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photochemistry

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https://www.readbyqxmd.com/read/28723093/plasmonic-aerogels-as-a-3d-nanoscale-platform-for-solar-fuels-photocatalysis
#1
Paul A DeSario, Jeremy J Pietron, Adam Dunkelberger, Todd H Brintlinger, Olga Baturina, Rhonda M Stroud, Jeffrey C Owrutsky, Debra R Rolison
We use plasmonic Au-TiO2 aerogels as a platform in which to marry synthetically thickened particle-particle junctions in TiO2 aerogel networks and Au||TiO2 interfaces and then investigate their cooperative influence on photocatalytic hydrogen (H2) generation under both broadband (i.e., UV + visible light) and visible-only excitation. In doing so, we elucidate the dual functions that incorporated Au can play as a water reduction/H2 generation co-catalyst and as a plasmonic sensitizer. We also introduce non-plasmonic Pt co-catalyst nanoparticles into our composite aerogels in order to leverage the catalytic water-reducing abilities of Pt...
July 19, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28723091/protomer-specific-photochemistry-investigated-using-ion-mobility-mass-spectrometry
#2
James N Bull, Neville J A Coughlan, Evan John Bieske
The utility of tandem ion mobility mass spectrometry coupled with electronic spectroscopy to investigate protomer-specific photochemistry is demonstrated by measuring the photoisomerization response for protomers of protonated 4-dicyanomethylene-2-methyl-6-para-dimethylaminostyryl-4H-pyran (DCM) molecules. The target DCMH(+) species, has three protomers that are distinguished by their different collision cross-sections with He, N2, and CO2 buffer gases, trends in abundance with ion source conditions, and from their photoisomerization responses...
July 19, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28719191/relationships-between-dissolved-organic-matter-composition-and-photochemistry-in-lakes-of-diverse-trophic-status
#3
Andrew Chapin Maizel, Jing Li, Christina K Remucal
The North Temperate Lakes-Long Term Ecological Research site includes seven lakes in northern Wisconsin that vary in hydrology, trophic status, and landscape position. We examine the molecular composition of dissolved organic matter (DOM) within these lakes using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) and quantify DOM photochemical activity using probe compounds. Correlations between the relative intensity of individual molecular formulas and reactive species production demonstrate the influence of DOM composition on photochemistry...
July 18, 2017: Environmental Science & Technology
https://www.readbyqxmd.com/read/28708985/ultrastructural-protein-and-photosynthetic-alterations-induced-by-pb-and-cd-in-cynara-cardunculus-l-and-its-potential-for-phytoremediation
#4
C Arena, F Figlioli, M C Sorrentino, L G Izzo, F Capozzi, S Giordano, V Spagnuolo
The effects of cadmium and lead were investigated in Cynara cardunculus L. Plant uptake by root and shoot, changes in cell ultrastructure and photosynthetic efficiency, photosynthetic key protein levels, as well as regulation of stress-induced Hsp70 were examined. Cynara cardunculus accumulated Cd and Pb in their tissue, with a different trend for the two metals. The prompt translocation of Cd to the shoot may justify the ultrastructural injuries, especially observed in chloroplasts. However, Cd- treated plants did not show any decline in photochemistry; it is likely that Cd in shoot tissue triggers defense mechanisms, increasing the level of proteins involved in photosynthesis (i...
July 11, 2017: Ecotoxicology and Environmental Safety
https://www.readbyqxmd.com/read/28707899/experimental-and-dft-computational-insight-into-nitrosamine-photochemistry-oxygen-matters
#5
Ashwini A Ghogare, Ciro J Debaz, Marilene Silva Oliveira, Inna Abramova, Prabhu P Mohapatra, Kitae Kwon, Edyta M Greer, Fernanda Manso Prado, Hellen Paula Valerio, Paolo Di Mascio, Alexander Greer
A nitrosamine photooxidation reaction is shown to generate a peroxy intermediate by experimental physical-organic methods. The irradiation of phenyl and methyl-substituted nitrosamines in the presence of isotopically labeled 18-oxygen revealed an O atom was trapped from a peroxy intermediate to trimethylphosphite or triphenylphosphine, or by nitrosamine itself, forming two moles of nitramine. The unstable peroxy intermediate can be trapped at low temperature in post-photolyzed solution in the dark. Chemiluminescence is also observed upon thermal decomposition of the peroxy intermediate, i...
