bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elektronische Kommunikation zwischen zwei [10]Cycloparaphenylenen und Bisazafulleren (C59N)2 induziert durch kooperative Komplexierung
Authors: Rio Jérémy , Beeck Sebastian , Rotas Georgios , Ahles Sebastian , Jacquemin Denis , Tagmatarchis Nikos , Ewels Chris , Wegner Hermann A. 
Published: March 2018

AbstractEin Komplex aus [10]Cycloparaphenylen ([10]CPP) mit dem Bisazafulleren (C59N)2 wurde experimentell und computerchemisch untersucht. In dieser Struktur sind zwei [10]CPP‐Ringe an das dimere Azafulleren gebunden, [10]CPP⊃(C59N)2⊂[10]CPP. Die beobachteten photophysikalischen und Redox‐Eigenschaften lassen auf eine elektronische Interaktion zwischen den Komponenten schließen, insbesondere mit dem zweiten [10]CPP. Im Gegensatz zu [10]CPP⊃C60, in dem nur eine vernachlässigbare elektronische Kommunikation zwischen den Komponenten beobachtet wurde, konnte zwischen dem [10]CPP und dem (C59N)2 durch Lichtanregung ein Ladungstransferphänomen induziert werden, ähnlich einem mit einem CPP eingekapselten Metallofulleren. Solch elektronenreiche Fullerenspezies zeigen C60‐artige Grundzustandseigenschaften und verhalten sich im angeregten Zustand wie Metallofullerene. Diese Eigenschaft eröffnet neue Möglichkeiten für die Konstruktion von funktionalen supramolekularen Architekturen mit organischen Materialien.
Biokatalytische Oxidationsreaktionen – aus der Sicht eines Chemikers
Authors: Dong JiaJia , Fernández‐Fueyo Elena , Hollmann Frank , Paul Caroline E. , Pesic Milja , Schmidt Sandy , Wang Yonghua , Younes Sabry , Zhang Wuyuan 
Published: March 2018

AbstractEnzyme gewinnen immer mehr Bedeutung als Katalysatoren für organische Oxidationsreaktionen. Mit Oxidoreduktasen stehen dem Chemiker vielseitige Werkzeuge für selektive und effiziente Oxidationsreaktionen zur Verfügung. Ihr Spektrum reicht von einfachen Alkoholoxidationen bis hin zur stereoselektiven Halogenierung nicht‐aktivierter C‐H‐Bindungen. Für viele biokatalytische Oxidationen ist bisher kein chemisches Pendant bekannt. Daher ermöglichen Oxidoreduktasen kürzere Syntheserouten. Darüber hinaus sind die generell milderen Reaktionsbedingungen biokatalytischer Oxidationen attraktiv. In diesem Aufsatz fassen wir einige aktuelle Entwicklungen im Bereich der biokatalytischen Oxidation zusammen. Wir beschreiben auch derzeitige Grenzen und vielversprechende Lösungsansätze.
Ein weiterer “unerhörter” Wieland‐Mechanismus bestätigt: Wasserstoffbildung aus Wasserstoffperoxid, Formaldehyd und Natriumhydroxid
Authors: Czochara Robert , Litwinienko Grzegorz , Korth Hans‐Gert , Ingold Keith U. 
Published: March 2018

