Home About us Contact
|
Home About us Contact | ||
|
|
||
Singlet Oxygen Production (singlet + oxygen_production)
Selected AbstractsElectrochemical Monitoring of Singlet Oxygen ProductionELECTROANALYSIS, Issue 21 2009Duncan Sharp Abstract The exploitation of singlet oxygen generating compounds as a means of targeted therapies drives the need to develop methods for assessing the efficacy of such compounds and their capacity for generating the reactive oxygen species. Degradation of diphenylisobenzofuran by singlet oxygen is widely used as a spectroscopic probe but its application can be problematic. An alternative detection strategy exploiting the electrochemical monitoring of the quencher concentration, by square wave voltammetry, has been shown to provide a more sensitive and flexible option that could be used to address the increasing interest in photosensitizing materials. [source] Photoprotection by Porcine Eumelanin Against Singlet Oxygen Production,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Alice Wang Melanin, a major pigment found in retinal pigment epithelium (RPE) cells, is considered to function in dual roles, one protective and one destructive. By quenching free radical species and reactive oxygen species (ROS) melanin counteracts harmful redox stress. However, melanin is also thought to be capable of creating ROS. In this destructive role, melanin increases redox strain in the cell. This study uses readily available eumelanin extracted from porcine RPE cells as a more authentic model than synthetic melanin to determine specific mechanisms of melanin activity with regard to singlet oxygen in the presence and absence of rose bengal, a singlet-oxygen photosensitizer. Optical detection of singlet-oxygen was determined by monitoring the bleaching of p -nitrosodimethylaniline in the presence of histidine. Production of singlet oxygen in aqueous oxygen-saturated solutions of rose bengal without eumelanin was readily accomplished. In contrast, detection of singlet oxygen in oxygen-saturated solutions of eumelanin without rose bengal failed, consistent with results of others. However, a significant decrease in singlet oxygen production by rose bengal was observed in the presence of eumelanin. After correction for light absorption and chemical bleaching of eumelanin, the results show that eumelanin also provides a photoprotective mode arising from chemistry, that is, not just the physical process of light absorption followed by energy dissipation as heat. [source] Mechanism of DNA Damage Photosensitized by Trisbipyrazyl Ruthenium Complex.PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2000Unusual Role of Cu/Zn Superoxide Dismutase ABSTRACT Trisbipyrazyl ruthenium(II) (Ru[bpz]32+) was examined as DNA photosensitizer. Damage resulting from the photolysis of synthetic oligonucleotides has been monitored by polyacrylamide gel electrophoresis. Photoadduct formation is found on both single- and double-stranded oligonucleotides. On oligonucleotide duplex, oxidative damage occurs selectively at the 5,G of the 5,GG3, site and to a lesser extent at the 5,G of a GA sequence. These findings suggest the involvement of electron transfer and show that this mechanism is the main DNA damaging process involved in Ru(bpz)32+ photosensitization. In addition, photoadducts and oxidative damage are both highly affected by an increase of salt concentration in the reaction medium, stressing the importance of direct interactions between nucleic acid bases and the excited ruthenium complex for efficient electron transfer. On single-stranded oligonucleotides, all the guanines are oxidized to the same extent. In this case, oxidative damage, which is not affected by an increase of salt in the solution, has been attributed, in part, to singlet oxygen. More importantly, Cu/Zn superoxide dismutase (SOD) strongly enhances the yield of all damage, correlated to an increase of both electron transfer and singlet oxygen production. This original activity of SOD is the first example of bioactivation of a polyazaaromatic ruthenium complex. [source] NMDA potentiation by visible light in the presence of a fluorescent neurosteroid analogueTHE JOURNAL OF PHYSIOLOGY, Issue 12 2009Lawrence N. Eisenman N -Methyl- d -aspartate (NMDA) receptors are widely studied because of their importance in synaptic plasticity and excitotoxic cell death. Here we report a novel method of potentiating NMDA receptors with fluorescence excited by blue (480 nm) light. In the presence of 300 nm of a (7-nitro-2,1,3-benzoxadiazol-4-yl) amino (NBD)-tagged neuroactive steroid carrier C2-NBD-(3,,5,)-3-hydroxypregnan-20-one (C2-NBD 3,5,P), responses of cultured hippocampal neurons to 10 ,m NMDA were potentiated to 219.2 ± 9.2% of the baseline response (100%) by a 30 s exposure to 480 nm light. The potentiation decayed back to baseline with a time constant of 80.6 s. Responses to 1 ,m and 100 ,m NMDA were potentiated to 147.9 ± 9.6% and 174.1 ± 15.6% of baseline, respectively, suggesting that visible-light potentiation is relatively insensitive to NMDA concentration. Peak autaptic NMDA responses were potentiated to 178.9 ± 22.4% of baseline. Similar potentiation was seen with 10 ,m NBD-lysine, suggesting that visible-light potentiation is not a steroid effect. Potentiation was also seen with a steroid analogue in which the NBD was replaced with fluorescein, suggesting that NBD is not the only fluorophore capable of supporting visible-light potentiation. UV light and redox potentiation of NMDA receptors largely occluded subsequent blue light potentiation (127.7 ± 7.4% and 120.2 ± 6.2% of baseline, respectively). The NR1a(C744A,C798A) mutant that is insensitive to redox and UV potentiation was also largely unaffected by visible-light potentiation (135.0 ± 10.0% of baseline). Finally, we found that the singlet oxygen scavenger furfuryl alcohol decreased visible-light potentiation. Collectively, these data suggest that visible-light potentiation of NMDA receptors by fluorescence excitation shares mechanisms with UV and redox potentiation and may involve singlet oxygen production. [source] | ||||||||||