- Evolution of Photooxidation Products upon Irradiation of Phenyl Azide in the Presence of Molecular Oxygen
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The reaction of phenylnitrene with oxygen was reinvestigated by irradiating phenyl azide (1) in O2-saturated acetonitrile solutions.Quantum yields of the disappearance of 1 are calculated from absorption spectral changes, and primary photoproducts are determined by using high-pressure liquid chromatography.The photochemistry of the reaction products (azobenzene, azoxybenzene, nitrobenzene, and nitrosobenzene) are also examined, including measurements of quantum yields and determinations of primary photoproducts and product ratios.A reaction sequence is presented to account for the photooxidation products afforded upon irradiation of 1 in the presence of oxygen.The reaction of phenylnitrene with oxygen is an effective termination step in the autocatalytic chain decomposition of 1.
- Go, Celia Lee,Waddell, Walter H.
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- REACTION OF CHLOROPHYLL WITH 2,2'-DITHIOBIS(5-NITROPYRIDINE)
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Chlorophyll a reacts photochemically with 2,2'-dithiobis(5-nitropyridine), incorporating 5-nitropyridinethiyl residues.On nmr evidence, substitution occurs principally at the α and δ meso positions, and not at the β.The products are markedly less fluoresc
- Seely, G. R.
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- Carbon Dioxide-promoted Electrochemical Reduction of Aromatic Nitro Compounds to Azoxy Compounds in Acetonitrile
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CO2 was found to promote electrochemical reduction of aromatic nitro compounds in acetonitrile even in the absence of a proton source to produce multi-electron reduction products, azoxy compounds as well as smaller amounts of azo and hydroxylamino compounds.
- Ohba, Tomoyuki,Ishida, Hitoshi,Yamaguchi, Tomohiro,Horiuchi, Tomohiro,Ohkubo, Katsutoshi
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- Kinetic Analysis of the Photoinitiated Autocatalytic Chain Decomposition of Phenyl Azide. A Molecular Explosion in Solution
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Quantum yields of disappearance of pheny azide were determined for oxygen-purged, oxygen-saturated, and air-saturated solutions in acetonitrile ranging in concentration () from 1.40E-5 to 7.93E-1 M.A kinetic analysis of a simplified four-step reaction mechanism, based upon the reaction of phenylnitrene and phenyl azide to form two phenylnitrenes, affords a mathematical expression that relates experimentally determined Φ(-PhN3) values to experimentally measured , I0 (intensity of the excitation light), and V0 (volume of solution irradiated) values.One general expression accurately fits 56 experimental determinations of Φ(-PhN3), correctly relating it to and I0, whereby Φ(-PhN3) increases with increasing 2 and decreases with increasing I0.The Φ(-PhN3) data along with the kinetic analysis provide definitive evidence of the first molecular explosion in solution as a result of the photoinitiated autocatalytic (branching) chain decomposition reaction of phenyl azide.
- Costantino, Joseph P.,Richter, Helen W.,Go, Celia H. Lee,Waddell, Walter H.
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- FIRST EXAMPLE OF TETRAALKYL SUBSTITUTED DITELLURIDE DICATION SALT FROM 1,5-DITELLURACYCLOOCTANE
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A new cyclic bis-telluride, 1,5-ditelluracyclooctane (1), has been synthesized.Two-electron oxidation of 1 with two equivalents of NOBF4 or NOPF6 afforded a novel ditelluride dication BF4- or PF6- salt 2 which was characterized by 12
- Fujihara, Hisashi,Ninoi, Takeshi,Akaishi, Ryouichi,Erata, Tomoki,Furukawa, Naomichi
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- Evidence for stepwise nitrogen extrusion and ring expansion upon photolysis of phenyl azide
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The temperature dependence of the products formed on photolysis of two independent precursors of phenylnitrene has been studied. The identity of the product-forming intermediates (triplet phenylnitrene versus ketene imine) produced on photolysis of phenyl azide and benzenesulfoximine in the presence of diethylamine show the same qualitative variation with temperature. An excited state of the nitrene precursor is not responsible for the known temperature dependence of the distribution of stable products. The data are consistent with stepwise formation of singlet phenylnitrene and subsequent expansion to azacycloheptatetraene. The singlet and triplet energies of phenyl azide have been determined by energy transfer.
- Marcinek, Andrzej,Leyva, Elisa,Whitt, David,Platz, Matthew S.
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- Investigations of the thermal inversion rates of azobenzenes in supercritical and gaseous CO2: A shift from the energy-transfer-limited to the TST-valid region at low densities
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Studies of slow thermal Z E isomerization reactions around the N=N double bond of azobenzenes in supercritical and gaseous carbon dioxide revealed that a shift from the energytransfer-limited to the TST-valid region predicted by Kramers takes place at rel
- Usui, Toshinori,Funahushi, Shigenobu,Takagi, Hideo D.,Asano, Tsutomu
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- Nematicons in azobenzene liquid crystals
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We review our comprehensive investigation of light self-localization phenomena in planarly configured azobenzene liquid crystals. Cis-trans isomerization of azobenzene molecules and related changes in the order parameter of the liquid crystals support a h
- Serak, Svetlana V.,Tabiryan, Nelson V.,Assanto, Gaetano
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- Palladium-catalyzed direct ortho-sulfonylation of azobenzenes with arylsulfonyl chlorides via C-H activation
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A highly efficient and practical procedure to direct ortho-sulfonylation of azobenzenes' C-H bond with arylsulfonyl chlorides has been developed. The method was applicable to both electron-rich and electron-deficient substrates and delivered good yields f
- Xia, Chengcai,Wei, Zhenjiang,Shen, Chao,Xu, Jun,Yang, Yong,Su, Weike,Zhang, Pengfei
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- PHOTOINITIATED AUTOCATALYTIC CHAIN DECOMPOSITION OF PHENYL AZIDE.
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Quantum yields of disappearance of phenyl azide ( phi -PhN//3) were determined for 10** minus **5-10** minus **1 M acetonitrile solutions at room temperature by monitoring changes in its electronic absorption spectra. For dilute solutions, phi -PhN//3 equals 0. 5; however, at higher concentrations phi -PhN//3 values greatly exceed unit efficiency and indicate a chain decomposition mechanism. At ca. 2 multiplied by 10** minus **1 M, phi -PhN//3 approximately equals 3000! A plot of left bracket phi -PhN//3 right bracket vs. log left bracket PhN//3 right bracket appears exponential and since a plot of the chain length, n, vs. left bracket PhN//3 right bracket is linear (r**2 equals 0. 972), when n is calculated from an exponential function, the experimental results provide evidence for a branching chain reaction also known as an autocatalytic (spontaneously explosive) reaction. The branching chain mechanism is thought to result from reaction of a phenyl nitrene intermediate with a ground-state phenyl azide molecule to form two phenyl nitrenes. A 1,4-tetraazadiene or triaza species may also participate in the chain reaction.
- Go,Waddell
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- Kinetic study of thermal Z to e isomerization reactions of azobenzene and 4-dimethvlaniino-4′-nitroazobenzene in Ionic Liquids [1-R-3- methyliniidazolium bis(trifluoromethylsulfonyl)imide with R = Butyl, Pentyl, and Hexyl]
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Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4′-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl. and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the vis cosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4′- nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 104-107 s -1.
