bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multicomponent Syntheses based upon Copper‐Catalyzed Alkyne‐Azide Cycloaddition
Authors: Hassan Sidra , Müller Thomas J. J. 
Published: February 2015

AbstractThe copper‐catalyzed alkyne‐azide cycloaddition (CuAAC) is a highly versatile, regioselective synthesis of 1,4‐disubstituted 1,2,3‐triazoles under mild reaction conditions and has found numerous applications in medicinal, bioorganic, and materials chemistry in the past one and a half decades. By virtue of the enormous tolerance for functional groups and the mild reaction conditions, CuAAC has become increasingly important in combination with multicomponent reactions (MCR), either in a domino or in a consecutive fashion. While the majority of CuAAC‐based MCR are founded on the in situ or en route generation of azides, one‐pot generation of alkynes and the concatenation with other MCR are rapidly catching up and novel sequences for efficient one‐pot syntheses of triazole‐based structures in a multicomponent fashion are constantly evolving. This review summarizes important contributions of CuAAC‐based MCR including MCR‐type applications in polymer science.magnified image
Palladium‐Catalyzed Construction of Spirooxindoles by Arylative Cyclization of 3‐(γ,δ‐Disubstituted)allylidene‐2‐Oxindoles
Authors: Kim Ko Hoon , Moon Hye Ran , Lee Junseong , Kim Jae Nyoung 
Published: February 2015

AbstractThe palladium‐catalyzed, one‐pot arylative cyclization of 3‐(γ,δ‐disubstituted)allylidene‐2‐oxindoles afforded spirodihydronaphthalene‐2‐oxindole frameworks via an oxidative Heck arylation (Fujiwara–Moritani reaction), an allylic palladium migration, and an aryl CH bond functionalization/arylation cascade of reactions. This is a first example of the palladium‐catalyzed oxidative arylation and an aryl CH bond functionalization/arylation cascade reaction which involves an electrophilic arylative quenching of a π‐allylpalladium intermediate and a regio‐controlled aryl CH bond activation assisted by a weak palladium‐arene interaction.magnified image
Sodium Iodide‐Catalyzed Direct α‐Alkoxylation of Ketones with Alcohols via Oxidation of α‐Iodo Ketone Intermediates
Authors: Zhu Cuiju , Zhang Yuanfei , Zhao Huaiqing , Huang Shijun , Zhang Min , Su Weiping 
Published: February 2015

AbstractThe direct α‐alkoxylation of ketones with alcohols via a sodium iodide‐catalyzed oxidative cross‐coupling has been developed. This protocol enables a range of alkyl aryl ketones to cross‐couple with an array of alcohols in synthetically useful yields. The mechanistic studies provided solid evidence supporting that an α‐iodo ketone was a key reaction intermediate, being converted into an α‐alkoxylated ketone via further oxidation to a hypervalent iodine species rather than a common nucleophilic substitution, and was generated from the ketone starting material via a radical intermediate. These new mechanism insights should have an effect on the design of iodide‐catalyzed oxidative cross‐coupling reactions between nucleophiles.magnified image
Metal‐Free, Room‐Temperature, Radical Alkoxycarbonylation of Aryldiazonium Salts through Visible‐Light Photoredox Catalysis
Authors: Guo Wei , Lu Liang‐Qiu , Wang Yue , Wang Ya‐Ni , Chen Jia‐Rong , Xiao Wen‐Jing 
Published: February 2015

AbstractThe first radical alkoxycarboxylation of aryldiazonium salts using CO gas through visible‐light‐induced photoredox catalysis (16 W blue LEDs) has been developed. This reaction is entirely metal‐free, is carried out at room temperature with a low loading of an organic dye as a photocatalyst (0.5 mol %), and provides a wide range of arylcarboxylic acid esters in high yields. Importantly, this photocatalytic system can be successfully extended to other carboxylation reactions.
Selektive Kontrolle der Bildung von Calciumsulfat‐Polymorphen bei Raumtemperatur
Authors: Tritschler Ulrich , Van Driessche Alexander E. S. , Kempter Andreas , Kellermeier Matthias , Cölfen Helmut 
Published: February 2015

