254-nm Radiation Research Articles

Effect of radioprotective agents in sporulation medium on Bacillus subtilis spore resistance to hydrogen peroxide, wet heat and germicidal and environmentally relevant UV radiation

To determine the effects of cysteine, cystine, proline and thioproline as sporulation medium supplements on Bacillus subtilis spore resistance to hydrogen peroxide (H(2)O(2)), wet heat, and germicidal 254 nm and simulated environmental UV radiation. Bacillus subtilis spores were prepared in a chemically defined liquid medium, with and without supplementation of cysteine, cystine, proline or thioproline. Spores produced with thioproline, cysteine or cystine were more resistant to environmentally relevant UV radiation at 280-400 and 320-400 nm, while proline supplementation had no effect. Spores prepared with cysteine, cystine or thioproline were also more resistant to H(2)O(2) but not to wet heat or 254-nm UV radiation. The increases in spore resistance attributed to the sporulation supplements were eliminated if spores were chemically decoated. Supplementation of sporulation medium with cysteine, cystine or thioproline increases spore resistance to solar UV radiation reaching the Earth's surface and to H(2)O(2). These effects were eliminated if the spores were decoated, indicating that alterations in coat proteins by different sporulation conditions can affect spore resistance to some agents. This study provides further evidence that the composition of the sporulation medium can have significant effects on B. subtilis spore resistance to UV radiation and H(2)O(2). This knowledge provides further insight into factors influencing spore resistance and inactivation.

Optical properties of pulsed laser heated soot

To investigate the transient change of soot optical properties resulting from pulsed laser heating of soot in a cooled exhaust plume we have simultaneously performed cw light extinction at 405 and 830 nm and elastic light scattering at 1064 nm. A reversible increase to the 830-nm light extinction of up to 7%, observed during the time period where the soot was hot, suggests a temperature-dependent light absorption refractive index function, E(m λ ). At low fluence, small permanent increases of E(m λ ) of <2% were also observed. 405-nm extinction measurements revealed that the soot likely contained material which continued to absorb 405-nm radiation when desorbed, thus complicating measurement interpretation. 1064-nm light scattering measurements showed a gradual decrease of scattering propensity with increasing laser fluence up to the point of material loss, which is consistent with the expected decrease of the structure factor of the soot aggregates as they expand. It is concluded that variations of the optical properties are occurring at the time of laser-induced incandescence (LII) emission, which should be accounted for in time-resolved LII measurement interpretation.

P/Si-TiO 2 transparent films with high anatase stability and photocatalytic activity

The anatase-TiO 2 transparent films, containing 3 mol% of Si and P elements (as dopants), were synthesized using a process combining the sol–gel method and spin-coating technique. Effects of relative ratio of dopants and calcination temperature on phase transformation, grain growth, surface morphology, light transmittance, band-gap energy and photocatalytic activity of the P/Si-TiO 2 films were examined and their results were compared with those of the undoped-TiO 2 and Si-TiO 2 films. The P/Si-TiO 2 films calcined at temperature between 600 and 900 °C adhered strongly to the surface of fused-silica substrate and were composed of anatase-TiO 2 monophase. The photocatalytic activities of the films were measured and represented using a characteristic time constant ( τ) for the methylene blue (MB) photodegradation. The small τ stands for high photocatalytic ability of the film. The P/Si-TiO 2 film, containing equalmolar Si and P dopants, calcined at 800 °C gave the best performance in photocatalysis; this film had τ=5.7 h and decomposed about 90 mole% of MB in the water after 12 h of the 365-nm UV light irradiation.

Low bias photoelectrocatalytic (PEC) performance for organic vapour degradation using TiO2/WO3 nanocomposite

In this study, a novel photoelectrocatalytic (PEC) flat-plate type device used in the gas-phase was fabricated by the technology of screen printing. The TiO2/WO3 nanocomposite (2:8 in mole ratio) was prepared by a simple milling-anneal method and printed onto the device. The obtained device was attempted to investigate the PEC performance by applying low biases for degrading the volatile organic compounds (VOCs). The apparent pseudo-first-order kinetic model was used to describe the degradation process. The results showed that the applied low bias had a distinct enhancement effect on the degradation activity compared to photocatalytic (PC) degradation. The PEC degradation rate under UV-light (365nm) irradiation by applying only 0.2V bias was about 12.28×10−3min−1, which was 2.42 times of PC degradation rate. Under the blue-light (475nm) irradiation, the composite still had good degradation efficiency and the rate constant was about 2.6×10−3min−1. Furthermore, the explanation was proposed that the degradation activity of TiO2/WO3 composite could show obviously enhancement for gas-phase PEC process by applying bias at a very low level, compared to pure TiO2.

