- Reversing Chemoselectivity: Simultaneous Positive and Negative Catalysis by Chemically Equivalent Rims of a Cucurbit[7]uril Host
-
Enzyme catalysis has always been an inspiration and an unattainable goal for chemists due to features such as high specificity, selectivity, and efficiency. Here, we disclose a feature neither common in enzymes nor ever described for enzyme mimics, but one that could prove crucial for the catalytic performance of the latter, namely the ability to catalyze and inhibit two different reactions at the same time. Remarkably, this can be realized by two identical, spatially resolved catalytic sites. In the future, such a synchronized catalyst action could be used not only for controlling chemoselectivity, as in the present case, but also for regulating other types of chemical reactivity.
- Rad, Nazar,Danylyuk, Oksana,Sashuk, Volodymyr
-
supporting information
p. 11340 - 11343
(2019/07/16)
-
- Induction of chirality in 4,4′-azopyridine by halogen-bonding interaction with optically active ditopic donors
-
Optically active ditopic halogen bond donors bearing two 4-iodotetrafluorophenyl groups were obtained by reaction of chiral diols with iodopentafluorobenzene. Co-crystallization of these donors with anti-4,4′-azopyridine afforded binary complexes containing infinite chains of the alternating component molecules connected by halogen bonds. The solid state CD measurements confirmed that complexation induces optical activity of the azo chromophore due to the twisting of the aryl-N═N system or external chiral perturbation exerted by host molecules.
- Alfuth, Jan,Chojnacki, Jaros?aw,Po?oński, Tadeusz,Olszewska, Teresa
-
p. 5512 - 5517
(2019/04/04)
-
- Thermally Twistable, Photobendable, Elastically Deformable, and Self-Healable Soft Crystals
-
The first example of a smart crystalline material, the 2:1 cocrystal of probenecid and 4,4′-azopyridine, which responds reversibly to multiple external stimuli (heat, UV light, and mechanical pressure) by twisting, bending, and elastic deformation without fracture is reported. This material is also able to self-heal on heating and cooling, thereby overcoming the main setbacks of molecular crystals for future applications as crystal actuators. The photo- and thermomechanical effects and self-healing capabilities of the material are rooted in reversible trans–cis isomerization of the azopyridine unit and crystal-to-crystal phase transition. Fairly isotropic intermolecular interactions and interlocked crisscrossed molecular packing secure high elasticity of the crystals.
- Gupta, Poonam,Karothu, Durga Prasad,Ahmed, Ejaz,Naumov, Pan?e,Nath, Naba K.
-
supporting information
p. 8498 - 8502
(2018/07/14)
-
- Dehydrogenation of the NH?NH Bond Triggered by Potassium tert-Butoxide in Liquid Ammonia
-
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
-
supporting information
p. 870 - 873
(2017/01/14)
-
- Characterization and magnetic properties of two novel copper(II) coordination polymers prepared by different synthetic techniques
-
Two novel ternary Cu(II) coordination polymers with formulas {[Cu(μ2-AZPY)(H2BTC)2]}n (1) and {[Cu(μ2-AZPY)(μ2-HBTC)(H2O)]·AZPY}n (2) (AZPY – trans-4,4′-azobis(pyridine), BTC – benzene-1,3,5-tricarboxylate) have been synthesized using the solvothermal or diffusion techniques, respectively. Compounds were characterized by single crystal X-ray diffraction, thermogravimetry, infrared spectroscopy, elemental analysis and AAS. Removal of water and AZPY from the framework of 2 was investigated by wide-angle X-ray scattering measurements during in-situ heating. A magnetic study showed on antiferromagnetic coupling in 1 and 2 and magnetic properties may be influenced by both crystal field (CF) and inter-molecular interactions. The effective magnetic moment decreases from the values μeff = 4.97 μB for 1 and μeff = 3.39 μB for 2 at T = 290 K to the values of μeff = 1.41 μB for 1 and μeff = 1.27 μB for 2 at T = 2 K. The origin of the observed behavior is discussed.
