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Angewandte Chemie (International Ed. in... Feb 2011Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular... (Review)
Review
Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.
Topics: Biological Products; Photochemical Processes; Photochemistry
PubMed: 21246702
DOI: 10.1002/anie.201002845 -
Organic Letters Apr 2001[reaction: see text]. An approach to the asymmetric intramolecular meta photocycloaddition of phenoxyalkenes is described. The beta-cyclodextrin complexes of several...
[reaction: see text]. An approach to the asymmetric intramolecular meta photocycloaddition of phenoxyalkenes is described. The beta-cyclodextrin complexes of several phenoxyalkenes have been synthesized and irradiated in the solid phase. The effect of the CD-hosting on the regio- and enantioselectivity is discussed. Values of ee up to 17% were obtained.
Topics: Alkenes; Chromatography, High Pressure Liquid; Cyclodextrins; Magnetic Resonance Spectroscopy; Models, Chemical; Photochemistry
PubMed: 11348187
DOI: 10.1021/ol0156345 -
Harmful Algae Mar 2017A series of ten photolysis experiments was conducted with sediments exposed to Microcystis sp. blooms to determine if sunlight is capable of mobilizing the biotoxin...
A series of ten photolysis experiments was conducted with sediments exposed to Microcystis sp. blooms to determine if sunlight is capable of mobilizing the biotoxin microcystin-LR (MC-LR) into the water column. There was a net photorelease of MC-LR in irradiated suspensions in all cases relative to dark controls, ranging from 0.4 to 192μgLg into the dissolved phase. This should be viewed as a minimum estimate of photorelease due to concurrent photodegradation of dissolved toxin. Dissolved MC-LR concentrations in a sediment suspension increased linearly in the aqueous phase during a six-hour irradiation with simulated sunlight suggesting that longer exposure times produce greater quantities of MC-LR. There was a significant positive correlation between photorelease of toxin and percent organic carbon of the resuspended material, implying that organic-rich sediments yield the greatest photorelease of MC-LR upon exposure to full spectrum sunlight. Samples exposed to photosynthetically active radiation (400nm-700nm) were responsible for less than 2% of the photorelease compared to full spectrum exposures. Model calculations indicate that photochemical processing of bloom impacted sediments could be responsible for as much as 100% of the average standing stock of MC-LR in a freshwater pond located in southeastern North Carolina, where surface water concentrations were also measured. Mass spectrometric analysis revealed a new peak in light exposed flasks that appears to be a photo-induced isomerized product of MC-LR. Photoproduction from resuspended sediments therefore represents a significant but previously unrecognized source of highly toxic MC-LR and photoproducts of unknown toxicity and fate to aquatic ecosystems.
Topics: Geologic Sediments; Microcystis; Photochemistry; Sunlight
PubMed: 28366384
DOI: 10.1016/j.hal.2017.01.002 -
Chemical Society Reviews Dec 2007A tutorial review is presented to inform and inspire the reader to develop and integrate strong scientific links between liquid crystals and holographic data storage,... (Review)
Review
A tutorial review is presented to inform and inspire the reader to develop and integrate strong scientific links between liquid crystals and holographic data storage, from a materials scientist's viewpoint. The principle of holographic data storage as a means of providing a solution to the information storage demands of the 21st century is detailed. Holography is a small subset of the much larger field of optical data storage and similarly, the diversity of materials used for optical data storage is enormous. The theory of polarisation holography which produces holograms of constant intensity, is discussed. Polymeric liquid crystals play an important role in the development of materials for holographic storage and photoresponsive materials based on azobenzene are targeted for discussion due to their ease of photo-reversion between trans- and cis-states. Although the final polymer may not be liquid crystalline, irradiation can induce ordered domains. The mesogens act in a co-operative manner, enhancing refractive indices and birefringences. Surface relief gratings are discussed as a consequence of holographic storage. Cholesteric polymers comprising azobenzene are briefly highlighted. Irradiation causing cis-trans-isomerisation can be used to control helix pitch. A brief mention of liquid crystals is also made since these materials may be of future interest since they are optically transparent and amenable to photo-induced anisotropy.
Topics: Computer Storage Devices; Information Storage and Retrieval; Light; Liquid Crystals; Molecular Structure; Optics and Photonics; Photochemistry; Polymers; Stereoisomerism; Surface Properties
PubMed: 17982514
DOI: 10.1039/b706242g -
Nanoscale Feb 2014Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great... (Review)
Review
Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.
Topics: Boron Compounds; Catalysis; Halogens; Nanostructures; Photochemistry; Ultraviolet Rays
PubMed: 24430623
DOI: 10.1039/c3nr05529a -
Molecules (Basel, Switzerland) Jun 2010After Mallory described in 1964 the use of iodine as catalyst for the photochemical cyclisation of stilbenes, this reaction has proven its effectiveness in the synthesis... (Review)
Review
After Mallory described in 1964 the use of iodine as catalyst for the photochemical cyclisation of stilbenes, this reaction has proven its effectiveness in the synthesis of phenanthrenes, other PAHs and phenacenes with a surprisingly large selection of substituents. The "early age" of the reaction was reviewed by Mallory in 1984 in a huge chapter in the Organic Reactions series, but the development has continued. Alternative conditions accommodate more sensitive substituents, and isomers can be favoured by sacrificial substituents. Herein the further developments and applications of this reaction after 1984 are discussed and summarized.
