Towards atomically precise supported catalysts from monolayer-protected clusters: the critical role of the support.
a B Abstract Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, we show that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au-ligand species or ligand-free metallic Au0 clusters. On Lewis acidic s...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Häkkinen H, Longo A, de Boed E, Mammen N, van der Linden M, Honkala K, de Jongh P, Donoeva B Tags: Chemistry Source Type: research

Magneto-Chiral Dichroism: A Playground for Molecular Chemists.
Abstract Magneto-chiral dichroism (MChD) is a non-reciprocal manifestation of light-matter interaction that can be observed in chiral systems possessing a magnetization, either spontaneous or induced by an external magnetic field. It features a differential absorption or emission of unpolarized light that depends on the relative orientation of the magnetization with respect to the direction of light propagation and on the absolute configuration of the system. Molecular chemistry is the best-suited route towards systems combining chirality and magnetism. Nowadays, the investigation of MChD is still in its infa...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Atzori M, Rikken GLJA, Train C Tags: Chemistry Source Type: research

Linear and Star-Shaped Extended Di- and Tristyrylbenzenes: Synthesis, Characterization and Optical Response to Acid and Metal Ions.
Abstract Two linear 1,4-distyrylbenzenes and five star-shaped 1,3,5-tristyrylbenzene derivatives (L2a-L2b, Y0-Y3 and YNBu) were synthesized and spectroscopically characterized. The photophysical properties, optical response to acid and metal ions were investigated. Upon backbone extension of linear distyrylbenzenes or the introduction of dibutylanilines, the electronic spectra are red-shifted. Incorporation of electron-deficient pyridyl units does not significantly affect the optical properties. Variation of the number of pyridine rings and substitution pattern tune the fluorescence response to acids and metal ion...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Zhang H, Kotlear EA, Kushida S, Maier S, Rominger F, Freudenberg J, Bunz UH Tags: Chemistry Source Type: research

Understanding the 1,3-Dipolar Cycloadditions of Allenes.
Abstract We have quantum chemically studied the reactivity, site-, and regioselectivity of the 1,3-dipolar cycloaddition reaction between methyl azide and various allenes, including the archetypal allene propadiene, heteroallenes, and cyclic allenes, using density functional theory (DFT). The  1,3-dipolar  cycloaddition reactivity of linear (hetero)allenes decreases as the number of heteroatoms in the allene increases and the formation of the 1,5-adduct is, in all cases, favored over the 1,4-adduct, both effects find their origin from the strength of the primary orbital interactions . The cycloaddition r...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Yu S, Vermeeren P, van Dommelen K, Bickelhaupt M, Hamlin TA Tags: Chemistry Source Type: research

Metal-Free, NIS-Induced Regioselective Iodophosphoryloxylation of Alkenes with P(O)-OH bonds.
Abstract A simple and efficient method for the regioselective iodophosphoryloxylation of alkenes with P(O)-OH bonds has been established by using NIS (N-iodosuccinimide) as the iodination reagent under transition-metal-free conditions. The present protocol is compatible with different functional groups, and suitable for various alkenes and P(O)-OH compounds. A variety of functionalized β-iodo-1-ethyl phosphinic/phosphoric acid esters are obtained in good to excellent yields, which could be further transformed to diversified building blocks for the synthesis of bioactive compounds, pharmaceuticals and function...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Xiong B, Xu S, Zhu Y, Yao L, Zhou C, Liu Y, Tang KW, Wong WY Tags: Chemistry Source Type: research

Catalytic light-triggered reduction promoted by a dithienylethene derivative.
Abstract A pyridinium substituted dithienylethene derivative was used for the first time as an efficient photo-reducing agent of two different substrates. This reaction exhibits high catalytic yields due to the continuous regeneration of the initial state of the photochromic molecule. PMID: 32220098 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Cobo S, Khettabi A, Grempka A, Lafolet F, Chatir E, Leconte N, Collomb MN, Jouvenot D Tags: Chemistry Source Type: research

A layered tin bismuth selenide with three different building blocks that account for an extremely large lattice parameter of 283 Å.
A layered tin bismuth selenide with three different building blocks that account for an extremely large lattice parameter of 283 Å. Chemistry. 2020 Mar 27;: Authors: Nentwig M, Eisenburger L, Heinke F, Souchay D, Oeckler O Abstract The layered compound Sn 2.8(4) Bi 20.2(4) Se 27 exhibits an extraordinarily long-periodic 150 R stacking sequence. The crystal structure contains three different building blocks, which form upon the addition of Sn to a Bi-rich bismuth selenide. Sn-doped Bi 2 double ("2") layers similar to those in elemental bismuth, Sn 0.3 Bi 1.7 Se 3 quintuple ("5"...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Nentwig M, Eisenburger L, Heinke F, Souchay D, Oeckler O Tags: Chemistry Source Type: research

