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Chemical Science

Alejandro Méndez-Ardoy, Nagula Markandeya, Xuesong Li, Yu-Tang Tsai, Gilles Pecastaings, Thierry Buffeteau, Victor Maurizot, Luca Muccioli, Frédéric Castet, Ivan Huc, Dario M Bassani
Aromatic foldamers are bioinspired architectures whose potential use in materials remains largely unexplored. Here we report our investigation of vertical and horizontal charge transport over long distances in helical oligo-quinolinecarboxamide foldamers organized as single monolayers on Au or SiO2. Conductive atomic force microscopy showed that vertical conductivity is efficient and that it displays a low attenuation with foldamer length (0.06 Å(-1)). In contrast, horizontal charge transport is found to be negligible, demonstrating the strong anisotropy of foldamer monolayers...
October 1, 2017: Chemical Science
Grant J Sherborne, Sven Adomeit, Robert Menzel, Jabor Rabeah, Angelika Brückner, Mark R Fielding, Charlotte E Willans, Bao N Nguyen
A mechanistic investigation of Ullmann-Goldberg reactions using soluble and partially soluble bases led to the identification of various pathways for catalyst deactivation through (i) product inhibition with amine products, (ii) by-product inhibition with inorganic halide salts, and (iii) ligand exchange by soluble carboxylate bases. The reactions using partially soluble inorganic bases showed variable induction periods, which are responsible for the reproducibility issues in these reactions. Surprisingly, more finely milled Cs2CO3 resulted in a longer induction period due to the higher concentration of the deprotonated amine/amide, leading to suppressed catalytic activity...
October 1, 2017: Chemical Science
Nina G Bozhanova, Mikhail S Baranov, Natalia V Klementieva, Karen S Sarkisyan, Alexey S Gavrikov, Ilia V Yampolsky, Elena V Zagaynova, Sergey A Lukyanov, Konstantin A Lukyanov, Alexander S Mishin
We present protein-PAINT - the implementation of the general principles of PAINT (Point Accumulation for Imaging in Nanoscale Topography) for live-cell protein labeling. Our method employs the specific binding of cell-permeable fluorogenic dyes to genetically encoded protein tags. We engineered three mutants of the bacterial lipocalin Blc that possess different affinities to a fluorogenic dye and exhibit a strong increase in fluorescence intensity upon binding. This allows for rapid labeling and washout of intracellular targets on a time scale from seconds to a few minutes...
October 1, 2017: Chemical Science
Jiun-Le Shih, Santa Jansone-Popova, Christopher Huynh, Jeremy A May
An unusual transition metal-free cascade reaction of alkynyl carbonazidates was discovered to form azasilacyclopentenes. Mild thermolysis afforded the products via a series of cyclizations, rearrangements, and an α-silyl C-H bond insertion (rather than the more common Wolff rearrangement, 1,2-shift, or β-silyl C-H insertion) to form silacyclopropanes. A mechanistic proposal for the sequence was informed by control experiments and the characterization of reaction intermediates. The substrate scope and post-cascade transformations were also explored...
October 1, 2017: Chemical Science
Xiaoqiang Huang, Shipeng Luo, Olaf Burghaus, Richard D Webster, Klaus Harms, Eric Meggers
We report an unusual reaction design in which a chiral bis-cyclometalated rhodium(iii) complex enables the stereocontrolled chemistry of photo-generated carbon-centered radicals and at the same time catalyzes an enantioselective sulfonyl radical addition to an alkene. Specifically, employing inexpensive and readily available Hantzsch esters as the photoredox mediator, Rh-coordinated prochiral radicals generated by a selective photoinduced single electron reduction are trapped by allyl sulfones in a highly stereocontrolled fashion, providing radical allylation products with up to 97% ee...
October 1, 2017: Chemical Science
Ji Won Han, Jieun Jung, Yong-Min Lee, Wonwoo Nam, Shunichi Fukuzumi
Photocatalytic hydroxylation of benzene to phenol by dioxygen (O2) occurs under visible light irradiation of an O2-saturated acetonitrile solution containing [Ru(II)(Me2phen)3](2+) as a photocatalyst, [Co(III)(Cp*)(bpy)(H2O)](2+) as an efficient catalyst for both the water oxidation and benzene hydroxylation reactions, and water as an electron source in the presence of Sc(NO3)3. The present study reports the first example of photocatalytic hydroxylation of benzene with O2 and H2O, both of which are the most green reagents, under visible light irradiation to afford a high turnover number (e...