Topics: Cyclization; Iodine; Molecular Structure; Oxidation-Reduction; Photochemistry; Stilbenes
PubMed: 20657445
DOI: 10.3390/molecules15064334 -
The Journal of Physical and Colloid... Mar 1948
Topics: Ketones; Photochemistry
PubMed: 18904936
DOI: 10.1021/j150459a014 -
Nanoscale Apr 2012The creation of core-shell nanocomposites (CSNs) has attracted considerable attention and developed into an increasingly important research area at the frontier of... (Review)
Review
The creation of core-shell nanocomposites (CSNs) has attracted considerable attention and developed into an increasingly important research area at the frontier of advanced materials chemistry. CSNs, which are nanoscaled assemblies with a chemical composition that is different on the surface compared to the core region, have found versatile applications in many fields, such as electrooptics, quantum dots, microscopy labels, drug delivery, chemical sensors, nanoreactors and catalysis. This review is primarily focused on the applications of metal core@semiconductor shell nanocomposites in heterogeneous photocatalysis, including photocatalytic nonselective processes for environmental remediation, selective organic transformations to fine chemicals and water splitting to clean hydrogen energy. It is hoped that this minireview can inspire multidisciplinary research interest in the precisely morphology-controlled synthesis of a variety of metal core@semiconductor shell nanoassemblies and their wide applications in the realm of heterogeneous photocatalysis.
Topics: Catalysis; Metal Nanoparticles; Models, Biological; Nanocomposites; Nanoshells; Photochemical Processes; Photochemistry; Semiconductors
PubMed: 22362188
DOI: 10.1039/c2nr00009a -
Molecules (Basel, Switzerland) Jan 2017This short review provides the current state-of-the-art of in situ coupling of ultrasound to chemical deposition methods. A synergetic action of the ultrasound and light... (Review)
Review
This short review provides the current state-of-the-art of in situ coupling of ultrasound to chemical deposition methods. A synergetic action of the ultrasound and light radiation or electrical fields may result in new powerful methodologies, and these include sonophotodeposition and sonoelectrodeposition processes. The effect of ultrasound is explained on the base of different physical mechanisms emerging from cavitation phenomenon. Some possible mechanisms of the interactions between ultrasound and photochemical and electrochemical processes are discussed here. The application of sonophotodeposition and sonoelectrodeposition as green energy sources in the syntheses of different nanomaterials is also reviewed.
Topics: Chemistry Techniques, Synthetic; Electrochemical Techniques; Nanostructures; Photochemical Processes; Photochemistry; Ultrasonic Waves
PubMed: 28146131
DOI: 10.3390/molecules22020216 -
Nanoscale Feb 2014Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large... (Review)
Review
Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large band gap of TiO2 and massive recombination of photogenerated electron-hole pairs limit its photocatalytic and photovoltaic efficiency. Therefore, increasing research attention is now being directed towards engineering the surface structure of TiO2 at the most fundamental and atomic level namely morphological control of {001} facets in the range of microscale and nanoscale to fine-tune its physicochemical properties, which could ultimately lead to the optimization of its selectivity and reactivity. The synthesis of {001}-faceted TiO2 is currently one of the most active interdisciplinary research areas and demonstrations of catalytic enhancement are abundant. Modifications such as metal and non-metal doping have also been extensively studied to extend its band gap to the visible light region. This steady progress has demonstrated that TiO2-based composites with {001} facets are playing and will continue to play an indispensable role in the environmental remediation and in the search for clean and renewable energy technologies. This review encompasses the state-of-the-art research activities and latest advancements in the design of highly reactive {001} facet-dominated TiO2via various strategies, including hydrothermal/solvothermal, high temperature gas phase reactions and non-hydrolytic alcoholysis methods. The stabilization of {001} facets using fluorine-containing species and fluorine-free capping agents is also critically discussed in this review. To overcome the large band gap of TiO2 and rapid recombination of photogenerated charge carriers, modifications are carried out to manipulate its electronic band structure, including transition metal doping, noble metal doping, non-metal doping and incorporating graphene as a two-dimensional (2D) catalyst support. The advancements made in these aspects are thoroughly examined, with additional insights related to the charge transfer events for each strategy of the modified-TiO2 composites. Finally, we offer a summary and some invigorating perspectives on the major challenges and new research directions for future exploitation in this emerging frontier, which we hope will advance us to rationally harness the outstanding structural and electronic properties of {001} facets for various environmental and energy-related applications.
Topics: Catalysis; Photochemistry; Titanium
PubMed: 24384624
DOI: 10.1039/c3nr04655a