Search results for "photolysis"
showing 10 items of 81 documents
A Combined Experimental and Theoretical Approach to the Photogeneration of 5,6-Dihydropyrimidin-5-yl Radicals in Nonaqueous Media
2016
The chemical fate of radical intermediates is relevant to understand the biological effects of radiation and to explain formation of DNA lesions. A direct approach to selectively generate the putative reactive intermediates is based on the irradiation of photolabile precursors. But, to date, radical formation and reactivity have only been studied in aqueous media, which do not completely mimic the micro environment provided by the DNA structure and its complexes with proteins. Thus, it is also important to evaluate the photogeneration of nucleoside-based radicals in nonaqueous media. The attention here is focused on the independent generation of 5,6-dihydropyrimidin-5-yl radicals in organic…
Regio- and stereo-selectivity in the intramolecular quenching of the excited benzoylthiophene chromophore by tryptophan
2000
Laser flash photolysis studies on the photobehaviour of a series of bichromophoric derivatives bearing benzoylthiophene and tryptophan groups have shown that the efficiency of the intramolecular quenching process depends on both the stereochemistry of the chiral centers and the relative ketone versus tryptophan orientation. Perez Prieto, Julia, Julia.Perez@uv.es
Ethane-Bridged Zinc-Porphyrin Dimers in Langmuir-Shäfer Thin Films: Structural and Spectroscopic Properties
2006
This work reports on the structural and spectroscopic properties of ethane-bridged Zn porphyrin dimers (1) in Langmuir-Scha¨fer (LS) thin films by combining scanning force microscopy (SFM) with film balance, UV-vis absorption, fluorescence, and nanosecond laser flash photolysis measurements. Results show that depending on the surface pressure the Langmuir films of pure 1 can be arranged in two different condensed phases, whereas SFM of the LS films shows characteristic fractal networks constituted by nanoscopic aggregates. The spectral findings agree with a picture in which 1 is apparently present in the anti conformation but aggregated in a sort of H-type structure whose optical features r…
Novel Lipophilic Lanthanide Bis-Phthalocyanines Functionalized by Pentadecylphenoxy Groups: Synthesis, Characterization and UV-Photostability
2012
Novel sandwich-type phthalocyanines containing a rare earth metal core (Pr, Nd, Eu-Lu) and macrocycles peripherally substituted by pentadecylphenoxy groups were synthesized using a cardanol-based phthalonitrile precursor and the respective lanthanide acetate. Additionally, the metal free-base analog compound was studied for comparison. The purified reaction products were all found to be thick and viscous substances at room temperature, showing liquid crystalline behavior with a distinct increase in fluidity at ca. 40 ° C. The complexes are readily soluble in chloroalkyl solvents and dissolve fairly well in DMF with some tendency to form aggregates. Besides they are strongly hydrophobic and …
Photolysis of N-hydroxpyridinethiones: a new source of hydroxyl radicals for the direct damage of cell-free and cellular DNA.
1996
N-Hydroxypyridine-2-thione (2-HPT), known to release hydroxyl radicals on irradiation with visible light, and two related compounds, viz. N-hydroxypyridine-4-thione (4-HPT) and N-hydroxyacridine-9-thione (HAT), were tested for their potency to induce DNA damage in L1210 mouse leukemia cells and in isolated DNA from bacteriophage PM2. DNA single-strand breaks and modifications sensitive to various repair endonucleases (Fpg protein, endonuclease III, exonuclease III, T4 endonuclease V) were quantified. Illumination of cell-free DNA in the presence of 2-HPT and 4-HPT gave rise to damage profiles characteristic for hydroxyl radicals, i.e. single-strand breaks and the various endonuclease-sensit…
Combined Theoretical and Experimental Study of the Photophysics of Asulam
2013
The photophysics of the neutral molecular form of the herbicide asulam has been described in a joint experimental and theoretical, at the CASPT2 level, study. The unique π → π* aromatic electronic transition (f, ca. 0.5) shows a weak red-shift as the polarity of the solvent is increased, whereas the fluorescence band undergoes larger red-shifts. Solvatochromic data point to higher dipole moment in the excited state than in the ground state (μ(g)μ(e)). The observed increase in pKa in the excited state (pKa* - pKa, ca. 3) is consistent with the results of the Kamlet-Abboud-Taft and Catalán et al. multiparametric approaches. Fluorescence quantum yield varies with the solvent, higher in water (…
Light-Induced Protein-Matrix Uncoupling and Protein Relaxation in Dry Samples of Trehalose-Coated MbCO at Room Temperature
2005
In humid samples of trehalose-coated carboxy-myoglobin (MbCO), thermally driven conformational relaxation takes place after photodissociation of the carbon monoxide (CO) molecule at room temperature. In such samples, because of the extreme viscosity of the external matrix, photodissociated CO cannot diffuse out of the protein and explores the whole (proximal and distal side) heme pocket, experiencing averaged protein heme pocket structures, as a result of the presence of Brownian motions. At variance, in very dry samples, a lower portion of the photodissociated CO diffuses from the distal to the proximal heme pocket side probing in nonaveraged structures. We revisit here the flash photolysi…
Complement pore genesis observed in erythrocyte membranes by fluorescence microscopic single-channel recording
1991
The formation and opening of single complement pores could be directly observed in erythrocyte ghosts by confocal laser-scanning microscopy employing the recently introduced method of fluorescence microscopic single-channel recording. Resealed sheep erythrocyte ghosts were incubated with human complement. By limiting the concentration of C8, the eighth component of complement, the fraction of cells rendered permeable for the small polar fluorescent probe Lucifer Yellow was varied between 0.50 and 0.90. Under each condition the flux rate, k, of Lucifer Yellow was determined for a substantial number of ghosts. By analysing the sample population distribution of k the flux rate k1 of ghosts wit…
8-Azido-adenosine 5'-triphosphate as a Photoaffinity Label for Bacterial F1 ATPase
1978
1. 8-Azido-adenosine 5'-triphosphate (n83ATP) is a suitable photoaffinity label for F1 ATPase from Micrococcus luteus. The nucleotide is a substrate in the presence of bivalent cations and inhibits the enzyme irreversibly upon irradiation with ultraviolet light above 300 nm. 2. More than 80% of the label is covalently bound to the beta subunits in the presence of bivalent cations. Labeling and inactivation is decreased by protection with ADP, ATP or adenyl-5'-yl imidodiphosphate. To a much smaller degree the alpha subunits also become labeled. 3. n83AMP does not specifically bind to the beta subunits upon irradiation. Like n83ATP and n83ADP, it also labels the alpha subunits to a small exte…
Optical release of caged glutamate for stimulation of neurons in the in vitro slice preparation
2005
Optical stimulation techniques prove useful to map func- tional inputs in the in vitro brain slice preparation: Glutamate released by a focused beam of UV light induces action potentials, which can be detected in postsynaptic neurons. The direct activation effect is influenced by factors such as compound concentration, focus depth, light absorption in the tissue, and sensitivity of different neuronal do- mains. We analyze information derived from direct stimulation ex- periments in slices from rat barrel cortex and construct a computa- tional model of a layer V pyramidal neuron that reproduces the experimental findings. The model predictions concerning the influ- ence of focus depth on inpu…