Articoli di riviste: "Tandem photochemical reaction"

1

Saunthwal, Rakesh K., James Mortimer, Andrew J. Orr-Ewing e Jonathan Clayden. "Enantioselective one-carbon expansion of aromatic rings by simultaneous formation and chromoselective irradiation of a transient coloured enolate". Chemical Science 13, n. 7 (2022): 2079–85. http://dx.doi.org/10.1039/d1sc06684f.

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Irradiation of a mixture of aromatic amide and chiral base leads to a tandem reaction sequence in which dearomatization forms a chromophore capable of photochemical rearrangement leading to overall asymmetric expansion of the aromatic ring.

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Hoffmann, Norbert, Samuel Bertrand, Siniša Marinković e Jens Pesch. "Efficient radical addition of tertiary amines to alkenes using photochemical electron transfer". Pure and Applied Chemistry 78, n. 12 (1 gennaio 2006): 2227–46. http://dx.doi.org/10.1351/pac200678122227.

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An efficient photoinduced radical addition of tertiary amine, mainly cyclic derivatives, to electron-deficient alkenes was developed. The reaction was applied to the asymmetric synthesis of the pyrrolizidine alkaloids laburnine and isoretronecanol. The method was then optimized for the addition of a larger variety of tertiary amines, in particular acyclic ones. Radical tandem addition cyclization reactions with unsaturated tertiary amines have also been investigated. A detailed mechanistic study using isotopic labeling enabled the optimization of a corresponding reaction with N,N-dialkylaniline derivatives. The origin of the high reaction stereoselectivity achieved with menthyloxyfuranone was elucidated. The radical addition of tertiary amines was also performed with heterogeneous photocatalysis using inorganic semiconductors as sensitizers.

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Chiminelli, Maurizio, Gabriele Scarica, Andrea Serafino, Luciano Marchiò, Rosanna Viscardi e Giovanni Maestri. "Visible-Light-Promoted Tandem Skeletal Rearrangement/Dearomatization of Heteroaryl Enallenes". Molecules 29, n. 3 (25 gennaio 2024): 595. http://dx.doi.org/10.3390/molecules29030595.

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Access to complex three-dimensional molecular architectures via dearomatization of ubiquitous aryl rings is a powerful synthetic tool, which faces, however, an inherent challenge to overcome energetic costs due to the loss of aromatic stabilization energy. Photochemical methods that allow one to populate high-energy states can thus be an ideal strategy to accomplish otherwise prohibitive reaction pathways. We present an original dearomative rearrangement of heteroaryl acryloylallenamides that leads to complex fused tricycles. The visible-light-promoted method occurs under mild conditions and tolerates a variety of functional groups. According to DFT modeling used to rationalize the outcome of the cascade, the reaction involves a sequential [2+2] allene–alkene photocycloaddition, which is followed by a selective retro- [2+2] step that paves the way for the dearomatization of the heteroaryl partner. This scenario is original with respect to the reported photochemical reactivity of similar substrates and thus holds promise for ample future developments.

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Hou, Yunyan, e Peter Wan. "A pentacene intermediate via formal intramolecular photoredox of a 6,13-pentacenequinone in aqueous solution". Canadian Journal of Chemistry 85, n. 12 (1 dicembre 2007): 1023–32. http://dx.doi.org/10.1139/v07-117.

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The formal intramolecular photoredox reaction (or tandem phototautomerizations) of aromatic ketones in aqueous solution discovered in our laboratory has been extended to a number of acenequinones. In particular, we were interested in whether the photoredox reaction could be applied to 2-(hydroxymethyl)-6,13-pentacenequinone (4), which would result in 2-formyl-6,13-dihydroxypentacene (10) and hence offer a photochemical method for synthesizing a pentacene derivative. Whereas a number of acenequinones displayed a range of photoredox reactivity, photolysis of 4 in acidic aqueous solution (pH < 3) resulted in a clean intramolecular photoredox reaction, via an enol intermediate, to give 10 (green compound; Φ ~ 0.2 at pH 1), which was too reactive for isolation or trapping by standard ArOH trapping agents such as acetic anhydride. These reactions may be viewed as a one-way photochemical intramolecular “redox switch” from quinone to hydroquinone with concurrent oxidation of an attached hydroxymethyl (alcohol) moiety. Without the attached alcohol moiety, these acenequinones are photostable in aqueous solution. The trend in observed relative reactivity may be partially rationalized by examining changes in molecular orbital coefficients observed in the calculated HOMOs and LUMOs (at the AM1 level).Key words: pentacene, acenequinones, photoredox, enol, acid catalysis.