July 14, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28702929/the-mechanism-behind-top-down-uvpd-experiments-making-sense-of-apparent-contradictions
#6
Ryan R Julian
Top-down ultraviolet photodissociation (UVPD) allows greater sequence coverage than any other currently available method, often fracturing the vast majority of peptide bonds in whole proteins. At the same time, UVPD can be used to dissociate noncovalent complexes assembled from multiple proteins without breaking any covalent bonds. Although the utility of these experiments is unquestioned, the mechanism underlying these seemingly contradictory results has been the subject of many discussions. Herein, some fundamental considerations of photochemistry are briefly summarized within the context of a proposed mechanism that rationalizes the experimental results obtained by UVPD...
July 12, 2017: Journal of the American Society for Mass Spectrometry
https://www.readbyqxmd.com/read/28699261/npq-t-a-chlorophyll-fluorescence-parameter-for-rapid-estimation-and-imaging-of-non-photochemical-quenching-of-excitons-in-photosystem-ii-associated-antenna-complexes
#7
Stefanie Tietz, Christopher C Hall, Jeffrey A Cruz, David M Kramer
In photosynthesis, light energy is absorbed by light-harvesting complexes and used to drive photochemistry. However, a fraction of absorbed light is lost to non-photochemical quenching (NPQ) that reflects several important photosynthetic processes to dissipate excess energy. Currently, estimates of NPQ and its individual components (qE , qI , qZ and qT ) are measured from pulse-amplitude-modulation (PAM) measurements of chlorophyll fluorescence yield and require measurements of the maximal yield of fluorescence in fully dark-adapted material (Fm ), when NPQ is assumed to be negligible...
August 2017: Plant, Cell & Environment
https://www.readbyqxmd.com/read/28696118/fusion-of-ultraviolet-visible-and-infrared-transient-absorption-spectroscopy-data-to-model-ultrafast-photo-isomerization
#8
Bruno Debus, Maylis Orio, Julien Réhault, Gotard Burdzinski, Cyril Ruckebusch, Michel Sliwa
Ultrafast photo-isomerization reactions generally start at higher excited state with excess of internal vibrational energy and occur via conical intersections. This leads to ultrafast dynamics which are difficult to investigate with a single transient absorption spectroscopy technique, be it in the UV-vis or IR domain. On one hand, the information available in the UV-vis is limited as only slight spectral changes are observed for different isomers. On the other hand, the interpretation of vibrational spectra is strongly hindered by intramolecular relaxation and vibrational cooling...
July 11, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28692892/photochemical-behavior-of-dissolved-and-colloidal-organic-matter-in-estuarine-and-oceanic-waters
#9
Wen-Zhuo Zhu, Gui-Peng Yang, Hong-Hai Zhang
Chromophoric dissolved organic matter (CDOM), carbohydrates, and amino acids were analyzed to investigate the photochemistry of total dissolved (<0.22μm) organic matter (DOM), high-molecular-weight (HMW, 1kDa-0.22μm) DOM and low-molecular-weight (LMW, <1kDa) DOM at stations in the Yangtze River and its coastal area, and in the Western Pacific Ocean. Results revealed that the humic-like and tryptophan-like CDOM fluorescent components in riverine, coastal, and oceanic surface waters were photodegraded during irradiation...
July 7, 2017: Science of the Total Environment
https://www.readbyqxmd.com/read/28688397/femtosecond-dynamics-of-the-2-methylallyl-radical-a-computational-and-experimental-study
#10
Anja Röder, Kevin Issler, Lionel Poisson, Alexander Humeniuk, Matthias Wohlgemuth, Michel Comte, Fabien Lepetit, Ingo Fischer, Roland Mitric, Jens Petersen
We investigate the photodynamics of the 2-methylallyl radical by femtosecond time-resolved photoelectron imaging. The experiments are accompanied by field-induced surface hopping dynamics calculations and the simulation of time-resolved photoelectron intensities and anisotropies, giving insight into the photochemistry and nonradiative relaxation of the radical. 2-methylallyl is excited at 236 nm, 238 nm, and 240.6 nm into a 3p Rydberg state, and the subsequent dynamics is probed by multiphoton ionization using photons of 800 nm...