Fluorodynamers displaying tunable fluorescence on constitutional exchanges in solution and at solid film-solution interface.
Abstract Dynamic covalent polymers -the dynamers- are adaptive materials that offer timely variant adaptive macroscopic organization across extended scales. In the current study, imine exchange reactions and fluorescence transfer can occur at the interfaces between various solutions and solid state dynameric films. The fluorescence quenching upon imine formations for designed fluorogen was successfully demonstrated, and this tunable fluorescence was further used to study the re-composition of a solid film. Moreover, the dynamic covalent films also exhibited responsiveness to competing amines and acid/base conditio...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Si M, Zhu W, Zhang Y, Barboiu M, Chen J Tags: Chemistry Source Type: research

Electrochemical Iodine-Mediated Oxidation of Enamino-Esters to 2H-Azirine-2-Carboxylates supported by Design of Experiments.
Abstract An electrochemical iodine-mediated transformation of enamino-esters for the synthesis of 2 H -azirine-2-carboxylates is presented. In addition, a thermic conversion of azirines to 4-carboxy-oxazoles in quantitative yield without purification was described. Both classes 2 H -azirines-2-carboxylates and the 4-carboxy-oxazoles are substructures in natural products and therefore are of considerable interest for synthetic and pharmaceutical chemists. The optimization was not performed in a conventional manner with a one-factor-at-a-time process but with a Design of Experiments ( DoE ) approach. Beside a broad ...
Source: Chemistry - March 27, 2020 Category: Chemistry Authors: Hilt G, Babaoglu E Tags: Chemistry Source Type: research

Multi-color fluorescent carbon dots: Non-size effect dominate graphitized sp2 conjugated domain and surface state energy level co-modulate band-gap.
Abstract Four types of carbon dots with various color (blue, green, yellow and red) emissions have been synthesized under solvent-free condition from citric acid and different nitrogen sources (DMF, urea, ethanamide and formamide). By detailed characterization and comparion, it is comfimed that the graphitized sp2 conjugated domain and surface functional groups such as C-O and C=N play synergitic roles in adujusting fluorescence properties. Notable, the size effect is not the dominant mechanism to achieve multi-color fluorescence emissions in our work. The structural configuration of carbon dots further influences...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Wei S, Yin X, Li H, Du X, Zhang L, Yang Q, Yang R Tags: Chemistry Source Type: research

Structure and Bonding in a Diamond-Shaped Tin Cluster Possessing a cyclo-Sn4 Core.
Abstract A tetrameric cluster composed entirely of (aryl)Sn units, [DMPSn] 4 (DMP = 2,6-dimesitylphenyl), has been prepared by reduction of [DMPSnCl] 2 with a variety of reductants. This cluster was characterized in solution by multinuclear NMR spectroscopies, as well as in the solid-state by single crystal X-ray diffraction analysis. This species is stereochemically nonrigid in solution and possesses a folded cyclo -Sn 4 core that undergoes rapid ring-flipping at higher temperatures. The solid-state molecular structure is remarkably unsymmetrical and possesses a nearly planar cyclo -Sn 4 core. The DMP substituent...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Handford RC, Wheeler TA, Tilley TD Tags: Chemistry Source Type: research

Ruthenium-Catalyzed Site-Selective Trifluoromethylations and (Per)Fluoroalkylations of Anilines and Indoles.
Abstract Introducing (per)fluoroalkyl groups into arenes continues to be an interesting, but challenging area in organofluorine chemistry. We herein report a novel ortho-selective C-H perfluoroalkylation including trifluoromethylations of anilines and indoles without the need of protecting groups using R f I and R f Br as commercially available reagents. The availability and price of the starting materials as well as the inherent selectivity make this novel methodology attractive for the synthesis of diverse (per)fluoroalkylated building blocks, e.g. for bio-active compounds and materials. PMID: 32216068 [Pub...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Li Y, Neumann H, Beller M Tags: Chemistry Source Type: research

Distannabarrelenes with three Coordinated Sn(II) atoms.
Abstract Crystalline 1,4-distannabarrelene compounds [(ADC Ar ) 3 Sn 2 ]SnCl 3 ( 3-Ar ) (ADC Ar = {CC(NDipp)CAr}; Dipp = 2,6-iPr 2 C 6 H 3 , Ar = Ph or DMP; DMP = 4-Me 2 NC 6 H 4 ) derived from anionic dicarbenes Li(ADC Ar ) ( 2-Ar ) (Ar = Ph or DMP) have been reported. The cationic moiety of 3-Ar features a barrelene framework with three coordinated Sn(II) atoms at the 1,4-positions, whereas the anionic unit SnCl 3 is formally derived from SnCl 2 and chloride ion. The all carbon substituted bis-stannylenes 3-Ar have been characterized by NMR spectroscopy and X-ray diffraction. DFT calculations reveal that the HOM...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Ghadwal R, Sharma MK, Glodde T, Neumann B, Stammler HG Tags: Chemistry Source Type: research

