bluuebunny/crossref_metadata_2025_split huggingface dataset:
Helical‐Ribbon Formation by a β‐Amino Acid Modified Amyloid β‐Peptide Fragment
Authors: Castelletto Valeria , Hamley Ian W. , Hule Rohan A. , Pochan Darrin 
Published: February 2009

AbstractFamilienzuwachs: Die Einführung von β‐Aminosäureresten in ein modifiziertes Amyloid‐β‐peptidfragment ergibt definierte helicale Nanobänder (siehe Kryo‐TEM‐Aufnahme), die β‐Stränge mit hauptsächlich senkrechter Orientierung zur Bandachse enthalten. Die Bänder ordnen sich bei höherer Konzentration in einer nematischen Phase an, die sich bei Anlegen von Scherkräften ausrichtet. Diese Bandstruktur ist ein neues Mitglied der bekannten Familie von β‐Peptid‐Sekundärstrukturen.magnified image
Dynamische Kristalle: visuell wahrnehmbare mechanochemische Lumineszenzänderungen von Gold‐ und anderen Übergangsmetallkomplexen
Authors: Balch Alan L. 
Published: February 2009

AbstractUngewöhnliche Lumineszenzänderung: Bei bestimmten Kristallkomplexen von Gold, Platin und Vanadium bewirkt ein Zermahlen der Kristalle deutliche Veränderungen der Lumineszenz oder Farbe. Im Bild ist die Umwandlung von farblosem [(F5C6Au)2(μ‐1,4‐CN2C6H4)]‐Kristallpulver von einer blau emittierenden Form (λmax=415 nm) in eine gelb/grün emittierende Form (λmax=533 nm) beim Zermahlen zu sehen. Der Prozess ist reversibel.magnified image
Universal Scaffold for Fluorescent Conjugated Organoborane Polymers
Authors: Li Haiyan , Jäkle Frieder 
Published: February 2009

AbstractAufgemotzte Polymere: Ein vielseitiges und stark emittierendes konjugiertes Polymergerüst wird erhalten, wenn Nucleophile labile Bromatome am Rückgrat eines Fluorenylboran‐Polymers ersetzen (siehe Bild). Durch solche einfachen Modifizierungen lassen sich die Stabilität sowie das thermische und photophysikalische Verhalten einstellen, sodass lumineszierende Polymere mit Anionenbindungsvermögen zugänglich werden.magnified image
Photoprogrammable Organic Light‐Emitting Diodes
Authors: Zacharias Philipp , Gather Malte C. , Köhnen Anne , Rehmann Nina , Meerholz Klaus 
Published: February 2009

AbstractLicht im Speicher: Der Einbau eines vernetzbaren photochromen Dithienylperfluorcyclopentens (DTE) in organische Leuchtdioden (OLEDs) ermöglicht die Individualisierung der Emissionsfläche, z. B. für die Anwendung in Anzeigeelementen. Das Arbeitsprinzip beruht auf dem Schalten der Injektionsbarriere für Löcher (positive Ladungsträger). Sehr große AN/AUS‐Verhältnisse von bis zu 3000 für die Stromstärke und die Elektrolumineszenz wurden erreicht.magnified image
Icosahedral DNA Nanocapsules by Modular Assembly
Authors: Bhatia Dhiraj , Mehtab Shabana , Krishnan Ramya , Indi Shantinath S. , Basu Atanu , Krishnan Yamuna 
Published: February 2009

AbstractIn der Falle: Durch molekulare Selbstorganisation erzeugte DNA‐Polyeder könnten als Nanokäfige für den gerichteten Transport von verkapselten Spezies dienen. Das Funktionsprinzip wurde für den komplexesten aller DNA‐basierten platonischen Festkörper gezeigt: Während der stufenweisen Amalgamierung diskreter Polyeder zu Ikosaedern wurden Gold‐Nanopartikel (GNPs) aus der Lösung eingekapselt (siehe Illustration und TEM‐Bild ikosaederischer Käfige mit verkapselten GNPs).magnified image
Highly Enantioselective Pictet–Spengler Reactions with α‐Ketoamide‐Derived Ketimines: Access to an Unusual Class of Quaternary α‐Amino Amides
Authors: Bou‐Hamdan Farhan R. , Leighton James L. 
Published: February 2009

