bluuebunny/crossref_metadata_2025_split huggingface dataset:
Iron‐Catalyzed Direct Diazidation for a Broad Range of Olefins
Authors: Yuan Yong‐An , Lu Deng‐Fu , Chen Yun‐Rong , Xu Hao 
Published: November 2015

AbstractReported herein is a new iron‐catalyzed diastereoselective olefin diazidation reaction which occurs at room temperature (1–5 mol % of catalysts and d.r. values of up to >20:1). This method tolerates a broad range of both unfunctionalized and highly functionalized olefins, including those that are incompatible with existing methods. It also provides a convenient approach to vicinal primary diamines as well as other synthetically valuable nitrogen‐containing building blocks which are difficult to obtain with alternative methods. Preliminary mechanistic studies suggest that the reaction may proceed through a new mechanistic pathway in which both Lewis acid activation and iron‐enabled redox‐catalysis are crucial for selective azido‐group transfer.
Probing the Lipid Annular Belt by Gas‐Phase Dissociation of Membrane Proteins in Nanodiscs
Authors: Marty Michael T. , Hoi Kin Kuan , Gault Joseph , Robinson Carol V. 
Published: November 2015

AbstractInteractions between membrane proteins and lipids are often crucial for structure and function yet difficult to define because of their dynamic and heterogeneous nature. Here, we use mass spectrometry to demonstrate that membrane protein oligomers ejected from nanodiscs in the gas phase retain large numbers of lipid interactions. The complex mass spectra that result from gas‐phase dissociation were assigned using a Bayesian deconvolution algorithm together with mass defect analysis, allowing us to count individual lipid molecules bound to membrane proteins. Comparison of the lipid distributions measured by mass spectrometry with molecular dynamics simulations reveals that the distributions correspond to distinct lipid shells that vary according to the type of protein–lipid interactions. Our results demonstrate that nanodiscs offer the potential for native mass spectrometry to probe interactions between membrane proteins and the wider lipid environment.
Layered Electron Acceptors by Dimerization of Acenes End‐ Capped with 1,2,5‐Thiadiazoles
Authors: Xia Debin , Guo Xin , Chen Long , Baumgarten Martin , Keerthi Ashok , Müllen Klaus 
Published: November 2015

AbstractLayered electron acceptors D1–4 equipped with terminal 1,2,5‐thiadiazole groups have been constructed using a one‐pot protocol of acene dimerization. Their molecular structures are determined using single‐crystal X‐ray diffraction analysis. Photophysical and electrochemical properties of these molecules present a marked dependence on conjugation length and molecular geometry. An aggregation‐induced emission peak and an intramolecular excimer emission (IEE) band were observed for D2 and D4, respectively. This work paves the way for the efficient synthesis of layered heteroacenes.
Visible‐Light Photoredox‐Catalyzed C−H Difluoroalkylation of Hydrazones through an Aminyl Radical/Polar Mechanism
Authors: Xu Pan , Wang Guoqiang , Zhu Yuchen , Li Weipeng , Cheng Yixiang , Li Shuhua , Zhu Chengjian 
Published: November 2015

AbstractAn unprecedented visible‐light‐induced direct C−H bond difluoroalkylation of aldehyde‐derived hydrazones was developed. This reaction represents a new way to synthesize substituted hydrazones. The salient features of this reaction include difluorinated hydrazone synthesis rather than classical amine synthesis, extremely mild reaction conditions, high efficiency, wide substrate scope, ease in further transformations of the products, and one‐pot syntheses. Mechanistic analyses and theoretical calculations indicate that this reaction is enabled by a novel aminyl radical/polar crossover mechanism, with the aminyl radical being oxidized into the corresponding aminyl cation through a single electron transfer (SET) process.
Plasmonic Surfaces for Cell Growth and Retrieval Triggered by Near‐Infrared Light
Authors: Giner‐Casares Juan J. , Henriksen‐Lacey Malou , García Isabel , Liz‐Marzán Luis M. 
Published: November 2015

