bluuebunny/crossref_metadata_2025_split huggingface dataset:
London’sche Dispersionswechselwirkungen in der Molekülchemie – eine Neubetrachtung sterischer Effekte
Authors: Wagner J. Philipp , Schreiner Peter R. 
Published: August 2015

AbstractDie London’sche Dispersion, die den attraktiven Teil des Van‐der‐Waals‐Potentials beschreibt, wurde lange als Element struktureller Stabilität in der molekularen Chemie unterschätzt. Als solches beeinflusst sie auch entscheidend die chemische Reaktivität und Katalyse. Ihre Vernachlässigung ist auf die Annahme zurückzuführen, dass die Dispersionswechselwirkung schwach sei, was nur für eine einzelne paarweise Wechselwirkung zweier Atome stimmt. Für Strukturen zunehmender Größe kann die gesamte Dispersionsstabilisierung mehrere zehn kcal mol−1 betragen. Dieser Aufsatz soll die Wichtigkeit inter‐ und intramolekularer Dispersion anhand von Beispielen für die erste Vollperiode verdeutlichen. Die Synergie aus Experiment und Theorie hat ein Niveau erreicht, auf dem Dispersionseffekte sehr genau verstanden werden können. Als Konsequenz daraus werden wir wohl unser Verständnis bezüglich sterischer Hinderung und stereoelektronischer Effekte überdenken müssen. Die Quantifizierung von Dispersionsenergiedonoren wird unsere Fähigkeiten verbessern, komplexe molekulare Strukturen und Katalysatoren zu entwickeln.
Clicked Isoreticular Metal–Organic Frameworks and Their High Performance in the Selective Capture and Separation of Large Organic Molecules
Authors: Li Pei‐Zhou , Wang Xiao‐Jun , Tan Si Yu , Ang Chung Yen , Chen Hongzhong , Liu Jia , Zou Ruqiang , Zhao Yanli 
Published: August 2015

AbstractThree highly porous metal–organic frameworks (MOFs) with a uniform rht‐type topological network but hierarchical pores were successfully constructed by the assembly of triazole‐containing dendritic hexacarboxylate ligands with ZnII ions. These transparent MOF crystals present gradually increasing pore sizes upon extension of the length of the organic backbone, as clearly identified by structural analysis and gas‐adsorption experiments. The inherent accessibility of the pores to large molecules endows these materials with unique properties for the uptake of large guest molecules. The visible selective adsorption of dye molecules makes these MOFs highly promising porous materials for pore‐size‐dependent large‐molecule capture and separation.
Final‐Stage Site‐Selective Acylation for the Total Syntheses of Multifidosides A–C
Authors: Ueda Yoshihiro , Furuta Takumi , Kawabata Takeo 
Published: August 2015

AbstractThe first total syntheses of multifidosides A–C have been achieved. The synthetic strategy is characterized by catalytic site‐selective acylation of unprotected glycoside precursors in the final stage of the synthesis. High functional‐group tolerance of the site‐selective acylation, promoted by an organocatalyst, enabled the conventionally difficult molecular transformation in a predictable and reliable manner. An advantage of this strategy is to avoid the risks of undesired side reactions during the removal of the protecting groups at the final stage of the total synthesis.
Synthese überbrückter Diketopiperazine mit Hilfe des persistenten Radikaleffekts und eine formale Synthese von Bicyclomycin
Authors: Amatov Tynchtyk , Pohl Radek , Císařová Ivana , Jahn Ullrich 
Published: August 2015

AbstractEin konzeptionell neuer und vereinheitlichter Zugang zu vielfältigen überbrückten Diketopiperazinen (DKP) mit variabler Ringgröße wurde auf der Basis des persistenten Radikaleffekts entwickelt. Die Methode ermöglicht einen Zugang zu den Grundgerüsten überbrückter Diketopiperazinalkaloide und wurde in einer formalen Synthese des Antibiotikums Bicyclomycin angewendet.
Zum Mechanismus des Wasserstoffatomtransfers von Wasser auf den heteronuklearen Oxidcluster [Ga2Mg2O5].+: außergewöhnliche Effekte der elektronischen Struktur
Authors: Li Jilai , Zhou Shaodong , Wu Xiao‐Nan , Tang Shiya , Schlangen Maria , Schwarz Helmut 
Published: August 2015

