Dynamics and mechanism of light harvesting in UV photoreceptor UVR8

Photosynthetic pigments form light-harvesting networks to enable nearly perfect quantum efficiency in photosynthesis via excitation energy transfer. However, similar light-harvesting mechanisms have not been reported in light sensing processes in other classes of photoreceptors during light-mediated signaling. Here, based on our earlier report, we mapped out a striking energy-transfer network composed of 26 structural tryptophan residues in the plant UV-B photoreceptor UVR8. The spectra of the tryptophan chromophores are tuned by the protein environments, funneling all excitation energy to a cluster of four tryptophan residues, a pyramid center, where the excitation-induced monomerization is initiated for cell signaling. With extensive site-directed mutagenesis, various time-resolved fluorescence techniques, and combined QM/MM simulations, we determined the energy-transfer rates for all donor–acceptor pairs, revealing the time scales from tens of picoseconds to nanoseconds. The overall light harvesting quantum efficiency by the pyramid center is significantly increased to 73%, compared to a direct excitation probability of 35%. UVR8 is the only photoreceptor discovered so far using a natural amino-acid tryptophan without utilizing extrinsic chromophores to form a network to carry out both light harvesting and light perception for biological functions.

The light-harvesting network from distal and peripheral to central tryptophans with transfer efficiencies determined from measured energy-transfer rates.     

Fluorescence Excitation Spectrum of Bilirubin in Blood: A Model for the Action Spectrum for Phototherapy of Neonatal Jaundice

A recent report (Lamola et al. 2013 Pediatric Research, 74, 54–60) presents a semiempirical model for facile calculation of an action spectrum for bilirubin photochemistry in vivo using the most current knowledge of the optics of neonatal skin. The calculations indicate that competition for phototherapy light by hemoglobin in the skin is the predominant factor that defines the spectrum of light absorbed by bilirubin. If the latter is correct, a valid physical analog of the calculated spectrum is the excitation spectrum of bilirubin in blood. The fluorescence excitation spectrum was recorded and, indeed, found to be very similar to the calculated spectrum. Both spectra exhibit maxima near 476 nm and widths at half height of about 50 nm. This result supports the conclusion that light between 460 and 490 nm is most effective for phototherapy of neonatal jaundice.     

Verbindungen mit Schichtstrukturen in den Systemen CuGa5S8/CuIn5S8 und AgGa5S8/AgIn5S8

Compounds with Layered Structures in the Systems CuGa₅S₈/CuIn₅S₈ and AgGa₅S₈/AgIn₅S₈ The title systems have been investigated by single crystal and powder X‐ray diffraction methods on quenched samples. In the system AgGa_xIn_5–xS₈ spinel type phases are formed up to x < 2. A compound crystallising with a hexagonal layered structure is obtained for 2 < x ≤ 3. The crystal structure of this layered phase has been solved on a single crystal of composition AgGa₃In₂S₈: space group P6₃mc, Z = 2, a = 380.80 and c = 3076.4 pm. The structure is isotypic to the Zn₂In₂S₅ (II a) type. The sample AgGa₄InS₈ crystallises in a Wurtzite like structure with a = 377.25 and c = 616.1 pm. In the system CuGa_xIn_5–xS₈ a new compound with layered structure has been detected for 1 ≤ x ≤ 2 which crystallises hexagonally with a = 380.28 and c = 3073.4 pm (x = 2). For the spinel CuIn₅S₈ an exchange of In by Ga is not detected.     

UVR emissions from solaria in Australia and implications for the regulation process

To assist in the development of the 2008 Australian/New Zealand standard on solaria and related regulations, Australian Radiation Protection and Nuclear Safety Agency scientists visited a number of tanning establishments during 2008 to measure the intensity and spectral distribution of the ultraviolet radiation (UVR) emissions from a range of solaria. The 2002 Australian/New Zealand Standard "Solaria for cosmetic purposes" (AS/NZS 2635) allowed a maximum UVR output from solaria of UV Index 60, a compromise between the solarium industry who wanted no upper limit and the health agencies who wanted to limit intensity. Of the 20 solaria examined in detail, only one had emissions of intensity less than UV Index 12, typical of mid-latitude summer sunlight, 15 units emitted more than UV Index 20, while three units emitted at intensities above UV Index 36, the maximum allowed by the new standard, AS/NZS 2635 (2008) and would thus not comply. UVA emissions ranged from 98W·m(-2) up to a maximum of 438W·m(-2) , more than six times the UVA content of mid-latitude summer sunshine. The results indicate that solaria users in Australia have access to solaria that are high intensity units with both significantly higher UVB and UVA emissions than sunlight, with implications for resultant adverse health effects.     