The Forgotten Pyrazines: Exploring the Dakin-West Reaction.
Abstract Pyrazines are an underreported class of N-heterocycles available from nitrogen-rich biomass presenting an interesting functional alternative for current aromatics. In this work we explore access to pyrazines obtained from amino acids using the 90 year old Dakin-West reaction. After a qualitative screening several functional proteinogenic amino acids proved good substrates for this reaction, which were successfully scaled to multigram scale production of the corresponding intermediate α-acetamido ketones. Subsequently, we optimized the conditions towards pyrazine formation using δ-amino-levulin...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Orru R, Wurdemann M, Niţu C, De Wildemann S, Bernaerts K Tags: Chemistry Source Type: research

Probing relaxation dynamics in five-coordinate dysprosium single-molecule magnets.
We report a new family of five-coordinate Lanthanide Single-Molecule Magnets (Ln SMMs) [Dy(Mes*O) 2 (THF) 2 X] (Mes*= 2,4,6-tri-tert-butylphenyl; X = Cl, 1 ; Br, 2 ; I, 3 ) with energy barriers to magnetic reversal amongst the highest reported for any SMM to date. The five-coordinate Dy(III) ions have distorted square pyramidal geometries, with halide anions on the apex, and two Mes*O ligands mutually trans- to each other, and the two THF molecules forming the second trans- pair. These geometrical features lead to a large magnetic anisotropy in these complexes giving Orbach energy barriers above 1200 K. QTM and Raman relax...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Parmar V, Ortu F, Ma X, Chilton N, Clerac R, Mills DP, Winpenny R Tags: Chemistry Source Type: research

Enantioselective 1,3-Dipolar [6+4] Cycloaddition of Pyrylium Ions and Fulvenes towards Cyclooctanoids.
en ML Abstract Organocatalytic enantioselective 1,3-dipolar [6+4] cycloadditions of pyrylium ion intermediates with fulvenes promoted by a chiral primary amine catalyst have been developed to proceed in moderate to good yields and high enantioselectivities. The resultant chiral bicyclo[6.3.0]undecane scaffold containing a transannular bridging ether is densely functionalised providing a rigid scaffold for further manipulations. Computational studies give important insights into the role of the primary amine catalyst. Analysis of the reaction shows that the catalytic reaction proceeds in a step-wise manner and rati...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Jørgensen KA, McLeod D, Cherubini-Celli A, Sivasothirajah N, McCulley CH, Christensen ML Tags: Chemistry Source Type: research

Yldiide Ligands as Building Blocks for Polynuclear Coinage Metal Complexes: Metal Squares, Triangles and Chains.
Abstract Yldiides have unique electronic properties and donor abilities, but as ligands in transition metal complexes they are scarcely represented in the literature. Here, the controlled synthesis of a series of polynuclear gold yldiide complexes derived from triphenyl(cyanomethyl)phosphonium bromide, [Ph 3 PCH 2 CN]Br, under mild conditions is described. Anionic dinuclear NBu4 [(AuX) 2 {C(CN)PPh 3 }] (X = Cl, C 6 F 5 ) or trinuclear derivatives NBu 4 [Au 3 X 2 {C(CN)PPh 3 }] bearing terminal chloride or pentafluorophenyl groups and bridging yldiide ligands have been prepared. These compounds evolve in solution g...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Gimeno MC, Johnson A Tags: Chemistry Source Type: research

Unique β-Turn Peptoid Structures and their Application as Asymmetric Catalysts.
Unique β-Turn Peptoid Structures and their Application as Asymmetric Catalysts. Chemistry. 2020 Mar 26;: Authors: Drapaneni C, Ghosh P, Ghosh T, Maayan G Abstract Peptoids - N-substituted glycine oligomers - represent an important class of peptidomimetics that can fold into three-dimensional structures in solution. Most of the folded peptoid structures, however, resemble helices, and this can limit their applications, specifically in asymmetric catalysis. Herein we describe, for the first time, unique examples of pyrrolidine-based β-turn-like peptoids and characterize them both in the solid ...
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Drapaneni C, Ghosh P, Ghosh T, Maayan G Tags: Chemistry Source Type: research

Poly methyl methacrylate-assisted exfoliation of graphite and its use in acrylonitrile-butadiene-styrene composites.
In this study, we propose the use of poly methyl methacrylate (PMMA) as a stabilizing agent for the production of graphene flakes in a low boiling point solvent, i.e., acetone. The graphene dispersions produced in the mixture acetone-PMMA increases the concentration by +175 %, and contain a higher percentage of few-layer graphene flakes (
Source: Chemistry - March 26, 2020 Category: Chemistry Authors: Gentiluomo S, Thorat SB, Del Rio Castillo AE, Toth PS, Panda JK, Pellegrini V, Bonaccorso F Tags: Chemistry Source Type: research