AbstractDer Mechanismus der durch den heteronuklearen Oxidcluster [Ga2Mg2O5].+ vermittelten homolytischen Spaltung der O‐H‐Bindung in Wasser wurde mittels moderner Gasphasenexperimente und quantenchemischer Rechnungen eingehend untersucht. Basierend auf den theoretischen Untersuchungen lassen sich drei Reaktionswege unterscheiden: Neben der klassischen Übertragung eines Wasserstoffatoms (hydrogen‐atom transfer, HAT) auf ein radikalisches Sauerstoffatom existieren zwei mechanistisch unterschiedliche, protonengekoppelte Elektronenübertragungen (proton‐coupled electron transfer, PCET). Nach Koordination des Wassermoleküls an ein Magnesiumatom des Clusters zeichnet sich der energetisch günstigste Reaktionsweg durch einen intramolekularen Protonentransfer auf das freie Elektronenpaar eines verbrückenden Sauerstoffatoms sowie durch eine Reorganisation der Elektronenstruktur des Clusters aus. Dabei werden zwei strukturell identische OH‐Gruppen generiert, von denen eine – in Übereinstimmung mit Isotopenmarkierungsexperimenten – im weiteren Verlauf der Reaktion abgespalten wird.
Vinylation of Unprotected Phenols Using a Biocatalytic System
Authors: Busto Eduardo , Simon Robert C. , Kroutil Wolfgang 
Published: August 2015

AbstractReadily available substituted phenols were coupled with pyruvate in buffer solution under atmospheric conditions to afford the corresponding para‐vinylphenol derivatives while releasing only one molecule of CO2 and water as the by‐products. This transformation was achieved by designing a biocatalytic system that combines three biocatalytic steps, namely the CC coupling of phenol and pyruvate in the presence of ammonia, which leads to the corresponding tyrosine derivative, followed by deamination and decarboxylation. The biocatalytic transformation proceeded with high regioselectivity and afforded exclusively the desired para products. This method thus represents an environmentally friendly approach for the direct vinylation of readily available 2‐, 3‐, or 2,3‐disubstituted phenols on preparative scale (0.5 mmol) that provides vinylphenols in high yields (65–83 %).
Electrostatic Localization of RNA to Protocell Membranes by Cationic Hydrophobic Peptides
Authors: Kamat Neha P. , Tobé Sylvia , Hill Ian T. , Szostak Jack W. 
Published: August 2015

AbstractCooperative interactions between RNA and vesicle membranes on the prebiotic earth may have led to the emergence of primitive cells. The membrane surface offers a potential platform for the catalysis of reactions involving RNA, but this scenario relies upon the existence of a simple mechanism by which RNA could become associated with protocell membranes. Here, we show that electrostatic interactions provided by short, basic, amphipathic peptides can be harnessed to drive RNA binding to both zwitterionic phospholipid and anionic fatty acid membranes. We show that the association of cationic molecules with phospholipid vesicles can enhance the local positive charge on a membrane and attract RNA polynucleotides. This phenomenon can be reproduced with amphipathic peptides as short as three amino acids. Finally, we show that peptides can cross bilayer membranes to localize encapsulated RNA. This mechanism of polynucleotide confinement could have been important for primitive cellular evolution.
Ultrasmall Black Phosphorus Quantum Dots: Synthesis and Use as Photothermal Agents
Authors: Sun Zhengbo , Xie Hanhan , Tang Siying , Yu Xue‐Feng , Guo Zhinan , Shao Jundong , Zhang Han , Huang Hao , Wang Huaiyu , Chu Paul K. 
Published: August 2015