Abstract1923 berichteten Wieland und Wingler, dass an der Wasserstoff‐produzierenden Reaktion von Wasserstoffperoxid mit Formaldehyd in basischer Lösung keine freien Wasserstoffatome (H.) beteiligt sind. Sie postulierten als Zwischenstufe Bis(hydroxymethyl)peroxid (HOCH2OOCH2OH), das anschließend in H2 und Formiat zerfällt und schlugen einen Mechanismus vor, der heutzutage als “konzertierter Prozess” betrachtet würde. Seit dieser Zeit wurden verschiedene andere (widersprüchliche) “Mechanismen” vorgeschlagen. NMR‐ und Raman‐spektroskopische sowie kinetische Untersuchungen, speziell die Bestimmung des Deuterium‐kinetischen Isotopeneffekts (DKIE), belegen nun, dass in dieser basenabhängigen Reaktion beide H‐Atome im H2 von der CH2‐Gruppe des Formaldehyds stammen und nicht von den OH‐Gruppen von HOCH2OOCH2OH oder Wasser. Quantenchemische CBS‐QB3‐ und W1BD‐Rechnungen bestätigen, dass die H2‐Freisetzung über einen konzertierten Prozess verläuft, der durch doppelte Deprotonierung von HOCH2OOCH2OH stark beschleunigt wird. Ein Weg über freie Radikale kann ausgeschlossen werden.
Reversible Magnetic Agglomeration: A Mechanism for Thermodynamic Control over Nanoparticle Size
Authors: Bleier Grant C. , Watt John , Simocko Chester K. , Lavin Judith M. , Huber Dale L. 
Published: March 2018

AbstractWe present a method for the synthesis and precise size control of magnetic nanoparticles in a reversible magnetic agglomeration mechanism. In this approach, nanoparticles nucleate and grow until a critical susceptibility is reached, in which magnetic attraction overcomes dispersive forces, leading to agglomeration and precipitation. This phase change in the system arrests nanoparticle growth and gives true thermodynamic control over the size of nanoparticles. We then show that increasing the alkyl chain length of the surfactant, and hence increasing steric stabilization, allows nanoparticles to grow to larger sizes before agglomeration occurs. Therefore, simply by choosing the correct surfactant, the size and magnetic properties of iron nanoparticles can be tailored for a particular application. With the continuous addition of the precursor solution, we can repeat the steps of nucleation, growth, and magnetic agglomeration indefinitely, making the approach suitable for large scale syntheses.
Catalytic Enantioselective 1,3‐Alkyl Shift in Alkyl Aryl Ethers: Efficient Synthesis of Optically Active 3,3′‐Diaryloxindoles
Authors: Gade Amol B. , Bagle Pradip N. , Shinde Popat S. , Bhardwaj Vipin , Banerjee Subhrashis , Chande Ajit , Patil Nitin T. 
Published: March 2018

AbstractReported is the first organocatalytic asymmetric 1,3‐alkyl shift in alkyl aryl ethers for the synthesis of chiral 3,3′‐diaryloxindoles using a chiral Brønsted acid catalyst. Preliminary results showed that each enantiomer of the 3,3′‐diaryloxindole, and a racemic mixture, showed different antiproliferative activities against HeLa cell lines by using an MTT assay.
Charge Transport between Coupling Colloidal Perovskite Quantum Dots Assisted by Functional Conjugated Ligands
Authors: Dai Jinfei , Xi Jun , Li Lu , Zhao JingFeng , Shi Yifei , Zhang Wenwen , Ran Chenxin , Jiao Bo , Hou Xun , Duan Xinhua , Wu Zhaoxin 
Published: March 2018

AbstractLong alkyl‐chain capping ligands are indispensable for preparing stable colloidal quantum dots. However, its insulating feature blocks efficient carrier transport among QDs, leading to inferior performance in light‐emitting diodes (LEDs). The trade‐off between conductivity and colloidal stability of QDs has now been overcome. Methylamine lead bromide (MAPbBr3) QDs with a conjugated alkyl‐amine, 3‐phenyl‐2‐propen‐1‐amine (PPA), as ligands were prepared. Owing to electron cloud overlapping and the delocalization effect of conjugated molecules, the conductivity and carrier mobility of PPA‐QDs films increased almost 22 times over that of OA‐QD films without compromising colloidal stability and photoluminescence. PPA‐QDs LEDs exhibit a maximum current efficiency of 9.08 cd A−1, which is 8 times of that of OA‐QDs LEDs (1.14 cd A−1). This work provides critical solution for the poor conductivity of QDs in applications of energy‐related devices.
Synthesis of Non‐Classical Arylated C‐Saccharides through Nickel/Photoredox Dual Catalysis
Authors: Dumoulin Audrey , Matsui Jennifer K. , Gutiérrez‐Bonet Álvaro , Molander Gary A. 
Published: March 2018