Synthesis, DNA binding, photo-induced DNA cleavage, cytotoxicity and apoptosis studies of copper(II) complexes

Two new Cu(II) complexes, [Cu(acac)(dpq)Cl] (1) and [Cu(acac)(dppz)Cl] (2) (acac = acetylacetonate, dpq = dipyrido[3,2-d:20,30-f]quinoxaline, dppz = dipyrido[3,2-a:20,30-c] phenazine), have been synthesized and their DNA binding, photo-induced DNA cleavage activity and cell cytotoxicity are studied. The complexes show good binding propensity to calf thymus DNA in the order: 2(dppz) >1(dpq). Furthermore, two complexes exhibit efficient DNA cleavage activity on natural light or UV-A (365nm) irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. The photo-induced DNA cleavage activity of the dppz complex 2 is found to be more efficient than its dpq analogue. In vitro study of the photocytotoxicity of two complexes on HeLa cells indicate that both of them have the potential to act as effective anticancer drugs, with IC50 values of 5.25±0.83μM (1) and 4.40±0.52μM (2) in the natural light, and 2.57±0.92μM (1) and 2.18±0.52μM (2) in UV-A light. In addition, to detect an apoptotic HeLa body, cells were stained with Hoechst 33342 dye.

Degradation of natural organic matter in surface water using vacuum-UV irradiation

The use of vacuum-UV (VUV) radiation to degrade natural organic matter (NOM) and the main variables affecting the efficiency of this process were investigated using an annular photoreactor. After 180min of irradiation with VUV, the total organic carbon (TOC) decreased from 4.95ppm to 0.3ppm. Also, decadic absorption coefficients of the water at 185nm and 254nm decreased from 3.2cm−1 to 2.85cm−1, and 0.225cm−1 to 0cm−1, respectively. The reactor operation was kinetically controlled for Reynolds numbers greater than 600, changes of pH between 5 and 9 had little effect, and increases in alkalinity decreased the process efficacy. Additionally, H2O2/VUV and VUV processes were compared to H2O2/UV and UV processes, where the formers showed greater effectiveness with complete mineralization of NOM as opposed to partial oxidation with H2O2/UV, and no mineralization with UV alone. Modeling and analysis of the photon flux and absorption in the reactor showed that 99% of the 185nm radiation was absorbed by the water in the reactor. In comparison, only 48% of the 254nm radiation was absorbed by the water. The overall quantum efficiency of the mineralization for VUV was 0.10 for 50% TOC reduction.

ChemInform Abstract: Photochemical Cycloaddition Reactions of Cyanoacetylene and Dicyanoacetylene.

Photolysis of cyanoacetylene with 185- or 206-nm light yields 1,3,5-tricyanobenzene while 254-nm radiation yields a mixture of tetracyanocyclooctatetraenes, 1,2,4- and 1,3,5-tricyanobenzene. A polymer of cyanoacetylene is the major photoproduct. 1,3,5-Tricarbomethoxybenzene was the only photoproduct identified from the irradiation of methyl propiolate at 254 nm. Mono-, di-, and tricyanobenzenes are formed by irradiation of mixtures of acetylene and cyanoacetylene at 185, 206, and 254 nm along with trace amounts of cyclooctatetraenes. No photoadducts were detected on photolysis of mixtures of cyanoacetylene and CO or HCN. The tetracyanocyclooctatetraene structures were established by UV, MS, and NMR analyses. The 1H NMR of the product mixture exhibited a singlet at delta 7.028 consistent with either 1 or 2 and two singlets at delta 6.85 and 6.91 assigned to 3. Photolysis of mixtures of dicyanoacetylene and acetylene with either 185- or 206-nm light yielded 1,2-dicyanobenzene and (E,Z)-1-buten-3-yne-1,4-dicarbonitrile. These products were also obtained using 254-nm light along with a mixture of tetracyanocyclooctatetraenes. The same three singlets were observed in this product mixture as were observed in the tetracyanocyclooctatetraenes obtained from cyanoacetylene. From this observation it was concluded that the delta 7.02 signal is due to 2 and not 1. The photolysis of cyanoacetylene and dicyanoacetylene in the presence of ethylene with 185-nm light yields 1-cyanocylobutene and 1,2-dicyanocyclobutene, respectively. 2-Cyanobutadiene and 2,3-dicyanobutadiene are the photoproducts with 254-nm light. Reaction pathways are proposed to explain these findings.

