Presence Of UV-A Radiation Research Articles

Exploring the photocatalytic activity of nanometric magnetite for PET materials degradation under UV light

Regular and spherical aggregates composed by 40 ​nm of magnetite particles were prepared by solvothermal conditions. Fe3O4 nanoparticles coated by a 20 ​nm thickness silica layer, were also prepared. The degradation of polyethylene terephthalate can be explained by a photolysis process for Fe3O4@SiO2 composite. On the other hand, Fe3O4 has been proved to be an efficient peroxymonosulphate activator in the presence of UV-A radiation. The synergistic effect between the photolysis and radical-mediated processes may be responsible for the enhanced catalytic properties. The magnetic properties of the catalyst enable an easy way of separation from the water media after the treatment. This study opens a new research field for the utilization of highly oxidant species as an alternative to the conventional harmful chemical recycling processes.

Assessment of Photo-Induced Cytotoxic Activity of Cachrys sicula and Cachrys libanotis Enriched-Coumarin Extracts against Human Melanoma Cells.

Photochemotherapy is one of the most interesting current therapeutic approaches for the treatment of melanoma. Different classes of naturally occurring phytochemicals demonstrated interesting photoactive properties. The aim of this study was to evaluate the photocytotoxic potential of two Cachrys species from Southern Italy: C. sicula and C. libanotis (Apiaceae). The enriched-coumarin extracts were obtained from aerial parts through both traditional maceration and pressurized cyclic solid-liquid (PCSL) extraction using Naviglio extractor®. Qualitative and quantitative analyses of furanocoumarins were performed with GC-MS. The photocytotoxic effects were verified on C32 melanoma cells irradiated at a dose of 1.08 J/cm2. The apoptotic responses were also assessed. Moreover, phenolic content and the in vitro antioxidant potential were estimated. Xanthotoxin, bergapten, and isopimpinellin were identified. All the samples induced concentration-dependent photocytotoxic effects (IC50 ranging from 3.16 to 18.18 μg/mL). The C. libanotis sample obtained with Naviglio extractor® was the most effective one (IC50 = 3.16 ± 0.21 μg/mL), followed by C. sicula sample obtained with the same technique (IC50 = 8.83 ± 0.20 μg/mL). Both Cachrys samples obtained through PCSL induced up-regulation of apoptotic signals such as BAX (Bcl2-associated X protein) and PARP (poly ADP-ribose polymerase) cleavage. Moreover, these samples proved to be more photoactive, giving a greater upregulation of p21 protein in the presence of UVA radiation. Obtained results suggest that investigated species could be promising candidates for further investigations aimed to find new potential drugs for the photochemotherapy of skin cancer.

Visible light plays a significant role during bacterial inactivation by the photo-fenton process, even at sub-critical light intensities

The aim of this research is to clarify the contribution of sunlight wavelengths, irradiance and Fe2+/H2O2 during bacterial disinfection by the photo-Fenton process in clear surface waters. We considered different solar spectrum distributions (visible, UVA-Visible), sub-critical irradiances (0–400 W/m2), focusing on the action modes of E. coli inactivation by the constituents involved in the composite process, at low μM reactants concentration (Fe2+/H2O2) in in ultrapure (MQ) water. We report that solar disinfection improved with Fenton reagents (photo-Fenton process) is a reality from very low light irradiance values (200 W/m2), and made possible even without the presence of UVA radiation, even when using low quantities of the Fenton reagents (0.5 mg/L Fe2+, 5 mg/L H2O2). Under light exposure, H2O2 was found to augment the intracellular Fenton process and Fe2+ to initiate further, distinct oxidative actions. Finally, validation was performed in Lake Geneva water over a wider irradiance range, where the photo-Fenton process was found to be reagent-dependent in low irradiance, shifting to light-driven in the higher values.

