bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Frustrated and Confused Lewis Pair
Authors: McQuilken Alison C. , Dao Quang Minh , Cardenas Allan Jay P. , Bertke Jeffery A. , Grimme Stefan , Warren Timothy H. 
Published: October 2016

AbstractWe report a new class of frustrated Lewis pairs (FLPs) by the hydroboration of bulky isocyanates iPr2ArNCO (iPr2Ar=2,6‐iPr2C6H3) and Ph2tBuArNCO (Ph2tBuAr=2,6‐Ph2‐4‐tBuC6H2) with Piers’ borane (HB(C6F5)2). While hydroboration of smaller isocyanates such as iPr2ArNCO leads to isocyanate—N/B FLP adducts, hydroboration of the bulkier Ph2tBuArNCO allows isolation of the substrate‐free aminoborane with a short, covalent N−B bond. This confused FLP reversibly binds unsaturated substrates such as isocyanates and isocyanides, suggesting the intermediacy of a “normal” FLP along the reaction pathway, supported by high‐level DFT studies and variable‐temperature NMR spectroscopy. These results underscore the possibility of FLP behavior in systems that possess no obvious frustrated Lewis acid–base interaction.
Nucleophile‐Directed Stereocontrol Over Glycosylations Using Geminal‐Difluorinated Nucleophiles
Authors: Schumann Benjamin , Parameswarappa Sharavathi G. , Lisboa Marilda P. , Kottari Naresh , Guidetti Fabio , Pereira Claney L. , Seeberger Peter H. 
Published: October 2016

AbstractThe glycosylation reaction is the key transformation in oligosaccharide synthesis, but it is still difficult to control in many cases. Stereocontrol during cis‐glycosidic linkage formation relies almost exclusively on tuning the glycosylating agent or the reaction conditions. Herein, we use nucleophile‐directed stereocontrol to manipulate the stereoselectivity of glycosylation reactions. Placing two fluorine atoms in close proximity to the hydroxy group of an aliphatic amino alcohol lowers the oxygen nucleophilicity and reverses the stereoselectivity of glycosylations to preferentially form the desired cis‐glycosides with a broad set of substrates. This concept was applied to the design of a cis‐selective linker for automated glycan assembly. Fluorination of an amino alcohol linker does not impair glycan immobilization and lectin binding as illustrated by glycan microarray experiments. These fluorinated linkers enable the facile generation of α‐terminating synthetic glycans for the formation of glycoconjugates.
Base‐Resolution Analysis of Cisplatin–DNA Adducts at the Genome Scale
Authors: Shu Xiaoting , Xiong Xushen , Song Jinghui , He Chuan , Yi Chengqi 
Published: October 2016

AbstractCisplatin, one of the most widely used anticancer drugs, crosslinks DNA and ultimately induces cell death. However, the genomic pattern of cisplatin–DNA adducts has remained unknown owing to the lack of a reliable and sensitive genome‐wide method. Herein we present “cisplatin‐seq” to identify genome‐wide cisplatin crosslinking sites at base resolution. Cisplatin‐seq reveals that mitochondrial DNA is a preferred target of cisplatin. For nuclear genomes, cisplatin–DNA adducts are enriched within promoters and regions harboring transcription termination sites. While the density of GG dinucleotides determines the initial crosslinking of cisplatin, binding of proteins to the genome largely contributes to the accumulative pattern of cisplatin–DNA adducts.
Alleno‐Acetylenic Cage (AAC) Receptors: Chiroptical Switching and Enantioselective Complexation of trans‐1,2‐Dimethylcyclohexane in a Diaxial Conformation
Authors: Gropp Cornelius , Trapp Nils , Diederich François 
Published: October 2016

