1) and -1.00V (peak 2). The experimental and voltammetric parameters were optimised, and the analytical curves were constructed and compared to similar curves performed by high performance liquid chromatography coupled to ultraviolet-visible spectrophotometric detector (HPLC/UV-vis). The responses were directly proportional to diquat concentration in a large interval of concentration, and the calculated detection limits were very similar, around 10 mu g L(-1) (10 ppb) for voltammetric and chromatographic experiments. These values were lower than the maximum residue limit established for natural water by the Brazilian Environmental Agency. The recovery percentages in pure electrolyte, natural water and potato samples showed values from 70% to 130%, demonstrating that the voltammetric methodology proposed is suitable for determining any contamination by diquat in different samples, minimising the toxic residues due to the use of liquid mercury or the adsorptive process relative to use of other solid surfaces. (C) 2009 Published by Elsevier B.V.

Cationic and neutral phenylmercury(II) complexes with heterocyclic thione ligands. X-ray structures of [HgPh(dmpymtH)][BF(4)] center dot H(2)O and [{HgPh}(2)(mu-dtu)]

The neutral complex [HgPh(dmpymt)] 1 (dmpymtH = 4,6-dimethylpyrimidine-2(1H)-thione) reacts with HBF(4) to give the cationic complex [HgPh(dmpymtH)][BF(4)] 2. The X-ray molecular structure of the later revealed a [2+1] coordination sphere about the mercury(II) atom (C-Hg-S and Hg center dot center dot center dot N). In the dinuclear complex [(HgPh)(2)(mu-dtu)] 3 [dtuH(2) = 2,4(1H,3H)-pyrimidinedithione or dithiouracil] the coordination spheres are also [2+1] although dissimilar regarding the Hg center dot center dot center dot N secondary bonds. NMR spectroscopy ((1)H, (13)C and (199)Hg) studies were undertaken in solution and the results discussed in the light of the X-ray structures. (C) 2008 Elsevier B. V. All rights reserved.

The Isolation and Characterization of Multiply Antibiotic Resistant Strains of Fish Pathogenic Flavobacterium Species

Since the development of the first antibiotics in the 1940’s, there has been widespread overuse in both clinical and agricultural applications. Antibiotic resistance has become a significant problem as a result of subsequent dissemination of antibiotics into the environment, and multiply-resistant strains of bacteria are now a major pathogenic threat. In this study eight separate strains of Flavobacterium responsible for recent disease outbreaks in fish hatcheries throughout Maine were collected and analyzed. All eight strains were found to be resistant to high levels of a number of different antibiotics, including those used for aquaculture as well as human chemotherapeutic applications. Flavobacterium isolates were also shown phenotypically to transfer antibiotic resistance determinants using a conjugation mating system in which Flavobacterium was the donor and Escherichia coli DH5- alpha was the recipient. This experiment suggests that it may be possible for Flavobacterium strains to transfer their multiple antibiotic resistance determinants to human pathogenic bacterial strains. Importantly, none of the hatcheries from which the Flavobacterium isolates were obtained had ever used antibiotics to treat their fish stock. It is possible that there is another selective agent responsible for the development of antibiotic resistance in the absence of antibiotic pressure. Mercury is one possible candidate, as all of the strains tested were resistant to mercuric chloride and it is known that genes encoding antibiotic resistance can be carried on the same mobile genetic elements that encode for mercury resistance. Preliminary data also suggest that the majority of the Flavobacterium isolates contain genes for mercuric ion reduction, which would confirm the mercury resistance genotype.

A Broad-spectrum mer Operon in a Multi-drug Resistant Strain of the Fish Pathogen, Aeromonas salmonicida.