- Almá?i, Miroslav,Zeleňák, Vladimír,Zeleňáková, Adriana,Vargová, Zuzana,Císa?ová, Ivana
-
-
- 4,4'-azobis(halopyridinium) derivatives: Strong multidentate halogen-bond donors with a redox-active core
-
In summary, an easily accessible class of highly potent bis(pyridinium)-based multidentate XB donors has been introduced, which, in addition to their inherent XB acidity, also include a built-in redox option. In the previously established benchmark reaction to test the carbon-bromine bond-activation potential of XB donors, these compounds (2a, 2a', and 2b) are slightly more effective than bis(imidazolium)- based XB donors. Initially, the analysis of the overall process was complicated by the oxidation of bromide to elemental bromine by the azobis(halopyridinium) compounds during the reaction. The bromine thus formed was part of an additional activation process, which could, however, be suppressed by addition of cyclohexene. Two directions will be pursued in future work: since we demonstrated the activation capabilities of pyridinium-based XB donors towards carbon-bromine bonds, we plan to develop other types of activating reagents with redox-innocent bridging motives. Parallel to this, we strive to exploit the coupled oxidation/ XB-activation potential of the activators presented herein in suitable reactions.
- Kniep, Florian,Walter, Sebastian M.,Herdtweck, Eberhardt,Huber, Stefan M.
-
supporting information; experimental part
p. 1306 - 1310
(2012/03/26)
-
- Easily prepared azopyridines as potent and recyclable reagents for facile esterification reactions. An efficient modified mitsunobu reaction
-
(Chemical Equation Presented) The 2,2′-, 3,3′-, and 4,4′-azopyridines (azpy) and their alkyl pyridinium ionic liquids were studied as a new class of electron-deficient reagents for Mitsunobu esterification reactions. Among these compounds, 4,4′-azopyridine was found to be the most suitable one for esterification and thioesterification reactions. This new reagent promises to provide general and complementary solutions for separation problems in Mitsunobu reactions without restricting the reaction scope and facilitates the isolation of its hydrazine byproduct. The pyridine hydrazine byproduct can be simply recycled to its azopyridine by an oxidation reaction.
- Iranpoor, Nasser,Firouzabadi, Habib,Khalili, Dariush,Motevalli, Somayeh
-
p. 4882 - 4887
(2008/09/21)
-
- Iron(II) molecular framework materials with 4,4′-azopyridine
-
Three new iron(II) molecular-framework materials incorporating the bridging ligand 4,4′-azopyridine (azpy) have been synthesized and structurally characterized: Fe2(azpy)4(NCS)4 ·(azpy) (A), Fe(azpy)(NCSe)2(EtOH)2 · (azpy) (B), and Fe(azpy)2(NCSe)2 · 2(MeCN) (C). A and C consist of non-interpenetrating (4,4) grids of iron(II) centres bridged by azpy ligands with non-coordinating azpy ligands or acetonitrile molecules occupying the spaces within and between the layers. For B, hydrogen-bonding interactions between coordinated ethanol molecules and non-coordinated azpy ligands link linear Fe-azpy chains to give a two-dimensional framework. CSIRO 2005.
- Halder, Gregory J.,Kepert, Cameron J.
-
p. 311 - 314
(2007/10/03)
-
- Mass spectrometric characterization and gas-phase chemistry of self-assembling supramolecular squares and triangles
-
A detailed mass spectrometric characterization of self-assembling polynuclear metal complexes is described. The complexes can only be ionized as intact species under a surprisingly narrow range of conditions by electrospray ionization. Comparison with the results from NMR experiments shows that several solution-phase features of these squares and triangles (such as trends in bond energies, ligand-exchange reactions, or square-triangle equilibria) are qualitatively reflected in the gas-phase data. Consequently, mass spectrometry represents a valuable method for the characterization of these compounds. Nevertheless, the formation of unspecific aggregates during the ionization process occurs and its implications are discussed. Beyond the chemistry in solution, the fragmentation pathways of these complexes in the gas phase have been studied by infrared multiphoton dissociation (IRMPD) experiments. The results of IRMPD studies allow us to draw conclusions with respect to the structure and energetics of fragmentation products. In this tandem MS experiment, reaction pathways can be observed directly which can hardly be analyzed in solution. According to these results, the equilibration of triangles and squares involves the supramolecular analogue of a neighboring-group effect.
