bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term acclimatization to high‐altitude hypoxia modifies interhemispheric functional and structural connectivity in the adult brain
Authors: Chen Ji , Li Jinqiang , Han Qiaoqing , Lin Jianzhong , Yang Tianhe , Chen Ziqian , Zhang Jiaxing
Published: June 2016

Background

Structural and functional networks can be reorganized to adjust to environmental pressures and physiologic changes in the adult brain, but such processes remain unclear in prolonged adaptation to high‐altitude (HA) hypoxia. This study aimed to characterize the interhemispheric functionally and structurally coupled modifications in the brains of adult HA immigrants.

Methods

We performed resting‐state functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) in 16 adults who had immigrated to the Qinghai‐Tibet Plateau (2300–4400 m) for 2 years and in 16 age‐matched sea‐level (SL) controls. A recently validated approach of voxel‐mirrored homotopic connectivity (VMHC) was employed to examine the interhemispheric resting‐state functional connectivity. Areas showing changed VMHC in HA immigrants were selected as regions of interest for follow‐up DTI tractography analysis. The fiber parameters of fractional anisotropy and fiber length were obtained. Cognitive and physiological assessments were made and correlated with the resulting image metrics.

Results

Compared with SL controls, VMHC in the bilateral visual cortex was significantly increased in HA immigrants. The mean VMHC value extracted within the visual cortex was positively correlated with hemoglobin concentration. Moreover, the path length of the commissural fibers connecting homotopic visual areas was increased in HA immigrants, covarying positively with VMHC.

Conclusions

These observations are the first to demonstrate interhemispheric functional and structural connectivity resilience in the adult brain after prolonged HA acclimatization independent of inherited and developmental effects, and the coupled modifications in the bilateral visual cortex indicate important neural compensatory mechanisms underlying visual dysfunction in physiologically well‐acclimatized HA immigrants. The study of human central adaptation to extreme environments promotes the understanding of our brain's capacity for survival.
Structural Insights into Conformation Differences between DNA/TNA and RNA/TNA Chimeric Duplexes
Authors: Anosova Irina , Kowal Ewa A. , Sisco Nicholas J. , Sau Sujay , Liao Jen‐yu , Bala Saikat , Rozners Eriks , Egli Martin , Chaput John C. , Van Horn Wade D.
Published: June 2016

Threose nucleic acid (TNA) is an artificial genetic polymer capable of heredity and evolution, and is studied in the context of RNA chemical etiology. It has a four‐carbon threose backbone in place of the five‐carbon ribose of natural nucleic acids, yet forms stable antiparallel complementary Watson–Crick homoduplexes and heteroduplexes with DNA and RNA. TNA base‐pairs more favorably with RNA than with DNA but the reason is unknown. Here, we employed NMR, ITC, UV, and CD to probe the structural and dynamic properties of heteroduplexes of RNA/TNA and DNA/TNA. The results indicate that TNA templates the structure of heteroduplexes, thereby forcing an A‐like helical geometry. NMR measurement of kinetic and thermodynamic parameters for individual base pair opening events reveal unexpected asymmetric “breathing” fluctuations of the DNA/TNA helix. The results suggest that DNA is unable to fully adapt to the conformational constraints of the rigid TNA backbone and that nucleic acid breathing dynamics are determined from both backbone and base contributions.
Base‐Free Transfer Hydrogenation of Nitroarenes Catalyzed by Micro‐Mesoporous Iron Oxide
Authors: Datta Kasibhatta J. , Rathi Anuj K. , Gawande Manoj B. , Ranc Vaclav , Zoppellaro Giorgio , Varma Rajender S. , Zboril Radek
Published: June 2016

An efficient and practical protocol for the transfer hydrogenation of nitroarenes was developed, which uses flower‐shaped micro‐mesoporous iron oxide (MMIO) with formic acid as the reducing agent and tris[(2‐diphenylphosphino)‐ethyl]phosphine as the ligand in the absence of an additional base. The recyclable catalytic system enables the reduction of the nitro group in a broad range of substrates to yield valuable amines and shows a high tolerance to sensitive functional groups.
Mechanism and Origins of Ligand‐Controlled Selectivity of Rhodium‐Catalyzed Intermolecular Cycloadditions of Vinylaziridines with Alkynes
Authors: Zhang Xinwen , Zou Hongyan , Huang Genping
Published: June 2016

