A study of the durability of boundary films

The frictional properties of solid surfaces are modified by the adsorption of organic molecular films. The lifetime of a monomolecular film of a fatty acid which was deposited on a surface to form a solid/monolayer/air interface has been investigated.The continual presence of an agglomerate has been observed during frictional contact under boundary lubrication conditions. This agglomerate is composed of several substances resulting from the deterioration and recombination of fatty acid molecules with each other and/or the surrounding media.     

A two-dimensional high-performance thin-layer chromatographic screening method for sulphonamides in animal tissues

Summary A procedure for the identification of sulphonamides in edible animal tissues by two-dimensional high-performance thin-layer chromatography is described. Sixteen sulphonamides can be detected at an absolute level of 10 ng. The absolute detection limit of the sulphonamide standards is 1 ng. After extraction of the sulphonamides with chloroform/acetone, the acidified extract is concentrated and purified using a cation-exchange solid phase extraction column. The column is treated with ammonia vapour and the sulphonamides are then eluted with methanol. Blank samples of edible animal tissues spiked with sulphonamides (frequently used in Belgium) result in very good separation.

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Identifizierung von sulfonamiden in geweben von schlachttieren mittels zweidimensionaler hochleistungsdünnschichtchromatographie

Zusammenfassung Eine Methode zur Identifizierung von Sulfonamiden in Geweben von Schlachttieren mittels zweidimensionaler Hochleistungsdünnschichtchromatographie wird beschrieben. 16 Sulfonamide können identifiziert werden, wobei die absolute Empfindlichkeitsgrenze bei 10 ng liegt. Die absolute Nachweisgrenze für die Referenzsubstanzen liegt bei 1 ng. Nach Extraktion der Sulfonamide mit Chloroform-Aceton wird die angesäuerte Extraktlösung auf einer Kationenaustausch-Extraktionssäule eingeengt und gereinigt. Die Säule wird mit Ammoniakdämpfen behandelt und die Sulfonamide werden anschliessend mit Methanol eluiert. Die den Gewebeextrakten zugefügten in Belgien häufig verwendeten Sulfonamide konnten sehr gut voneinander getrennt werden.

     

Polymorphisme de l'hydrure de magnesium sous haute pression

The structural relationships in magnesium hydride have been studied under P-T conditions up to 80 kbar and 900°C. α-MgH₂ of rutile structure in normal conditions transforms into two new phases under high pressures : β-MgH₂ and γ-MgH₂ respectively with a hexagonal (pseudocubic) and an orthorhombic unit-cell structure·β-MgH₂ maybe related to a fluorite type form (with an eight-coordination for Mg) transforming when releasing pressure into γ-MgH₂ of α-PbO₂ type (with a six-coordination for Mg). The density of α-MgH₂ and γ-MgH₂ are very similar but the density of the β-MgH₂ fluorite form is some 25 % greater than that of the rutile type. Thus MgH₂ seems to exhibit under high pressure conditions the typical behavior of number of rutile type compounds MX₂ such as fluorides or oxides.     

Structure, orientation, and conformational changes in transmembrane domains of multidrug transporters

Multidrug transporter proteins promote the active transmembrane efflux of noxious drugs, thereby decreasing their accumulation in the intracellular medium and reducing their therapeutic efficiency. Expression of such proteins drastically reduces the efficiency of chemotherapeutic treatments against cancer and various infectious diseases. To overcome major difficulties related to the crystallization of membrane proteins, other experimental approaches have been developed to gain information on the structural changes involved in drug transport. We examine here and illustrate with a few examples how infrared and fluorescence spectroscopy can provide new insights into the structure of the membrane domains of multidrug transporters in particular. Such domains contain the drug-binding site(s) and mediate the passage of substrates across the cell membrane.     

