Impact of geometric properties of silica supports on metallocene catalyst behavior

The objective of this work was to evaluate the effect of the physical properties of several different commercial silicas on the performance of metallocene catalysts when used in gas and slurry phase polymerization. A lot is known about how the chemistry of the silica effects the polymerization and the final product, but very little is described in the literature concerning parameters such as pore volume and pore diameter. This work dealt with these issues by using two different metallocenes in homo and copolymerization of ethylene and ethylene 1-hexene respectively. In terms of silica porosity, the metallocene/MAO catalyst supported on the silica with lower pore volume appears to polymerize faster than the one which is supported on the silica with higher pore volume. This behavior can be attributed to [email protected] the fact that the fragmentation of the growing catalyst/polymer particle with lower pore volume will be faster than its counterpart. In terms of mean particle size, if other physical properties like pore volume, pore diameter and surface area of the silica supported metallocene/MAO catalysts are kept similar along with the metal loadings, the smaller catalyst particles are more active than their bigger counterparts. This effect of particle size on instantaneous activity seems to be the same at different monomer pressures and in the presence and absence of a comonomer (like 1-hexene). Finally, the effect of pore diameter is very complex. The normal trend would be the smaller the pore diameter the faster the polymerization should be, due to the reasons explained for the pore volume. However, by using the technique we employed for the previous parameters, it was not possible to draw a valid conclusion. It seems that MAO penetration depends on the pore size, and that it might not penetrate into particles with small pore diameters

Formulation des latex adhésifs en vue d’améliorer les propriétés barrières à l'eau et à l'oxygène

L'objectif de la présente thèse est d'améliorer les propriétés barrières du MetPET en conditions sévères. Plus précisément d'établir les corrélations structure-propriétés : structure du primaire d'accroche déposé en ligne sur le film PET avant métallisation et propriétés barrières et d'adhésion métal en condition sèche et humide du composite final obtenu (MetPET). L'approche choisie est la polymérisation en émulsion en régime semi-continu. Cette approche permettra d'apporter un caractère hydrophobe (phase 1-Coeur) favorisant la barrière à l'humidité et un caractère hydrophile (phase 2-Ecorce) en surface présentant des groupes fonctionnels favorables à l'adhésion métal en condition humide. De plus nous avons aussi investigué l'influences de divers additifs de formulations afin d'optimiser les propriétés du primaire d'accroche. Les latex présentant une structure de type cœur/écorce est très favorable pour la barrière à l'humidité. En effet ces latex présentent une perméabilité à l'eau sensiblement plus faible que les latex sans structure (100% composition de l'écorce). Concernant la perméabilité à l'oxygène celle-ci est principalement assurée par la couche métallique. La formulation de nos latex cœur/écorce par des agents mouillants s'est révélé indispensable pour assurer un bon étalement de nos latex sur le substrat PET. En effet nos latex issus de la synthèse ont été synthétisés avec un minimum de tensio-actif, ce qui a eu pour effet négatif d'obtenir une tension de surface trop élevée pour assurer leur mouillabilité sur le film PET. De plus cet agent mouillant a aussi montré une influence positive sur les performances d'adhésion de la couche métal sur le film PET traité avec le primaire d'accroche. La formulation de nos latex cœur/écorce par un réticulant a montré un influence positive sur les propriétés barrières aux gaz et sur les performances d'adhésion métal. Cet agent réticulant tend à favoriser la réticulation entre particule et ainsi favoriser la formation d'un film continu barrière à l'eau. De plus celui-ci apporte des fonctions de type azoté favorable aux interactions avec les atomes métallique (aluminium)The proposition of this work is to improve the barrier property of a laminate aimed to be applied in the field of packaging for foodstuffs. This laminate is constituted by a PET substrate metallized with aluminum deposited under vacuum. Given that PET is not a strongly polar polymer it is necessary to improve its adhesion to metals. This study was carried out in order to understand if there is a way to make sure that the polar groups will be bonded to the metal without being disturbed by the conditions of the environment. Our approach was the semi-batch emulsion polymerization, followed by the restructuration of the initial system (regular spherical polymeric nanoparticles) by changing its original morphology. Finally, the latexes were formulated by using variable amounts of compounds that were expected to improve the properties of the final material in terms of barrier and metallic adhesion. A part of the latexes synthesized in the scope of this work was submitted to pilot trials in an industrial line of PET extrusion. The latexes were used to coat the PET inline. The core-shell nanoparticles presented a lower permeability to water than the particles synthesized in the absence of the seed. This was related to the tortuosity promoted by the core, which increases the pathway of a diffusing molecule. The permeability to oxygen was found to be mainly related to the metallic layer. Given that the latexes were synthesized with the minimum amount of tensioactive necessary to originate stable dispersions, the wettability agent was found to be indispensable for the proper spreading of the coatings onto the PET. Furthermore, this compound played an important role on the adhesion property of the films. The cure agent, in the correct concentration, promotes the adhesion to metallic substrates. Moreover, this compound helped to prevent the interaction of the wettability agent with the water, decreasing consequently the plasticization of the structure in conditions of high humidit