In this report, the mechanism of the rhodium‐catalyzed intermolecular cycloaddition of vinylaziridines with alkynes is investigated by means of density functional theory calculations. The calculations show that the reaction is initiated by a C−N oxidative addition to form the Rh–allyl complex, from which the migratory insertion of the alkyne into the Rh−N bond was found to take place in a 1,2‐fashion. The subsequent competing direct C−C reductive elimination and alkenyl isomerization/ C−C reductive elimination led to the [3+2] and [5+2] cycloadditions, respectively. The experimentally observed ligand‐controlled selectivity is reproduced quite well by the calculations. Importantly, it turns out that the steric repulsion between the ligand and the alkenyl moiety has a profound impact on the direct C−C reductive elimination and the alkenyl isomerization, which enables the selectivity switch between the [3+2] and [5+2] cycloaddition upon change of ligand.
Mesoporous Titanium Dioxide Nanofibers with a Significantly Enhanced Photocatalytic Activity
Authors: Ghosh Monoj , Lohrasbi Mehdi , Chuang Steven S. C. , Jana Sadhan C.
Published: June 2016

Mesoporous TiO2 nanofibers with controlled diameter, crystal size, and anatase versus rutile crystal structures are produced by calcination at 500–700 °C of precursor nanofibers of polyvinylpyrrolidone and titanium isopropoxide, obtained from a scalable gas jet fiber spinning process. These TiO2 nanofibers are used in the photocatalytic oxidation of gas‐phase ethanol at room temperature on exposure to UV irradiation. The experimental trends are analyzed using electron–hole (e‐h) charge recombination inferred from high‐intensity photoluminescence emission spectra, specific surface area, crystallinity, and the proportions of anatase and rutile phases. The nanofibers show a photocatalytic activity that is up to an order of magnitude higher than that of commercial‐grade P25 TiO2 nanoparticles because of slower e‐h recombination phenomena in the former. The results show that ethanol undergoes complete oxidation into CO2 and H2O on the nanofibers without the accumulation of the intermediate products acetaldehyde and formic acid.
Lithium–Oxygen Cells: An Analytical Model to Explain Key Features in the Discharge Voltage Profiles
Authors: Rinaldi Ali , Wijaya Olivia , Hoster Harry
Published: June 2016

Lithium–oxygen (Li–O2) cells are popular because of their potentially high energy density. A characteristic fingerprint of a given cell is the voltage profile during constant‐current discharge. We suggest that the typical initial dip and the following increase of the voltage result from a temporary increase and slow decrease in the concentration of dissolved superoxide, respectively, feeding into the Nernst equation. The steady‐state superoxide concentration decreases as the surface area of the solid precipitation product (Li2O2) increases. Importantly, these products bury the electrochemically active carbon surface. Assuming that the electrochemical step only occurs on bare carbon, the Tafel equation provides an expression for the increasing overpotential as a result of the shrinking effective electrode area. This boils the discharge voltage profile down to the sum of two logarithms, grasping all relevant features in the recorded discharge voltage profiles.
Development and Characterization of High‐Performance Sodium‐Ion Cells based on Layered Oxide and Hard Carbon
Authors: Keller Marlou , Vaalma Christoph , Buchholz Daniel , Passerini Stefano
Published: June 2016

The front cover artwork is provided by members of the “Electrochemistry for Batteries” group at the Helmholtz Institute Ulm (Germany). The image exemplifies the use of sodium‐ion cells with good overall electrochemical performance and their successful application in the power grid of the future. Read the full text of the Article at 10.1002/celc.201600152.
Synthesis and Metalation of Doubly o‐Phenylene‐Bridged Cyclic Bis(dipyrrin)s with Highly Bent Skeleton of Dibenzoporphyrin(2.1.2.1)
Authors: Kuzuhara Daiki , Furukawa Wataru , Kitashiro Aya , Aratani Naoki , Yamada Hiroko
Published: June 2016