October 1, 2017: Chemical Science
Johannes Preindl, Shyamal Chakrabarty, Jérôme Waser
Many abundant and highly bioactive natural alkaloids contain an indolizidine skeleton. A simple, high yielding method to synthesize this scaffold from N-heterocycles was developed. A wide range of pyridines, quinolines and isoquinolines reacted with donor-acceptor (DA)-aminocyclopropanes via an ytterbium(iii) catalyzed [3 + 2] annulation reaction to give tetrahydroindolizine derivatives. The products were obtained with high diastereoselectivities (dr > 20 : 1) as anti-isomers. Additionally, the formed aminals could be easily converted into secondary and tertiary amines through iminium formation followed by reduction or nucleophile addition...
October 1, 2017: Chemical Science
Ekaterina Slavko, Mark S Taylor
Diarylborinic acids catalyze the formation of linear polyesters from glycerol, a trifunctional, carbohydrate-based monomer. The selective activation of 1,2-diols over isolated alcohols by the organoboron catalyst results in polymers that are essentially free of branching or cross-linking and possess a high fraction of 1,3-enchained glycerol units, as assessed by (1)H and (13)C NMR spectroscopy. The ability to generate well-defined polyester architectures from glycerol is significant in light of the numerous applications of such macromolecules, particularly in the biomedical area...
October 1, 2017: Chemical Science
Kaixiang Zhang, Ruijie Deng, Yupeng Sun, Ling Zhang, Jinghong Li
Chemically functionalized and nanostructured materials, which mimic the features of the natural extracellular matrix, provide a tool to organize cell surface receptors into nanoscale clusters and manipulate cell functions. However, the existing materials are mainly based on static structures. Herein, we developed a DNA based structure-switchable and multivalent material that acts as a 'nano-spring', enabling reversible control of membrane receptor function at the cell surface. This 'nano-spring' can be easily synthesized by rolling circle amplification and finely tuned by changing the circular template design...
October 1, 2017: Chemical Science
Georg Meisl, Luke Rajah, Samuel A I Cohen, Manuela Pfammatter, Anđela Šarić, Erik Hellstrand, Alexander K Buell, Adriano Aguzzi, Sara Linse, Michele Vendruscolo, Christopher M Dobson, Tuomas P J Knowles
The formation of filaments from naturally occurring protein molecules is a process at the core of a range of functional and aberrant biological phenomena, such as the assembly of the cytoskeleton or the appearance of aggregates in Alzheimer's disease. The macroscopic behaviour associated with such processes is remarkably diverse, ranging from simple nucleated growth to highly cooperative processes with a well-defined lagtime. Thus, conventionally, different molecular mechanisms have been used to explain the self-assembly of different proteins...
October 1, 2017: Chemical Science
Cheng Jin, Ting Fu, Ruowen Wang, Hui Liu, Jianmei Zou, Zilong Zhao, Mao Ye, Xiaobing Zhang, Weihong Tan
Molecular beacons (MBs) are simple, but practical, fluorescent nanoprobes widely used to detect small molecules, nucleic acids and proteins. However, some challenges still remain when MBs are employed in complex biological environments, such as instability and non-target interference. To meet such challenges, we have designed and synthesized fluorinated molecular beacons (FMBs) as functional DNA nanomolecules for cellular imaging, in which the stem sequence is simply composed of artificial nucleotides with 3,5-bis(trifluoromethyl)benzene (F) as the surrogate base of natural A, T, C and G bases...
October 1, 2017: Chemical Science
Guillaume De Bo, David A Leigh, Charlie T McTernan, Shoufeng Wang
A pair of enantioselective switchable bifunctional catalysts are shown to promote a range of conjugate addition reactions in up to 95 : 5 e.r. and 95% conversion. Each catalyst can be switched OFF using conditions that switch the other catalyst ON. Catalyst ON : OFF ratios of up to 98 : 2 and 1 : 99 were achieved, with a ratio of reaction rates of up to 16 : 1 between the ON and OFF states, maintained over complete ON-OFF-ON and OFF-ON-OFF cycles. However, simultaneous operation of the catalyst pair in the same reaction vessel, which in principle could allow product handedness to be switched by simple E-Z isomerisation of the catalyst pair, was unsuccessful...
October 1, 2017: Chemical Science
K Delaney Hook, John T Chambers, Ryan Hili
We have developed a novel high-throughput screening platform for the discovery of small-molecules catalysts for bond-forming reactions. The method employs an in vitro selection for bond-formation using amphiphilic DNA-encoded small molecules charged with reaction substrate, which enables selections to be conducted in a variety of organic or aqueous solvents. Using the amine-catalysed aldol reaction as a catalytic model and high-throughput DNA sequencing as a selection read-out, we demonstrate the 1200-fold enrichment of a known aldol catalyst from a library of 16...
