Excited-state absorption of meso-tetrasulfonatophenyl porphyrin: Effects of pH and micelles

The influence of the environment on the excited state transitions of meso-tetrakis(p-sulfonatophenyl) porphyrin (TPPS) is reported. TPPS was investigated in protonated and non-protonated forms, and in the presence of the cationic cetyltrimethylammonium bromide (CTAB) micelles. The singlet excited-state absorption spectra were measured by using the white-light continuum Z-scan technique and the triplet–triplet absorption spectra were acquired employing an association of laser flash photolysis and Z-scan techniques. Our results show that the perseveration of the molecular symmetry, upon excitation, depends on the state of multiplicity of the molecules, as well as on the environment and structural characteristics of the porphyrin. Additionally, it was observed that for excited molecules, the ring distortion caused by the protonation of porphyrin ring has great influence on the changes observed for the symmetry and vibronic structure. The results clearly show that the porphyrin investigated is a promising candidate for optical limiting applications for all investigated environments.     

7-(Dialkylamino)coumarin-4-yl]methyl-Caged Compounds as Ultrafast and Effective Long-Wavelength Phototriggers of 8-Bromo-Substituted Cyclic Nucleotides

[7-(Dimethylamino)coumarin-4-yl]methyl (DMACM) and [7-(diethylamino)coumarin-4-yl]methyl (DEACM) esters of 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) and 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) are described as novel caged compounds for 8-bromo-substituted cyclic nucleotides. Synthesis is accomplished by treatment of the free acids of the cyclic nucleotides with the corresponding 7(dialkylamino)-substituted 4(diazomethyl)coumarins. Irradiation of the DMACM- and DEACM-caged cyclic nucleotides with UV light stimulates the release of the cyclic nucleotides within roughly a nanosecond. The new caged compounds are resistant to hydrolysis in aqueous buffers and exhibit long-wavelength absorption properties with maxima at 400 nm, high extinction coefficients, and high quantum yields (0.15-0.31). Their favorable properties render these compounds the most efficient and rapid phototriggers of 8-bromo-substituted cyclic nucleotides known. The usefulness of the compounds for physiological studies under nondamaging light conditions was examined in HEK293 cells expressing the alpha subunit of the cyclic-nucleotide-gated (CNG) channel of cone photoreceptors (CNGA3) and of olfactory neurons (CNGA2) by using confocal laser scanning microscopy and the patch clamp technique.     

二甲基硫醚的光解特性

本文对二甲基硫醚（ＤＭＳ）在有氧、无氧及有Ｈ２Ｏ２存在的情况下紫外光辐照，然后在２０ｍ长光程 籍富里叶红外光谱仪测定光解产物的吸光谱，实验表明在无氧的情况下ＤＭＳ的Ｃ－Ｓ键断裂，并生成ＣＨ３ＳＳＣＨ３及Ｃ２Ｈ６，在有氧存在下生成ＨＣＨＯ及ＣＨ３ＳＯ３Ｈ〈在有Ｈ２Ｏ２存在下生成ＣＨ３ＳＳＣＨ３，本文讨论了的可能机理，合理地解释光解产物的生成。     

新型除草剂异丙草胺在水中的光降解残留研究

采用高效液相色谱法(HPLC)和气-质联用技术(GC-MS)研究了新型除草剂异丙草胺在不同性质的模拟天然水体中的光降解残留情况,建立了光降解过程中异丙草胺浓度的HPLC定量分析方法。用含腐植酸的水样(HAW)、含丙酮的水样(AW)、低溶解氧含量的水样(LDOW)和纯水(PW)模拟了不同性质的天然水体。实验结果表明,浓度测定方法的回收率99％,标准偏差<0.4,变异系数<1.5％,最低检测浓度为5.47×10~(-6)g/L,最小检测量为5.47×10~(-11)g.相同的光照条件下,异而草胺的降解速率r和水体性质有直接关系,其大小顺序依次为:r_(HAW)>r_(LDOW)>r_(AW)>r_(PW)。在不同水样的光解反应中均发现两种主要光解产物,经鉴定是分子中C—Cl的断裂形成的2-羟基-N-(2-乙基-6-甲苯基)-N-[(1-甲乙氧基)-甲基]-乙酰胺和8-乙基-2-羰基-N-[(1-甲基乙氧基)-甲基]-苯并[b]二氢吡定。     