Iron(0) mediated stereoselective (3+2)-cycloaddition of thiochalcones via a diradical intermediate.
igand W Abstract Reactions of α,β-unsaturated aromatic thioketones 1 (thiochalcones) with Fe 3 (CO) 12 leading to η 4 -1-thia-1,3-diene iron tricarbonyl complexes 2 , [FeFe] hydrogenase mimics 3 , and the thiopyrane adduct 4 are described. Obtained products have been characterized by X-ray crystallography and by computational methods. Completely regio- and diastereoselective formation of the five-membered ring system in products 3 , containing four stereogenic centers, can be explained by an unprecedented, stepwise (3+2)-cycloaddition of two thiochalcone molecules mediated by Fe 3 (CO) 12 . Quantum ...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Mloston G, Buday P, Seeber P, Neumann C, Abul-Futouh H, Görls H, Gräfe S, Matczak P, Kupfer S, Weigand W Tags: Chemistry Source Type: research

Low-temperature solution crystallization of nanostructured oxides and thin films.
Abstract The increasing demand of high-performance crystalline oxide nanomaterials for applications in current and emergent technologies is pushing research on alternative and sustainable synthesis processes, ideally complying with the principles of Green Chemistry. In this framework, wet-chemistry approaches are particularly promising, since they are typically based on soft synthesis processes, in terms of temperature and pressure, or use water and/or non-toxic alcohols as solvents. Solution methods are low-cost and simple approaches to the synthesis of nanomaterials but, to achieve sustainable, environmentally f...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Bretos I, Diodati S, Jimenez R, Tajoli F, Ricote J, Bragaggia G, Franca M, Calzada ML, Gross S Tags: Chemistry Source Type: research

Efficient Fused Ring Extension of A-D-A-type Nonfullerene Acceptors via Symmetric Replicating Core Unit Strategy.
Abstract Extension of a fused aromatic ring core is beneficial for enhancing the intramolecular charge transfer and effective π-conjugation in A-D-A type non-fullerene acceptors (NFAs). In this work, a novel strategy involving extension of fused-ring core by symmetrically replicating core unit was developed, and a novel symmetric fused-12-ring NFA, LC81 was synthesized. When paired with the wide-bandgap polymer donor, PBT1-C, the corresponding organic solar cells (OSCs) showed a high-power conversion efficiency (PCE) of 12.71%, much higher than that of the device based on reference NFA, TPTT-4F. Moreover, the L...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Sun Y, Xia T, Li C, Ryu HS, Guo J, Min J, Woo HY Tags: Chemistry Source Type: research

Hydroboration of alkenes catalysed by a nickel N-heterocyclic carbene complex: reaction and mechanistic aspects.
Abstract The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η 5 -C 5 Me 5 )Cl(IMes)] (IMes = 1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in the presence of a catalytic amount of potassium tert -butoxide, and joins the very exclusive club of nickel catalysts for this important transformation. Interestingly, the regioselectivity can be reversed in some cases by using pinacolborane instead of catecholborane. Mechanistic investigations involving control experiments, 1 H and 11 B NMR spectroscopy, cyclic voltammetry,...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Ulm F, Cornaton Y, Djukic JP, Chetcuti MJ, Ritleng V Tags: Chemistry Source Type: research

Ruthenium(II)-Catalyzed Double Annulation of Quinones: Step-Economical Access to Valuable Bioactive Compounds.
ann L Abstract Double ruthenium(II)-catalyzed alkyne annulations of quinones were accomplished. Thus, we report a strategy that provides step-economical access to valuable quinones with a wide range of applications. C-H/N-H activations for alkyne annulations of naphthoquinones provided challenging polycyclic quinoidal compounds by forming four new bonds in one step. The singular power of the thus-obtained compounds was reflected by their antileukemic activity. PMID: 32212283 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: da Silva Júnior EN, de Carvalho RL, Almeida RG, Rosa LG, Fantuzzi F, Rogge T, Costa PMS, Pessoa C, Jacob C, Ackermann L Tags: Chemistry Source Type: research

CpTiCl2-Catalyzed Cross-Coupling between Internal Alkynes and Ketones: a Novel Concept in the Synthesis of Halogenated, Conjugated Dienes.
Abstract A novel concept for the synthesis of halogenated, conjugated dienes is disclosed: the CpTiCl 2 -catalyzed coupling of keto-alkynes, in the presence of Me 3 SiBr/Et 3 N·HBr.  This reaction provided five-, six- and seven-membered carbocycles, nitrogenated heterocyles, as well as six-membered oxygenated heterocycles leading a brominated, conjugated diene in their structure. These products showed highly reactivity in Diels-Alder, Suzuki and Sonogashira reactions, giving complex chemical structures in only three steps from the corresponding acyclic keto-alkyne. We believe that this strategy paves t...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Roldan-Molina E, M Nievas M, R Navarro JA, Oltra JE Tags: Chemistry Source Type: research

