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https://www.readbyqxmd.com/read/29644774/preparation-of-cyclobutene-acetals-and-tricyclic-oxetanes-via-photochemical-tandem-and-cascade-reactions
#1
Julien Buendia, Zong Chang, Hendrik Eijsberg, Régis Guillot, Angelo Frongia, Francesco Secci, Juan Xie, Sylvie Robin, Thomas Boddaert, David J Aitken
We describe a photochemical reaction paradigm using two starting materials, a cyclopent-2-enone and an alkene, which are transformed in a controlled manner via the initial [2+2]-photocycloaddition adducts into cyclobutene aldehydes (conveniently trapped as stable acetals) or unprecedented angular tricyclic 4:4:4 oxetane-containing skeletons. These compounds are formed via tandem or triple cascade photochemical reaction processes, respectively. Small libraries of each compound class have been prepared, suggesting that this photochemistry paradigm opens new opportunities for fine synthesis design and for widening molecular diversity...
April 12, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29643225/understanding-unravelling-carotenoid-excited-singlet-states
#2
REVIEW
Hideki Hashimoto, Chiasa Uragami, Nao Yukihira, Alastair T Gardiner, Richard J Cogdell
Carotenoids are essential light-harvesting pigments in natural photosynthesis. They absorb in the blue-green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and thus expand the wavelength range of light that is able to drive photosynthesis. This process is an example of singlet-singlet excitation energy transfer, and carotenoids serve to enhance the overall efficiency of photosynthetic light reactions. The photochemistry and photophysics of carotenoids have often been interpreted by referring to those of simple polyene molecules that do not possess any functional groups...
April 2018: Journal of the Royal Society, Interface
https://www.readbyqxmd.com/read/29628099/protecting-the-photosynthetic-performance-of-snap-bean-under-free-air-ozone-exposure
#3
Lu Zhang, Yasutomo Hoshika, Elisa Carrari, Kent O Burkey, Elena Paoletti
Tropospheric ozone (O3 ) is a major air pollutant and causes serious injury to vegetation. To protect sensitive plants from O3 damage, several agrochemicals have been assessed, including cytokinin (e.g., kinetin, KIN) and ethylenediurea (EDU) with cytokinin-like activity. In higher plant, leaves are primarily injured by O3 and protective agrochemicals are often applied by leaf spraying. To our knowledge, the mitigating abilities of EDU and KIN have not been compared directly in a realistic setup. In the present research, impacts of elevated O3 (2× ambient O3 , 24hr per day, for 8days) on an O3 sensitive line (S156) of snap bean (Phaseolus vulgaris), which is often used for biomonitoring O3 pollution, were studied in a free air controlled exposure system...
April 2018: Journal of Environmental Sciences (China)
https://www.readbyqxmd.com/read/29627997/sulfidic-anion-concentrations-on-early-earth-for-surficial-origins-of-life-chemistry
#4
Sukrit Ranjan, Zoe R Todd, John D Sutherland, Dimitar D Sasselov
A key challenge in origin-of-life studies is understanding the environmental conditions on early Earth under which abiogenesis occurred. While some constraints do exist (e.g., zircon evidence for surface liquid water), relatively few constraints exist on the abundances of trace chemical species, which are relevant to assessing the plausibility and guiding the development of postulated prebiotic chemical pathways which depend on these species. In this work, we combine literature photochemistry models with simple equilibrium chemistry calculations to place constraints on the plausible range of concentrations of sulfidic anions (HS- , HSO3 - , SO3 2- ) available in surficial aquatic reservoirs on early Earth due to outgassing of SO2 and H2 S and their dissolution into small shallow surface water reservoirs like lakes...
April 8, 2018: Astrobiology
https://www.readbyqxmd.com/read/29626896/a-walk-through-the-approximations-of-ab-initio-multiple-spawning
#5
Benoit Mignolet, Basile F E Curchod
Full multiple spawning offers an in principle exact framework for excited-state dynamics, where nuclear wavefunctions in different electronic states are represented by a set of coupled trajectory basis functions that follow classical trajectories. The couplings between trajectory basis functions can be approximated to treat molecular systems, leading to the ab initio multiple spawning method which has been successfully employed to study the photochemistry and photophysics of several molecules. However, a detailed investigation of its approximations and their consequences is currently missing in the literature...