Facile synthesis of dibenzoporphyrins(2.1.2.1) has been successfully reported by the simple condensation reaction of o‐dipyrrolylbenzene with various aldehydes in the presence of a Lewis acid. This reaction enables the preparation of various dibenzoporphyrin(2.1.2.1) derivatives with p‐substituted phenyl groups, five‐membered heterocycles, and ethynyl groups at the meso‐positions. Dibenzoporphyrins(2.1.2.1) consist of two dipyrrin units that are connected by o‐phenylene bridges, which adopt highly bent saddle‐shaped structures; this was confirmed by X‐ray diffraction analysis. We found that dibenzoporphyrin(2.1.2.1) can be described as a 20π antiaromatic conjugated system, but practically, it is not an antiaromatic macrocycle, which we revealed by 1H NMR spectroscopy. The redox potentials had good correlations with Hammett substituent constant (σp) of the substituents at the meso‐positions. The free‐base dibenzoporphyrin(2.1.2.1) was able to form the metal complexes with nickel(II), copper(II), palladium(II), platinum(II), and tin(IV) ions. These results suggested that dibenzoporphyrin(2.1.2.1) derivatives can be utilized as novel macrocyclic dianionic tetradentate ligands for various metal ions to give complexes with varying optical and electrochemical properties.
One‐Step Synthesis of Silver Nanoparticle‐Decorated Hydroxyapatite Nanowires for the Construction of Highly Flexible Free‐Standing Paper with High Antibacterial Activity
Authors: Xiong Zhi‐Chao , Zhu Ying‐Jie , Chen Fei‐Fei , Sun Tuan‐Wei , Shen Yue‐Qin
Published: June 2016

A highly flexible and free‐standing paper with high antibacterial activity made from silver nanoparticle (AgNP)‐decorated ultralong hydroxyapatite nanowires (HAPNWs) is reported. The HAPNWs@AgNPs nanocomposites were obtained from a facile one‐step solvothermal process and utilized for the construction of highly flexible and free‐standing inorganic paper through a simple vacuum‐filtration procedure. The structure and properties of the HAPNWs@AgNPs paper were characterized in detail. Scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs show that AgNPs are highly dispersed and stabilized in the nanocomposite and exhibit a narrow particle size distribution. The effects of the concentration of silver nitrate, solvothermal temperature and time on the product were systematically investigated. This method is simple, convenient and reproducible. The as‐prepared HAPNWs@AgNPs paper shows long‐time sustained silver‐ion release, high antibacterial activity against both Gram‐negative and Gram‐positive bacteria, and good biocompatibility. Overall, this work provides a novel pathway for the preparation of a new type of highly flexible, free‐standing and antibacterial inorganic paper made from silver nanoparticle‐decorated hydroxyapatite nanowires for various applications, as a promising functional biomaterial.
Ascorbic Acid‐Assisted Synthesis of Mesoporous Sodium Vanadium Phosphate Nanoparticles with Highly sp2‐Coordinated Carbon Coatings as Efficient Cathode Materials for Rechargeable Sodium‐Ion Batteries
Authors: Hung Tai‐Feng , Cheng Wei‐Jen , Chang Wen‐Sheng , Yang Chang‐Chung , Shen Chin‐Chang , Kuo Yu‐Lin
Published: June 2016