- Baba, Keita,Ono, Hajime,Itoh, Eri,Itoh, Sumitaka,Noda, Kyoko,Usui, Toshinori,Ishihara, Koji,Inamo, Masahiko,Takagi, Hideo D.,Asano, Tsutomu
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- Dual behavior of ZSM-5 as bronsted acid and electron acceptor in the adsorption of N,N'-diphenylhydrazine
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Incorporation of N,N'-diphenylhydrazine into HZSM-5 led to the formation of azobenzene and aniline (70-80 mol-% mass balance). The formation of azobenzene can be followed by the appearance in diffuse reflectance UV/Vis spectroscopy of a characteristic band (λmax = 420 nm). IR spectra of the extracted solids indicate that some aniline is retained in the zeolite, probably due to acid-base interaction with active sites. The products are rationalized by two competing mechanisms: the formation of azobenzene by electron transfer to an oxidizing site, the generation of aniline by proton transfer from a Bronsted acid site. A long-wavelength diffuse-reflectance band (λmax = 800 nm) in the initial stages of the reaction supports the intermediacy of a radical cation. These results show that acid zeolites can exhibit a dual behavior against basic substrates with low oxidation potential, serving simultaneously as electron acceptor and Bronsted acid.
- Marti, Vicente,Fornes, Vicente,Garcia, Hermenegildo,Roth, Heinz Dieter
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- Synthesis and photochromic property of cis-azobenzene complex with a binuclear η6-areneruthenium(II) unit
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A cis-azobenzene complex with a binuclear ruthenium(II) unit bridged by alkoxo ligands which are tethered to η6-arene donors (4) was synthesized from corresponding binuclear acetonitrile complex (3) and trans-azobenzene irradiated by UV light (300 nm 510 nm) in acetonitrile, 4 mostly dissociated to transazobenzene and 3 with the photostationary ratio 3/4 = 92/8.
- Miyaki, Yoshiharu,Onishi, Takafumi,Kurosawa, Hideo
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- Oxidation of Aromatic Amines by N-Chloroanilides. Direction of Polarity of the Nitrogen-Chlorine Bond
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The effect of substituents in the aromatic ring as well as in the acyl moiety of some N-chloroanilides i, Et, PhCH2, Ph> on the kinetics of oxidation of aniline and p-toluidine has been studi
- Kumar, Arun,Bhattacharjee, Gurudas
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- Femtosecond photoisomerization of cis-azobenzene
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Femtosecond transient absorption measurements of the photoisomerization of azobenzene excited at 435 nm in the long-wavelength (nπ*) band are presented. For cis-azobenzene the experiments reveal an extremely fast photoproduct formation with a dominating 1
- Naegele,Hoche,Zinth,Wachtveitl
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- Modification of photochemical reactivity by nafion. Photocyclization and photochemical cis-trans isomerization of azobenzene
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The photophysical and photochemical behavior of azobenzene (AB) incorporated into solvent-swollen acid form Nafion (Nafion-H+) membranes were examined. In water-swollen Nafion-H+ membrane AB exhibits strong fluorescence at room temperature, which has never been observed in isotropic solvents. Photolysis of AB adsorbed in water-swollen Nafion-H+ results in its cyclization to give benzo[c]cinnoline (BC) and benzidine (BZ) in quantitative yield. The product distribution is very dependent upon the number of AB molecules in each water cluster of the Nafion membrane (occupancy number). In the case of the occupancy number greater than 2, BC and BZ are formed equimolarly, while when only one AB molecule exists in each water cluster, BC is exclusively produced. The AB molecules incorporated into methanol-swollen Nafion-H+ membrane do not emit fluorescence and only undergo cis-trans isomerization when they are photoirradiated. These observations suggest that in water-swollen Nafion-H+ AB molecules are solublized in the fluorocarbon/water interface, and the protons of the Nafion-H+ participate in the photochemical and photophysical processes of AB. On the other hand, in methanol-swollen Nafion-H+ membrane AB molecules are located in the methanol pools, and their photochemical and photophysical behaviors are not intervened by the Nafion protons.
- Tung, Chen-Ho,Guan, Jing-Qu
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- Mechanism of thermal isomerization of azobenzene in zeolite cavities
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The life time of cis-azobenzene in zeolite supercage is twenty times longer than that in benzene at room temperature. The kinetic studies indicate that the thermal isomerization proceeds through inversion mechanism. Activation parameters show that the zeo
- Kuriyama, Yasunao,Oishi, Shigero
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- Zr(OH)4-Catalyzed Controllable Selective Oxidation of Anilines to Azoxybenzenes, Azobenzenes and Nitrosobenzenes
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The selective oxidation of aniline to metastable and valuable azoxybenzene, azobenzene or nitrosobenzene has important practical significance in organic synthesis. However, uncontrollable selectivity and laborious synthesis of the expensive required catalysts severely hinders the uptake of these reactions in industrial settings. Herein, we have pioneered the discovery of Zr(OH)4 as an efficient heterogeneous catalyst capable of the selective oxidation of aniline, using either peroxide or O2 as oxidant, to selectively obtain various azoxybenzenes, symmetric/unsymmetric azobenzenes, as well as nitrosobenzenes, by simply regulating the reaction solvent, without the need for additives. Mechanistic experiments and DFT calculations demonstrate that the activation of H2O2 and O2 is primarily achieved by the bridging hydroxyl and terminal hydroxyl groups of Zr(OH)4, respectively. The present work provides an economical and environmentally friendly strategy for the selective oxidation of aniline in industrial applications.
- Long, Yu,Luo, Nan,Ma, Jiantai,Qin, Jiaheng,Sun, Fangkun,Wang, Wei David,Zhou, Pan-Pan
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supporting information
(2021/12/09)
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- London Dispersion in Alkane Solvents
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The importance of London dispersion interactions in solution is an ongoing debate. Although the significance of dispersion for structure and stability is widely accepted, the degree of its attenuation in solution is still not properly understood. Quantita
- Strauss, Marcel A.,Wegner, Hermann A.
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supporting information
p. 779 - 786
(2020/11/30)
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- Azobenzene: a Visible-Light Chemical Actinometer for the Characterization of Fluidic Photosystems
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(E)-Azobenzene is introduced as a suitable chemical actinometer in the visible spectral range (440–540 nm) for photon flux determination of fluidic microphotoreactors or for assessing efficiency of visible light photo-induced reactions, its evaluation is straightforward without tedious analytics. Photoisomerization quantum yields (ΦE→Z) of (E)-azobenzene were accurately determined upon irradiation at several wavelengths and in different solvents based on well-known diarylethene.
- Roseau, Mélanie,De Waele, Vincent,Trivelli, Xavier,Cantrelle, Francois Xavier,Penhoat, Ma?l,Chausset-Boissarie, La?titia
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- Design of phase-transition molecular solar thermal energy storage compounds: compact molecules with high energy densities
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A series of compact azobenzene derivatives were investigated as phase-transition molecular solar thermal energy storage compounds that exhibit maximum energy storage densities around 300 J g?1. The relative size and polarity of the functional g
- Qiu, Qianfeng,Gerkman, Mihael A.,Shi, Yuran,Han, Grace G. D.
