The protective role of melanin against UV damage in human skin

Human skin is repeatedly exposed to UVR that influences the function and survival of many cell types and is regarded as the main causative factor in the induction of skin cancer. It has been traditionally believed that skin pigmentation is the most important photoprotective factor, as melanin, besides functioning as a broadband UV absorbent, has antioxidant and radical scavenging properties. Besides, many epidemiological studies have shown a lower incidence for skin cancer in individuals with darker skin compared to those with fair skin. Skin pigmentation is of great cultural and cosmetic importance, yet the role of melanin in photoprotection is still controversial. This article outlines the major acute and chronic effects of UVR on human skin, the properties of melanin, the regulation of pigmentation and its effect on skin cancer prevention.     

Preliminary investigation of a medium power argon radiofrequency capacitively coupled plasma as atomization cell in atomic fluorescence spectrometry of cadmium

The single ring electrode radiofrequency capacitively coupled plasma torch (SRTr.f.CCP) operated at 275W, 27.12 MHz and Ar flow rate below 0.7 lmin(-1) was investigated for the first time as atomization cell in atomic fluorescence spectrometry (AFS) using electrodeless discharge lamps (EDL) as primary radiation source and charged coupled devices as detector. The signal to background ratio (SBR) and limit of detection for Cd determination by EDL-SRTr.f.CCP-AFS were compared to those obtained in atomic emission spectrometry using the same plasma torch. The detection limit in fluorescence was 4.3 ngml(-1) Cd compared to 65 ngml(-1) and 40 ngml(-1) reported in r.f.CCP-atomic emission (AES) equipped with single or double ring electrode. The lower detection limit in EDL-SRTr.f.CCP-AFS is due to a much better SBR in fluorescence. The limit of detection was also compared to those in atomic fluorescence with inductively coupled plasma (0.4 ngml(-1)), microwave plasma torch (0.25 ngml(-1)) and air-acetylene flame (8 ngml(-1)). The influence of light-scattering through the plasma and the secondary reflection of the primary radiation on the wall of the quartz tube on the analytical performance are discussed. The non-spectral matrix effects of Ca, Mg and easily ionized elements are much lower in EDL-SRTr.f.CCP-AFS compared to SRTr.f.CCP-AES. The new technique was applied in the determination of Cd in contaminated soils, industrial hazardous waste (0.4-370 mgkg(-1)) and water (113 microgl(-1)) with repeatability of 4-8% and reproducibility in the range of 5-12%, similar to those in ICP-AES. The results were checked by the analysis of a soil and water CRM with a recovery degree of 97+/-9% and 98+/-4%, for a confidence limit of 95%. The present EDL-SRTr.f.CCP-AFS is a promising technique for Cd determination in environmental samples.     

Validation of the Tessier scheme for speciation of metals in soil using the Bland and Altman test

The Tessier extraction method was used for speciation of Cu, Pb, Zn, As, Fe and Mn in a large concentration range in contaminated soil with various mineralogical compositions. The results were compared by X-ray fluorescence spectrometry (XRF) as a reference method using the Bland and Altman test. A sum of five fractions (exchangeable, bound to carbonates, Fe-Mn oxides, organic matter and residual forms) was compared with the total content determined on solid matrix by the reference method. A good agreement between the methods in the whole concentration range was found for Cu, Zn, As, and Fe. For Mn and Pb, XRF was found suitable to verify the sequential extraction only for concentrations above 250 mg kg⁻¹. This was a consequence of a poorer reproducibility of Pb extraction using the Tessier scheme due to a great difference in the mineralogical composition and the diversity of the Pb species identified in soil. The poorer result of Mn was attributed to the spectral interference of Fe in XRF. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Carbon supported CdSe nanocrystals

Insights to the mechanism of CdSe nanoparticle attachment to carbon nanotubes following the hot injection method are discussed. It was observed that the presence of water improves the nanotube coverage while Cl containing media are responsible for the shape transformation of the nanoparticles and further attachment to the carbon lattice. The experiments also show that the mechanism taking place involves the right balance of several factors, namely, low passivated nanoparticle surface, particles with well-defined crystallographic facets, and interaction with an organics-free sp2 carbon lattice. Furthermore, this procedure can be extended to cover graphene by quantum dots.     

