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https://www.readbyqxmd.com/read/28636313/iodine-iii-reagents-in-radical-chemistry
#1
Xi Wang, Armido Studer
The chemistry of hypervalent iodine(III) compounds has gained great interest over the past 30 years. Hypervalent iodine(III) compounds show valuable ionic reactivity due to their high electrophilicity but also express radical reactivity as single electron oxidants for carbon and heteroatom radical generation. Looking at ionic chemistry, these iodine(III) reagents can act as electrophiles to efficiently construct C-CF3, X-CF3 (X = heteroatom), C-Rf (Rf = perfluoroalkyl), X-Rf, C-N3, C-CN, S-CN, and C-X bonds...
June 21, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28621375/roles-of-phenol-groups-and-auxiliary-ligand-of-copper-ii-complexes-with-tetradentate-ligands-in-the-aerobic-oxidation-of-benzyl-alcohol
#2
Guangli Zhan, Wei Zhong, Zhenhong Wei, Zhenzhen Liu, Xiaoming Liu
Herein, six copper(ii) complexes with multidentate ligands, [Cu(HL1)(OAc)(HOAc)] (1), [Cu(HL2)(OAc)] (2), [Cu(HL3)(OAc)] (3), [CuL4(OAc)] (4), [Cu(HL2)Cl] (5), and [Cu(HL3)Cl] (6) {H2L1 = [bis(3-tert-butyl-2-hydroxybenzyl)](2-pyridylmethyl)amine, H2L2 = [(3-tert-butyl-2-hydoxybenzyl)(3-trifluoromethyl-2-hydroxybenzyl) (2-pyridylmethyl)]amine, H2L3 = [bis(3-trifluoromethyl-2-hydroxybenzyl)] (2-pyridylmethyl)amine, and HL4 = [bis(2-pyridylmethyl)] (3-tert-butyl-2-hydroxybenzyl)amine}, are reported. The complexes were characterized by UV-vis spectroscopy, high-resolution mass spectrometry, X-ray single-crystal diffraction analysis and electrochemistry...
June 16, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28609611/selective-aliphatic-carbon-carbon-bond-activation-by-rhodium-porphyrin-complexes
#3
Ching Tat To, Kin Shing Chan
The carbon-carbon bond activation of organic molecules with transition metal complexes is an attractive transformation. These reactions form transition metal-carbon bonded intermediates, which contribute to fundamental understanding in organometallic chemistry. Alternatively, the metal-carbon bond in these intermediates can be further functionalized to construct new carbon-(hetero)atom bonds. This methodology promotes the concept that the carbon-carbon bond acts as a functional group, although carbon-carbon bonds are kinetically inert...
June 13, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28608610/identification-of-stable-znii-oxyl-species-enforced-by-mfi-and-its-reversible-reactivity-with-o%C3%A2-at-rt
#4
Yasushige Kuroda, Akira Oda, Takahiro Ohkubo, Takahi Yumura, Hisayoshi Kobayashi
Although a terminal oxyl species bound to certain metal ions is believed to be the intermediate for various oxidation reactions such as O-O bond generation in the photosystem II (PSII), its identification has been elusive. Herein, we report unambiguous identification of a stable ZnII-oxyl species enforced by an MFI-type-zeolite lattice and its reversible reactivity with O₂ at room temperature: [ZnII-O·]+ + O₂ ⇄ [ZnII-O₃·]+. Such intriguing characteristics were evidenced by in situ spectroscopic studies coupled with quantum chemical calculation, i...
June 13, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28606531/all-natural-bio-plastics-using-starch-betaglucan-composites
#5
Domenico Sagnelli, Jacob J K Kirkensgaard, Concetta Valeria L Giosafatto, Natalia Ogrodowicz, Krzysztof Kruczała, Mette S Mikkelsen, Jean-Eudes Maigret, Denis Lourdin, Kell Mortensen, Andreas Blennow
Grain polysaccharides represent potential valuable raw materials for next-generation advanced and environmentally friendly plastics. Thermoplastic starch (TPS) is processed using conventional plastic technology, such as casting, extrusion, and molding. However, to adapt the starch to specific functionalities chemical modifications or blending with synthetic polymers, such as polycaprolactone are required (e.g. Mater-Bi). As an alternative, all-natural and compostable bio-plastics can be produced by blending starch with other polysaccharides...