Highly Polarized Coumarin Derivatives Revisited: Solvent-controlled Competition Between Proton Coupled Electron Transfer and Twisted Intramolecular Electron Transfer.
Abstract Linking a polarized coumarin unit with an aromatic substituent via an amide bridge results in weak electronic coupling affecting the intramolecular electron transfer (ET) process. As a result of this, interesting solvent-dependent photophysical properties can be observed. In polar solvents, electron transfer in coumarin derivatives of this type induces a mutual twist of electron-donating and electron-accepting molecular units (TICT process) that opens radiationless decay processes (internal conversion). In the dyad with the strongest intramolecular hydrogen bond, the planar form is stabilized so twisting ...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Morawski O, Kielesiński Ł, Gryko DT, Sobolewski A Tags: Chemistry Source Type: research

Complementary Site-Selective Halogenation of Nitrogen-Containing (Hetero)Aromatics with Superacids.
eau S Abstract Site-selective functionalization of arenes that is complementary to classical aromatic substitution reactions remains a long-standing quest in organic synthesis. Exploiting the generation of halenium ion through oxidative process and the protonation of the nitrogen containing function in HF/SbF 5 , the chlorination and iodination of classically inert C sp2 -H bonds of aromatic amines occurs. Furthermore, the superacid promoted (poly)protonation of the molecules acts as a protection, favoring the late-stage selective halogenation of natural alkaloids and active pharmaceutical ingredients. PMID: ...
Source: Chemistry - March 25, 2020 Category: Chemistry Authors: Mamontov A, Martin-Mingot A, Métayer B, Karam O, Zunino F, Bouazza F, Thibaudeau S Tags: Chemistry Source Type: research

Lead Doped Ti-Oxo Clusters as Molecular Models of Perovskite-type PbTiO3 and Electron Transport Material in Solar Cells.
Abstract In this work, we successfully prepared Pb-doped titanium-oxo clusters with core structures as isolated perovskite PbTiO3 species. In the obtained highly symmetric Pb8Ti7-oxo cluster, the central TiO6 octahedra are orthogonally extended to adjacent ones in corner-sharing way and the doped 8 Pb ions form a cubic arrangement, making it the first molecular model of perovskite PbTiO3. Moreover, they show high solution stability confirmed by MALDI-TOF-MS measurements. Based on such solution processability, they can be easily spin-coated into homogeneous films, which were further applied as electron transport ma...
Source: Chemistry - March 24, 2020 Category: Chemistry Authors: Zhou S, Li C, Fu H, Cao J, Zhang J, Zhang L Tags: Chemistry Source Type: research

Boosting visible-light photocatalytic redox reaction by charge separation in SnO2/ZnSe(N2H4)0.5 heterojunction nanocatalysts.
Abstract Herein, we report environmental photocatalysts with attractive catalytic properties prepared by introducing SnO 2 quantum dots (QDs) directly attached onto ZnSe(N 2 H 4 ) 0.5 substrates to induce advantageous charge separation. The SnO 2 /ZnSe(N 2 H 4 ) 0.5 nanocomposites could be easily synthesized via a one-pot hydrothermal process. Owing to the absence of capping ligands, the attached SnO 2 QDs displayed superior photocatalytic properties, generating many exposed reactive surfaces. Moreover, the addition of a specified amount of SnO 2 boosted the visible-light photocatalytic activity; however, the pres...
Source: Chemistry - March 24, 2020 Category: Chemistry Authors: Kim Y, Jeong DW, Lee J, Song MY, Lee SM, Choi J, Jang DJ, Kim HJ Tags: Chemistry Source Type: research

Collective Effects of Electron Affinity and Steric Hindrance of Trifluoromethyl on the π-Bridge in Designing Blue Thermally Activated Delayed Fluorescence Emitters.
This study provides practical design strategy for blue TADF materials particularly when planar and less crowded group is used as donor. PMID: 32212179 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - March 24, 2020 Category: Chemistry Authors: Li J, Li H, Liu D, Huang T, Li D Tags: Chemistry Source Type: research

The CH- π interaction in protein - carbohydrate binding: Bioinformatics and in vitro quantification.
In this study we analyzed the CH-π interactions employing bioinformatics (data mining, structural analysis), several experimental (ITC, X-ray crystallography) and computational techniques. The Protein Data Bank (PDB) has been used as a source of structural data. PDB contains over 12 000 protein complexes with carbohydrates.  Stacking interactions are very frequently present in such complexes (about 39% of identified structures). The calculations and the ITC measurement results suggest that the CH-π stacking contribution to the overall binding energy ranges from 4 kcal/mol up to 8 kcal/mol. All the results s...
Source: Chemistry - March 24, 2020 Category: Chemistry Authors: Houser J, Kozmon S, Mishra D, Hammerová Z, Wimmerová M, Koca J Tags: Chemistry Source Type: research

Molecular Interrogation to Crack the Case of O-GlcNAc.
Abstract The O-linked β-N-acetylglucosamine (O-GlcNAc) modification, termed O-GlcNAcylation, is an essential and dynamic post-translational modification in cells. O-GlcNAc transferase (OGT) installs this modification on serine and threonine residues while O-GlcNAcase (OGA) hydrolyzes it. O-GlcNAc modifications are found on thousands of intracellular proteins involved in diverse biological processes. Dysregulation of O-GlcNAcylation and O-GlcNAc cycling enzymes has been detected in many diseases including cancer, diabetes, cardiovascular and neurodegenerative diseases. In this minireview, we will discuss ...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Estevez A, Zhu D, Blankenship C, Jiang J Tags: Chemistry Source Type: research