Monitoring of the Parasite Load in the Digestive Tract of <i>Rhodnius prolixus</i> by Combined qPCR Analysis and Imaging Techniques Provides New Insights into the Trypanosome Life Cycle

<div><p>Background</p><p>Here we report the monitoring of the digestive tract colonization of <i>Rhodnius prolixus</i> by <i>Trypanosoma cruzi</i> using an accurate determination of the parasite load by qPCR coupled with fluorescence and bioluminescence imaging (BLI). These complementary methods revealed critical steps necessary for the parasite population to colonize the insect gut and establish vector infection.</p><p>Methodology/Principal Findings</p><p>qPCR analysis of the parasite load in the insect gut showed several limitations due mainly to the presence of digestive-derived products that are thought to degrade DNA and inhibit further the PCR reaction. We developed a real-time PCR strategy targeting the <i>T</i>. <i>cruzi</i> repetitive satellite DNA sequence using as internal standard for normalization, an exogenous heterologous DNA spiked into insect samples extract, to precisely quantify the parasite load in each segment of the insect gut (anterior midgut, AM, posterior midgut, PM, and hindgut, H). Using combined fluorescence microscopy and BLI imaging as well as qPCR analysis, we showed that during their journey through the insect digestive tract, most of the parasites are lysed in the AM during the first 24 hours independently of the gut microbiota. During this short period, live parasites move through the PM to establish the onset of infection. At days 3–4 post-infection (p.i.), the parasite population begins to colonize the H to reach a climax at day 7 p.i., which is maintained during the next two weeks. Remarkably, the fluctuation of the parasite number in H remains relatively stable over the two weeks after refeeding, while the populations residing in the AM and PM increases slightly and probably constitutes the reservoirs of dividing epimastigotes.</p><p>Conclusions/Significance</p><p>These data show that a tuned dynamic control of the population operates in the insect gut to maintain an equilibrium between non-dividing infective trypomastigote forms and dividing epimastigote forms of the parasite, which is crucial for vector competence.</p></div

Comparison of time-course development of epimastigotes and trypomastigotes expressing luciferase in the digestive tract of <i>R</i>. <i>prolixus</i> during the first 24 h p.i., in the presence or absence of <i>R</i>. <i>rhodnii</i>.

<p>(A) Representative values of the luminescence emission for epimastigotes and trypomastigotes at 6 h and 24 h. Epi 6 h vs. Epi 24 h, P<0.01; Trypo 6 h vs. Trypo 24 h, P<0.0001. ANOVA followed by Tukey's multiple comparisons test. (B) Quantification of the BLI signal emitted by adult insects infected with various amounts of epimastigotes (Epi) or trypomastigotes (Trypo). (C) Quantification of the BLI signal emitted by gut microbiota-free first instar nymphs fed with epimastigote (Epi) or trypomastigote (Trypo) forms (10⁷ cells/ml), in the presence or absence of <i>R</i>. <i>rhodnii</i>. In each stage ± bacteria, 6 h vs. 24 h, P<0.001. ANOVA followed by Tukey's multiple comparisons test.</p

BLI of infected insects after feeding.

<p><i>In vivo</i> (A, B) and e<i>x vivo</i> (C) BLI showing that at one to two weeks after refeeding, most of the parasites remains densely packed in the rectum, as evidenced by the punctuated luminescent signal located at the end of the digestive tract.</p

Real-time monitoring of <i>R</i>. <i>prolixus</i> gut colonization by <i>T</i>. <i>cruzi</i> in natural conditions.

