Chemoselective catalytic hydrogenation of acrolein on Ag(111): effect of molecular orientation on reaction selectivity

The adsorption and hydrogenation of acrolein on the Ag(111) surface has been investigated by high resolution synchrotron XPS, NEXAFS, and temperature programmed reaction. The molecule adsorbs intact at all coverages and its adsorption geometry is critically important in determining chemoselectivity toward the formation of allyl alcohol, the desired but thermodynamically disfavored product. In the absence of hydrogen adatoms (H(a)), acrolein lies almost parallel to the metal surface; high coverages force the C=C bond to tilt markedly, likely rendering it less vulnerable toward reaction with hydrogen adatoms. Reaction with coadsorbed H(a) yields allyl alcohol, propionaldehyde, and propanol, consistent with the behavior of practical dispersed Ag catalysts operated at atmospheric pressure: formation of all three hydrogenation products is surface reaction rate limited. Overall chemoselectivity is strongly influenced by secondary reactions of allyl alcohol. At low H(a) coverages, the C=C bond in the newly formed allyl alcohol molecule is strongly tilted with respect to the surface, rendering it immune to attack by H(a) and leading to desorption of the unsaturated alcohol. In contrast with this, at high H(a) coverages, the C=C bond in allyl alcohol lies almost parallel to the surface, undergoes hydrogenation by H(a), and the saturated alcohol (propanol) desorbs.

Detection of Salmonella enteritidis in eggs by the polymerase chain reaction

A polymerase chain reaction (PCR) for the specific detection of the gene sequence, sefA, encoded by all isolates of Salmonella enteritidis, was developed. The PCR could detect as few as four S enteritidis washed bacterial cells but egg contents inhibited the PCR. Eggs spiked with 50 S enteritidis bacterial cells were homogenised, inoculated into buffered peptone water and grown at 37 degrees C for 16 hours, when the PCR was successful. A positive internal control was developed to differentiate between true and false negative PCR results for the detection of S enteritidis. In a limited trial of the egg handling procedures and the PCR, one of 250 chickens' eggs from retail outlets was found to be contaminated with S enteritidis.

Ozonolysis of methyl oleate monolayers at the air–water interface: oxidation kinetics, reaction products and atmospheric implications

Ozonolysis of methyl oleate monolayers at the air–water interface results in surprisingly rapid loss of material through cleavage of the C[double bond, length as m-dash]C bond and evaporation/dissolution of reaction products. We determine using neutron reflectometry a rate coefficient of (5.7 ± 0.9) × 10−10 cm2 molecule−1 s−1 and an uptake coefficient of [similar]3 × 10−5 for the oxidation of a methyl ester monolayer: the atmospheric lifetime is [similar]10 min. We obtained direct experimental evidence that <2% of organic material remains at the surface on atmospheric timescales. Therefore known long atmospheric residence times of unsaturated fatty acids suggest that these molecules cannot be present at the interface throughout their ageing cycle, i.e. the reported atmospheric longevity is likely to be attributed to presence in the bulk and viscosity-limited reactive loss. Possible reaction products were characterized by ellipsometry and uncertainties in the atmospheric fate of organic surfactants such as oleic acid and its methyl ester are discussed. Our results suggest that a minor change to the structure of the molecule (fatty acid vs. its methyl ester) considerably impacts on reactivity and fate of the organic film.

Effect of Lithium Nitrate on the Alkali-Silica Reaction Gel

Lithium nitrate has been used to prevent and to mediate the expansion caused by alkali-silica reaction (ASR). However, there is limited information on how it affects the existing reaction products caused by ASR. The aim of the present work is to determine the modifications caused by the LiNO3 treatment on the structure of the gel produced by ASR. ASR gel samples obtained from a concrete dam were exposed to an aqueous solution of lithium nitrate and sodium hydroxide with molar LiNO3/NaOH = 0.74, and the resulting products were analyzed by X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance of Si-29, Na-23, and Li-7. The treatment of the gel samples produces significant structural modifications in ASR products. A new amorphous silicate compound incorporating Li+ ions is formed, with an average silicate network that can be described as linear in contrast with the layered structure of the original gel. This elimination of the layered structure after the Li-based treatments may be related to the reduction of the tendency of the gel to expand. Also, several crystalline compounds containing potassium indicate the release of this species from the original ASR gel.