MoCl5参与的芳香化合物的C—H活化及原位C—C键偶联反应

五氯化钼;芳烃C—H键活化;原位偶联反应     

UVB Monochromatic Action Spectrum for the Inhibition of Photosynthetic Oxygen Production in the Green Alga Dunaliella saha

The effect of monochromatic UVB (280–315 nm) irradiation on the photosynthetic activity of the marine green alga Dunaliella salina was investigated by monitoring the rate of oxygen exchange. Samples were irradiated with narrow bands centered at different UV wavelengths (281, 290, 300, 310 and 322 nm). In a first set of experiments the samples were preirradiated keeping constant the irradiance and varying exposure time. By increasing UVB fluence, a wavelength-dependent decrease in the rate of oxygen production was observed. In a second set of experiments oxygen exchange was monitored simultaneously to UVB irradiation. The decline in the rate of oxygen production was sharper at short wavelengths and faster with increasing UVB photon flux density. The photon fluence action spectra derived from the two sets of experiments are in good agreement and indicate a decrease in the UVB-inhibiting effectiveness of two orders of magnitude from about 0.2 (mmol m-2)-1 at 281 nm to about 0.003 (mmol m-2)-1 at 322 nm. The photon flux density action spectrum derived from the second set of experiments indicates a smoother decrease from about 0.2 (pmol s-l m-2)-1 at 281 nm to about 0.05 (pmol s-l m-z)-l at 310 nm.     

苯并三氮唑对18-8钢应力腐蚀开裂的缓蚀作用

利用慢应变速率技术（SSRT），并结合电化学极化曲线和阻抗实验方法研究了苯并三氮唑（BTA）添加剂对1Cr18Ni9Ti奥氏体不锈钢在0．5mol·L－1HCl＋0．5mol·L－1NaCl溶液中应力腐蚀和均匀腐蚀的缓蚀作用．结果表明，这种添加剂的缓蚀作用主要是抑制腐蚀的阳极过程而产生的．     

Comparative Action Spectrum for Ultraviolet Light Killing of Mouse Melanocytes from Different Genetic Coat Color Backgrounds

The photobiology of mouse melanocyte lines with different pigment genotypes was studied by measuring colony-forming ability after irradiation. The cell lines were wild-type black (melan-a) and the mutants brown (melan-b) and albino (melan-c). Four lamps emitting various UV wavelengths were used. These were germicidal (UVC, 200–280 Dm), 82.3% output at 254 nm, TL01 (UVB, 280–320 nm), 64.2% at 310–311 nm, FS20, broadband with peak output at 312 nm and Alisun-S (UVA, 320–400 nm), broadband with peak output at 350–354 nm. Appropriate filtration reduced the contaminating UVC to nonlethal levels for the longer waverange lamps. Wild-type melan-a was resistant to UVC and UVA compared to the other two cell lines, but the differences were small. The melan-c cell line was more resistant to UVB and markedly more resistant to FS20 than the pigmented lines. With the exception of FS20 responses, melan-b was more sensitive than melan-a to killing by the various UV lamps. There were more pyrimidine dimers (cyclobutane dimers and 6–4 photoproducts) produced in melan-a than in melan-c cells by UVC, UVB and FS20 lamps. Unlike melan-c, melan-a and melan-b showed a strong free radical signal of melanin character with a detectable contribution of pheomelanin-like centers. The contribution of pheome-lanin was higher in melan-b than in melan-a, while the total melanin content in these two cell lines was comparable. The abundant melanin granules of wild-type melan-a melanocytes were well melanized and ellipsoidal, whereas those of melan-b melanocytes tended to be spherical. In the albino line (melan-c) the melanocytes contained only early-stage melanosomes, all of which were devoid of melanin. The results indicate that pigment does not protect against direct effect DNA damage in the form of pyrimidine dimers nor does it necessarily protect against cell death. High pigment content is not very protective against killing by UVC and UVA, and it may photosensitize in UVB the very wavelength range that is of greatest concern with respect to the rising incidence in skin cancer, especially melanoma. It is clear from these studies that, in pigment cells, monochromatic results cannot predict polychromatic responses and that cell death from solar irradiations is a complex phenomenon that depends on more than DNA damage.     

