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EPR Measurements (epr + measurement)
Selected AbstractsDetermination of Wavelength-Specific UV Protection Factors of Sunscreens in Intact Skin by EPR Measurement of UV-Induced Reactive Melanin RadicalPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Leslie Lund ABSTRACT There remains an unmet need for skin tissue-based assays for the measurement of the UVA protection and efficacy of sunscreens. Here we describe development of a novel electron paramagnetic resonance assay that uses the photogeneration of reactive melanin radical as a measure of UV light penetration to melanocytes in situ in skin. We have used areas of focal melanocytic hyperplasia in the skin of Monodelphis domestica to model the human nevus. We show that we are able to use this assay to determine the monochromatic protection factors (mPF) of research and commercial sunscreens at specific narrow wavebands of UVB, UVA and blue visible light. Both commercial sunscreens, a sun protection factor (SPF) 4 and an SPF 30 product, had mPFs in the UVB range that correlated well with their claimed SPF. However, their mPF in the UVA ranges were only about one-third of claimed SPF. This technique can be used to design and assay sunscreens with optimally balanced UVA and UVB protection. [source] Bulky Pyrazolate-Based Compartmental Ligand Scaffolds: Encapsulation of an Edge-Sharing Cu6O2 Bitetrahedral Core,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2008Anna Sachse Abstract Upon reaction with Cu(OAc)2·H2O, pyrazole-based ligands with two appended imine chelate arms in the 3- and 5-positions of the pyrazole and bulky substituents at the imine-N yield Cu6 complexes [L2Cu6(,-OAc)6(,4 -O)2] (1a,b). They feature an unusual {Cu6(,4 -O)2}-bitetrahedral core, only the second example of this structural motif. ESI mass spectrometric and UV/Vis data confirm that the Cu6 complexes stay intact in solution, and magnetic and high-field EPR measurements reveal an S = 0 ground state with the first excited triplet at ,E , 95 cm,1. Although the new hexanuclear systems are too complex for deriving all individual exchange constants from powder susceptibility data, a rough idea of the complete energy level spectrum could be obtained.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Outer sphere mutagenesis of Lactobacillus plantarum manganese catalase disrupts the cluster coreFEBS JOURNAL, Issue 6 2003Mechanistic implications X-ray crystallography of the nonheme manganese catalase from Lactobacillus plantarum (LPC) [Barynin, V.V., Whittaker, M.M., Antonyuk, S.V., Lamzin, V.S., Harrison, P.M., Artymiuk, P.J. & Whittaker, J.W. (2001) Structure9, 725,738] has revealed the structure of the dimanganese redox cluster together with its protein environment. The oxidized [Mn(III)Mn(III)] cluster is bridged by two solvent molecules (oxo and hydroxo, respectively) together with a µ1,3 bridging glutamate carboxylate and is embedded in a web of hydrogen bonds involving an outer sphere tyrosine residue (Tyr42). A novel homologous expression system has been developed for production of active recombinant LPC and Tyr42 has been replaced by phenylalanine using site-directed mutagenesis. Spectroscopic and structural studies indicate that disruption of the hydrogen-bonded web significantly perturbs the active site in Y42F LPC, breaking one of the solvent bridges and generating an ,open' form of the dimanganese cluster. Two of the metal ligands adopt alternate conformations in the crystal structure, both conformers having a broken solvent bridge in the dimanganese core. The oxidized Y42F LPC exhibits strong optical absorption characteristic of high spin Mn(III) in low symmetry and lower coordination number. MCD and EPR measurements provide complementary information defining a ferromagnetically coupled electronic ground state for a cluster containing a single solvent bridge, in contrast to the diamagnetic ground state found for the native cluster containing a pair of solvent bridges. Y42F LPC has less than 5% of the catalase activity and much higher Km for H2O2 (,1.4 m) at neutral pH than WT LPC, although the activity is slightly restored at high pH where the cluster is converted to a diamagnetic form. These studies provide new insight into the contribution of the outer sphere tyrosine to the stability of the dimanganese cluster and the role of the solvent bridges in catalysis by dimanganese catalases. [source] Pulsed and cw EPR studies on hydrogen atoms encaged in octasilsesquioxane moleculesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006R. S. Schoenfeld Abstract We report on the synthesis of hydrogen atoms in different Si8O12R8 cages (R = (CH2)nH with n = 0,3) by both radiation chemistry and ion implantation. The efficiencies of both mechanisms have been studied quantitatively and attempts to optimise the process have been made. Spectral properties and relaxation times were investigated using both cw and pulsed EPR measurements. The Hahn Echo decay behaviour and the dependence of T1 and T2 on the side groups R of the cage revealed information about the predominant relaxation mechanisms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Incorporation of nitrogen acceptors in ZnO powderPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006D. Pfisterer Abstract We report on the preparation and characterization of N-doped ZnO powders. EPR measurements revealed the presence of N-acceptors similar to those found in single crystals (Aiso = 1.225 mT, Aaniso = 0.864 mT, g, = 1.9953, g, = 1.9633). The photoluminescence of the samples shows donor to shallow acceptor recombinations. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||