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Liang, Yan Ru, Yu Yun Wen, Xiao Yan Hong, Zhen Bin Gong e Wen Quan Li. "Laboratory Simulation Study of Photo-Degradation Process of Fenvalerate in Aqueous Solution". Applied Mechanics and Materials 312 (febbraio 2013): 886–92. http://dx.doi.org/10.4028/www.scientific.net/amm.312.886.

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A laboratory-made the efficient photochemical degradation experimental device, combined with high performance liquid chromatography-tandem diode array detector device (DAD), fluorescence detector (FLD), mass spectrometer detector (MS), research fenvalerate its photo degradation. The structure of the spectral characteristics is the product, photo degradation reaction kinetics of degradation products, suggesting fenvalerate light chemical degradation process in an aqueous solution. The spectral characteristics of fenvalerate under ultraviolet light can be degraded into smaller organic molecules; maternal and main product have strong UV - visible absorption, fenvalerate are weakly fluorescent substance in the aqueous solution. The major products are strong fluorescent substance. Almost no effect The photo degradation kinetic data show fenvalerate photo degradation in an aqueous solution to approximate a reaction of the reaction; pesticide initial concentration, the pH value of the aqueous solution of pesticides photo degradation reaction rate; To accelerate the increase of salinity, light intensity fenvalerate in aqueous photo degradation reaction rate; significant influence of small organic molecules, with the type of small organic molecules.

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Ren, Jia, Elissia T. Franklin e Yu Xia. "Uncovering Structural Diversity of Unsaturated Fatty Acyls in Cholesteryl Esters via Photochemical Reaction and Tandem Mass Spectrometry". Journal of The American Society for Mass Spectrometry 28, n. 7 (17 aprile 2017): 1432–41. http://dx.doi.org/10.1007/s13361-017-1639-6.

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7

Li, Hai-Fang, Jing Zhao, Wenbo Cao, Wenpeng Zhang, Yu Xia e Zheng Ouyang. "Site-Specific Photochemical Reaction for Improved C=C Location Analysis of Unsaturated Lipids by Ultraviolet Photodissociation". Research 2022 (12 febbraio 2022): 1–12. http://dx.doi.org/10.34133/2022/9783602.

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Unraveling the complexity of the lipidome requires the development of novel approaches to facilitate structural identification and characterization of lipid species with isomer-level discrimination. Ultraviolet photodissociation tandem mass spectrometry (UVPD MS/MS) is a promising tool for structure determination of lipids. The sensitivity of UVPD for lipid analysis however is limited mainly due to weak absorption of UV photons by a C=C. Herein, a C=C site-specific derivatization, the Paternò-Büchi (PB) reaction, was used to incorporate a chromophore to the C=C moiety in fatty acyls, leading to significantly improved UVPD efficiency and sensitivity for pinpointing C=C locations. The wavelength-dependent photodissociation of the PB products demonstrated 4-CF3-benzophenone as the best reagent for UVPD in terms of the efficiency of generating C=C diagnostic fragments and simplicity for C=C location assignments. We demonstrated the effectiveness of this approach for the shotgun profiling of C=C location isomers in different lipid classes from complex lipid extracts, highlighting its potential to advancing the identification of the C=C bond locations in unsaturated lipids.

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Ma, Xiaoxiao, Leelyn Chong, Ran Tian, Riyi Shi, Tony Y. Hu, Zheng Ouyang e Yu Xia. "Identification and quantitation of lipid C=C location isomers: A shotgun lipidomics approach enabled by photochemical reaction". Proceedings of the National Academy of Sciences 113, n. 10 (22 febbraio 2016): 2573–78. http://dx.doi.org/10.1073/pnas.1523356113.

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The field of lipidomics has been significantly advanced by mass spectrometric analysis. The distinction and quantitation of the unsaturated lipid isomers, however, remain a long-standing challenge. In this study, we have developed an analytical tool for both identification and quantitation of lipid C=C location isomers from complex mixtures using online Paternò–Büchi reaction coupled with tandem mass spectrometry (MS/MS). The potential of this method has been demonstrated with an implementation into shotgun lipid analysis of animal tissues. Among 96 of the unsaturated fatty acids and glycerophospholipids identified from rat brain tissue, 50% of them were found as mixtures of C=C location isomers; for the first time, to our knowledge, the quantitative information of lipid C=C isomers from a broad range of classes was obtained. This method also enabled facile cross-tissue examinations, which revealed significant changes in C=C location isomer compositions of a series of fatty acids and glycerophospholipid (GP) species between the normal and cancerous tissues.