AbstractCalciumsulfat ist ein in der Natur weit verbreitetes und technologisch wichtiges Mineral mit breitem Anwendungsspektrum. Allerdings stellte die Kontrolle der CaSO4‐Polymorphie und damit der Materialeigenschaften nach wie vor eine beträchtliche Herausforderung dar, und bis jetzt gibt es keine universelle Methode für die selektive Herstellung der verschiedenen hydratisierten und wasserfreien Formen unter milden Bedingungen. Hier berichten wir über die erste erfolgreiche Synthese von reinem Anhydrit aus einer Lösung bei Raumtemperatur. Erreicht wurde dies durch Ausfällen von Calciumsulfat in alkoholischen Medien mit niedrigen Wassergehalten. Durch Variieren der Wassermenge gelang es uns außerdem, zwischen einzelnen Polymorphen zu schalten und das Ergebnis der Reaktion fein abzustimmen, um entweder eine gewünschte CaSO4‐Phase in reiner Form oder binäre Mischungen mit festgelegten Zusammensetzungen herzustellen. Das Konzept bietet die volle Kontrolle über die Auswahl der Phasen in der CaSO4‐Mineralisation und könnte die gezielte Herstellung entsprechender Materialien für diverse Anwendungsgebiete ermöglichen.
Natriumionenbatterien für die elektrochemische Energiespeicherung
Authors: Kundu Dipan , Talaie Elahe , Duffort Victor , Nazar Linda F. 
Published: February 2015

AbstractFortschrittliche Energiespeichertechnologien sind von immenser Bedeutung für tragbare elektronische Geräte, Elektrofahrzeuge, die Stromspeicherung in Kraftwerken und den Lastausgleich von Stromnetzen auf der Basis erneuerbarer Energien wie Solarenergie und Windkraft. Für die ersten zwei dieser Anwendungen haben sich Lithiumionenbatterien erfolgreich bewährt. Für die zwei letzteren Fälle scheint es jedoch sinnvoll, einen Schritt weiterzugehen – hin zum nächsten Alkalimetall im Periodensystem, dem Natrium. Eine flächendeckende Einführung von Natriumionenbatterien erfordert deren intensive Erforschung, einschließlich der Entdeckung neuer Materialien und ihrer Elektrochemie. Dieser Aufsatz fasst den aktuellen Stand der Forschung auf dem Gebiet der Natriumionenbatterien zusammen.
Excimers Beyond Pyrene: A Far‐Red Optical Proximity Reporter and its Application to the Label‐Free Detection of DNA
Authors: Han Garam , Kim Dongwook , Park Younbong , Bouffard Jean , Kim Youngmi 
Published: February 2015

AbstractA family of organic chromophores that, like pyrene, forms emissive excimers is reported. Their chemical and photophysical properties are superior to pyrene for the design of chemo‐ and biosensors. Unlike hydrophobic pyrene, which requires excitation by cell‐damaging UV irradiation, these polar dyes absorb strongly in the visible range, and their excimers emit brightly in the red to far‐red region of the electromagnetic spectrum. The intensity of the emission signal is greatly increased upon formation of a preassociated dimer that is triggered upon aggregation or crystallization. In demonstration of the potential of this new family of excimer‐forming dyes, a probe that is capable of detecting label‐free DNA in water down to 10 pM and also doubles as a visualization agent for DNA in gel electrophoresis is reported.
Perfekte Raumfüllung – Fullerengäste in sternförmigen Oligophenylenvinylen‐Mesogenen
Authors: Lehmann Matthias , Hügel Markus 
Published: February 2015

AbstractSternförmige Oligophenylenvinylen(OPV)‐Mesogene sind formtreu und weisen formal zwischen ihren Armen große Freiräume auf. Ein Mesogen mit Armen aus drei Phenylenethenylen‐Wiederholungseinheiten packt dicht in einer kolumnar‐helikalen Anordnung. Das Anbringen eines Fullerens über einen kurzen Abstandhalter (Spacer) führt zu einer außergewöhnlichen Erhöhung der Mesophasenstabilität. Röntgenstreuung und Modellierung bestätigen die Selbstorganisation zur Tripelhelix, in der Fullerene den Freiraum zwischen den Armen der Sternmesogene perfekt ausfüllen.
Formale anti‐Carbopalladierungen nicht‐aktivierter Alkine: Voraussetzungen, mechanistische Untersuchungen und Anwendungen
Authors: Pawliczek Martin , Schneider Tobias F. , Maaß Christian , Stalke Dietmar , Werz Daniel B. 
Published: February 2015

AbstractFormale anti‐Carbopalladierungsreaktionen von C‐C‐Dreifachbindungen sind ungewöhnliche, aber äußerst nützliche Transformationen. Alkine, die gezielt anti‐Carbopalladierungsprodukte ergeben, werden vorgestellt. Voraussetzung ist der Ausschluss anderer Reaktionswege, um eine cis‐trans‐Isomerisierung der entstehenden Doppelbindung zu ermöglichen. Der entscheidende mechanistische Schritt wurde sowohl experimentell als auch theoretisch untersucht. Eine intramolekulare Version der Reaktion ermöglicht die einfache Herstellung sowohl von oligocyclischen Produkten als auch von Dibenzofuranen.
The Kinetic Isotope Effect as a Probe of Spin Crossover in the CH Activation of Methane by the FeO+ Cation
Authors: Mai Binh Khanh , Kim Yongho 
Published: February 2015