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p. 9458 - 9461
(2021/09/22)
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- Bifunctional Cs?Au/Co3O4 (Basic and Redox)-Catalyzed Oxidative Synthesis of Aromatic Azo Compounds from Anilines
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An eco-friendly alkali-promoted (Cs?Au/Co3O4) catalyst, with redox and basic properties for the oxidative dehydrogenative coupling of anilines to symmetrical and unsymmetrical aromatic azo compounds, was developed. We realized a base additive- and molecular O2 oxidant-free process (using air), with reasonable reusability of the catalyst achieved under milder reaction conditions. Notably, the enhanced catalytic activity was also linked to the increased basic site concentration, low reduction temperatures, and the effect of lattice oxygen on the nanomaterials. The increased basic strength of the cation-promoted catalyst improved the electron density of the active Au species, resulting in higher yields of the desired aromatic azo compounds.
- Akinnawo, Christianah Aarinola,Alimi, Oyekunle Azeez,Fapojuwo, Dele Peter,Meijboom, Reinout,Mogudi, Batsile M.,Onisuru, Oluwatayo Racheal,Oseghale, Charles O.
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supporting information
p. 5063 - 5073
(2021/09/30)
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- Oxidative dehydrogenation of hydrazines and diarylamines using a polyoxomolybdate-based iron catalyst
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We report an efficient method for the oxidative dehydrogenation of hydrazines and diarylamines in aqueous ethanol using Anderson-type polyoxomolybdate-based iron(iii) as a catalyst and hydrogen peroxide as an oxidant. A series of azo compounds and tetraarylhydrazines were obtained in moderate to excellent yields. The reaction conditions and substrate scopes are complementary or superior to those of more established protocols. In addition, the catalyst shows good stability and reusability in water. The preliminary mechanistic studies suggest that a radical process is involved in the reaction.
- Huang, Lei,Qiu, Shiqin,Wei, Yongge,Xie, Jingyan,Yu, Han,Zeng, Xianghua,Zhao, Weizhe
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supporting information
p. 7677 - 7680
(2021/08/09)
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- Rhodium(III)-catalyzed regioselective C–H nitrosation/annulation of unsymmetrical azobenzenes to synthesize benzotriazole N-oxides via a RhIII/RhIII redox-neutral pathway
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A Rh(III)-catalyzed regioselective C–H nitrosation/annulation reaction of unsymmetrical azobenzenes with [NO][BF4] has been developed to achieve high-yielding syntheses of benzotriazole N-oxides with excellent functional group tolerance. Computational studies have revealed that this oxidative C–H functionalization reaction involves an interesting redox-neutral Rh(III)/Rh(III) pathway without the change of Rh oxidation state.
- Zhang, Yuanfei,Chen, Zhe-Ning,Su, Weiping
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- Electrosynthesis of Azobenzenes Directly from Nitrobenzenes
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The electrochemical reduction strategy of nitrobenzenes is developed. The chemistry occurs under ambient conditions. The protocol uses inert electrodes and the solvent, DMSO, plays a dual role as a reducing agent. Its synthetic value has been demonstrated by the highly efficient synthesis of symmetric, unsymmetric and cyclic azo compounds.
- Ma, Yanfeng,Wu, Shanghui,Jiang, Shuxin,Xiao, Fuhong,Deng, Guo-Jun
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p. 3334 - 3338
(2021/10/29)
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- A mild and selective Cu(II) salts-catalyzed reduction of nitro, azo, azoxy, N-aryl hydroxylamine, nitroso, acid halide, ester, and azide compounds using hydrogen surrogacy of sodium borohydride
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The first mild, in situ, single-pot, high-yielding well-screened copper (II) salt-based catalyst system utilizing the hydrogen surrogacy of sodium borohydride for selective hydrogenation of a broad range of nitro substrates into the corresponding amine under habitancy of water or methanol like green solvents have been described. Moreover, this catalytic system can also activate various functional groups for hydride reduction within prompted time, with low catalyst-loading, without any requirement of high pressure or molecular hydrogen supply. Notably, this system explores a great potential to substitute expensive traditional hydrogenation methodologies and thus offers a greener and simple hydrogenative strategy in the field of organic synthesis.
- Kalola, Anirudhdha G.,Prasad, Pratibha,Mokariya, Jaydeep A.,Patel, Manish P.
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p. 3565 - 3589
(2021/10/12)
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- Rhodium-terpyridine Catalyzed Transfer Hydrogenation of Aromatic Nitro Compounds in Water
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A rhodium terpyridine complex catalyzed transfer hydrogenation of nitroarenes to anilines with i-PrOH as hydrogen source and water as solvent has been developed. The catalytic system can work at a substrate/catalyst (S/C) ratio of 2000, with a turnover frequency (TOF) up to 3360 h?1, which represents one of the most active catalytic transfer hydrogenation systems for nitroarene reduction. The catalytic system is operationally simple and the protocol could be scaled up to 20 gram scale. The water-soluble catalyst bearing a carboxyl group could be recycled 15 times without significant loss of activity.
- Liu, Yuxuan,Miao, Wang,Tang, Weijun,Xue, Dong,Xiao, Jianliang,Wang, Chao,Li, Changzhi
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p. 1725 - 1729
(2021/06/01)
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- Calculated oxidation potentials predict reactivity in Baeyer-Mills reactions
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Azobenzenes are widely used as dyes and photochromic compounds, with the Baeyer-Mills reaction serving as the most common method for their preparation. This transformation is often plagued by low yields due to the formation of undesired azoxybenzene. Here, we explore electronic effects dictating the formation of the azoxybenzene side-product. Using calculated oxidation potentials, we were able to predict reaction outcomes and improve reaction efficiency simply by modulating the oxidation potential of the arylamine component.
- Gingrich, Phillip W.,Olson, David E.,Tantillo, Dean J.,Tombari, Robert J.,Tuck, Jeremy R.,Yardeny, Noah
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supporting information
p. 7575 - 7580
(2021/09/22)
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- Microwave-assisted reduction of aromatic nitro compounds with novel oxo-rhenium complexes
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The reduction of several aromatic nitro compounds to amines by means of the two novel catalytic systems ([IMes]2ReOBr3)/PhSiH3 and ([Py]3ReNOBr2)/PhSiH3 under microwave irradiation is here reported. These two systems were able to perform the reduction of nitro groups with higher TON and TOF when compared with previously reported systems based on oxo-rhenium core under standard heating, although they showed a lesser broad reaction scope compared with the known systems.
- Blacque, Olivier,Grieco, Gabriele
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- Computational Design and Synthesis of a Deeply Red-Shifted and Bistable Azobenzene
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We computationally dissected the electronic and geometrical influences of ortho-chlorinated azobenzenes on their photophysical properties. X-ray analysis provided the insight that trans-tetra-ortho-chloro azobenzene is conformationally flexible and thus subject to molecular motions. This allows the photoswitch to adopt a range of red-shifted geometries, which account for the extended n → π? band tails. On the basis of our results, we designed the di-ortho-fluoro di-ortho-chloro (dfdc) azobenzene and provided computational evidence for the superiority of this substitution pattern to tetra-ortho-chloro azobenzene. Thereafter, we synthesized dfdc azobenzene by ortho-chlorination via 2-fold C-H activation and experimentally confirmed its structural and photophysical properties through UV-vis, NMR, and X-ray analyses. The advantages include near-bistable isomers and an increased separation of the n → π? bands between the trans- and cis-conformations, which allows for the generation of unusually high levels of the cis-isomer by irradiation with green/yellow light as well as red light within the biooptical window.
- Konrad, David B.,Savasci, G?kcen,Allmendinger, Lars,Trauner, Dirk,Ochsenfeld, Christian,Ali, Ahmed M.
