Increased eumelanin expression and tanning is induced by a superpotent melanotropin [Nle4-D-Phe7]-alpha-MSH in humans

Seven normal volunteers (six males and one female) with tanning skin types III or IV (Fitzpatrick scale) were given 10 daily subcutaneous injections of a superpotent synthetic analog of alpha-melanocyte stimulating hormone (alpha-MSH) over two weeks. This agent, [Nle4-D-Phe7]alpha-MSH, also called Melanotan-I (MT-I), was administered at a dose of 0.16 mg/kg/day (Monday-Friday), over a two week period. Tanning was measured serially using computerized light reflectance. This regimen induced tanning at 3 of 8 anatomic sites including the face, neck and forearm by comparison of baseline to (1) the end of the daily dosing period, (day 14), and (2) one week later, (day 21). Shave biopsies of the forearm taken at baseline and day 21 were analyzed by high performance liquid chromatography for eumelanin content which was measured as the permanganate oxidation product, pyrrole-2,3,5-tricarboxylic acid or PTCA. Pheomelanin content was measured as the hydroiodic acid digestion product, aminohydroxyphenylalanine (AHP). Eumelanin was also measured in the forehead skin samples of three subjects. The HPLC results show that mean (+/- SD) baseline eumelanin (PTCA) levels in forehead skin (n = 3) averaged 1.38 (+/- 0.87) ng/mg of wet skin tissue weight. Higher mean baseline levels of PTCA were detected in forearm skin (2.06 +/- 0.28 ng/mg wet weight, n = 7). One week after MT-I treatments ended, there was a mean (SD) 49% (+/- 17.6%) increase in forehead skin PTCA levels compared to baseline (P = 0.019, n = 3, by paired sample T-test). The mean (SD) increase in forearm skin PTCA levels was 98% (+/- 25.4%) over the same period (P = 0.003). In contrast, forearm pheomelanin expression following MT-I treatment did not significantly change from baseline. Overall, the MT-I regimen increased the eumelanin: pheomelanin ratio in forearm skin from 51:1 at baseline to 86:1 following MT-I (P = 0.054 by paired sample T-test). These results show that the tanning induced by MT-I in the face and forearm is associated with a significant increase in the eumelanin content of the human skin.     

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Ohne Zusammenfassung     

Endogenous and exogenous hydrogen influence on amorphous silicon thin films analysis by pulsed radiofrequency glow discharge optical emission spectrometry

During the last decade the photovoltaic industry has been growing rapidly. One major strategy to reduce the production costs is the use of thin film solar cells based on hydrogenated amorphous silicon (a-Si:H). The potential of pulsed radiofrequency glow discharge coupled to optical emission spectrometry (rf-PGD-OES) for the analysis of such type of materials has been investigated in this work. It is known that when hydrogen is present in the argon discharge, even in small quantities, significant changes can occur in the emission intensities and sputtering rates measured. Therefore, a critical comparison has been carried out by rf-PGD-OES, in terms of emission intensities, penetration rates and depth resolution for two modes of hydrogen introduction in the discharge, manually external hydrogen in gaseous form (0.2% H₂–Ar) or internal hydrogen, sputtered as a sample constituent. First, a comparative optimisation study (at 600 Pa and 50 W) was performed on conducting materials and on a silicon wafer varying the pulse parameters: pulse frequency (500 Hz–20 kHz) and duty cycle (12.5–50%). Finally, 600 Pa, 50 W, 10 kHz and 25% duty cycle were selected as the optimum conditions to analyse three types of hydrogenated samples: an intrinsic, a B-doped and a P-doped layer based on a-Si:H. Enhanced emission intensities have been measured for most elements in the presence of hydrogen (especially for silicon) despite the observed reduced sputtering rate. The influence of externally added hydrogen and that of hydrogen sputtered as sample constituent from the analysed samples has been evaluated.     

Experimental demonstration of ray-optical refraction with confocal lenslet arrays

We observe imaging through windows comprising pairs of confocal lenslet arrays that have different focal lengths but that are otherwise identical. Image space is stretched in the longitudinal direction only. Such windows are examples of METATOYs, optical components that can change light-ray direction in ways that appear wave-optically forbidden.     