AbstractTwo‐state reactivity (TSR) is often used to explain the reaction of transition‐metal–oxo reagents in the bare form or in the complex form. The evidence of the TSR model typically comes from quantum‐mechanical calculations for energy profiles with a spin crossover in the rate‐limiting step. To prove the TSR concept, kinetic profiles for CH activation by the FeO+ cation were explored. A direct dynamics approach was used to generate potential energy surfaces of the sextet and quartet H‐transfers and rate constants and kinetic isotope effects (KIEs) were calculated using variational transition‐state theory including multidimensional tunneling. The minimum energy crossing point with very large spin–orbit coupling matrix element was very close to the intrinsic reaction paths of both sextet and quartet H‐transfers. Excellent agreement with experiments were obtained when the sextet reactant and quartet transition state were used with a spin crossover, which strongly support the TSR model.
Fragment Screening and Druggability Assessment for the CBP/p300 KIX Domain through Protein‐Observed 19F NMR Spectroscopy
Authors: Gee Clifford T. , Koleski Edward J. , Pomerantz William C. K. 
Published: February 2015

Abstract19F NMR spectroscopy of labeled proteins is a sensitive method for characterizing structure, conformational dynamics, higher‐order assembly, and ligand binding. Fluorination of aromatic side chains has been suggested as a labeling strategy for small‐molecule ligand discovery for protein–protein interaction interfaces. Using a model transcription factor binding domain of the CREB binding protein (CBP)/p300, KIX, we report the first full small‐molecule screen using protein‐observed 19F NMR spectroscopy. Screening of 508 compounds and validation by 1H–15N HSQC NMR spectroscopy led to the identification of a minimal pharmacaphore for the MLL‐KIX interaction site. Hit rate analysis for the CREB‐KIX and MLL‐KIX sites provided a metric to assess the ligandability or “druggability” of each interface informing future medicinal chemistry efforts. The structural information from the simplified spectra and data collection speed, affords a new screening tool for analysis of protein interfaces and discovery of small molecules.
A Nuclear Singlet Lifetime of More than One Hour in Room‐Temperature Solution
Authors: Stevanato Gabriele , Hill‐Cousins Joseph T. , Håkansson Pär , Roy Soumya Singha , Brown Lynda J. , Brown Richard C. D. , Pileio Giuseppe , Levitt Malcolm H. 
Published: February 2015

AbstractNuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are supremely important techniques with numerous applications in almost all branches of science. However, until recently, NMR methodology was limited by the time constant T1 for the decay of nuclear spin magnetization through contact with the thermal molecular environment. Long‐lived states, which are correlated quantum states of multiple nuclei, have decay time constants that may exceed T1 by large factors. Here we demonstrate a nuclear long‐lived state comprising two 13C nuclei with a lifetime exceeding one hour in room‐temperature solution, which is around 50 times longer than T1. This behavior is well‐predicted by a combination of quantum theory, molecular dynamics, and quantum chemistry. Such ultra‐long‐lived states are expected to be useful for the transport and application of nuclear hyperpolarization, which leads to NMR and MRI signals enhanced by up to five orders of magnitude.
Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation
Authors: Gao Wei , Lee Hiang Kwee , Hobley Jonathan , Liu Tianxi , Phang In Yee , Ling Xing Yi 
Published: February 2015

AbstractWe demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble’s surface temperature between 21–135 °C and its encapsulated water temperature between 21–74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12‐fold superior reaction rate constant for methylene blue degradation than at room temperature.
Noncanonical Amino Acids to Improve the pH Response of pHLIP Insertion at Tumor Acidity
Authors: Onyango Joab O. , Chung Michael S. , Eng Chee‐Huat , Klees Lukas M. , Langenbacher Rachel , Yao Lan , An Ming 
Published: February 2015