October 1, 2017: Chemical Science
Dominic Auerhammer, Merle Arrowsmith, Holger Braunschweig, Rian D Dewhurst, J Oscar C Jiménez-Halla, Thomas Kupfer
The reaction of [(cAAC(Me))BH3] (cAAC(Me) = 1-(2,6-(i)Pr2C6H3)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) with a range of organolithium compounds led to the exclusive formation of the corresponding (dihydro)organoborates, Li(+)[(cAAC(Me)H)BH2R](-) (R = sp(3)-, sp(2)-, or sp-hybridised organic substituent), by migration of one boron-bound hydrogen atom to the adjacent carbene carbon of the cAAC ligand. A subsequent deprotonation/salt metathesis reaction with Me3SiCl or spontaneous LiH elimination yielded the neutral cAAC-supported mono(organo)boranes, [(cAAC(Me))BH2R]...
October 1, 2017: Chemical Science
Virginia Mazzini, Vincent S J Craig
The importance of electrolyte solutions cannot be overstated. Beyond the ionic strength of electrolyte solutions the specific nature of the ions present is vital in controlling a host of properties. Therefore ion specificity is fundamentally important in physical chemistry, engineering and biology. The observation that the strengths of the effect of ions often follows well established series suggests that a single predictive and quantitative description of specific-ion effects covering a wide range of systems is possible...
October 1, 2017: Chemical Science
Yubing Huang, Xianwei Li, Xu Wang, Yue Yu, Jia Zheng, Wanqing Wu, Huanfeng Jiang
Sulfur-containing nitriles have important research value in the life sciences due to their diverse biological activities resulting from the sulfur and cyano functional groups. Herein, a copper-catalyzed cyanothiolation of N-tosylhydrazones with thiocyanates to generate α-arylthioalkanenitriles bearing sulfur-substituted quaternary carbon center atoms has been described. This novel protocol involves the procedure of copper carbene species promoting S-CN bond cleavage and C-CN/C-S bond reconstruction to introduce both sulfur and cyano groups onto a single carbon center...
October 1, 2017: Chemical Science
Iván Rivilla, Abel de Cózar, Thomas Schäfer, Frank J Hernandez, Alexander M Bittner, Aitziber Eleta-Lopez, Ali Aboudzadeh, José I Santos, José I Miranda, Fernando P Cossío
A novel catalytic system based on covalently modified DNA is described. This catalyst promotes 1,3-dipolar reactions between azomethine ylides and maleimides. The catalytic system is based on the distortion of the double helix of DNA by means of the formation of Pt(ii) adducts with guanine units. This distortion, similar to that generated in the interaction of DNA with platinum chemotherapeutic drugs, generates active sites that can accommodate N-metallated azomethine ylides. The proposed reaction mechanism, based on QM(DFT)/MM calculations, is compatible with thermally allowed concerted (but asynchronous) [π4s + π2s] mechanisms leading to the exclusive formation of racemic endo-cycloadducts...
October 1, 2017: Chemical Science
Kun Ho Kenny Park, Rui Chen, David Y-K Chen
Herein we report a rationally designed, serial point-to-axial and axial-to-point stereoinduction and its integration into multi-step and target-oriented organic synthesis. In this proof-of-concept study, the configurational stability of several carefully designed atropisomeric intermediates and the fidelity of their unconventional stereoinductions were systematically investigated. The highly functionalized prepared synthetic intermediate was further applied in a novel chemical method to access the morphinans and it is potentially applicable to other structurally related alkaloids...
October 1, 2017: Chemical Science
Haibin Xiao, Chuanchen Wu, Ping Li, Wen Gao, Wen Zhang, Wei Zhang, Lili Tong, Bo Tang
As one of the complications of diabetes, liver injury results in significant hazards. Therefore, accurately diagnosing diabetes-induced liver injury beforehand is crucial for the warning and treatment of hepatic diseases. Diabetes-induced liver injury can cause changes in the microstructure and morphology of liver tissue, leading to changes in the hydrophilic and hydrophobic domains in the endoplasmic reticulum (ER), which is closely associated with changes in cellular ER polarity. So, differences in the ER polarity can indicate the degree of diabetes-induced liver injury...
October 1, 2017: Chemical Science
Lei Zhang, Xile Hu
Photoredox catalysis has been developed to achieve oxidative C-H chlorination of aromatic compounds using NaCl as the chlorine source and Na2S2O8 as the oxidant. The reactions occur at room temperature and exhibit exclusive selectivity for C(sp(2))-H bonds over C(sp(3))-H bonds. The method has been used for the chlorination of a diverse set of substrates, including the expedited synthesis of key intermediates to bioactive compounds and a drug.
October 1, 2017: Chemical Science
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