Silver Nanoparticles Obtained in PAH/PAA-Based Multilayers by Photochemical Reaction

Carboxylic acid groups in PAH/PAA-based multilayers bind silver cations by ion exchange with the acid protons. The aggregation and spatial distribution of the nanoparticles proved to be dependent oil the process used to reduce the silver acetate aqueous solution. The reducing method with ambient light formed larger nanoparticles with diameters ranging from 4-50 nm in comparison with the reduction method using UV light, which gave particles with diameters of 2-4 nm The high toughness of samples reduced by ambient light is a result of two population distributions of particle sizes caused by different mechanisms when compared with the UV light process. According to these phenomena, a judicious choice of the spectral source call be used as a way to control the type and size of silver nanoparticles formed on PEMs. Depending on the energy of the light source, the Ag nanoparticles present cubic and/or hexagonal crystallographic structures, as confirmed by XRD. Beyond the kinetically controlled process of UV photoinduced cluster formation, the annealing produced by UV light allowed a second mechanism to modify the growth rates, spatial distribution, and phases.

Evaluation of the counterimmunoelectrophoresis reaction as a serodiagnosis test for swine leptospirosis

Avaliou-se a reação de contraimunoeletroforese (CIE) como teste gênero-específico para diagnóstico da leptospirose suína, usando-se três extratos solúveis de Leptospira sp, sorovares pomona, icterohaemorrhagiae e patoc, obtidos pelo tratamento com Triton X-100 a quente e aplicados a amostras de soro de suínos subdivididos em três grupos: Grupo 1, 10 suínos experimentalmente infectados com estirpe Pomona; Grupo 2, 50 suínos naturalmente infectados e Grupo 3, controle. As amostras de soros foram submetidas à reação de CIE e os resultados comparados aos da Soroaglutinação Microscópica (SAM), técnica de referência pela WHO. Os Grupos 1 e 3 foram monitorados por 93 dias após a inoculação (p.i.). Pela SAM a soroconversão do Grupo 1 ocorreu por volta do 10º dia p.i., enquanto pela CIE, empregando-se qualquer extrato antigênico, foi anterior à SAM. Quando a CIE foi realizada frente a antigeno homólogo à infecção, seus resultados foram equivalentes aos da SAM, não se verificando o mesmo frente aos antígenos heterólogos. Neste aspecto, os Grupos 1 e 3 mostraram comportamento diferente pois não houve diferença significativa entre os resultados da CIE frente aos três antígenos, o que poderia significar serem independentes do sorovar responsável pelo surto ou infectante. Embora a CIE seja segura, rápida, de fácil execução, de baixo custo e ideal para análise em grande escala de amostras, revelou-se de limitada capacidade gênero-específica, o que não é desejavel para testes de triagem de campo; mas poderia ser útil na detecção precoce de resposta sorológica em relação à SAM.

Structural and functional characterization of an acidic platelet aggregation inhibitor and hypotensive phospholipase A(2) from Bothrops jararacussu snake venom

