Simultaneous extraction and catalytic adsorptive stripping voltammetric measurement of Cr(VI) in solid samples

A fast, simple, sensitive and economical method for Cr(VI) extraction and determination in solid samples was developed and evaluated. The presented protocol for Cr(VI) determination in solid samples allows for simultaneous extraction and determination of Cr(VI) in one step. The procedure is based on a quantitative extraction method in which the complexing properties of diethylenetriaminepentaacetic acid (DTPA) were exploited to extract total Cr(VI) (soluble and insoluble forms) from the solid sample. A catalytic adsorptive stripping voltammetric technique is employed for direct determination of Cr(VI) in the extract. The effects of analytical parameters such as temperature, pH, composition and concentration of the supporting electrolyte (which simultaneously plays the role of extractant), extraction and accumulation time were investigated. The accuracy of the proposed procedure was tested by analyzing certified reference materials CRM 013 Paint Chips and CRM 019 Ash. The results obtained were compared with the results obtained using two other reference extraction procedures. The effects of potentially interfering ions which generally accompany Cr(VI) in natural samples on the Cr(VI) determination, with special notice to Cr(III) interference, are reported.     

Antimicrobial activity of parabens in submicron emulsions stabilized with lecithin

Antimicrobial efficacy of methyl and propylparaben combination as potential preservatives for submicron emulsions, and the effect of oil and lecithin concentration on the microbial growth were investigated. Parabens were ineffective in standard or doubled concentrations as per pharmacopoeial criteria. Poor growth inhibition and multiplication of reference strains point to protective and growth properties of submicron emulsions. No correlation was observed between oil/lecithin ratio and efficacy of parabens; partitioning of the latter into the oily phase and lipophilic domains could be the reason for such effect. Further studies are necessary to establish a stable and safe composition of such formulations.     

Reduced-illuminance autofluorescence imaging in ABCA4-associated retinal degenerations

The health of the retinal pigment epithelium (RPE) can be estimated with autofluorescence (AF) imaging of lipofuscin, which accumulates as a byproduct of retinal exposure to light. Lipofuscin may be toxic to the RPE, and its toxicity may be enhanced by short-wavelength (SW) illumination. The high-intensity and SW excitation light used in conventional AF imaging could, at least in principle, increase the rate of lipofuscin accumulation and/or increase its toxicity. We considered two reduced-illuminance AF imaging (RAFI) methods as alternatives to conventional AF imaging. RAFI methods use either near-infrared (NIR) light or reduced-radiance SW illumination for excitation of fluorophores. We quantified the distribution of RAFI signals in relation to retinal structure and function in patients with the prototypical lipofuscin accumulation disease caused by mutations in ABCA4. There was evidence for two subclinical stages of macular ABCA4 disease involving hyperautofluorescence of both SW- and NIR-RAFI with and without associated loss of visual function. Use of RAFI methods and microperimetry in future clinical trials involving lipofuscinopathies should allow quantification of subclinical disease expression and progression without subjecting the diseased retina/RPE to undue light exposure.     

Chronic Activation of AMPK Induces Mitochondrial Biogenesis through Differential Phosphorylation and Abundance of Mitochondrial Proteins in Dictyostelium discoideum

Mitochondrial biogenesis is a highly controlled process that depends on diverse signalling pathways responding to cellular and environmental signals. AMP-activated protein kinase (AMPK) is a critical metabolic enzyme that acts at a central control point in cellular energy homeostasis. Numerous studies have revealed the crucial roles of AMPK in the regulation of mitochondrial biogenesis; however, molecular mechanisms underlying this process are still largely unknown. Previously, we have shown that, in cellular slime mould Dictyostelium discoideum, the overexpression of the catalytic α subunit of AMPK led to enhanced mitochondrial biogenesis, which was accompanied by reduced cell growth and aberrant development. Here, we applied mass spectrometry-based proteomics of Dictyostelium mitochondria to determine the impact of chronically active AMPKα on the phosphorylation state and abundance of mitochondrial proteins and to identify potential protein targets leading to the biogenesis of mitochondria. Our results demonstrate that enhanced mitochondrial biogenesis is associated with variations in the phosphorylation levels and abundance of proteins related to energy metabolism, protein synthesis, transport, inner membrane biogenesis, and cellular signalling. The observed changes are accompanied by elevated mitochondrial respiratory activity in the AMPK overexpression strain. Our work is the first study reporting on the global phosphoproteome profiling of D. discoideum mitochondria and its changes as a response to constitutively active AMPK. We also propose an interplay between the AMPK and mTORC1 signalling pathways in controlling the cellular growth and biogenesis of mitochondria in Dictyostelium as a model organism.     

