Lipase-catalyzed synthesis of hydrophobically modified dextrans: activity and regioselectivity of lipase from Candida rugosa

Vinyl decanoate-modified dextran macromolecules (DexT40-VD) were synthesized in dimethyl sulfoxide at 50°C using lipase AY from Candida rugosa for catalyzing transesterification between polysaccharide and vinyl fatty esters. The extent of dextran modification (quantified by the molar ratio of attached alkyl tails to sugar repeat units) with native-, pH-adjusted-, 18-crown-6 ether pretreated pH-adjusted-, and stepwise addition of pretreated lipase AY yielded <3%, 49%, 64% and 96% modified dextran respectively. Lipase AY accelerated the transesterification of DexT40 from 2- to 63-fold higher than the non-catalyzed system. This procedure was extended to other acyl donors showing that modification pattern exhibited regioselectivity depending on acyl donor structure. Regioselectivity equaled between 2- and 3-OH with saturated fatty acyl donors. The 2-OH was favored for unsaturated fatty acyl donors, while sterically hindered acyl donors oriented modification toward 3-OH position. DexT40-VD at 96% modification was a water-insoluble polymer forming 150nm diameter nanoparticles in water which can be used as drug carrier systems.     

Mycobacterium behavior in wastewater treatment plant, a bacterial model distinct from Escherichia coli and Enterococci

Mycobacteria are waterborne emerging pathogens causing infections in human. Mycobacteria have been previously isolated from wastewater and sludge, but their densities were not estimated due to cultural biases. In order to evaluate the impact of wastewater treatment processes on mycobacteria removal, we used a real time PCR method. First we compared six DNA extraction methods and second we used the more efficient DNA extraction procedure (i.e., enzymatic lysis combined with hexadecyltrimethylammonium bromide-NaCl procedure) in order to quantify Mycobacterium. With the aim to identify parameters that could serve as indicator of mycobacterial behavior, mycobacterial densities were measured in parallel to those of Escherichia coli and enterococci, and to concentrations of chemical parameters usually monitored in wastewater. Mycobacterium reached 5.5 × 10? ± 3.9 × 10? copies/L in the influent, but was not detected in the effluent after decantation and biofiltration. Most mycobacteria (98.6 ± 2.7%, i.e. 2.4 ± 0.7 log??) were removed by the physical-chemical decantation, and the remaining mycobacteria were removed by biofiltration. In contrast, enterococci and E. coli were lightly removed by decantation step and mainly removed by biofiltration. Our results showed that Mycobacterium corresponds to a hydrophobic behavior linked to insoluble compound removal, whereas enterococci and E. coli refer to hydrophilic behaviors linked to soluble compound removals.     

Could any graph be turned into a small-world?

In addition to statistical graph properties (diameter, degree, clustering, etc.), Kleinberg [The small-world phenomenon: an algorithmic perspective, in: Proc. 32nd ACM Symp. on Theory of Computing (STOC), 2000, pp. 163–170] showed that a small-world can also be seen as a graph in which the routing task can be efficiently and easily done in spite of a lack of global knowledge. More precisely, in a lattice network augmented by extra random edges (but not chosen uniformly), a short path of polylogarithmic expected length can be found using a greedy algorithm with a local knowledge of the nodes. We call such a graph a navigable small-world since short paths exist and can be followed with partial knowledge of the network. In this paper, we show that a wide class of graphs can be augmented into navigable small-worlds.     

Effect of iron enrichment with GIC or FeCl3 on the pore structure and reactivity of coking coal

The effect of a Lewis acid addition to a coking coal on the porosity and reactivity towards steam of the resulting iron enriched coal chars are studied. GIC (FeCl₃ graphite intercalation compound) or free FeCl₃ are used as iron containing additives. Coal iron enrichment was performed using either directly FeCl₃ in vapour phase, or by mixing of coal and additives in decaline or by common grinding of coal and additives under argon. Iron enriched coals were carbonized at 750°C (heating RATE = 5°C min) and activation made with pure steam at 800°C to a burn-off off of 50 wt%. The pore structures of coal chars before and after activation were evaluated on the basis of CO₂ and C₆H₆ sorption at 25°C. A significant development of the microporosity is observed in the iron enriched char before activation and its steam reactivity is also increased. After activation, BET surface area values are increased in presence of iron, and porosity is mainly microporous.     

