bluuebunny/crossref_metadata_2025_split huggingface dataset:
Catalytic Asymmetric C−H Functionalization under Photoredox Conditions by Radical Translocation and Stereocontrolled Alkene Addition
Authors: Wang Chuanyong , Harms Klaus , Meggers Eric 
Published: September 2016

AbstractThis work demonstrates how photoredox‐mediated C(sp3)−H activation through radical translocation can be combined with asymmetric catalysis. Upon irradiation with visible light, α,β‐unsaturated N‐acylpyrazoles react with N‐alkoxyphthalimides in the presence of a rhodium‐based chiral Lewis acid catalyst and the photosensitizer fac‐[Ir(ppy)3] to provide a C−C bond‐formation product with high enantioselectivity (up to 97 % ee) and, where applicable, with some diastereoselectivity (3.0:1 d.r.). Mechanistically, the synthetic strategy exploits a radical translocation (1,5‐hydrogen transfer) from an oxygen‐centered to a carbon‐centered radical with a subsequent stereocontrolled radical alkene addition.
A new numerical model for the analysis on low‐velocity impact damage evolution of carbon fiber reinforced resin composites
Authors: Qu Peng , Sun Xiaochen , Ping Lu , Zhang Dawei , Jia Yuxi 
Published: September 2016

ABSTRACTA new numerical simulation method was proposed to predict the mechanical behavior of carbon fiber reinforced resin composites under low‐velocity impact load. The impact damage evolution can be characterized in the form of energy dissipation which can be calculated through the new numerical model. The evolution mechanism of delamination was analyzed through distinguishing between the normal induced delamination and tangential slip induced delamination. The drop weight tests were conducted on composite laminates with five kinds of stacking sequence. Experimental analysis was also presented in this article. The damage area and distribution was investigated through ultrasonic C‐scan. The prediction had a good agreement with the experimental results through the comparison of impact response. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44374.
Thermoresponsive crosslinked isocyanate‐free polyurethanes by Diels‐Alder polymerization
Authors: Dolci Elena , Froidevaux Vincent , Michaud Guillaume , Simon Frédéric , Auvergne Rémi , Fouquay Stéphane , Caillol Sylvain 
Published: September 2016

ABSTRACTThis new study is a continuation of our previous work on thermocleavable nonisocyanate polyurethanes (NIPUs), but it is focused on crosslinked networks. Two systems are studied: the first system involves a dicyclocarbonate adduct with a PPO‐bicyclocarbonate and a triamine as crosslinker. The second system involves a tetracyclocarbonate DA adduct as crosslinker with the same PPO‐bicyclocarbonate and a difunctional amine. Firstly, Diels‐Alder adducts are synthesized and characterized. Then they are copolymerized to yield two types of cleavable polymer networks. The thermal behavior of synthesized polymers is fully characterized. Finally, by SEC, it was demonstrated that the obtained NIPU polymer chains are sliced up by rDA reaction. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44408.
Biologically Inspired C−H and C=C Oxidations with Hydrogen Peroxide Catalyzed by Iron Coordination Complexes
Authors: Olivo Giorgio , Cussó Olaf , Costas Miquel 
Published: September 2016

AbstractThe development of catalysts for the selective oxidation of readily available hydrocarbons or organic precursors into oxygenated products is a long‐standing goal in organic synthesis. In the last decade, some iron coordination complexes have shown the potential to fit this role. These catalysts can mimic the O−O activation mode of far more sophisticated iron oxygenase enzymes, generating powerful yet selective oxidants. In this review, we report state‐of‐the‐art C−H and C=C oxidations catalyzed by non‐heme iron complexes and H2O2 as the oxidant. Finally, we briefly describe some novel oxidative reactivity and the perspectives of this chemistry.
Regression in thin melanoma is associated with nodal recurrence after a negative sentinel node biopsy
Authors: Rubinstein Jill C. , Han Gang , Jackson Laura , Bulloch Kaleigh , Ariyan Stephan , Narayan Deepak , Rothberg Bonnie G. , Han Dale 
Published: September 2016