AbstractFour enantiopure 1,3‐diethynylallenes (DEAs) with OH termini were attached to the rim of a resorcin[4]arene cavitand. The system undergoes conformational switching between a cage form, closed by a circular H‐bonding array, and an open form, with the tertiary alcohol groups reaching outwards. The cage form is predominant in apolar solvents, and the open conformation in small, polar solvents. Both states were confirmed in solution and in X‐ray co‐crystal structures. ECD spectra of the alleno‐acetylenic cages (AACs) are highly conformation sensitive, the longest wavelength Cotton effect at 304 nm switches from Δϵ=+191 m−1 cm−1 for open (P)4‐AAC⊂acetonitrile to Δϵ=−691 m−1 cm−1 (ΔΔϵ=882 m−1 cm−1) for closed (P)4‐AAC⊂cyclohexane. Complete chiral resolution of (±)‐trans‐1,2‐dimethylcyclohexane was found in the X‐ray structures, with (P)4‐AAC exclusively bound to the (R,R)‐ and (M)4‐AAC to the (S,S)‐guest. Guest inclusion occurs in a higher energy diaxial conformation.
Hydrogels reinforced with nanoclays with improved response rate
Authors: Djonlagic Jasna , Lancuski Anica , Nikolic Marija S. , Rogan Jelena , Ostojic Sanja , Petrovic Zoran 
Published: October 2016

ABSTRACTTwo series of semiinterpenetrating networks (SIPN) based on linear hydrophilic poly(vinyl alcohol) (PVA) and thermo‐responsive poly(N‐isopropylacrylamide) (PNIPA), physically crosslinked with inorganic clay, are presented. The hydrogels with different crosslinking densities were prepared by varying the content of clay from 1 to 6 wt % and contained linear interpenetrant, PVA in the range of 0.5–1.5 wt %. The effect of clay content on swelling/deswelling behavior and phase transition in PNIPA gels, as well as the feasibility of reinforcing the gels with high molecular weight PVA, were analyzed. The thermal response of hydrogels, followed by DSC, confirmed that the insertion of hydrophilic PVA did not have a significant effect on the onset of the volume phase transition temperature, while the response was faster. The equilibrium degree of swelling of SIPNs and PNIPA hydrogels was in the range of 9–79 and decreased with increasing content of clay. The internal morphology and surface wettability of the hydrogels were investigated by scanning electron microscope analysis and contact angle measurements, respectively. The network structural parameters of the PNIPA and SIPN nanocomposites hydrogels, such as the average molecular weight between crosslinks, Mc, and effective crosslinking density, Ne, were determined by dynamic mechanical analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44535.
Resolving some chronological problems at Nombe rock shelter in the highlands of Papua New Guinea
Authors: DENHAM TIM , MOUNTAIN MARY‐JANE 
Published: October 2016

ABSTRACTNew AMS radiocarbon dating at Nombe rock shelter in Simbu Province, Papua New Guinea confirms human use from c.25500–19600 calBP and corroborates previous chronostratigraphic interpretations for four major periods of cultural deposition. The original conventional radiocarbon dating program was largely undertaken on bone and flowstones, due to the limitations of dating small charcoal fragments in the 1970s and 1980s before the advent of, and widespread access to, AMS dating. Here, 18 new AMS dates on small fragments of charcoal hand‐picked from previously collected sediment samples enable an evaluation that largely confirms previous dating. These findings are significant because they indicate that the chronostratigraphy, at least for the portion of the site redated thus far, is comparatively robust. Primarily, the new dating results indicate the chronostratigraphy for the early and mid‐Holocene, a period crucial for understanding the emergence of agriculture in the highlands, is well preserved at the site.
Synthesis, Structures, Resolution, and Chiroptical Properties of 1,16‐Diaryl‐Substituted Benzo[5]helicene Derivatives
Authors: Lin Wei‐Bin , Li Meng , Fang Lei , Shen Yun , Chen Chuan‐Feng 
Published: October 2016