Aeromonas salmonicida AS03, a potential fish pathogen, was isolated from Atlantic salmon, Salmo salar, in 2003. This strain was found to be resistant to ≥1000 mM HgCl2 and ≥32 mM phenylmercuric acetate as well as multiple antimicrobials. Mercury (Hg) and antibiotic resistance genes are often located on the same mobile genetic elements, so the genetic determinants of both resistances and the possibility of horizontal gene transfer were examined. Specific PCR primers were used to amplify and sequence distinctive regions of the mer operon. A. salmonicida AS03 was found to have a pDU1358-like broad-spectrum mer operon, containing merB as well as merA, merD, merP, merR and merT, most similar to Klebsiella pneumonaie plasmid pRMH760. To our knowledge, the mer operon has never before been documented in Aeromonas spp. PCR and gene sequencing were used to identify class 1 integron associated antibiotic resistance determinants and the Tet A tetracycline resistance gene. The transposase and resolvase genes of Tn1696 were identified through PCR and sequencing with Tn21 specific PCR primers. We provide phenotypic and genotypic evidence that the mer operon, the aforementioned antibiotic resistances, and the Tn1696 transposition module are located on a single plasmid or conjugative transposon that can be transferred to E. coli DH5α through conjugation in the presence of low level Hg and absence of any antibiotic selective pressure. Additionally, the presence of low-level Hg or chloramphenicol in the mating media was found to stimulate conjugation, significantly increasing the transfer frequency of conjugation above the transfer frequency measured with mating media lacking both antibiotics and Hg. This research demonstrates that mercury indirectly selects for the dissemination of the antibiotic resistance genes of A. salmonicida AS03.

A broad-spectrum mer operon in a multi-drug resistant strain of the fish pathogen, Aeromonas salmonicida

Aeromonas salmonicida AS03, a potential fish pathogen, was isolated from Atlantic salmon, Salmo salar, in 2003. This strain was found to be resistant to ≥1000 mM HgCl2 and ≥32 mM phenylmercuric acetate as well as multiple antimicrobials. Mercury (Hg) and antibiotic resistance genes are often located on the same mobile genetic elements, so the genetic determinants of both resistances and the possibility of horizontal gene transfer were examined. Specific PCR primers were used to amplify and sequence distinctive regions of the mer operon. A. salmonicida AS03 was found to have a pDU1358-like broad-spectrum mer operon, containing merB as well as merA, merD, merP, merR and merT, most similar to Klebsiella pneumonaie plasmid pRMH760. To our knowledge, the mer operon has never before been documented in Aeromonas spp. PCR and gene sequencing were used to identify class 1 integron associated antibiotic resistance determinants and the Tet A tetracycline resistance gene. The transposase and resolvase genes of Tn1696 were identified through PCR and sequencing with Tn21 specific PCR primers. We provide phenotypic and genotypic evidence that the mer operon, the aforementioned antibiotic resistances, and the Tn1696 transposition module are located on a single plasmid or conjugative transposon that can be transferred to E. coli DH5α through conjugation in the presence of low level Hg and absence of any antibiotic selective pressure. Additionally, the presence of low-level Hg or chloramphenicol in the mating media was found to stimulate conjugation, significantly increasing the transfer frequency of conjugation above the transfer frequency measured with mating media lacking both antibiotics and Hg. This research demonstrates that mercury indirectly selects for the dissemination of the antibiotic resistance genes of A. salmonicida AS03.

Avaliação do risco de exposição ao mercúrio elementar em uma Unidade de Terapia Intensiva

O metal mercúrio é conhecido pela sua grande toxidade apesar de seu emprego difundido. Desde a Antigüidade, se reconhece sua ação tóxica na exposição ocupacional. Em alguns ambientes laborais, os riscos são maiores, como é o caso de hospitais, que utilizam o mercúrio elementar em vários equipamentos, especialmente em termômetros de verificação da temperatura corporal, largamente empregados. Como na instituição objeto deste estudo foram quebrados 148 termômetros em uma Unidade de Terapia Intensiva no período de um ano, esta pesquisa objetivou a realização de uma avaliação de alguns indicadores ambientais neste espaço de trabalho e de alguns indicadores biológicos e psicológicos em uma amostra de trabalhadores desta unidade, que se dispuseram a participar da pesquisa. A avaliação de tais indicadores são recomendados como pertinentes pela literatura (ATSDR, 1989). Não se detectou em nenhuma das avaliações realizadas, índices acima das normas estabelecidas. Interpreta-se que a temperatura da unidade (20ºC) reduz a possibilidade do mercúrio se volatizar e intoxicar os trabalhadores. As regras de higiene, típicas do contexto hospitalar, e a rotina de rápido recolhimento dos resíduos dos termômetros quebrados e seu acondicionamento em recipientes com tampa são os principais fatores explicativos para os índices encontrados.