Polyynes Production in a Solvent-Submerged Electric Arc Between Graphite Electrodes. III. Chemical Reactivity and Stability Toward Air, Ozone, and Light

Since polyynes are easily accessible with the submerged electric arc synthesis between graphite electrodes, the chemical behavior of polyynes solutions in different solvents has been explored. It has been found that surprisingly the polyynes solutions, with polyynes having up to 16 carbon atoms arranged in a chain, are stable in air over 1 week time in the dark. These solutions react relatively slowly with ozone while add rapidly and completely bromine. The polyynes solutions are instead quite easily photolyzed under the action of UV radiation both in air and under N₂. Two different light sources were used in the study: a low pressure mercury lamp emitting almost a monochromatic radiation at 254 nm and an high pressure mercury lamp emitting in a broad wavelength range in the ultraviolet. With the former monochromatic light source, it has been demonstrated the possibility to perform a selective photolysis of selected polyynes in a mixture of homologous series.     

Radiation- and Photo-Induced Oxidation Pathways of Methionine in Model Peptide Backbone under Anoxic Conditions

Within the reactive oxygen species (ROS) generated by cellular metabolisms, hydroxyl radicals (HO^•) play an important role, being the most aggressive towards biomolecules. The reactions of HO^• with methionine residues (Met) in peptides and proteins have been intensively studied, but some fundamental aspects remain unsolved. In the present study we examined the biomimetic model made of Ac-Met-OMe, as the simplest model peptide backbone, and of HO^• generated by ionizing radiation in aqueous solutions under anoxic conditions. We performed the identification and quantification of transient species by pulse radiolysis and of final products by LC-MS and high-resolution MS/MS after γ-radiolysis. By parallel photochemical experiments, using 3-carboxybenzophenone (CB) triplet with the model peptide, we compared the outcomes in terms of short-lived intermediates and stable product identification. The result is a detailed mechanistic scheme of Met oxidation by HO^•, and by CB triplets allowed for assigning transient species to the pathways of products formation.     

太阳能光化学利用方式及应用评述

论述了太阳能光化学利用的主要方式,即光电化学利用、光分解利用、光合作用和光敏化学利用.阐明了这几种利用方式的基本原理、过程和实际应用.重点评述了具有潜在实用价值的光电化学及光分解利用,指出了其优缺点,并对发展趋势做了展望.     

异喹啉的脉冲辐解和激光光解研究

用脉冲辐解和激光光解相结合,研究了异喹啉这种难降解杂环化合物在紫外光作用下的变化和与HO·的反应.结果表明,在波长为266nm的激光作用下,异喹啉不仅发生光激发,而且发生单光子电离,其量子产额为1.58×10-4.异喹啉光电离产生的阳离子自由基可以脱去质子,其pKa为5.50.异喹啉可以与HO·发生反应,其反应速率常数为3.4×109 mol-1·dm3·s-1.本工作的研究将为photo-Fenton法降解异喹啉提供理论上的依据.     

核黄素(维生素B2)的光化学活性粒子:潜在的光生物学效应

应用３３７ｎｍ激光光解时间分辨吸收技术,通过考察核黄素（维生素Ｂ２）激发三重态的自猝灭及与酚类抗氧经剂的抽氢反应,核黄素阴离子自由基与氧气的电子转移反应,模拟了黄素在体内产生具有潜在光生物效应的活性粒子的途径,得到了一系列重要的动力学参数。为研究核黄素在体内的氧化还原作用,扩展它作为光敏化剂的用途提供了理论基础。