AbstractPrognostic markers for nodal metastasis in thin melanoma patients are debated. We present a single institution study looking at factors predictive of nodal disease in thin melanoma patients. Retrospective review from 1997 to 2012 identified 252 patients with thin melanoma (≤1 mm) who underwent a sentinel lymph node biopsy (SLNB). Node‐positive patients included positive SLNB patients and negative SLNB patients who developed a nodal recurrence (false‐negative SLNB). Clinicopathologic characteristics were correlated with nodal status and outcome. Median follow‐up was 45.5 months. Twelve of 252 patients (4.8%) were node‐positive including six positive SLNB (2.4%) and six false‐negative SLNB (2.4%) patients. No clinicopathologic factors were significantly correlated with nodal disease. For the six false‐negative SLNB patients, median time to nodal recurrence was 37.5 months. Regression was seen in only 16% of cases, but the rate increased to 60% for false‐negative SLNB cases. Both age (odds ratio [OR]: 1.09, 95% CI: 1.01–1.17; P = 0.02) and regression (OR: 8.33, 95% CI: 1.34–52.63; P = 0.02) were significantly associated with nodal recurrence after a negative SLNB on univariable analysis. Nodal disease in thin melanoma patients was seen in 4.8% of cases. Although regression was not correlated with nodal metastasis, it was correlated with a false‐negative SLNB. Patients with thin melanoma and regression may need more intensive surveillance after a negative SLNB. Further study is needed to determine if the same immune mechanisms that result in regression in primary tumors also lead to regression in lymph nodes, which may decrease detection of melanoma nodal metastases.
Covalent Tethering and Residues with Bulky Hydrophobic Side Chains Enable Self‐Assembly of Distinct Amyloid Structures
Authors: Ruiz Jérémy , Boehringer Régis , Grogg Marcel , Raya Jésus , Schirer Alicia , Crucifix Corinne , Hellwig Petra , Schultz Patrick , Torbeev Vladimir 
Published: September 2016

AbstractPolymorphism is a common property of amyloid fibers that complicates their detailed structural and functional studies. Here we report experiments illustrating the chemical principles that enable the formation of amyloid polymorphs with distinct stoichiometric composition. Using appropriate covalent tethering we programmed self‐assembly of a model peptide corresponding to the [20–41] fragment of human β2‐microglobulin into fibers with either trimeric or dimeric amyloid cores. Using a set of biophysical and biochemical methods we demonstrated their distinct structural, morphological, and templating properties. Furthermore, we showed that supramolecular approaches in which the peptide is modified with bulky substituents can also be applied to modulate the formation of different fiber polymorphs. Such strategies, when applied to disease‐related peptides and proteins, will greatly help in the evaluation of the biological properties of structurally distinct amyloids.
Challenging Thermodynamics: Hydrogenation of Benzene to 1,3‐Cyclohexadiene by Ru@Pt Nanoparticles
Authors: Weilhard Andreas , Abarca Gabriel , Viscardi Janine , Prechtl Martin H. G. , Scholten Jackson D. , Bernardi Fabiano , Baptista Daniel L. , Dupont Jairton 
Published: September 2016

AbstractSince the earliest reports on catalytic benzene hydrogenation, 1,3‐cyclohexadiene and cyclohexene have been proposed as key intermediates. However, the former has never been obtained with remarkable selectivity. Herein, we report the first partial hydrogenation of benzene towards 1,3‐cyclohexadiene under mild conditions in a catalytic biphasic system consisting of Ru@Pt nanoparticles (NPs) in ionic liquid (IL). The tandem reduction of [Ru(COD)(2‐methylallyl)2] (COD=1,5‐cyclooctadiene) followed by decomposition of [Pt2(dba)3] (dba=dibenzylideneacetone) in 1‐n‐butyl‐3‐methylimidazolium hexafluorophosphate (BMI⋅PF6) IL under hydrogen affords core–shell Ru@Pt NPs of 2.9±0.2 nm. The hydrogenation of benzene (60 °C, 6 bar of H2) dissolved in n‐heptane by these bimetallic NPs in BMI⋅PF6 affords 1,3‐cyclohexadiene with an unprecedented 21 % selectivity at 5 % benzene conversion. Conversely, almost no 1,3‐cyclohexadiene was observed when using monometallic Pt0 or Ru0 NPs under the same reaction conditions and benzene conversions. This study reveals that the selectivity is related to synergetic effects of the bimetallic composition of the catalyst material as well as to the performance under biphasic reaction conditions. It is proposed that colloidal metal catalysts in ILs and under multiphase conditions (“dynamic asymmetric mixtures”) can operate far from the thermodynamic equilibrium akin to chemically active membranes.
Carbopalladation Cascades Using Carbon–Carbon Triple Bonds: Recent Advances to Access Complex Scaffolds
Authors: Düfert Alexander , Werz Daniel B. 
Published: September 2016

