聚烯烃的光化学与辐射化学改性

本文介绍了光化学及幅射化学交联的机理及其对聚合物结构与性能的影响,举例说明了它们在聚烯烃薄膜与电缆改性上的应用。     

纳米TiO2的复合改性及其光催化性能

采用甲基丙烯酸甲酯、硝酸镧对纳米TiO2进行复合改性,以亚甲基蓝作为光催化降解对象,讨论改性条件对纳米TiO2光催化性能的影响.结果表明,纳米TiO2经过改性后,其光催化性能均有所提高,尤其是经过硝酸镧复合改性后,其光催化性能明显好于未改性纳米TiO2和单一改性纳米TiO2.甲基丙烯酸甲酯用量、硝酸镧用量、热处理温度、热处理时间对纳米TiO2光催化性能均有影响.复合改性纳米TiO2的较佳工艺条件为:甲基丙烯酸甲酯用量为44.09%,硝酸镧用量为2.31%,热处理温度为500℃,热处理时间为5 h.     

Chemical Modification of Phage-Displayed Helix-Loop-Helix Peptides to Construct Kinase-Focused Libraries

Conformationally constrained peptides hold promise as molecular tools in chemical biology and as a new modality in drug discovery. The construction and screening of a target-focused library could be a promising approach for the generation of de novo ligands or inhibitors against target proteins. Here, we have prepared a protein kinase-focused library by chemically modifying helix-loop-helix (HLH) peptides displayed on phage and subsequently tethered to adenosine. The library was screened against aurora kinase A (AurA). The selected HLH peptide Bip - 3 retained the α-helical structure and bound to AurA with a K_D value of 13.7 μM. Bip - 3 and the adenosine-tethered peptide Bip - 3 - Adc provided IC₅₀ values of 103 μM and 7.7 μM, respectively, suggesting that Bip - 3 - Adc bivalently inhibited AurA. In addition, the selectivity of Bip - 3 - Adc to several protein kinases was tested, and was highest against AurA. These results demonstrate that chemical modification can enable the construction of a kinase-focused library of phage-displayed HLH peptides.     

Polymer-Bound Chiroptical Molecular Switches; Photochemical Modification of the Chirality of Thin Films

Photobistable chiral polymers were obtained by covalent attachment of inherently dissymmetric 2-hydroxy-9-(7′methyl-1′,2′,3′,4′-tetrahydrophenanthrene-4′-ylidene)-9H-thioxanthene to methacrylate copolymers with appropriate spacers. Upon irradiation at 300 nm the optical activity of thin films of these polymers could be altered.     

Photochemical Etching of Silicon

Silicon that was immersed in hydrofluoric acid can be etched photochemically by laser, and it was found to produce long and regular columnar structure, if the laser power density is greater than 10 mW/mm². Another criterion is that the laser wavelength should be at the blue end of visible spectrum. Fine wires with diameter 300–200 nm were also observed at the top of these columns. The dimension of these fine wires is near to quantum confinement dimension, thus can be taken as supporting evidence for quantum confinement. The photoluminescence spectra full width half maximum was narrower than that from porous silicon fabricated from conventional anodisation method. The narrower full width was attributed to the uniformity of the porous silicon structure. A physical model is proposed to explain the observed strong directional etching. The model showed that once the etch sites have randomly initiated, the etching rate becomes directional under the influence of laser. The intensity of laser controls the etching direction such that silicon columns are formed if the intensity of the laser is strong enough.     

Photochemical dechlorination of PCBs

An effective process scheme for photochemical PCBs dechlorination reaction in alkaline isopropylalcohol has been studied. Based on the experimental obs     

Photochemical degradation of thermoplastics

The general mechanism of polymer photodegradation is outlined, and various aspects are then discussed with reference to polyolefins, particularly polyethylene. It is shown that various impurities accelerate degradation and that carbonyl groups play a complex role in the process. Polyolefins can be stabilised against photodegradation by incorporation of suitable u.v. stabilisers or pigments, and the principles involved, including the synergism between u.v. stabilisers and antioxidants, are discussed.     

Photochemical studies of rancidity

1. Experiments with oils irradiated by means of color filters selected so that successive portions of the visible spectrum are absorbed show that blue light is more conducive to the formation of peroxides and the development of rancidity than the red end of the spectrum for the same time of irradiation. 2. The results of these experiments seem to indicate that the formation of peroxides and the development of rancidity are accelerated in proportion to the amount of blue light transmitted by the filter. 3. The development of rancidity does not necessarily parallel the formation of peroxides. This is shown by the fact that an oil protected by green and not organoleptically rancid may have a peroxide value as high as, or higher than, an oil which has not been so protected and which is rancid. 4. Experiments show that, with respect to the formation of peroxides and the development of rancidity, lard, and animal fat, responds to selective light in the same way as do corn and cotton-seed oils. 5. Containers or wrappers designed for enclosing oil-bearing foods should exclude both ends of the visible spectrum, more especially the blue, in order to prevent or delay the development of rancidity. 6. The color which affects the development of rancidity the least is green delimited by 4,900 to 5,800 Ångström units.     

