bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probing Helical Hydrophobic Binding Sites in Branched Starch Polysaccharides Using NMR Spectroscopy
Authors: Beeren Sophie R. , Meier Sebastian , Hindsgaul Ole 
Published: October 2013

AbstractBranched starch polysaccharides are capable of binding multiple hydrophobic guests, but their exploitation as multivalent hosts and in functional materials is limited by their structural complexity and diversity. Linear α(1–4)‐linked glucose oligosaccharides are known to bind hydrophobic guests inside left‐handed single helices in solution and the solid state. Here, we describe the development of an amphiphilic probe that binds to linear α(1–4)‐linked glucose oligosaccharides and undergoes a conformational switch upon complexation, which gives rise to dramatic changes in the 1H NMR spectrum of the probe. We use this probe to explore hydrophobic binding sites in the branched starch polysaccharides amylopectin and β‐limit dextrin. Diffusion‐ordered (DOSY), nuclear Overhauser effect (NOESY) and chemical shift perturbation (HSQC) NMR experiments are utilised to provide evidence that, in aqueous solution, branched polysaccharides bind hydrophobic guests in well‐defined helical binding sites, similar to those reported for complexation by linear oligosaccharides. By examining the binding affinity of the probe to systematically enzymatically degraded polysaccharides, we deduce that the binding sites for hydrophobic guests can be located on internal as well as external branches and that proximal α(1–6)‐linked branch points weaken but do not prevent complexation.
Ionic Liquid Crystals Derived from Amino Acids
Authors: Mansueto Markus , Frey Wolfgang , Laschat Sabine 
Published: October 2013

AbstractNovel chiral amino acid derived ionic liquid crystals with amine and amide moieties as spacers between the imidazolium head group and the alkyl chain were synthesised. The key step in the synthesis utilised the relatively uncommon SO3 leaving group in a microwave‐assisted reaction. The mesomorphic properties of the mesogens were determined by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X‐ray diffraction. All liquid crystalline salts exhibit a smectic A mesophase geometry with strongly interdigitated bilayer structures. An increase of the steric bulk of the stereogenic centre hindered the formation of mesophases. In case of phenylalanine‐derived derivatives a mesomorphic behaviour was observed for shorter alkyl chains as compared to other amino acid derivatives indicating an additional stabilising effect by the phenyl moiety.
Facile Tuning of Luminescent Platinum(II) Schiff Base Complexes from Yellow to Near‐Infrared: Photophysics, Electrochemistry, Electrochemiluminescence and Theoretical Calculations
Authors: Reid Ellen F. , Cook Vernon C. , Wilson David J. D. , Hogan Conor F. 
Published: October 2013

AbstractThe photophysical and related properties of platinum(II) Schiff base complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. A series of such complexes, differing only in the number and positioning of methoxy substituents on the phenoxy ring, were synthesised and their photophysical, electrochemical and electrochemiluminescent (ECL) properties investigated. Theoretical calculations were performed in order to gain further insight into the relationship between structure and properties in these materials. By positioning methoxy groups para and/or ortho to either the imine or the oxygen group on the ligand, electron density could be directed selectively toward the LUMO or HOMO as required. This allowed the emission colour (both photoluminescent and electrochemiluminescent) to be tuned over a wide range between 587 and 739 nm. The variation in orbital energies was also manifested in the positions of the absorption bands and the redox properties of the complexes, as well as in the NMR shifts for the uncoordinated ligands. All reported complexes displayed intense electrochemiluminescence (ECL), which could be initiated either by annihilation or co‐reactant pathways. The relationship between the electrochemical and photophysical properties and the efficiency of the ECL is discussed. For two of the complexes solid‐state ECL could be generated from electrodeposited layers of the complex.
High‐Efficiency Encapsulation of Pt Nanoparticles into the Channel of Carbon Nanotubes as an Enhanced Electrocatalyst for Methanol Oxidation
Authors: Zhang Jianan , Guo Shaojun , Wei Junyi , Xu Qun , Yan Wenfu , Fu Jianwei , Wang Shoupei , Cao Mingjing , Chen Zhimin 
Published: October 2013