Photochemical activity and the structure of chloroplasts in Arabidopsis thaliana L. mutants deficient in phytochrome A and B

The reduced content of photoreceptors, such as phytochromes, can decrease the efficiency of photosynthesis and activity of the photosystem II (PSII). For the confirmation of this hypothesis, the effect of deficiency in both phytochromes (Phy) A and B (double mutant, DM) in 7-27-day-old Arabidopsis thaliana plants on the photosynthetic activity was studied in absence and presence of UV-A radiation as a stress factor. The DM with reduced content of apoproteins of PhyA and PhyB and wild type (WT) plants with were grown in white and red light (WL and RL, respectively) of high (130μmol quanta m-2 s-1) and low (40μmol quanta m-2 s-1) intensity. For DM and WT grown in WL, no notable difference in the photochemical activity of PSII was observed. However, the resistance of the photosynthetic apparatus (PA) to UV-A and the rate of photosynthesis under light saturation were lower in the DM compared to those in the WT. Growth in RL, when the photoreceptors of blue light-cryptochromes-are inactive, resulted in the significant decrease of the photochemical activity of PSII in DM compared to that in WT including amounts of QB-non-reducing complexes of PSII and noticeable enhancement of thermal dissipation of absorbed light energy. In addition, marked distortion of the thylakoid membrane structure was observed for DM grown in RL. It is suggested that not only PhyA and PhyB but also cryptochromes are necessary for normal functioning of the PA and formation of the mechanisms of its resistance to UV-radiation.

Protective effect of UV-A radiation during acclimation of the photosynthetic apparatus to UV-B treatment

We examined the acclimation response of the photosynthetic apparatus of barley (Hordeum vulgare L.) to a combination of UV-A and UV-B radiation (UVAB) and to UV-B radiation alone. Our aim was to evaluate whether UV-A radiation prevents UV-B-induced damage to the photosynthetic apparatus and whether UV-A pre-acclimation is required to mitigate the negative influence of UV-B radiation. Barley plants were grown from seeds under low photosynthetically active radiation (50 μmol m−2 s−1) either in the absence or presence of UV-A radiation (UVA− and UVA+ plants, respectively). After 8 days of development, plants were exposed simultaneously to UV-A and UV-B radiation for the next 6 days. Additionally, UVA− plants were exposed to UV-B radiation alone. The UVA+ plants had a higher CO2 assimilation rate near the light-saturation region (AN) and a higher content of both total chlorophylls (Chls) and total carotenoids than the UVA− plants. Chls content, AN, the potential quantum yield of photosystem II (PSII) photochemistry (FV/FM), the capacity of light-induced thermal energy dissipation and the efficiency of excitation energy transfer within PSII remained the same or even increased in both UVA+ and UVA− plants after UVAB treatment. On the contrary, exposure of UVA− plants to UV-B radiation itself led to a reduction in all these characteristics. We revealed that the presence of UV-A radiation during UVAB treatment not only mitigated but completely eliminated the negative effect of UV-B radiation on the functioning of the photosynthetic apparatus and that UV-A pre-acclimation was not crucial for development of this UV-A-induced resistance against UV-B irradiation.

Chemical and photochemical reactivity of 6-hydroxymethyl-7,8-dihydropterin in aqueous solutions

6-Hydroxymethyl-7,8-dihydropterin (H2Hmp) is an intermediate in the biosynthesis of folate, a precursor of coenzymes involved in the metabolism of nucleotides and amino acids. In this work, we have investigated the reactions undergone by H2Hmp in aqueous solutions at physiological pH, in the absence and in the presence of UV-A radiation (320–400 nm). In air-equilibrated solutions, H2Hmp undergoes slow thermal oxidation (half-life 37 h) to yield 7,8-dihydroxanthopterin (H2Xap) as the main product. The reaction of H2Hmp with hydrogen peroxide also yields H2Xap as a main product. In contrast, UV-A excitation of H2Hmp leads to the formation of a dimer identified by electrospray ionization mass spectrometry. The corresponding quantum yield of H2Hmp consumption (Φ−R) was independent of O2 and reactant concentration and has a value of 0.10 (±0.02), more than twice higher than that measured for other 6-subtituted 7,8-dihydropterins. Copyright © 2012 John Wiley & Sons, Ltd.