Transformation champ proche — champ lointain bidimensionnelle et monodimensionnelle appliquée à des mesures de SER

In high frequency thercs measurement of large target must be done at important distances, so the distance of measurement (Fraunhofer’s distance) R is given by R ≥ 2d² /λ where d is the tranversal length of the target and λ the radiation wavelength. In this paper we present a method for target that are large relative to the curvature of the spherical wavefront and the curvature of the cylindrical wavefront. A two-dimensional analytical algorithm transforms the spherical wave (near-field) measurement into the desired plane wave (far-field) and a one-dimensionnal analytical algorithm transforms the cylindrical wave (near-field) measurement into the desired plane wave (far-field). We present some results on simulations and measurements. A comparison of one-dimensional and two-dimensional methods demonstrates the efficiency of the two dimensional methods.     

Biobased packaging for improving preservation of fresh common mushrooms (Agaricus bisporus L.)

Freshness of common mushrooms was related to the internal atmosphere composition during modified atmosphere packaging (MAP) experiments at 20 °C and 80% RH with stretchable polyvinylchloride (PVC) film, paper, and the same paper coated with a wheat gluten solution. MAP with the stretchable film led to a detrimental deterioration of mushrooms after only one day of storage: dark brown blotches appeared and almost 30% of mushrooms exhibited open veil. This was due to the formation of condensed water at the inner surface of the material and onto mushrooms combined to a high O₂ partial pressure (16 kPa) in the headspace. Wheat gluten (WG) coated paper was the most effective to improve the shelf-life of mushrooms since it allowed the preservation of a fair colour, unbroken veils, and an acceptable texture during 3 days. This beneficial effect was attributed to the combination of a medium CO₂ (9.5 kPa) and low O₂ (2.5 kPa) partial pressure, without condensation. The main drawback of using WG-coated paper was its high water vapour permeability that led to an important weight loss (3.8 wt.% on day 3). However it did not affect the overall quality of mushrooms within the storage duration.

Industrial relevance

Even with the development of micro-perforated materials that provide the largest range of O₂ and CO₂ permeability values, several limitations are still encountered for synthetic MAP applications such as

– an insufficient perm-selectivity ratio that remains lower than 6 (value of 1 for micro-perforated material): generated atmosphere cannot reach both low O₂ and low CO₂ partial pressures and then are not adapted to CO₂-sensitive fresh produces.

– unattractive water condensation at the inner surface of the packaging that might occur due to a low water vapour permeability, favouring the development of microorganisms.

– their non biodegradability.

Previous studies reported a high selectivity ratio and a high water vapour permeability for biodegradable materials made from crops proteins (wheat gluten, for instance) that appeared well adapted for fresh fruits and vegetables preservation. However, despite low cost and such interesting functional properties, these materials exhibited poor mechanical properties and cannot be used as packaging material. Combination with other materials, such as cellulosic fibres, appeared to one way to get round this major drawback without losing its biodegradability. Indeed paper exhibits an environmental-friendliness potential (recyclability, sustainability, biodegradability, and compostability) and a high versatility in food packaging.By choosing common mushrooms, known to be sensitive to high CO₂ content, and a stretchable PVC film, commonly used to over-wrap mushrooms in tray (on European market), we demonstrate that this material was greatly less effective than a new biobased material (wheat gluten film coated onto paper) developed in collaboration with Smurfit Worldwide Research Center. This work confirms the interest in developing functionalised paper based packaging material with agro-based polymers adapted to the storage of fresh fruits and vegetable storage in ambient temperature.     

Interdiffusion between silica thin films and soda-lime glass substrate during annealing at high temperature

We study the diffusive interaction between soda-lime glass substrates and sputtered aluminum-doped silica thin films at 650°C, the temperature of commercial soda-lime glass shaping or tempering. A first rapid migration of alkali ions from substrate to thin film has been described in a companion paper (J Am Ceram Soc. 2018;101:1516). Using the same samples as (J Am Ceram Soc. 2018;101:1516), we focus here on later interactions, when the layer is consumed by the substrate resulting from diffusive interactions. Using Secondary Ion Mass Spectroscopy profilometry, we show that the interdiffusion rate increases with the aluminum doping content of the layer. We show that the alkali uptake of silica layers accelerates diffusive exchanges with the substrate, consistently with a decrease of viscosity of the layer. Diffusion profiles of silicon are well reproduced when solving the diffusion equation for a diffusivity having an exponential dependence with silicon concentration. The diffusivity of aluminum is shown to be 10 times slower than the diffusion of silicon. Specific exchanges of the two network formers with network modifiers are deduced from the composition-space trajectories, providing evidence for multicomponent diffusive couplings between species.     