AbstractPt‐based nanostructures serving as anode catalysts for the methanol oxidation reaction (MOR) have been widely studied for many years. Nevertheless, challenging issues such as poor reaction kinetics and the short‐term stability of the MOR are the main drawbacks of such catalysts and limit their applications. Herein, we have developed a facile approach to encapsulate Pt nanoparticles (NPs) inside the nanochannels of porous carbon nanotubes (CNTs; Pt‐in‐CNTs) as a new enhanced electrocatalytic material. The as‐prepared CNTs offer simultaneously ordered diffusion channels for ions and a confinement effect for the NPs, which both facilitate the promotion of catalytic kinetics and avoid the Ostwald ripening of Pt NPs, thus leading to high activity and durable cycle life as an anode catalyst for MOR. This work provides a new approach for enhancing the stability and activity by optimizing the structure of the catalyst, and the Pt‐in‐CNTs represent the most durable catalysts ever reported for MOR.
Dysprosium Complexes and Their Micelles as Potential Bimodal Agents for Magnetic Resonance and Optical Imaging
Authors: Debroye Elke , Laurent Sophie , Vander Elst Luce , Muller Robert N. , Parac‐Vogt Tatjana N. 
Published: October 2013

AbstractSix diethylene triamine pentaacetic acid (DTPA) bisamide derivatives functionalized with p‐toluidine (DTPA‐BTolA), 6‐aminocoumarin (DTPA‐BCoumA), 1‐naphthalene methylamine (DTPA‐BNaphA), 4‐ethynylaniline (DTPA‐BEthA), p‐dodecylaniline (DTPA‐BC12PheA) and p‐tetradecyl‐aniline (DTPA‐BC14PheA) were coordinated to dysprosium(III) and the magnetic and optical properties of the complexes were examined in detail. The complexes consisting of amphiphilic ligands (DTPA‐BC12PheA and DTPA‐BC14PheA) were further assembled into mixed micelles. Upon excitation into the ligand levels, the complexes display characteristic DyIII emission with quantum yields of 0.3–0.5 % despite the presence of one water molecule in the first coordination sphere. A deeper insight into the energy‐transfer processes has been obtained by studying the photophysical properties of the corresponding GdIII complexes. Since the luminescence quenching effect is decreased by the intervention of non‐ionic surfactant, quantum yields up to 1 % are obtained for the micelles. The transverse relaxivity r2 per DyIII ion at 500 MHz and 310 K reaches a maximum value of 27.4 s−1 mM−1 for Dy‐DTPA‐BEthA and 36.0 s−1 mM−1 for the Dy‐DTPA‐BC12PheA assemblies compared with a value of 0.8 s−1 mM−1 for Dy‐DTPA. The efficient T2 relaxation, especially at high magnetic field strengths, is sustained by the high magnetic moment of the dysprosium ion, the coordination of water molecules with slow water exchange kinetics and long rotational correlation times. These findings open the way to the further development of bimodal optical and magnetic resonance imaging probes starting from single lanthanide compounds.
Vaulted Biaryls in Catalysis: A Structure–Activity Relationship Guided Tour of the Immanent Domain of the VANOL Ligand
Authors: Guan Yong , Ding Zhensheng , Wulff William D. 
Published: October 2013

AbstractThe active site in the BOROX catalyst is a chiral polyborate anion (boroxinate) that is assembled in situ from three equivalents of B(OPh)3 and one of the VANOL ligand by a molecule of substrate. The substrates are bound to the boroxinate by H bonds to oxygen atoms O1–O3. The effects of introducing substituents at each position of the naphthalene core of the VANOL ligand are systematically investigated in an aziridination reaction. Substituents in the 4,4′‐ and 8,8′‐positions have a negative effect on catalyst performance, whereas, substituents in the 7‐ and 7′‐positions have the biggest impact in a positive direction.
Distinct Stepwise Reduction of a NickelNickel‐Bonded Compound Containing an α‐Diimine Ligand: From Perpendicular to Coaxial Structures
Authors: Dong Qingsong , Yang Xiao‐Juan , Gong Shida , Luo Qiong , Li Qian‐Shu , Su Ji‐Hu , Zhao Yanxia , Wu Biao 
Published: October 2013