Partial protection of photosynthetic apparatus from UV-B-induced damage by UV-A radiation

Alteration in the photosynthetic apparatus of clusterbean ( Cyamopsis tetraganoloba) cotyledons owing to UV-B irradiation in the absence or presence of UV-A radiation (UV-A + UV-B) during steady phase of its growth has been studied. UV-B radiation induces a decline in the photosynthetic pigments content and O 2 evolution along with a modification in the absorption spectra of chloroplasts. UV-A + UV-B irradiation moderately reverses these changes. The partial restoration of F V/ F M value and other fluorescence transient parameters in UV-A + UV-B treated sample compared to that of UV-B treated one suggest that UV-A helps in developing a protective pathway against UV-B-induced impairment. UV-B-mediated alteration in S state transition of Mn cluster associated with oxygen evolving complex, as appeared from TL glow curves, is retrieved by UV-A radiation and Car is considered to negotiate against UV-B-induced damage of photosynthetic apparatus.

UV-B radiation increases cell permeability and damages nitrogen incorporation mechanisms in Nannochloropsis gaditana

This study shows the response of Nannochloropsis gaditana, a marine nannoplanktonic species, exposed to UV radiation for 7 days. PAR, UV-A and UV-B ratios used were within the range likely to be observed in nature, a photoperiod of 12L:12D was maintained, and light irradiances were modified daily to promote cell acclimation. Growth, pigment content, internal nitrogen and carbon content, and photochemical efficiency using PAM fluorometry were assessed in nutrient replete cultures. Cell size, autofluorescence and cell permeability were analysed by flow cytometry. Results showed a cessation of growth after day 3 and a progressive decrease was observed in Fv/Fm values in cultures exposed to UV-B (plus UV-A and PAR). Flow cytometry analysis also demonstrated an increase in membrane permeability caused by UV-B damage. Cells that showed an increase in membrane permeability also exhibited a proportional decrease in cellular nitrogen content. The results support the conclusion that UV-B radiation can affect N. gaditana nitrogen incorporation mechanisms by direct damage or indirectly by damage to membrane structure and to the photosynthetic apparatus with resulting effects on energy and reductant demand. In contrast, the presence of UV-A radiation was beneficial to cells exposed to PAR plus UV-A when compared to those exposed to only-PAR from day 4. This response resulted in cells with a higher nitrogen content and without changes in membrane permeability.

Photocatalytic Treatment of Cibacron Brilliant Yellow 3G-P (Reactive Yellow 2 Textile Dye)

The photocatalytic treatment of a textile dye wastewater, cibacron brilliant yellow 3G-P (reactive yellow 2), under the presence of UV-A radiation was studied. Treatment of test solutions containing 100 mg/L cibacron brilliant yellow dye with two types of photocatalysts, Degussa P25 and Hombikat UV 100 titanium dioxide, were investigated. The efficiency of these two commercial photocatalysts was compared in the presence and absence of hydrogen peroxide (H2O2). H2O2 concentration of 15 mM showed the best efficiency toward the photocatalytic treatment of the textile dye at the concentrations tested. Both decolorization and mineralization were significantly improved by using 15 mM H2O2. The treatment efficiency of the photocatalytic degradation of reactive yellow 2 was determined in terms of both adsorption kinetics and total mineralization. The decolorization and mineralization followed first order kinetics with a rate constant of 0.09 min−1 for decolorization with Degussa P25 titanium dioxide in the presence of H2O2. 71.3% chloride and 27.9% sulphate were yielded after complete decolorization in the photocatalytic treatment of the dye. However, only 0.78% yield of the nitrate was obtained by photocatalysis. The formation of intermediates was not significant compared to the original dye solution in terms of absorbance.

Phylloplane fungi of hawaiian plants and their photosensitivity to polyacetylenes from Bidens species

Many polyacetylenes are toxic to living organisms in the presence of UV-A radiation. These effects have led to speculation about the putative functions of polyacetylenes in the organisms which produce them. Nineteen species of phylloplane yeasts and yeast-like fungi were isolated from species of Hawaiian Bidens with and without leaf acetylenes, and from other Hawaiian plants. Although all these organisms, members of the Sporobolomycetaceae, Cryptococcaceae and Fungi Imperfecti, were photosensitive to some polyacetylenes and resistant to others, there was no correlation between the presence or absence of leaf polyacetylenes and the distribution of these saphrophytes among species of Bidens. Nevertheless, it is significant that the only pathogenic species isolated in this study, Colletotrichum gloeosporiodes (Penzig) Penzig et Sacc., did not colonize Bidens leaves containing C 13 aromatic acetylenes to which it is extremely sensitive in vitro.