AbstractAlkynes are one of the most versatile functional groups as synthetic handles. They allow for a direct access to partially or fully substituted alkenes through difunctionalization reactions. A prominently utilized transformation for these sequences is the carbopalladation of alkynes, which can be followed by various termination steps such as aromatizations, dearomatizations, cross‐coupling reactions, or pericyclic processes, amongst others. This Minireview provides an overview of the recent literature published in the field of carbopalladation chemistry, both with a focus on methodology as well as its application in the syntheses of complex molecular scaffolds, natural products, and functional molecules.
Sequential Barium‐Catalysed N−H/H−Si Dehydrogenative Cross‐Couplings: Cyclodisilazanes versus Linear Oligosilazanes
Authors: Bellini Clément , Roisnel Thierry , Carpentier Jean‐François , Tobisch Sven , Sarazin Yann 
Published: September 2016

AbstractStarting from Ph3SiH, the barium precatalyst Ba[CH(SiMe3)2]2⋅(THF)3was used to produce the disilazane Ph3SiN(Bn)SiPh2NHBn (4) by sequential N−H/H−Si dehydrogenative couplings with BnNH2and Ph2SiH2. Substrate scope was extended to other amines and hydrosilanes. This smooth protocol gives quantitative yields and full chemoselectivity. Compound4and the intermediates Ph3SiNHBn and Ph3SiN(Bn)SiHPh2were structurally characterised. Further attempts at chain extension by dehydrocoupling of Ph2SiH2with4instead resulted in cyclisation of this compound, forming the cyclodisilazanec‐(Ph2Si‐NBn)2(5) which was crystallographically authenticated. The ring‐closure mechanism leading to5upon release of C6H6was determined by complementary experimental and theoretical (DFT) investigations. Ba[CH(SiMe3)2]2⋅(THF)3and4react to afford the reactive Ba{N(Bn)SiPh2N(Bn)SiPh3}2, which was characterised in situ by NMR spectroscopy. Next, in a stepwise process, intramolecular nucleophilic attack of the metal‐bound amide on the terminal silicon atom generates a five‐coordinate silicate. It is followed by turnover‐limiting β‐C6H5transfer to barium; this releases5and forms a transient [Ba]−Ph species, which undergoes aminolysis to regenerate [Ba]−N(Bn)SiPh2N(Bn)SiPh3. DFT computations reveal that the irreversible production of5through such a stepwise ring‐closure mechanism is much more kinetically facile (ΔG≠=26.2 kcal mol−1) than an alternative σ‐metathesis pathway (ΔG≠=48.2 kcal mol−1).
Activation of Aromatic C−C Bonds of 2,2’‐Bipyridine Ligands
Authors: Fombona Sergio , Espinal‐Viguri Maialen , Huertos Miguel A. , Díaz Jesús , López Ramón , Menéndez M. Isabel , Pérez Julio , Riera Lucía 
Published: September 2016

Abstract4,4’‐Disubstituted‐2,2′‐bipyridine ligands coordinated to MoII and ReI cationic fragments become dearomatized by an intramolecular nucleophilic attack from a deprotonated N‐alkylimidazole ligand in cis disposition. The subsequent protonation of these neutral complexes takes place on a pyridine carbon atom rather than at nitrogen, weakening an aromatic C−C bond and affording a dihydropyridyl moiety. Computational calculations allowed for the rationalization of the formation of the experimentally obtained products over other plausible alternatives.
Towards Enzyme‐like, Sustainable Catalysis: Switchable, Highly Efficient Asymmetric Synthesis of Enantiopure Biginelli Dihydropyrimidinones or Hexahydropyrimidinones
Authors: Lillo V. J. , Saá J. M. 
Published: September 2016

AbstractOrganocatalysts displaying a network of cooperative hydrogen bonds (NCHB) have been employed in an enzyme‐like manner for a direct, switchable synthesis of enantiopure hexahydropyrimidinones (HHPMs) or dihydropyrimidinones (DHPMs), which starts at a common, easily accessible α‐ureidosulfone stage. The NCHB organocatalyst exploits all its potential as a pure hydrogen‐bond biomimetic catalyst even in the presence of organic bases. This one‐pot, diastereo‐ and enantioselective synthetic procedure has been proven to be robust, scalable, highly efficient, and environmentally benign. A straightforward and truly practical entry to enantiopure HHPMs is reported for the first time.
Functional Group Interconversion: Decarbonylative Borylation of Esters for the Synthesis of Organoboronates
Authors: Guo Lin , Rueping Magnus 
Published: September 2016