Active Metal Template Synthesis and Characterization of a Nanohoop [c2]Daisy Chain Rotaxane.
Abstract Molecules and materials that demonstrate large amplitude responses to minor changes in their local environment play an important role in the development of new forms of nanotechnology. Molecular daisy chains are a type of a mechanically interlocked molecule that are particularly sensitive to such changes where, in the presence of certain stimuli, the molecular linkage enables muscle-like movement between a reduced-length contracted form and an increased-length expanded form.  To date, all reported syntheses of molecular daisy chains are accomplished via passive-template methods, resulting in a majori...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Van Raden J, Jarenwattananon N, Zakharov L, Jasti R Tags: Chemistry Source Type: research

Widely Electronically Tunable 2,6-Disubstituted Dithieno[1,4]thia-zines - Electron-Rich Fluorophores up to Intense NIR Emission.
TJJ Abstract 2,6-Difunctionalized dithieno[1,4]thiazines were efficiently synthesized by (pseudo)five- or (pseudo)three-component one-pot processes based on lithiation-electrophilic trapping sequences. As supported by structure-property relationships, the thiophene anellation mode predominantly controls the photophysical and electrochemical properties and the electronic structures (as obtained by DFT calculations). From molecular geometries and redox potentials to fluorescence quantum yields in solution, the interaction of the dithieno[1,4]thiazine-core with the substituents causes striking differences within the ...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: May L, Müller TJJ Tags: Chemistry Source Type: research

Extracellular matrix proteins involved in Alzheimer's disease.
Abstract Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and characterized by cognitive and memory impairments. Emerging evidence suggests that the extracellular matrix (ECM) biomacromolecules in brain plays an important role in etiology of AD. It has been detected that the levels of ECM proteins have been changed in the brains of AD patients and animal models. Some ECM components, e.g., elastin and heparan sulfate proteoglycans, are considered to promote the upregulation of extracellular amyloid-β (Aβ) proteins. In addition, collagen VI and laminin are shown to have interac...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Ma J, Ma C, Li J, Sun Y, Ye F, Liu K, Zhang H Tags: Chemistry Source Type: research

Hetero Diels-Alder Reactions with a Dicationic Urea Azine Derived Azo Dienophile and Their Use for the Synthesis of an Electron-Rich Pentacene.
Abstract Herein, we report the first hetero Diels-Alder (DA) reactions with a stable, dicationic urea azine derived azo dienophile, synthesised by two-electron oxidation of the neutral urea azine. Several charged DA products were synthesised in good yield and fully characterised. The DA adduct of anthracene is in thermal equilibrium with the reactants at room temperature, and the reaction enthalpy and entropy were determined from the temperature-dependent equilibrium constant. Furthermore, base addition to solutions of the pentacene DA product leads to deprotonation, cleavage of the N-N bond and formation of an el...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Himmel HJ, Werr M, Kaifer E Tags: Chemistry Source Type: research

Reversible N-Heterocyclic Carbene-Induced α-H Abstraction In Tungsten (VI) Imido Dialkyl Dialkoxide Complexes.
Reversible N-Heterocyclic Carbene-Induced α-H Abstraction In Tungsten (VI) Imido Dialkyl Dialkoxide Complexes. Chemistry. 2020 Mar 23;: Authors: Musso JV, Benedikter M, Wang D, Frey W, Altmann H, Buchmeiser MR Abstract The first reversible  N -heterocyclic carbene (NHC) induced  α -H elimination in tungsten (VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CHPh)2(OtBu)2 (Ar = 2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated ...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Musso JV, Benedikter M, Wang D, Frey W, Altmann H, Buchmeiser MR Tags: Chemistry Source Type: research

Oligophenyls with Multiple Disulphide Bridges as Higher Homologues of Dibenzo[c,e][1,2]dithiin - Synthesis and Application in Lithium-ion Batteries.
n K Abstract Higher homologues of dibenzo[ c , e ][1,2]dithiin are synthesized from oligophenyls bearing multiple methylthio groups. Single-crystal X-ray ana-lyses reveal their non-planar structures and helical enantiomers of higher meta -congener 6 . Such [1,2]dithiin homologues are demonstrated to be applicable to lithium-ion bat--teries as cathode, displaying a high capacity of 118 mAh g -1 at a current density of 50 mA g -1 . PMID: 32202685 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Sonnenschein C, Narita A, Ender CP, Wang F, Schollmeyer D, Feng X, Müllen K Tags: Chemistry Source Type: research