Fragmented messages : a reading of L.P. Hartley's novel The go-between

A intenção deste trabalho é efetuar uma leitura do romance O Mensageiro, do autor inglês L.P. Hartley, na forma de uma jornada ao país estrangeiro do passado do protagonista-narrador. Tal leitura é uma espécie de convite aceito para a viagem, que esteticamente deixa sugestões sob a forma de truques, fragmentos de mensagens veladas, expressões ambíguas, sombras, vazios no caminho. Todavia, Mercúrio, o mensageiro dos antigos deuses, o protetor dos viajantes, o trapaceiro, é agora um ser indistinto, cuja imagem e função passou por grandes transformações ao longo da viagem até a modernidade. Guerras, restos de experiências traumáticas coletivas e pessoais são recuperadas na rota movediça do narrador melancólico, sob a forma de substância própria para a narração. Nietzsche e Walter Benjamin são companheiros na trajetória, provendo o suporte teórico básico para a viagem.

“The Wire”: O que a série de TV diz sobre os #baltimoreriots

Não é raro que o universo da ficção se misture com a realidade nas redes sociais – sobretudo quando a ficção ajuda a entender e explicar acontecimentos da política ou da economia, por exemplo. Foi o que ocorreu esta semana nos Estados Unidos, em virtude da mobilização popular em Baltimore em protestos pela morte do jovem negro Freddie Gray sob custódia da polícia em 19 de abril. A prestigiada série de TV americana “The Wire”, produzida pela HBO de 2002 a 2008 e que aborda diversos prismas sociopolíticos de Baltimore, vem sendo lembrada com frequência no contexto dos protestos.

Atividade β-D-N-Acetilglucosaminidásica de enzimas imobilizadas extraídas da Artemia franciscana e possíveis aplicações biotecnológicas

A β-D-N-acetilglucosaminidase extracted and partially isolated from crustacean Artemia franciscana by ammonium sulfate precipitation and filtration gel chromatography Bio Gel A 1.5m. the enzyme was immobilized on ferromagnetic Dacron yielding a insoluble active derivative with 5.0 units/mg protein and 10.35% of the soluble enzyme activity. β-D-N-acetilglucosaminidase-ferromagnetic Dacron was easily removed from the reaction mixture by a magnetic field, it was reused for ten times without loss in its activity. The ferromagnetic Dacron was better activated at pH 5.0. The particles visualized at scanning electron microscope (SEM) had presented different sizes, varying between 721nm and 100µm. Infra red confirmed immobilization on support, as showed by primary amino peaks at 1640 and 1560 cm-1 . The immobilize enzyme presented Km of 2.32 ± 0.48 mM and optimum temperature of 50°C. Bought presented the same thermal stable of the soluble enzyme and larger enzymatic activity at pH 5.5. β-D-N-acetilglucosaminidase-Dacron ferromagnético showed sensible for some íons as the silver (AgNO3), with loss of activity. The β-D-N acetilglucosaminidase activity for mercury chloride (HgCl2), whom is one of the most toxic substance joined in nature, it was presented activity already diminished at 0,01mM and lost total activity at 4mM, indicating sensitivity for this type of metal. β-D-N-acetilglucosaminidase-ferromagnetic Dacron showed degradative capacity on heparan sulfate, the enzyme still demonstrated degradative capacity on heparan sulphate, suggesting a possible application to produce fractions of this glycosaminoglycan

Purificação e caracterização de uma ß-N-acetillhexosaminadase extraída do mamífero marinho Sotalia fluviatilis

This report shows 2232 times purification of a βNAcetylhexosaminidase from hepatic extracts from the sea mammal Sotalia fluviatilis homogenate with final recovery of 8,4%. Sequenced steps were utilized for enzyme purification: ammonium sulfate fractionation, Biogel A 1.5 m, chitin, DEAESepharose and hydroxyapatite chromatographies. The protein molecular mass was estimated in 10 kDa using SDSPAGE and confirmed by MALDITOF. It was found to have an optimal pH of 5.0 and a temperature of 60°C. Using pnitrophenylNAcetylβDglycosaminide apparent Km and Vmax values were of 2.72 mM and 0.572 nmol/mg/min, respectively. The enzyme was inhibited by mercury chloride (HgCl2) and sodium dodecil sulfate (SDS)