AbstractAn efficient route to the synthesis of benzo[5]helicene derivatives functionalized on the interior side of the helix was developed, and resulted in a series of 1,16‐diaryl‐substituted benzo[5]helicene derivatives starting from easily available 7‐methoxytetralone. X‐ray crystal structures showed that the benzo[5]helicene derivatives had highly helical, twisted structures, and could all create hierarchical packing architectures with alternating P and M layers in the solid state. Moreover, seven pairs of enantiomers based on 1,16‐diaryl‐substituted benzo[5]helicene derivatives were also obtained by efficient resolution through HPLC with semipreparative chiral columns. The enantiomers all showed clear mirror‐image circular dichroism (CD) spectra and high specific optical rotations, and their absolute configurations were determined by X‐ray crystallography. Interestingly, a helical nanotubular structure was formed by the self‐assembly of one enantiomer through halogen bonding. Furthermore, the enantiomers were found to have high racemization barriers and thermostability, which might be caused by the introduction of aryl substituents at the C1(C16) position.
Different long‐term trends of extra‐tropical cyclones and windstorms in ERA‐20C and NOAA‐20CR reanalyses
Authors: Befort Daniel J. , Wild Simon , Kruschke Tim , Ulbrich Uwe , Leckebusch Gregor C. 
Published: October 2016

AbstractNOAA 20th century and ERA‐20C reanalysis datasets are evaluated regarding the representation of extra‐tropical cyclones and windstorms over the Northern and Southern Hemisphere during the respective 6‐month winter seasons. The results indicate substantial differences in low‐frequency variability between the two datasets – especially in the first half of the 20th century – expressed in different signs and/or magnitudes of long‐term trends. This is hampering a reliable analysis of real long‐term trends of cyclone and windstorm activity. However, higher‐frequency variability is in good agreement between both datasets especially for the Northern Hemisphere.
Deriving cloud microphysics from radiometric measurements in the Amazon Basin
Authors: Correia Alexandre L. , Catandi Patricia B. 
Published: October 2016

AbstractA prototype suite comprised of calibrated radiometric cameras was developed to derive estimates of key cloud properties such as brightness temperature and droplet effective radius, with high spatial and temporal resolution. The system was assembled aboard an airplane to measure shortwave radiation scattered by clouds, and longwave infrared radiation emitted by clouds. This allowed deriving cloud droplet radii in shallow cumuli, with values ranging from about 6 to 14 µm. The measured longwave radiance was inverted using Planck's equation to derive the brightness temperature, with results ranging between −18 °C and +15 °C.
Parallel online multi‐wavelength (2D) fluorescence spectroscopy in each well of a continuously shaken microtiter plate
Authors: Ladner Tobias , Beckers Mario , Hitzmann Bernd , Büchs Jochen 
Published: October 2016

AbstractSmall‐scale high‐throughput screening devices are becoming increasingly important in bioprocess development. Conventional dipping probes for process monitoring are often too large to be used in these devices. Thus, optical measurements are often the method of choice. Even some parameters that cannot directly be measured by fluorescence become accessible via sensitive fluorescence dyes. However, not all compounds of interest are measurable by this technique. Recent studies applying multi‐wavelength (2D) fluorescence spectroscopy in combination with chemometrics have shown that information on numerous analytes is obscured by the fluorescence data. Hitherto, this measurement technique has only been available on the scale of stirred tank fermenters. This work introduces a new device for multi‐wavelength (2D) fluorescence spectroscopy in each well of a continuously shaken microtiter plate. Using a combination of spectrograph and CCD detector, the required time per measurement cycle in a 48‐well microtiter plate was 0.5 h. Cultures of Hansenula polymorpha and Escherichia coli are monitored. The concentrations of glycerol, glucose and acetate as well as pH are determined using partial least square (PLS) models. Because a pH‐sensitive fluorescence dye was not required, no dependency of the pKa of a fluorescence dye exists, and measurements in the low pH range can be obtained.
Peptide‐based supramolecular hydrogels for delivery of biologics
Authors: Li Yi , Wang Feihu , Cui Honggang 
Published: October 2016

