bluuebunny/crossref_metadata_2025_split huggingface dataset:
PC‐Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine–Boranes
Authors: Johnson Heather C. , Weller Andrew S. 
Published: July 2015

Abstract{Rh(xantphos)}‐based phosphido dimers form by PC activation of xantphos (4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B⋅NMeH2 and dimeric [H2BNMe2]2 from H3B⋅NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization.
18F‐Labeling of Aryl‐SCF3, ‐OCF3 and ‐OCHF2 with [18F]Fluoride
Authors: Khotavivattana Tanatorn , Verhoog Stefan , Tredwell Matthew , Pfeifer Lukas , Calderwood Samuel , Wheelhouse Katherine , Lee Collier Thomas , Gouverneur Véronique 
Published: July 2015

AbstractWe report that halogenophilic silver(I) triflate permits halogen exchange (halex) nucleophilic 18F‐fluorination of aryl‐OCHFCl, ‐OCF2Br and ‐SCF2Br precursors under mild conditions. This AgI‐mediated process allows for the first time access to a range of 18F‐labeled aryl‐OCHF2, ‐OCF3 and ‐SCF3 derivatives, inclusive of [18F]riluzole. The 18F‐labeling of these medicinally important motifs expands the radiochemical space available for PET applications.
Aqueous Self‐Assembly of Purely Hydrophilic Block Copolymers into Giant Vesicles
Authors: Brosnan Sarah M. , Schlaad Helmut , Antonietti Markus 
Published: July 2015

AbstractSelf‐assembly of macromolecules is fundamental to life itself, and historically, these systems have been primitively mimicked by the development of amphiphilic systems, driven by the hydrophobic effect. Herein, we demonstrate that self‐assembly of purely hydrophilic systems can be readily achieved with similar ease and success. We have synthesized double hydrophilic block copolymers from polysaccharides and poly(ethylene oxide) or poly(sarcosine) to yield high molar mass diblock copolymers through oxime chemistry. These hydrophilic materials can easily assemble into nanosized (<500 nm) and microsized (>5 μm) polymeric vesicles depending on concentration and diblock composition. Because of the solely hydrophilic nature of these materials, we expect them to be extraordinarily water permeable systems that would be well suited for use as cellular mimics.
Covalent Protein Labeling by Enzymatic Phosphocholination
Authors: Heller Katharina , Ochtrop Philipp , Albers Michael F. , Zauner Florian B. , Itzen Aymelt , Hedberg Christian 
Published: July 2015

AbstractWe present a new protein labeling method based on the covalent enzymatic phosphocholination of a specific octapeptide amino acid sequence in intact proteins. The bacterial enzyme AnkX from Legionella pneumophila has been established to transfer functional phosphocholine moieties from synthetically produced CDP‐choline derivatives to N‐termini, C‐termini, and internal loop regions in proteins of interest. Furthermore, the covalent modification can be hydrolytically removed by the action of the Legionella enzyme Lem3. Only a short peptide sequence (eight amino acids) is required for efficient protein labeling and a small linker group (PEG‐phosphocholine) is introduced to attach the conjugated cargo.
Age‐Dependent Levels of 5‐Methyl‐, 5‐Hydroxymethyl‐, and 5‐Formylcytosine in Human and Mouse Brain Tissues
Authors: Wagner Mirko , Steinbacher Jessica , Kraus Theo F. J. , Michalakis Stylianos , Hackner Benjamin , Pfaffeneder Toni , Perera Arshan , Müller Markus , Giese Armin , Kretzschmar Hans A. , Carell Thomas 
Published: July 2015

AbstractThe absolute levels of 5‐hydroxymethylcytosine (hmC) and 5‐methylcytosine (mC) in human brain tissues at various ages were determined. Additionally, absolute levels of 5‐formylcytosine (fC) in adult individuals and cytosine modification levels in sorted neurons were quantified. These data were compared with age‐related fC, hmC, and mC levels in mouse brain samples. For hmC, an initial steady increase is observed, which levels off with age to a final steady‐state value of 1.2 % in human brain tissue. This level is nearly twice as high as in mouse cerebral cortex. In contrast, fC declines rapidly with age during early developmental stages, thus suggesting that while hmC is a stable epigenetic mark, fC is more likely an intermediate of active DNA demethylation during early brain development. The trends in global cytosine modification dynamics during the lifespan of an organism are conserved between humans and mice and show similar patterns in different organs.
One‐pot Unsymmetrical Ketone Synthesis Employing a Pyrrole‐Bearing Formal Carbonyl Dication Linchpin Reagent
Authors: Heller Stephen T. , Newton James N. , Fu Tingting , Sarpong Richmond 
Published: July 2015