Photochemical Flow Reactions

The versatility of photochemical flow processes is rapidly expanding, and we suggest that this technique is capable of broadening the general appeal and impact of photochemistry similar or even to a greater extent to what microwave technology has done to thermal processes. This review highlights the recent developments that support this suggestion as well as the technological challenges that have yet to be resolved. Continuous photoflow reactions allow for better control over heating and mixing, are safer to operate on scale-up, in particular if LEDs are used in place of Hg lamps, they offer a higher surface/volume ratio and more efficient light penetration than batch mode photoreactions, and furthermore allow for the removal of products in-line to avoid secondary decompositions and poor conversions.     

Secretory Peptides as Bullets: Effector Peptides from Pathogens against Antimicrobial Peptides from Soybean

Soybean is an important crop as both human food and animal feed. However, the yield of soybean is heavily impacted by biotic stresses including insect attack and pathogen infection. Insect bites usually make the plants vulnerable to pathogen infection, which causes diseases. Fungi, oomycetes, bacteria, viruses, and nematodes are major soybean pathogens. The infection by pathogens and the defenses mounted by soybean are an interactive and dynamic process. Using fungi, oomycetes, and bacteria as examples, we will discuss the recognition of pathogens by soybean at the molecular level. In this review, we will discuss both the secretory peptides for soybean plant infection and those for pathogen inhibition. Pathogenic secretory peptides and peptides secreted by soybean and its associated microbes will be included. We will also explore the possible use of externally applied antimicrobial peptides identical to those secreted by soybean and its associated microbes as biopesticides.     

Photochemical applications of phase-modulus interdependencies

After an accolade to Joshua Jortner, we trace the influences of his chemistry background in his physics writings. On the way, we note the richness of physics in principles (or large-scale laws) and the fact-orientedness of chemistry. Next we turn to a recent laser-induced electron-detachment experiment and utilize analytic properties of the developing wave packet in the (complex) time domain, studied by us previously, to relate the phase of the optimized laser field to its intensity. It is suggested that these results can be used to reduce the labor of pulse optimization in phase-intensity controlled reaction dynamics. Phase-intensity inter-dependencies are also established in simulated results (obtained with the electron nuclear dynamics END-algorithm) for photoexcited hydrogen molecules.     

二苯氯甲烷的光化学合成

以无水氯化锌为催化剂,苯与氯化苄为原料,经Friedel Crafts反应制得二苯甲烷,收率为72 6%;在可见光照射下,二苯甲烷与氯气发生自由基取代反应生成二苯氯甲烷。通过系列实验得出了二苯氯甲烷光化学合成的优化工艺条件:n(二苯甲烷)∶n(氯气)=1∶1 02,光源采用碘钨灯,反应温度90～100℃,通氯时间12h,以二苯甲烷计二苯氯甲烷收率82 2%,产品质量分数≥98%,通过红外和质谱对其结构进行了确证。     

Photochemical preparation of polymer-clay composites

Polymer–clay composites of poly([2-(methacryloxy)ethyl]trimethylammonium chloride) and various clayey minerals have been prepared by visible light-induced free radical polymerization. The starting monomer–clay formulation contained: (i) the initiating dye, Rose bengal derivative, (2′[6-(3-trimethylaminopropoxy)-2,4-diiodo-3-oxo-3H-xanthen-9-yl]-benzyloxy-propyltrimethyl-ammonium dibromide, DBEE); (ii) the electron donor, 2-(dimethyl-amino)ethyl methacrylate; and (iii) the crosslinking monomer, poly(ethylene glycol) dimethacrylate. The method allows to prepare 1–2 mm thick foils that can be formed under both artificial lights and the sunlight exposition. The foil is flexible and insoluble in water. The clay is not rinsed out from the composite even after hundreds of hours of water treatment. The obtained composites do not exhibit good mechanical properties.     

几个有合成价值的光化学反应

光化学反应是以洁净、节能、节约为目标的化学合成方法 ,它为有机合成化学提供了新途径、新方法和新技术 ,是合成化学中最活跃、最有生命力的研究领域之一 ,深入研究光化学反应必将为现代有机合成的发展注入新的活力 .本论文重点研究了具有应用价值的烯烃光敏氧化、脱肟成酮光敏氧化及汉斯酯 1 ,4 二氢吡啶衍生物芳香化等光化学反应 ,取得了一系列重要的研究结果 .1　烯烃的光敏氧化反应烯烃的光敏氧化反应是具有重要应用前景的光化学反应之一 .敏化剂的优劣直接影响反应的产率和选择性 .我们利用Nafion膜特殊的结构特点 ,制备了以Nafion膜…     

Photochemical Degradation of Recycled High-Impact Polystyrene

Photooxidative aging of high-impact polystyrene sheets at 25°C was followed for different intervals of 25, 40, 50, 75, and 80 h. Five different types of samples were used, viz. virgin, and recycled once, twice, three, and four times. The optical properties of exposed samples exhibited changes as a result of discoloration. The transmittance and reflection deceases whereas absorbance increases with increasing recycling of high-impact polystyrene.     

Photochemical Tendering Activity of Sulphur Dyes

The photochemical tendering activity of a series of sulphur dyes on cotton cloth has been assessed in terms of (I) the changes in the physical and chemical properties of the fibre and (2) the extent of fading of the dyes and the formation of hydrogen peroxide during exposure.