Biophysical Features of Bacillithiol,the Glutathione Surrogate of Bacillus subtilis and other Firmicutes

Bacillithiol (BSH) is the major low‐molecular‐weight (LMW) thiol in many low‐G+C Gram‐positive bacteria (Firmicutes). Evidence now emerging suggests that BSH functions as an important LMW thiol in redox regulation and xenobiotic detoxification, analogous to what is already known for glutathione and mycothiol in other microorganisms. The biophysical properties and cellular concentrations of such LMW thiols are important determinants of their biochemical efficiency both as biochemical nucleophiles and as redox buffers. Here, BSH has been characterised and compared with other LMW thiols in terms of its thiol pK_a, redox potential and thiol–disulfide exchange reactivity. Both the thiol pK_a and the standard thiol redox potential of BSH are shown to be significantly lower than those of glutathione whereas the reactivities of the two compounds in thiol–disulfide reactions are comparable. The cellular concentration of BSH in Bacillus subtilis varied over different growth phases and reached up to 5 mM , which is significantly greater than previously observed from single measurements taken during mid‐exponential growth. These results demonstrate that the biophysical characteristics of BSH are distinctively different from those of GSH and that its cellular concentrations can reach levels much higher than previously reported.     

Determination of corrosion potential of coated hollow spheres

Copper hollow spheres were created on porous iron particles by electro-less deposition. The consequent Ni plating was applied to improve the mechanical properties of copper hollow micro-particles. Corrosion properties of coated hollow spheres were investigated using potentiodynamic polarisation method in 1 mol dm⁻³ NaCl solution. Surface morphology and composition were studied by scanning electron microscopy (SEM), light microscopy (LM) and energy-dispersive X-ray spectroscopy (EDX). Original iron particles, uncoated copper spheres and iron particles coated with nickel were studied as the reference materials. The effect of particle composition, particularly Ni content on the corrosion potential value was investigated. The results indicated that an increase in the amount of Ni coating layer deteriorated corrosion resistivity of coated copper spheres. Amount of Ni coating layer depended on conditions of Ni electrolysis, mainly on electrolysis time and current intensity. Corrosion behaviour of sintered particles was also explored by potentiodynamic polarisation experiments for the sake of comparison. Formation of iron rich micro-volumes on the particle surface during sintering caused the corrosion potential shift towards more negative values. A detailed study of the morphological changes between non-sintered and sintered micro-particles provided explanation of differences in corrosion potential (E_corr).     

Towards a Universal Method for the Stable and Clean Functionalization of Inert Perfluoropolymer Nanoparticles: Exploiting Photopolymerizable Amphiphilic Diacetylenes

Highly fluorinated materials are being widely investigated due to a number of peculiar properties, which are potentially useful for various applications, including use as lubricants, anti‐adhesive films, and substitutes for biological fluids for biomedical utilization. However, at present such potential is still poorly exploited. One of the major drawbacks that hampers the rapid development of nanoscale fluoro‐hybrid devices is the remarkable inertness of perfluoropolymeric materials that lack reactive functionalities, as they do not offer any functional groups that can be employed to covalently anchor organic molecules on their surface. In this paper, a convenient method for the stable biofunctionalization of strongly unreactive perfluoropolymer nanoparticles (PnPs) is reported. PnPs are easily coated with newly synthesized asymmetric diacetylenic monomer compounds (ADMs), thanks to PnP’s high propensity to interact with hydrophobic moieties. Once monomerically adsorbed onto PnPs, such suitably designed ADMs enable the formation of a robust polymeric shell around the perfluoroelastomer core via a clean UV‐promoted localized photopolymerization. Given the peculiar optical characteristics of PnPs, the coating of the particles can be monitored step by step using light scattering, which also allows estimation of the fraction of reacted monomers by competitive adsorption with smaller particles. The potential of this method for the biofunctionalization of PnPs is demonstrated with representative proteins and carbohydrates. Among them, the extension to avidin–biotin technology may broaden the scope and applicability of this strategy to potentially a large number of molecules of biomedical interest.     

RELATION BETWEEN THE DISSOLUTION REACTIVITY OF POWDER SUBSTANCES AND EFFICIENCY OF THEIR ELECTROPLATING

ABSTRACT

The importance of the passivation layer on Fe powder surfaces formed by oxides, hydroxides, and/or salts and water molecules is pointed out for both electrochemical oxidative dissolution of iron powder and electrodeposition of Ni layer on it. This layer behaves as ohmic contact resistance. The layer thickness affects the surface reactivity of the powder and is influenced by the way of preactivation the powder prior to the electrochemical process. A reliable voltammetric method reflecting the surface reactivity was found, theoretically treated, and experimentally verified by measuring the rate of electrochemical dissolution of Fe powder. The efficiency of Ni electrodeposition on this powder was determined in a series of independent electrolyses. The correlation between both later mentioned parameters was satisfying for small powder particle fractions as well as for activation procedures which include chemical step.     