On the Aging Effects of 4H-SiC Schottky Photodiodes Under High Intensity Mercury Lamp Irradiation

Ultraviolet (UV) germicidal irradiation uses high-power 254-nm radiation from low-pressure mercury discharge lamps to kill or inactivate viral, bacterial, and fungal species. Since UV germicidal irradiation effectiveness depends primarily on the UV dose delivered to the microorganisms, it is essential to monitor the power emitted from the source by using appropriate UV-light detectors. We report on preliminary aging tests performed on high signal-to-noise ratio 4H-SiC Schottky photodiodes under high intensity mercury lamp irradiation (10 mW/cm2).

Photochemistry in an Azo-Containing Banana-Shaped Liquid Crystal

By triangular wave method, the polarization currents of an azo-containing banana-shaped antiferroelectric liquid crystal were investigated as a function of the time of 365-nm ultraviolet irradiation. Under the 365-nm irradiation, the polarization currents were observed to evolve with the time of ultraviolet irradiation until they diminished. The roles of photoisomerization, photolysis and thermolysis were discussed for the azo-containing banana-shaped liquid crystal.

Thermo- and Photo-Degradation of LDPE and PP Films Using Metal Oxides as Catalysts

Degradation of LDPE and PP films using the photo sensitive metal oxides or pro-oxidants (e.g. Fe2O3, CuxO, ZnO, and TiO2 at various particle sizes) as the catalysts in both thermo- and photo-oxidation of plastic films with oxygen followed by photolytic process to give free radicals has been studied. Our preliminary study in hexane solution found that the carbonyl index (CI) increased under the shortwave ultraviolet (254nm) significantly greater than under the longer wave (366nm) due to its greater energy and highly absorbed by the pro-oxidants generating more free radical concentration which could then be photolysed into carbonyl compounds. The pro-oxidant blended PE and PP films under ultraviolet (254nm) irradiation showed the carbonyl index elevation at the beginning and then reducing to a constant level similarly in most cases. This probably suggested that the carbonyl primarily formed and degraded into other free radicals. Under shortwave ultraviolet irradiation for 72 hours, the LDPE films containing nano-sized rutile-TiO2 and nano-sized anatase-TiO2 (1%w/w) were able to reduce the film tensile strength by 32% and 55%, respectively. The film containing micron-sized commercial TiO2 lower the film tensile strength only by 7-10%. However, the tensile strength of the TiO2 blended PP films tends to increase possibly because the rate of cross linkage exceeds the rate of scission.

Enhancing thermal stability and photocatalytic activity of anatase-TiO2 nanoparticles by co-doping P and Si elements

The Si/P–TiO2 nanoparticles, with a molar ratio [Si + P]/[Si/P–TiO2] = 0.03, were synthesized using a sol–gel method. The effects of relative ratios of dopants (i.e., R ≡ [P]/([Si + P]) and calcination temperatures on phase transformation, grain growth, and photocatalytic activity of the gel-derived Si/P–TiO2 were examined. While the Si–TiO2 (i.e., R = 0) had its anatase structure stabilize at 700 °C for 2 h, the Si/P–TiO2 (i.e., 0.33 ≤ R < 1) and P–TiO2 (i.e., R = 1) were able to preserve the anatase-TiO2 at temperature as high as 900 °C. Although at 900 °C the phosphorus elements in Si/P–TiO2 nanoparticles were partly excluded to the particles’ surface and tended to fuse the adjacent particles together, which may lead to a large reduction in their specific surface areas and photocatalytic activities, the Si/P–TiO2 with high silicon contents, such as the particles of R = 0.5 and 0.33, were still composed of loosely packed nanoparticles and showed good photocatalytic ability. In whole, the Si/P–TiO2 nanoparticles of R = 0.5 calcined at 600–900 °C gave the superior performance in photocatalytic activity, under both 365-nm UV light and white light irradiation.