April 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29626862/transient-isomers-in-the-photodissociation-of-bromoiodomethane
#6
Moreno Marcellini, Alexandr Nasedkin, Burkhard Zietz, Jonas Petersson, Jonathan Vincent, Federico Palazzetti, Erik Malmerberg, Qingyu Kong, Michael Wulff, David van der Spoel, Richard Neutze, Jan Davidsson
The photochemistry of halomethanes is fascinating for the complex cascade reactions toward either the parent or newly synthesized molecules. Here, we address the structural rearrangement of photodissociated CH2 IBr in methanol and cyclohexane, probed by time-resolved X-ray scattering in liquid solution. Upon selective laser cleavage of the C-I bond, we follow the reaction cascade of the two geminate geometrical isomers, CH2 I-Br and CH2 Br-I. Both meta-stable isomers decay on different time scales, mediated by solvent interaction, toward the original parent molecule...
April 7, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29625087/the-peculiar-npq-regulation-in-the-stramenopile-phaeomonas-sp-challenges-the-xanthophyll-cycle-dogma
#7
N Berne, T Fabryova, F Bistaz, P Cardol, B Bailleul
In changing light conditions, photosynthetic organisms develop different strategies to maintain a fine balance between light harvesting, photochemistry, and photoprotection. One of the most widespread photoprotective mechanisms consists in the dissipation of excess light energy in the form of heat in the photosystem II antenna, which participates to the Non Photochemical Quenching (NPQ) of chlorophyll fluorescence. It is tightly related to the reversible epoxidation of xanthophyll pigments, catalyzed by the two enzymes, the violaxanthin deepoxidase and the zeaxanthin epoxidase...
April 3, 2018: Biochimica et Biophysica Acta
https://www.readbyqxmd.com/read/29624198/sequence-dependence-on-dna-photochemistry-a-computational-study-of-photodimerization-pathways-in-tpdc-and-dcpt-dinucleotides
#8
Lara Martínez-Fernández, Roberto Improta
The excited states involved in the main photodimerization paths in TpdC and dCpT are mapped by PCM/TD-M052X calculations, considering different dinucleotide conformers. As for TT steps, a cyclobutane pyrimidine dimer (CPD) is formed on the PES of the lowest energy exciton, delocalized over two stacked pyrimidines; 6-4 pyrimidine-pyrimidone (64-PP) adduct's formation involves instead a 5'-ter → 3'-ter charge transfer state. For dCpT, 64-PP dimerization occurs via a two-step reaction, which proceeds through an oxetane intermediate...
April 6, 2018: Photochemical & Photobiological Sciences
https://www.readbyqxmd.com/read/29621719/effect-of-combined-waterlogging-and-salinity-stresses-on-euhalophyte-suaeda-glauca
#9
Huimin Duan, Yanchun Ma, Ranran Liu, Qiang Li, Yang Yang, Jie Song
Salinity and waterlogging are abiotic stresses that have a significant impact on agricultural production and ecosystem conservation. The response of euhalophyte Suaeda glauca to waterlogging and salinity stresses was investigated. The results revealed that waterlogging markedly decreased seedling emergence. Compared to drained conditions, waterlogging inhibited the shoot dry weight, net photosynthetic rate, stomatal conductance, maximal efficiency of PSII photochemistry and chlorophyll content at salinity. Salinity decreased these values in both waterlogged and drained conditions, while the opposite trend was found in intercellular CO2 concentrations...
March 28, 2018: Plant Physiology and Biochemistry: PPB
https://www.readbyqxmd.com/read/29620135/how-nature-covers-its-bases
#10
Samuel Boldissar, Mattanjah S de Vries
The response of DNA and RNA bases to ultraviolet (UV) radiation has been receiving increasing attention for a number of important reasons: (i) the selection of the building blocks of life on an early earth may have been mediated by UV photochemistry, (ii) radiative damage of DNA depends critically on its photochemical properties, and (iii) the processes involved are quite general and play a role in more biomolecules as well as in other compounds. A growing number of groups worldwide have been studying the photochemistry of nucleobases and their derivatives...
April 5, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29615679/an-accessible-visible-light-actinometer-for-the-determination-of-photon-flux-and-optical-pathlength-in-flow-photo-microreactors
#11
Anca Roibu, Senne Fransen, M Enis Leblebici, Glen Meir, Tom Van Gerven, Simon Kuhn
Coupling photochemistry with flow microreactors enables novel synthesis strategies with higher efficiencies compared to batch systems. Improving the reproducibility and understanding of the photochemical reaction mechanisms requires quantitative tools such as chemical actinometry. However, the choice of actinometric systems which can be applied in microreactors is limited, due to their short optical pathlength in combination with a large received photon flux. Furthermore, actinometers for the characterization of reactions driven by visible light between 500 and 600 nm (e...
