Search results for "PHOTOCHEMISTRY"
showing 10 items of 2034 documents
Hole burning and pressure phenomena in chromoproteins
1993
Abstract We investigated the behavior of spectral holes under pressure at various frequencies within the inhomogeneous band for two proteins, namely myoglobin and horseradish peroxidase. In order to achieve narrow bandwidth hole burning, the heme chromophore was replaced by protoporphyrin IX and mesoporphyrin IX, respectively. In myoglobin, we found that the pressure induced shift of the holes varied in a strongly non-linear fashion, when the burn-frequency was tuned across the absorption band. In horseradish peroxidase the pressure shift was linear with burn-frequency but changed in a dramatic fashion upon complex formation with a substrate molecule. These observations are interpreted with…
Heme symmetry, vibronic structure, and dynamics in heme proteins: ferrous nicotinate horse myoglobin and soybean leghemoglobin.
2000
We report the visible and Soret absorption bands, down to cryogenic temperatures, of the ferrous nicotinate adducts of native and deuteroheme reconstituted horse heart myoglobin in comparison with soybean leghemoglobin-a. The band profile in the visible region is analyzed in terms of vibronic coupling of the heme normal modes to the electronic transition in the framework of the Herzberg–Teller approximation. This theoretical approach makes use of the crude Born–Oppenheimer states and therefore neglects the mixing between electronic and vibrational coordinates; however, it takes into account the vibronic nature of the visible absorption bands and allows an estimate of the vibronic side bands…
Thermal broadening of the Soret band in heme complexes and in heme-proteins: role of iron dynamics
1994
We report the thermal broadening of the Soret band in heme-CO, heme-OH and protoporphyrin IX in the temperature range 300-20 K. For protoporphyrin IX the temperature dependent Gaussian line broadening follows the behavior predicted by the harmonic approximation in the entire temperature range investigated. In contrast, for heme-CO and heme-OH the harmonic behavior is obeyed only up to about 180 K and an anomalous line broadening increase is observed at higher temperatures. This effect is attributed to the onset of anharmonic motions of the iron atom with respect to the porphyrin plane. Comparison with previously reported analogous data for heme proteins enables us to suggest that the onset …
Selective photocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxaldehyde by polymeric carbon nitride-hydrogen peroxide adduct
2018
Abstract Polymeric carbon nitride-hydrogen peroxide adduct (PCN-H2O2) has been prepared, thoroughly characterised and its application for selective photocatalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxaldehyde (FDC) in aqueous suspension has been studied. The PCN-H2O2 adduct is stable in aqueous suspension under UV and solar irradiation up to 100 °C. It is also stable up to 200 °C if heated in air, while at temperatures close to 300 °C its decomposition takes place. Based on the obtained characterisation data it has been proposed that H2O2 attaches to the non-polymerised carbon nitride species and to the heptazine nitrogen atoms, thus producing strong hydrogen bond…
Supported H3PW12O40 for 2-propanol (photo-assisted) catalytic dehydration in gas-solid regime: The role of the support and of the pseudo-liquid phase…
2016
Abstract Catalytic and photocatalytic 2-propanol dehydration was carried out by using a supported Keggin heteropolyacid H3PW12O40 (PW12). Binary materials were prepared by impregnation and/or solvothermal treatment by using commercial supports: SiO2 (Mallinckrodt), TiO2 (Evonik P25) and multiwall carbon nanotubes (Sunnano) or home solvothermically prepared SiO2 and TiO2. All the materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM) coupled with EDX microanalysis, specific surface area measurements, diffuse reflectance spectroscopy (DRS), FTIR and Raman spectroscopy. (Photo)catalytic 2-propanol dehydration was studied in gas-solid regim…
Volatility of secondary organic aerosol during OH radical induced ageing
2011
The aim of this study was to investigate oxidation of SOA formed from ozonolysis of <i>&alpha;</i>-pinene and limonene by hydroxyl radicals. This paper focuses on changes of particle volatility, using a Volatility Tandem DMA (VTDMA) set-up, in order to explain and elucidate the mechanism behind atmospheric ageing of the organic aerosol. The experiments were conducted at the AIDA chamber facility of Karlsruhe Institute of Technology (KIT) in Karlsruhe and at the SAPHIR chamber of Forchungzentrum Jülich (FZJ) in Jülich. A fresh SOA was produced from ozonolysis of <i>&alpha;</i>-pinene or limonene and then aged by enhanced OH exposure. As an OH radical source in…
Intrinsic defects induced by β-irradiation in silica
2002
We report an electron paramagnetic resonance study of defects induced by β-irradiation in natural and synthetic samples of high purity commercial silica. Data are collected for the E′ centers and a resonance satellite signal split by 1.36 mT. By comparison with the effects of γ-irradiation it is shown that the mechanisms of defect generation are the same for the two irradiation sources and that in the high-dose limit they involve intrinsic defects of the glassy matrix. Moreover, the high concentration of defects generated by β-irradiation modifies the EPR spectrum due to spin–spin interaction.
Isolation of cross-coupling products in model studies on the photochemical modification of proteins by tiaprofenic acid
1999
To gain insight into the chemical nature of drug-induced photoallergy, model studies have been carried out on the photochemical modification of proteins by tiaprofenic acid. Irradiation of decarboxylated tiaprofenic acid (DTPA) in the presence of p-cresol leads to C–C- and C–O-connected p-cresol “dimers”, together with DTPA hydrodimers. The p-cresol–DTPA cross-coupling product was not detected in this reaction. However, a product of this type is formed using a more hindered phenol, such as 2,6-di-tert-butylphenol. Similar results are obtained when tiaprofenic acid (TPA) or its methyl ester are used as photosensitizers. The observed formation of “dimers” can be related to protein photo-cross…
Time-Resolved Luminescence of Nanocrystalline Inorganic Complex Oxides
2007
Two types of complex nanosized oxides – cerium doped Y3Al5O12 (YAG) and CaWO4– have been studied by means of time-resolved luminescence spectroscopy. Comparative study of time-resolve luminescence characteristics of cerium doped YAG single crystal, nanopowders and nanoceramic as well as for CaWO4 macro- and nanocrystals has been done. Two components in the decay kinetic of Ce3+ related emission in YAG nanocrystals were detected and it was suggested that a different energy transfer rate to volume and surface Ce3+ ions takes place. It is shown that the segregation of Ce3+ ions near nanoparticles surface and/or dislocation lines plays a crucial role in degradation of light yield of cerium rela…
Luminescence properties of AlN nanostructures revealed under UV light irradiation
2007
The luminescence properties of the AlN nanostructures – nanorods and nanotips -revealed under the UV irradiation are similar to those of the AlN ceramics. Presumably they are induced by the recombination processes in the oxygen-related centers. All the studied luminescence processes (photoluminescence, thermoluminescence and optically stimulated luminescence) in the nanostructures occur mainly through the host lattice excitation. That may be explained by the smaller concentration of the defect centers and more perfect structure of the host lattice of the nanostructures compared to the ceramics. The small mutual differences revealed in the spectra and TL curves of the AlN nanotips and nanoro…