AbstractN‐Arylamide wurden als effiziente steuernde und aktivierende Gruppen für Lewis‐saure Chlorosilane im ersten einfachen und allgemeinen Verfahren für die hoch enantioselektive Pictet‐Spengler‐Reaktion mit Ketiminen aus α‐Ketoamiden eingesetzt. Als Produkte werden quartäre α‐Aminosäure‐Derivate erhalten (siehe Schema).magnified image
Challenging the Metallocene Dominance in Actinide Chemistry with a Soft PNP Pincer Ligand: New Uranium Structures and Reactivity Patterns
Authors: Cantat Thibault , Graves Christopher R. , Scott Brian L. , Kiplinger Jaqueline L. 
Published: February 2009

AbstractU wie ungewohnt: Der Austausch von C5Me5 gegen einen „weichen“ PNP‐ Pinzettenliganden mit besonderen elektronischen und sterischen Eigenschaften erzeugte neue Reaktivitäts‐ und Strukturmuster in der Actinoidenreihe (siehe Bild, py–O=Pyridin‐N‐oxid). Die neuen Liganden unterstützen nicht nur niedervalente Uranverbindungen, sondern auch hochvalente Uran(VI)‐Spezies.magnified image
Parallel Kinetic Resolution Approach to the Cyathane and Cyanthiwigin Diterpenes Using a Cyclopropanation/Cope Rearrangement
Authors: Miller Laura C. , Ndungu J. Maina , Sarpong Richmond 
Published: February 2009

AbstractParallel gearbeitet: Die stereodivergente parallele kinetische Racematspaltung eines Diengemischs mithilfe der Davies‐Katalysatoren [Rh2{(S)‐dosp}4] oder [Rh2{(R)‐dosp}4] zur Vermittlung einer Sequenz aus Vinyldiazoacetat‐Cyclopropanierung und Cope‐Umlagerung liefert zwei diastereomere, enantiomerenangereicherte Cycloheptadiene, die den natürlichen Antipoden der Titel‐Diterpenoide entsprechen (siehe Schema).magnified image
Is Cyanide Really a Strong‐Field Ligand?
Authors: Nakamura Mikio 
Published: February 2009

AbstractIron man or weakling? Ligand‐field strengths are conveniently expressed by the empirical spectrochemical series. Although cyanide has been deeply entrenched as a strong‐field ligand, a couple of recent examples cast doubt toward the position of this ligand, namely the high‐spin (S=2) states of [CrII(CN)5]3− and [FeII(tpp)(CN)]−. tpp=meso‐tetraphenylporphinate.magnified image
Helical‐Ribbon Formation by a β‐Amino Acid Modified Amyloid β‐Peptide Fragment
Authors: Castelletto Valeria , Hamley Ian W. , Hule Rohan A. , Pochan Darrin 
Published: February 2009

AbstractAn addition to the family: The introduction of β‐amino acid residues into a modified amyloid β peptide fragment resulted in well‐defined helical nanoribbons (see cryo‐TEM image) comprising β strands mainly oriented perpendicular to the ribbon axis. The nanoribbons order into a flow‐aligning nematic phase at higher concentration. The β‐strand nanoribbon structure is an addition to the known set of secondary structures adopted by β‐peptides.magnified image
From Ionic Liquids to Supramolecular Polymers
Authors: Craig Stephen L. 
Published: February 2009

AbstractCharging forward: Ionic interactions presented in a multivalent fashion in small‐molecule ionic liquids lead to functional polymer‐like materials (see picture) that are consistent with the formation of a supramolecular ionic network. For example, the ionic material formed from a dication consisting of two covalently linked tetraalkyl phosphonium moieties and a porphyrin tetracarboxylate has a viscosity of 106 Pa s at 25 °C.magnified image
The Imidazopyridine Derivative JK184 Reveals Dual Roles for Microtubules in Hedgehog Signaling
Authors: Cupido Tommaso , Rack Paul G. , Firestone Ari J. , Hyman Joel M. , Han Kyuho , Sinha Surajit , Ocasio Cory A. , Chen James K. 
Published: February 2009

AbstractEradicating hedgehogs: The title molecule has been previously identified as a potent inhibitor of the Hedgehog signaling pathway, which gives embryonic cells information needed to develop properly. This molecule is shown to modulate Hedgehog target gene expression by depolymerizing microtubules, thus revealing dual roles of the cytoskeleton in pathway regulation (see figure).magnified image
Synthesis of Goethite by Separation of the Nucleation and Growth Processes of Ferrihydrite Nanoparticles Using Microfluidics
Authors: Abou‐Hassan Ali , Sandre Olivier , Neveu Sophie , Cabuil Valérie 
Published: February 2009