Herein, mesoporous sodium vanadium phosphate nanoparticles with highly sp2‐coordinated carbon coatings (meso‐Na3V2(PO4)3/C) were successfully synthesized as efficient cathode material for rechargeable sodium‐ion batteries by using ascorbic acid as both the reductant and carbon source, followed by calcination at 750 °C in an argon atmosphere. Their crystalline structure, morphology, surface area, chemical composition, carbon nature and amount were systematically explored. Following electrochemical measurements, the resultant meso‐Na3V2(PO4)3/C not only delivered good reversible capacity (98 mAh g−1 at 0.1 A g−1) and superior rate capability (63 mAh g−1 at 1 A g−1) but also exhibited comparable cycling performance (capacity retention: ≈74 % at 450 cycles at 0.4 A g−1). Moreover, the symmetrical sodium‐ion full cell with excellent reversibility and cycling stability was also achieved (capacity retention: 92.2 % at 0.1 A g−1 with 99.5 % coulombic efficiency after 100 cycles). These attributes are ascribed to the distinctive mesostructure for facile sodium‐ion insertion/extraction and their continuous sp2‐coordinated carbon coatings, which facilitate electronic conduction.
A Mechanistic Investigation of the Visible‐Light Photocatalytic Trifluoromethylation of Heterocycles Using CF3I in Flow
Authors: Su Yuanhai , Kuijpers Koen P. L. , König Niels , Shang Minjing , Hessel Volker , Noël Timothy
Published: June 2016

Photocatalytic radical trifluoromethylation strategies have impacted the synthesis of trifluoromethyl‐containing molecules. However, mechanistic aspects concerning such transformations remain poorly understood. Here, we describe in detail the mechanism of the visible‐light photocatalytic trifluoromethylation of N‐methylpyrrole with gaseous CF3I in flow. The use of continuous‐flow microreactor technology allowed for the determination of different important parameters with high precision (e.g., photon flux, quantum yield, reaction rate constants) and for the handling of CF3I in a convenient manner. Our data indicates that the reaction occurs through a reductive quenching mechanism and that there is no radical chain process present.
Exploiting the Distal Reactivity of Indolyl Methylenemalononitriles: An Asymmetric Organocatalyzed [4+2] Cycloaddition with Enals Enables the Assembly of Elusive Dihydrocarbazoles
Authors: Rassu Gloria , Curti Claudio , Zambrano Vincenzo , Pinna Luigi , Brindani Nicoletta , Pelosi Giorgio , Zanardi Franca
Published: June 2016

An unprecedented technique for the in situ generation of indolyl ortho‐quinodimethanes from 2‐methylindole‐based methylenemalononitriles by amine‐mediated remote C(sp3)−H deprotonation was developed. These intermediates were efficiently trapped by diverse enals to provide a rapid entry to 2,9‐dihydro‐1H‐carbazole‐3‐carboxyaldehyde structures through a formal asymmetric [4+2] eliminative cycloaddition governed by a α,α‐diphenylprolinol trimethylsilyl ether catalyst.
Flexible association modelling and prediction with semi‐competing risks data
Authors: Li Ruosha , Cheng Yu
Published: June 2016

Semi‐competing risks data involve a non‐terminal event time, such as time to disease progression, and a terminal event time such as time to death. Existing methods for handling semi‐competing risks data often assume that the underlying association between the two event times follows a pre‐specified copula with unknown association parameters, which often correspond to the strength of association. In this article we propose a flexible association model that does not require pre‐specifying a copula. Therefore our methods facilitate a convenient and robust evaluation of the underlying association pattern, as well as the association strength. Furthermore the proposed association model leads to a robust estimator for the conditional survival probability of the terminal event given the non‐terminal event. The methods were also extended to handle left‐truncation. Both the association and survival estimators were shown to feature desirable asymptotic properties and satisfactory numerical performance. Our methods were successfully applied to a diabetes data set to study the association between time to diabetic nephropathy and time to death, and to predict the mortality rate given the onset time of nephropathy. The Canadian Journal of Statistics 44: 361–374; 2016 © 2016 Statistical Society of Canada
Guidelines for the Synthesis of Small‐Molecule Irreversible Probes Targeting G Protein‐Coupled Receptors
Authors: Jörg Manuela , Scammells Peter J.
Published: June 2016