Electrocatalytic reductive dimerization of the 2,2′-bipyridyl tungsten alkylidyne complex [W(CC6H4NMe2-4)(NCMe)(CO)2{κ-2,2′-(NC5H4)2}]

Potentiometric measurements have shown that the cationic 2,2′-bipyridyl tungsten alkylidyne complex [W(CC₆H₄NMe₂-4)(NCMe)(CO)₂{κ²-2,2′-(NC₅H₄)₂}][PF₆] (2) is electroactive in MeCN solution with a reduction (E_pc ≈ −1.0 V vs. ferrocene) leading to complex dimerization, identified by a number of electrochemical markers. Multiple redox cycles have led to the partial deposition of the dimerized product on the electrode surface, which appears to electrocatalyze subsequent coupling cycles. Comparison with electrochemical measurements of related alkylidyne complexes, including the precursor complex [W(CC₆H₄NMe₂-4)(O₂CCF₃)(CO)₂{κ²-2,2′- (NC₅H₄)₂}] (1), has provided indirect evidence of intermolecular bond formation between κ²-2,2′-bipyridyl ligands. The cationic complex 2 has additionally been the subject of gamess computational analysis, revealing calculated ν_max(CO) stretching absorptions in good agreement with measured parameters. This study has also permitted a molecular orbital analysis, which has indicated an energy-accessible LUMO almost entirely located on the 2,2′-bipyridyl ligand of complex 2, the purported site for dimerization. It is believed that occupation of this orbital upon reduction of compound 2 leads to a short-lived metastable precursor to 2,2′-bipyridyl ring coupling. Furthermore, a very weak π-antibonding interaction of the metal-alkylidyne π-framework with the MeCN ligand in the occupied frontier molecular orbitals of complex 2 has been noted and compared with a surprisingly significant π interaction with the carboxylate group in complex 1.     

Measurements of the generalized electric and magnetic polarizabilities of the proton at low Q2 using the virtual-compton-scattering reaction

The mean square polarizability radii of the proton have been measured for the first time in a virtual-Compton-scattering experiment performed at the MIT-Bates out-of-plane scattering facility. Response functions and polarizabilities obtained from a dispersion analysis of the data at Q2 = 0.057 GeV2/c2 are in agreement with O(p3) heavy baryon chiral perturbation theory. The data support the dominance of mesonic effects in the polarizabilities.     

Blue quantum fog: chiral condensation in quantum helimagnets

It is shown that a condensation transition involving a chiral order parameter can occur in itinerant helimagnets, in analogy to the transition between the isotropic phase and the phase known as blue fog or blue phase III in cholesteric liquid crystals. It is proposed that such a transition is the explanation for recent neutron scattering results in MnSi. Predictions are made that will allow for experimental tests of this proposal.     

Electrical transport and specific heat of a Cr+2.2 at% Al single crystal

Electrical resistivity, thermoelectric power and specific heat measurements are reported for a Cr+2.2 at% Al alloy single crystal, having an Al content close to the triple point on the magnetic phase diagram of the Cr–Al alloy system. A weak resistivity component of spin-density-wave origin, not previously observed in alloys near the triple point concentration, is isolated at low temperatures. Its presence is confirmed by the thermoelectric measurements. The specific heat measurements suggest a maximum in the density of states at the Fermi energy for alloy concentrations close to the triple point, a point that appears to be a particular type of critical point for the Cr–Al alloy system.     

Evaluation of Liquid Chromatography and Capillary Electrophoresis for the Elucidation of the Artificial Colorants Brilliant Blue and Azorubine in Red Wines

Summary Liquid chromatography (LC) and capillary electrophoresis (CE) have been compared for the analysis of the dyes brilliant blue and azorubine in red wines. A liquid-liquid extraction procedure followed by an ion-pair LC method was developed to separate the dyes from the wine polyphenols allowing reliable UV-spectral identification of the target dyes with limits of detection of 10 and 20 ppb for azorubine and brilliant blue, respectively. Because adulteration of wine with dyes is usually in the ppm level, CE proved to be a good alternative for the LC method. CE could be applied after a simple sample clean-up step by SPE eliminating interference from the bulk of the polyphenols. Although LC proved to be more sensitive compared to CE, the latter is more effective in reducing interferences from other wine components and showed the typical advantages of CE such as low solvent consumption and speed of analysis.