AbstractBlack phosphorus quantum dots (BPQDs) were synthesized using a liquid exfoliation method that combined probe sonication and bath sonication. With a lateral size of approximately 2.6 nm and a thickness of about 1.5 nm, the ultrasmall BPQDs exhibited an excellent NIR photothermal performance with a large extinction coefficient of 14.8 Lg−1 cm−1 at 808 nm, a photothermal conversion efficiency of 28.4 %, as well as good photostability. After PEG conjugation, the BPQDs showed enhanced stability in physiological medium, and there was no observable toxicity to different types of cells. NIR photoexcitation of the BPQDs in the presence of C6 and MCF7 cancer cells led to significant cell death, suggesting that the nanoparticles have large potential as photothermal agents.
1,2‐Phosphaborines: Hybrid Inorganic/Organic P–B Analogues of Benzene
Authors: Barnard Jonathan H. , Brown Paul A. , Shuford Kevin L. , Martin Caleb D. 
Published: August 2015

AbstractPhotolysis of the cyclic phosphine oligomer [PPh]5 in the presence of pentaarylboroles leads to the formation of 1,2‐phosphaborines by the formal insertion of a phenylphosphinidene fragment into the endocyclic CB bond. The solid‐state structure features a virtually planar central ring with bond lengths indicating significant delocalization. Appreciable ring current in the 1,2‐phosphaborine core, detected in nuclear independent chemical shift (NICS) calculations, are consistent with aromatic character. These products are the first reported 1,2‐BPC4 conjugated heterocycles and open a new avenue for BP as a valence isoelectronic substitute for CC in arene systems.
Whole‐Genome Sequencing of a Single Viral Species from a Highly Heterogeneous Sample
Authors: Han Hee‐Sun , Cantalupo Paul G. , Rotem Assaf , Cockrell Shelley K. , Carbonnaux Martial , Pipas James M. , Weitz David A. 
Published: August 2015

AbstractMetagenomic studies suggest that only a small fraction of the viruses that exist in nature have been identified and studied. Characterization of unknown viral genomes is hindered by the many genomes populating any virus sample. A new method is reported that integrates drop‐based microfluidics and computational analysis to enable the purification of any single viral species from a complex mixed virus sample and the retrieval of complete genome sequences. By using this platform, the genome sequence of a 5243 bp dsDNA virus that was spiked into wastewater was retrieved with greater than 96 % sequence coverage and more than 99.8 % sequence identity. This method holds great potential for virus discovery since it allows enrichment and sequencing of previously undescribed viruses as well as known viruses.
A Reduced 2Fe2S Cluster Probe of Sulfur–Hydrogen versus Sulfur–Gold Interactions
Authors: Crouthers Danielle J. , Ding Shengda , Denny Jason A. , Bethel Ryan D. , Hsieh Chung‐Hung , Hall Michael B. , Darensbourg Marcetta Y. 
Published: August 2015

AbstractThe Ph3PAu+ cation, renowned as an isolobal analogue of H+, was found to serve as a proton surrogate and form a stable Au2Fe2 complex, [(μ‐SAuPPh3)2{Fe(CO)3}2], analogous to the highly reactive dihydrosulfide [(μ‐SH)2{Fe(CO)3}2]. Solid‐state X‐ray diffraction analysis found the two SAuPPh3 and SH bridges in anti configurations. VT NMR studies, supported by DFT computations, confirmed substantial barriers of approximately 25 kcal mol−1 to intramolecular interconversion between the three stereoisomers of [(μ‐SH)2{Fe(CO)3}2]. In contrast, the largely dative SAu bond in μ‐SAuPPh3 facilitates inversion at S and accounts for the facile equilibration of the SAuPPh3 units, with an energy barrier half that of the SH analogue. The reactivity of the gold‐protected sulfur atoms of [(μ‐SAuPPh3)2{Fe(CO)3}2] was accessed by release of the gold ligand with a strong acid to generate the [(μ‐SH)2{Fe(CO)3}2] precursor of the [FeFe]H2ase‐active‐site biomimetic [(μ2‐SCH2(NR)CH2S){Fe(CO)3}2].
Rare‐Earth‐Metal Nitridophosphates through High‐Pressure Metathesis
Authors: Kloß Simon David , Schnick Wolfgang 
Published: August 2015

