Ultrafiltrative separation of rhamnolipid from culture medium

Classic methods of biosurfactant separation are difficult and require large amounts of organic solvents, thus generate high amounts of waste. This work presents and discusses in detail an original procedure to separate rhamnolipid from fermentation broth using high performance membrane techniques. Due to the unique properties of surface active agents, such as capability of forming aggregates above the critical micelle concentration, it is possible to easily purify the biosurfactant with high efficacy using inexpensive and commonly used membranes. In this article, two-stage ultrafiltration is proposed as a method for separating and purifying rhamnolipid from the culture medium. The obtained purified rhamnolipid solution was capable of reducing surface tension of water down to 28.6 mN/m at critical micelle concentration of 40 mg/l. Separation of rhamnolipid was confirmed by HPLC; three types of rhamnolipids were identified (RL1, RL2, RL4), with considerable predominance of RL2

Oxidation of Hydrocarbons on the Surface of Tin Dioxide Chemical Sensors

The paper presents the results of our investigation on the effect of the molecular structure of organic vapors on the characteristics of resistive chemical gas sensors. The sensors were based on tin dioxide and prepared by means of thick film technology. The electrical and catalytic examinations showed that the abstraction of two hydrogen atoms from the organic molecule and formation of a water in result of reaction with a chemisorbed oxygen ion, determine the rate of oxidation reactions, and thus the sensor performance. The rate of the process depends on the order of carbon atoms and Lewis acidity of the molecule. Therefore, any modification of the surface centers of a sensor material, modifies not only the sensor sensitivity, but also its selectivity

Adsorption of Silver Nanoparticles on Glass Beads Surface

Colloidal silver is widely used owing to its specific properties, which enable it to be applied in various fields. In this work, adsorption of commercially available silver nanoparticles (AgNPs; NanoSilver PVP 1000) on glass beads was investigated. The glass microspheres (70–110 μm) were used as model particles. The adsorption of AgNPs on the glass beads surface was investigated in terms of adsorbent dosage. The adsorption isotherm was determined with the adsorbent dosage of 100 g/l and the AgNPs in range 100–1000 mg/l. It was found that adsorption isotherm data best fitted the Langmuir model. Kinetics of AgNPs adsorption onto glass beads followed a pseudo-second-order model. The interaction between glass microspheres surface and polyvinylpyrrolidone (PVP)-coated AgNPs is due to hydrogen bonding with oxygen of carbonyl groups of PVP and silanol groups on the glass surface

Silver nanoparticles as a control agent against facades coated by aerial algae—A model study of <i>Apatococcus lobatus</i> (green algae)

<div><p>Aerial algae are an important biological factor causing the biodegradation of building materials and facades. Conservation procedures aimed at the protection of historic and utility materials must be properly designed to avoid an increase of the degradation rate. The aim of the present study was to investigate the effect of silver nanoparticles (AgNP) synthetized with features contributing to the accessibility and toxicity (spherical shape, small size) on the most frequently occurring species of green algae in aerial biofilms and thus, the most common biodegradation factor–<i>Apatococcus lobatus</i>. Changes in the chloroplasts structure and the photosynthetic activity of the cells under AgNP exposure were made using confocal laser microscopy and digital image analysis and the estimation of growth inhibition rate was made using a biomass assay. In the majority of cases, treatment with AgNP caused a time and dose dependant degradation of chloroplasts and decrease in the photosynthetic activity of cells leading to the inhibition of aerial algae growth. However, some cases revealed an adaptive response of the cells. The response was induced by either a too low, or—after a short time—too high concentration of AgNP. Taken together, the data suggest that AgNP may be used as a biocide against aerial algal coatings; however, with a proper caution related to the concentration of the nanoparticles.</p></div

Extinction of chlorophyll fluorescence emission in the <i>A</i>. <i>lobatus</i> cells treated with AgNP concentrations.

<p>The digital images were captured every hour/day of the experiment using the Leica TCS SP8 Confocal Laser Microscope.</p

The photosynthetic activity inhibition ratio (RIA^ph) and the growth inhibition ratio (RI^g) of the <i>A</i>. <i>lobatus</i> cells treated with AgNP concentrations at every hour/day of the experiment and the concurrent chlorophyll fluorescence intensity (^chlFI) and biomass (B) of the control cells; the statistical significance at the 0.05 level.

<p>The photosynthetic activity inhibition ratio (RIA^ph) and the growth inhibition ratio (RI^g) of the <i>A</i>. <i>lobatus</i> cells treated with AgNP concentrations at every hour/day of the experiment and the concurrent chlorophyll fluorescence intensity (^chlFI) and biomass (B) of the control cells; the statistical significance at the 0.05 level.</p

Percentage of the growing inhibition rate and the biocidal effect of AgNP against aerophytic algal cells after 14 days of AgNP exposure.

<p>Percentage of the growing inhibition rate and the biocidal effect of AgNP against aerophytic algal cells after 14 days of AgNP exposure.</p