Effects of ultraviolet irradiation on substituted polyacetylenes

Effects of UV irradiation on various substituted polyacetylenes were examined. Upon irradiation in air, main-chain scission and crosslinking occurred with a wide range of probabilities dependent on the nature of substituents. For example, poly(2-alkyne)s rapidly degraded to low molecular weights, whereas polymers from aromatic monosubstituted acetylenes [e.g., poly(o-CF₃-phenylacetylene)] were quite stable. Several other polyacetylenes [e.g., poly(1-Me₃Si-1-propyne)] showed intermediate degradability. Polymer degradation was minimal in vaccum. The polymers irradiated in air contained C?O and O? H groups, and dissolved in polar solvents which are nonsolvents for the initial polymers. These results indicate that oxidation causes degradation. Only poly(1-chloro-1-alkyne)s of the polyacetylenes studied, formed gels upon UV irradiation. The amount of the gel was larger, when the polymer was irradiated in vacuum than in air. Further, the longer the alkyl pendant in the polymer, the higher the gel fraction. Differences between photo-and thermal degradations are discussed.     

Development and intercalibration of ultraviolet solar actinometers

Ultraviolet (UV) sunlight actinometers were developed based on the photolysis of nitrate and nitrite. Photon exposures ( i.e. time-integrated irradiances) were quantified from the photochemical production of salicylic acid (SA) or p -hydroxybenzoic acid (pHBA) formed by the reaction of the hydroxyl radical with benzoic acid. The solar response bandwidth for the nitrate actinometer in quartz tubing was 322 ± 11 nm during the Spring of 1999, while the response bandwidth of the Mylar D-filtered nitrite actinometer was 355 ± 25 nm. Intercomparisons of the nitrate and nitrite actinometers with a Smithsonian Environmental Research Center SR-18 scanning UV-B radiometer (SERC SR-18) and an Optronics OL-754 spectroradiometer (OL-754) were performed during the summer of 1998, and the winter and spring of 1999. Photon exposures determined by the nitrate actinometer were in excellent agreement with the SERC SR-18, with a slope (95% confidence interval [CI]) of 0.98 ± 0.01 based on SA production and 0.94 ± 0.02 based on pHBA production. Excellent agreement was also found between the nitrite actinometer and the OL-754, with a slope (95% CI) of 1.00 ± 0.01 using SA production and 1.00 ± 0.02 using pHBA production. These actinometers are well suited for use in the water column and are sufficiently sensitive to determine photon exposures below the 0.1% UV light-level.     

Direct correlation between work function of indium-tin-oxide electrodes and solar cell performance influenced by ultraviolet irradiation and air exposure

We report on reversible changes of the work function (WF) values of indium-tin-oxide (ITO) under prolonged ultraviolet (UV) and air exposure. The WF of ITO is reduced from 4.7 eV to 4.2 eV by photon absorption in ITO under UV illumination or an air mass 1.5 solar simulator (100 mW cm(-2)). Air or oxygen exposure is found to increase the WF of ITO (UV-exposed) to a value of 4.6 eV. These changes of ITO's WF lead to reversible variations of the performance of organic photovoltaic devices where ITO acts primarily as the electron collecting or hole collecting electrode. These variations can be reflected in the disappearance (or appearance) of an S-shaped kink in the J-V characteristics upon continuous UV or solar simulator illumination (or air exposure). This reversible phenomenon is ascribed to the adsorption and desorption of oxygen on the surface and grain boundaries of ITO. The use of surface modifiers to either decrease or increase the WF of ITO in organic photovoltaic devices with inverted and conventional geometries is also shown to be an effective route to stabilize the device performance under UV illumination.     

Tyrosine formation from phenylalanine by ultraviolet irradiation

When phenylalanine was irradiated at ultraviolet (UV) light, p-tyrosine, m-tyrosine and o-tyrosine were identified as hydroxylated products. From p-tyrosine and m-tyrosine, the formation of L-3,4-dihydroxyphenylalanine (DOPA) was observed. The hydroxylation of phenylalanine was prevented by radical scavengers, e.g., catalase, superoxide dismutase, sodium thiocyanate, mannitol, potassium iodide and thiourea. Replacement of air with nitrogen gas prevented the hydroxylation, but did not depress it completely. The addition of H2O2 increased significantly the hydroxylation of phenylalanine. These results suggest that the hydroxylation of phenylalanine by UV irradiation may be caused by .OH formed during the decomposition of H2O.     