AbstractA nickelnickel‐bonded complex, [{Ni(μ‐L.−)}2] (1; L=[(2,6‐iPr2C6H3)NC(Me)]2), was synthesized from reduction of the LNiBr2 precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)3]⋅[{Ni(μ‐L.−)}2] (2; DME=1,2‐dimethoxyethane), [Na(Et2O)]Na[(L.−)NiNiL2−] (3), and [Na(Et2O)]2Na[L2−NiNiL2−] (4). Here L represents the neutral ligand, L.− denotes its radical monoanion, and L2− is the dianion. All of the four compounds feature a short NiNi bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular (1 and 2) and the coaxial (3 and 4) structure, in which the metalmetal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, NiNi bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations.
Heterogeneous CuII‐Catalysed Solvent‐Controlled Selective N‐Arylation of Cyclic Amides and Amines with Bromo‐iodoarenes
Authors: Kundu Debasish , Bhadra Sukalyan , Mukherjee Nirmalya , Sreedhar Bojja , Ranu Brindaban C. 
Published: October 2013

AbstractA selective N‐arylation of cyclic amides and amines in DMF and water, respectively, catalysed by CuII/Al2O3 has been achieved. This protocol has been employed for the synthesis of a library of arenes bearing a cyclic amide and an amine moiety at two ends, including a few scaffolds of therapeutic importance. The mechanism has been established based on detailed electron paramagnetic resonance (EPR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), UV diffuse reflectance spectroscopy (DRS) and inductively coupled plasma‐mass spectrometry (ICP‐MS) studies of the catalyst at different stages of the reaction. The CuII/Al2O3 catalyst was recovered and recycled for subsequent reactions.
A New Chiral Binaphthalene‐Based Fluorescence Polymer Sensor for the Highly Enantioselective Recognition of Phenylalaninol
Authors: Wei Guo , Zhang Shuwei , Dai Chunhui , Quan Yiwu , Cheng Yixiang , Zhu Chengjian 
Published: October 2013

AbstractA new (S)‐binaphthalene‐based polymer (P‐1) was synthesized by the polymerization of 5,5′‐((2,5‐dibutoxy‐1,4‐phenylene)bis(ethyne‐2,1‐diyl))bis(2‐hydroxy‐3‐(piperidin‐1‐ylmethyl) benzaldehyde (M‐1) with (S)‐2,2′‐dimethoxy‐(1,1′‐binaphthalene)‐3,3′‐diamine (M‐2) through the formation of a Schiff base; the corresponding chiral polymer (P‐2) could be obtained by the reduction of polymer P‐1 with NaBH4. Chiral polymer P‐1 exhibited a remarkable “turn‐on” fluorescence‐enhancement response towards (D)‐phenylalaninol and excellent enantioselective recognition behavior with enantiomeric fluorescence difference ratios (ef) as high as 8.99. More importantly, chiral polymer P‐1 displays a bright blue fluorescence color change upon the addition of (D)‐phenylalaninol under a commercially available UV lamp, which can be clearly observed by the naked eye. On the contrary, chiral polymer P‐2 showed weaker enantioselective fluorescence ability towards the enantiomers of phenylalaninol.
Integrated Hollow Mesoporous Silica Nanoparticles for Target Drug/siRNA Co‐Delivery
Authors: Ma Xing , Zhao Yun , Ng Kee Woei , Zhao Yanli 
Published: October 2013

