Durability of crosslinked polydimethylsyloxanes: the case of composite insulators

Most applications of silicones are linked to their hydrophobic properties and (or) their high resistance to ageing (e.g. thermal ageing and photoageing). However, when placed in extreme environments, these materials can fail as in the case of epoxy/fiber glass composite powerlines insulators, where crosslinked polymethylsyloxanes (PDMSs) are used as the protective envelope (housing) of the insulator. We report on the behavior of both pure/noncrosslinked PDMSs and typical formulations used in industrial insulators, i.e. containing peroxide crosslinked PDMS, alumina trioxide hydrated (ATH) and silica. Special attention is paid on both (i) the sources of potential degradation and (ii) the best analytical methods that can be applied to the study of very complex formulations. (i) Aside from conventional types of ageing such as photo-ageing and thermal, hydrolytic, and service life ageings, treatments with acidic vapors, plasma and ozone possibly generating species from the reaction of a high electric field with air were also performed, which allowed to accelerate electrical and out-door ageings and to obtain differently aged materials. (ii) Aside from conventional analytical methods of polymer degradation such as FTIR/ATR spectroscopy and SEC, TG, hardness measurements, more specific methods like photo/DSC, TG/IR, thermoporosimetry, resistivity and density measurements were also performed to characterize the chemical and physical evolutions of polymer materials. In particular, it was found that treatment with nitric acid vapor has detrimental effects on the properties of both fire retardants (e.g. ATH) and PDMSs, affecting the hardness and resistivity of the formulated material.     

Preferential Oxidation of Carbon Monoxide in the Presence of Hydrogen (PROX) over Noble Metals and Transition Metal Oxides: Advantages and Drawbacks

The steam reforming reaction of hydrocarbons and organic fuels, in general, is followed by a two-stage reaction of water gas shift, which allows increasing the hydrogen yield and a final purification step for CO removal to use hydrogen in an ammonia plant or a PEM fuel cell. This paper is focused on the CO Preferential Oxidation, CO PROX (or CO selective oxidation in excess hydrogen) reaction, considered as the simplest and cost effective process to achieve the less than 10 ppm CO. The objective of this paper is to review the performances of noble metals (Pt, Ru, Rh, Pd), gold and transition metal oxides catalysts in this reaction. Although the results reported are largely influenced by the experimental conditions (reactant flow composition, mass of catalyst, duration of experiment …) a comparison of advantages and drawbacks for each type of catalysts is proposed in terms of activity and selectivity as well as of CO₂ and H₂O influences. A special attention will be paid to copper-doped ceria catalysts which appear to be very active and selective in a range of temperatures appropriate for fuel cell application. The performances, the stability and the low cost of these formulations compared to noble metal-based catalysts make them very attractive for an industrial application.     

Fluorescent agonists for the Torpedo nicotinic acetylcholine receptor

We have synthesized a series of fluorescent acylcholine derivatives carrying different linkers that vary in length and structure and connect the acylcholine unit to the environment-sensitive fluorophores 7-(diethylamino)coumarin-3-carbonyl (DEAC) or N-(7-nitrobenz-2-oxa-1,3-diazol-yl) (NBD). The pharmacological properties of the fluorescent analogues were investigated on heterologously expressed nicotinic acetylcholine receptor (nAChR) from Torpedo californica and on oocytes transplanted with nAChR-rich Torpedo marmorata membranes. Agonist action strongly depends on the length and the structure of the linker. One particular analogue, DEAC-Gly-C6-choline, showed partial agonist behavior with about half of the maximum response of acetylcholine, which is at least 20 times higher than those observed with previously described fluorescent dansyl- and NBD-acylcholine analogues. Binding of DEAC-Gly-C6-choline to Torpedo nAChR induces a strong enhancement of fluorescence intensity. Association and displacement kinetic experiments revealed dissociation constants of 0.5 nM for the alphadelta-binding site and 15.0 nM for the alphagamma-binding site. Both the pharmacological and the spectroscopic properties of this agonist show great promise for characterizing the allosteric mechanism behind the function of the Torpedo nAChR, as well as for drug-screening studies.     

Development of a PCR test to differentiate between Staphylococcus aureus and Staphylococcus intermedius

The presence of Staphylococcus intermedius in food remains unclear because routine laboratory analysis does not discriminate between S. intermedius and Staphylococcus aureus, a major cause of food poisoning. Both species share many phenotypic characteristics, including coagulase and thermonuclease production. In both species, some strains can produce enterotoxin and therefore can be the cause of food poisoning outbreaks. Although the ID32 Staph System (bioMérieux, SA, Marcy l'Etoile, France), based on a miniaturized phenotypic characterization, gives satisfactory results for discriminating between these two species, some rapid molecular PCR-based methods have been developed to identify S. aureus specifically, but they do not identify S. intermedius. Here, we developed a rapid, accurate, and discriminative multiplex PCR method that targets species-specific sequences in the nuc gene, which encodes thermonuclease in the two species. The test includes an internal positive control that targets a highly conserved region of 16S ribosomal RNA gene (rDNA). A total of 116 strains were used to validate our test. The test gave no signal on the following Staphylococcus species: S. epidermidis, S. chromogenes, S. hyicus, S. warneri, S. xylosus, S. lentus, and S. sciuri. It allowed a 100% successful discrimination between S. aureus (44 strains tested) and S. intermedius (57 strains) isolated from different origins.     