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supporting information
p. 6538 - 6547
(2020/04/08)
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- Trichloroisocyanuric Acid Mediated Oxidative Dehydrogenation of Hydrazines: A Practical Chemical Oxidation to Access Azo Compounds
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A highly efficient, metal-free, chemical oxidation of hydrazines has been implemented using environmentally friendly TCCA as oxidant. This benign protocol provides straightforward access to a wide range of azo compounds in THF in excellent yield. Altogether, 35 azo compounds were obtained in this way and scale-up preparations were performed. Additionally, a plausible mechanism was also proposed. Step-economical process, mild reaction conditions, operational simplicity, high reaction efficiency, and easy scale-up highlight the practicality of this methodology.
- Cao, Guiyan,Hu, Yulai,Huang, Danfeng,Huo, Congde,Liu, Xuan,Su, Yingpeng,Wang, Ke-Hu,Yu, Jie,Zhang, Rong,Zhao, Yanan
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supporting information
p. 1103 - 1112
(2020/04/01)
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- A Cu-BTC metal-organic framework (MOF) as an efficient heterogeneous catalyst for the aerobic oxidative synthesis of imines from primary amines under solvent free conditions
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A Cu-BTC (MOF-199) [copper(ii)-benzene-1,3,5-tricarboxylate] catalyst has been synthesized and evaluated for imine synthesis from amine compounds under neat conditions. The performance of the Cu-BTC MOF was significantly higher than that of the CuO supported on Al2O3, TiO2 and SiO2 catalysts. The role of surface Lewis acid sites on the catalyst in the formation of imine products was illustrated by the pyridine-IR studies. The recovered Cu-BTC catalyst demonstrated consistent activity for five cycles under similar experimental conditions. The physicochemical properties of the catalysts were analyzed by XRD, BET-SA, FT-IR, UV-DRS, SEM, TEM, XPS and pyridine adsorbed DRIFT spectroscopy.
- Venu, Boosa,Shirisha, Varimalla,Vishali, Bilakanti,Naresh, Gutta,Kishore, Ramineni,Sreedhar, Inkollu,Venugopal, Akula
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supporting information
p. 5972 - 5979
(2020/04/27)
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- Tuneable Copper Catalysed Transfer Hydrogenation of Nitrobenzenes to Aniline or Azo Derivatives
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A highly versatile and flexible copper nanoparticle (Cu(0) NPs) catalytic system has been developed for the controlled and selective transfer hydrogenation of nitroarene. Interestingly, the final catalytic product is strongly dependent on the nature of the hydrogen donor source. The yield of nitrobenzene reduction to aniline increased from 20% to an almost quantitative yield over a range of alcohols, diols and aminoalcohols. In glycerol at 130 °C aniline was isolated in 93% yield. In ethanolamine, the reaction was conveniently performed at a lower temperature (55 °C) and gave selectively substituted azobenzene (92% yield). Experimental studies provide support for a reaction pathway in which the Cu(0) NPs catalysed transfer hydrogenation of nitrobenzene to aniline proceeds via the condensation route. The high chemoselectivity of both protocols has been proved in experiments on a panel of variously substituted nitroarenes. Enabling technologies, microwaves and ultrasound, used both separately and in combination, have successfully increased the reaction rate and reaction yield. (Figure presented.).
- Moran, Maria Jesus,Martina, Katia,Baricco, Francesca,Tagliapietra, Silvia,Manzoli, Maela,Cravotto, Giancarlo
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p. 2689 - 2700
(2020/05/18)
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- In Situ Observation of Photoswitching by NMR Spectroscopy: A Photochemical Analogue to the Exchange Spectroscopy Experiment
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We present 1D and 2D NMR experiments that provide in situ insights into photoinduced isomerizations. Irradiation during the mixing period of an exchange spectroscopy (EXSY) experiment leads to characteristic cross peaks in 2D spectra. The phototriggered e
- Stadler, Eduard,Tassoti, Sebastian,Lentes, Pascal,Herges, Rainer,Glasnov, Toma,Zangger, Klaus,Gescheidt, Georg
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p. 11367 - 11373
(2019/09/09)
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- Exploring London Dispersion and Solvent Interactions at Alkyl–Alkyl Interfaces Using Azobenzene Switches
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Interactions on the molecular level control structure as well as function. Especially interfaces between innocent alkyl groups are hardly studied although they are of great importance in larger systems. Herein, London dispersion in conjunction with solvent interactions between linear alkyl chains was examined with an azobenzene-based experimental setup. Alkyl chains in all meta positions of the azobenzene core were systematically elongated, and the change in rate for the thermally induced Z→E isomerization in n-decane was determined. The stability of the Z-isomer increased with longer chains and reached a maximum for n-butyl groups. Further elongation led to faster isomerization. The origin of the intramolecular interactions was elaborated by various techniques, including 1H NOESY NMR spectroscopy. The results indicate that there are additional long-range interactions between n-alkyl chains with the opposite phenyl core in the Z-state. These interactions are most likely dominated by attractive London dispersion. This work provides rare insight into the stabilizing contributions of highly flexible groups in an intra- as well as an intermolecular setting.
- Strauss, Marcel A.,Wegner, Hermann A.
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supporting information
p. 18552 - 18556
(2019/11/19)
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- Electrochemical dehydrogenation of hydrazines to azo compounds
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A strategy for the electrochemical dehydrogenation of hydrazine compounds is disclosed under ambient conditions. This protocol proceeded smoothly in ethanol by employing electrons as clean oxidants. Its synthetic value is well demonstrated by the highly efficient synthesis of symmetric and unsymmetric azo compounds. It is an environmentally friendly transformation and the present protocol was effective on a large scale.
- Du, Ke-Si,Huang, Jing-Mei
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supporting information
p. 1680 - 1685
(2019/04/08)
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- Aerobic C(sp2)-H Hydroxylations of 2-Aryloxazolines: Fast Access to Excited-State Intramolecular Proton Transfer (ESIPT)-Based Luminophores
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The direct hydroxylation of 2-aryloxazolines via a deprotonative magnesiation using TMPMgCl·LiCl and subsequent oxidation with molecular oxygen or air as a green oxidant is reported. This method proceeds under mild conditions at room temperature with high regioselectivity and chemoselectivity. The obtained phenols exhibit tunable luminescence properties, induced by excited-state intramolecular proton transfer. This method opens a new opportunity for the sustainable synthesis of luminescent organic molecules.
- G?bel, Dominik,Clamor, Nils,Lork, Enno,Nachtsheim, Boris J.
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supporting information
p. 5373 - 5377
(2019/06/07)
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- Iron and Nitrogen Co-Doped Mesoporous Carbon-Based Heterogeneous Catalysts for Selective Reduction of Nitroarenes
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A facile fabrication of Fe and N co-doped mesoporous carbon (MC), as an efficient heterogeneous catalyst for the highly selective reduction of nitroarenes, is described. The Fe and N co-doped MC nanosheets are easily synthesized via a hydrothermal reaction between citrate acid and magnesium citrate, followed by calcination in the presence of melamine and potassium ferrocyanide. The Fe?N complex provides a unique active site for the selective reduction of 1-chloro-4-nitrobenzene, leading to the production of (E)-1,2-bis(4-chlorophenyl)diazene with a selectivity of >96%, in 40 mins. Control experiments based on non-doped, N-doped, and Fe-doped MC nanosheets demonstrate that selectivity greatly depends on the catalyst active component type, and that non-doped MC significantly contributes to the high efficiencies observed in the selective synthesis of azoxy compound intermediates. A broad range of substrates, including extra-functional groups on the nitroarenes rings, were successfully converted to the corresponding azo compounds at mild conditions with high selectivity. (Figure presented.).
