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Zhenjun Chang, Dirk Henkensmeier, Ruiyong Chen
By using a one-step epoxide ring-opening reaction between 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-hydroxy-TEMPO) and glycidyltrimethylammonium cation (GTMA+), we synthesize a cation-grafted TEMPO (g+-TEMPO) and study its electrochemical performance against a Zn2+/Zn anode in a hybrid redox flow battery. To conduct Cl- counter anions, a crosslinked methylated polybenzimidazole (PBI) membrane was prepared and placed between the catholyte and anolyte. Compared to 4-hydroxy-TEMPO, the positively charged g+-TEMPO exhibits enhanced reaction kinetics...
July 17, 2017: ChemSusChem
Cheng Zhou, Lin Zhu, Yue Xie, Feiyue Li, Xin Xiao, Zhongyou Ma, Jianfei Wang
Soil saline-alkalization is a major abiotic stress that leads to low iron (Fe) availability and high toxicity of sodium ions (Na(+)) for plants. It has recently been shown that plant growth promoting rhizobacteria (PGPR) can enhance the ability of plants to tolerate multiple abiotic stresses such as drought, salinity, and nutrient deficiency. However, the possible involvement of PGPR in improving saline-alkaline tolerance of plants and the underlying mechanisms remain largely unknown. In this study, we investigated the effects of Bacillus licheniformis (strain SA03) on the growth of Chrysanthemum plants under saline-alkaline conditions...
2017: Frontiers in Plant Science
Erik D Hedegård, Ulf Ryde
Lytic polysaccharide monooxygenases (LPMOs) are copper metalloenzymes that can enhance polysaccharide depolymerization through an oxidative mechanism, making them interesting for the production of biofuel from cellulose. However, the details of this activation are unknown; in particular, the nature of the intermediate that attacks the glycoside C-H bond in the polysaccharide is not known, and a number of different species have been suggested. The homolytic bond-dissociation energy (BDE) has often been used as a descriptor for the bond-activation power, especially for inorganic model complexes...
July 11, 2017: Journal of Biological Inorganic Chemistry: JBIC
Paulin Nkolo, Gérard Audran, Raphael Bikanga, Paul Brémond, Sylvain R A Marque, Valérie Roubaud
Throughout the last decade, the effect of electron withdrawing groups (EWGs) has been known to play a role - minor or moderate depending on the nitroxyl fragment R1R2NO - in the change in the homolysis rate constant (kd) for C-ON bond homolysis in alkoxyamines (R1R2NOR). It has been shown that the effect of EWGs on kd is described by a linear relationship with the electrical Hammett constant σI. Since then, linear multi-parameter relationships f(σRS,ν,σI) have been developed to account for the effects involved in the changes in kd, which are the stabilization of the released radical (σRS) and the bulkiness (ν) and polarity (σI) of the alkyl fragment...
July 10, 2017: Organic & Biomolecular Chemistry
Xican Li
Current in vitro antioxidant assays have several limitations, which frequently cause inconsistent results. The study develops a new antioxidant assay using 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical (PTIO•). After the investigation of various factors, the experimental protocol was briefly recommended as follows: PTIO• and the sample solution were added to phosphate buffer (pH 7.4, 50 mM), incubated at 37°C for 2 hours, and then spectrophotometrically measured at 557 nm. The validation test based on 20 pure compounds and 30 lyophilized-aqueous-extracts suggested that PTIO•-scavenging had a good linear relationship, stability, and reproducibility...
July 10, 2017: Journal of Agricultural and Food Chemistry
Guizhi Fan, Tingting Nie, Jin Sheng Fan, Yaguang Zhan
The aim of this study was to assay by NMR the metabolites which contribute to betulin production. 8-day-old suspended birch (Betula platyphylla) cells were treated by sodium nitroprusside (SNP) treatment, an NO donor, and 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO), an NO-specific scavenger. The results showed that betulin production was increased by five times after SNP treatment, similar with that of the control under cPTIO treatment. Forty one metabolites were detected after SNP treatment or cPTIO treatment...
June 30, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Cheng Zhou, Lin Zhu, Zhongyou Ma, Jianfei Wang
Without physical contact with plants, certain plant growth-promoting rhizobacteria (PGPR) can release volatile organic compounds (VOCs) to regulate nutrient acquisition and induce systemic immunity in plants. However, whether the PGPR-emitted VOCs can induce cadmium (Cd) tolerance of plants and the underlying mechanisms remain elusive. In this study, we probed the effects of Bacillus amyloliquefaciens (strain SAY09)-emitted VOCs on the growth of Arabidopsis plants under Cd stress. SAY09 exposure alleviates Cd toxicity in plants with increased auxin biosynthesis...
June 28, 2017: Genes
Hisayuki Hosoo, Aiki Marushima, Yukio Nagasaki, Aki Hirayama, Hiromu Ito, Sandra Puentes, Arnela Mujagic, Hideo Tsurushima, Wataro Tsuruta, Kensuke Suzuki, Hirofumi Matsui, Yuji Matsumaru, Tetsuya Yamamoto, Akira Matsumura
BACKGROUND AND PURPOSE: Reperfusion therapy by mechanical thrombectomy is used to treat acute ischemic stroke. However, reactive oxygen species generation after reperfusion therapy causes cerebral ischemia-reperfusion injury, which aggravates cerebral infarction. There is limited evidence for clinical efficacy in stroke for antioxidants. Here, we developed a novel core-shell type nanoparticle containing 4-amino-4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (nitroxide radical-containing nanoparticles [RNPs]) and investigated its ability to scavenge reactive oxygen species and confer neuroprotection...
June 27, 2017: Stroke; a Journal of Cerebral Circulation
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
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 27, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
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
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
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
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
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
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
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
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
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
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
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