紫外光引发甲基丙烯酸甲酯乳液聚合

以60W高压汞灯为光源,以偶氮二异丁氰(AIBN)为主要光引发剂,以甲基丙烯酸甲酯(MMA)为单体进行乳液聚合,考察了光照时间、单体浓度、光引发剂浓度等因素对单体转化率的影响;采用透射电镜观察了乳胶粒的形态,并测定了其尺寸.结果表明,转化率随光照时间和单体浓度的增加而上升;当光引发剂质量分数为3%时单体转化率最高.     

Solid-state ultraviolet irradiation of some maleimides and bismaleimides

The solid-state photoreactivity of a series of maleimides and bismaleimides is studied Various crystalline maleimides are found to dimerize on irradiation by ultraviolet light Based on this discovery, the photopolymerizability of the related bismaleimides in the crystalline state is examined. As a result it is found that some N,N,-alkylenebismaleimides polymerize into highly crystalline polymers. The polymers do not melt below their decomposition temperature (>300°C) and are practically insoluble in all solvents. The obtained irradiation products are different from the reaction products of the solution-phase photochemistry. Closely related bismaleimides, such as members of a homologous series, show substantial differences in their solid-state photochemical behavior; on excitation they either lead to polymers or are not reactive. This indicates that the solid-state photoreactivity of maleimides and bismaleimides is controlled by the geometry of their crystal structure.     

Phytochemicals for prevention of solar ultraviolet radiation-induced damages

While solar light is indispensable for sustenance of life, excessive exposure can cause several skin-related disorders. The UV part of solar radiation, in particular, is linked to disorders ranging from mild inflammatory effects of the skin to as serious as causing several different types of cancers. Changes in lifestyle together with depletion in the atmospheric ozone layer during the last few decades have led to an increase in the incidence of skin cancer. Skin cancers consisting of basal and squamous cell carcinomas are especially linked to the UVB part of solar radiation. Reducing excessive exposure to solar radiation is desirable; however, as this approach is unavoidable, it is suggested that other novel strategies be developed to reduce the effects of solar radiation to skin. One approach to reduce the harmful effects of solar radiation is through the use of phytochemicals, an approach that is popularly known as "Photochemoprotection." In recent years many phytochemicals with potential antioxidant properties have been identified and found to be photoprotective in nature. We describe here some of the most popular phytochemicals being studied that have the potential to reduce the harmful effects associated with solar UV radiation.     

Anatomical distribution of solar ultraviolet exposures among cyclists

Exposure to solar ultraviolet (UV) radiation is the major environmental factor implicated in the development of melanoma and other skin cancers, as well as eye damage and skin photoaging. Outdoor recreational activities such as cycling are increasingly pursued for health benefits, however little information is available regarding potential adverse effects of excessive sun exposure in this setting, nor about the anatomical distribution of solar dose. Polysulphone badges (UV dosimeters) were attached to the head, backs of hands and ankles of 22 cyclists during a seven-day charity bicycle ride in Queensland, Australia. Average daily exposures exceeded one minimal erythemal dose (MED) at all body sites except the ankle. Significant differences in UV dose among the various body sites were noted, with highest exposures recorded on the top of the head. Mean doses received at the ankle (0.94 MED), back of the hand (1.28 MED) and side of the head (1.14 MED) were 51%, 71% and 63% of those received at the top of the head (1.80 MED), respectively. These data indicate that cycling exposes adherents to substantial doses of UV radiation. Moreover, our observations suggest that even vertically-oriented, potentially shaded sites such as the lower leg typically receive doses of solar radiation no less than half of maximally exposed sites.     

