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Chemistry: a European Journal

Stephanie Bellinger, Maryam Hatamimoslehabadi, Seema Bag, Farha Mithila, Jeffrey La, Mathieu Frennete, Samir Laoui, David Szalda, Chandra Yelleswarapu, Jonathan Rochford
The synthesis and characterization of a series of donor-π-acceptor-π-donor (D-A-D) curcuminoid molecules are here presented incorporating π-extended aryl and electron-donating amino terminal functionalization. Computational evaluation shows these molecules possess quadrupolar character with the lowest energy transitions displaying high molar extinction coefficients with broad tunability through manipulation of terminal donating groups. Consistent with their quadrupolar nature, these molecules show varying degrees of solvatochromic behavior in both their absorption and emission spectra which has been analyzed by Lippert-Mataga and Kamlet-Taft analysis...
November 17, 2017: Chemistry: a European Journal
Vera Krewald, Leticia Gonzalez
The search for molecular catalysts that efficiently activate or cleave the dinitrogen molecule is ongoing. While many thermal dinitrogen cleavage catalysts are known, the photochemical activation of N₂ has received considerably less attention. In this paper, we present the first computational study of the osmium dimer [Os(II,III)₂(µ-N₂)(NH₃)₁₀]5+, which was shown to be capable of dinitrogen photocleavage. Despite its deceptively simple geometry, it has a complex electronic structure with a valence-delocalized and electronically degenerate ground state...
November 17, 2017: Chemistry: a European Journal
Fredrik Schaufelberger, Brian J J Timmer, Olof Ramström
Catalyst discovery from systems of potential precursors is a challenging endeavor. Herein, a new strategy applying dynamic chemistry to the identification of catalyst precursors from C-H activation of imines is proposed and evaluated. Using hydroacylation of imines as a model reaction, the selection of an organometallic reactive intermediate from a dynamic imine system, involving many potential directing group/metal entities, is demonstrated. The identity of the amplified reaction intermediate with the best directing group could be resolved in situ via ESI-MS, and coupling of the procedure to an iterative deconvolution protocol generated a system with high screening efficiency...
November 17, 2017: Chemistry: a European Journal
Bo Chen, Chan Zhang, Libo Niu, Xiaozhen Shi, Huiling Zhang, Xingwang Lan, Guoyi Bai
Ultrasmall ZnO nanoparticles anchored on N-doped carbons with silica support (ZnO/SiO2-NC) were fabricated from chitosan and metal ions using a one-pot self-assembly strategy, and were successfully applied to the synthesis of 2-arylbenzimidazoles under mild conditions. These catalysts showed excellent stability and could be used six times without loss of conversion and selectivity. Using silica gel and biomass chitosan as a source of hydrophilic N-doped carbon facilitated the uniform dispersion of the ZnO nanoparticles in methanol and therefore their contact with reactants, contributing to a high catalytic performance...
November 17, 2017: Chemistry: a European Journal
Zuowei Xie, Yangjian Quan, Zaozao Qiu
Carboranes are a class of carbon-boron molecular clusters with unusual thermal and chemical stabilities. They have been proved as very useful building blocks in supramolecular design, optoelectronics, nanomaterials, boron neutron capture therapy agents and organometallic/coordination chemistry. Thus, the functionalization of o-carboranes has received growing interests. Over the past decades, most of the works in this area have been focused on cage carbon functionalization as the weakly acidic cage C-H proton can be readily deprotonated by strong bases...
November 17, 2017: Chemistry: a European Journal
Kiron Kumar Ghosh, Manuel van Gemmeren
A generally applicable Pd-catalyzed protocol for the β- C(sp3)-H arylation of propionic acid and related α-branched aliphatic acids is reported. Enabled by the use of N-acetyl-β-alanine as ligand our protocol delivers a broad range of arylation products. Notably, the highly challenging propionic acid, which lacks any acceleration through the Thorpe-Ingold effect, can be employed as substrate with synthetically useful yields. Furthermore, the scalability and synthetic applicability of the protocol are demonstrated...