Concentration of flavonoids and phenolic compounds in aqueous and ethanolic propolis extracts through nanofiltration

Propolis has a variable and complex chemical composition with high concentration of flavonoids and phenolic compounds present in the extract. The extract varies with the solvent used in extraction. Ethanol extracts more phenolic acid and polar compounds than water. Before their use in industry, extracts must be concentrated but the use of high temperatures can degrade some compounds. Membrane processes is an option that allows concentration at low temperatures. Nanofiltration was carried out with aqueous and ethanolic extracts and each extract results in two distinct fractions: permeate and retentate. The capacity of the membrane to retain the compounds was verified by spectrophotometric analysis: for aqueous solution, the membrane retained around 94% of the phenolic compounds and 99% of the flavonoids, while for the ethanolic solution these values were 53% and 90%, respectively. Ferulic acid retention index was 1.00 and 0.88 to aqueous and ethanolic solutions, respectively. Thus, the nanofiltration process showed high efficiency in the concentration of propolis extracts.     

Volatile compound production in Agave duranguensis juice fermentations using four native yeasts and NH4Cl supplementation

Nitrogen has a significant effect on the fermentation rate and the chemical composition of alcoholic beverages. Nitrogen deficiency during fermentation of Agave juice for mescal production can lead to slow fermentations and end-products with low aromatic compound variety. In this study, the effects of NH₄Cl supplementation on volatile compound formation in Agave duranguensis juice fermented at 28?°C with the native yeast strains Saccharomyces cerevisiae ITD00185, Hanseniaspora uvarum ITD00108, Torulaspora delbrueckii ITD00110 and Kluyveromyces marxianus ITD00211 were analysed. Nitrogen content in the Agave juice unsupplemented with NH₄Cl was low. In the control treatments, the four yeasts consumed nitrogen at approximately the same rate, almost completely finishing by 24?h. Nitrogen supplementation increased biomass production with S. cerevisie, H. uvarum and T. delbrueckii but not with K. marxianus. K. marxianus consumed the total assimilable nitrogen more slowly than the other strains in the supplemented fermentations. In addition, the volatile compound profile differed between the studied yeasts. Volatile compound production by S. cerevisiae, H. uvarum and K. marxianus was higher in the supplemented fermentations, compared to the unsupplemented ones. In T. delbrueckii, the initial volatile compound concentrations remained unchanged, or decreased for some compounds, with nitrogen supplementation. The initial acetic acid and vanillin concentrations decreased with all strains tested and nitrogen supplementation. Furthermore, the concentration of higher alcohols increased with S. cerevisiae and H. uvarum in the NH₄Cl-supplemented fermentations, but they decreased with T. delbrueckii and K. marxianus. In conclusion, the addition of an inorganic nitrogen source promotes microorganism metabolism, increases biomass formation and benefits the fermentation process.     

Antioxidant activity and polyphenol contents in Brazilian green propolis extracts prepared with the use of ethanol and water as solvents in different pH values

Propolis is a natural product with a variable and complex chemical composition associated with its high concentration on polyphenolic compounds. The effect of pH variation (2.0, 3.0, 4.3, 6.0 and 8.0) during aqueous and ethanolic propolis extraction was studied for up to 10 days. Total phenols and flavonoids contents were measured for the extracts by spectrophotometric assays. Antioxidant activity was measured by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP) and ferric thiocyanate (FTC) methods. The best time of extraction was up to 5 days for all samples. Basic aqueous extracts (pH 8.0) resulted in a higher concentration of compounds than the extract without pH modification, reaching an increase of 160% in flavonoids and 25% in phenols. Ethanolic extracts with pH variation resulted in an extract with 50% less polyphenols and 6% less flavonoids than extract without pH modification. The antioxidant activity was highest for ethanolic extract at pH 4.3 and aqueous extract at pH 8.0 – almost 90% and 45%, respectively, in DPPH method – and was related to the level of polyphenols by Pearson's correlations.     

Social and Heuristic Approaches to Credibility Evaluation Online

The tremendous amount of information available online has resulted in considerable research on information and source credibility. The vast majority of scholars, however, assume that individuals work in isolation to form credibility opinions and that people must assess information credibility in an effortful and time‐consuming manner. Focus group data from 109 participants were used to examine these assumptions. Results show that most users rely on others to make credibility assessments, often through the use of group‐based tools. Results also indicate that rather than systematically processing information, participants routinely invoked cognitive heuristics to evaluate the credibility of information and sources online. These findings are leveraged to suggest a number of avenues for further credibility theorizing, research, and practice.     

Measurement of Hydrodynamics and Dissolved Oxygen with a Polarographic Microelectrode

Besides for electrochemical analysis, polarographic electrodes can be used for the determination of hydrodynamic parameters in aqueous media. For this latter application, a three-segment microelectrode has been developed with which vectorial hydrodynamic parameters (liquid velocity and turbulence intensity) can be determined via electrodiffusion. With oxygen instead of the normally used ferri-/ferrocyanide system, the microelectrode can be employed for hydrodynamic measurements in aerated aqueous solutions independent on coalescence behavior. Experiments show that in contrast to Laser-Doppler Anemometry and Hotfilm Anemometry the electrodiffusion electrode can also be used in aerated solid suspensions. Moreover, using the probe with oxygen as the depolarizer, it is possible to measure hydrodynamic parameters and dissolved oxygen concentration at the same time. As an example, the simultaneous determination of hydrodynamics and oxygen in aerobic batch fermentation (Erwinia herbicola) is presented.