September 15, 2017: Carbohydrate Polymers
https://www.readbyqxmd.com/read/28598474/anisotropic-longitudinal-electronic-relaxation-affects-dnp-at-cryogenic-temperatures
#6
E M M Weber, H Vezin, J G Kempf, G Bodenhausen, D Abergél, D Kurzbach
We report the observation of anisotropic longitudinal electronic relaxation in nitroxide radicals under typical dynamic nuclear polarization conditions. This anisotropy affects the efficiency of dynamic nuclear polarization at cryogenic temperatures of 4 K and high magnetic fields of 6.7 T. Under our experimental conditions, the electron paramagnetic resonance spectrum of nitroxides such as TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl) is only partly averaged by electronic spectral diffusion, so that the relaxation times T1e(ω) vary across the spectrum...
June 21, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28586133/noncovalent-immobilization-of-molecular-electrocatalysts-for-chemical-synthesis-efficient-electrochemical-alcohol-oxidation-with-a-pyrene-tempo-conjugate
#7
Amit Das, Shannon S Stahl
Electrocatalytic methods for organic synthesis could offer sustainable alternatives to traditional redox reactions, but strategies are needed to enhance the performance of molecular catalysts designed for this purpose. The synthesis of a pyrene-tethered TEMPO derivative (TEMPO=2,2,6,6-tetramethylpiperidinyl-N-oxyl) is described, which undergoes facile in situ noncovalent immobilization onto a carbon cloth electrode. Cyclic voltammetry and controlled potential electrolysis studies demonstrate that the immobilized catalyst exhibits much higher activity relative to 4-acetamido-TEMPO, an electronically similar homogeneous catalyst...
June 6, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/28582606/2-2-6-6-tetramethylpiperydinyl-1-oxyl-tempo-functionalized-benzoxazines-prepared-with-a-one-pot-synthesis-for-reactive-crosslinkable-initiators-of-nitroxide-mediated-polymerization
#8
Yi-Jen Han, Ying-Ling Liu
In this work, the incorporation of a 2,2,6,6-tetramethylpiperydinyl-1-oxyl (TEMPO) group to a benzoxazine ring is performed using a one-pot synthesis for the preparation of TEMPO-functionalized benzoxazine compounds and polymers as reactive and crosslinkable initiators for nitroxide-mediated polymerization (NMP). The TEMPO-functionalization reaction of benzoxazine, traced with (1) H NMR, is conducted with sequential radical transfer and coupling reactions. Moreover, polystyrene-grafted polybenzoxazine copolymers are prepared with the TEMPO-benzoxazine initiator and NMP of styrene...
June 5, 2017: Macromolecular Rapid Communications
https://www.readbyqxmd.com/read/28567466/application-of-primary-halogenated-hydrocarbons-for-the-synthesis-of-3-aryl-and-3-alkyl-indolizines
#9
Yan Liu, Huayou Hu, Junyu Zhou, Wenhui Wang, Youliang He, Chao Wang
Indolizine is an important heterocyclic compound with several interesting properties that make it suitable for numerous applications in many fields, such as biology, medicine and materials. However, the synthesis of 3-alkyl indolizines from bulky primary halogenated alkanes has not yet been reported. Herein, a transition-metal-free synthetic route to 3-aryl and 3-alkyl indolizines from electron-deficient alkenes, pyridines and primary halogenated hydrocarbons has been reported for the first time using a tandem reaction...
June 14, 2017: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/28558469/electrocatalytic-water-oxidation-by-a-homogeneous-copper-catalyst-disfavors-single-site-mechanisms
#10
Sara J Koepke, Kenneth M Light, Peter E VanNatta, Keaton M Wiley, Matthew T Kieber-Emmons
Deployment of solar fuels derived from water requires robust oxygen-evolving catalysts made from earth abundant materials. Copper has recently received much attention in this regard. Mechanistic parallels between Cu and single-site Ru/Ir/Mn water oxidation catalysts, including intermediacy of terminal Cu oxo/oxyl species, are prevalent in the literature; however, intermediacy of late transition metal oxo species would be remarkable given the high d-electron count would fill antibonding orbitals, making these species high in energy...
June 15, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28534620/hydrogen-atom-transfer-hat-processes-promoted-by-the-quinolinimide-n-oxyl-radical-a-kinetic-and-theoretical-study
#11
Gino A DiLabio, Paola Franchi, Osvaldo Lanzalunga, Andrea Lapi, Fiorella Lucarini, Marco Lucarini, Marco Mazzonna, Viki Kumar Prasad, Barbara Ticconi
A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the quinolinimide-N-oxyl radical (QINO) was performed in CH3CN. The HAT rate constants are significantly higher than those observed with the phthalimide-N-oxyl radical (PINO) as a result of enthalpic and polar effects due to the presence of the N-heteroaromatic ring in QINO. The relevance of polar effects is supported by theoretical calculations conducted for the reactions of the two N-oxyl radicals with toluene, which indicate that the HAT process is characterized by a significant degree of charge transfer permitted by the π-stacking that occurs between the toluene and the N-oxyl aromatic rings in the transition state structures...