April 3, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29613798/a-comprehensive-experimental-and-computational-spectroscopic-study-of-hexacyanoferrate-complexes-in-water-from-the-infrared-to-x-ray-wavelengths
#12
Matthew R Ross, Amity Andersen, Zachary W Fox, Yu Zhang, Kiryong Hong, Jae-Hyuk Lee, Amy A Cordones, Anne M March, Gilles Doumy, Stephen H Southworth, Matthew A Marcus, Robert W Schoenlein, Shaul Mukamel, Niranjan Govind, Munira Khalil
We present a joint experimental and computational study of the hexacyanoferrate aqueous complexes at equilibrium in the 250 meV to 7.15 keV regime. The experiments and the computations include the vibrational spectroscopy of the cyanide ligands, the valence electronic absorption spectra and Fe 1s core hole spectra using element-specific resonant X-ray absorption and emission techniques. Density functional theory (DFT) based quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations are performed to generate explicit solute-solvent configurations, which serve as inputs for the spectroscopy calculations of the experiments spanning the IR to X-ray wavelengths...
April 3, 2018: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/29602587/off-line-and-real-time-monitoring-of-acetaminophen-photodegradation-by-an-electrochemical-sensor
#13
Silvia Berto, Luca Carena, Enrico Chiavazza, Matteo Marletti, Andrea Fin, Agnese Giacomino, Mery Malandrino, Claudia Barolo, Enrico Prenesti, Davide Vione
The photochemistry of N-acetyl-para-aminophenol (acetaminophen, APAP) is here investigated by using differential pulse voltammetry (DPV) analysis to monitor APAP photodegradation upon steady-state irradiation. The purpose of this work is to assess the applicability of DPV to monitor the photochemical behaviour of xenobiotics, along with the development of an electrochemical set-up for the real-time monitoring of APAP photodegradation. We here investigated the APAP photoreactivity towards the main photogenerated reactive transients species occurring in sunlit surface waters (hydroxyl radical HO, carbonate radical CO3 - , excited triplet state of anthraquinone-2-sulfonate used as proxy of the chromophoric DOM, and singlet oxygen1 O2 ), and determined relevant kinetic parameters...
March 13, 2018: Chemosphere
https://www.readbyqxmd.com/read/29601726/atmospheric-oh-oxidation-of-three-chlorinated-aromatic-herbicides
#14
Trey Murschell, Delphine K Farmer
Chlorinated phenoxy acids are a widely-used class of herbicides, and have been found in remote regions far from sources. However, the atmospheric chemistry of these compounds is poorly understood. We use an oxidative flow reactor coupled to chemical ionization mass spectrometry to investigate OH oxidation of two chlorinated phenoxyacid herbicides (2-methyl-4-chlorophenoxyacetic acid (MCPA) and mecoprop-p) and one chlorinated pyridine herbicide (triclopyr). We determine reaction rates between the herbicide and OH (kOH) for mecoprop-p of 1...
March 30, 2018: Environmental Science & Technology
https://www.readbyqxmd.com/read/29595247/visible-light-driven-bromide-oxidation-and-ligand-substitution-photochemistry-of-a-ru-diimine-complex
#15
Guocan Li, Matthew David Brady, Gerald J Meyer
The complex [Ru(deeb)(bpz)2]2+ (RuBPZ2+, deeb = 4,4'-diethylester-2,2'-bipyridine, bpz = 2,2'-bipyrazine) forms a single ion pair with bromide, [RuBPZ2+, Br-]+, with Keq = 8400 ± 200 M-1 in acetone. The RuBPZ2+ displayed photoluminescence (PL) at room temperature with a lifetime of 1.75 µs. The addition of bromide to a RuBPZ2+ acetone solution led to significant PL quenching and Stern-Volmer plots showed upward curvature. Time-resolved PL measurements identified two excited state quenching pathways, static and dynamic, which were operative towards [RuBPZ2+, Br-]+ and free RuBPZ2+, respectively...