Obtenção de filtro cerâmico a partir da diatomita e casca de arroz carbonizada visando tratamento de efluente têxtil

The effluents released by the textile industry have high concentrations of alkali, carbohydrates, proteins, in addition to colors containing heavy metals. Therefore, a filter was prepared aiming primarily to the removal of color. In order to prepare this filter, rice hulls and diatomite were used, which have in their structure, basically amorphous hydrated silica. The silica exists in three crystalline forms: quartz, tridymite and cristobalite. In accordance with the above considerations, this study was divided into two stages; the first corresponds to the preparation of the filter and the second to carry out the tests in the effluent/filter in order to verify the efficiency of the color removal. First, the raw material was subjected to a chemical analysis and XRD, and then the diatomite was mixed, via humid, with a planetarium windmill with 20 %, 40 %, 60 % and 80 % of rice husk ash. To the mixture, 5 % carboxymethylcellulose (CMC) was added as a binder at room temperature. The samples were uniaxially compacted into metallic matrix of 0.3 x 0.1 cm² of area at a pressure of 167 MPa by means of hydraulic press and then sintered at temperatures of 1,000 °C, 1,200 °C and 1,400 °C for 1 h and submitted to granulometry test using laser, linear retraction, water absorption, apparent porosity and resistance to bending, DTA, TMA and XRD. To examine the pore structure of the samples scanning electron microscope (SEM) was used. Also tests were carried out in a mercury porosimeter to verify the average size of the pores and real density of the samples. In the second stage, samples of the effluent were collected from a local industry, whose name will be preserved, located in Igapó, in the State of Rio Grande do Norte - RN. The effluent was first pretreated before filtration and then subjected to a treatment of flotation. The effluent was then characterized before and after filtration, with parameters of color, turbidity, suspended solids, pH, chemical and biochemical oxygen demand (COD and BOD). Thus, through the XRD analysis the formation of cristobalite α in all samples was observed. The best average size of pore was found to be 1.75 μm with 61.04 % apparent porosity, thus obtaining an average 97.9 % color removal and 99.8 % removal of suspended solid

Desenvolvimento de membranas porosas de alumina para fins de tratamento de efluente industrial têxtil

Textile production has been considered as an activity of high environmental impact due to the generation of large volumes of waste water with high load of organic compounds and strongly colored effluents, toxic and difficult biodegradability. This thesis deals with obtaining porous alumina ceramic membranes for filtration of textile effluent in the removal of contaminants, mainly color and turbidity. Two types of alumina with different particle sizes as a basis for the preparation of formulation for mass production of ceramic samples and membranes. The technological properties of the samples were evaluated after using sintering conditions: 1,350ºC-2H, 1,450ºC-30M, 1,450ºC-2H, 1,475ºC-30M and 1,475ºC-2H. The sintered samples were characterized by XRD, XRF, AG, TG, DSC, DL, AA, MEA, RL, MRF-3P, SEM and Intrusion Porosimetry by Mercury. After the characterization, a standard membrane was selected with their respective sintering condition for the filterability tests. The effluent was provided by a local Textile Industry and characterized at the entry and exit of the treatment plant. A statistical analysis was used to study the effluent using the following parameters: pH, temperature, EC, SS, SD, oil and grease, turbidity, COD, DO, total phosphorus, chlorides, phenols, metals and fecal coliform. The filtered effluent was evaluated by using the same parameters. These results demonstrate that the feasibility of the use of porous alumina ceramic membranes for removing contaminants from textile effluent with improved average pore size of 0.4 micrometre (distribution range varying from 0,025 to 2.0 micrometre), with total porosity of 29.66%, and average percentages of color removal efficiency of 89.02%, 92.49% of SS, turbidity of 94.55%, metals 2.70% (manganese) to 71.52% (iron) according to each metal and COD removal of 72.80%