AbstractDeveloping a synthetic method to target an broad spectrum of unknown phases can lead to fascinating discoveries. The preparation of the first rare‐earth‐metal nitridophosphate LiNdP4N8 is reported. High‐pressure solid‐state metathesis between LiPN2 and NdF3 was employed to yield a highly crystalline product. The in situ formed LiF is believed to act both as the thermodynamic driving force and as a flux to aiding single‐crystal formation in dimensions suitable for crystal structure analysis. Magnetic properties stemming from Nd3+ ions were measured by SQUID magnetometry. LiNdP4N8 serves as a model system for the exploration of rare‐earth‐metal nitridophosphates that may even be expanded to transition metals. High‐pressure metathesis enables the systematic study of these uncharted regions of nitride‐based materials with unprecedented properties.
Self‐Assembly of α‐Helical Polypeptides Driven by Complex Coacervation
Authors: Priftis Dimitrios , Leon Lorraine , Song Ziyuan , Perry Sarah L. , Margossian Khatcher O. , Tropnikova Anna , Cheng Jianjun , Tirrell Matthew 
Published: August 2015

AbstractReported is the ability of α‐helical polypeptides to self‐assemble with oppositely‐charged polypeptides to form liquid complexes while maintaining their α‐helical secondary structure. Coupling the α‐helical polypeptide to a neutral, hydrophilic polymer and subsequent complexation enables the formation of nanoscale coacervate‐core micelles. While previous reports on polypeptide complexation demonstrated a critical dependence of the nature of the complex (liquid versus solid) on chirality, the α‐helical structure of the positively charged polypeptide prevents the formation of β‐sheets, which would otherwise drive the assembly into a solid state, thereby, enabling coacervate formation between two chiral components. The higher charge density of the assembly, a result of the folding of the α‐helical polypeptide, provides enhanced resistance to salts known to inhibit polypeptide complexation. The unique combination of properties of these materials can enhance the known potential of fluid polypeptide complexes for delivery of biologically relevant molecules.
Monitoring of Endogenous Hydrogen Sulfide in Living Cells Using Surface‐Enhanced Raman Scattering
Authors: Li Da‐Wei , Qu Lu‐Lu , Hu Kai , Long Yi‐Tao , Tian He 
Published: August 2015

AbstractHydrogen sulfide (H2S) has emerged as an important gasotransmitter in diverse physiological processes, although many aspects of its roles remain unclear, partly owing to a lack of robust analytical methods. Herein we report a novel surface‐enhanced Raman scattering (SERS) nanosensor, 4‐acetamidobenzenesulfonyl azide‐functionalized gold nanoparticles (AuNPs/4‐AA), for detecting the endogenous H2S in living cells. The detection is accomplished with SERS spectrum changes of AuNPs/4‐AA resulting from the reaction of H2S with 4‐AA on AuNPs. The SERS nanosensor exhibits high selectivity toward H2S. Furthermore, AuNPs/4‐AA responds to H2S within 1 min with a 0.1 μM level of sensitivity. In particular, our SERS method can be utilized to monitor the endogenous H2S generated in living glioma cells, demonstrating its great promise in studies of pathophysiological pathways involving H2S.
Conversion of Anthranilate Synthase into Isochorismate Synthase: Implications for the Evolution of Chorismate‐Utilizing Enzymes
Authors: Plach Maximilian G. , Löffler Patrick , Merkl Rainer , Sterner Reinhard 
Published: August 2015