Leaching test for calcined kaolinite and kaolinite/TiO<Subscript>2</Subscript> photoactive composite

Kaolinite is a suitable material for fixing TiO₂ nanoparticles in a composite form. The kaolinite/TiO₂ composite has promising photoactive properties which are as important as is the possible impact of the composite on the environment. Accordingly, the stability of the kaolinite/TiO₂ composite dried at 105°C (KTI1) and calcined at 600 °C (KTI6) and the stability of the original kaolinite treated at various temperatures (105–800 °C) were studied by the leaching test in accordance with European standard BS EN 12457-2:2002 (British Standards Institution, 2002). The stability was evaluated on the basis of elements leached from the materials to extraction agents. Atomic emission spectrometry with inductively coupled plasma was used for determining the concentration of elements. In order to better understand the process of calcination and the structure changes in the kaolinite/TiO₂ composite and calcined kaolinite, the materials were evaluated using X-ray powder diffraction and infrared spectroscopy with Fourier transformation. The processes of kaolinite dehydroxylation and metakaolinite formation were observed. Kaolinite is an appropriate carrier for composite preparation due to its stability even after its treatment at high temperatures. The experiments confirmed the TiO₂ nanoparticles to be very strongly bound to the kaolinite surface. On the other hand, the experiments demonstrated that the presence of TiO₂ on the kaolinite surface caused the release of Al in high concentrations to the final extracts, especially after kaolinite/TiO₂ composite calcination.     

Formation of coordination compounds with aniline in the interlayer space of Ca<Superscript>2+</Superscript>-, Cu<Superscript>2+</Superscript>- and Fe<Superscript>3+</Superscript>-exchanged montmorillonite

The influence of Ca²⁺-, Cu²⁺- and Fe³⁺-exchanged montmorillonite (MMT) on the type of interaction with aniline in the interlayer space of MMT has been studied by means of X-ray powder diffraction and infrared spectra. Results of X-ray diffraction showed that aniline was successfully intercalated into the interlayer space of MMT. Based on IR spectra evaluation, aniline was indirectly coordinated through a water-bridge in Ca²⁺- and Fe³⁺-MMT and it was indirectly coordinated through a water-bridge as well as protonated in Cu²⁺-MMT (the spectrum of protonated aniline showed deformation and changes in the NH ₃ ⁺ absorption at approximately 1521 cm^?1). It is important to point out that Cu²⁺-MMT indirect coordination and protonation occur simultaneously.     

On improper interval edge colourings

We study improper interval edge colourings, defined by the requirement that the edge colours around each vertex form an integer interval. For the corresponding chromatic invariant (being the maximum number of colours in such a colouring), we present upper and lower bounds and discuss their qualities; also, we determine its values and estimates for graphs of various families, like wheels, prisms or complete graphs. The study of this parameter was inspired by the interval colouring, introduced by Asratian, Kamalian (1987). The difference is that we relax the requirement on the original colouring to be proper.     

Isotachophoretic determination of hydrosulfite and metabisulfite in technical samples