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9

Janechek, Nathan J., Rachel F. Marek, Nathan Bryngelson, Ashish Singh, Robert L. Bullard, William H. Brune e Charles O. Stanier. "Physical properties of secondary photochemical aerosol from OH oxidation of a cyclic siloxane". Atmospheric Chemistry and Physics 19, n. 3 (8 febbraio 2019): 1649–64. http://dx.doi.org/10.5194/acp-19-1649-2019.

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Abstract. Cyclic volatile methyl siloxanes (cVMS) are high-production chemicals present in many personal care products. They are volatile, hydrophobic, and relatively long-lived due to slow oxidation kinetics. Evidence from chamber and ambient studies indicates that oxidation products may be found in the condensed aerosol phase. In this work, we use an oxidation flow reactor to produce ∼100 µg m−3 of organosilicon aerosol from OH oxidation of decamethylcyclopentasiloxane (D5) with aerosol mass fractions (i.e., yields) of 0.2–0.5. The aerosols were assessed for concentration, size distribution, morphology, sensitivity to seed aerosol, hygroscopicity, volatility and chemical composition through a combination of aerosol size distribution measurement, tandem differential mobility analysis, and electron microscopy. Similar aerosols were produced when vapor from solid antiperspirant was used as the reaction precursor. Aerosol yield was sensitive to chamber OH and to seed aerosol, suggesting sensitivity of lower-volatility species and recovered yields to oxidation conditions and chamber operation. The D5 oxidation aerosol products were relatively non-hygroscopic, with an average hygroscopicity kappa of ∼0.01, and nearly non-volatile up to 190 ∘C temperature. Parameters for exploratory treatment as a semi-volatile organic aerosol in atmospheric models are provided.

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10

Bertrand, Samuel, Norbert Hoffmann, Jean-Pierre Pete e Véronique Bulach. "Stereoselective radical-tandem reaction of aniline derivatives with (5R)-5-menthyloxy-2,5-dihydrofuran-2-one initiated by photochemical induced electron transfer". Chemical Communications, n. 22 (1999): 2291–92. http://dx.doi.org/10.1039/a906051k.

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11

Murphy, Robert C., Toshiaki Okuno, Christopher A. Johnson e Robert M. Barkley. "Determination of Double Bond Positions in Polyunsaturated Fatty Acids Using the Photochemical Paternò-Büchi Reaction with Acetone and Tandem Mass Spectrometry". Analytical Chemistry 89, n. 16 (2 agosto 2017): 8545–53. http://dx.doi.org/10.1021/acs.analchem.7b02375.

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12

Bertrand, Samuel, Norbert Hoffmann, Jean-Pierre Pete e Veronique Bulach. "ChemInform Abstract: Stereoselective Radical-Tandem Reaction of Aniline Derivatives with (5R)-5-Menthyloxy-2,5-dihydrofuran-2-one Initiated by Photochemical Induced Electron Transfer." ChemInform 31, n. 23 (8 giugno 2010): no. http://dx.doi.org/10.1002/chin.200023142.

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13

Trucksess, Mary W., Carol M. Weaver, Carolyn J. Oles, Lydia V. Rump, Kevin D. White, Joseph M. Betz e Jeanne I. Rader. "Use of Multitoxin Immunoaffinity Columns for Determination of Aflatoxins and Ochratoxin A in Ginseng and Ginger". Journal of AOAC INTERNATIONAL 90, n. 4 (1 luglio 2007): 1042–49. http://dx.doi.org/10.1093/jaoac/90.4.1042.

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Abstract Conditions were optimized for the simultaneous, alkaline, aqueous methanol extraction of aflatoxins (AFL), i.e., B1 (AFB1), B2 (AFB2), G1 (AFG1), and G2 (AFG2), and ochratoxin A (OTA) with subsequent purification, isolation, and determination of the toxins in ginseng and ginger. Powdered roots were extracted with methanol0.5% NaHCO3 solution (7 + 3). After shaking and centrifugation, the supernatant was diluted with 100 mM phosphate buffer containing 1% Tween 20 and filtered through glass microfiber filter paper. The filtrate was then passed through an immunoaffinity column, and the toxins were eluted with methanol. The AFL were separated and determined by reversed-phase liquid chromatography (RPLC) with fluorescence detection after postcolumn UV photochemical derivatization. OTA was separated and determined by RPLC with fluorescence detection. Recoveries of AFL added at 216 ng/g and OTA added at 18 ng/g to ginseng were 7280 and 8695%, respectively. Recoveries of AFL and OTA added to ginger were similar to those for ginseng. A total of 39 commercially available ginger products from 6 manufacturers were analyzed. Twenty-six samples were found to be contaminated with AFL at 131 ng/g and 29 samples, with OTA at 110 ng/g. Ten samples contained no AFL or OTA. Ten ginseng finished products were also analyzed; 3 contained AFL at 0.1 ng/g and 4 contained OTA at levels ranging from 0.4 to 1.8 ng/g. LC/tandem mass spectrometry with multiple-reaction monitoring of 3 collisionally induced product ions from the protonated molecular ions of OTA, AFB1, and AFG1 was used to confirm the identities of the toxins in extracts of the finished products.