AbstractA hollow mesoporous silica nanoparticle (HMSNP) based drug/siRNA co‐delivery system was designed and fabricated, aiming at overcoming multidrug resistance (MDR) in cancer cells for targeted cancer therapy. The as‐prepared HMSNPs have perpendicular nanochannels connecting to the internal hollow cores, thereby facilitating drug loading and release. The extra volume of the hollow core enhances the drug loading capacity by two folds as compared with conventional mesoporous silica nanoparticles (MSNPs). Folic acid conjugated polyethyleneimine (PEI‐FA) was coated on the HMSNP surfaces under neutral conditions through electrostatic interactions between the partially charged amino groups of PEI‐FA and the phosphate groups on the HMSNP surfaces, blocking the mesopores and preventing the loaded drugs from leakage. Folic acid acts as the targeting ligand that enables the co‐delivery system to selectively bind with and enter into the target cancer cells. PEI‐FA‐coated HMSNPs show enhanced siRNA binding capability on account of electrostatic interactions between the amino groups of PEI‐FA and siRNA, as compared with that of MSNPs. The electrostatic interactions provide the feasibility of pH‐controlled release. In vitro pH‐responsive drug/siRNA co‐delivery experiments were conducted on HeLa cell lines with high folic acid receptor expression and MCF‐7 cell lines with low folic acid receptor expression for comparison, showing effective target delivery to the HeLa cells through folic acid receptor meditated cellular endocytosis. The pH‐responsive intracellular drug/siRNA release greatly minimizes the prerelease and possible side effects of the delivery system. By simultaneously delivering both doxorubicin (Dox) and siRNA against the Bcl‐2 protein into the HeLa cells, the expression of the anti‐apoptotic protein Bcl‐2 was successfully suppressed, leading to an enhanced therapeutic efficacy. Thus, the present multifunctional nanoparticles show promising potentials for controlled and targeted drug and gene co‐delivery in cancer treatment.
Formation of Quaternary Stereogenic Centers by Copper‐Catalyzed Asymmetric Conjugate Addition Reactions of Alkenylaluminums to Trisubstituted Enones
Authors: Müller Daniel , Alexakis Alexandre 
Published: October 2013

AbstractAlkenylaluminums undergo asymmetric copper‐catalyzed conjugate addition (ACA) to β‐substituted enones allowing the formation of stereogenic all‐carbon quaternary centers. Phosphinamine–copper complexes proved to be particularly active and selective compared with phosphoramidite ligands. After extensive optimization, high enantioselectivities (up to 96 % ee) were obtained for the addition of alkenylalanes to β‐substituted enones. Two strategies for the generation of the requisite alkenylaluminums were explored allowing for the introduction of aryl‐ and alkyl‐substituted alkenyl nucleophiles. Moreover, alkyl‐substituted phosphinamine (SimplePhos) ligands were identified for the first time as highly efficient ligands for the Cu‐catalyzed ACA.
Regio‐ and Stereochemical Studies on the Nitroso‐Diels–Alder Reaction with 1,2‐Disubstituted Dienes
Authors: Galvani Gilles , Lett Robert , Kouklovsky Cyrille 
Published: October 2013

AbstractThe regioselectivity of the nitroso‐Diels–Alder reaction between unsymmetrical acyclic dienes and Boc‐nitroso (Boc=tert‐butoxycarbonyl) reagent or the Wightman chiral chloronitroso reagents has been studied. With the Boc‐nitroso reagent, the selectivity is a consequence of steric effects at the C1‐position in the diene and electronic effects at the C2‐position in the diene. The combination of an unprotected hydroxyethyl side chain at C1 and an electron‐withdrawing group at C2 allows complete regioselectivity in favour of the proximal isomer. The same isomer was obtained exclusively with the chiral nitroso reagent with high enantioselectivities. A model based on steric effects is proposed.
Highly Hydrogenated Graphene through Microwave Exfoliation of Graphite Oxide in Hydrogen Plasma: Towards Electrochemical Applications
Authors: Eng Alex Yong Sheng , Sofer Zdenek , Šimek Petr , Kosina Jiri , Pumera Martin 
Published: October 2013

