Search results for "PHOTOCHEMICAL"

Role of ΔpH in the mechanism of zeaxanthin-dependent amplification of qE

1995

Abstract The influence of zeaxanthin on the high-energy-state fluorescence quenching (qE) and the pH dependence of the maximum chlorophyll fluorescence yield (Fm) was examined in spinach thylakoids. High contents of zeaxanthin were achieved using different pretreatments. A pronounced, zeaxanthin-dependent amplification of non-photochemical quenching (NPQ) was exclusively found in thylakoids containing zeaxanthin, synthesized in the dark via the buildup of an artificial ΔpH. These thylakoids also showed a significant quenching of chlorophyll fluorescence in the range pH 5.5–6.3, where no or only slight quenching was visible in zeaxanthin-free thylakoids. Thylakoids containing high amounts of…

Ru(bpy)2Cl2: A catalyst able to shift the course of the photorearrangement in the Boulton-Katritzky reaction

2015

The Boulton-Katritzky reaction represents one of the most popular and efficient strategies used to realize azole-into-azole conversions. For example, under different experimental conditions, it allows the rearrangement of Z-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazoles (1) into 2-aryl-4-benzoylamino-5-phenyl-2H-1,2,3-triazoles (2) in very high yields. Moreover, we have recently realized this conversion also by UV-photostimulation. Now we have enlarged the scope of the reaction irradiating with visible or UV light an acetonitrile solution of some Z-arylhydrazones (1a-e) in the presence of catalytic amounts of Ru(bpY)(2)Cl-2. We have observed the unexpected formation of the 1-aryl-5-…

Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy

2014

Monitoring the dynamics of protonation and protein backbone conformation changes during the function of a protein is an essential step towards understanding its mechanism. Protonation and conformational changes affect the vibration pattern of amino acid side chains and of the peptide bond, respectively, both of which can be probed by infrared (IR) difference spectroscopy. For proteins whose function can be repetitively and reproducibly triggered by light, it is possible to obtain infrared difference spectra with (sub)microsecond resolution over a broad spectral range using the step-scan Fourier transform infrared technique. With -10(2)-10(3) repetitions of the photoreaction, the minimum num…

DNA Oxidation Photoinduced by Norharmane Rhenium(I) Polypyridyl Complexes: Effect of the Bidentate N,N′-Ligands on the Damage Profile

2018

Re(I)--polypyridyl complexes have interesting and distinctive photochemical and photosensitizing properties. This work describes the capability to induce (or photoinduce) DNA damage of three Re(I)-complexes with a naturally occurring alkaloid called norharmane (nHo) as ligand: [Re(CO)₃ (nHo)(L)]CF₃ SO₃ where L=2,2'-bipyridine (ReBpy), phenanthroline (RePhen) or dipyrido[3,2-a:2',3'-c]phenazine (ReDppz). The interaction of the complexes with DNA was investigated by steady-state and time-resolved spectroscopy. Data show that the mode and strength of interaction depend on the chemical structure of the bidentate ligand. The complexes show a major static contribution to the overall interaction, …

Photochemical sample treatment for extracts clean up in PCB analysis from sediments.

2013

Sample purification can be considered the most polluting step of the whole analytical process for PCBs determination in sediment samples. The use of photochemical sample treatment represents an alternative methodology for extracts clean up allowing for a reduction of the used amount of organic solvents. The first application of a photochemical sample treatment for the selective removal or reduction of organic substances interfering with PCBs analyses in sediments is reported. The method's efficiency and robustness were compared with currently used chromatographic purification. Quality parameters such as recovery, linearity and reproducibility were studied. The entire procedure was validated…

Photocrosslinkable polyaspartamide/polylactide copolymer and its porous scaffolds for chondrocytes

2017

With the aim to produce, by a simple and reproducible technique, porous scaffolds potentially employable for tissue engineering purposes, in this work, we have synthesized a methacrylate (MA) copolymer of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) and polylactic acid (PLA). PHEA-PLA-MA has been dissolved in organic solvent at different concentrations in the presence of NaCl particles with different granulometry, and through UV irradiation and further salt leaching technique, various porous scaffolds have been prepared. Obtained samples have been characterized by scanning electron microscopy and their porosity has been evaluated as well as their degradation profile in aqueous medium in…

Solvent dependent photochemical reactivity of 3-allyloxy-1,2,4-oxadiazoles

2009

Dicopper(II) metallacyclophanes with photoswitchable oligoacene spacers: a joint experimental and computational study on molecular magnetic photoswit…

2018

Dinuclear copper(II) complexes of the metallacyclophane-type, (nBu4N)4[Cu2(2,6-anba)2] (1) and (nBu4N)4[Cu2(1,5-naba)2]·4H2O (2) with photoactive 2,6-anthracene-(2,6-anba) and 1,5-naphthalenebis(oxamate) (1,5-naba) bridging ligands, are reported. They undergo a thermally reversible, solid-state photomagnetic (ON/OFF) switching between the moderately strong antiferromagnetically coupled dicopper(II) species and the corresponding magnetically uncoupled [4+4] photocycloaddition product. Density functional calculations give further insights on the intramolecular (“pseudo-bimolecular”) photocycloaddition reaction of the two facing 2,6-anthracene or 1,5-naphthalene spacers in this novel family of…

Green Oxidation of Alcohols to Carbonyl Compounds by Heterogeneous Photocatalysis

2010

Hydrothermal Synthesis of Ionic Liquid [Bmim]OH-Modified TiO2 Nanoparticles with Enhanced Photocatalytic Activity under Visible Light

2010

TiO(2) nanocomposites modified with the ionic liquid [Bmim]OH are synthesized by a hydrothermal procedure. X-ray diffraction, Zeta-potential measurement, TEM, thermogravimetric analysis, photoluminescence, UV/Vis, FTIR, and X-ray photoelectron spectroscopy are used to characterize the TiO(2) nanocomposites. The TiO(2) nanocomposites consist of pure anatase particles of about 10 nm. The modification of [Bmim]OH on the surface of the TiO(2) particles extends the TiO(2) absorption edge to the visible-light region. The electrochemical redox potentials indicated that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of [Bmim]OH match well with the valen…