Variability estimation of urban wastewater biodegradable fractions by respirometry

This paper presents a methodology for assessing the variability of biodegradable chemical oxygen demand (COD) fractions in urban wastewaters. Thirteen raw wastewater samples from combined and separate sewers feeding the same plant were characterised, and two optimisation procedures were applied in order to evaluate the variability in biodegradable fractions and related kinetic parameters. Through an overall optimisation on all the samples, a unique kinetic parameter set was obtained with a three-substrate model including an adsorption stage. This method required powerful numerical treatment, but improved the identifiability problem compared to the usual sample-to-sample optimisation. The results showed that the fractionation of samples collected in the combined sewer was much more variable (standard deviation of 70% of the mean values) than the fractionation of the separate sewer samples, and the slowly biodegradable COD fraction was the most significant fraction (45% of the total COD on average). Because these samples were collected under various rain conditions, the standard deviations obtained here on the combined sewer biodegradable fractions could be used as a first estimation of the variability of this type of sewer system.     

Plasma hormone levels in normal and lead-treated pregnant mice

Dietary lead (0.5%) was given to mice which, after mating, exhibited a vaginal plug. Estradiol, progesterone and prostaglandins E and F 2 alpha were determined in the plasma by radioimmuno assay at different times thereafter. The increase in estradiol and decrease in prostaglandins prior implantation are not greatly altered by lead treatment, whereas the subsequent increase in progesterone and later in estradiol is abolished. It is concluded that the lower number of pregnancies seen in lead-treated mothers is due to a maternal hormonal imbalance caused by lead.     

Modified Galacto- or Fuco-Clusters Exploiting the Siderophore Pathway to Inhibit the LecA- or LecB-Associated Virulence of Pseudomonas aeruginosa

Galacto- and fuco-clusters conjugated with one to three catechol or hydroxamate motifs were synthesised to target LecA and LecB lectins of Pseudomonas aeruginosa (PA) localised in the outer membrane and inside the bacterium. The resulting glycocluster–pseudosiderophore conjugates were evaluated as Trojan horses to cross the outer membrane of PA by iron transport. The data suggest that glycoclusters with catechol moieties are able to hijack the iron transport, whereas those with hydroxamates showed strong nonspecific interactions. Mono- and tricatechol galactoclusters ( G1C and G3C ) were evaluated as inhibitors of infection by PA in comparison with the free galactocluster ( G0 ). All of them exhibited an inhibitory effect between 46 to 75 % at 100 μM, with a higher potency than G0 . This result shows that LecA localised in the outer membrane of PA is involved in the infection mechanism.     

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.     

Mitigation of Temperature Gradients in the Buffer Tank of a Natural Circulation Loop Simulating Passive Decay Heat Removal in a Pool Type Reactor

Abstract

This study considers the decay heat removal through passive systems (i.e., natural convection) in the pool-type experimental reactor MYRRHA (SCK?CEN). The low velocities associated with natural convection may cause a degradation of the thermal mixing in the upper plenum of the reactor: buoyancy dominated phenomena, such as stratification, buoyant jets or convective cells may occur. The large temperature gradients associated with these phenomena may induce thermal loads on the structure, compromising its integrity. The objectives of this work are, in order, (1) achieving an understanding of the fluid mechanics leading to the formation of thermal gradients in the upper plenum and (2) mitigating the temperature gradients the upper plenum’s geometry. The methodology chosen to address the problem is experimental. A ''two-dimensional'' water facility modeling a slab of the reactor's primary loop was designed. Simultaneous measurements of velocity and temperature were performed in the model's buffer tank using thermocouples and innovative optical imaging techniques. It was observed that vertical thermal gradients develop in the tank because of the combined effect of stratification and advection. Important reductions of local gradients were observed when changing porosity and position of upper plenum’s buffer plates.     

Investigations of geometrical structure and morphology of samples made of hard machinable materials after wire electrical discharge machining and vibro‐abrasive finishing

In this article the results concerned influence of processing conditions of the wire electrical discharge machining and vibro‐abrasive machining on the surface layer and morphology of samples made of hard machinable materials used in aircraft industry like: Titanium 5553 β, Inconel 617, Hastelloy X and Magnesium AZ31 have been presented. For this purpose the cubic and cylindrical samples made of hard machinable alloys have been prepared using optimal electric parameters of wire‐cut electrical discharge machining and finally they have been polished using circular vibratory finishing technology and different ceramic shaped stones.