Irreversible probes have been proven to be useful pharmacological tools in the study of structural and functional features in drug receptor pharmacology. They have been demonstrated to be particularly valuable for the isolation and purification of receptors. Furthermore, irreversible probes are helpful tools for the identification and characterization of binding sites, thereby supporting the advancement of rational drug design. In this Minireview, we provide insight into universal strategies and guidelines to successfully synthesize irreversible probes that target G protein‐coupled receptors (GPCRs). We provide an overview of commonly used chemoreactive and photoreactive groups, and make a comparison of their properties and potential applications. Furthermore, there is a particular focus on synthetic approaches to introduce these reactive groups based on commercially available reagents.
A Comprehensive Discussion of HMBC Pulse Sequences: 4. Establishing Two‐Bond Correlations from HMBC and Related Experiments
Authors: Saurí Josep , Martin Gary E. , Furrer Julien
Published: June 2016

The utility of the HMBC experiment for structure elucidation is unquestionable, but the nature of the coupling pathways leading to correlations in an HMBC experiment creates the potential for misinterpretation. This misinterpretation potential is intimately linked to the size of the long‐range heteronuclear couplings involved, and may become troublesome in those cases of a particularly strong 2JCH correlation that might be mistaken for a 3JCH correlation or a 4JCH correlation of appreciable strength that could be mistaken for a weaker 3JCH correlation. To address these potential avenues of confusion, work from several laboratories has been focused on the development of what might be considered “coupling pathway edited” long‐range heteronuclear correlation experiments that are derived from or related to the HMBC experiment. The first example of an effort to address the problems associated with correlation path length was seen in the heteronucleus‐detected XCORFE experiment described by Reynolds and co‐workers that predated the development of the HMBC experiment. Proton‐detected analogs of the HMBC experiment intended to differentiate 2JCH correlations from nJCH correlations where n = 3, 4, include the 2J,3J‐HMBC, HMBC‐RELAY, H2BC, edited‐HMBC, and HAT H2BC experiments. The principles underlying the critical components of each of these experiments are discussed and experimental verification of the results that can be obtained using model compounds are shown. This contribution concludes with a brief discussion of the 1,1‐ADEQUATE experiments that provide an alternative means of identifying adjacent protonated and non‐protonated carbon correlations by exploiting 1JCC correlations at natural abundance.
Is State‐State Investment Arbitration an Old Option for Latin America?
Authors: Lubambo Murilo
Published: June 2016

International arbitration is a recognized way to resolve economic conflicts. This article asks if state‐state investment arbitration (SSIA) is an option for Latin America. It examines the language of investment treaty provisions, cases and arbitral awards involving states, and treaty‐making practice in the region. The analysis shows some complementarity between the mechanisms of investor‐state arbitration (ISA) and SSIA; sometimes, the latter is the only option. This article concludes that SSIA is neither a backlash nor a more effective mechanism compared to ISA. SSIA constitutes an opportunity for both home and host Latin American states to balance their investment treaty commitments.
Quantifying the spatiotemporal dynamics in a chorus frog (Pseudacris) hybrid zone over 30 years
Authors: Engebretsen Kristin N. , Barrow Lisa N. , Rittmeyer Eric N. , Brown Jeremy M. , Moriarty Lemmon Emily
Published: June 2016

Although theory suggests that hybrid zones can move or change structure over time, studies supported by direct empirical evidence for these changes are relatively limited. We present a spatiotemporal genetic study of a hybrid zone between Pseudacris nigrita and P. fouquettei across the Pearl River between Louisiana and Mississippi. This hybrid zone was initially characterized in 1980 as a narrow and steep “tension zone,” in which hybrid populations were inferior to parentals and were maintained through a balance between selection and dispersal. We reanalyzed historical tissue samples and compared them to samples of recently collected individuals using microsatellites. Clinal analyses indicate that the cline has not shifted in roughly 30 years but has widened significantly. Anthropogenic and natural changes may have affected selective pressure or dispersal, and our results suggest that the zone may no longer best be described as a tension zone. To the best of our knowledge, this study provides the first evidence of significant widening of a hybrid cline but stasis of its center. Continued empirical study of dynamic hybrid zones will provide insight into the forces shaping their structure and the evolutionary potential they possess for the elimination or generation of species.
Habitat‐mediated timing of migration in polar bears: an individual perspective
Authors: Cherry Seth G. , Derocher Andrew E. , Lunn Nicholas J.
Published: June 2016