AbstractA one‐pot procedure for the synthesis of unsymmetrical ketones utilizing a pyrrole‐bearing carbonyl linchpin reagent (carbonyl linchpin N,O‐dimethylhydroxylamine pyrrole; CLAmP) is reported. In contrast to other carbonyl dielectrophile equivalents, CLAmP enables the synthesis of ketones from a variety of organolithium and Grignard reagents. The electrophilic nature of CLAmP enables the addition of less reactive as well as thermally unstable nucleophiles. CLAmP was designed to form kinetically stable tetrahedral intermediates upon the addition of organometallic nucleophiles. Evidence for the existence of persistent tetrahedral intermediates was obtained through in situ IR studies.
Acid–Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization
Authors: Lewis Jennifer D. , Van de Vyver Stijn , Román‐Leshkov Yuriy 
Published: July 2015

AbstractHf‐, Sn‐, and Zr‐Beta zeolites catalyze the cross‐aldol condensation of aromatic aldehydes with acetone under mild reaction conditions with near quantitative yields. NMR studies with isotopically labeled molecules confirm that acid‐base pairs in the Si‐O‐M framework ensemble promote soft enolization through α‐proton abstraction. The Lewis acidic zeolites maintain activity in the presence of water and, unlike traditional base catalysts, in acidic solutions.
Dimeric TADDOL Phosphoramidites in Asymmetric Catalysis: Domino Deracemization and Cyclopropanation of Sulfonium Ylides
Authors: Klimczyk Sebastian , Misale Antonio , Huang Xueliang , Maulide Nuno 
Published: July 2015

AbstractA gold‐catalyzed asymmetric cyclopropanation of unactivated olefins with sulfonium ylides in the presence of a bimetallic catalyst with a novel dimeric TADDOL‐phosphoramidite ligand is reported. This transformation allows a rare gold‐catalyzed dynamic deracemization of chiral racemic substrates, where the same catalyst is responsible for several synergistic tasks in solution. The products are useful building blocks in synthesis and enable expeditious access to natural products.
Substrate‐Tuned Catalysis of the Radical S‐Adenosyl‐L‐Methionine Enzyme NosL Involved in Nosiheptide Biosynthesis
Authors: Ji Xinjian , Li Yongzhen , Ding Wei , Zhang Qi 
Published: July 2015

AbstractNosL is a radical S‐adenosyl‐L‐methionine (SAM) enzyme that converts L‐Trp to 3‐methyl‐2‐indolic acid, a key intermediate in the biosynthesis of a thiopeptide antibiotic nosiheptide. In this work we investigated NosL catalysis by using a series of Trp analogues as the molecular probes. Using a benzofuran substrate 2‐amino‐3‐(benzofuran‐3‐yl)propanoic acid (ABPA), we clearly demonstrated that the 5′‐deoxyadenosyl (dAdo) radical‐mediated hydrogen abstraction in NosL catalysis is not from the indole nitrogen but likely from the amino group of L‐Trp. Unexpectedly, the major product of ABPA is a decarboxylated compound, indicating that NosL was transformed to a novel decarboxylase by an unnatural substrate. Furthermore, we showed that, for the first time to our knowledge, the dAdo radical‐mediated hydrogen abstraction can occur from an alcohol hydroxy group. Our study demonstrates the intriguing promiscuity of NosL catalysis and highlights the potential of engineering radical SAM enzymes for novel activities.
Direct Imaging of Highly Anisotropic Photogenerated Charge Separations on Different Facets of a Single BiVO4 Photocatalyst
Authors: Zhu Jian , Fan Fengtao , Chen Ruotian , An Hongyu , Feng Zhaochi , Li Can 
Published: July 2015

AbstractSpatially resolved surface photovoltage spectroscopy (SRSPS) was employed to obtain direct evidence for highly anisotropic photogenerated charge separation on different facets of a single BiVO4 photocatalyst. Through the controlled synthesis of a single crystal with preferentially exposed {010} facets, highly anisotropic photogenerated hole transfer to the {011} facet of single BiVO4 crystals was observed. The surface photovoltage signal intensity on the {011} facet was 70 times stronger than that on the {010} facets. The influence of the built‐in electric field in the space charge region of different facets on the anisotropic photoinduced charge transfer in a single semiconductor crystal is revealed.
A Molecular Platform for Multistate Near‐Infrared Electrochromism and Flip‐Flop, Flip‐Flap‐Flop, and Ternary Memory
Authors: Cui Bin‐Bin , Tang Jian‐Hong , Yao Jiannian , Zhong Yu‐Wu 
Published: July 2015

