Joachim Hoentsch

The effects of hyaluronan and its fragments on lipid models exposed to UV irradiation

The effects of hyaluronan and its degradation products on irradiation-induced lipid peroxidation were investigated. Liposomal skin lipid models with increasing complexity were used. Hyaluronan and its fragments were able to reduce the amount of lipid peroxidation secondary products quantified by the thiobarbituric acid (TBA) assay. The qualitative changes were studied by mass spectrometry. To elucidate the nature of free radical involvement electron paramagnetic resonance (EPR) studies were carried out. The influence of hyaluronan and its fragments on the concentration of hydroxyl radicals generated by the Fenton system was examined using the spin trapping technique. Moreover, the mucopolysaccharides ability to react with stable radicals was checked. The quantification assay of 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) showed no concentration changes of the stable radical caused by hyaluronan. Hyaluronan was found to exhibit prooxidative effects in the Fenton assay in a concentration dependent manner. A transition metal chelation was proposed as a mechanism of this behavior. Considering human skin and its constant exposure to UV light and oxygen and an increased pool of iron in irradiated skin the administration of hyaluronan or its fragments in cosmetic formulations or sunscreens could be helpful for the protection of the human skin.

Role of Ascorbic Acid in Stratum Corneum Lipid Models Exposed to UV Irradiation

AbstractPurpose. The effects of ascorbic acid on Stratum corneum lipid models following ultraviolet irradiation were studied adding iron ions as transition metal catalysts. Methods. Lipid peroxidation was quantified by the thiobarbituric acid assay. The qualitative changes were studied on a molecular level by mass spectrometry. To elucidate the nature of free radical involvement we carried out electron paramagnetic resonance studies. The influence of ascorbic acid on the concentration of hydroxyl radicals was examined using the spin trapping technique. Moreover, we checked the vitamins ability to react with stable radicals. Results. Ascorbic acid was found to have prooxidative effects in all lipid systems in a concentration dependent manner. The degradation products of ascorbic acid after its prooxidative action were detected. The concentration of the hydroxyl radicals in the Fenton assay was decreased by ascorbic acid. The quantification assay of 2,2-diphenyl-1-picrylhydrazyl hydrate showed reduced concentration levels of the stable radical caused by ascorbic acid. Conclusions. Considering human skin and its constant exposure to UV light and oxygen, an increased pool of iron ions in irradiated skin and the depletion of co-antioxidants, the administration of ascorbic acid in cosmetic formulations or in sunscreens could unfold adverse effects among the Stratum corneum lipids.

Optical absorption, luminescence, and electron paramagnetic resonance (EPR) spectroscopy of crystalline to metamict zircon: Evidence for formation of uranyl, manganese, and other optically active centers

Abstract A spectroscopic study on seven natural zircon crystals representing varying coloration and degree of short-range order has been conducted using Raman, optical absorption (OA), time-resolved laserinduced luminescence (TRL), and electron paramagnetic resonance (EPR) spectroscopy. There is a systematic increase in the line width of the central Gd3+ transition in the EPR spectra with decreasing short-range order as defined by Raman spectroscopy. In the luminescence spectra, the broad-band yellow photoluminescence centered at about 560 nm is restricted to samples with a high degree of short-range order. In contrast, photoluminescence related to trivalent rare earth elements was detected in zircon with both intermediate and high degrees of short-range order, but not in one heterogeneous, intermediate to highly metamict sample. Furthermore, short-lived greenish luminescence, typical of uranyl ions, could be detected in the luminescence spectra of partly and strongly metamict zircon. Reabsorption lines related to the presence of tetravalent U were found in luminescence spectra of both well-ordered and metamict samples. These observations give evidence for the occurrence of hexavalent U, besides the tetra- and pentavalent forms in natural zircon. It appears that pentavalent U initially present in crystalline zircon converted to tetra- and hexavalent U in highly metamict samples. For a well-ordered green zircon crystal from Caldas Minas, Minas Gerais (Brazil), spectra of Mn2+ (or Mn4+) were detected by both EPR and luminescence spectroscopy, demonstrating that Mn centers may be present in this mineral. Potential color centers are discussed. Green coloration of natural zircon cannot be assigned exclusively to the presence of U4+ as suggested previously. Furthermore, no significant influence of the Nb4+ center on zircon coloration, including reddish color, was found. Yellow coloration may be related to the absorption due to charge-transfer bands of Pr4+.

EPR, ESE and pulsed ENDOR study of nitrogen related centers in 4H-SiC wafers grown by different technologies

D-band electron paramagnetic resonance (EPR) measurements as well as X and Q-band field-swept Electron Spin Echo (ESE) and pulsed Electron Nuclear Double Resonance (ENDOR) studies were performed on a series of n-type 4H-SiC wafers grown by different techniques including sublimation sandwich method (SSM), physical vapor transport (PVT) and modified Lely method. Depending on the C/Si ratio and the growth temperature the n-type 4H-SiC wafers revealed, besides a triplet due to nitrogen residing on the cubic site (Nc), two nitrogen (N) related EPR spectra with g||=2.0055, g⊥=2.0010 and g||=2.0063, g⊥=2.0005 with different intensities. In the samples with low C/Si ratio the EPR spectrum with g|| =2.0055, g⊥=2.0010 consists of a triplet with low intensity which is tentatively explained as a N-related complex, while in the samples with high C/Si ratio the triplet is transformed into one structureless line of high intensity, which is explained as being due to an exchange interaction between N donors. In the samples grown at low temperature with enhanced carbon concentration the EPR line with g||=2.0063, g⊥=2.0005 and a small hyperfine (hf) interaction dominates the EPR spectrum. It is attributed to N on the hexagonal lattice site. The interpretation of the EPR data is supported by activation energies and donor concentrations obtained from Hall effect measurements for three donor levels in this series of 4H-SiC samples.

The Jahn-Teller effect in Cr5+ -doped PbTiO3: a multi-frequency electron paramagnetic resonance study.

Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti(4+) sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400 K at 9 GHz (X), 34 GHz (Q) and 94 GHz (W band). The [Formula: see text] Jahn-Teller effect stabilizes the vibronic ground state of the 3d(1) electron of the Cr(5+) ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D(4h). The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti- or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr(5+)O6(12-) are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200 K.