A method for determination of metabisulfite and hydrosulfite in poultice and decolorant by isotachophoresis was developed. Metabisulfite and hydrosulfite are ionizable oxoanions of sulfur of similar character that can easily be oxidized to sulfates. To protect the analytes from oxidation the solid samples were dissolved in a 1% (w/v) solution of formaldehyde. Hydrosulfite and metabisulfite present in the samples were transformed by the reaction with formaldehyde to stable compounds, hydroxymethanesulfinate and hydroxymethanesulfonate that were determined isotachophoretically without any pretreatment except for sample filtering and degassing. A capillary of 0.4 mm i.d. and 100 mm effective length made of fluorinated ethylene-propylene copolymer was filled with an electrolyte system consisting of 10 mmol L⁻¹ HCl + 11 mmol L⁻¹ imidazole, 0.15% (w/v) hydroxyethylcellulose, pH 6.0 (leading electrolyte) and 5 mmol L⁻¹ benzoic acid + 6 mmol L⁻¹ imidazole, pH 6.5 (terminating electrolyte). Separation was performed at a driving current of 80 μA and for detection current was decreased to 30 μA. Using contactless conductivity detection, the calibration curves in the tested concentration range up to 2.5 mmol L⁻¹ were linear for both metabisulfite and hydrosulfite complexes. The concentration detection limits for metabisulfite and hydrosulfite were 2.9 and 3.4 μmol L⁻¹, respectively. For 1 mmol L⁻¹ concentration, values of R.S.D. (n = 6) were 2.6% for hydrosulfite and 0.8% for metabisulfite. Isotachophoretic determination took about 20 min. The elaborated isotachophoretic procedure is simple to perform, sufficiently sensitive and accurate. In addition to this, low cost of analyses makes the method an alternative procedure to methods used so far for the determination of oxoanions of sulfur.     

Racemization of secondary alcohols catalyzed by cyclopentadienylruthenium complexes: evidence for an alkoxide pathway by fast beta-hydride elimination-readdition

The racemization of sec-alcohols catalyzed by pentaphenylcyclopentadienyl-ruthenium complex 3a has been investigated. The mechanism involves ruthenium-alkoxide intermediates: reaction of tert-butoxide ruthenium complex 4 with a series of sec-alcohols with different electronic properties gave ruthenium complexes bearing a secondary alkoxide as a ligand. The characterization of these alkoxide complexes by NMR spectroscopy together with a study of the reaction using in situ IR spectroscopy is consistent with a mechanism in which the alkoxide substitution step and the beta-hydride elimination step occur without CO dissociation. The alkoxide substitution reaction is proposed to begin with hydrogen bonding of the incoming alcohol to the active ruthenium-alkoxide intermediate. Subsequent alkoxide exchange can occur via two pathways: i) an associative pathway involving a eta3-CpRu intermediate; or ii) a dissociative pathway within the solvent cage. Racemization at room temperature of a 1:1 mixture of (S)-1-phenylethanol and (S)-1-phenyl-[D4]-ethanol gave only rac-1-phenylethanol, and rac-1-phenyl-[D4]-ethanol, providing strong support for a mechanism in which the substrate stays coordinated to the metal center throughout the racemization, and does not leave the coordination sphere. Furthermore, racemization of a sec-alcohol bearing a ketone moiety within the same molecule does not result in any reduction of the original ketone, which rules out a mechanism where the intermediate ketone is trapped within the solvent cage. These results are consistent with a mechanism where eta3-Ph(5)C(5)-ruthenium intermediates are involved. Competitive racemization on nondeuterated and alpha-deuterated alpha-phenylethanols was used to determine the kinetic isotope effect kH/kD for the ruthenium-catalyzed racemization. The kinetic isotope effect kH/kD for p- X-C(6)H(4)CH(OH)CH(3) was 1.08, 1.27 and 1.45 for X=OMe, H, and CF3, respectively.     

Determination of extractable chromium from leather

Abstract  People are exposed to chromium ions from leather materials due to everyday contact with different textile objects. The problem is that Cr(VI) is extremely toxic and may cause contact allergic dermatitis on the skin and may also be a trigger for many diseases. Huge amounts of chromium ions are released by waste waters to rivers after chromium-tanning processes in the leather industry; the presence of chromium is not only a problem for human health, but also for the environment. For this reason it is extremely important to monitor the presence of chromium as Cr(VI) and as total chromium. This study aims to present an appropriate analytical method for monitoring Cr(VI) and the total chromium present on leather materials. Applying this method to chromium-tanned leather samples, it was observed that the amounts of total chromium as well as of Cr(VI) are higher than prescribed and recommended by different regulations. Chromium(VI) exceeded the limit of 3 mg/kg in the majority of tested materials, while the total chromium exceeded the limit of 50 mg/kg in all tested samples. For this reason, it is recommended to avoid direct and prolonged contact of those materials with the skin. Graphical abstract