AbstractA diruthenium complex with a redox‐active amine bridge has been designed, synthesized, and studied by single‐crystal X‐ray analysis and DFT and TDDFT calculations. It shows three well‐separated redox processes with exclusive near‐infrared (NIR) absorbance at each redox state. The electropolymerized film of a related vinyl‐functionalized complex displays multistate NIR electrochromism with low operational potential, good contrast ratio, and long retention time. Flip‐flop, flip‐flap‐flop, and ternary memories have been realized by using the obtained film (ca. 15–20 nm thick) with three electrochemical inputs and three NIR optical outputs that each displays three levels of signal intensity.
Synergistic Catalysis: Metal/Proton‐Catalyzed Cyclization of Alkynones Toward Bicyclo[3.n.1]alkanones
Authors: Zhu Shifa , Zhang Qiaohui , Chen Kai , Jiang Huanfeng 
Published: July 2015

AbstractA highly efficient and practical synergistically metal/proton‐catalyzed Conia–ene reaction for the synthesis of bicyclo[3.n.1]alkanones has been developed. This synergistic catalysis was successfully utilized in modifying natural compounds such as methyl dihydrojasmonate, α,β‐thujone, and 5α‐cholestan‐3‐one. Furthermore, the bridged carbonyl group of bicyclo[3.2.1]alkanones could be easily attacked by nucleophiles to give the ring‐opened cycloheptenone products or bicyclo[4.2.1]amide in excellent yields. These reactions provide rapid access to a diverse range of cyclic structures from simple starting materials or naturally occurring compounds.
Synthesis and properties of cross‐linked polymers from epoxidized rubber seed oil and triethylenetetramine
Authors: Abduh Muhammad Yusuf , Iqbal Muhammad , Picchioni Francesco , Manurung Robert , Heeres Hero J. 
Published: July 2015

ABSTRACTA series of epoxidized oils were prepared from rubber seed, soybean, jatropha, palm, and coconut oils. The epoxy content varied from 0.03 to 7.4 wt %, in accordance with the degree of unsaturation of the oils (lowest for coconut, highest for rubber seed oil). Bulk polymerization/curing of the epoxidized oils with triethylenetetramine (in the absence of a catalyst) was carried out in a batch setup (1 : 1 molar ratio of epoxide to primary amine groups, 100°C, 100 rpm, 30 min) followed by casting of the mixture in a steel mold (180°C, 200 bar, 21 h) and this resulted in cross‐linked resins. The effect of relevant pressing conditions such as time, temperature, pressure, and molar ratio of the epoxide and primary amine groups was investigated and modeled using multivariable nonlinear regression. Good agreement between experimental data and model were obtained. The rubber seed oil‐derived polymer has a Tg of 11.1°C, a tensile strength of 1.72 MPa, and strain at break of 182%. These values are slightly higher than for commercial epoxidized soybean oil (Tg of 6.9°C, tensile strength of 1.11 MPa, and strain at break of 145.7%). However, the comparison highlights the potential for these novel resins to be used at industrial/commercial level. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42591.
Uniform mPEG‐b‐PMETAC enables pH‐responsive delivery of insulin
Authors: Li Zongjun , Zhang Yifei , Lu Diannan , Liu Zheng 
Published: July 2015

ABSTRACTA cationic block copolymer (mPEG‐b‐PMETAC) with uniform molecular weight was synthesized using atom transfer radical polymerization. Insulin was reversibly encapsulated by mPEG‐b‐PMETAC via electrostatic interaction. The secondary and tertiary structures of insulin during the assembly and delivery processes were monitored by circular dichroism and fluorescence spectrum. The effects of pH and salt concentration on encapsulation were examined, respectively. Enhanced stability of the encapsulated insulin against proteolysis by trypsin and chymotrypsin was demonstrated. Insulin can be encapsulated and delivered from an mPEG‐b‐PMETAC assembly by tuning the pH and ionic strength, which determines the electrostatic interaction between insulin and the polymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42596.
Nitrile rubber/hindered phenol exterminated hyperbranched polyester materials with improved damping and mechanical performance
Authors: Yang Yuan , Zhao Yun‐Feng , Zhan Mao‐Sheng , Wang Jian‐Yue , Zhao Chuan , Liu Xiao‐Yan , Zhang Ji‐Hua 
Published: July 2015