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Buendia, Julien, Zong Chang, Hendrik Eijsberg, Régis Guillot, Angelo Frongia, Francesco Secci, Juan Xie, Sylvie Robin, Thomas Boddaert e David J. Aitken. "Preparation of Cyclobutene Acetals and Tricyclic Oxetanes through Photochemical Tandem and Cascade Reactions". Angewandte Chemie 130, n. 22 (26 aprile 2018): 6702–6. http://dx.doi.org/10.1002/ange.201803571.

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Buendia, Julien, Zong Chang, Hendrik Eijsberg, Régis Guillot, Angelo Frongia, Francesco Secci, Juan Xie, Sylvie Robin, Thomas Boddaert e David J. Aitken. "Preparation of Cyclobutene Acetals and Tricyclic Oxetanes through Photochemical Tandem and Cascade Reactions". Angewandte Chemie International Edition 57, n. 22 (28 maggio 2018): 6592–96. http://dx.doi.org/10.1002/anie.201803571.

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16

Cheng, Jian, Bin Zheng, Sheng Cheng, Guoying Zhang e Jinming Hu. "Metal-free carbon monoxide-releasing micelles undergo tandem photochemical reactions for cutaneous wound healing". Chemical Science 11, n. 17 (2020): 4499–507. http://dx.doi.org/10.1039/d0sc00135j.

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Metal-free carbon monoxide-releasing polymers (CORPs) are synthesized via a direct polymerization approach, exhibiting not only improved stability but also accelerated wound healing performance as compared to CORM-3.

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Bertrand, Samuel, Norbert Hoffmann, Stéphane Humbel e Jean Pierre Pete. "Diastereoselective Tandem Addition−Cyclization Reactions of Unsaturated Tertiary Amines Initiated by Photochemical Electron Transfer (PET)". Journal of Organic Chemistry 65, n. 25 (dicembre 2000): 8690–703. http://dx.doi.org/10.1021/jo001166l.

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18

Chanmanee, Wilaiwan, Mohammad Fakrul Islam, Brian H. Dennis e Frederick M. MacDonnell. "Solar photothermochemical alkane reverse combustion". Proceedings of the National Academy of Sciences 113, n. 10 (22 febbraio 2016): 2579–84. http://dx.doi.org/10.1073/pnas.1516945113.

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A one-step, gas-phase photothermocatalytic process for the synthesis of hydrocarbons, including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13, from CO2 and water is demonstrated in a flow photoreactor operating at elevated temperatures (180–200 °C) and pressures (1–6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A parametric study of temperature, pressure, and partial pressure ratio revealed that temperatures in excess of 160 °C are needed to obtain the higher Cn products in quantity and that the product distribution shifts toward higher Cn products with increasing pressure. In the best run so far, over 13% by mass of the products were C5+ hydrocarbons and some of these, i.e., octane, are drop-in replacements for existing liquid hydrocarbons fuels. Dioxygen was detected in yields ranging between 64% and 150%. In principle, this tandem photochemical–thermochemical process, fitted with a photocatalyst better matched to the solar spectrum, could provide a cheap and direct method to produce liquid hydrocarbons from CO2 and water via a solar process which uses concentrated sunlight for both photochemical excitation to generate high-energy intermediates and heat to drive important thermochemical carbon-chain-forming reactions.

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Marinković, Siniša, e Norbert Hoffmann. "Diastereoselective Radical Tandem Addition-Cyclization Reactions of Aromatic Tertiary Amines by Semiconductor-Sensitized Photochemical Electron Transfer". European Journal of Organic Chemistry 2004, n. 14 (luglio 2004): 3102–7. http://dx.doi.org/10.1002/ejoc.200400102.