June 6, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28532685/nitroxide-4-hydroxy-2-2-6-6-tetramethylpiperidine-1-oxyl-tempol-inhibits-the-reductase-activity-of-protein-disulfide-isomerase-via-covalent-binding-to-the-cys400-residue-on-cxxc-redox-motif-at-the-a-active-site
#12
Gérsika Bitencourt Santos, Lucia Gonzalez-Perilli, Mauricio Mastrogiovanni, Adrián Aicardo, Cláudio Daniel Cerdeira, Andrés Trostchansky, Maísa Ribeiro Pereira Lima Brigagão
BACKGROUND AND AIM: Oxidative stress arising from inflammatory processes is a serious cause of cell and tissue damage. Tempol is an efficient antioxidant with superoxide dismutase-like activity. The purpose of this paper is to address the inhibition of protein disulfide isomerase (PDI), an essential redox chaperone whose active sites contain the Cys-Gly-His-Cys (CXXC) motif, by the nitroxide Tempol. RESULTS: In the presence of Tempol (5-120 μM), the reductase activity of PDI was reversibly affected both in vitro and in activated mice neutrophils, with an IC50 of 22...
June 25, 2017: Chemico-biological Interactions
https://www.readbyqxmd.com/read/28521553/glutaraldehyde-polymerized-hemoglobin-and-tempol-polyhb-tempol-has-superoxide-dismutase-activity-that-can-attenuate-oxidative-stress-on-endothelial-cells-induced-by-superoxide-anion
#13
Mengdi Wu, Kun Feng, Qiuhui Li, Huiya Ma, Hongli Zhu, Yudou Xie, Gaofei Yan, Chao Chen, Kunping Yan
A Tempol compound with an amine group (4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, NH2-Tempol) was cross-linked to hemoglobin in a one-step polymerization reaction to produce a novel hemoglobin-based oxygen carrier (HBOC) designated PolyHb-Tempol. The reaction parameters, including the reaction time, pH, temperature, and ratio of reactants, were optimized, and the physiochemical properties of the resulting product were characterized. PolyHb-Tempol didn't show any toxicity towards endothelial cells. Furthermore, from observations of cell morphology and viability, PolyHb-Tempol showed a significant ability to inhibit or eliminate oxidative stress induced by superoxide free radicals...
May 18, 2017: Artificial Cells, Nanomedicine, and Biotechnology
https://www.readbyqxmd.com/read/28513669/the-open-cubane-oxo-oxyl-coupling-mechanism-dominates-photosynthetic-oxygen-evolution-a-comprehensive-dft-investigation-on-o-o-bond-formation-in-the-s4-state
#14
Yu Guo, Hui Li, Lan-Lan He, Dong-Xia Zhao, Li-Dong Gong, Zhong-Zhi Yang
The dioxygen formation mechanism of biological water oxidation in nature has long been the focus of argument; many diverse mechanistic hypotheses have been proposed. Based on a recent breakthrough in the resolution of the electronic and structural properties of the oxygen-evolving complex in the S3 state, our density functional theory (DFT) calculations reveal that the open-cubane oxo-oxyl coupling mechanism, whose substrates preferably originate from W2 and O5 in the S2 state, emerges as the best candidate for O-O bond formation in the S4 state...
May 31, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28495446/mechanism-of-hrp-catalyzed-nitrite-oxidation-by-h2o2-revisited-effect-of-nitroxides-on-enzyme-inactivation-and-its-catalytic-activity
#15
Amram Samuni, Eric Maimon, Sara Goldstein
The peroxidative activity of horseradish peroxidase (HRP) undergoes progressive inactivation while catalyzing the oxidation of nitrite by H2O2. The extent of inactivation increases as the pH increases, [nitrite] decreases or [H2O2] increases, and is accompanied by a loss of the Soret peak of HRP along with yellow-greenish coloration of the solution. HRP-catalyzed nitrite oxidation by H2O2 involves not only the formation of compounds I and II as transient heme species, but also compound III, all of which in turn, oxidize nitrite yielding (•)NO2...