- Wang, Jitao,Yu, Xiaochun,Shi, Chongyang,Lin, Dajie,Li, Jun,Jin, Huile,Chen, Xian,Wang, Shun
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supporting information
p. 3525 - 3531
(2019/06/24)
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- Hole Catalysis as a General Mechanism for Efficient and Wavelength-Independent Z → E Azobenzene Isomerization
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Whereas the reversible reduction of azobenzenes has been known for decades, their oxidation is destructive and as a result has been notoriously overlooked. Here, we show that a chain reaction leading to quantitative Z → E isomerization can be initiated before reaching the destructive anodic peak potential. This hole-catalyzed pathway is accessible to all azobenzenes, without exception, and offers tremendous advantages over the recently reported reductive, radical-anionic pathway because it allows for convenient chemical initiation without the need for electrochemical setups and in the presence of air. In addition, catalytic amounts of metal-free sensitizers, such as methylene blue, can be used as excited-state electron acceptors, enabling a shift of the excitation wavelength to the far red of the azobenzene absorption (up to 660 nm) and providing quantum yields exceeding unity (up to 200%). Our approach will boost the efficiency and sensitivity of optically dense liquid-crystalline and solid photoswitchable materials. Video Abstract: [Figure presented] Molecular switches are a key ingredient in stimulus-responsive and adaptive materials and devices. Light is among the most attractive stimuli, yet photoswitches often require intense irradiation with high-energy UV light and suffer from inefficient switching as well as fatigue. Thus, the design of robust and efficient photoswitches constitutes an important challenge to boost the sensitivity and energy efficiency of the respective materials and devices. Here, we describe that the isomerization of azobenzene switches from their less stable Z isomer back to the more stable E isomer can be triggered by tiny, i.e., catalytic, amounts of holes caused by chemical, electrochemical, or photochemical oxidation. Our method is generally applicable to the entire family of azobenzene switches, does not require expensive equipment, and allows the reliable and efficient operation of these photoswitches by using red light with quantum efficiencies up to 200%. An efficient and generally applicable method is developed for operating azobenzene molecular switches by using catalytic amounts of holes (via an oxidant) or photons (via a photosensitizer). The pathway allows for indirect Z → E photoisomerization using lower-energy light than required for direct azobenzene excitation and with high quantum yields exceeding unity. The method should help to enhance the sensitivity of photoresponsive materials and devices with high optical density.
- Goulet-Hanssens, Alexis,Rietze, Clemens,Titov, Evgenii,Abdullahu, Leonora,Grubert, Lutz,Saalfrank, Peter,Hecht, Stefan
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supporting information
p. 1740 - 1755
(2018/06/29)
-
- Photoinduced viscosity control of lecithin-based reverse wormlike micellar systems using azobenzene derivatives
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This report describes the controlled viscosity changes of photoresponsive reverse wormlike micellar systems formed by soybean lecithin (SoyPC), d-ribose, and azobenzene derivatives in decane. UV light irradiation produces a significant (150-fold) decrease in solution viscosity by triggering a structural transformation of the wormlike micelles. Subsequent visible light irradiation leads to recovery of the initial micellar structure and elevated solution viscoelasticity. This dramatic, reversible variation in solution viscosity by light irradiation can be applied to cosmetics, personal care products, and device components.
- Akamatsu, Masaaki,Shiina, Mayu,Shrestha, Rekha Goswami,Sakai, Kenichi,Abe, Masahiko,Sakai, Hideki
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p. 23742 - 23747
(2018/07/13)
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- Monitoring: Cis -to- trans isomerization of azobenzene using terahertz time-domain spectroscopy
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We present terahertz time-domain spectroscopy (THz-TDS) to explore the conformational dynamics of thermally induced and photoinduced isomerization of azobenzene. The essence of the method is that isomerization of azobenzene proceeds via large structural c
- Zhou, Lu,Chen, Ligang,Ren, Guanhua,Zhu, Zhongjie,Zhao, Hongwei,Wang, Huabin,Zhang, Weili,Han, Jiaguang
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p. 27205 - 27213
(2018/11/20)
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- A metal-catalyst-free oxidative coupling of anilines to aromatic azo compounds in water using bleach
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A simple route toward the synthesis of symmetrical and unsymmetrical aromatic azo compounds through oxidative coupling of anilines using widely available NaOCl is presented. This metal catalyst-free protocol is performed in water and affords the desired products in high yields.
- de Souza, Gabriela F.P.,von Zuben, Theodora W.,Salles, Airton G.
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supporting information
p. 3753 - 3755
(2018/09/21)
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- Oxidative dimerization of anilines with heterogeneous sulfonic acid catalysts
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We report herein that suitably supported perfluorosulfonic acids can catalyze the oxidative dimerization of anilines using hydrogen peroxide as a clean oxidant. The reaction does not require the use of organic solvents and affords desired azobenzenes and water as products, minimizing the formation of wastes. The metal-free solid catalyst shows remarkable activity and selectivity for the reaction, which occurs under very mild conditions and with broad functional group tolerance.
- Paris, Emanuele,Bigi, Franca,Cauzzi, Daniele,Maggi, Raimondo,Maestri, Giovanni
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supporting information
p. 382 - 386
(2018/02/07)
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- Preparation of carbon-based AuAg alloy nanoparticles by using the heterometallic [Au4Ag4] cluster for efficient oxidative coupling of anilines
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We herein report the preparation of unique heteroatom-doped and carbon-based AuAg alloy nanoparticles (NPs) via the pyrolysis of a structurally defined octanuclear heterometallic Au(i)-Ag(i) cluster [Au4Ag4(Dppy)4(Tab)sub
- Gao, Bin-Bin,Zhang, Min,Chen, Xu-Ran,Zhu, Da-Liang,Yu, Hong,Zhang, Wen-Hua,Lang, Jian-Ping
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supporting information
p. 5780 - 5788
(2018/04/30)
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- Cage Encapsulated Gold Nanoparticles as Heterogeneous Photocatalyst for Facile and Selective Reduction of Nitroarenes to Azo Compounds
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A discrete nanoscopic organic cage (OC1R) has been synthesized from a phenothiazine based trialdehyde treating with chiral 1,2-cyclohexanediamine building block via dynamic imine bond formation followed by reductive amination. The cage compound has been characterized by several spectroscopic methods, which advocate that OC1R has trigonal prismatic shape formed via [2 + 3] self-assembled imine condensation followed by imine reduction. This newly designed cage has aromatic walls and porous interior decorated with two cyclic thioether and three vicinal diamine moieties suitable for binding gold ions to engineer the controlled nucleation and stabilization of ultrafine gold nanoparticles (AuNPs). The functionalized confined pocket of the cage has been used for the controlled synthesis of AuNPs with narrow size distribution via encapsulation of Au(III) ions. Inductively coupled plasma mass spectrometric (ICP-MS) analysis revealed that the composite Au@OC1R has very high (?68 wt %) gold loading. In distinction, reduction of gold salts in absence of the cage yielded structureless agglomerates. The fine-dispersed cage anchored AuNPs (Au@OC1R) have been finally used as potential heterogeneous photocatalyst for very facile and selective conversion of nitroarenes to respective azo compounds at ambient temperature in just 2 h reaction time. Exceptional chemical stability and reusability without any agglomeration of AuNPs even after several cycles of use are the potential features of this material. The composite Au@OC1R represents the first example of organic cage supported gold nanoparticles as photocatalyst.