AbstractMicrofluidic synthesis is used to form nanoparticles by separate nucleation and growth processes using two microreactors (see picture) operating under different temperature and flow conditions. Ferrihydrite nanoparticles precipitated in the first microreactor are aged under continuous flow in a second microtubular reactor, leading to goethite nanoparticles. TMAOH=tetramethylammonium hydroxide.magnified image
Photoprogrammable Organic Light‐Emitting Diodes
Authors: Zacharias Philipp , Gather Malte C. , Köhnen Anne , Rehmann Nina , Meerholz Klaus 
Published: February 2009

AbstractEnlightening the memory: The integration of a crosslinkable photochromic dithienylperfluorocyclopentene (DTE) into organic light‐emitting diodes (OLED) allows for the individualization of the emissive area of the OLED device, for example, for signage applications. The operation principle is based on switching the injection barrier for holes (positive charge carriers). Very large ON/OFF ratios of up to 3000 for current as well as electroluminescence have been achieved.magnified image
Icosahedral DNA Nanocapsules by Modular Assembly
Authors: Bhatia Dhiraj , Mehtab Shabana , Krishnan Ramya , Indi Shantinath S. , Basu Atanu , Krishnan Yamuna 
Published: February 2009

AbstractIt's a trap! DNA polyhedra formed through molecular self‐assembly may function as nanocapsules for the targeted delivery of encapsulated entities. This functional aspect was demonstrated for the most complex DNA‐based platonic solid: During the stepwise amalgamation of discrete polyhedra to form icosahedra, gold nanoparticles (GNPs) were encapsulated from solution (see illustration and TEM image of icosahedral cages containing GNPs).magnified image
Highly Enantioselective Pictet–Spengler Reactions with α‐Ketoamide‐Derived Ketimines: Access to an Unusual Class of Quaternary α‐Amino Amides
Authors: Bou‐Hamdan Farhan R. , Leighton James L. 
Published: February 2009

Abstract“Quat's” the story? N‐Aryl amides are effective directing/activating groups for chlorosilane Lewis acids. This aspect has been exploited for the development of the first simple and general method for the highly enantioselective Pictet–Spengler reaction of ketimines derived from α‐ketoamides leading to quaternary α‐amino acid derivatives (see scheme).magnified image
Challenging the Metallocene Dominance in Actinide Chemistry with a Soft PNP Pincer Ligand: New Uranium Structures and Reactivity Patterns
Authors: Cantat Thibault , Graves Christopher R. , Scott Brian L. , Kiplinger Jaqueline L. 
Published: February 2009

AbstractA soft embrace for U: Replacement of C5Me5 by the soft PNP pincer ligand is a successful strategy to promote new reactivities and support new structures for the actinide series (see picture, py–O=pyridine‐N‐oxide). The specific electronic and steric properties of the PNP ligand enable access to previously unreported structures not available for the C5Me5 ligand set and support not only low‐valent uranium but also the high‐valent uranium(VI) ion.magnified image
Parallel Kinetic Resolution Approach to the Cyathane and Cyanthiwigin Diterpenes Using a Cyclopropanation/Cope Rearrangement
Authors: Miller Laura C. , Ndungu J. Maina , Sarpong Richmond 
Published: February 2009

AbstractParallel effort: Stereodivergent parallel kinetic resolution of a racemic mixture of dienes using Davies' [Rh2{(S)‐dosp}4] or [Rh2{(R)‐dosp}4] catalysts promotes a tandem vinyl diazoacetate cyclopropanation/Cope rearrangement sequence to afford two diastereomeric, enantioenriched cycloheptadienes, which correspond to the natural antipodes of the title diterpenoids (see scheme).magnified image
Characteristic reactions of group 9 transition metal compounds in organic synthesis
Authors: Omae Iwao 
Published: February 2009

AbstractGroup 9 metal compounds in organic synthesis have two characteristic reactions. The first occurs because the group 9 metals have a high affinity to carbon–carbon or carbon–nitrogen π‐bonds. The first type of characteristic reactions in these group 9 metal compounds includes Pauson–Khand reactions, the Pauson–Khand‐type reactions ([2 + 2 + 1] cyclization), the other cyclizations and coupling reactions. The second occurs because the group 9 metals have a high affinity to carbonyl groups. The second type of characteristic reactions includes carbonylations such as hydroformylations, the carbonylations of methanol, amidocarbonylations and other carbonylations. The first characteristic reactions are applied for the synthesis of fine chemicals such as pharmaceuticals and agrochemicals. However, the second characteristic reactions are utilized not only for fine chemicals but also for important bulk commodity chemicals such as aldehydes, carboxylic acids and alcohols. Copyright © 2009 John Wiley & Sons, Ltd.
Business strategies for transitions towards sustainable systems
Authors: Loorbach Derk , van Bakel Janneke C. , Whiteman Gail , Rotmans Jan 
Published: February 2009