AbstractThe demand for therapeutic biologics has rapidly grown over recent decades, creating a dramatic shift in the pharmaceutical industry from small molecule drugs to biological macromolecular therapeutics. As a result of their large size and innate instability, the systemic, topical, and local delivery of biologic drugs remains a highly challenging task. Although there exist many types of delivery vehicles, peptides and peptide conjugates have received continuously increasing interest as molecular blocks to create a great diversity of supramolecular nanostructures and hydrogels for the effective delivery of biologics, due to their inherent biocompatibility, tunable biodegradability, and responsiveness to various biological stimuli. In this context, we discuss the design principles of supramolecular hydrogels using small molecule peptides and peptide conjugates as molecular building units, and review the recent effort in using these materials for protein delivery and gene delivery.
DNA‐Templated Synthesis of Perylenediimide Stacks Utilizing Abasic Sites as Binding Pockets and Reactive Sites
Authors: Takada Tadao , Ido Misa , Ashida Akane , Nakamura Mitsunobu , Yamana Kazushige 
Published: October 2016

AbstractDNA is considered to be a promising biomolecule as a template and scaffold for arranging and organizing functional molecules on the nanoscale. The construction and evaluation of DNAs containing multiple functional molecules that are useful for optoelectronic devices and sensors has been studied. In this paper we report the efficient incorporation of perylenediimide (PDI) units into DNA by using abasic sites both as binding sites and as reactive sites and the construction of PDI stacks within the DNA structure, accomplished through the preorganization of the PDI units in the hydrophobic pocket within the DNA. Our approach could become a valuable method for construction of DNA/chromophore hybrid structures potentially useful for the design of DNA‐based devices and biosensors.
Switch in Cofactor Specificity of a Baeyer–Villiger Monooxygenase
Authors: Beier Andy , Bordewick Sven , Genz Maika , Schmidt Sandy , van den Bergh Tom , Peters Christin , Joosten Henk‐Jan , Bornscheuer Uwe T. 
Published: October 2016

AbstractBaeyer–Villiger monooxygenases (BVMOs) catalyze the oxidation of ketones to esters or lactones by using molecular oxygen and a cofactor. Type I BVMOs display a strong preference for NADPH. However, for industrial purposes NADH is the preferred cofactor, as it is ten times cheaper and more stable. Thus, we created a variant of the cyclohexanone monooxygenase from Acinetobacter sp. NCIMB 9871 (CHMOAcineto); this used NADH 4200‐fold better than NADPH. By combining structure analysis, sequence alignment, and literature data, 21 residues in proximity of the cofactor were identified and targeted for mutagenesis. Two combinatorial variants bearing three or four mutations showed higher conversions of cyclohexanone with NADH (79 %) compared to NADPH (58 %) as well as specificity. The structural reasons for this switch in cofactor specificity of a type I BVMO are especially a hydrogen‐bond network coordinating the two hydroxy groups of NADH through direct interactions and bridging water molecules.
Sorption‐Enhanced Steam Reforming of Glycerol over Ni–hydrotalcite: Effect of Promotion with Pt
Authors: Dewoolkar Karan D. , Vaidya Prakash D. 
Published: October 2016

AbstractSorption‐enhanced steam reforming of glycerol (SESRG) is a promising method for the sustainable production of hydrogen (H2). In this work, composites of Ni and cationic‐modified hydrotalcite (HTlc) were promoted with Pt, thus resulting in two novel hybrid materials Pt‐NiMgHTlc and Pt‐NiCuHTlc. Activity trials for SESRG were performed in a fixed‐bed reactor in the range 673–873 K and it was found that the promotion with Pt improved H2 purity and multi‐cycle durability. The best results were achieved when Pt‐NiCuHTlc was employed at T=823 K: a H2 concentration of 98.7 mol % and adsorption capacity of 1.34 mol CO2/kg sorbent was achieved. When the multi‐cycle performance was tested for 20 cycles, it was found that NiMgHTlc, NiCuHTlc, Pt‐NiMgHTlc, and Pt‐NiCuHTlc were stable for 5, 8, 13, and 18 cycles. Finally, a likely reaction pathway for SESRG over the investigated multifunctional materials was proposed.
Tyrosine‐Based Ionic Liquid Crystals: Switching from a Smectic A to a Columnar Mesophase by Exchange of the Spherical Counterion
Authors: Neidhardt Manuel M. , Wolfrum Manpreet , Beardsworth Stuart , Wöhrle Tobias , Frey Wolfgang , Baro Angelika , Stubenrauch Cosima , Giesselmann Frank , Laschat Sabine 
Published: October 2016