AbstractThe development of synthetic tools to introduce saccharide derivatives into functionally complex molecules is of great interest, particularly in the field of drug discovery. Herein, we report a new route toward highly functionalized, arylated saccharides, which involves nickel‐catalyzed cross‐coupling of photoredox‐generated saccharyl radicals with a range of aryl‐ and heteroaryl bromides, triggered by an organic photocatalyst. In contrast to existing methods, the mild reaction conditions achieve arylation of saccharide motifs while leaving the anomeric carbon available, thus providing access to a class of arylated glycosides that has been underexplored until now. To demonstrate the potential of this strategy in late‐stage functionalization, a variety of structurally complex molecules incorporating saccharide moieties were synthesized.
Biosynthesis of the Polycyclic System in the Antifungal HSAF and Analogues from Lysobacter enzymogenes
Authors: Li Yaoyao , Wang Haoxin , Liu Yan , Jiao Yujie , Li Shanren , Shen Yuemao , Du Liangcheng 
Published: March 2018

AbstractThe biocontrol agent Lysobacter enzymogenes produces polycyclic tetramate macrolactams (PoTeMs), including the antifungal HSAF. To elucidate the biosynthesis of the cyclic systems, we identified eleven HSAF precursors/analogues with zero, one, two, or three rings through heterologous expression of the HSAF gene cluster. A series of combinatorial gene expression and deletion experiments showed that OX3 is the “gatekeeper” responsible for the formation of the first 5‐membered ring from lysobacterene A, OX1 and OX2 are responsible for formation of the second ring but with different selectivity, and OX4 is responsible for formation of the 6‐membered ring. In vitro experiments showed that OX4 is an NADPH‐dependent enzyme that catalyzes the reductive cyclization of 3‐dehydroxy alteramide C to form 3‐dehydroxy HSAF. Thus, the multiplicity of OX genes is the basis for the structural diversity of the HSAF family, which is the only characterized PoTeM cluster that involves four redox enzymes in the formation of the cyclic system.
Revealing the Formation Mechanism of CsPbBr3 Perovskite Nanocrystals Produced via a Slowed‐Down Microwave‐Assisted Synthesis
Authors: Li Yanxiu , Huang He , Xiong Yuan , Kershaw Stephen V. , Rogach Andrey L. 
Published: March 2018

AbstractWe developed a microwave‐assisted slowed‐down synthesis of CsPbBr3 perovskite nanocrystals, which retards the reaction and allows us to gather useful insights into the formation mechanism of these nanoparticles, by examining the intermediate stages of their growth. The trends in the decay of the emission intensity of CsPbBr3 nanocrystals under light exposure are well correlated with their stability against decomposition in TEM under electron beam. The results show the change of the crystal structure of CsPbBr3 nanocrystals from a deficient and easier to be destroyed lattice to a well crystallized one. Conversely the shift in the ease of degradation sheds light on the formation mechanism, indicating first the formation of a bromoplumbate ionic scaffold, with Cs‐ion infilling lagging a little behind. Increasing the cation to halide ratio towards the stoichiometric level may account for the improved radiative recombination rates observed in the longer reaction time materials.
Biocatalytic Oxidation Reactions: A Chemist's Perspective
Authors: Dong JiaJia , Fernández‐Fueyo Elena , Hollmann Frank , Paul Caroline E. , Pesic Milja , Schmidt Sandy , Wang Yonghua , Younes Sabry , Zhang Wuyuan 
Published: March 2018