- Mondal, Bijnaneswar,Mukherjee, Partha Sarathi
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p. 12592 - 12601
(2018/10/05)
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- Glass wool: a novel support for heterogeneous catalysis
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Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material-glass wool-can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp3-Csp3 couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp2 couplings (Sonogashira couplings). The use of glass wool as a catalyst support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical heterogeneous catalysts with excellent potential for flow photo-chemistry application.
- Elhage, Ayda,Wang, Bowen,Marina, Nancy,Marin, M. Luisa,Cruz, Menandro,Lanterna, Anabel E.,Scaiano, Juan C.
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p. 6844 - 6852
(2018/09/11)
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- When Do Strongly Coupled Diradicals Show Strongly Coupled Reactivity? Thermodynamics and Kinetics of Hydrogen Atom Transfer Reactions of Palladium and Platinum Bis(iminosemiquinone) Complexes
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The 2,2′-biphenylene-bridged bis(iminosemiquinone) complexes (tBuClip)M [tBuClipH4 = 4,4′-di-tert-butyl-N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-2,2′-diaminobiphenyl; M = Pd, Pt] can be reduced to the bis(aminophenoxide) complexes (tBuClipH2)M by reaction with hydrazobenzene (M = Pd) or by catalytic hydrogenation (M = Pt). The palladium complex with one aminophenoxide ligand and one iminosemiquinone ligand, (tBuClipH)Pd, is generated by comproportionation of (tBuClip)Pd with (tBuClipH2)Pd in a process that is both slow (0.06 M-1 s-1 in toluene at 23 °C) and only modestly favorable (Kcom = 1.9 in CDCl3), indicating that both N-H bonds have essentially the same bond strength. The mono(iminoquinone) complex (tBuClipH)Pt has not been observed, indicating that the platinum analogue shows no tendency to comproportionate (Kcom tBuClipH2)Pt to (tBuClip)Pd occurring with ?G° = ?8.9 kcal mol-1. The palladium complex (tBuClipH2)Pd reacts with nitroxyl radicals in two observable steps, with the first hydrogen transfer taking place slightly faster than the second. In the platinum analogue, the first hydrogen transfer is much slower than the second, presumably because the N-H bond in the monoradical complex (tBuClipH)Pt is unusually weak. Using driving force-rate correlations, it is estimated that this bond has a BDFE of 55.1 kcal mol-1, which is 7.1 kcal mol-1 weaker than that of the first N-H bond in (tBuClipH2)Pt. The two radical centers in the platinum, but not the palladium, complex thus act in concert with each other and display a strong thermodynamic bias toward two-electron reactivity. The greater thermodynamic and kinetic coupling in the platinum complex is attributed to the stronger metal-ligand ? interactions in this compound.
- Conner, Kyle M.,Arostegui, AnnaMaria C.,Swanson, Daniel D.,Brown, Seth N.
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p. 9696 - 9707
(2018/08/28)
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- Structure and Reactivity of Half-Sandwich Rh(+3) and Ir(+3) Carbene Complexes. Catalytic Metathesis of Azobenzene Derivatives
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Traditional rhodium carbene chemistry relies on the controlled decomposition of diazo derivatives with [Rh2(OAc)4] or related dinuclear Rh(+2) complexes, whereas the use of other rhodium sources is much less developed. It is now shown that half-sandwich carbene species derived from [Cp?MX2]2 (M = Rh, Ir; X = Cl, Br, I, Cp? = pentamethylcyclopentadienyl) also exhibit favorable application profiles. Interestingly, the anionic ligand X proved to be a critical determinant of reactivity in the case of cyclopropanation, epoxide formation and the previously unknown catalytic metathesis of azobenzene derivatives, whereas the nature of X does not play any significant role in 'OH insertion reactions. This perplexing disparity can be explained on the basis of spectral and crystallographic data of a representative set of carbene complexes of this type, which could be isolated despite their pronounced electrophilicity. Specifically, the donor/acceptor carbene 10a derived from ArC( - N2)COOMe and [Cp?RhCl2]2 undergoes spontaneous 1,2-migratory insertion of the emerging carbene unit into the Rh-Cl bond with formation of the C-metalated rhodium enolate 11. In contrast, the analogous complexes 10b,c derived from [Cp?RhX2]2 (X = Br, I) as well as the iridium species 13 and 14 derived from [Cp?IrCl2]2 are sufficiently stable and allow true carbene reactivity to be harnessed. These complexes are competent intermediates for the catalytic metathesis of azobenzene derivatives, which provides access to α-imino esters that would be difficult to make otherwise. Rather than involving metal nitrenes, the reaction proceeds via aza-ylides that evolve into diaziridines; a metastable compound of this type has been fully characterized.
- Tindall, Daniel J.,Werlé, Christophe,Goddard, Richard,Philipps, Petra,Farès, Christophe,Fürstner, Alois
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supporting information
p. 1884 - 1893
(2018/02/17)
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- Electrocatalytic Z → E Isomerization of Azobenzenes
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A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo) switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z → E) by the same wavelength of light, which normally triggers E → Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.
- Goulet-Hanssens, Alexis,Utecht, Manuel,Mutruc, Dragos,Titov, Evgenii,Schwarz, Jutta,Grubert, Lutz,Bléger, David,Saalfrank, Peter,Hecht, Stefan
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supporting information
p. 335 - 341
(2017/05/16)
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- Photoswitchable nanoporous films by loading azobenzene in metal-organic frameworks of type HKUST-1
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Photoswitchable metal-organic frameworks (MOFs) enable the dynamic remote control of their key properties. Here, a readily producible approach is presented where photochromic molecules, i.e. azobenzene (AB) and o-tetrafluoroazobenzene (tfAB), are loaded in MOF films of type HKUST-1. These nanoporous films, which can be reversibly switched with UV/visible or only visible light, have remote-controllable guest uptake properties.
- Müller, Kai,Wadhwa, Jasmine,Singh Malhi, Jasleen,Sch?ttner, Ludger,Welle, Alexander,Schwartz, Heidi,Hermann, Daniela,Ruschewitz, Uwe,Heinke, Lars
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supporting information
p. 8070 - 8073
(2017/07/22)
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- Rapid and facile chemical actinometric protocol for photo-microfluidic systems using azobenzene and NMR spectroscopy
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In this study, the photon flux inside a photomicroreactor was determined using chemical actinometry via the photoisomerization of azobenzene at 365 nm. For this purpose, a differential equation, in which the only external data are the tabulated absorption
- El Achi, Nassim,Bakkour, Youssef,Chausset-Boissarie, La?titia,Penhoat, Ma?l,Rolando, Christian
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p. 29815 - 29820
(2017/07/10)
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- The absorption spectrum of: Cis -azobenzene
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Azobenzene is a prototypical photochromic molecule existing in two isomeric forms, which has numerous photochemical applications that rely on a precise knowledge of the molar absorption coefficients (?). Careful analysis revealed that the previously repor
- Vetráková, ?ubica,Ladányi, Vít,Al Anshori, Jamaludin,Dvo?ák, Pavel,Wirz, Jakob,Heger, Dominik
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p. 1749 - 1756
(2017/12/26)
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- Dehydrogenation of the NH?NH Bond Triggered by Potassium tert-Butoxide in Liquid Ammonia
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A novel strategy for the dehydrogenation of the NH?NH bond is disclosed using potassium tert-butoxide (tBuOK) in liquid ammonia (NH3) under air at room temperature. Its synthetic value is well demonstrated by the highly efficient synthesis of aromatic azo compounds (up to 100 % yield, 3 min), heterocyclic azo compounds, and dehydrazination of phenylhydrazine. The broad application of this strategy and its benefit to chemical biology is proved by a novel, convenient, one-pot synthesis of aliphatic diazirines, which are important photoreactive agents for photoaffinity labeling.