AbstractSynthetic strategies were developed to prepare l‐tyrosine‐based ionic liquid crystals with structural variations at the carboxylic and phenolic OH groups as well as the amino functionality. Salt metathesis additionally led to counterion variation. The liquid‐crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X‐ray diffraction (WAXS, SAXS). The symmetrical ILC chlorides bearing the same alkyl chain at both the ester and ether but either an acyclic or cyclic guanidinium group displayed enantiotropic SmA2 mesophases with phase widths of 31–88 K irrespective of the head group. It was particularly the replacement of chloride in the acyclic guanidinium ILC by hexafluorophosphate that induced a phase change from SmA2 to Colr. This phase change was attributed to a higher curvature of the interface due to the larger anion, which increased the effective head group cross‐sectional area of the amphiphilic ILC. The unsymmetrical acyclic guanidinium chlorides, bearing a constant C14 ester and variable alkyl chains on the phenolic position, formed enantiotropic SmA2 phases. The derivative with the largest difference in chain lengths, however, displayed a Colr phase, resulting from discoid aggregates of the cone‐shaped guanidinium chloride. The results are discussed in terms of the packing parameters, which indicate that the phase behaviour of the thermotropic tyrosine‐based ILCs shows analogies to those of lyotropic liquid crystals.
Metal‐Free Reaction of ortho‐Carbonylated Alkynyl‐Substituted Arylaldehydes with Common Amines: Selective Access to Functionalized Isoindolinone and Indenamine Derivatives
Authors: Cao Ziping , Zhu Hongbo , Meng Xin , Guan Jun , Zhang Qiang , Tian Laijin , Sun Xuejun , Chen Guang , You Jinmao 
Published: October 2016

AbstractHerein we describe a reaction of ortho‐carbonylated alkynyl‐substituted arylaldehydes with common primary amines that can provide functionalized isoindolinone and 3‐hydroxylindenamine products in high yields. Depending on the substituent size of primary amines, two distinct reaction pathways were exploited selectively, that are, an initial aza‐conjugate addition followed by hydrogen transfer to access isoindolinone framework and a unique oxa‐conjugate addition followed by Petasis–Ferrier rearrangement to afford indenamine derivatives. In the presence of Et3N, the reaction property of small primary amines was changed, proceeding to afford 3‐hydroxylindenamine derivatives efficiently. These products contain interesting substructures that exist in many natural products and bioactive molecules. The reaction features contain the use of transition‐metal‐free catalysts, simple operation, broad substrate scope, and product diversity.
Arylimido‐Bridged Dinuclear Ti(μ‐NAr)2Ti Scaffold for Alkyne Insertion into the ortho‐C−H Bond of Arylimido Ligands
Authors: Nagae Haruki , Hato Wataru , Kawakita Kento , Tsurugi Hayato , Mashima Kazushi 
Published: October 2016