AbstractOxidation chemistry using enzymes is approaching maturity and practical applicability in organic synthesis. Oxidoreductases (enzymes catalysing redox reactions) enable chemists to perform highly selective and efficient transformations ranging from simple alcohol oxidations to stereoselective halogenations of non‐activated C−H bonds. For many of these reactions, no “classical” chemical counterpart is known. Hence oxidoreductases open up shorter synthesis routes based on a more direct access to the target products. The generally very mild reaction conditions may also reduce the environmental impact of biocatalytic reactions compared to classical counterparts. In this Review, we critically summarise the most important recent developments in the field of biocatalytic oxidation chemistry and identify the most pressing bottlenecks as well as promising solutions.
Trimethylsilyl‐Protected Alkynes as Selective Cross‐Coupling Partners in Titanium‐Catalyzed [2+2+1] Pyrrole Synthesis
Authors: Chiu Hsin‐Chun , Tonks Ian A. 
Published: March 2018

AbstractTrimethylsilyl (TMS)‐protected alkynes served as selective alkyne cross‐coupling partners in titanium‐catalyzed [2+2+1] pyrrole synthesis. Reactions of TMS‐protected alkynes with internal alkynes and azobenzene under the catalysis of titanium imido complexes yielded pentasubstituted 2‐TMS‐pyrroles with greater than 90 % selectivity over the other nine possible pyrrole products. The steric and electronic effects of the TMS group were both identified to play key roles in this highly selective pyrrole synthesis. This strategy provides a convenient method to synthesize multisubstituted pyrroles as well as an entry point for further pyrrole diversification through facile modification of the resulting 2‐silyl pyrrole products, as demonstrated through a short formal synthesis of the marine natural product lamellarin R.
Reaction of B2(o‐tol)4 with CO and Isocyanides: Cleavage of the C≡O Triple Bond and Direct C−H Borylations
Authors: Katsuma Yuhei , Tsukahara Nana , Wu Linlin , Lin Zhenyang , Yamashita Makoto 
Published: March 2018

AbstractThe reaction of highly Lewis acidic tetra(o‐tolyl)diborane(4) with CO afforded a mixture of boraindane and boroxine by the cleavage of the C≡O triple bond. 13C labeling experiments confirmed that the carbon atom in the boraindane stems from CO. Simultaneously, formation of boroxine 3 could be considered as borylene transfer to capture the oxygen atom from CO. The reaction of diborane(4) with tBu−NC afforded an azaallene, while the reaction with Xyl−NC furnished cyclic compounds by direct C−H borylations.
The Chemistry behind Catechol‐Based Adhesion
Authors: Saiz‐Poseu J. , Mancebo‐Aracil J. , Nador F. , Busqué F. , Ruiz‐Molina D. 
Published: March 2018

AbstractThe adhesion of some marine organisms to almost any kind of surface in wet conditions has aroused increasing interest in recent decades. Numerous fundamental studies have been performed to understand the scientific basis of this behaviour, with catechols having been found to play a key role. Several novel bio‐inspired adhesives and coatings with value‐added performances have been developed by taking advantage of the knowledge gained from these studies. To date there has been no detailed overview focusing exclusively on the complex mode of action of these materials. The aim of this Review is to present recent investigations that elucidate the origin of the strong and versatile adsorption capacities of the catechol moiety and the effects of extrinsic factors that play important roles in the overall adhesion process, such as pH value, solvent, and the presence of metal ions. The aim is to detail the chemistry behind the astonishing properties of natural and synthetic catechol‐based adhesive materials.
Highly Stereoselective Synthesis of 1,3‐Dienes through an Aryl to Vinyl 1,4‐Palladium Migration/Heck Sequence
Authors: Hu Tian‐Jiao , Li Meng‐Yao , Zhao Qian , Feng Chen‐Guo , Lin Guo‐Qiang 
Published: March 2018