- Wang, Lei,Ishida, Akiko,Hashidoko, Yasuyuki,Hashimoto, Makoto
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supporting information
p. 870 - 873
(2017/01/14)
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- Continuous-flow oxidative homocouplings without auxiliary substances: Exploiting a solid base catalyst
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The catalytic oxidative dimerization of aromatic amines and acetylenes is of outstanding synthetic importance among homocoupling reactions. Both transformations necessitate the use of extraneous bases and ligands, which contains significant disadvantages as concerns environmental impacts and process costs. We exploited the inherent basic character of a copper-containing layered double hydroxide to facilitate the catalytic homocouplings of alkynes and aniline derivatives without the need for any auxiliary substances. The reactions were studied in a continuous-flow system to achieve extended parameter spaces for chemical intensification, and also to avoid undesired reaction pathways by means of strategic control over the residence time. Valuable 1,4-disubstituted 1,3-diynes and diversely substituted aromatic azo compounds were achieved chemoselectively in excellent yields and in short process times even on preparative scales.
- ?tv?s, Sándor B.,Georgiádes, ádám,Mészáros, Rebeka,Kis, Koppány,Pálinkó, István,Fül?p, Ferenc
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-
- Ruthenium-catalyzed meta/ortho-selective C-H alkylation of azoarenes using alkyl bromides
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meta/ortho-Selective CAr-H (di)alkylation reactions of azoarenes have been achieved via [Ru(p-cymene)Cl2]2 catalyzed ortho-metalation using various types of alkyl bromides. Particularly, dual meta-alkylation of azoarene and reduction offer an attractive strategy for the synthesis of meta-alkylanilines, which are difficult to access via traditional aniline functionalization methods.
- Li, Gang,Ma, Xingxing,Jia, Chunqi,Han, Qingqing,Wang, Ya,Wang, Junjie,Yu, Liuyang,Yang, Suling
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supporting information
p. 1261 - 1264
(2017/02/05)
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- Correction to: Electrocatalytic Z → E isomerization of azobenzenes (Journal of the American Chemical Society (2017) 139 (335-341) DOI: 10.1021/jacs.6b10822)
-
Page 339. In Figure 6, the x-axis is labeled incorrectly. The unit should be seconds instead of minutes. The corrected Figure 6 is displayed below. (Figure Presented).
- Goulet-Hanssens, Alexis,Utecht, Manuel,Mutruc, Dragos,Titov, Evgenii,Schwarz, Jutta,Grubert, Lutz,Bléger, David,Saalfrank, Peter,Hecht, Stefan
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p. 9410 - 9410
(2017/07/24)
-
- Transition Metal-Free Iodosobenzene-Promoted Direct Oxidative 3-Arylation of Quinoxalin-2(H)-ones with Arylhydrazines
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A transition metal-free iodosobenzene-promoted direct oxidative 3-arylation of quinoxalin-2(H)-ones was developed using various arylhydrazines under air. The protocol affords a variety of 3-arylquinoxalin-2(H)-one derivatives in moderate to good yields. This method provides a rapid access to biologically interesting benzo[g]quinoxalinones and pyrido[3,4-b]pyrazinones. The present methodology features high functional group tolerance including base-sensitive groups as well as allyl- and benzyl-substituted quinoxalin-2(H)-ones under mild reaction conditions. (Figure presented.).
- Paul, Sanjay,Ha, Ji Hyeon,Park, Ga Eul,Lee, Yong Rok
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p. 1515 - 1521
(2017/05/05)
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- Azo-aromatic functionalized polyethylene by nitroxide radical coupling (NRC) reaction: Preparation and photo-physical properties
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The nitroxide radical coupling (NRC) reaction between the 4-(phenylazo)-benzoyl-2,2,6,6-tetramethylpiperidine-1-oxyl radical (AzO-TEMPO) or the 4-(2-thienylazo)-benzoyl-2,2,6,6-tetramethylpiperidine-1-oxyl radical (ThiO-TEMPO) and polyethylene macroradicals allowed the preparation of "functional" polyolefins bearing covalently grafted azo-aromatic chromophores. A comparison of the photo-physical behavior of the free and grafted RO-TEMPO molecules was carried out by UV-Vis spectroscopy irradiating the free RO-TEMPO solutions and the functionalized polymer films at 366 and 254 nm. Results evidenced the transfer of the photo-physical properties of the chromophores to the polymer matrix. Interestingly, some different isomerization abilities and kinetics between the free and grafted RO-TEMPO moieties, depending on the nature of the aromatic group bonded to the diazo-moiety and on the structure of the polymer matrix, were observed. Indeed, when the chromophores were grafted to the polymer, the isomerization resulted to be less efficient in terms of photo-isomerization degree and isomerization rate than in solution, suggesting a strong effect of the semi-crystalline matrix especially in the case of the more rigid HDPE. Finally the determination of the water contact angle of the functionalized polymers, before and after photo-isomerization, confirmed the occurrence of the isomerization and evidenced an increase of the wettability of the polymer surface owing to the process.
- Cicogna, Francesca,Domenichelli, Ilaria,Coiai, Serena,Bellina, Fabio,Lessi, Marco,Spiniello, Roberto,Passaglia, Elisa
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p. 366 - 377
(2015/12/18)
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- One-step synthesis of poly(ethyleneglycol dimethacrylate)-microspheres-supported nano-Au catalyst in methanol-water solution under γ-ray radiation
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A sub-micron sized highly-crosslinked poly(ethyleneglycol dimethacrylate) (PEGDMA) microsphere supported nano-Au catalyst (PEGDMA@AuNP) was successfully prepared through a one-step synthesis method at room temperature and ambient pressure, taking advantage of the γ-ray radiation effect on a simple one-pot system, i.e. a methanol-water solution containing EGDMA, 4-VP, and HAuCl4. Electron microscopy, XPS, and XRD analyses proved that AuNPs of several nanometers had been synthesized and loaded simultaneously with the formation of crosslinked PEGDMA microspheres when the adsorbed dose rate and the initial concentration of HAuCl4 were controlled within a narrow range, i.e. 35-80 Gy min-1 and below 1 mmol L-1 of [HAuCl4]. The size of the prepared PEGDMA@AuNP microspheres changed little with the dose rate, but decreased with the initial [HAuCl4], from 900 nm at 0.1 mmol L-1 to 680 nm at 1 mmol L-1. At the same time, the size of AuNPs increases with the initial [HAuCl4], from 8 nm at 0.1 mmol L-1 to 35 nm at 1 mmol L-1. The prepared PEGDMA@AuNP microspheres can be dispersed stably in both water and organic solvent, CH3CN. They exhibit excellent catalytic efficiency not only on the reduction of Fe(CN)63- by NaBH4 in aqueous solution, but also on the cis-trans isomerization of azobenzenes in CH3CN at room temperature. A satisfactory repeatability of the catalytic performance of the prepared PEGDMA@AuNP microspheres was achieved in organic solvents. This work opens a new green simple and economic way to the synthesis of efficient and chemically-stable polymer-supported nano-metal catalysts.