Microstructure, rheology and storage stability of low-fat yoghurt structured by carrot cell wall particles

Plant cell wall particles derived from fruits and vegetables are natural fibre materials with a low calorie content that can be used as a healthy alternative to gum stabilisers and starches for structuring low-fat yoghurt. In this study we investigated the effect of cell wall particle (CWP) addition on the gelation kinetics, viscoelastic properties, microstructure, texture and whey loss of the set yoghurt gels as a function of CWP concentration, particle size and storage time. Three particle sizes of dried carrot CWP (d_0.5 = 34, 71 and 80 ??m) were produced from an industrial carrot pomace. Rehydrated CWP was added to skim milk prior to acidification. The results showed that the addition of carrot CWP accelerated the rate of pH reduction and induced earlier gelation. The gel viscoelastic properties were enhanced with increased CWP concentration. This was accompanied with progressive reduction in the whey loss. The smallest cell wall particles (d_0.5 = 34 ??m) gave better gel strength and lower whey loss compared to the larger CWP particles, possibly due to higher contact between the CWP and casein particles thus contributing to the stronger gel network. The CLSM images of yoghurt gels containing CWP showed that carrot CWP occupied the void space within casein particle network. The enhanced gel strength and reduced whey loss achieved by the addition of CWP were maintained throughout the 28 day storage period. The reduction of fermentation processing by almost 1 h, yet still achieving good gel properties for the yoghurt type product could be a significant benefit from a manufacturing point of review.     

Probiotics intake and metabolic syndrome: A proposal

Probiotics are practical tools to provide the modulation of microbiota. The ingestion of food or ingredients containing anti-inflammatory activity components as probiotics should be useful in obesity control and associated co-morbidities treatment. Metabolic syndrome is a metabolic dysfunction associated with visceral obesity and insulin resistance, in which the alterations in host-microbiota interactions play an important role. Besides diet and physical activity, new strategies are necessary to control metabolic syndrome, and as consequence improving quality of life. This article revises the actual knowledge concerning probiotic intake and obesity as a proposal to control metabolic syndrome.     

Modeling heat resistance of Bacillus weihenstephanensis and Bacillus licheniformis spores as function of sporulation temperature and pH

Although sporulation environmental factors are known to impact on Bacillus spore heat resistance, they are not integrated into predictive models used to calculate the efficiency of heating processes. This work reports the influence of temperature and pH encountered during sporulation on heat resistance of Bacillus weihenstephanensis KBAB4 and Bacillus licheniformis AD978 spores. A decrease in heat resistance (δ) was observed for spores produced either at low temperature, at high temperature or at acidic pH. Sporulation temperature and pH maximizing the spore heat resistance were identified. Heat sensitivity (z) was not modified whatever the sporulation environmental factors were. A resistance secondary model inspired by the Rosso model was proposed. Sporulation temperatures and pHs minimizing or maximizing the spore heat resistance (T(min(R)), T(opt(R)), T(max(R)), pH(min(R)) and pH(opt(R))) were estimated. The goodness of the model fit was assessed for both studied strains and literature data. The estimation of the sporulation temperature and pH maximizing the spore heat resistance is of great interest to produce spores assessing the spore inactivation in the heating processes applied by the food industry.     

Proteolytic activity monitored by fluorescence resonance energy transfer through quantum-dot-peptide conjugates

Proteases are enzymes that catalyse the breaking of specific peptide bonds in proteins and polypeptides. They are heavily involved in many normal biological processes as well as in diseases, including cancer, stroke and infection. In fact, proteolytic activity is sometimes used as a marker for some cancer types. Here we present luminescent quantum dot (QD) bioconjugates designed to detect proteolytic activity by fluorescence resonance energy transfer. To achieve this, we developed a modular peptide structure which allowed us to attach dye-labelled substrates for the proteases caspase-1, thrombin, collagenase and chymotrypsin to the QD surface. The fluorescence resonance energy transfer efficiency within these nanoassemblies is easily controlled, and proteolytic assays were carried out under both excess enzyme and excess substrate conditions. These assays provide quantitative data including enzymatic velocity, Michaelis-Menten kinetic parameters, and mechanisms of enzymatic inhibition. We also screened a number of inhibitory compounds against the QD-thrombin conjugate. This technology is not limited to sensing proteases, but may be amenable to monitoring other enzymatic modifications.