AbstractMethods for efficient detachment of cells avoiding damage are required in tissue engineering and regenerative medicine. We introduce a bottom–up approach to build plasmonic substrates using micellar block copolymer nanolithography to generate a 2D array of Au seeds, followed by chemical growth leading to anisotropic nanoparticles. The resulting plasmonic substrates show a broad plasmon band covering a wide part of the visible and near‐infrared (NIR) spectral ranges. Both human and murine cells were successfully grown on the substrates. A simple functionalization step of the plasmonic substrates with the cyclic arginylglycylaspartic acid (c‐RGD) peptide allowed us to tune the morphology of integrin‐rich human umbilical vein endothelial cells (HUVEC). Subsequent irradiation with a NIR laser led to highly efficient detachment of the cells with cell viability confirmed using the MTT assay. We thus propose the use of such plasmonic substrates for cell growth and controlled detachment using remote near‐IR irradiation, as a general method for cell culture in biomedical applications.
A Self‐Assembled Respiratory Chain that Catalyzes NADH Oxidation by Ubiquinone‐10 Cycling between Complex I and the Alternative Oxidase
Authors: Jones Andrew J. Y. , Blaza James N. , Bridges Hannah R. , May Benjamin , Moore Anthony L. , Hirst Judy 
Published: November 2015

AbstractComplex I is a crucial respiratory enzyme that conserves the energy from NADH oxidation by ubiquinone‐10 (Q10) in proton transport across a membrane. Studies of its energy transduction mechanism are hindered by the extreme hydrophobicity of Q10, and they have so far relied on native membranes with many components or on hydrophilic Q10 analogues that partition into membranes and undergo side reactions. Herein, we present a self‐assembled system without these limitations: proteoliposomes containing mammalian complex I, Q10, and a quinol oxidase (the alternative oxidase, AOX) to recycle Q10H2 to Q10. AOX is present in excess, so complex I is completely rate determining and the Q10 pool is kept oxidized under steady‐state catalysis. The system was used to measure a fully‐defined KM value for Q10. The strategy is suitable for any enzyme with a hydrophobic quinone/quinol substrate, and could be used to characterize hydrophobic inhibitors with potential applications as pharmaceuticals, pesticides, or fungicides.
Practical Organocatalytic Synthesis of Functionalized Non‐C2‐Symmetrical Atropisomeric Biaryls
Authors: Gao Hongyin , Xu Qing‐Long , Keene Craig , Yousufuddin Muhammed , Ess Daniel H. , Kürti László 
Published: November 2015

AbstractAn organic acid catalyzed direct arylation of aromatic C(sp2)H bonds in phenols and naphthols for the preparation of 1,1′‐linked functionalized biaryls was developed. The products are non‐C2‐symmetrical, atropoisomeric, and represent previously untapped chemical space. Overall this transformation is operationally simple, does not require an external oxidant, is readily scaled up (up to 98 mmol), and the structurally diverse 2,2′‐dihydroxy biaryl (i.e., BINOL‐type), as well as 2‐amino‐2′‐hydroxy products (i.e., NOBIN‐type) are formed with complete regioselectivity. Density‐functional calculations suggest that the quinone and imino‐quinone monoacetal coupling partners are exclusively arylated at their α‐position by an asynchronous [3,3]‐sigmatropic rearrangement of a mixed acetal species which is formed in situ under the reaction conditions.
Three‐dimensional Carbon Nitride/Graphene Framework as a High‐Performance Cathode for Lithium‐Ion Batteries
Authors: Huang Yanshan , Tang Yanping , Mai Yiyong , Wang Xinjing , Wang Chi , Han Sheng , Zhang Fan , Wu Dongqing , Feng Xinliang 
Published: November 2015

AbstractA three‐dimensional polymeric carbon nitride/graphene framework (CN/GF) was fabricated by the ionic self‐assembly of graphene oxide and protonated polymeric carbon nitride nanosheets. As the cathode material in lithium‐ion batteries, CN/GF showed an excellent reversible capacity of 184 mA h g−1 at 0.05 A g−1 for 150 cycles and maintained the capacity of 60 mA h g−1 at 5 A g−1.
De Novo Design of Xeno‐Metallo Coiled Coils
Authors: Slope Louise N. , Peacock Anna F. A. 
Published: November 2015

AbstractBioinorganic chemists aspire to achieve the same exquisite and highly controlled inorganic chemistry featured in biology. An exciting mimetic approach involves the use of miniature artificial protein scaffolds designed de novo (often based on the coiled coil (CC) scaffold), for reproducing native metal ion sites and their function. Recently, there is increased interest, instead, in the design of xeno‐metal sites within CC assemblies. This involves incorporating either non‐biological metal ions, cofactors or non‐proteinogenic amino acid ligands for metal ion coordination, whilst retaining a minimal CC protein scaffold. Using this approach, one should be able to create functional designs with unique and unusual properties, which combine the advantages of both biology and ‘traditional’ non‐biological inorganic chemistry. It is the recent progress with respect to the design of xeno‐metallo CCs which will be discussed in this Focus Review.
Expression, purification, and characterization of mouse nesfatin‐1 in Escherichia coli
Authors: Xiao Chunlan , Liu Junyi , Tang Yanchun , Chen Junyong , Wu Xiaopeng , Bi Feng , Zhang Jing 
Published: November 2015