November 17, 2017: Chemistry: a European Journal
Venkataramanan Mahalingam, Venkata N K B Adusumalli, Heramba V S R M Koppisetti
Intense white light emission is observed from colloidal single component NaYF4:Ce3+/Tm3+/Mn2+ nanocrystals. This combination is interesting as it uses Mn2+ ions instead of green and red emitting Ln3+ ions which are expensive and less abundant. The single band blue emission of Tm3+ ions was combined with the broadband greenish yellow emission of Mn2+ ions to produce strong white light emission using Ce3+ ions as excitation source. Interestingly, there is hardly any re-absorption of blue emission by Mn2+ ions and the spectrum matches the commercial Ce3+-doped YAG phosphor coated over blue LED...
November 17, 2017: Chemistry: a European Journal
Xu Han, Chuan Tian, Ingrid Gandra, Valeria Eslava, Diana Galindres, Edgar Vargas, Roger Leblanc
Different tail enigneered resorcinarenes have been examined towards the insulin fibrillation via experimental and computational studies. The resorcinarene showed a promising effect on the inhibition of insulin fibrillalition via ThT assay, CD spectra, and AFM images. Both ThT assay and computational results indicate the tail from the resorcinarene has an impact on insulin fibrillation by either inhibition or promotion because of the resident position on insulin. These observations have significant biological implications in the design of lead drug molecules as well as the development of potential therapeutic strategies...
November 16, 2017: Chemistry: a European Journal
Filip Vlahovic, Maja Gruden, Marcel Swart
The origin for the rotational barrier of organometallic vs inorganic sandwich complexes has remained enigmatic for the past decades. Here, we investigate in detail what causes the substantial barrier for titanodecaphosphacene through spin-state consistent density functional theory. Orbital interactions are shown to be the determining factor.
November 16, 2017: Chemistry: a European Journal
Carlos Martín-Fernández, M Merced Montero-Campillo, Ibon Alkorta, Manuel Yáñez, Otilia Mó, José Elguero
The proton affinity of the hydroxyl group of a series of compounds YHxOH (x=0-3, Y = Li, Na, Be, Mg, B, Al, Si, P, S, Cl, H) always increases upon interaction with Lewis bases LB = NH3, H2CNH, HCN, according to electronic structure calculations carried out at the G4 level of theory. The LB:YHxOH complexes experiment proton affinity enhancements from 24.8 to 304.8 kJ·mol-1 on its OH group with respect to the free compounds. This enhancement is related to the ability of these YHxOH compounds, acting as Lewis acids, to form non-covalent interactions of different kinds...
November 16, 2017: Chemistry: a European Journal
Alexander S Karns, Monalisa Goswami, Bas de Bruin
We report a new method for the synthesis of indolines from o-aminobenzylidine N-tosylhydrazones proceeding through a cobalt(III)-carbene radical intermediate. This methodology employs the use of inexpensive commercially-available reagents and allows for the transformation of easily derivatized benzaldehyde-derived precursors to functionalized indoline products. This transformation takes advantage of the known propensity of radicals to undergo rapid intramolecular 1,5-hydrogen atom transfer (1,5-HAT) to form more stabilized radical intermediates...
November 16, 2017: Chemistry: a European Journal
Somnath Das, Palani Natarajan, Burkhard König
The C-H amination of benzene derivatives was achieved using DDQ as photocatalyst and BocNH₂ as the amine source under aerobic conditions and visible light irradiation. Electron-deficient and electron-rich benzenes react as substrates with moderate to good product yields. The amine scope of the reaction comprises Boc-amine, carbamates, pyrazoles, sulfonimide and urea. Preliminary mechanistic investigations indicate a charge transfer complex between the amine and DDQ as essential intermediate of the reaction...
November 16, 2017: Chemistry: a European Journal
Hannah Kurz, Charles Lochenie, Kristina G Wagner, Sandra Schneider, Matthias Karg, Birgit Weber
Two phenanthroline-derived Schiff base-like ligands with a covalently-linked Ru(II) phosphorescent unit were synthesised and converted into bimetallic Ru(II)-Ni(II) complexes. The optical properties were studied to examine a possible photoluminescence quenching through a non-radiative energy transfer upon Coordination Induced Spin State Switch (CISSS) at the Ni(II) centre. Therefore the metalloligands and the Ni(II) complexes were studied by UV-Vis absorbance as well as steady-state and time-resolved emission spectroscopy in MeCN and pyridine solutions...
November 16, 2017: Chemistry: a European Journal
Carmen Sousa, Alex Domingo, Coen de Graaf
The second-order spin-orbit coupling is evaluated in two transition metal complexes to establish the effect on the deactivation mechanism of the excited low-spin state in systems that undergo spin transitions under the influence of light. We compare the standard perturbational approach to calculate the second-order interaction with a variational strategy based on effective Hamiltonian theory and show that the former one can only be applied in some special cases and even then gives results that largely overestimate the interaction...