AbstractAn efficient aryl to vinyl 1,4‐palladium migration/Heck sequence was developed for the stereoselective synthesis of 1,3‐dienes. High stereoselectivity was observed not only for 1,3‐dienes bearing two similar aryl groups at terminal positions, but also for those with configurations shown to be unfavorable with previous methods.
Ultrastable Imine‐Based Covalent Organic Frameworks for Sulfuric Acid Recovery: An Effect of Interlayer Hydrogen Bonding
Authors: Halder Arjun , Karak Suvendu , Addicoat Matthew , Bera Saibal , Chakraborty Amit , Kunjattu Shebeeb H. , Pachfule Pradip , Heine Thomas , Banerjee Rahul 
Published: March 2018

AbstractA rapid and scalable synthesis of six new imine‐linked highly porous and crystalline COFs is presented that feature exceptionally high chemical stability in harsh environments including conc. H2SO4 (18 m), conc. HCl (12 m), and NaOH (9 m). This is because of the presence of strong interlayer C−H⋅⋅⋅N hydrogen bonding among the individual layers, which provides significant steric hindrance and a hydrophobic environment around the imine (−C=N−) bonds, thus preventing their hydrolysis in such an abrasive environment. These COFs were further converted into porous, crystalline, self‐standing, and crack‐free COF membranes (COFMs) with extremely high chemical stability for their potential applications for sulfuric acid recovery. The as‐synthesized COFMs exhibit unprecedented permeance for acetonitrile (280 Lm−2 h−1 bar−1) and acetone (260 Lm−2 h−1 bar−1).
High Electromagnetic Field Enhancement of TiO2 Nanotube Electrodes
Authors: Öner Ibrahim Halil , Querebillo Christine Joy , David Christin , Gernert Ulrich , Walter Carsten , Driess Matthias , Leimkühler Silke , Ly Khoa Hoang , Weidinger Inez M. 
Published: March 2018

AbstractWe present the fabrication of TiO2 nanotube electrodes with high biocompatibility and extraordinary spectroscopic properties. Intense surface‐enhanced resonance Raman signals of the heme unit of the redox enzyme Cytochrome b5 were observed upon covalent immobilization of the protein matrix on the TiO2 surface, revealing overall preserved structural integrity and redox behavior. The enhancement factor could be rationally controlled by varying the electrode annealing temperature, reaching a record maximum value of over 70 at 475 °C. For the first time, such high values are reported for non‐directly surface‐interacting probes, for which the involvement of charge‐transfer processes in signal amplification can be excluded. The origin of the surface enhancement is exclusively attributed to enhanced localized electric fields resulting from the specific optical properties of the nanotubular geometry of the electrode.
Ethylene diamine grafted nanoporous UiO‐66 as an efficient basic catalyst in the multi‐component synthesis of 2‐aminithiophenes
Authors: Erfaninia N. , Tayebee R. , Dusek M. , Amini M.M. 
Published: March 2018

This study demonstrates ED‐UiO‐66 as a novel and effective solid nanoporous basic catalyst prepared through the amine grafting onto the pores of UiO‐66. The manufactured nanoparticles were identified by FT‐IR, XRD, TGA, FESEM, TEM, CHN and BET and the characterization results certified formation of a single phase nanoporous substance with the medium grain size less than 90 nm. The synthesized material was employed as an efficient catalyst for the preparation of 2‐aminotiophenes through the Gewald method. This thermochemically stable nanocatalyst was environmentally safe, reusable and economic. Therefore, this methodology can be simply extended for industrial goals.
Model free kinetics coupled with finite element method for curing simulation of thermosetting epoxy resins
Authors: Tao Qi , Pinter Gerald , Antretter Thomas , Krivec Thomas , Fuchs Peter 
Published: March 2018

ABSTRACTA finite element method algorithm for epoxy curing degree simulation was developed in Abaqus by integrating the discretized analytical solution of the model free kinetics into its user subroutines. This method was verified by nonisothermal and isothermal DSC experiments of an epoxy resin. By means of this method, the real manufacturing press cycle could be simulated regarding temperature distribution and curing degree with advanced curing degree‐dependent material properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46408.
Morphology and performance of poly(vinylidene fluoride) flat sheet membranes: Thermodynamic and kinetic aspects
Authors: Enayatzadeh Mohammad , Mohammadi Toraj 
Published: March 2018