AbstractNesfatin‐1 is a newly discovered satiety molecule expressed mainly in the hypothalamic nuclei. It suppresses both short‐term and long‐term appetite. Six synthetic deoxyoligonucleotides overlapped by PCR encoding nesfatin‐1 were cloned into a pET28a vector after the hexa‐histidine‐tagged multiple cloning sites sequence with an enterokinase recognition site incorporated in‐between. The recombinant plasmid was transformed into Escherichia coli strain Rosetta to express the fusion protein, which constituted 27% of the total cell proteins. After purified by Ni‐sepharose affinity chromatography, the fusion protein was treated with enterokinase to release nesfatin‐1. The nesfatin‐1 sample was further purified with reverse‐phase high performance liquid chromatography (HPLC), and its molecular weight was determined by mass spectrometry. The biological activities of recombinant nesfatin‐1 were also assessed using in vivo animal models. The method described here promises to produce about 8 mg biologically active nesfatin‐1 with homogeneity over 98% from 1‐L shaking flask culture of E. coli, which can be considered as an easy and cost‐effective way to synthesize nesfatin‐1.
Optimization of thermophilic trans‐isoprenyl diphosphate synthase expression in Escherichia coli by response surface methodology
Authors: Piccolomini Angelica A. , Fiabon Alex , Borrotti Matteo , De Lucrezia Davide 
Published: November 2015

AbstractWe optimized the heterologous expression of trans‐isoprenyl diphosphate synthase (IDS), the key enzyme involved in the biosynthesis of trans‐polyisoprene. trans‐Polyisoprene is a particularly valuable compound due to its superior stiffness, excellent insulation, and low thermal expansion coefficient. Currently, trans‐polyisoprene is mainly produced through chemical synthesis and no biotechnological processes have been established so far for its large‐scale production. In this work, we employed D‐optimal design and response surface methodology to optimize the expression of thermophilic enzymes IDS from Thermococcus kodakaraensis. The design of experiment took into account of six factors (preinduction cell density, inducer concentration, postinduction temperature, salt concentration, alternative carbon source, and protein inhibitor) and seven culture media (LB, NZCYM, TB, M9, Ec, Ac, and EDAVIS) at five different pH points. By screening only 109 experimental points, we were able to improve IDS production by 48% in close‐batch fermentation.
Reactivity Controlling Factors for an Aromatic Carbon‐Centered σ,σ,σ‐Triradical: The 4,5,8‐Tridehydroisoquinolinium Ion
Authors: Vinueza Nelson R. , Jankiewicz Bartłomiej J. , Gallardo Vanessa A. , LaFavers Gregory Z. , DeSutter Dane , Nash John J. , Kenttämaa Hilkka I. 
Published: November 2015

AbstractThe chemical properties of the 4,5,8‐tridehydroisoquinolinium ion (doublet ground state) and related mono‐ and biradicals were examined in the gas phase in a dual‐cell Fourier‐transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The triradical abstracted three hydrogen atoms in a consecutive manner from tetrahydrofuran (THF) and cyclohexane molecules; this demonstrates the presence of three reactive radical sites in this molecule. The high (calculated) electron affinity (EA=6.06 eV) at the radical sites makes the triradical more reactive than two related monoradicals, the 5‐ and 8‐dehydroisoquinolinium ions (EA=4.87 and 5.06 eV, respectively), the reactivity of which is controlled predominantly by polar effects. Calculated triradical stabilization energies predict that the most reactive radical site in the triradical is not position C4, as expected based on the high EA of this radical site, but instead position C5. The latter radical site actually destabilizes the 4,8‐biradical moiety, which is singlet coupled. Indeed, experimental reactivity studies show that the radical site at C5 reacts first. This explains why the triradical is not more reactive than the 4‐dehydroisoquinolinium ion because the C5 site is the intrinsically least reactive of the three radical sites due to its low EA. Although both EA and spin–spin coupling play major roles in controlling the overall reactivity of the triradical, spin–spin coupling determines the relative reactivity of the three radical sites.
Gold‐ or Silver‐Catalyzed Syntheses of Pyrones and Pyridine Derivatives: Mechanistic and Synthetic Aspects
Authors: Preindl Johannes , Jouvin Kévin , Laurich Daniel , Seidel Günter , Fürstner Alois 
Published: November 2015