AbstractThe pH low insertion peptide (pHLIP) offers the potential to deliver drugs selectively to the cytoplasm of cancer cells based on tumor acidosis. The WT pHLIP inserts into membranes with a pH50 of 6.1, while most solid tumors have extracellular pH (pHe) of 6.5–7.0. To close this gap, a SAR study was carried out to search for pHLIP variants with improved pH response. Replacing Asp25 with α‐aminoadipic acid (Aad) adjusts the pH50 to 6.74, matching average tumor acidity, and replacing Asp14 with γ‐carboxyglutamic acid (Gla) increases the sharpness of pH response (transition over 0.5 instead of 1 pH unit). These effects are additive: the Asp14Gla/Asp25Aad double variant shows a pH50 of 6.79, with sharper transition than Asp25Aad. Furthermore, the advantage of the double variant over WT pHLIP in terms of cargo delivery was demonstrated in turn‐on fluorescence assays and anti‐proliferation studies (using paclitaxel as cargo) in A549 lung cancer cells at pH 6.6.
A General and Mild Catalytic α‐Alkylation of Unactivated Esters Using Alcohols
Authors: Guo Le , Ma Xiaochen , Fang Huaquan , Jia Xiangqing , Huang Zheng 
Published: February 2015

AbstractCatalytic α‐alkylation of esters with primary alcohols is a desirable process because it uses low‐toxicity agents and generates water as the by‐product. Reported herein is a NCP pincer/Ir catalyst which is highly efficient for α‐alkylation of a broad scope of unactivated esters under mild reaction conditions. For the first time, alcohols alkylate unactivated α‐substituted acyclic esters, lactones, and even methyl and ethyl acetates. This method can be applied to the synthesis of carboxylic acid derivatives with diverse structures and functional groups, some of which would be impossible to access by conventional enolate alkylations with alkyl halides.
Highly Efficient Synthesis of Monodisperse Poly(ethylene glycols) and Derivatives through Macrocyclization of Oligo(ethylene glycols)
Authors: Zhang Hua , Li Xuefei , Shi Qiuyan , Li Yu , Xia Guiquan , Chen Long , Yang Zhigang , Jiang Zhong‐Xing 
Published: February 2015

AbstractA macrocyclic sulfate (MCS)‐based approach to monodisperse poly(ethylene glycols) (M‐PEGs) and their monofunctionalized derivatives has been developed. Macrocyclization of oligo(ethylene glycols) (OEGs) provides MCS (up to a 62‐membered macrocycle) as versatile precursors for a range of monofunctionalized M‐PEGs. Through iterative nucleophilic ring‐opening reactions of MCS without performing group protection and activation, a series of M‐PEGs, including the unprecedented 64‐mer (2850 Da), can be readily prepared. Synthetic simplicity coupled with versatility of this new strategy may pave the way for broader applications of M‐PEGs.
The Emerging Chemistry of Sodium Ion Batteries for Electrochemical Energy Storage
Authors: Kundu Dipan , Talaie Elahe , Duffort Victor , Nazar Linda F. 
Published: February 2015

AbstractEnergy storage technology has received significant attention for portable electronic devices, electric vehicle propulsion, bulk electricity storage at power stations, and load leveling of renewable sources, such as solar energy and wind power. Lithium ion batteries have dominated most of the first two applications. For the last two cases, however, moving beyond lithium batteries to the element that lies below—sodium—is a sensible step that offers sustainability and cost‐effectiveness. This requires an evaluation of the science underpinning these devices, including the discovery of new materials, their electrochemistry, and an increased understanding of ion mobility based on computational methods. The Review considers some of the current scientific issues underpinning sodium ion batteries.
A Perfect Match: Fullerene Guests in Star‐Shaped Oligophenylenevinylene Mesogens
Authors: Lehmann Matthias , Hügel Markus 
Published: February 2015

AbstractStar‐shaped oligophenylenevinylene (OPV) mesogens are shape‐persistent and possess formally large void space. A mesogen with three styrene repeating units packs densely in a columnar helical arrangement. Attachment of one fullerene through a short spacer results in an exceptional increase of the mesophase stability. X‐ray scattering and modeling evidence a triple‐helical arrangement in which the fullerene perfectly fills the void space between the arms of the star mesogen.
Construction of a New Class of Tetracycline Lead Structures with Potent Antibacterial Activity through Biosynthetic Engineering
Authors: Lešnik Urška , Lukežič Tadeja , Podgoršek Ajda , Horvat Jaka , Polak Tomaž , Šala Martin , Jenko Branko , Harmrolfs Kirsten , Ocampo‐Sosa Alain , Martínez‐Martínez Luis , Herron Paul R. , Fujs Štefan , Kosec Gregor , Hunter Iain S. , Müller Rolf , Petković Hrvoje 
Published: February 2015