ABSTRACTIn this study, poly(vinylidene fluoride) (PVDF) membranes were prepared using two different solvents with various polymer concentrations to investigate the predominant kinetic or thermodynamic aspects of membrane preparation in a phase separation process. For this purpose, dimethyl sulfoxide (DMSO) as a weak solvent and N‐2‐methylpyrrolidone (NMP) as a strong solvent were used with polymer concentrations between 8 and 15 wt %. Scanning electron microscopy and water content, contact angle, and pore size measurements were used to assess the factors affecting the physicochemical properties of the prepared membranes. The results showed that in the case of NMP, the membrane structure is mainly controlled by thermodynamic parameters, while when using DMSO, kinetic parameters are predominant. According to the results, the prepared PVDF‐based membranes with DMSO exhibited a relatively denser top layer and less permeation compared to the NMP/PVDF membranes. The difference between the viscosities of the casting solutions with equal polymer concentrations in DMSO and NMP was considered to be the main effective factor in solvent/nonsolvent exchange, resulting in denser top layers in the DMSO/PVDF membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46419.
Electrospinning preparation of a graphene oxide nanohybrid proton‐exchange membrane for fuel cells
Authors: Zhang Shaopeng , Li Dan , Kang Jingxin , Ma Guiping , Liu Yong 
Published: March 2018

ABSTRACTProton‐exchange membrane (PEM) is a core component of fuel cells that provides a channel for proton migration and transport. Prevailing PEMs fabricated using well‐established casting techniques have several limitations such as low proton conductivity, high fuel permeability, and poor stability. To overcome these shortcomings, this article introduces a graphene oxide (GO)‐based nanohybrid Nafion nanofiber membrane prepared using a facile electrospinning technique. On the one hand, electrospinning nanofibers provide efficient transport paths for protons, which tremendously enhance the proton conductivity. On the other hand, GO doping in PEM improves the self‐humidification, stabilities (mechanical, thermal, and chemical), and proton conductivity and reduces the fuel permeability. In this research, nanofiber membranes were obtained from Nafion solutions containing 0, 0.1, and 0.2 wt % GO via electrospinning. The morphology, structure, mechanical properties, proton conductivity, water uptake, and swelling properties of the membranes were studied. The results demonstrated that the comprehensive performance of PEM was significantly improved. The new findings may promote the wide application of PEM fuel cells. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2018,135, 46443.
Influence of the morphological structure of carbon nanotubes on the viscoelasticity of PMMA‐based nanocomposites
Authors: Lin Xiang , Li Ke , Gough Timothy , Coates Phil , Wang Dongrui , Zhang Liang 
Published: March 2018

ABSTRACTThe rheological behavior of polymeric nanocomposites provides major determination for their processability. In this work, three carbon nanotubes (CNTs) with varied geometries were adopted as nanofiller and then were introduced into poly(methyl methacrylate) (PMMA) matrix with different loadings (0.07–1.0 wt %). The different preparation routine led to varied CNTs dispersion states, on which the shear viscosity and the compressibility of their melts were proved to be sensitive. The technology for the preparation of their nanocomposites played a crucial role in controlling their rheological behavior. With melting blended bare CNTs, the dynamic shear viscosity of PMMA/CNTs increased with the increase of CNTs content, accompanied by aggregated CNTs in which no polymer matrix was entrapped. With the help of surface modification and pre‐mixing, well dispersed CNTs were obtained and a rather low aggregation rate ca. 0.029% was revealed. The well dispersed CNTs with an organic layer which was constructed by small molecules and presented lower viscosity. Such CNTs led to no remarkable clusters within polymer host and played the role of lubricant with an increased‐mobility layer, which can be reflected from the weighted relaxation time spectra. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46444.