Abstract3‐Oxo‐5‐alkynoic acid esters, on treatment with a carbophilic catalyst, undergo 6‐endo‐dig cyclization reactions to furnish either 2‐pyrones or 4‐pyrones in high yields. The regiochemical course can be dialed in by the proper choice of the alcohol part of the ester and the π‐acid. This transformation is compatible with a variety of acid‐sensitive groups as witnessed by a number of exigent applications to the total synthesis of natural products, including pseudopyronine A, hispidine, phellinin A, the radininol family, neurymenolide, violapyrone, wailupemycin and an unnamed brominated 4‐pyrone of marine origin. Although the reaction proceeds well in neutral medium, the rate is largely increased when HOAc is used as solvent or co‐solvent, which is thought to favor the protodeauration of the reactive alkenyl‐gold intermediates as the likely rate‐determining step of the catalytic cycle. Such intermediates are prone to undergo diauration as an off‐cycle event that sequesters the catalyst; this notion is consistent with literature data and supported by the isolation of the gem‐diaurated complexes 12 and 15. Furthermore, silver catalysis allowed access to be gained to 2‐alkoxypyridine and 2‐alkoxyisoquinoline derivatives starting from readily available imidate precursors.
Dual Lewis Acid/Lewis Base Catalyzed Acylcyanation of Aldehydes: A Mechanistic Study
Authors: Laurell Nash Anna , Hertzberg Robin , Wen Ye‐Qian , Dahlgren Björn , Brinck Tore , Moberg Christina 
Published: November 2015

AbstractA mechanistic investigation, which included a Hammett correlation analysis, evaluation of the effect of variation of catalyst composition, and low‐temperature NMR spectroscopy studies, of the Lewis acid–Lewis base catalyzed addition of acetyl cyanide to prochiral aldehydes provides support for a reaction route that involves Lewis base activation of the acyl cyanide with formation of a potent acylating agent and cyanide ion. The cyanide ion adds to the carbonyl group of the Lewis acid activated aldehyde. O‐Acylation by the acylated Lewis base to form the final cyanohydrin ester occurs prior to decomplexation from titanium. For less reactive aldehydes, the addition of cyanide is the rate‐determining step, whereas, for more reactive, electron‐deficient aldehydes, cyanide addition is rapid and reversible and is followed by rate‐limiting acylation. The resting state of the catalyst lies outside the catalytic cycle and is believed to be a monomeric titanium complex with two alcoholate ligands, which only slowly converts into the product.
From an Isolable Acyclic Phosphinosilylene Adduct to Donor‐Stabilized SiE Compounds (E=O, S, Se)
Authors: Hansen Kerstin , Szilvási Tibor , Blom Burgert , Irran Elisabeth , Driess Matthias 
Published: November 2015

AbstractReaction of the arylchlorosilylene‐NHC adduct ArSi(NHC)Cl [Ar=2,6‐Trip2C6H3; NHC=(MeC)2(NMe)2C:] 1 with one molar equiv of lithium diphenylphosphanide affords the first stable NHC‐stabilized acyclic phosphinosilylene adduct 2 (ArSi(NHC)PPh2), which could be structurally characterized. Compound 2, when reacted with one molar equiv selenium and sulfur, affords the silanechalcogenones 4 a and 4 b (ArSi(NHC)(E)PPh2, 4 a: E=Se, 4 b: E=S), respectively. Conversion of 2 with an excess of Se and S, through additional insertion of one chalcogen atom into the SiP bond, leads to 3 a and 3 b (ArSi(NHC)(E)‐E‐P(E)Ph2, 3 a: E=Se, 3 b: E=S), respectively. Additionally, the exposure of 2 to N2O or CO2 yielded the isolable NHC‐stabilized silanone 4 c, Ar(NHC)(Ph2P)SiO.
Fluid dynamics study of the flow and pressure drop analysis of a non‐Newtonian fluid through annular ducts with unusual cross‐sections
Authors: Bicalho Isabele Cristina , Mognon José Lucas , Ataíde Carlos Henrique , Duarte Claudio Roberto 
Published: November 2015