Reactions SRN1: Partie 15. Action de sulfanions sur la chloro-5 iodo-7 hydroxy-8 quinoleine

The ethere derived from 5-chloro 7-iodo 8-hydroxy quinoline react under irradiation with aliphatic, aromatic, heterocyclic or heteroaromatic sulfanions or with the diethyl phosphite anion almost exclusively on position 7 by S_RN1 substitution of iodine. Factors influencing the reaction of the dihaloaromatic substrates toward either mono- or disubstitution (nature of the nucleofugic group, structure of nucleophile) are discussed.     

5-Naphthylazo-8-hydroxyquinoline (5NA8HQ) as a novel corrosion inhibitor for mild steel in hydrochloric acid solution

In this study, 5-naphthylazo-8-hydroxyquinoline (5NA8HQ) was synthesized, characterized, and tested as a corrosion inhibitor for mild steel in 1 M HCl solution in the temperature range 20 to 50 °C. Weight-loss and potentiodynamic polarization measurements were used to analyse the corrosion behaviour of the metal in the absence and presence of different concentrations of the inhibitor. Analyses of surface film and inhibited solutions by FT-IR and UV–visible spectroscopy enabled us to clarify aspects of the inhibition mechanism. Further examination using X-ray diffraction confirmed the action of 5NA8HQ as an effective inhibitor of corrosion of mild steel in acidic media. The results obtained showed that this compound was a good inhibitor of corrosion. The inhibition is of mixed anodic–cathodic nature with predominance of anodic character. The Langmuir isotherm was found to accurately describe the adsorption behaviour of 5NA8HQ. Spectrophotometric analysis showed the formation of a layer at the surface of the corroded sample; this was interpreted as formation of complexes between 5NA8HQ and metal cations present in the steel structure.     

Ecotypic differences in responses of Arabidopsis thaliana L. to elevated polychromatic UV-A and UV-B+A radiation in the natural environment: a positive correlation between UV-B+A inhibition and growth rate

The effects of supplementary ultraviolet-A (UV-A) and ultraviolet-B+A (UV-B+A) in the natural environment on the growth and morphology of various ecotypes of Arabidopsis thaliana were investigated. The ecotypes investigated were Columbia (Col-4), Landsberg erecta (Ler-0), Cvi-0, Wassilewskija, Enkheim-D, Aa-0 and Di-1. The mutant hy-4 was also used. Results varied with the radiation treatment, ecotype and parameter measured. Plants subjected to elevated UV-A were both insensitive (all parameters Cvi-0 and Col-4) and sensitive. When responses to UV-A occurred they were mostly inhibitory (all significant responses of Di-1 and Enkheim-D, most parameters of Wassilewskija, and some parameters of hy-4), however, promotive affects were observed for some parameters of Aa-0 and Ler-0. Supplementary UV-B+A inhibited all parameters of Di-1 and Enkheim-D and most parameters of Col-4, Ler-0 and hy-4, but Wassilewskija, Aa-0 and Cvi-0 were mostly insensitive. The magnitude of the UV-B+A response varied with ecotype (compare Di-1 with Ler-0). Some ecotypes were sensitive to UV-A but not UV-B+A (Aa-0), whereas others (Ler-0, Col-4) show the opposite sensitivities. A linear relationship is reported between the degree of UV-B+A inhibition of each ecotype and growth rate. The higher the growth rate the more susceptible the ecotype is to UV-B+A inhibition. This relationship holds for the majority of growth parameters measured.     

Action Spectrum for Sporulation and Photoavoidance in the Plasmodium of Physarum polycephalum, as Modified Differentially by Temperature and Starvation

Abstract— The Plasmodium of the myxomycete Physarum polycephalum sporulates in bright natural environments, suggesting a relationship between photobehavior and sporulation. Thus, the action spectra for two light-dependent phenomena as well as the effects of other environmental conditions have been studied. Sporulation like photo-avoidance responded to UVC (near 270 nm) and near IR (near 750 nm) in addition to the well-documented UVA (near 350 nm) and blue (near 460 nm) regions. Sporulation and photoavoidance had similar sensitivities in the shorter wavelengths, while the former was about 100 times more sensitive in near IR. The Plasmodium moved away from light in a wide spectral range. Starvation and high temperature at 31°C (25°C in standard conditions) reduced photoavoidance to UVA and to blue light, respectively. A high fluence rate of UVC suppressed the rhythmic contraction of the Plasmodium, and the action spectrum peaked at 270 nm. These results indicate that the Physarum Plasmodium may stay at brighter places not by positive phototaxis but by weakening the negative phototaxis to sunlight or by other possible taxes such as hydrotaxis. There may be at least four different photo-systems in the Plasmodium.     