Roles of Small, Acid-Soluble Spore Proteins and Core Water Content in Survival of Bacillus subtilis Spores Exposed to Environmental Solar UV Radiation

Spores of Bacillus subtilis contain a number of small, acid-soluble spore proteins (SASP) which comprise up to 20% of total spore core protein. The multiple alpha/beta-type SASP have been shown to confer resistance to UV radiation, heat, peroxides, and other sporicidal treatments. In this study, SASP-defective mutants of B. subtilis and spores deficient in dacB, a mutation leading to an increased core water content, were used to study the relative contributions of SASP and increased core water content to spore resistance to germicidal 254-nm and simulated environmental UV exposure (280 to 400 nm, 290 to 400 nm, and 320 to 400 nm). Spores of strains carrying mutations in sspA, sspB, and both sspA and sspB (lacking the major SASP-alpha and/or SASP-beta) were significantly more sensitive to 254-nm and all polychromatic UV exposures, whereas the UV resistance of spores of the sspE strain (lacking SASP-gamma) was essentially identical to that of the wild type. Spores of the dacB-defective strain were as resistant to 254-nm UV-C radiation as wild-type spores. However, spores of the dacB strain were significantly more sensitive than wild-type spores to environmental UV treatments of >280 nm. Air-dried spores of the dacB mutant strain had a significantly higher water content than air-dried wild-type spores. Our results indicate that alpha/beta-type SASP and decreased spore core water content play an essential role in spore resistance to environmentally relevant UV wavelengths whereas SASP-gamma does not.

Exposure and development of thick polydimethylglutarimide films for MEMS applications using 254-nm irradiation

Polydimethylglutarimide PMGI-based resists are finding increasing use in microelectromechanical systems MEMS as both sacrificial and structural materials. PMGI-based resists are commercially available and were originally designed for use in bilayer lift-off applications. Literature on deep-UV exposure and development of PMGI films is limited to films less than 2.5 m in thickness, and use only tetramethylammonium hydroxide TMAH-based developers. We investigate the exposure and development of PMGI films greater than 6 m in thickness using the two main classes of developer for PMGI, TMAH, and tetraethylammonium hydroxide TEAH-based developers. At these thicknesses, a nonuniform dose through the film due to the optical absorption of the PMGI leads to large gradients in the dissolution properties. We report etch rates as a function of surface dose and development time. Additionally a model is developed to provide a basic predictor of development depth and other important data for fabrication process planning and development.

Synthesis of Gd 3PO 7:Eu 3+ nanospheres via a facile combustion method and optical properties

Eu 3+-doped Gd 3PO 7 nanospheres with an average diameter of ∼300 nm and a narrow size distribution have been prepared by a facile combustion method and structurally characterized by X-ray diffraction and field emission scanning electron microscopy. The luminescent properties were systemically studied by the measurement of excitation/emission spectra, and emission spectra under different temperatures, as well as by photostability. The strong red-emission intensity peaking at 614 nm originates the 5 D 0→ 7 F 2 transition and is observed under 254-nm irradiation, indicating that Eu 3+ ions in Gd 3PO 7 mainly occupied non-centrosymmetry sites. The CIE1931 XY chromaticity coordinates of Gd 3PO 7:Eu 3+ nanospheres are ( x=0.654, y=0.345) in the red area, which is near the National Television Standard Committee standard chromaticity coordinates for red. Thus, Gd 3PO 7:Eu 3+ nanospheres may be potential red-emitting phosphors for PDP and Xe-based mercury-free lamps.

Physicochemical Characteristics of ZnS Immobilized on Spherical Activated Carbon for Removing HA(Humic Acid)

In this study, spherical activated carbons contained ZnS(Zn-SPAC) were successfully prepared through carbonization/activation processes. Strong acid ion exchange resin as starting material of Zn-SPAC was treated by 0.01 N zinc solution. Ion exchange treatment was performed from one time to three times for controling zinc content. The ion exchanged resins was activated under N2/H2O-vapor atmosphere at 900 °C for 0.5 hr following by carbonization treatment at 700 °C under N2 atmosphere. The Zn-SPAC samples were measured physicochemical characteristics such as X-ray patterns, SEM image, energy dispersive X-ray spectra, BET specific surface area, intensity and zinc content and used to remove humic acid(HA) in batch reactor for measuring photochemical activity. The X-ray patterns were appeared ZnS type. The Zn-SPAC had large BET specific surface area and their shape was spherical with a diameter about 350 ~ 400 μm. When the Zn-SPAC were dosed in UV reactor, the HA removal efficiency increased upto 60 % at 4hr. The order hand, the HA removal efficiency by only UV-C(λmax =254nm) irradiation was not good about 15 %. Therefore, we infer that the Zn-SPAC have good photochemical activity and presented possibility of photocatalyst for water purification.