AbstractA new and efficient nickel‐catalyzed decarbonylative borylation reaction of carboxylic acid esters with bis(pinacolato)‐diboron has been developed. This transformation allows access to structurally diverse aryl as well as alkenyl and alkyl boronate esters with high reactivity, broad substrate scope, and excellent functional‐group tolerance. Further experiments show that this protocol can be carried out on a gram scale and applied to orthogonal synthetic strategies.
Fine needle aspiration cytology of IgG4‐related disease: A potential diagnostic pitfall?
Authors: Kaur Rajwant , Mitra Suvradeep , Rajwanshi Arvind , Das Ashim , Nahar Saikia Uma , Dey Pranab 
Published: September 2016

BackgroundIgG4‐related disease (IgG4‐RD) is a tumefactive fibro‐inflammatory lesion that can affect any organ system in the body. Till date, no cytological data on IgG4‐RD are available and this is the first study depicting the cytopathology features of IgG4‐RD.Aim and ObjectiveTo describe the cytopathological features and potential diagnostic errors of IgG4‐RD.Materials and MethodsThe cytological features of 10 histopathology proven IgG4‐RD cases (11 samples) were retrospectively reviewed along with corresponding histopathology.ResultsThe cellularity of the cytology smears was low (36.4%) to moderate (45.4%) to high (18.1%). The low cellularity correlated well with the pattern C in histopathology (predominant fibrosis pattern). The non‐epithelial background showed a preponderance of lymphocytes along with polymorphs and spindle‐shaped fibroblasts. Most of these cases showed the presence of plasma cells and eosinophils. Epithelial atypia was seen in 18.2% cases.ConclusionThe causes of misdiagnosis were low cellularity, epithelial atypia, and non‐representative background. The important diagnostic clues to suspect a diagnosis of IgG4‐RD include low cellularity despite adequate effort, inflammatory background rich in lymphocytes and spindle cells admixed with a few plasma cells and eosinophils along with radiological features and raised serum IgG4 Diagn. Cytopathol. 2017;45:14–21. © 2016 Wiley Periodicals, Inc.
Nadolol reduces insulin sensitivity in liver cirrhosis: a randomized double‐blind crossover trial
Authors: Lee Wai Gin , Murphy Rinki , McCall John L. , Gane Edward J. , Soop Mattias , Tura Andrea , Plank Lindsay D. 
Published: September 2016

AbstractBackgroundLiver cirrhosis is frequently complicated by portal hypertension leading to increased mortality from variceal bleeding and hepatic decompensation. Noncardioselective β‐blockers not only reduce portal hypertension and prevent variceal bleeding in cirrhosis but also impair glucose tolerance and insulin sensitivity in other settings. This study aimed to determine whether nonselective β‐blockade with nadolol impairs glucose metabolism in liver cirrhosis.MethodsA randomized, double‐blind, placebo‐controlled crossover trial of nadolol in cirrhotic patients examined insulin sensitivity, disposition index, and glucose tolerance. Stable cirrhotic patients of mixed etiology underwent an intravenous glucose tolerance test and hyperinsulinemic‐euglycemic clamp for the measurement of insulin secretion and insulin sensitivity (n = 16) and a 75‐g oral glucose tolerance test (n = 17). These measurements were conducted twice (after 3 months of treatment with nadolol or placebo and, after a 1‐month washout period, after 3 months on the alternative treatment). Total body fat and plasma catecholamines were measured at the end of each 3‐month treatment.ResultsCompared with placebo, nadolol treatment reduced insulin sensitivity (79.7 ± 10.1 vs 99.6 ± 10.3 μL/kg fat‐free mass·min−1·(mU/L)−1, P = .005). Insulin secretion was unchanged (P = .24), yielding a lower disposition index with nadolol (6083 ± 2007 vs 8692 ± 2036, P = .050). There was no change in total body fat or plasma catecholamines. A 2‐hour plasma glucose concentration from the oral glucose tolerance test was higher on nadolol than placebo (10.8 ± 0.9 vs 9.9 ± 0.9 mmol/L, P = .035).ConclusionsNadolol significantly worsened insulin sensitivity, glycemia, and disposition index in patients with liver cirrhosis. These findings may have significant clinical implications because cirrhosis is already associated with an increased prevalence of diabetes.
Why do larger mothers produce larger offspring? A test of classic theory
Authors: Cameron Hayley , Monro Keyne , Malerba Martino , Munch Stephan , Marshall Dustin 
Published: September 2016