ABSTRACTHindered phenol exterminated hyperbranched polyester (mHBP) is fabricated by esterification reaction. The mHBP is introduced into nitrile rubber (NBR) to prepare NBR/mHBP blends. Structure, damping and mechanical properties of NBR/mHBP blends are investigated by Fourier transform infrared spectroscopy (FTIR), 1H‐NMR, dynamic mechanical thermal analyzer (DMTA), and tensile tester. FTIR spectra of the blends illustrate the intermolecular hydrogen bonding between the NBR and mHBP, contributing to the improvement of damping and mechanical properties. The results indicate that, with the increasing mHBP content, the Tg of the blends shifted to a higher temperature with a broadening temperature range and improved mechanical properties, showing an application in adjusting the Tg and temperature range without decreasing of loss factor. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42605.
Chemical and bonding effects of exposing uncured PBI‐NBR insulation to ambient conditions
Authors: Parry Shawn , Pancoast Justin , Mildenhall Scott 
Published: July 2015

ABSTRACTUncured Polybenzimidazole‐Nitrile Butadiene Rubber (PBI‐NBR) insulation experiences altered chemical and bonding phenomena if exposed to ambient conditions while in a sheet‐stock configuration. Multiple lots of a PBI‐NBR formulation exposed to ambient and slightly elevated temperature (100°F) conditions experience bonding degradation when vulcanized to a metal substrate. Chemical analyses show that tallow amine (clay particle surfactant) accumulates at the surface of uncured NBR as a function of ambient and 100°F exposure time. Additionally, thin film analyses suggest surface oxidation of NBR polymers when exposed to the ambient environment. Mechanical and chemical observations imply a correlation between vulcanized bonding performance with tallow amine diffusion and polymer surface reaction. The diffusion and reactivity of chemical species found in the PBI‐NBR formulation has implications to other fields employing these components. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42636.
Immunohistochemical Studies of Cytoskeletal and Extracellular Matrix Components in Dogfish Scyliorhinuscanicula L. Notochordal Cells
Authors: Restović Ivana , Vukojević Katarina , Paladin Antonela , Saraga‐Babić Mirna , Bočina Ivana 
Published: July 2015

ABSTRACTImmunofluorescence and immunohistochemical techniques were used to define the distribution of cytoskeletal (cytokeratin 8, vimentin) and extracellular matrix components (collagen type I, collagen type II, hyaluronic acid, and aggrecan) and bone morphogenetic proteins 4 and 7 (BMP4 and BMP7) in the notochord of the lesser spotted dogfish Scyliorhinus canicula L. Immunolocalization of hyaluronic acid was observed in the notochord, vertebral centrum, and neural and hemal arches, while positive labeling to aggrecan was observed in the ossified centrum, notochord, and the perichondrium of the hyaline cartilage. Type I collagen was observed in the mineralized cartilage of the vertebral bodies, the notochord, the fibrocartilage of intervertebral disc, and the perichondrium. A positive labeling to type II collagen was observed in the inner part of the cartilaginous vertebral centrum and the notochord, as well as in the neural arch and muscle tissue, but there was no appreciable labeling of the hyaline cartilage. The presence of both BMP4 and BMP7 was seen in the mineralized vertebral centrum, notochordal cells, and neural arch. The notochordal cells expressed both cytokeratin 8 and vimentin, but predominantly vimentin. Hyaluronic acid, collagen type I, and collagen type II expression confirmed the presence of a mixture of notochordal and fibrocartilaginous tissue in the intervertebral disc, while BMPs confirmed the presence of an ossification in the cartilaginous skeleton of the spotted dogfish. Anat Rec, 298:1700–1709, 2015. © 2015 Wiley Periodicals, Inc.
Zugspannungs‐Dehnungs‐Beziehung für UHPFRC in Anlehnung an DAfStb‐Richtlinie Stahlfaserbeton
Authors: Oettel Vincent , Empelmann Martin 
Published: July 2015