AbstractDinuclear titanium dialkyl complexes bridged by two μ‐arylimido ligands, [CpTi(CH2SiMe3)(μ‐NAr)]2 (Cp=cyclopentadienyl) activated an ortho‐aryl C−H bond of an μ‐arylimido ligand to form a four‐membered titanacycle. The subsequent insertion reaction of 1‐(trimethylsilyl)propyne into a metal–carbon bond of the four‐membered titanacycle yielded the corresponding six‐membered titanacycle. Further ortho‐C−H bond activation of the other μ‐arylimido ligand and an insertion reaction proceeded to give dinuclear titanium complexes with two six‐membered titanacycles. An Eyring plot in the temperature range 130–150 °C revealed activation parameters for the alkenylation reaction, and deuterium‐labeling experiments showed that the C−H bond activation step is the rate determining step. Relative Gibbs free energies of the starting complexes, reaction intermediates, and transition states were calculated by using DFT calculations.
Synthesis and Self‐Assembly of Cyclic 2,7‐Anthrylene Ethynylene 1,3‐Phenylene Ethynylene Trimer with a Planar Conformation
Authors: Takaki Yuta , Ozawa Ryota , Kajitani Takashi , Fukushima Takanori , Mitsui Masaaki , Kobayashi Kenji 
Published: October 2016

AbstractCyclic arylene ethynylene hexamer 1, composed of alternating 2,7‐anthrylene ethynylene units and meta‐phenylene ethynylene units, was synthesized. It shows C3 symmetry and possesses a flat and rigid conformation with a large equilateral triangle‐like cavity. Macrocycle 1 self‐associates through π–π stacking interactions between the anthracene‐containing macrocyclic aromatic cores with indefinite‐association constant KE=6980 m−1 in CDCl3 at 303 K. Macrocycle 1 also self‐assembles into π‐stacked nanofibers in the drop‐cast film.
Nanocomposites through the Chemistry of Single‐Source Precursors: Understanding the Role of Chemistry behind the Design of Monolith‐Type Nanostructured Titanium Nitride/Silicon Nitride
Authors: Bechelany Mirna Chaker , Proust Vanessa , Lale Abhijeet , Miele Philippe , Malo Sylvie , Gervais Christel , Bernard Samuel 
Published: October 2016

AbstractMonolith‐type titanium nitride/silicon nitride nanocomposites, denoted as TiN/Si3N4, have been prepared by a reaction of polysilazanes with a titanium amide precursor, warm pressing of the resultant polytitanosilazanes, and subsequent pyrolysis of the green bodies at 1400 °C. Initially, a series of polytitanosilazanes was synthesized and the role of the chemistry behind their synthesis was studied in detail by using solid‐state NMR spectroscopy, elemental analysis, and molecular‐weight measurements. The intimate relationship between the chemistry and the processability of these precursors is discussed. Polytitanosilazanes display the appropriate requirements for facile processing in solution and as a melt, but they must be treated with liquid ammonia to be adapted for solid‐state processing, that is, warm‐pressing, to design dense and mechanically stable structures after pyrolysis. We provide a comprehensive mechanistic study of the nanocomposite conversion based on solid‐state NMR spectroscopy coupled with thermogravimetric experiments. HRTEM images coupled with XRD and Raman spectroscopy confirmed the unique nanostructural features of the nanocomposites, which appear to be a result of the molecular origin of the materials. The as‐obtained samples are composed of an amorphous Si3N4 matrix, in which TiN nanocrystals are homogeneously formed in situ in the matrix during the process. The hardness and Young moduli were measured and are discussed.
Synthesis of Multivalent Organotellurium Chain‐Transfer Agents by Post‐modification and Their Applications in Living Radical Polymerization
Authors: Fan Weijia , Nakamura Yasuyuki , Yamago Shigeru 
Published: October 2016

AbstractFunctionalized or multivalent organotellurium chain‐transfer agents (CTAs) for living radical polymerization were synthesized by post‐modification, which involved the condensation between a carboxylic‐acid‐functionalized CTA and various amines in excellent yields without affecting the reactive tellurium moiety. The CTAs exhibited high synthetic versatility for radical polymerization and gave structurally well‐controlled polymers, such as multiarmed polymers, from various monomers. Because all new CTAs are easily available on a large scale by simple purification, the current method significantly facilitates macromolecular engineering based on organotellurium‐mediated radical polymerization (TERP).