May 8, 2017: Free Radical Biology & Medicine
https://www.readbyqxmd.com/read/28492666/dna-friendly-cu-ii-tempo-catalyzed-5-hydroxymethylcytosine-specific-oxidation
#16
Taku Matsushita, Yuya Moriyama, Genta Nagae, Hiroyuki Aburatani, Akimitsu Okamoto
The mixture of copper(ii) perchlorate and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mildly and specifically oxidized 5-hydroxymethylcytosine to yield 5-formylcytosine because of its allyl alcohol specificity. The genomic DNA oxidized at 5-hydroxymethylcytosine by the copper(ii)/TEMPO oxidation was efficiently analyzed using various practical methods: DNA cleavage by piperidine, specific functionalization by hydrazone formation, and genome-wide high-resolution microarray.
May 11, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28482335/nitric-oxide-mediates-brassinosteroid-induced-flavonoid-biosynthesis-in-camellia-sinensis-l
#17
Xin Li, Lan Zhang, Golam Jalal Ahammed, Zhi-Xin Li, Ji-Peng Wei, Chen Shen, Peng Yan, Li-Ping Zhang, Wen-Yan Han
Flavonoids are one of the key secondary metabolites determining the quality of tea. Although exogenous brassinosteroid (BR), a steroidal plant hormone, can stimulate polyphenol biosynthesis in tea plants (Camellia sinensis L.), the relevance of endogenous BR in flavonoid accumulation and the underlying mechanisms remain largely unknown. Here we show that BR enhances flavonoid concentration in tea leaves by inducing an increase in the endogenous concentration of nitric oxide (NO). Notably, exogenous BR increased levels of flavonoids as well as NO in a concentration dependent manner, while suppression of BR levels by an inhibitor of BR biosynthesis, brassinazole (BRz), decreased the concentrations of both flavonoids and NO in tea leaves...
July 2017: Journal of Plant Physiology
https://www.readbyqxmd.com/read/28481527/aerobic-oxidation-of-4-alkyl-n-n-dimethylbenzylamines-catalyzed-by-n-hydroxyphthalimide-protonation-driven-control-over-regioselectivity
#18
Massimo Bietti, Osvaldo Lanzalunga, Andrea Lapi, Teo Martin, Marco Mazzonna, Mariangela Polin, Michela Salamone
A change in regioselectivity has been observed in the hydrogen atom transfer (HAT) reactions from 4-alkyl-N,N-dimethylbenzylamines (alkyl = ethyl, isopropyl, and benzyl) to the phthalimide N-oxyl radical (PINO) by effect of protonation. This result can be rationalized on the basis of an acid-induced deactivation of the C-H bonds α to nitrogen toward HAT to PINO as evidenced by the 10(4)-10(7)-fold decrease in the HAT rate constants in acetonitrile following addition of 0.1 M HClO4. This acid-induced change in regioselectivity has been successfully applied for selective functionalization of the less activated benzylic C-H bonds para to the CH2N(CH3)2 group in the aerobic oxidation of 4-alkyl-N,N-dimethylbenzylamines catalyzed by N-hydroxyphthalimide in acetic acid...
May 17, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28464859/lyophilized-aqueous-extracts-of-mori-fructus-and-mori-ramulus-protect-mesenchymal-stem-cells-from-%C3%A2-oh-treated-damage-bioassay-and-antioxidant-mechanism
#19
Qian Jiang, Xican Li, Yage Tian, Qiaoqi Lin, Hong Xie, Wenbiao Lu, Yuguang Chi, Dongfeng Chen
BACKGROUND: Mori Fructus and Mori Ramulus are two traditional Chinese herbal medicines from mulberries. The present work explores their beneficial effects on •OH-treated mesenchymal stem cells (MSCs) and discusses possible mechanisms. METHODS: Lyophilized aqueous extracts of Mori Fructus (LAMF) and Mori Ramulus (LAMR) were prepared and analyzed using HPLC. LAMF and LAMR (along with morin) were further investigated for their effects on •OH-treated MSCs using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl (MTT) assay...
May 2, 2017: BMC Complementary and Alternative Medicine
https://www.readbyqxmd.com/read/28444914/dynamic-nuclear-polarization-studies-on-deuterated-nitroxyl-spin-probes
#20
D David Jebaraj, Hideo Utsumi, A Milton Franklin Benial
Detailed dynamic nuclear polarization and electron spin resonance studies were carried out for 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl, 3-carboxy-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl,3-methoxycarbonyl-2,2,5,5-tetramethy pyrolidine-1-oxyl nitroxyl radicals and their corresponding deuterated nitroxyl radicals, used in Overhauser-enhanced magnetic resonance imaging for the first time. The dynamic nuclear polarization parameters such as dynamic nuclear polarization (DNP) factor, longitudinal relaxivity, saturation parameter, leakage factor and coupling factor were estimated for deuterated nitroxyl radicals...
April 26, 2017: Magnetic Resonance in Chemistry: MRC
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