Stability, structure and reconstruction of 1H-edges in MoS2.
We present density functional studies of the edges of single-layer 1H-MoS 2 . This phase presents a rich variability of edges that can influence the morphology and properties of MoS 2 nano-objects, play an important role in industrial chemical processes, and find future applications in energy storage, electronics and spintronics. For so-called Mo-100%S edges we confirm vertical S-dimers are stable, however we also identify a family of metastable edges combining Mo atoms linked by two-electron donor symmetrical disulfide ligands and four-electron donor unsymmetrical disulfide ligands. These may be entropically favoured, pot...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Sayed-Ahmad-Baraza Y, Ewels C Tags: Chemistry Source Type: research

Electro-olefination - a Catalyst Free  Stereoconvergent Strategy for the Functionalization of Alkenes.
Electro-olefination - a Catalyst Free Stereoconvergent Strategy for the Functionalization of Alkenes. Chemistry. 2020 Mar 23;: Authors: Baumann AN, Music A, Dechent J, Müller N, Jagau TC, Didier D Abstract Conventional methods carrying out C(sp2)-C(sp2) bond formations are typically mediated by transition-metal based catalysts. Herein, we conceptualize a complementary avenue to access such bonds by exploiting the potential of electrochemistry in combination with organoboron chemistry. We demonstrate a transition metal catalyst-free electrocoupling between (hetero)aryls and alkenes via readil...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Baumann AN, Music A, Dechent J, Müller N, Jagau TC, Didier D Tags: Chemistry Source Type: research

Conformation-Dependent Response to Protonation of Diphenanthrioctaphyrin(1.1.1.0.1.1.1.0) - A Route to Pseudorotaxane-like Structures.
Abstract Diphenanthrioctaphyrin(1.1.1.0.1.1.1.0), an expanded carbaporphyrinoid incorporating two phenanthrenylene moieties, exists as two separate, yet interconvertible, locked stereoisomers. These species demonstrate complex dynamic behavior upon protonation, consisting of multiple conformational rearrangements and anion-binding events. Formation of one of the final dicationic forms is accompanied by an inclusion of a complex anion(s) within the macrocyclic cavity yielding a pseudorotaxane-like host-guest complex. Protonation with trifluoroacetic or dichloroacetic acids followed by neutralization afforded the co...
Source: Chemistry - March 23, 2020 Category: Chemistry Authors: Szyszko B, Przewoznik M, Bialek MJ, Bialonska A, Chmielewski P, Latos-Grazynski L Tags: Chemistry Source Type: research

Bright Luminous and Stable CsPbBr3@PS Microspheres Prepared via Facile Anti-solvent Method using CTAB as Double Modifier.
Abstract The past decade has witnessed the increasing interest in cesium lead halide perovskite quantum dots (PQDs) for their excellent optical properties with higher photoluminescence efficiency and tunable emission wavelengths widely applied in white LED, photovoltaic devices etc. Here we report the preparation of CsPbBr 3 PQDs by a facile anti-solvent method by using a conventional quaternary ammonium bromide  (CTAB) as a double modifier, both proper alkyl group protection and bromine source donator. The as-formed PQDs are well-monodispersed cube with a size of 10-15 nm and high photoluminescence quan...
Source: Chemistry - March 22, 2020 Category: Chemistry Authors: Liu J, Zhou J, Lin H, Yu Y, Zuo S, Li B Tags: Chemistry Source Type: research

Enhanced Photocatalytic Hydrogen Production by Hybrid Streptavidin-Diiron Catalysts.
Abstract Hybrid protein-organometallic catalysts are being explored for selective catalysis of a number of reactions, because they utilize the complementary strengths of proteins and of organometallic complex. Here, we present an artificial hydrogenase, StrepH2, built by incorporating a biotinylated [Fe-Fe] hydrogenase organometallic mimic within streptavidin. This strategy takes advantage of the remarkable strength and specificity of biotin-streptavidin recognition, which drives quantitative incorporation of the biotinylated diironhexacarbonyl center into streptavidin, as confirmed by UV-Vis spectroscopy and X-ra...
Source: Chemistry - March 22, 2020 Category: Chemistry Authors: Roy A, Vaughn M, Tomlin J, Booher G, Kodis G, Simmons C, Allen J, Ghirlanda G Tags: Chemistry Source Type: research

Discovery, synthesis and evaluation of a novel ketol-acid reductoisomerase inhibitor.
Abstract Ketol-acid reductoisomerase (KARI), the second enzyme in the branched-chain amino acid biosynthesis pathway, is a potential drug target for bacterial infections including Mycobacterium tuberculosis . Here, we have screened the Medicines for Malaria Venture Pathogen Box against purified M. tuberculosis ( Mt ) KARI and identified two compounds that have K i values below 200 nM. In Mt cell susceptibility assays one of these compounds exhibited an IC 50 value of 0.8 μM. Co-crystallization of this compound, 3-((methylsulfonyl)methyl)-2 H -benzo[ b ][1,4]oxazin-2-one (MMV553002), in complex with Staphylococc...
Source: Chemistry - March 21, 2020 Category: Chemistry Authors: Bayaraa T, Kurz JL, Patel KM, Hussein WM, Bilyj JK, West NP, Schenk G, McGeary RP, Guddat LW Tags: Chemistry Source Type: research