- Chen, Jinxing,Chen, Feng,Wang, Yiyao,Wang, Mozhen,Wu, Qichao,Zhou, Xiao,Ge, Xuewu
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p. 55878 - 55883
(2016/07/06)
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- Mesoporous manganese oxide catalyzed aerobic oxidative coupling of anilines to aromatic azo compounds
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Herein we introduce an environmentally friendly approach to the synthesis of symmetrical and asymmetrical aromatic azo compounds by using air as the sole oxidant under mild reaction conditions in the presence of cost-effective and reusable mesoporous manganese oxide materials.
- Dutta, Biswanath,Biswas, Sourav,Sharma, Vinit,Savage, Nancy Ortins,Alpay, S. Pamir,Suib, Steven L.
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supporting information
p. 2171 - 2175
(2016/02/18)
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- First use of p-tert-butylcalix[4]arene-tetra-O-acetate as a nanoreactor having tunable selectivity towards cross azo-compounds by trapping silver ions
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p-tert-Butylcalix[4]arene-tetra-O-acetate was established for the first time as a member of the nanoreactor series, even without having any -OH group. The nano range distribution of this nanoreactor was ascertained by DLS, SEM and TEM studies. The capability of this cavitand towards hosting amines in a competitive manner generates a new green pathway for cross coupling of aromatic amines to give the corresponding azo-compounds. In this context, using p-tert-butylcalix[4]arene-tetra-O-acetate as a nanoreactor and silver nitrate as a catalyst, we got the cross azo-compound in good to excellent yields in the eco-friendly solvent water. This green methodology is also applicable for the synthesis of respective homo-compounds.
- Sarkar, Piyali,Mukhopadhyay, Chhanda
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supporting information
p. 442 - 451
(2016/01/30)
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- Surfactant directed Ag1?xNix alloy nanoparticle catalysed synthesis of aromatic azo derivatives from aromatic amines
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A bimetallic and multiply twinned Ag1?xNix (x?=?0.2, 0.4, 0.6, 0.8) alloy nanoparticle (MTANP), for the first time has been explored as an efficient heterogeneous catalyst in the industrially important reaction conversion of aromatic amines to the symmetric or asymmetric azobenzenes by the activation of aerobic molecular oxygen. Here, we demonstrated that the as-synthesized and optimized Ag0.6Ni0.4 alloy NPs showed breakthrough in catalytic performance, enabling quantitative aromatic amine conversion and absolute selectivity in azobenzenes (100%) under aerobic green reaction conditions without using the environmentally unfriendly nitrites and any other hazardous materials. A high stability and recyclability of the catalyst are observed and investigated by several instrumental techniques. The key to the effective process is found to be size effect, electronic effect and structural defect, and the presence of surfactant at the surfaces of the AgNi MTANP catalyst.
- Kumar, Mukesh,Soni, Kiran,Yadav, Geeta Devi,Singh, Surendra,Deka, Sasanka
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-
- Palladium-Catalyzed Oxidative Synthesis of Unsymmetrical Azophenols
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A straightforward palladium-catalyzed oxidative hydroxylation of azobenzenes is reported. The developed methodology tolerates various functional groups and allows the synthesis of diverse unsymmetrical azophenols under mild conditions in good to excellent yields. A complementary procedure was also investigated by in situ generation of PIFA. This study represents the first general method for the synthesis of o-hydroxyazobenzenes starting from simple azoarenes.
- Nguyen, Thi Hong Long,Gigant, Nicolas,Delarue-Cochin, Sandrine,Joseph, Delphine
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p. 1850 - 1857
(2016/03/15)
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- Multicomponent Coupling Cyclization Access to Cinnolines via in Situ Generated Diazene with Arynes, and α-Bromo Ketones
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A transition-metal-free multicomponent coupling cyclization reaction was explored involving arynes, tosylhydrazine, and α-bromo ketones. The reaction proceeds via a formal [2 + 2 + 2] cycloaddition, giving access to cinnoline derivatives in moderate yields under mild conditions. Three chemical bonds were formed-two C-N bonds and one C-C bond-in a single step.
- Shu, Wen-Ming,Ma, Jun-Rui,Zheng, Kai-Lu,Wu, An-Xin
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p. 196 - 199
(2016/02/03)
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- Mechanistic insight into the Z-E isomerization catalysis of azobenzenes mediated by bare and core-shell gold nanoparticles
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We explored the catalytic effect of 15 nm diameter gold nanoparticles (AuNPs) upon the thermal Z-E isomerization reaction of azobenzene and nine 4 and 4-4′ substituted azobenzenes (ABs). The kinetics follows a first order rate in ranges of [ABs] = 5 to 50
- Simoncelli, Sabrina,Aramendía, Pedro F.
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p. 2110 - 2116
(2015/04/14)
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- Nitric Oxide Catalysis of Diazene E / Z Isomerization
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Nitric oxide is an efficient catalyst for the cis-trans (E/Z) isomerization of diazenes. We compare the effect of room temperature solutions bearing low concentrations of nitric oxide, nitrogen dioxide, or oxygen on the rate of cis-trans isomerization, CTI, of the alkene bond in stilbene and on the azo double bond in azobenzene, as well as in four azo derivatives as measured by UV-vis spectroscopy. These rate enhancements can be as large as 3 orders of magnitude for azobenzene in solution. A mechanism is proposed where catalysis is promoted by the interaction of the nitric oxide with the diazene nitrogen lone pairs. Density functional theory, B3LYP/6-311++g suggests that the binding of NO to the diazene should be weak and reversible but that its NO adduct has an E/Z isomerization barrier of 7.5 kcal/mol.
- Bohle, D. Scott,Rosadiuk, Kristopher A.
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p. 7145 - 7151
(2015/08/11)
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- Structure-Correlation NMR Spectroscopy for Macromolecules Using Repeated Bidirectional Photoisomerization of Azobenzene
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Control over macromolecular structure offers bright potentials for manipulation of macromolecular functions. We here present structure-correlation NMR spectroscopy to analyze the correlation between polymorphic macromolecular structures driven by photoisomerization of azobenzene. The structural conversion of azobenzene was induced within the mixing time of a NOESY experiment using a colored light source, and the reverse structural conversion was induced during the relaxation delay using a light source of another color. The correlation spectrum between trans- and cis-azobenzene was then obtained. To maximize the efficiency of the bidirectional photoisomerization of azobenzene-containing macromolecules, we developed a novel light-irradiation NMR sample tube and method for irradiating target molecules in an NMR radio frequency (rf) coil. When this sample tube was used for photoisomerization of an azobenzene derivative at a concentration of 0.2 mM, data collection with reasonable sensitivity applicable to macromolecules was achieved. We performed isomerization of an azobenzene-cross-linked peptide within the mixing time of a NOESY experiment that produced cross-peaks between helix and random-coil forms of the peptide. Thus, these results indicate that macromolecular structure manipulation can be incorporated into an NMR pulse sequence using an azobenzene derivative and irradiation with light of two types of wavelengths, providing a new method for structural analysis of metastable states of macromolecules.
- Nagashima, Toshio,Ueda, Keisuke,Nishimura, Chiaki,Yamazaki, Toshio
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p. 11544 - 11552
(2015/11/24)
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