Steady-state and transient photocurrents in rubrene single crystal free-space dielectric transistors

We report results of photocurrent studies performed on rubrene single crystal transistors in the air-gap configuration under 405nm irradiation. The phototransistors show a strong photoresponse indicative of photoconduction. Under illumination, the phototransistors show an average threshold voltage shift of 22V and a maximum photosensistivity of 2.65×103. A small persistent photoconductivity effect is observed in the transistors tested under continuous illumination which is explained by delayed recombination aided by spatial separation of the photocarriers. Photocurrent transients measured by applying short pulses on the other hand show a complete recovery in the microsecond regime implying immediate recombination.

Specific‐wavelength visible light irradiation inhibits bacterial growth of Porphyromonas gingivalis

The effects of laser irradiation on Porphyromonas gingivalis have been reported, but the results are still controversial regarding the efficiency because of the differences of the light sources and irradiation conditions. The aim of this study was to determine the wavelength and irradiation conditions under which the most effective inhibitory effect on P. gingivalis growth was seen without any photosensitizers. Using an Okazaki large spectrograph, monochromatic light spectra ranging from 400 to 700 nm were evaluated to determine which spectra effectively inhibited bacterial growth. Moreover, using a monochromatic 405-nm irradiating device, the effects of various irradiating conditions on P. gingivalis growth were examined. Growth of bacteria irradiated at 400 nm and 410 nm was significantly suppressed compared with a nonirradiated control, whereas wavelengths of 430 nm and longer produced no significant inhibition. A constant energy density of 15 J/cm2 was found to be enough to show an inhibitory effect. Significant inhibition of bacterial growth was found after only 1 min at 50 mW/cm2 irradiation. These results indicate that P. gingivalis growth is specifically suppressed by 405-nm light irradiation, suggesting that visible blue light irradiation is a promising means for eradicating periodontopathogenic bacteria from periodontal lesions.

Highlighted Generation of Fluorescence Signals Using Simultaneous Two-Color Irradiation on Dronpa Mutants

Dronpa absorbs blue light and emits bright green fluorescence. It can also be converted by strong irradiation at 490 nm to a nonfluorescent state, which can then be switched back to the original emissive state with irradiation at 400 nm. Through semirandom mutagenesis studies, we have developed two mutants of Dronpa that show efficient photoswitching kinetics. Compared to Dronpa, the mutants can be turned off by blue light more efficiently. Thus, excitation with an argon laser line (488 nm) makes the mutants quickly become dark such that no substantial fluorescence signals can be observed. Excitation with a violet laser diode (405 nm) also produces no fluorescence signals. Simultaneous 488- and 405-nm irradiation, however, results in a rapid oscillation between the two states, thereby keeping the emissive state population large enough to produce sufficiently bright fluorescence signals.

The effect of UV-irradiation on poly(vinyl alcohol) composites with montmorillonite

Poly(vinyl alcohol), PVA, microcomposites with montmorillonite, MMT, were prepared by their mixing in aqueous colloidal solution. Thin films of composites obtained by solvent evaporation were exposed to 254-nm radiation. The course of photochemical reactions leading to various products was monitored by FTIR and UV–vis spectroscopy. The chain scission reaction was confirmed by measurement of average molecular weights and polydispersity using gel permeation chromatography (GPC) method. The crosslinking was minor process whereas oxidation and degradation appeared more efficient in exposed PVA/MMT. It was found that the presence of clay filler (MMT) has slight influence on PVA photooxidative degradation.

Effects of ultraviolet (254nm) irradiation on egg hatching and adult emergence of the flour beetles, Tribolium castaneum, T. confusum and the almond moth, Cadra cautella.

The eggs of the stored grain pests, Tribolium castaneum (Herbst), T. confusum (Duval) (Coleoptera: Tenebrionidae) and Cadra cautella (Walker) (Lepidoptera; Pyralidae) belonging to three age groups, 1, 2, and 3 days-old, were exposed to ultraviolet (UV) radiation with 254nm wavelength (UV-C) for different durations to determine irradiation effects on egg-hatching and adult emergence. An increase in time of exposure to UV-rays caused a gradual decrease in the percentage of hatching of eggs in all age groups of eggs. No hatching occurred after 24 minutes of exposure in 2 and 3 day-old eggs of T. confusum. C. cautella eggs were less sensitive to UV-rays than were T. castaneum and T. confusum eggs. All the exposure periods significantly reduced the eclosion of adults in all the experimental insects. No adults emerged when 3 day-old eggs of T. castaneum were irradiated for 16 or 24 minutes, or from 2 and 3 day-old eggs T. confusum irradiated for 16 or 24 minutes.