AbstractHydrogenated graphenes exhibit a variety of properties with potential applications in devices, ranging from a tunable band gap to fluorescence, ferromagnetism, and the storage of hydrogen. We utilize a one‐step microwave‐irradiation process in hydrogen plasma to create highly hydrogenated graphene from graphite oxides. The procedure serves the dual purposes of deoxygenation and concurrent hydrogenation of the carbon backbone. The effectiveness of the hydrogenation process is investigated on three different graphite oxides (GOs), which are synthesized by using the Staudenmaier, Hofmann, and Hummers methods. A systematic characterization of our hydrogenated graphenes is performed using UV/Vis spectroscopy, SEM, AFM, Raman spectroscopy, FTIR spectroscopy, X‐ray photoelectron spectroscopy (XPS), combustible elemental analysis, and electrical conductivity measurements. The highest hydrogenation extent is observed in hydrogenated graphene produced from the Hummers‐method GO, with a hydrogen content of 19 atomic % in the final product. In terms of the removal of oxygen groups, microwave exfoliation yields graphenes with very similar oxygen contents despite differences in their parent GOs. In addition, we examine the prospective application of hydrogenated graphenes as electrochemical transducers through a cyclic voltammetry (CV) study. The highly hydrogenated graphenes exhibit fast heterogeneous electron‐transfer rates, suggestive of their suitability for electrochemical applications in electrodes, supercapacitors, batteries, and sensors.
Enantiopurity Determination of the Enantiomers of the Triple Reuptake Inhibitor Indatraline
Authors: Grimm Stefanie H. , Allmendinger Lars , Höfner Georg , Wanner Klaus T. 
Published: October 2013

ABSTRACTThe present study describes the development of two approaches for the determination of the enantiopurity of both enantiomers of indatraline. Initially, a method was developed using different chiral solvating agents (CSAs) for diastereomeric discrimination regarding signal separation in 1H nuclear magnetic resonance (NMR) spectroscopy, revealing MTPA as a promising choice for the differentiation of the indatraline enantiomers. This CSA was also tested for its ideal molar ratio, temperature, and solvent. Optimized conditions could be achieved that made determination of enantiopurity for (1R,3S)‐indatraline up to 98.9% enantiomeric excess (ee) possible. To quantify even higher enantiopurities, a high‐performance liquid chromatography (HPLC) method based on a modified β‐cyclodextrine phase was established. The influence of buffer type, concentration, pH value, percentage and kind of organic modifier, temperature, injection volume as well as sample solvent on chromatographic parameters was investigated. Afterwards, the reliability of the established HPLC method was demonstrated by validation according to the ICH guideline Q2(R1) regarding specificity, accuracy, precision, linearity, and quantitation limit. The developed method proved to be strictly linear within a concentration range of 1.25–1000 μM for the (1R,3S)‐enantiomer and 1.25‐750 μM for its mirror image that enables a reliable determination of enantiopurities up to 99.75% ee for the (1R,3S)‐enantiomer and up to 99.67% ee for the (1S,3R)‐enantiomer. Chirality 25:923–933, 2013. © 2013 Wiley Periodicals, Inc.
Bidirectional Chiral Inversion of Trantinterol Enantiomers After Separate Doses to Rats
Authors: Qin Feng , Wang Xintao , Jing Lijuan , Pan Li , Cheng Maosheng , Sun Guoxiang , Li Famei 
Published: October 2013