<p>Follow-up of parasite development in the anterior midgut (AM), posterior midgut (PM) and hindgut (H) post-infection (p.i.) and post-feeding (p.f.) in epimastigotes (A) and metacyclics trypomastigotes (B). Adult insects were fed with 10⁷ cells/ml. The arrowhead and arrow indicates, respectively, the time of the initial infection a trypomastigotes and refeeding (21 days p.i.). At several time points, the insects were dissected, and total DNA was extracted individually from the different gut segments and used to assess the parasite number by qPCR. Each time point represents an experiment (n = 8).</p

BLI time-course development of <i>T</i>. <i>cruzi</i> expressing luciferase in the insect digestive tract during the first 24 h p.i.

<p>(A) The images show the drastic reduction of the luminescence signal in the AM. (B) Quantification of the BLI signal emitted by the whole intestine obtained at different times as indicated in A. (C) <i>Ex vivo</i> BLI confirming that the signal was located exclusively in PM 24 hours p.i.. (D) Quantification of the BLI signal emitted by AM (a) and PM (b) at 0 and 24 hours after infection. (E) Effect of the microbiota on parasite lysis and BLI reduction. The insects were infected with parasites alone (Tc) or with parasites plus 2.5 x 10⁷ or 2.5 x 10⁸<i>Rhodococcus rhodnii</i> per ml of blood. Two independent experiments (n = 16) were conducted, and the results were analyzed by one-way ANOVA.</p

Real-time monitoring of <i>T</i>. <i>cruzi</i> loads in the different gut segments after <i>R</i>. <i>prolixus</i> infection.

<p>(A) Follow-up of parasite development in the anterior midgut (AM), posterior midgut (PM) and hindgut (H) post-infection (p.i.) and post-feeding (p.f.). Adult insects were fed with 10⁷ cells/ml of blood. The arrowhead and arrow indicates, respectively, the time of the initial infection and refeeding with a blood meal without parasites (21 days p.i.). Each time point represents three independent experiments (n≥8). The percentage of metacyclic trypomastigote forms (mean ± SE; n = 10) determined in the hindgut contents at 7 and 14 days p.i. and 14 days p.f. are indicated. (B) Monitoring of the DNA clearance of heat-killed parasites. Infections were performed with live parasites or parasites killed by incubation at 65°C during 2 hours before injection. n≥4 for each time point. (C) Comparison between the gut colonization of <i>R</i>. <i>prolixus</i> by <i>T</i>. <i>cruzi</i> Dm28c (left panel) and CL Brener (right panel). Each time point represents three independent experiments (n≥8). At several time points, the insects were dissected, and total DNA was extracted individually from the different gut segments and used to assess the parasite number by qPCR.</p

NEOTROPICAL CARNIVORES: a data set on carnivore distribution in the Neotropics

Mammalian carnivores are considered a key group in maintaining ecological health and can indicate potential ecological integrity in landscapes where they occur. Carnivores also hold high conservation value and their habitat requirements can guide management and conservation plans. The order Carnivora has 84 species from 8 families in the Neotropical region: Canidae; Felidae; Mephitidae; Mustelidae; Otariidae; Phocidae; Procyonidae; and Ursidae. Herein, we include published and unpublished data on native terrestrial Neotropical carnivores (Canidae; Felidae; Mephitidae; Mustelidae; Procyonidae; and Ursidae). NEOTROPICAL CARNIVORES is a publicly available data set that includes 99,605 data entries from 35,511 unique georeferenced coordinates. Detection/non-detection and quantitative data were obtained from 1818 to 2018 by researchers, governmental agencies, non-governmental organizations, and private consultants. Data were collected using several methods including camera trapping, museum collections, roadkill, line transect, and opportunistic records. Literature (peer-reviewed and grey literature) from Portuguese, Spanish and English were incorporated in this compilation. Most of the data set consists of detection data entries (n = 79,343; 79.7%) but also includes non-detection data (n = 20,262; 20.3%). Of those, 43.3% also include count data (n = 43,151). The information available in NEOTROPICAL CARNIVORES will contribute to macroecological, ecological, and conservation questions in multiple spatio-temporal perspectives. As carnivores play key roles in trophic interactions, a better understanding of their distribution and habitat requirements are essential to establish conservation management plans and safeguard the future ecological health of Neotropical ecosystems. Our data paper, combined with other large-scale data sets, has great potential to clarify species distribution and related ecological processes within the Neotropics. There are no copyright restrictions and no restriction for using data from this data paper, as long as the data paper is cited as the source of the information used. We also request that users inform us of how they intend to use the data