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Nakatani, Kazuhiko, Kaoru Adachi, Kazuhito Tanabe e Isao Saito. "Tandem Cyclizations Involving Carbene as an Intermediate: Photochemical Reactions of Substituted 1,2-Diketones Conjugated with Ene-Yne". Journal of the American Chemical Society 121, n. 36 (settembre 1999): 8221–28. http://dx.doi.org/10.1021/ja990763q.

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Bertrand, Samuel, Norbert Hoffmann, Stephane Humbel e Jean Pierre Pete. "ChemInform Abstract: Diastereoselective Tandem Addition-Cyclization Reactions of Unsaturated Tertiary Amines Initiated by Photochemical Electron Transfer (PET)." ChemInform 32, n. 17 (24 aprile 2001): no. http://dx.doi.org/10.1002/chin.200117044.

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22

Pretali, Luca, Angelo Albini, Alice Cantalupi, Federica Maraschi, Stefania Nicolis e Michela Sturini. "TiO2-Photocatalyzed Water Depollution, a Strong, yet Selective Depollution Method: New Evidence from the Solar Light Induced Degradation of Glucocorticoids in Freshwaters". Applied Sciences 11, n. 6 (11 marzo 2021): 2486. http://dx.doi.org/10.3390/app11062486.

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The photodegradation of the most prescribed glucocorticoids (GCs) was studied under relevant environmental conditions in the presence of suspended TiO2. The considered drugs included cortisone (CORT), hydrocortisone (HCORT), betamethasone (BETA), dexamethasone (DEXA), prednisone (PRED), prednisolone (PREDLO), and triamcinolone (TRIAM). The experiments were carried out at concentrations (50 µg L−1) close to the real ones in freshwater samples (tap and river) under simulated and natural sunlight, and their decomposition took place very efficiently under natural sunlight. The reactions were monitored by high-pressure liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). According to a pseudo-first-order decay, all drugs underwent degradation within 15 min, following different paths with respect to the direct photolysis. The observed kinetic constants, slightly lower in river than in tap water, varied from 0.29 to 0.61 min−1 with modest differences among GCs in the same matrix. Among main matrix macro-constituents, humic acids (HAs) were the most interfering species involved in GCs degradation. The photogenerated primary products were identified by HPLC-ESI-MS/MS, allowing to elucidate the general photochemical path of GCs. Finally, a comparison with literature data obtained using different advanced oxidation processes (AOPs) highlights the treatment efficiency with TiO2/solar light for removing such persistent aquatic contaminants.

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Aoyama, Hiromu. "Photochemical reactions of thiobenzamides bearing an allylic substituent on the nitrogen atom: double-bond migration via tandem 1,4- and 1,6-hydrogen transfer". Journal of the Chemical Society, Perkin Transactions 1, n. 12 (1997): 1851–54. http://dx.doi.org/10.1039/a700247e.

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Flores, J. M., D. F. Zhao, L. Segev, P. Schlag, A. Kiendler-Scharr, H. Fuchs, Å. K. Watne et al. "Evolution of the complex refractive index in the near UV spectral region in ageing secondary organic aerosol". Atmospheric Chemistry and Physics Discussions 14, n. 3 (14 febbraio 2014): 4149–87. http://dx.doi.org/10.5194/acpd-14-4149-2014.

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Abstract. The chemical and physical properties of secondary organic aerosol (SOA) formed by the photochemical degradation of biogenic and anthropogenic volatile organic compounds (VOC) are yet poorly constrained. The evolution of the complex refractive index (RI) of SOA, formed from purely biogenic VOC and mixtures of biogenic and anthropogenic VOC was studied over a diurnal cycle in the SAPHIR photochemical outdoor chamber in Jülich, Germany. The correlation of RI with SOA chemical and physical properties such as oxidation level and volatility was examined. The RI was retrieved by a newly developed broadband cavity enhanced spectrometer for aerosol optical extinction measurements in the near UV spectral region (360 to 420 nm). Chemical composition and volatility of the particles were monitored by a high resolution time of flight aerosol mass spectrometer, and a volatility tandem differential mobility analyzer. SOA was formed by ozonolysis of either (i) a mixture of biogenic VOC (α-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d10), or (iii) a mixture of biogenic and anthropogenic VOC. The SOA aged by ozone / OH reactions up to 29.5 h was found to be non-absorbing in all cases. The SOA with p-xylene-d10 showed an increase of the scattering component of the RI correlated with an increase of the O / C ratio and with an increase in the SOA density. There was a greater increase in the scattering component of the RI when the SOA was produced from the mixture of biogenic VOCs and anthropogenic VOC than from the sequential addition of the VOCs after the approximate same ageing time. The increase of the scattering component was inversely correlated with the SOA volatility. Two RI retrievals determined for the pure biogenic SOA showed a constant RI for up to 5 h of ageing. Mass spectral characterization shows the three types of the SOA formed in this study have significant amount of semivolatile components. The influence of anthropogenic VOCs on the oxygenated organic aerosol, and the atmospheric implications are discussed.