AbstractIm Gegensatz zur einaxialen Betondruckfestigkeit, die sich relativ einfach an Zylindern oder Würfeln ermitteln lässt, ist die Erfassung der zentrischen Betonzugfestigkeit wesentlich aufwendiger, da die Lasteinleitung mit Schwierigkeiten verbunden ist. Daher bietet sich die indirekte Ermittlung der zentrischen Zugfestigkeit über einen Biegezugversuch an. In diesem Fall muss jedoch die im Biegezugversuch bestimmte Kraft‐Verformungs‐Kurve in eine Zugspannungs‐Dehnungs‐Linie umgerechnet werden. Um das Zugspannungs‐Dehnungs‐Verhalten von ultrahochfestem Faserbeton (UHPFRC) zu untersuchen, wurden am iBMB, Fachgebiet Massivbau der TU Braunschweig, 4‐Punkt‐Biegeversuche mit Standard‐Biegebalken 15/15/70 cm aus ultrahochfestem Fein‐ oder Grobkornbeton mit unterschiedlichen Faserschlankheiten und ‐gehalten durchgeführt. Aufbauend auf den Versuchsergebnissen wurde, in Anlehnung an die DAfStb‐Richtlinie Stahlfaserbeton, eine Zugspannungs‐Dehnungs‐Beziehung für UHPFRC hergeleitet und mit der Finite‐Elemente‐Methode (FEM) validiert.Tensile Stress‐Strain Relationship for UHPFRC on the basis of DAfStb‐Richtlinie StahlfaserbetonThe concrete compressive strength can be easily determined by using cylinders or cubes, whilst determing the axial concrete tensile strength is much more complex due to its load instruction. Therefore, the axial tensile strength can be determined indirectly by bending test. In this case, however, the load‐displacement curve determined of the bending test has to be converted into a tensile stress‐strain curve. In order to analyse the tensile stress‐strain behavior of ultra‐high performance fiber reinforced concrete (UHPFRC), the iBMB, Division of Concrete Construction of the TU Braunschweig, has conducted 4‐point bending tests with standard bending beams 15/15/70 cm made of UHPFRC‐mortar or UHPFRC‐concrete which differed in fiber slenderness and fiber content. A tensile stress‐strain relation for UHPFRC based on the DAfStb‐Richtlinie Stahlfaserbeton was derived from the experimental results and finally validated by applying the finite element method (FEM).
Betonbau bei chemischem Angriff – neue DBV‐Arbeitshilfen
Authors: Siebert Björn 
Published: July 2015

AbstractIn verschiedenen Anwendungsgebieten ist der Baustoff Beton hohen Beanspruchungen von außen, z. B. durch betonaggressive Wässer, ausgesetzt, die die Dauerhaftigkeit des Bauwerks beeinträchtigen können. Für einen chemischen Angriff in natürlichen Böden und Grundwässern bestehen normative Vorgaben, um den Angriffsgrad anhand der Art und Konzentration der angreifenden Stoffe in Expositionsklassen einzustufen. Ob und inwieweit die Einstufungen für Böden und Grundwässer auch auf andere Bereiche mit chemischem Angriff auf Beton, z. B. Kraftwerksbau, Abwasseranlagen, Biogasanlagen etc., zu übertragen sind, ist stets im Einzelfall zu überprüfen.Um Beton mit einem für die jeweilige Exposition adäquaten chemischen Widerstand auszustatten, sind in der Regel die betontechnologischen Vorgaben der einschlägigen Regelwerke ausreichend. Bei besonders starker Beanspruchung werden darüber hinaus zusätzliche Maßnahmen erforderlich, die sowohl die Betontechnologie als auch die Bauausführung betreffen können. Über die Art und den Umfang solcher im jeweiligen Anwendungsgebiet zusätzlich erforderlichen Maßnahmen wird in der Fachwelt kontrovers diskutiert.Diese Problemstellungen in der Praxis aufgreifend, hat der Deutsche Beton‐ und Bautechnik‐Verein E.V. neue Arbeitshilfen herausgegeben, in denen auf die derzeitige Vorgehensweise bei der Bewertung des chemischen Angriffsgrads in unterschiedlichen Anwendungsgebieten des Betonbaus und bei der Festlegung geeigneter Schutzprinzipien eingegangen wird.Concrete structures under chemical attack – new DBV Guide to Good PracticeIn various fields of application concrete is highly stressed by the environmental exposure, e. g. by aggressive water, which may affect the durability of the structure. There are normative guidelines dealing with the chemical attack in natural soil and ground water which allow a classification of the attack in exposition classes on basis of the type and concentration of the corrosive substances. Whether and to what extent the classification criteria for soils and groundwater are transferable to other areas with chemical attack on concrete, e. g. power plants, wastewater treatment plants, biogas plants, etc. must always be checked individually.In order to provide concrete with an adequate chemical resistance, the requirements for the concrete technology according to the general standards and regulations are usually sufficient. For particularly high stresses additional measures are needed which can affect both the concrete technology and the construction. A controversial debate among experts exists with respect to the type and extent of such measures required in the respective field of application.With focus on these practical issues, the German Society for Concrete and Construction Technology (DBV) has published a new Guide to Good Practice which provides the common procedure for the evaluation of a chemical attack on concrete in different fields of application and deals with appropriate protection principles.