An acidic (pI similar to 4.5) phospholipase A(2) (BthA-I-PLA(2)) was isolated from Bothrops jararacussu snake venom by ion-exchange chromatography on a CM-Sepharose column followed by reverse phase chromatography on an RP-HPLC C-18 column. It is an similar to13.7 kDa single chain Asp49 PLA(2) with approximately 122 amino acid residues, 7 disulfide bridges, and the following N-terminal sequence: 'SLWQFGKMINYVMJGESGVLQYLSYGCYCGLGGQGQPTDATDRCCFVHDCC(51). Crystals of this acidic protein diffracted beyond 2.0 Angstrom resolution. These crystals are monoclinic and have unit cell dimensions of a = 33.9, b = 63.8, c = 49.1 Angstrom, and beta = 104.0degrees. Although not myotoxic, cytotoxic, or lethal, the protein was catalytically 3-4 tithes more active than BthTX-II, a basic D49 myotoxic PLA(2) from the same venom and other Bothrops venoms. Although it showed no toxic activity, it was able to induce time-independent edema, this activity being inhibited by EDTA. In addition, BthA-I-PLA(2) caused a hypotensive response in the rat and inhibited platelet aggregation, Catalytic, antiplatelet and other activities were abolished by chemical modification with 4-bromophenacyl bromide, which is known to covalently bind to His48 of the catalytic site. Antibodies raised against crude B. jararacussu venom recognized this acidic PLA(2), while anti-Asp49-BthTX-II recognized it weakly and anti-Lys49-BthTX-I showed the least cross-reaction. These data confirm that myotoxicity does not necessarily correlate with catalytic activity in native PLA(2) homologues and that either of these two activities may exist alone. BthA-I-PLA(2), in addition to representing a relevant molecular model of catalytic activity, is also a promising hypotensive agent and platelet aggregation inhibitor for further studies. (C) 2002 Elsevier B.V. All rights reserved.

Effect of electrolyte on the gelation and aggregation of SnO2 colloidal suspensions

Electrolytes may modify the physical-chemical characteristics of colloidal particle interfaces in suspension, which can favour gel or aggregate formation. The influence of NH4Cl loading on the aggregation and gelation of SnO2 colloidal suspensions was investigated using measurements of rheology, turbidity and infrared spectra. A rapid aggregate growth for samples with Cl- > 20 mM was observed. With increasing age, gelation was observed due to formation of interaggregate bonds. For concentration of Cl- between 20 and 9 mM, the aggregation process was slower allowing the formation of gel with a network which was not destroyed as the gel was submitted to a small rate of shear. As aging continues, the condensation reaction between OH groups gave rise to the formation of Sn-O bonds, irrespective of the electrolyte loading. © 1992 Elsevier Science Publishers B.V. All rights reserved.

Biocompatibility of New Calcium Aluminate Cement: Tissue Reaction and Expression of Inflammatory Mediators and Cytokines

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hot spots, hot moments, and spatio-temporal controls on soil CO2 efflux in a water-limited ecosystem

Soil CO2 efflux is the primary source of CO2 emissions from terrestrial ecosystems to the atmosphere. The rates of this flux vary in time and space producing hot moments (sudden temporal high fluxes) and hot spots (spatially defined high fluxes), but these high reaction rates are rarely studied in conjunction with each other. We studied temporal and spatial variation of soil CO2 efflux in a water-limited Mediterranean ecosystem in Baja California, Mexico. Soil CO2 efflux increased 522% during a hot moment after rewetting of soils following dry summer months. Monthly precipitation was the primary driver of the seasonal trend of soil CO2 efflux (including the hot moment) and through changes in soil volumetric water content (VWC) it influenced the relationship between CO2 efflux and soil temperature. Geostatistical analyses showed that the spatial dependence of soil CO2 efflux changed between two contrasting seasons (dry and wet). During the dry season high soil VWC was associated with high soil CO2 efflux, and during the wet season the emergence of a hot spot of soil CO2 efflux was associated with higher root biomass and leaf area index. These results suggest that sampling designs should accommodate for changes in spatial dependence of measured variables. The spatio-temporal relationships identified in this study are arguably different from temperate ecosystems where the majority of soil CO2 efflux research has been done. This study provides evidence of the complexity of the mechanisms controlling the spatio-temporal variability of soil CO2 efflux in water-limited ecosystems. (C) 2014 Elsevier Ltd. All rights reserved.

ESTIMATING REACTION CONSTANTS BY AB INITIO MOLECULAR MODELING: A STUDY ON THE OXIDATION OF PHENOL TO CATECHOL AND HYDROQUINONE IN ADVANCED OXIDATION PROCESSES

Molecular modeling is growing as a research tool in Chemical Engineering studies, as can be seen by a simple research on the latest publications in the field. Molecular investigations retrieve information on properties often accessible only by expensive and time-consuming experimental techniques, such as those involved in the study of radical-based chain reactions. In this work, different quantum chemical techniques were used to study phenol oxidation by hydroxyl radicals in Advanced Oxidation Processes used for wastewater treatment. The results obtained by applying a DFT-based model showed good agreement with experimental values available, as well as qualitative insights into the mechanism of the overall reaction chain. Solvation models were also tried, but were found to be limited for this reaction system within the considered theoretical level without further parameterization.