AbstractAntimicrobial resistance and the shortage of novel antibiotics have led to an urgent need for new antibacterial drug leads. Several existing natural product scaffolds (including chelocardins) have not been developed because their suboptimal pharmacological properties could not be addressed at the time. It is demonstrated here that reviving such compounds through the application of biosynthetic engineering can deliver novel drug candidates. Through a rational approach, the carboxamido moiety of tetracyclines (an important structural feature for their bioactivity) was introduced into the chelocardins, which are atypical tetracyclines with an unknown mode of action. A broad‐spectrum antibiotic lead was generated with significantly improved activity, including against all Gram‐negative pathogens of the ESKAPE panel. Since the lead structure is also amenable to further chemical modification, it is a platform for further development through medicinal chemistry and genetic engineering.
Robust Chemical Preservation of Digital Information on DNA in Silica with Error‐Correcting Codes
Authors: Grass Robert N. , Heckel Reinhard , Puddu Michela , Paunescu Daniela , Stark Wendelin J. 
Published: February 2015

AbstractInformation, such as text printed on paper or images projected onto microfilm, can survive for over 500 years. However, the storage of digital information for time frames exceeding 50 years is challenging. Here we show that digital information can be stored on DNA and recovered without errors for considerably longer time frames. To allow for the perfect recovery of the information, we encapsulate the DNA in an inorganic matrix, and employ error‐correcting codes to correct storage‐related errors. Specifically, we translated 83 kB of information to 4991 DNA segments, each 158 nucleotides long, which were encapsulated in silica. Accelerated aging experiments were performed to measure DNA decay kinetics, which show that data can be archived on DNA for millennia under a wide range of conditions. The original information could be recovered error free, even after treating the DNA in silica at 70 °C for one week. This is thermally equivalent to storing information on DNA in central Europe for 2000 years.
Noncovalent Hydrogel Beads as Microcarriers for Cell Culture
Authors: Wieduwild Robert , Krishnan Swati , Chwalek Karolina , Boden Annett , Nowak Mirko , Drechsel David , Werner Carsten , Zhang Yixin 
Published: February 2015

AbstractHydrogel beads as microcarriers could have many applications in biotechnology. However, bead formation by noncovalent cross‐linking to achieve high cell compatibility by avoiding chemical reactions remains challenging because of rapid gelation rates and/or low stability. Here we report the preparation of homogeneous, tunable, and robust hydrogel beads from peptide–polyethylene glycol conjugates and oligosaccharides under mild, cell‐compatible conditions using a noncovalent crosslinking mechanism. Large proteins can be released from beads easily. Further noncovalent modification allows for bead labeling and functionalization with various compounds. High survival rates of embedded cells were achieved under standard cell culture conditions and after freezing the beads, demonstrating its suitability for encapsulating and conserving cells. Hydrogel beads as functional system have been realized by generating protein‐producing microcarriers with embedded eGFP‐secreting insect cells.
Applying the Retro‐Enantio Approach To Obtain a Peptide Capable of Overcoming the Blood–Brain Barrier
Authors: Prades Roger , Oller‐Salvia Benjamí , Schwarzmaier Susanne M. , Selva Javier , Moros María , Balbi Matilde , Grazú Valeria , de La Fuente Jesus M. , Egea Gustavo , Plesnila Nikolaus , Teixidó Meritxell , Giralt Ernest 
Published: February 2015

AbstractThe blood–brain barrier (BBB) is a formidable physical and enzymatic barrier that tightly controls the passage of molecules from the blood to the brain. In fact, less than 2 % of all potential neurotherapeutics are able to cross it. Here, by applying the retro‐enantio approach to a peptide that targets the transferrin receptor, a full protease‐resistant peptide with the capacity to act as a BBB shuttle was obtained and thus enabled the transport of a variety of cargos into the central nervous system.
Enantioselective Enzymes by Computational Design and In Silico Screening
Authors: Wijma Hein J. , Floor Robert J. , Bjelic Sinisa , Marrink Siewert J. , Baker David , Janssen Dick B. 
Published: February 2015

AbstractComputational enzyme design holds great promise for providing new biocatalysts for synthetic chemistry. A strategy to design small mutant libraries of complementary enantioselective epoxide hydrolase variants for the production of highly enantioenriched (S,S)‐diols and (R,R)‐diols is developed. Key features of this strategy (CASCO, catalytic selectivity by computational design) are the design of mutations that favor binding of the substrate in a predefined orientation, the introduction of steric hindrance to prevent unwanted substrate binding modes, and ranking of designs by high‐throughput molecular dynamics simulations. Using this strategy we obtained highly stereoselective mutants of limonene epoxide hydrolase after experimental screening of only 37 variants. The results indicate that computational methods can replace a substantial amount of laboratory work when developing enantioselective enzymes.