AbstractChorismate‐utilizing enzymes play a vital role in the biosynthesis of metabolites in plants as well as free‐living and infectious microorganisms. Among these enzymes are the homologous primary metabolic anthranilate synthase (AS) and secondary metabolic isochorismate synthase (ICS). Both catalyze mechanistically related reactions by using ammonia and water as nucleophiles, respectively. We report that the nucleophile specificity of AS can be extended from ammonia to water by just two amino acid exchanges in a channel leading to the active site. The observed ICS/AS bifunctionality demonstrates that a secondary metabolic enzyme can readily evolve from a primary metabolic enzyme without requiring an initial gene duplication event. In a general sense, these findings add to our understanding how nature has used the structurally predetermined features of enzyme superfamilies to evolve new reactions.
Controlled Light‐Mediated Preparation of Gold Nanoparticles by a Norrish Type I Reaction of Photoactive Polymers
Authors: Mäsing Florian , Mardyukov Artur , Doerenkamp Carsten , Eckert Hellmut , Malkus Ursula , Nüsse Harald , Klingauf Jürgen , Studer Armido 
Published: August 2015

AbstractGold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light‐mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.
pH‐Responsive Pharmacological Chaperones for Rescuing Mutant Glycosidases
Authors: Mena‐Barragán Teresa , Narita Aya , Matias Dino , Tiscornia Gustavo , Nanba Eiji , Ohno Kousaku , Suzuki Yoshiyuki , Higaki Katsumi , Garcia Fernández José Manuel , Ortiz Mellet Carmen 
Published: August 2015

AbstractA general approach is reported for the design of small‐molecule competitive inhibitors of lysosomal glycosidases programmed to 1) promote correct folding of mutant enzymes at the endoplasmic reticulum, 2) facilitate trafficking, and 3) undergo dissociation and self‐inactivation at the lysosome. The strategy is based on the incorporation of an orthoester segment into iminosugar conjugates to switch the nature of the aglycone moiety from hydrophobic to hydrophilic in the pH 7 to pH 5 window, which has a dramatic effect on the enzyme binding affinity. As a proof of concept, new highly pH‐responsive glycomimetics targeting human glucocerebrosidase or α‐galactosidase with strong potential as pharmacological chaperones for Gaucher or Fabry disease, respectively, were developed.
Liquid‐Crystalline Mesogens Based on Cyclo[6]aramides: Distinctive Phase Transitions in Response to Macrocyclic Host–Guest Interactions
Authors: Li Xiaowei , Li Bao , Chen Long , Hu Jinchuan , Wen Chengdanyang , Zheng Qingdong , Wu Lixin , Zeng Huaqiang , Gong Bing , Yuan Lihua 
Published: August 2015

AbstractProducing macrocyclic mesogens that are responsive to guest encapsulation presents a significant challenge. Cyclo[6]aramides, a type of macrocycle with a hydrogen‐bond‐constrained backbone, exhibit thermotropic lamellar, discotic nematic, hexagonal, and rectangular columnar mesophases over a considerably wide temperature range, including at room temperature. Additionally, cyclo[6]aramides show unusual mesophase transitions from lamellar to hexagonal columnar phase mediated by macrocyclic host–guest (H–G) interactions between the macrocycles and alkylammonium salts. The phase transition, triggered by an organic guest engaging in H–G interactions with a macrocyclic cavity, provides a novel strategy for manipulating the properties of liquid‐crystalline materials. The crystal structure of a homologous cyclo[6]aramide reveals a disk‐shaped, near‐planar molecular backbone that facilitates intermolecular π–π stacking and leads to columnar assembly.
Zinc‐Catalyzed Dual C–X and C–H Borylation of Aryl Halides
Authors: Bose Shubhankar Kumar , Deißenberger Andrea , Eichhorn Antonius , Steel Patrick G. , Lin Zhenyang , Marder Todd B. 
Published: August 2015