AbstractThis paper develops a strategic perspective for business to contribute to the innovation of societal systems. Sustainability issues at the level of societal sectors cannot be addressed by single organizations but need to be thought of as systemic challenges in which business, government and civil society each play different roles. Sustainability involves structural changes over longer periods of time, and requires co‐evolutionary changes in technology, economy, culture and organizational forms. We propose that the transition management framework offers a fruitful way to analyze such co‐evolutionary processes of social transformation and subsequently develop strategies to influence and accelerate such processes. We present the case of two firms working in this new context of transition management in The Netherlands. From these cases we conceptualize a more general approach for business to redefine and reframe the societal context in which it is operating and develop novel business strategies. Copyright © 2009 John Wiley & Sons, Ltd and ERP Environment.
Green segmentation and environmental certification: insights from forest products
Authors: Thompson Derek W. , Anderson Roy C. , Hansen Eric N. , Kahle Lynn R. 
Published: February 2009

AbstractFirms engage inenvironmental marketingin order to appeal toenvironmentally conscious consumers. Within the context of the forest product industry, this research uses data from two studies to empirically test whether a relationship exists between demographic/psychographic characteristics and reported environmentally conscious intentions. In both studies, the results indicate that the environmental marketing of certified/ecolabeled forest products appeals to a segment of environmentally conscious consumers. This appeal occurs for both a value‐added product (furniture) and a non‐value‐added product (plywood). Thus, there is support for the argument that environmental marketing to environmentally conscious consumers can result in ‘green segmentation’. Key findings from this study suggest that those consumers reporting the strongest preferences for environmentally certified forest products were more willing to pay a premium for certified products, more likely to display environmentally conscious behavior and more likely to perceive that green consumer purchases effectively benefit the environment. These characteristics were most common among females and those familiar with the concept of environmental certification. Copyright © 2009 John Wiley & Sons, Ltd and EPR Environment.
NO Formation by Neuronal NO‐Synthase can be Controlled by Ultrafast Electron Injection from a Nanotrigger
Authors: Beaumont Edward , Lambry Jean‐Christophe , Blanchard‐Desce Mireille , Martasek Pavel , Panda Satya P. , van Faassen Ernst E. H. , Brochon Jean‐Claude , Deprez Eric , Slama‐Schwok Anny 
Published: February 2009

AbstractSynchronized catalysis in native enzyme: We used a photoactive nanotrigger (NT) to study the initial electron transfer to FAD in native neuronal NOS catalysis. Modeling and fluorescence spectroscopy showed that selective NT binding to NADPH sites is able to override Phe1395 regulation, thus permitting ultrafast injection of electrons into the protein electron pathway. That NT initiation of flavoenzyme catalysis led to the formation of NO is promising for time‐resolved X‐ray and other cellular applications.magnified imageNitric oxide synthases (NOSs) are unique flavohemoproteins with various roles in mammalian physiology. Constitutive NOS catalysis is initiated by fast hydride transfer from NADPH, followed by slower structural rearrangements. We used a photoactive nanotrigger (NT) to study the initial electron transfer to FAD in native neuronal NOS (nNOS) catalysis. Molecular modeling and fluorescence spectroscopy showed that selective NT binding to NADPH sites close to FAD is able to override Phe1395 regulation. Ultrafast injection of electrons into the protein electron pathway by NT photoactivation through the use of a femtosecond laser pulse is thus possible. We show that calmodulin, required for NO synthesis by constitutive NOS, strongly promotes intramolecular electron flow (6.2‐fold stimulation) by a mechanism involving proton transfer to the reduced FAD− site. Site‐directed mutagenesis using the S1176A and S1176T mutants of nNOS supports this hypothesis. The NT synchronized the initiation of flavoenzyme catalysis, leading to the formation of NO, as detected by EPR. This NT is thus promising for time‐resolved X‐ray and other cellular applications.
Discovery of Additional Members of the Tyrosine Aminomutase Enzyme Family and the Mutational Analysis of CmdF
Authors: Krug Daniel , Müller Rolf 
Published: February 2009