July 7, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28688387/ultraviolet-photochemistry-of-2-bromothiophene-explored-using-universal-ionization-detection-and-multi-mass-velocity-map-imaging-with-a-pimms2-sensor
#11
R A Ingle, C S Hansen, E Elsdon, M Bain, S J King, J W L Lee, M Brouard, C Vallance, R Turchetta, M N R Ashfold
The ultraviolet photochemistry of 2-bromothiophene (C4H3SBr) has been studied across the wavelength range 265-245 nm using a velocity-map imaging (VMI) apparatus recently modified for multi-mass imaging and vacuum ultraviolet (VUV, 118.2 nm) universal ionization. At all wavelengths, molecular products arising from the loss of atomic bromine were found to exhibit recoil velocities and anisotropies consistent with those reported elsewhere for the Br fragment [J. Chem. Phys. 142, 224303 (2015)]. Comparison between the momentum distributions of the Br and C4H3S fragments suggests that bromine is formed primarily in its ground ((2)P3/2) spin-orbit state...
July 7, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28684729/perchlorates-on-mars-enhance-the-bacteriocidal-effects-of-uv-light
#12
Jennifer Wadsworth, Charles S Cockell
Perchlorates have been identified on the surface of Mars. This has prompted speculation of what their influence would be on habitability. We show that when irradiated with a simulated Martian UV flux, perchlorates become bacteriocidal. At concentrations associated with Martian surface regolith, vegetative cells of Bacillus subtilis in Martian analogue environments lost viability within minutes. Two other components of the Martian surface, iron oxides and hydrogen peroxide, act in synergy with irradiated perchlorates to cause a 10...
July 6, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28682611/forbidden-chemistry-two-photon-pathway-in-2-2-cycloaddition-of-maleimides
#13
Mikhail V Tsurkan, Christiane Jungnickel, Michael Schlierf, Carsten Werner
Two-photon excitation provides high spatial resolution in three dimensions of the corresponding chemical or physical processes, allowing submicrometer structuring in stereolithography and three-dimensional (3D) microfabrication. While studying two-photon structuring applications, we observed an undescribed phenomenon in photochemistry that dictates reactivity of maleimide groups in two-photon mode. A low-absorbance transition formerly ignored in classical photochemistry has been found for maleimides. This transition was assigned to symmetry-breaking donor-acceptor complex formation, which revealed a formally forbidden pathway in [2+2] cycloaddition reactions of maleimide moieties...
July 18, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28675675/flash-vacuum-pyrolysis-techniques-and-reactions
#14
Curt Wentrup
While pyrolysis reactions have been performed since ancient times and been crucial for the invention of several technologies, the methodology now commonly known as flash vacuum pyrolysis, FVP (or flash vacuum thermolysis, FVT) had its early beginnings in the 1940s and1950s, mainly through mass spectrometric detection of pyrolytically formed free radicals. In the 1960s many organic chemists started performing FVP experiments with the purpose of isolating new and interesting compounds and understanding pyrolysis processes...
July 4, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28674335/photodynamic-action-of-single-walled-carbon-nanotubes
#15
Tatsuya Murakami
Photodynamic therapy is achieved by the combination of photosensitizers, harmless visible or near-infrared (NIR) light, and molecular oxygen (O2). Photosensitizers transfer their absorbed light energy to O2 to generate a major active species in photodynamic therapy, singlet oxygen. In this review, I will discuss the possibility of single-walled carbon nanotubes as NIR photosensitizers, while explaining the general photophysics and photochemistry underlying photodynamic therapy as well as summarizing recent advances in the purification technologies for single-walled carbon nanotubes to reduce their toxicity concerns...