AbstractA zinc‐catalyzed combined CX and CH borylation of aryl halides using B2pin2 (pin=OCMe2CMe2O) to produce the corresponding 1,2‐diborylarenes under mild conditions was developed. Catalytic CH bond activation occurs ortho to the halide groups if such a site is available or meta to the halide if the ortho position is already substituted. This method thus represents a novel use of a group XII catalyst for CH borylation. This transformation does not proceed via a free aryne intermediate, but a radical process seems to be involved.
Attachment of Norovirus to Histo Blood Group Antigens: A Cooperative Multistep Process
Authors: Mallagaray Alvaro , Lockhauserbäumer Julia , Hansman Grant , Uetrecht Charlotte , Peters Thomas 
Published: August 2015

AbstractHuman noroviruses recognize histo blood group antigens (HBGAs) as cellular attachment factors. Recently, it has been discovered that norovirus infection can be significantly enhanced by HBGA binding. Yet the attachment process and how it promotes host‐cell entry is only poorly understood. The binding of a norovirus protruding (P) domain of a predominant GII.4 Saga strain to HBGAs at atomic resolution was studied. So far, independent and equivalent multiple binding sites were held responsible for attachment. Using NMR experiments we show that norovirus‐HBGA binding is a cooperative multi‐step process, and native mass spectrometry reveals four instead of two HBGA binding sites per P‐dimer. An accompanying crystallographic study has disclosed four instead of two L‐fucose binding sites per P‐dimer of a related GII.10 strain1 further supporting our findings. We have uncovered a novel paradigm for norovirus‐HBGA recognition that will inspire further studies into norovirus–host interactions.
Ring Expansion of Epoxides under Brønsted Base Catalysis: Formal [3+2] Cycloaddition of β,γ‐Epoxy Esters with Imines Providing 2,4,5‐Trisubstituted 1,3‐Oxazolidines
Authors: Kondoh Azusa , Odaira Kenta , Terada Masahiro 
Published: August 2015

AbstractA novel ring‐expansion reaction of epoxides under Brønsted base catalysis was developed. The formal [3+2] cycloaddition reaction of β,γ‐epoxy esters with imines proceeds in the presence of triazabicyclodecene (TBD) as a superior Brønsted base catalyst to afford 2,4,5‐trisubstituted 1,3‐oxazolidines in a highly diastereoselective manner. This reaction involves the ring opening of the epoxides with the aid of the Brønsted base catalyst to generate α,β‐unsaturated esters having an alkoxide at the allylic position, which would formally serve as a synthetic equivalent of the 1,3‐dipole, followed by a cycloaddition reaction with imines in a stepwise fashion. This methodology enables the facile synthesis of enantioenriched 1,3‐oxazolidines from easily accessible enantioenriched epoxides.
Enzymatic Prenylation and Oxime Ligation for the Synthesis of Stable and Homogeneous Protein–Drug Conjugates for Targeted Therapy
Authors: Lee Joong‐jae , Choi Hyo‐Jung , Yun Misun , Kang YingJin , Jung Ji‐Eun , Ryu Yiseul , Kim Tae Yoon , Cha Young‐je , Cho Hyun‐Soo , Min Jung‐Joon , Chung Chul‐Woong , Kim Hak‐Sung 
Published: August 2015

AbstractTargeted therapy based on protein–drug conjugates has attracted significant attention owing to its high efficacy and low side effects. However, efficient and stable drug conjugation to a protein binder remains a challenge. Herein, a chemoenzymatic method to generate highly stable and homogenous drug conjugates with high efficiency is presented. The approach comprises the insertion of the CaaX sequence at the C‐terminal end of the protein binder, prenylation using farnesyltransferase, and drug conjugation through an oxime ligation reaction. MMAF and an EGFR‐specific repebody are used as the antitumor agent and protein binder, respectively. The method enables the precisely controlled synthesis of repebody–drug conjugates with high yield and homogeneity. The utility of this approach is illustrated by the notable stability of the repebody–drug conjugates in human plasma, negligible off‐target effects, and a remarkable antitumor activity in vivo. The present method can be widely used for generating highly homogeneous and stable PDCs for targeted therapy.