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Flores, J. M., D. F. Zhao, L. Segev, P. Schlag, A. Kiendler-Scharr, H. Fuchs, Å. K. Watne et al. "Evolution of the complex refractive index in the UV spectral region in ageing secondary organic aerosol". Atmospheric Chemistry and Physics 14, n. 11 (11 giugno 2014): 5793–806. http://dx.doi.org/10.5194/acp-14-5793-2014.

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Abstract. The chemical and physical properties of secondary organic aerosol (SOA) formed by the photochemical degradation of biogenic and anthropogenic volatile organic compounds (VOC) are as yet still poorly constrained. The evolution of the complex refractive index (RI) of SOA, formed from purely biogenic VOC and mixtures of biogenic and anthropogenic VOC, was studied over a diurnal cycle in the SAPHIR photochemical outdoor chamber in Jülich, Germany. The correlation of RI with SOA chemical and physical properties such as oxidation level and volatility was examined. The RI was retrieved by a newly developed broadband cavity-enhanced spectrometer for aerosol optical extinction measurements in the UV spectral region (360 to 420 nm). Chemical composition and volatility of the particles were monitored by a high-resolution time-of-flight aerosol mass spectrometer, and a volatility tandem differential mobility analyzer. SOA was formed by ozonolysis of either (i) a mixture of biogenic VOC (α-pinene and limonene), (ii) biogenic VOC mixture with subsequent addition of an anthropogenic VOC (p-xylene-d10), or (iii) a mixture of biogenic and anthropogenic VOC. The SOA aged by ozone/OH reactions up to 29.5 h was found to be non-absorbing in all cases. The SOA with p-xylene-d10 showed an increase of the scattering component of the RI correlated with an increase of the O / C ratio and with an increase in the SOA density. There was a greater increase in the scattering component of the RI when the SOA was produced from the mixture of biogenic VOCs and anthropogenic VOC than from the sequential addition of the VOCs after approximately the same ageing time. The increase of the scattering component was inversely correlated with the SOA volatility. Two RI retrievals determined for the pure biogenic SOA showed a constant RI for up to 5 h of ageing. Mass spectral characterization shows the three types of the SOA formed in this study have a significant amount of semivolatile components. The influence of anthropogenic VOCs on the oxygenated organic aerosol as well as the atmospheric implications are discussed.

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AOYAMA, H. "ChemInform Abstract: Photochemical Reactions of Thiobenzamides Bearing an Allylic Substituent on the Nitrogen Atom: Double-Bond Migration via Tandem 1,4- and 1,6-Hydrogen Transfer." ChemInform 28, n. 44 (3 agosto 2010): no. http://dx.doi.org/10.1002/chin.199744091.

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27

yu, xiaodan, Thomas Boddaert e David J. Aitken. "Functionalized alkylidenecyclobutanes from a cyclopent‐2‐enone substrate via a tandem photochemical transformation and an allylic substitution protocol". Advanced Synthesis & Catalysis, 4 ottobre 2023. http://dx.doi.org/10.1002/adsc.202300798.

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A four‐step metal‐free procedure is described for the transformation of 4‐hydroxy‐2‐methylcyclopent‐2‐enone derivatives into highly functionalized E‐alkylidenecyclobutanes featuring oxygenated tetrasubstituted centers. The key intermediate is a (cyclobutenyl)propane‐1,3‐diol diester, easily accessed via a tandem photochemical reaction, which undergoes an original Brønsted acid‐catalyzed allylic substitution reaction with alcohols to give the title products with ester‐protected primary alcohol side chains.

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Zhu, Yaqing, Fengchao Yi, Ningning Zhou, Yi Zhang, Ying Zhang, Xia Zhao e Kui Lu. "Photochemical tandem reaction of nitrogen containing heterocycles, bicyclo[1.1.1]pentane, and difluoroiodane(iii) reagents". Organic & Biomolecular Chemistry, 2024. http://dx.doi.org/10.1039/d4ob01020e.