Effects of ultraviolet light irradiation in biotreatment of organophosphates

Excess biomass accumulation in reactor biodegradation processes is undesirable: it increases the disposal cost and upsets the operation of biological reactors if not properly controlled. In this study, we investigated the feasibility of using ultraviolet (UV) light irradiation to reduce biomass accumulation and increase the specific biodegradation activity. UV irradiation has been widely used to introduce DNA damage in bacteria. Here we apply this technology to the biodegradation of organophosphates by recombinantEscherichia coli strains that contain arecA mutation and a cloned organophosphate hydrolase gene. We show that therecA negative strains after UV irradiation reduce the growth rate but increase the specific organophosphate hydrolase activity. This increase in specific enzyme activity is not owing to continued protein synthesis from the plasmid after the damage of chromosomal DNA by UV irradiation. Rather, it is likely to be caused by an increase in membrane permeability to the substrate. Kinetic analysis suggests that the membrane transport of paraoxon is the rate-limiting step in its biodegradation.     

Diarylethene microcrystals make directional jumps upon ultraviolet irradiation

Microcrystals of a diarylethene {1,2-bis[5'-methyl-2'-(2"-pyridyl)thiazolyl]perfluorocyclo-pentene} undergo jumps upon photoirradiation. These photochromic crystals present molecular structural changes upon irradiation with ultraviolet light because of reversible photocyclization reactions. When the energy absorbed by crystals reaches about 10 microJ, the uniaxial stress induced in the crystal lattice relaxes through directional jumps. If one prevents crystals from jumping, then parallel, equidistant cracks appear on crystal surfaces. These photomechanical effects could result from a Grinfeld surface instability.     

Simplified calibration for broadband solar ultraviolet radiation measurements

Aspects of different calibration procedures for erythemally weighing broadband radiometers are presented in this study. These instruments are common in projects dealing with ultraviolet radiation effects on humans. Many erythemally weighing broadband radiometers are still operated using a single calibration factor (cf) that is provided with the instrument. The individual characteristics of every instrument are strongly dependent on the total ozone amount and the solar elevation. Therefore, a calibration procedure also has to take into account the ozone concentrations and the solar elevation to compensate for the effects of the individual characteristics and to provide comparable measurements. Given the variation of the ozone concentrations and the solar elevation, an individual cf has to be calculated for every measurement. Using a simplified version of the calibration procedure, which is presented in this study, can lessen this effort. Taking into account the relevant meteorological conditions for a measuring site, a single cf is calculated to compensate the individual characteristics of the instruments and therefore deliver comparable measurements with less effort.     

Surface oxidation of cellulose fibers by vacuum ultraviolet irradiation

The efficacy of vacuum ultraviolet irradiation for oxidizing the surface of cellulose fibers was compared to that of the conventional wet and dry processes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 357–361, 1999     

Diffuse component of solar ultraviolet radiation in tree shade

The first set of quantitative data of diffuse erythemal UV and UV-A radiation in tree shade at a sub-tropical Southern Hemisphere latitude is presented. Over the summer, approximately 60% of the erythemal UV radiation in tree shade is due to the diffuse component. Similarly, approximately 56% of the UV-A radiation in tree shade is due to the diffuse component. In tree shade these diffuse UV percentages are relatively constant from the morning to noon to afternoon periods. In comparison, in full sun, there is a decrease in the percentage of diffuse UV from morning to noon to afternoon. The exposures to diffuse UV on a horizontal plane in tree shade between 9:00 EST and 15:00 EST are of the order of 4 MED (minimum erythemal dose) and 14 J cm(-2) for erythemal UV and UV-A, respectively. The high diffuse UV component in the shade may result in high UV exposures not only to unprotected parts of the body on a horizontal plane, but also in equally high UV irradiances to parts of the body, including the eyes and face, that are not UV protected.     

Effect of cysteine on bovine serum albumin (BSA) denaturation induced by solar ultraviolet (UVA, UVB) irradiation.