Domestic refrigeration practices with emphasis on hygiene: analysis of a survey and consumer recommendations

A Web-enabled survey was conducted to improve knowledge of home refrigeration practices of French consumers (n = 809), with an emphasis on hygiene, and this information was used to establish recommendations. The survey targeted a convenience sample of working people. Analysis of the survey responses revealed that efforts should be directed toward improvement of microbiological control measures. Only 37% of respondents made sure the temperature in their refrigerator was 4 degrees C or below. Only 37% of respondents reported that they systematically wrapped food. Sponges, known to be frequently highly contaminated, were used by 89% of the respondents to clean their refrigerator, which indicates the need to recommend disinfection of sponges before they are used for cleaning. Twenty-seven percent of respondents used sodium hypochlorite (bleach), but it was applied without previous cleaning (21% of the users) or in the commercial concentrated form (7% of the users). The permanent presence of water condensation on the shelves was noted by 2% of respondents, suggesting imperfect closure of the door, with a consequence of higher energy consumption and water available for microbial circulation and growth. Thus, an important recommendation is to check the door gaskets and to ensure the tight closure of the door. Seventy percent of the respondents declared that they never put warm or hot food in the refrigerator. However, many people, when orally questioned, acknowledged that they leave dishes at ambient temperature overnight before putting them in the refrigerator. It therefore is essential to recommend that perishable food not be left for more than 2 h at ambient temperature.     

Emissions of DEHP‐free PVC flooring

Degrading 2‐ethylhexyl‐containing PVC floorings (eg DEHP‐PVC floorings) and adhesives emit 2‐ethylhexanol (2‐EH) in the indoor air. The danger of flooring degradation comes from exposing occupants to harmful phthalates plasticisers (eg DEHP), but not from 2‐EH as such. Since the EU banned the use of phthalates in sensitive applications, the market is shifting to use DEHP‐free and alternative types of plasticisers in PVC products. However, data on emissions from DEHP‐free PVC floorings are scarce. This study aimed at assessing the surface and bulk emissions of two DEHP‐free PVC floorings over three years. The floorings were glued on the screed layer of concrete casts at 75%, 85%, and 95% RH. The volatile organic compounds (VOCs) were actively sampled using FLEC (surface emissions) and micro‐chamber/thermal extractor (µ‐CTE, bulk emissions) onto Tenax TA adsorbents and analyzed with TD‐GC‐MS. 2‐EH, C9‐alcohols, and total volatile organic compound (TVOC) emissions are reported. Emissions at 75% and 85% RH were similar. As expected, the highest emissions occurred at 95% RH. 2‐EH emissions originated from the adhesive. Because the two DEHP‐free floorings tested emitted C9‐alcohols at all tested RH, it makes the detection of flooring degradation harder, particularly if the adhesive used does not emit 2‐EH.     

Cover Feature: A Comparative Study of in vitro Assays for Predicting the Nonspecific Binding of PET Imaging Agents in vivo (ChemMedChem 7/2020)

Nonspecific binding (NSB) is a key parameter in optimizing PET imaging tracers. We compared the ability to predict NSB of three available methods: LIMBA, rat f_u,brain, and CHI(IAM). Even though NSB is often associated with lipophilicity, we observed that logD does not correlate with any of these assays, clearly indicating that lipophilicity, while influencing NSB, is insufficient to predict it. A cross-comparison of the methods showed that all three correlate and are useful predictors of NSB. The three assays, however, rank the molecules slightly differently, illustrating the challenge of comparing molecules within a narrow chemical space. We also noted that CHI(IAM) values more effectively predict V_NS, a measure of in vivo NSB in the human brain. CHI(IAM) measurements might be a closer model of the actual physicochemical interaction between PET tracer candidates and cell membranes, and seems to be the method of choice for the optimization of in vivo NSB.