November 16, 2017: Chemistry: a European Journal
Isabelle Gillaizeau, Sylvain Bertho, Romain Rey-Rodriguez, Pascal Retailleau, Cyril Colas
A novel regio- and diastereoselective iron-catalyzed intermolecular oxyazidation of enamides using various azidobenziodoxolone (ABX) derivatives is presented. A variety of alpha-N3 amino derivatives and of alpha-N3 piperidines is nicely synthesized in good yields and under mild reaction conditions. The reaction involves a radical process using cheap FeCl2 as the initiator.
November 16, 2017: Chemistry: a European Journal
Julian Papadopoulos, Kay Merkens, Thomas J J Müller
Novel E-configurated coumarin-based merocyanines were efficiently synthesized by a one-pot three-component Sonogashira coupling-Michael addition starting from triflyl coumarins, terminal alkynes and secondary amines. The photophysical properties of the synthesized yellow to orange merocyanines were studied by UV/Vis and fluorescence spectroscopy and rationalized by Hammett-Taft correlations and DFT and TD DFT calculations. Most compounds were only weakly fluorescent in solution; however, two compounds were investigated in more detail with respect to their aggregation behavior...
November 15, 2017: Chemistry: a European Journal
Chao Wei, Yan Zhang, Bingkun Yan, Yue Xu, Zhengzhen Du, Meidong Lang
Sulfur/selenium containing cyclic carbonate monomers (MR) are designed and synthesized by enzyme catalyzed intermolecular macro-ring closure of related diols. The proposed synthetic strategy is tolerant of other functionalities such as N-substituted groups. The ring opening polymerization (ROP) of MR occurs readily as a versatile route to generate a new family of main chain sulfur/selenium substituted aliphatic polycarbonates (PR) with predictable molecular weights (MW), narrow molecular-weight distribution and controlled copolymer composition...
November 15, 2017: Chemistry: a European Journal
David M Engelhard, Lukas M Stratmann, Guido H Clever
A series of artificial metal-base tetrads composed of a CuII cation coordinating to four pyridines, covalently attached to the ends of tetramolecular G-quadruplex DNA strands [LA-Dd(G4)]4 (LA-D = ligand derivatives), was systematically studied. Structurally, the square-planar [Cu(pyridine)4] complex behaves analogous to the canonical guanine quartet. Copper coordination to all studied ligand derivatives was found to increase G-quadruplex thermodynamic stability, tolerating a great variety of ligand linker lengths (1 - 5 atoms) and thus demonstrating the robustness of the chosen ligand design...
November 15, 2017: Chemistry: a European Journal
Christoph Schlepphorst, Mario Wiesenfeldt, Frank Glorius
The first enantioselective synthesis of imidazo[1,2-a]pyridines via direct hydrogenation was achieved using a ruthenium/N-heterocyclic carbene (NHC) catalyst. The reaction forgoes the need for protecting or activating groups, proceeds with complete regioselectivity, good to excellent yields, enantiomeric ratios of up to 98:2, and tolerates a broad range of functional groups. 5,6,7,8-Tetrahydroimidazo[1,2-a]pyridines, which are found in numerous bioactive molecules, are directly obtained by this method and its applicability was demonstrated by the (formal) synthesis of several functional molecules...
November 15, 2017: Chemistry: a European Journal
Nicolas Kerisit, Przemyslaw Gawel, Brian Levandowski, Yun-Fang Yang, Víctor García-López, Nils Trapp, Laurent Ruhlmann, Corinne Boudon, Kendall N Houk, François Diederich
A four-step synthesis of substituted 5,11-dicyano-6,12-diaryltetracenes was developed, starting from readily available para-substituted benzophenones. The key step of this straightforward route is the complex cascade reaction between tetraaryl[3]cumulenes and tetracyanoethene (TCNE) resulting in 5,5,11,11-tetracyano-5,11-dihydrotetracenes. The mechanism of this transformation was reinvestigated by means of theoretical calculations. The target tetracenes were obtained by a newly developed decyanation/aromatization reaction catalyzed by Cu(I) or Cu(II) complexes in solution, conditions compatible with a broad range of functional groups...
November 15, 2017: Chemistry: a European Journal
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