March 29, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29589975/the-photochemistry-of-unprotected-dna-and-dna-inside-bacillus-subtilis-spores-exposed-to-simulated-martian-surface-conditions-of-atmospheric-composition-temperature-pressure-and-solar-radiation
#16
Wayne L Nicholson, Andrew C Schuerger, Thierry Douki
DNA is considered a potential biomarker for life-detection experiments destined for Mars. Experiments were conducted to examine the photochemistry of bacterial DNA, either unprotected or within Bacillus subtilis spores, in response to exposure to simulated martian surface conditions consisting of the following: temperature (-10°C), pressure (0.7 kPa), atmospheric composition [CO2 (95.54%), N2 (2.7%), Ar (1.6%), O2 (0.13%), and H2 O (0.03%)], and UV-visible-near IR solar radiation spectrum (200-1100 nm) calibrated to 4 W/m2 of UVC (200-280 nm)...
March 28, 2018: Astrobiology
https://www.readbyqxmd.com/read/29580099/global-medicinal-chemistry-and-gpcr-conference-interview-with-stevan-djuric
#17
Stevan Djuric
Stevan Djuric speaks to Benjamin Walden, Commissioning Editor. Stevan Djuric is head of the global Medicinal Chemistry Leadership Team at AbbVie and is also Vice President of the Discovery Chemistry and Technology organization within their Discovery organization and chemistry outsourcing activities. He spoke at the Global-Medicinal-Chemistry and GPCR summit on the imperative to develop chemistry related technology that can reduce cycle time, cost of goods and improve probability of success. To this end, he discussed his efforts in the chemistry technology area with a focus on integrated synthesis-purification bioassay, and flow photochemistry and high temperature chemistry platforms...
March 27, 2018: Future Medicinal Chemistry
https://www.readbyqxmd.com/read/29573725/pretilachlor-toxicity-is-decided-by-discrete-photo-acclimatizing-conditions-physiological-and-biochemical-evidence-from-anabaena-sp-and-nostoc-muscorum
#18
Jitendra Kumar, Anuradha Patel, Sanjesh Tiwari, Santwana Tiwari, Prabhat Kumar Srivastava, Sheo Mohan Prasad
The current study was undertaken to elucidate the impact of the herbicide pretilachlor (3 µg ml-1 and 6 µg ml-1 ) on cyanobacteria, Nostoc muscorum ATCC 27893 and Anabaena sp. PCC 7120 under three levels of photoacclimatization (suboptimum, 25 µmol photon m-2 s-1 ; optimum, 75 µmol photon m-2 s-1 ; and supra-optimum, 225 µmol photon m-2 s-1 ) by analyzing certain physiological (biomass accumulation, photosynthesis, Chl a fluorescence and respiration) and biochemical parameters (photosynthetic pigments‒ chlorophyll a, carotenoids and phycocyanin; reactive oxygen species‒ O2 • ¯, H2 O2 , lipid peroxidation; antioxidant system‒ superoxide dismutase, peroxidise, catalase and glutathione-S-transferase)...
March 21, 2018: Ecotoxicology and Environmental Safety
https://www.readbyqxmd.com/read/29573313/combined-in-situ-illumination-nmr-uv-vis-spectroscopy-a-new-mechanistic-tool-in-photochemistry
#19
Andreas Seegerer, Philipp Nitschke, Ruth M Gschwind
Synthetic applications in photochemistry are booming. Despite great progress in developing new reactions, mechanistic investigations are still highly challenging. Therefore, we present a fully automated in situ triple combination of NMR spectroscopy, UV/Vis spectroscopy and illumination to allow simultaneous and time resolved detection of paramagnetic and diamagnetic species. This optical fiber based setup enables first acquisition of combined UV/Vis and NMR spectra in photocatalysis demonstrated on a conPET process...
March 24, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29571070/effect-of-pterin-impurities-on-the-fluorescence-and-photochemistry-of-commercial-folic-acid
#20
M Laura Dántola, M Noel Urrutia, Andrés H Thomas
Folic acid, or pteroyl‑l‑glutamic acid (PteGlu) is a conjugated pterin derivative that is used in dietary supplementation as a source of folates, a group of compounds essential for a variety of physiological functions in humans. Photochemistry of PteGlu is important because folates are not synthesized by mammals, undergo photodegradation and their deficiency is related to many diseases. We have demonstrated that usual commercial PteGlu is unpurified with the unconjugated oxidized pterins 6‑formylpterin (Fop) and 6‑carboxypterin (Cap)...
March 9, 2018: Journal of Photochemistry and Photobiology. B, Biology
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