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Ivatt, Peter D., Mathew J. Evans e Alastair C. Lewis. "Suppression of surface ozone by an aerosol-inhibited photochemical ozone regime". Nature Geoscience, 7 luglio 2022. http://dx.doi.org/10.1038/s41561-022-00972-9.

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AbstractAtmospheric ozone (O3) is a pollutant produced through chemical chain reactions where volatile organic compounds (VOCs), carbon monoxide and methane are oxidized in the presence of oxides of nitrogen (NOx). For decades, the controlling chain termination step has been used to separate regions into either ‘NOx limited’ (peroxyl-radical self-reactions dominate) or ‘VOC limited’ (hydroxyl radical (OH) + nitrogen dioxide (NO2) reaction dominates). The controlling regime would then guide policies for reducing emissions and so O3 concentrations. Using a chemical transport model, we show that a third ‘aerosol inhibited’ regime exists, where reactive uptake of hydroperoxyl radicals (HO2) onto aerosol particles dominates. In 1970, 2% of the Northern Hemisphere population lived in an aerosol-inhibited regime, but by 2014 this had increased to 21%; 60% more than lived in a VOC-limited regime. Aerosol-inhibited chemistry suppressed surface O3 concentrations in North America and Europe in the 1970s and is currently suppressing surface O3 over Asia. This third photochemical O3 regime leads to potential trade-off tensions between reducing particle pollution in Asia (a key current health policy and priority) and increasing surface O3, should O3 precursors emissions not be reduced in tandem.

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Li, Peifeng, Wanghui Zhao, Kaixuan Wang, Tao Wang e Biaobiao Zhang. "Photocatalytic Synthesis of Glycine from Methanol and Nitrate". Angewandte Chemie, 13 agosto 2024. http://dx.doi.org/10.1002/ange.202405370.

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Photocatalytic utilization of methanol and nitrate as carbon and nitrogen sources for the direct synthesis of amino acids could provide a sustainable way for the valorization of green “liquid sunlight” and nitrate waste. In this study, we developed an efficient photochemical method to synthesize glycine directly from methanol and nitrate, which cascades the C‐C coupling to form glycol, nitrate reduction to NH3, and finally C‐N coupling to generate glycine. Interestingly, the involved photocatalytic tandem reactions show a synergistic effect, in which the presence of nitrate is the dominant factor to enable the overall reaction and reach high synthetic efficiency. Ba2+‐TiO2 nanoparticles are confirmed as a feasible and efficient catalyst system for the photosynthesis of glycine with a remarkable glycine photosynthesis rate of 870 μmol gcat‐1 h‐1 under optimal conditions. This work establishes a novel catalytic system for amino acid synthesis from methanol and nitrate under mild conditions. These results also allow us to further suppose the formation pathways of amino acids on the primitive earth, as an extension to proposals based on the Miller–Urey experiments.

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Li, Peifeng, Wanghui Zhao, Kaixuan Wang, Tao Wang e Biaobiao Zhang. "Photocatalytic Synthesis of Glycine from Methanol and Nitrate". Angewandte Chemie International Edition, 13 agosto 2024. http://dx.doi.org/10.1002/anie.202405370.

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Photocatalytic utilization of methanol and nitrate as carbon and nitrogen sources for the direct synthesis of amino acids could provide a sustainable way for the valorization of green “liquid sunlight” and nitrate waste. In this study, we developed an efficient photochemical method to synthesize glycine directly from methanol and nitrate, which cascades the C‐C coupling to form glycol, nitrate reduction to NH3, and finally C‐N coupling to generate glycine. Interestingly, the involved photocatalytic tandem reactions show a synergistic effect, in which the presence of nitrate is the dominant factor to enable the overall reaction and reach high synthetic efficiency. Ba2+‐TiO2 nanoparticles are confirmed as a feasible and efficient catalyst system for the photosynthesis of glycine with a remarkable glycine photosynthesis rate of 870 μmol gcat‐1 h‐1 under optimal conditions. This work establishes a novel catalytic system for amino acid synthesis from methanol and nitrate under mild conditions. These results also allow us to further suppose the formation pathways of amino acids on the primitive earth, as an extension to proposals based on the Miller–Urey experiments.

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Mohamadpour, Farzaneh. "Photochemical synthesis of pyrano[2,3-d]pyrimidine scaffolds using photoexcited organic dye, Na2 eosin Y as direct hydrogen atom transfer (HAT) photocatalyst via visible light-mediated under air atmosphere". BMC Chemistry 17, n. 1 (7 febbraio 2023). http://dx.doi.org/10.1186/s13065-023-00912-7.