AbstractThis paper concerns an experimental and computational study of the laminar flow developed by a pseudoplastic fluid through a partially‐obstructed annulus, considering the effects of eccentricity and inner cylinder rotation. For the eccentric cases the eccentric rotation of the inner tube is applied, which is a novelty in the literature. Pressure drop experimental data are reported for flows of 3 and 9 m3/h of a 1 mg/g xanthan gum aqueous solution through a concentric and a 46 % eccentric annulus with partial obstruction of 6 mm, for cases with and without rotation of the inner cylinder (0 and 400 rpm). Numerical simulations were performed using computational fluid dynamics (CFD) techniques which allowed for reporting of axial velocity profiles, apparent viscosity distribution, and pressure drops for a range of eccentricity values (0, 23, and 46 %) and obstruction heights (0, 6, and 12 mm), which were systematically compared for cases with and without rotation of the inner tube (0 and 400 rpm). Comparisons between numerical calculations and the flow data indicated, in general, very close agreement. Eccentric rotation of the inner cylinder presented a distortion effect on the axial velocity and apparent viscosity profiles for the high eccentricity case (46 %) with high obstruction (12 mm), where two maxima regions were observed, one of them near the inner cylinder.
The Molecular Basis for Dual Fatty Acid Amide Hydrolase (FAAH)/Cyclooxygenase (COX) Inhibition
Authors: Palermo Giulia , Favia Angelo D. , Convertino Marino , De Vivo Marco 
Published: November 2015

AbstractThe design of multitarget‐directed ligands is a promising strategy for discovering innovative drugs. Here, we report a mechanistic study that clarifies key aspects of the dual inhibition of the fatty acid amide hydrolase (FAAH) and the cyclooxygenase (COX) enzymes by a new multitarget‐directed ligand named ARN2508 (2‐[3‐fluoro‐4‐[3‐(hexylcarbamoyloxy)phenyl]phenyl]propanoic acid). This potent dual inhibitor combines, in a single scaffold, the pharmacophoric elements often needed to block FAAH and COX, that is, a carbamate moiety and the 2‐arylpropionic acid functionality, respectively. Molecular modeling and molecular dynamics simulations suggest that ARN2508 uses a noncovalent mechanism of inhibition to block COXs, while inhibiting FAAH via the acetylation of the catalytic Ser241, in line with previous experimental evidence for covalent FAAH inhibition. This study proposes the molecular basis for the dual FAAH/COX inhibition by this novel hybrid scaffold, stimulating further experimental studies and offering new insights for the rational design of novel anti‐inflammatory agents that simultaneously act on FAAH and COX.
Reversible Photoisomerization of Spiropyran on the Surfaces of Au25 Nanoclusters
Authors: Udayabhaskararao T. , Kundu Pintu K. , Ahrens Johannes , Klajn Rafal 
Published: November 2015

AbstractAu25 nanoclusters functionalized with a spiropyran molecular switch are synthesized via a ligand‐exchange reaction at low temperature. The resulting nanoclusters are characterized by optical and NMR spectroscopies as well as by mass spectrometry. Spiropyran bound to nanoclusters isomerizes in a reversible fashion when exposed to UV and visible light, and its properties are similar to those of free spiropyran molecules in solution. The reversible photoisomerization entails the modulation of fluorescence as well as the light‐controlled self‐assembly of nanoclusters.
Functionalization of Highly Substituted 2,2′:6′,2″‐Terpyridine Derivatives
Authors: Hommes Paul , Reissig Hans‐Ulrich 
Published: November 2015

AbstractOn the basis of an easy access to 2,2′:6′,2″‐terpyridine derivatives bearing 6‐ and 6″‐methyl groups, the functionalization of these substituents was investigated. The direct oxidation or bromination of the methyl groups was not feasible on larger scale; however, a two‐step process employing oxidation to the pyridine N‐oxides followed by acetic anhydride promoted rearrangement (Boekelheide reaction) furnished the corresponding terpyridine derivatives with 6‐ and 6″‐acetoxymethyl groups in reasonable overall yields. These are excellent precursors for the synthesis of tetra‐ and pentadentate ligands, as demonstrated by several examples. This approach allowed access to a library of new functionalized 2,2′:6′,2″‐terpyridine derivatives.
On Forecasting Conflict in the Sudan: 2009–2012
Authors: Bessler David A. , Kibriya Shahriar , Chen Junyi , Price Edwin 
Published: November 2015

AbstractThis paper considers univariate and multivariate models to forecast monthly conflict events in the Sudan over the out‐of‐sample period 2009–2012. The models used to generate these forecasts were based on a specification from a machine learning algorithm fit to 2000–2008 monthly data. The model that includes previous month's wheat price performs better than a similar model which does not include past wheat prices (the univariate model). Both models did not perform well in forecasting conflict in a neighborhood of the 2012 ‘Heglig crisis’. Copyright © 2015 John Wiley & Sons, Ltd.