Action Spectrum for the Photophobic Response of Ciona intestinalis (Ascidieacea, Urochordata) Larvae Implicates Retinal Protein

Ascidian tadpole larvae change swimming behavior during the course of development. The photic behavior of the larvae of Ciona intestinalis was monitored by a computerized cell-tracking system with a time resolution of 0.1 s. Newly hatched larvae swim at an average speed of 1.4 mm/s but show no response to light stimuli. The swimming speed of the larvae became slower (0.4 mm/s) 3 h after hatching and they were induced to swim more rapidly by a sudden decrease in light intensity 4 h after hatching. During the course of development, the maximal speed of swimming behavior increased with time until 8 h after hatching and then plateaued. The action spectrum for the step-down photophobic response of the larvae was determined at around 8 h after hatching and was fitted to Dartnall's nomogram with the absorbance maximum of the pigment located at 505 nm. These results suggest retinal proteins in the ocellus of the larvae are the photoreceptors for the photobehavior.     

Action spectra for photoinduced inactivation of bacteriophage T7 sensitized by 8-methoxypsoralen and angelicin

The action spectrum (240-300 nm) for photoinactivation of unsensitized phage T7 and the action spectra (310-380 nm) for photoinactivation of phage T7 sensitized with 8-methoxypsoralen (8-MOP) and angelicin were measured by an automated method. For unsensitized phage T7 the action spectrum is in good agreement with the absorption spectrum. For sensitization with angelicin the action spectrum is similar to the absorption spectrum, but for sensitization with 8-MOP the spectra are different. The agreement between the T7 absorption and action spectra in the far-UV region is due to photodamage of DNA, leading to phage inactivation. The similarity in the action and absorption spectra in the near-UV region for sensitization with angelicin seems to be in accordance with the monofunctional photobinding of angelicin to DNA. The action spectrum for sensitization with 8-MOP has a maximum at about 320 nm and this suggests that, in addition to the monoadducts, the biadducts play a role in the inactivation of phage T7. Taking the number of bound furocoumarin molecules into consideration, the quantum efficiencies were estimated. Furocoumarin increases the quantum efficiency in the near-UV region and the values are similar to those obtained in far-UV light without psoralens.     

8-羟基喹啉铍及其衍生物电子光谱性质的含时密度泛函理论研究

运用密度泛函理论(DFT)B3LYP方法和abinitioHF单激发组态相互作用(CIS)法分别优化了有机金属配合物8-羟基喹啉铍(BeQ₂)及其3种衍生物分子的基态及最低激发单重态几何结构.系统分析了分子结构、前线分子轨道特征和能级分布规律以探索电子跃迁机理.应用含时密度泛函理论(TD-DFT)计算分子的电子光谱,揭示了BeQ₂及其衍生物的发光源于配体中π→π^*电子跃迁,指出通过配体修饰可以有效地影响配合物前线分子轨道分布,调整发光波段,并有效提高电荷转移量.     

Blue Light Requirement for HC03 Uptake and Its Action Spectrum in Monoraphidium braunii

The uptake and assimilation of HCO₃ by the green unicellular alga Monoraphidium braunii can be monitored by the alkalinization of the external medium or by the O₂ evolution associated with the uptake and reduction of this anion. The activation of HCO₃ uptake in this microalga required the irradiation of the cell suspensions with low photon fluence rates of short wavelength radiation. Thus, when the cells were irradiated with strong red light in the presence of HCO₃, very little alkalinization of the external medium or O₂ evolution could be observed. The O₂ evolution rates measured under red light could be due to the assimilation of the CO₂ derived from the HCO₃ present in the medium. The blue light-dependent O₂ evolution rates were not diminished by a periplasmic carbonic anhydrase inhibitor, suggesting that HCO₃ -dependent O₂ evolution was due to the photoactivation of a selective HCO₃ uptake system at the plasma membrane. The action spectrum for HCO₃- uptake in M. braunii was very similar to those reported for NO₃- and CI^- suggested that a flavoprotein may be the photoreceptor for this response.