- Schalley, Christoph A.,Mueller, Thomas,Linnartz, Petra,Witt, Matthias,Schaefer, Mathias,Luetzen, Arne
-
p. 3538 - 3551
(2007/10/03)
-
- Azopyridinium-containing [2]pseudorotaxanes and hydrazopyridinium-containing [2]catenanes
-
Benzylation of 4,4′-azopyridine, followed by counterion exchange, yields the bis(hexafluorophosphate) salt of the dibenzyl-4,4′-azopyridinium dication, which is bound by bis-p-phenylene-34-crown-10 (BPP34C10) and by 1,5-dioxynaphtho-38-crown-10 (1/5DN38C1
- Ashton, Peter R.,Brown, Christopher L.,Cao, Jianguo,Lee, Ju-Young,Newton, Simon P.,Raymo, Francisco M.,Stoddart, J. Fraser,White, Andrew J. P.,Williams, David J.
-
p. 957 - 965
(2007/10/03)
-
- A novel synthesis of unsymmetrical azo aromatics inaccessible by diazo-coupling reaction
-
A novel synthesis of unsymmetrical azo aromatics inaccessible by diazo-coupling reaction is reported. The synthesis involved the reaction of acetanilides with nitroarenes under moderate reaction conditions. A reaction pathway via a nitrosoarene intermediate involving elimination of the elements of the acetate anion, is proposed.
- Ayyangar,Naik,Srinivasan
-
p. 7253 - 7256
(2007/10/02)
-
- Photoreponsive Crown Ethers. Part 7. Proton and Metal Ion Catalyses in the cis-trans Isomerisation of Azopyridines and an Azopyridine-bridged Cryptand
-
A 2,2'-azopyridine-bridged crown ether (5) has been synthesised for the purpose of controlling the ion-binding functions by an on-off light switch mechanism.Since the trans-azopyridine moiety of compound (5) is vertically over the crown ether ring and the photoisomerised cis-azopyridine moiety of (5) is almost parallel to the crown ether plane, it would be expected that only the pyridine nitrogen of trans-(5) are capable of co-ordinating to metal ions bound into the crown ether ring.The thermal isomerisation of cis-2,2'-azopyridine to trans-2,2'-azopyridine was speeded up either by protonation of the pyridine nitrogen or by complexation with heawy-metal ions (e.g.Cu2+, Ni2+, and Co2+).Similarly, the thermal isomerisation of cis-(5) to trans-(5) was speeded up by protonation of azopyridine, but the metal ion catalysis was observed only for the metal ions which were bound into the crown ether ring (e.g.Cu2+ and Pb2+).The result of solvent extraction of alkali-metal ions with (5) was very similar to that with an azobenzene-bridged crown ether (1), indicating that the 2,2'-azopyridine-bridge of (5) has almost no effect on the extraction of alkali-metal ions.On the other hand, trans-(5) was capable of extracting considerable amounts of heavy-metal ions (Cu2+, Ni2+, CXo2+, and Hg2+), whereas photoisomerised cis-(5) scarcely extracted these metal ions.Such a difference in the extractability was not observed between trans-(1) and photoisomerised cis-(1).Neither the trans- nor the cis-form of 6,6'-bis(morpholinocarbonyl)-2,2'-azopyridine could extract these metal ions under comparable extraction conditions.These results suggest that pyridine nitrogens of trans-(5) are directed towards the crown ether plane so as to co-ordinate to metal ions in the crown ether ring, whereas those of cis-(5) have no such coordination ability due to the distorted configuration.Therefore, compound (5) would act as a 'photoresponse cryptand' for heavy metal ions.
- Shinkay, Seiji,Kouno, Takeshi,Kusano, Yumiko,Manabe, Osamu
-
p. 2741 - 2748
(2007/10/02)
-
- Seed treatment fungicides for control of seed-borne diseases
-
This invention relates to a method for controlling seedborne fungus diseases in plants, by applying to the seed a fungicidally effective amount of 4,4'-azodipyridine or acid salts of the formula STR1 wherein A is an acid having acidic dissociation constant greater than 1×10-6 ; and P is equal to the number of hydrogens on the acid A which have an acidic dissociation constant greater than 1×10-6.
- -
-
-