AbstractStereochemical antipoles: The myxobacteria Chondromyces crocatus and Myxococcus fulvus utilize tyrosine aminomutase (TAM) enzymes with opposite stereoselectivity to produce β‐Tyr building blocks, which are subsequently incorporated into potent secondary metabolites. The evolution of stereochemical preference within this expanding enzyme family is unexplored. Intriguingly, the mutation of one amino acid in the aminomutase CmdF from C. crocatus influences the enantiomeric excess of (R)‐β‐Tyr formation (see chromatograms).magnified imageThe tyrosine aminomutase (TAM) CmdF converts L‐Tyr preferentially to (R)‐β‐Tyr—a biosynthetic building block subsequently incorporated into the highly cytotoxic chondramides by the myxobacterium Chondromyces crocatus. Together with the similar enzymes SgcC4 from Streptomyces globisporus and MdpC4 from Actinomadura madurae, which preferentially produce (S)‐β‐Tyr, CmdF belongs to a novel 2,3‐aminomutase enzyme family closely related to the aromatic amino acid ammonia lyase. Although considerable insight into the underlying catalytic mechanism has been provided recently by structural and mechanistic studies, the key determinants of product specificity and stereochemical preference of TAM enzymes remain to be elucidated in detail. We report herein the discovery and heterologous expression of additional TAMs from prokaryotic sources. These studies reveal a high degree of evolutionary diversification within this expanding enzyme family. Attempts to genetically engineer CmdF to exhibit ammonia lyase‐type activity by the exchange of conserved sequence motifs were largely unsuccessful. However, the variation of a semiconserved glutamic acid residue was found to impact stereoselectivity. Replacement of this residue by lysine significantly increased the enantiomeric excess of (R)‐β‐Tyr from 69 to 97 % ee, while substitution with methionine promoted racemization. These results suggest that it should be possible to elucidate a mechanism for control of stereoselectivity in the TAM family by the application of directed evolution to CmdF. Furthermore, our findings indicate the potential to fine‐tune the catalytic properties of TAMs for their use as biocatalysts or in engineered biosynthetic pathways.
Investigation of the Substrate Specificity of Lacticin 481 Synthetase by Using Nonproteinogenic Amino Acids
Authors: Levengood Matthew R. , Kerwood Christopher C. , Chatterjee Champak , van der Donk Wilfred A. 
Published: February 2009

AbstractOne enzyme, many substrates. The substrate specificity of a lantibiotic biosynthetic enzyme, lacticin 481 synthetase, was probed by using synthetic prepeptides containing a variety of nonproteinogenic amino acids, including unnatural α‐amino acids, β‐amino acids, D‐amino acids, and peptoids.magnified imageLantibiotics are peptide antimicrobial compounds that are characterized by the thioether‐bridged amino acids lanthionine and methyllanthionine. For lacticin 481, these structures are installed in a two‐step post‐translational modification process by a bifunctional enzyme, lacticin 481 synthetase (LctM). LctM catalyzes the dehydration of Ser and Thr residues to generate dehydroalanine or dehydrobutyrine, respectively, and the subsequent intramolecular regio‐ and stereospecific Michael‐type addition of cysteines onto the dehydroamino acids. In this study, semisynthetic substrates containing nonproteinogenic amino acids were prepared by expressed protein ligation and [3+2]‐cycloaddition of azide and alkyne‐functionalized peptides. LctM demonstrated broad substrate specificity toward substrates containing β‐amino acids, D‐amino acids, and N‐alkyl amino acids (peptoids) in certain regions of its peptide substrate. These findings showcase its promise for use in lantibiotic and peptide‐engineering applications, whereby nonproteinogenic amino acids might impart improved stability or modulated biological activities. Furthermore, LctM permitted the incorporation of an alkyne‐containing amino acid that can be utilized for the site‐selective modification of mature lantibiotics and used in target identification.
Phosphorothioation of Oligonucleotides Strongly Influences the Inhibition of Bacterial (M.HhaI) and Human (Dnmt1) DNA Methyltransferases
Authors: Warncke Simon , Gégout Aline , Carell Thomas 
Published: February 2009

AbstractMethyltransferase inhibitors: Short double‐stranded oligonucleotides that have a hemimethylated target sequence and 5‐fluoro‐2′‐deoxycytidine as a suicide inhibitor as well as their phosphorothioated analogues were tested for their ability to inhibit the bacterial methyltransferase M.HhaI and the human Dnmt1 in vitro.magnified imageThe cytidine analogue 5‐fluoro‐2′‐deoxycytidine (dCF) is a mechanism‐based inhibitor of DNA methyltransferases. We report the synthesis of short 18‐mer dsDNA oligomers containing a triple‐hemimethylated CpG motive as a recognition sequence for the human methyltransferase Dnmt1. The DNA strands carry within these CpG islands dCF building blocks that function as mechanism‐based inhibitors of the analyzed methyltransferases. In addition, we replaced the phosphodiester backbones at defined positions by phosphorothioates. These hypermodified DNA strands were investigated as inhibitors of the DNA methyltransferases M.HhaI and Dnmt1 in vitro. We could show that both methylases behave substantially differently in respect to the amount of DNA backbone modification.