Long-term exposure to natural sun-light (UVA, UVB) induced fluorescence and caused disulfide bond formation in bovine serum albumin (BSA). The addition of cysteine enhanced the bond formation to such an extent that a solution of BSA was transformed into an insoluble gel. The disulfide bonds in the gels are derived from internal-SH groups of protein. This reaction occurred even if cysteine was added after exposure to ultraviolet (UV)-irradiation. Fluorescent substances seem to be involved in this reaction. On the other hand, low concentrations of cysteine (less than 5 mM) inhibited both fluorescence and disulfide bond formation. The addition of glutathione to BSA produced the same effect as that of cysteine. The addition of thiourea to BSA solution inhibited fluorescence, but did not inhibit disulfide bond formation. We assume that external-SH compounds such as cysteine and glutathione, which have high reactivity with hydroxyl radicals (.OH), act not only as free-radical scavengers, but also as radical mediators in the polymerization of protein through disulfide cross-links induced by UV-irradiation. Solar UVA as well as UVB irradiation are shown to have the same effect on the protein polymerization.     

Effect of ultraviolet irradiation on the cyclodehydration of polyamic acids

The general features of the effect of UV irradiation on the imidization of polyamic acids have been elucidated by using the analysis of thermal and mechanical properties of the polyimide obtained.An optimum method of photothermal imidization was found, in which a product with improved thermomechanical properties was obtained.

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Zusammenfassung Die allgemeinen Merkmale der Wirkung der UV-Bestrahlung auf die Imidisation von Polyamidsäuren wurde durch Einsatz der Analyse der thermischen und mechanischen Eigenschaften des erhaltenen Polyimids erläutert.Eine optimale Methode der photothermischen Imidisation wurde gefunden, durch welche ein Produkt mit verbesserten thermomechanischen Eigenschaften erhalten wurde.

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Vacuum ultraviolet irradiation on siliceous coatings on polycarbonate substrates

We studied the effect of vacuum ultraviolet (vuv) irradiation on siliceous coatings of polycarbonate (PC) substrates derived by the sol–gel method, with the aim of improving the abrasion resistance of the substrate surface. Methyltriethoxysilane with colloidal silica was used to prepare the sol solution. The sol solution was spin-coated on PC and this was followed by vuv irradiation with a Xe excimer lamp at 172 nm under N₂ atmosphere. The PC substrate with vuv irradiated coating retained its high transmittance in the visible region for about 3 or more times of scraping turns by a steel wool tester on the surface, compared with the non-irradiated or mercury lamp-irradiated coatings, which demonstrated the remarkable improvement of the abrasion resistance by the vuv irradiation. The chemical changes under the vuv irradiation were also investigated by FTIR–ATR spectroscopy, composition analysis conducted with X-ray photoelectron spectroscopy and hardness measurements. It was concluded that the vuv light irradiation resulted in degrading the Si–CH₃ bond in sol–gel derived siliceous coatings to yield hardening of the coatings. The transmittance of the coating in vuv region also increased with the Xe lamp irradiation.     

A numeric model to simulate solar individual ultraviolet exposure

Exposure to solar ultraviolet (UV) light is the main causative factor for skin cancer. UV exposure depends on environmental and individual factors. Individual exposure data remain scarce and development of alternative assessment methods is greatly needed. We developed a model simulating human exposure to solar UV. The model predicts the dose and distribution of UV exposure received on the basis of ground irradiation and morphological data. Standard 3D computer graphics techniques were adapted to develop a rendering engine that estimates the solar exposure of a virtual manikin depicted as a triangle mesh surface. The amount of solar energy received by each triangle was calculated, taking into account reflected, direct and diffuse radiation, and shading from other body parts. Dosimetric measurements (n = 54) were conducted in field conditions using a foam manikin as surrogate for an exposed individual. Dosimetric results were compared to the model predictions. The model predicted exposure to solar UV adequately. The symmetric mean absolute percentage error was 13%. Half of the predictions were within 17% range of the measurements. This model provides a tool to assess outdoor occupational and recreational UV exposures, without necessitating time-consuming individual dosimetry, with numerous potential uses in skin cancer prevention and research.     

紫外辐照法制备金属钴包覆苯乙烯-甲基丙烯酸共聚物复合粒子

紫外辐照法;钴;包覆;复合粒子;导电高分子;表面活性剂