Changes of the tocopherol and fatty acid contents in rapeseed oil during refining

Among the most important metabolic compounds there are some which are not synthesized by human and animal organisms and have to be supplied in appropriate quantities in due time. Vitamin E and the essential unsaturated fatty acids have crucial physiological significance, and their greatest quantities occur in plant oils. During refining, apart from unnecessary substances, nutritionally advantageous compounds are also being eliminated. In the present paper changes of tocochromanols taking place during refining of rapeseed oil obtained from seeds of two subsequent crops were investigated. It was observed that losses of tocopherols exceeded 30%, two thirds of which resulted from distilling off during deodorization. The ratio of vitamin E to essential unsaturated fatty acids expressed as the Harris coefficient decreased in the refined oil obtained from seeds of two subsequent crops by about 28%.     

Synthesis and photocatalytic performance of TiO<Subscript>2</Subscript> nanospheres–graphene nanocomposite under visible and UV light irradiation

In this article, we present a fast and simple method to produce TiO₂ nanospheres–graphene nanocomposite with high photocatalytic activity under visible and UV light irradiation. TiO₂ nanospheres were adsorbed on graphene in sol–gel process. First, titanium (IV) butoxide underwent hydrolysis in graphene oxide (GO) ethanol solution resulting in TiO₂ nanospheres deposition on GO. Next, the material was calcinated to generate the phase transition of TiO₂ into anatase and reduce GO to graphene. The detailed characterization of the material was performed via transmission electron microscopy, energy dispersive X-rays spectrometer, Fourier-transformed infrared spectroscopy, X-ray diffraction, and Raman spectroscopy. Interestingly, the band-gap energy of the prepared photocatalyst was drastically decreased in comparison with the commercial photocatalyst P25 from 3.05 to 2.36 eV. This influenced in the activation of the material under visible light and resulted in high photocatalytic activity in the process of phenol decomposition in visible and UV irradiation.     

Carbon-centered radicals in γ-irradiated bone substituting biomaterials based on hydroxyapatite

Gamma irradiated synthetic hydroxyapatite, bone substituting materials NanoBone(?) and HA Biocer were examined using EPR spectroscopy and compared with powdered human compact bone. In every case, radiation-induced carbon centered radicals were recorded, but their molecular structures and concentrations differed. In compact bone and synthetic hydroxyapatite the main signal assigned to the CO(2) (-) anion radical was stable, whereas the signal due to the CO(3) (3-) radical dominated in NanoBone(?) and HA Biocer just after irradiation. However, after a few days of storage of these samples, also a CO(2) (-) signal was recorded. The EPR study of irradiated compact bone and the synthetic graft materials suggest that their microscopic structures are different. In FT-IR spectra of NanoBone(?), HA Biocer and synthetic hydroxyapatite the HPO(4) (2-) and CO(3) (2-) in B-site groups are detected, whereas in compact bone signals due to collagen dominate.     

Enhancement of bio-electrocatalytic oxygen reduction at the composite film of cobalt porphyrin immobilized within the carbon nanotube-supported peroxidase enzyme

Combination of multi-walled carbon nanotubes, cobalt porphyrin, and peroxidase (horseradish, cabbage) enzyme in the film (deposited onto glassy carbon electrode substrate) produces a bio-electrocatalytic system capable of effective reduction of oxygen in such neutral media as 0.1 mol dm⁻³ KCl and 0.1 mol dm⁻³ KCl + 0.01 citrate buffer (pH 6).Carbon nanotubes have been modified with ultra-thin layers of 4-(pyrrole-1-yl) benzoic acid, or phosphododecamolybdate, to form stable colloidal suspensions of carbon nanostructures. The resulting inks have been utilized during sequential deposition of components. Co-existence of cobalt porphyrin, peroxidase enzyme together with dispersed carbon nanotubes leads to synergistic effect that is evident from some positive shift of the oxygen reduction voltammetric potentials (more than 50 mV in citrate buffer) and significant (ca. twice) increase of voltammetric currents (relative to those of the enzyme-free system). The multi-component bio-electrocatalytic film has also exhibited relatively higher activity towards reduction of hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at cobalt porphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at the horseradish or cabbage peroxidase enzymatic sites. An important function of carbon nanotubes is to improve transport of electrons within the bio-electrocatalytic multi-component film.     

Recent development in grain refinement by hydrostatic extrusion

Hydrostatic extrusion is an efficient method of grain refinement to the nanometer scale in metallic materials. The paper shows that it can be used directly to obtain a mean grain size smaller than 100 nm with a significant fraction of high angle grain boundaries in aluminum alloys, titanium, and iron. It is also demonstrated that grain size reduction to this level in some other materials, e.g., nickel, requires a combination of hydrostatic extrusion (HE), as the final operation, after some other methods of severe plastic deformation (SPD). Grain refinement in metallic materials by HE has a significant effect on their properties with a significant increase in mechanical strength and improvement of wear and corrosion resistance while maintaining an acceptable level of plasticity.