2017: Chemical & Pharmaceutical Bulletin
https://www.readbyqxmd.com/read/28671848/o2-polar-voc-complexes-h-bonding-versus-charge-dipole-interactions-and-the-non-innocence-of-formaldehyde
#16
Kellyn M Patros, Jennifer E Mann, Caroline Chick Jarrold
Anion photoelectron imaging was used to measure the photodetachment spectra of molecular complexes formed between O2(-) and a range of atmospherically relevant polar molecules, including species with a carbonyl group (acetone, formaldehyde) and alcohols (ethanol, propenol, butenol). Experimental spectra are analyzed using a combination of Franck-Condon simulations and electronic structure calculations. Strong charge-dipole interactions and H-bonding stabilize the complex anions relative to the neutrals, resulting in a ca...
July 3, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28665539/minimalistic-liquid-assisted-route-to-highly-crystalline-%C3%AE-zirconium-phosphate
#17
Yu Cheng, Xiaodong Tony Wang, Stephan Jaenicke, Gaik-Khuan Chuah
Zirconium phosphates have potential applications in areas of ion-exchange, catalysis, photochemistry, and biotechnology. However, synthesis methodologies to form crystalline α-zirconium phosphate (Zr(HPO₄)₂·H₂O) typically involve the use of excess phosphoric acid, addition of HF or oxalic acid and long reflux times or hydrothermal conditions. Herein we report on a minimalistic sustainable route using only zirconium oxychloride and concentrated phosphoric acid to form highly crystalline α-zirconium phosphate within hours...
June 30, 2017: ChemSusChem
https://www.readbyqxmd.com/read/28664966/water-chromophore-electron-transfer-determines-the-photochemistry-of-cytosine-and-cytidine
#18
Rafał Szabla, Holger Kruse, Jiří Šponer, Robert W Góra
Many of the UV-induced phenomena observed experimentally for aqueous cytidine were lacking the mechanistic interpretation for decades. These processes include the substantial population of the puzzling long-lived dark state, photohydration, cytidine to uridine conversion and oxazolidinone formation. Here, we present quantum-chemical simulations of excited-state spectra and potential energy surfaces of N1-methylcytosine clustered with two water molecules using the second-order approximate coupled cluster (CC2), complete active space with second-order perturbation theory (CASPT2), and multireference configuration interaction with single and double excitation (MR-CISD) methods...
July 21, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28663371/functional-characterization-of-a-constitutively-active-kinase-variant-of-arabidopsis-phototropin-1
#19
Jan Petersen, Shin-Ichiro Inoue, Sharon M Kelly, Stuart Sullivan, Toshinori Kinoshita, John Mackie Christie
Phototropins (phots) are plasma membrane-associated serine/threonine kinases that coordinate a range of processes linked to optimizing photosynthetic efficiency in plants. These photoreceptors contain two light-, oxygen- or voltage-sensing (LOV) domains within their N-terminus, with each binding one molecule of flavin mononucleotide (FMN) as a UV/blue light absorbing chromophore. Although phots contain two LOV domains, light-induced activation of the C-terminal kinase domain and subsequent receptor autophosphorylation is controlled primarily by the A'α-LOV2-Jα photosensory module...
June 29, 2017: Journal of Biological Chemistry
https://www.readbyqxmd.com/read/28650504/experimental-and-theoretical-studies-on-fluvastatin-primary-photoproduct-formation
#20
Dorota Jarmużek, Tomasz Pedzinski, Marcin Hoffmann, Tomasz Siodła, Kinga Salus, Donata Pluskota-Karwatka
Fluvastatin (FLV) belongs to the group of compounds referred to as statins, also known as 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors. Statins act as cholesterol-lowering agents and are among the most frequently prescribed drugs. They upregulate low-density lipoprotein receptors in the liver by binding to the active site of HMG-CoA reductase, which is the key enzyme in cholesterol biosynthesis. Statins have been detected as contaminants in natural waters and are susceptible to degradation upon exposure to light...
June 26, 2017: Physical Chemistry Chemical Physics: PCCP
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