ABSTRACTThe chiral inversion and pharmacokinetics of two enantiomers of trantinterol, a new β2 agonist, were studied in rats dosed (+)‐ or (−)‐trantinterol separately. Plasma concentrations of (+)‐ and (−)‐trantinterol were measured by chiral stationary phase liquid chromatography tandem mass spectroscopy (LC‐MS/MS). The apparent inversion ratio was calculated as the ratio of AUC0‐t of (−)‐trantinterol or (+)‐trantinterol inverted from their antipodes to the sum of the AUC0‐t of (−)‐ and (+)‐trantinterol. Following single intravenous administration, both given enantiomers declined in similar plasma concentrations, suggesting that the two enantiomers have approximately the same disposition kinetics by the route of intravenous administration. However, after single oral administration, plasma concentrations of uninverted (−)‐trantinterol at many timepoints were significantly higher than those of uninverted (+)‐trantinterol, suggesting that the two enantiomers undergo apparently different absorption or metabolism after oral administration. Significant bidirectional chiral inversion occurred after intravenous and oral administration of (+)‐ or (−)‐trantinterol. After dosing with optically pure enantiomer, the concentration of the administered enantiomer predominated in vivo. The AUC0‐36 of (+)‐trantinterol after intravenous and oral dosing of (−)‐trantinterol were 16.6 ± 5.2 and 33.3 ± 16%, respectively of those of total [(+) + (−)] trantinterol. The AUC0‐36 of (−)‐trantinterol after intravenous and oral dosing of (+)‐trantinterol were 19.6 ± 8.8 and 37.9 ± 4.5%, respectively, of those of total [(−) + (+)] trantinterol. After intravenous administration of (+)‐ and (−)‐trantinterol the chiral inversion ratios of the two enantiomers were not significantly different and similar results were found for oral administration. The extent of chiral inversion after intravenous administration was apparently lower, indicating that the bidirectional chiral inversion was not only systemic but also presystemic. Chirality 25:934–938, 2013.© 2013 Wiley Periodicals, Inc.
Significance of the Natural Occurrence of L‐ Versus D‐Pipecolic Acid: A Review
Authors: Vranova Valerie , Lojkova Lea , Rejsek Klement , Formanek Pavel 
Published: October 2013

ABSTRACTPipecolic acid naturally occurs in microorganisms, plants, and animals, where it plays many roles, including the interactions between these organisms, and is a key constituent of many natural and synthetic bioactive molecules. This article provides a review of current knowledge on the natural occurrence of pipecolic acid and the known and potential significance of its L‐ and D‐enantiomers in different scientific disciplines. Knowledge gaps with perspectives for future research identified within this article include the roles of the L‐ versus the D‐enantiomer of pipecolic acid in plant resistance, nutrient acquisition, and decontamination of polluted soils, as well as rhizosphere ecology and medical issues. Chirality 25:823–831, 2013. © 2013 Wiley Periodicals, Inc.
Enantioselective Liquid–Liquid Extraction of Zopiclone With Mandelic Acid Ester Derivatives
Authors: Peng Yangfeng , He Quan , Zuo Bin , Niu Haibo , Tong Tianzhong , Zhao Hongliang 
Published: October 2013

ABSTRACTEnantioselective liquid–liquid extraction of zopiclone was conducted by employing a series of (R)‐mandelic acid esters as chiral extractants. The effects of concentration of extractant, concentration of zopiclone, type of organic solvent, pH value, and temperature on the extraction efficiency were investigated. (R)‐o‐chloromandelic acid propyl ester was demonstrated to be an efficient chiral extractant for zopiclone resolution with a maximum enantioselectivity of 1.6. Chirality 25:952–956, 2013. © 2013 Wiley Periodicals, Inc.
Preparation and Characterization of Compact Binderless Zeolite Shapes with Faujasit and Linde Type A Structure
Authors: Schumann Kristin , Unger Baldur , Brandt Alfons , Fischer Gundula , Richter Hannes , Jänchen Jochen 
Published: October 2013

AbstractObwohl eine Vielzahl an industriellen Anwendungen für Zeolithe besteht, haben Bindemittel, die zu Herstellung von konventionellen Zeolithformkörpern benutzt werden, einen negativen Einfluss. Die Herstellung und Charakterisierung von mechanisch stabilen kompakten bindemittelfreien Zeolithformkörpern mit Faujasit‐ und Linde Typ A‐Struktur wird am Beispiel von Wabenkörper und Mehrkanalrohren beschrieben. Diese erhöhen aufgrund ihres hohen Zeolithanteils sowie ihrer großen Raumausfüllung beispielsweise die Effektivität von bekannten dynamischen Adsorptions‐, Katalyse‐ oder Filtrationsprozessen.