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AbstractThe Knoevenagel-Michael cyclocondensation of barbituric acid/1,3-dimethylbarbituric acid, malononitrile, and arylaldehyde derivatives was used to construct a multicomponent green tandem method for the metal-free synthesis of pyrano[2,3-d]pyrimidine scaffolds. At room temperature in aqueous ethanol, photo-excited state functions generated from Na2 eosin Y were employed as direct hydrogen atom transfer (HAT) catalysts by visible light mediated in the air atmosphere. This research looks towards expanding the use of a non-metallic organic dye that is both affordable and readily available. Because of its good yields, energy-effectiveness, high atom economy, time-saving qualities of the reaction, and operational simplicity, Na2 eosin Y is photochemically produced with the least amount of a catalyst. As a result, various ecological and sustainable chemical properties are met. Surprisingly, such cyclization may be carried out on a gram scale, indicating the reaction's potential industrial application.

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Zhang, Hanzhi, Jingdan Zhao, Zhenhua Tian e Hao Liu. "Structure Analysis of Unsaturated Polymyxin E Components Based on High Performance Liquid Chromatography – Quadrupole/ Time of Flight Tandem Mass Spectrometry and Photochemical Reaction". Current Pharmaceutical Analysis 18 (1 settembre 2022). http://dx.doi.org/10.2174/1573412918666220901150000.

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Background: Polymyxin E (PME), which is a complex of cationic cyclic lipodecapeptides, is used to treat multidrug-resistant gram-negative bacterial infections. Besides the main components PME1 and PME2, polymyxin containing unsaturated fatty acyl (FA) group with lower contents is hardly to determine the structure without chromatographic preparations and NMR. Introduction: The peptide sequences of PME components has been carried out based on high performance liquid chromatography-quadrupole / time-of-flight mass spectrometry (HPLC-Q/TOF-MS). However, the components with double bond on the FA, such as 2’, 3’-dehydro PME1, were difficult to be determined or easily misjudged by MS/MS. The transformation of such unsaturated components to be epoxidized components or di-hydroxylated components can promote the acquisition of more fragment ions in the MS/MS, so as to assist in judging the position of double bonds on FA. Methods: In this paper, the PME mixtures were dissolved in an equal proportion of 20% ACN aqueous solution and 2-acetylpyridine. The above PME solution was transferred to a quartz cuvette and irradiated with the ultraviolet lamp at 254 nm for 8h. The dehydro PME components were converted to be epoxy PMEs and dihydroxy PMEs. A fragmentation pathway of epoxidized components or di-hydroxylated components based on Q/TOF-MS/MS was proposed for the first time. Results: According to the characteristic ions of epoxidized components and di-hydroxylated components, 2’, 3’-epoxy PME1/E2 and 2’, 3’-dihydroxy PME1/E2 were confirmed. It can be inferred that the double bond is located at the 2’, 3’-position of FA. Conclusion: The structure of unsaturated PME component with double bond on the FA is elucidated by HPLC-Q/TOF-MS combined with photochemical reaction. This strategy is applicable to other lipopeptides containing unsaturated FA chain.

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Wang, Zhanyong, guipeng feng, xiaoying jiang, hanyue xue, qing xu e ran xia. "Recent Developments in C‐S, C‐Se Bond Formation via Three‐Component Reactions of Alkynes". European Journal of Organic Chemistry, 28 agosto 2024. http://dx.doi.org/10.1002/ejoc.202400844.

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Alkynes are valuable building blocks in organic synthesis. They can undergo three‐component difunctionalization to create sulfur or selenium‐containing compounds. Three‐component reactions of alkynes are atom economic, practical and regioselective. This review will disscuss decade developments, including C‐S and C‐Se bond formation via thiolation, sulfonylation and selenylation. Recent developments can be mainly categorized into three types. (1) Radical C‐S/S‐Se bond formation is a hot topic. Reactions initiated by S/Se radicals or other radicals exhibit two types of selectivities. Photochemical and electrochemical reactions under eco‐friendly conditions have been increasingly reported. (2) Some transformations involve electrophilic three‐membered ring intermediates. Thiiraniums, seleniraniums, and iodoniums are among the most prevalent species. They undergo ring‐opening by various nucleophiles and participate in tandem reactions. (3) Metal‐catalyzed reactions, a classic category, will also be discussed in the text. In the following section, we will provide an overview based on the mechanisms and substrates. The roles of added reagents will also be discussed.

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