Regioselective Hydroformylation of Internal and Terminal Alkenes via Remote Supramolecular Control.
Abstract Regioselective catalytic transformations using supramolecular directing groups are increasingly popular as it allows for control over challenging reactions that may otherwise be impossible. In most examples the reactive group and the directing group are close to each other and/or the linker between the directing group is very rigid. Achieving control over the regioselectivity using a remote directing group with a flexible linker is significantly more challenging due to the large conformational freedom of such substrates. Herein, we report the redesign of a supramolecular Rh-bisphosphite hydroformylation c...
Source: Chemistry - March 21, 2020 Category: Chemistry Authors: Linnebank PR, Ferreira SF, Kluwer AM, Reek J Tags: Chemistry Source Type: research

Electronic Consequences of Ligand Substitution at Heterometal Centers in Polyoxovanadium Clusters: Controlling the Redox Properties via Heterometal Coordination Number.
Abstract The rational control of the electrochemical properties of polyoxovandate-alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, we examine the electronic consequences of ligand substitution at the heteroion in a heterometal-functionalized cluster. The redox properties of [V 5 O 6 (OCH 3 ) 12 FeCl] ( 1-[V 5 FeCl] ) and [V 5 O 6 (OCH 3 ) 12 Fe]X ( 2-[V 5 Fe]X ; X = ClO 4 , OTf), were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochem...
Source: Chemistry - March 20, 2020 Category: Chemistry Authors: Meyer RL, Anjass MH, Petel BE, Brennessel WW, Streb C, Matson EM Tags: Chemistry Source Type: research

The ABC of Insulin: The Organic Chemistry of a Small Protein.
ar NM Abstract Insulin is a small protein crucial for regulating the blood glucose level in all animals. Since 1922 it has been used for the treatment of patients with diabetes. Despite consisting of just 51 amino acids, insulin contains 17 of the proteinogenic amino acids, A- and B-chains, three disulfide bridges, and it folds with 3 a-helices and a short b-sheet segment. Insulin associates into dimers and further into hexamers with stabilization by Zn2+ and phenolic ligands. Selective chemical modification of proteins is at the forefront of developments in chemical biology and biopharmaceuticals. Insulin's struc...
Source: Chemistry - March 20, 2020 Category: Chemistry Authors: Jensen KJ, Østergaard M, Kumar NM Tags: Chemistry Source Type: research

Structural Changes of Hierarchically Nanoporous Organosilica/Silica Hybrid Materials by Pseudomorphic Transformation.
röba M Abstract Herein, we report how pseudomorphic transformation of divinylbenzene (DVB)-bridged organosilica@controlled pore glasses (CPG) offers the possibility to generate hierarchically porous organosilica/silica hybrid materials. CPG is utilized to provide granular shape/size and macroporosity and the macropores of the CPG is impregnated with organosilica phase, forming hybrid system. By subsequent pseudomorphic transformation, an ordered mesopore phase is generated while maintaining the granular shape and macroporosity of the CPG. Surface areas and mesopore sizes in the hierarchical structure are tuna...
Source: Chemistry - March 20, 2020 Category: Chemistry Authors: Bilo M, Münzner M, Küster C, Enke D, Lee YJ, Fröba M Tags: Chemistry Source Type: research

Ultrasensitive and selective copper (II) detection: introducing a bioinspired and robust sensor.
We report a nanopore-based Cu(II) sensing system which allows for an ultrasensitive and selective detection of Cu(II) with the possibility for a broad range of applications, i.e. medical diagnostics. A fluorescent ATCUN-like peptide 5/6-FAM-Dap-β-Ala-His is employed to selectively bind Cu(II) ions in the presence of Ni(II) and Zn(II) and was crafted into ion track-etched nanopores. Upon Cu(II) binding the fluorescence of the peptide sensor is quenched, permitting the detection of Cu(II) in solution. The ion transport characteristics of peptide-modified nanopore are shown to be extremely sensitive and selective towards...
Source: Chemistry - March 20, 2020 Category: Chemistry Authors: Müller LK, Duznovic I, Tietze D, Weber W, Ali M, Stein V, Ensinger W, Tietze A Tags: Chemistry Source Type: research

Boranediyl- and Diborane(4)-1,2-diyl-bridged Platinum A-Frame Complexes.
hweig H Abstract Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt02 complex. While structurally analogous to well-known μ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt-B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt-B σ bonds. This is experimentally reflected in the low kinetic sta...
Source: Chemistry - March 20, 2020 Category: Chemistry Authors: Brunecker C, Müssig JH, Arrowsmith M, Fantuzzi F, Stoy A, Böhnke J, Hofmann A, Bertermann R, Engels B, Braunschweig H Tags: Chemistry Source Type: research