AbstractAcross a wide range of taxa, larger mothers produce larger offspring. Theory assumes that larger, more fecund mothers create higher local densities of siblings, and so larger mothers produce larger offspring to offset sibling competition. This assumption has been debated for over 30 yr, but direct empirical tests are surprisingly rare. Here, we test two key assumptions of classic theories that predict sibling competition drives maternal‐size–offspring‐size (MSOS) correlations: (1) independent effects of offspring size and sibling density on offspring performance or (2) as a product of an interaction between these two factors. To simultaneously test these alternative assumptions, we manipulate offspring size and sibling density in the marine invertebrate, Bugula neritina, and monitor offspring performance in the field. We found that depending on the fitness metric being considered, offspring size and sibling density can either independently or interactively affect offspring performance. Yet sibling density did not affect offspring performance in the ways that classic theories assume. Given our results, it is unlikely that sibling competition drives the positive MSOS correlation observed in this species. Empirical support for these classic theories remains lacking, suggesting alternative explanations are necessary.
Degradation of silicon wafers at high temperatures for epitaxial deposition
Authors: Rachow Thomas , Reber Stefan , Janz Stefan , Knapp Marius , Milenkovic Nena 
Published: September 2016

AbstractThe material quality degradation of silicon wafers by metal impurities, various crystal defects as well as light and thermally induced mechanisms is very important for the solar cell performance and has been investigated by various groups. In this paper, the material degradation during epitaxial deposition at high temperatures above 1100°C will be discussed. Annealing experiments in hydrogen atmosphere are done with the laboratory rapid thermal chemical vapor deposition reactor to mimic the thermal process conditions for epitaxial growth of silicon from the gas phase. A general investigation of crystallographic and electronic properties of n‐ and p‐type silicon wafers has been done between 950°C and 1150°C. A detailed sensitivity analysis of process parameters like cooling ramp, peak temperature, duration, and ambient gasses has been conducted. The degradation mechanism by metal impurities has been investigated by using silicon wafers with different diffusion barriers. Besides effective minority carrier lifetime, measurements by quasi steady state photo conductance, etch pit density, Raman spectroscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy measurements have been done. The presented results have been used to improve the deposition process of epitaxial thin‐film solar cells, the production of silicon foils with a thickness <80 μm, and the fabrication of epitaxial multi junction solar cells with silicon bottom cell.
Determining soil erosion rates on semi‐arid watersheds using radioisotope‐derived sedimentation chronology
Authors: Polyakov V. O. , Nichols M. N. , Nearing M. A. 
Published: September 2016

AbstractThis study investigates erosion dynamics of the past 90 years in three small semi‐arid watersheds with histories of grazing and vegetation change. Activity of 137Cs and excess 210Pb from 18 cores collected from sedimentation ponds were measured using a gamma spectrometer. The sediment was dated using a constant rate of supply (CRS) model. This study represents the first time that reservoir sediment accumulation rates determined from fallout isotopes have been verified by direct volumetric measurements of aggradation based on topographic surveys. Measured sedimentation in the ponds ranged between 1.9 and 2.3 cm y−1, representing average sediment delivery rates from the watersheds of between 0.6 and 2.0 t ha−1 y−1. These sediment delivery rates were in agreement with those established by other methods for similar catchments in the region. Past variations in sedimentation rates were identified and correlated with recorded history of anthropogenic disturbance. 137Cs and 210Pb methods are suitable for use in arid environments and can complement each other to increase reliability of erosion rate estimates. The abundance of stock ponds in southwestern USA presents an opportunity to quantify historic erosion and sediment transfer dynamics in areas that have not been well studied or instrumented. Published 2016. This article is a U.S. Government work and is in the public domain in the USA
Review of emerging contaminants in aquatic biota from Latin America: 2002–2016
Authors: Llorca Marta , Farré Marinella , Eljarrat Ethel , Díaz-Cruz Sílvia , Rodríguez-Mozaz Sara , Wunderlin Daniel , Barcelo Damià 
Published: September 2016

Abstract

Although it is known that emerging contaminants are widespread all over the globe, there is a gap of information about their distribution in some geographical areas, such as Latin America. The present bibliographic work reviews the available literature about the presence of organic emerging contaminants in Latin American freshwater and marine biota between 2002 and 2016 and includes 23 works from Argentina, Brazil, Chile, Colombia, Mexico, and Nicaragua. In particular, the present review provides an overview of the occurrence of continuously present contaminants such as pharmaceuticals, personal care products, and pyrethroid insecticides, as well as the new groups of persistent organic pollutants, the halogenated flame retardants and the perfluoroalkyl substances. A wide overview is provided, considering not only occurrence data but also effects and potential transfer through the food chain. Environ Toxicol Chem 2017;36:1716–1727. © 2016 SETAC