Estimating reaction constants by ab initio molecular modeling: a study on the oxidation of phenol to catechol and hydroquinone in advanced oxidation processes

Molecular modeling is growing as a research tool in Chemical Engineering studies, as can be seen by a simple research on the latest publications in the field. Molecular investigations retrieve information on properties often accessible only by expensive and time-consuming experimental techniques, such as those involved in the study of radical-based chain reactions. In this work, different quantum chemical techniques were used to study phenol oxidation by hydroxyl radicals in Advanced Oxidation Processes used for wastewater treatment. The results obtained by applying a DFT-based model showed good agreement with experimental values available, as well as qualitative insights into the mechanism of the overall reaction chain. Solvation models were also tried, but were found to be limited for this reaction system within the considered theoretical level without further parameterization.

Therapeutical potential of direct thrombin inhibitors for atherosclerotic vascular disease

Adverse cardiovascular events are the consequence of a molecular chain reaction at the site of vulnerable plaques. Key players are platelets and coagulation factors that are activated following plaque rupture and often cause arterial obstruction. Thrombin, a plasma serine protease, plays a role in hemostasis of coagulation as well as in thrombosis and cell growth, leading to restenosis and atherosclerosis. Interesting and promising new molecules, the direct thrombin inhibitors, have been shown to be as effective as the combination of glycoprotein IIb-IIIa inhibitors and heparin for the prevention of arterial thrombosis. Until recently, direct thrombin inhibitors could be applied only parenterally; therefore, therapy was limited to hospitalized patients. As a result of recent drug development, orally active direct thrombin inhibitors are now available and have been evaluated for the long-term treatment of venous thrombosis and arterial fibrillation. Due to their specific pharmacodynamic characteristics by binding directly to thrombin--and thus inhibiting platelet aggregation and fibrin generation--these novel drugs may also have therapeutic potential for the treatment of atherothrombotic disease and its complications such as myocardial infarction, stroke or limb ischemia.

Baylis-Hillman reaction assisted parallel synthesis of 3, 5-disubstituted isoxazoles and their in vivo bioevaluation as antithrombotic agents

The solution phase parallel synthesis involving reactions of Baylis-Hillman products of 3-substituted-5-isoxazolecarbaldehydes with nucleophiles and their in vivo antithrombotic evaluations are described along with the results of in vitro platelet aggregation inhibition assay of a few compounds. Results of the detailed evaluation of one of the compounds as an inhibitor of platelet aggregation are also presented.

Temporal genetic structure and relatedness in the Tufted Duck Aythya fuligula suggests limited kin association in winter

Conspecific aggregation of waterfowl in winter is a common example of animal flocking behaviour, yet patterns of relatedness and temporal substructure in such social groups remain poorly understood even in common species. A previous study based on mark-recapture data showed that Tufted Ducks Aythya fuligula caught on the same day were re-caught together in subsequent winters more often than expected by chance, suggesting stable assortments of ‘socially familiar’ individuals between wintering periods. The genetic relationships within these social groups were not clear. Based on 191 individuals genotyped at 10 microsatellite markers, we investigated the temporal genetic structure and patterns of relatedness among wintering Tufted Ducks at Lake Sempach, Switzerland, in two consecutive winters. We found no evidence of genetic differentiation between temporal groups within or between winters. The average levels of relatedness in temporal groups were low and not higher than expected in random assortments of individuals. However, Mantel tests performed for each sex separately revealed significant negative correlations between the pairwise relatedness coefficients and the number of days between the capture dates of pairs of wintering Tufted Duck in males and females. This pattern suggests the presence of a small number of co-migrating same-sex sibling pairs in wintering flocks of Tufted Ducks. Our findings provide one of the first genetic analyses of a common duck species outside the breeding season and contribute to the understanding of social interactions in long-distance migratory birds.