Migration phenology is largely determined by how animals respond to seasonal changes in environmental conditions. Our perception of the relationship between migratory behavior and environmental cues can vary depending on the spatial scale at which these interactions are measured. Understanding the behavioral mechanisms behind population‐scale movements requires knowledge of how individuals respond to local cues. We show how time‐to‐event models can be used to predict what factors are associated with the timing of an individual's migratory behavior using data from GPS collared polar bears (Ursus maritimus) that move seasonally between sea ice and terrestrial habitats. We found the concentration of sea ice that bears experience at a local level, along with the duration of exposure to these conditions, was most associated with individual migration timing. Our results corroborate studies that assume thresholds of >50% sea ice concentration are necessary for suitable polar bear habitat; however, continued periods (e.g., days to weeks) of exposure to suboptimal ice concentrations during seasonal melting were required before the proportion of bears migrating to land increased substantially. Time‐to‐event models are advantageous for examining individual movement patterns because they account for the idea that animals make decisions based on an accumulation of knowledge from the landscapes they move through and not simply the environment they are exposed to at the time of a decision. Understanding the migration behavior of polar bears moving between terrestrial and marine habitat, at multiple spatiotemporal scales, will be a major aspect of quantifying observed and potential demographic responses to climate‐induced environmental changes.
Corolla chirality does not contribute to directed pollen movement in Hypericum perforatum (Hypericaceae): mirror image pinwheel flowers function as radially symmetric flowers in pollination
Authors: Diller Carolina , Fenster Charles B.
Published: June 2016

Corolla chirality, the pinwheel arrangement of petals within a flower, is found throughout the core eudicots. In 15 families, different chiral type flowers (i.e., right or left rotated corolla) exist on the same plant, and this condition is referred to as unfixed/enantiomorphic corolla chirality. There are no investigations on the significance of unfixed floral chirality on directed pollen movement even though analogous mirror image floral designs, for example, enantiostyly, has evolved in response to selection to direct pollinator and pollen movement. Here, we examine the role of corolla chirality on directing pollen transfer, pollinator behavior, and its potential influence on disassortative mating. We quantified pollen transfer and pollinator behavior and movement for both right and left rotated flowers in two populations of Hypericum perforatum. In addition, we quantified the number of right and left rotated flowers at the individual level. Pollinators were indifferent to corolla chirality resulting in no difference in pollen deposition between right and left flowers. Corolla chirality had no effect on pollinator and pollen movement between and within chiral morphs. Unlike other mirror image floral designs, corolla chirality appears to play no role in promoting disassortative mating in this species.
Precocious reproduction increases at the leading edge of a mangrove range expansion
Authors: Dangremond Emily M. , Feller Ilka C.
Published: June 2016

Climate change‐driven shifts in species ranges are ongoing and expected to increase. However, life‐history traits may interact with climate to influence species ranges, potentially accelerating or slowing range shifts in response to climate change. Tropical mangroves have expanded their ranges poleward in the last three decades. Here, we report on a shift at the range edge in life‐history traits related to reproduction and dispersal. With a common garden experiment and field observations, we show that Rhizophora mangle individuals from northern populations reproduce at a younger age than those from southern populations. In a common garden at the northern range limit, 38% of individuals from the northernmost population were reproductive by age 2, but less than 10% of individuals from the southernmost population were reproductive by the same age, with intermediate amounts of reproduction from intermediate latitudes. Field observations show a similar pattern of younger reproductive individuals toward the northern range limit. We also demonstrate a shift toward larger propagule size in populations at the leading range edge, which may aid seedling growth. The substantial increase in precocious reproduction at the leading edge of the R. mangle range could accelerate population growth and hasten the expansion of mangroves into salt marshes.
Variation of life‐history traits of the Asian corn borer, Ostrinia furnacalis in relation to temperature and geographical latitude
Authors: Xiao Liang , He Hai‐Min , Huang Li‐Li , Geng Ting , Fu Shu , Xue Fang‐Sen
Published: June 2016

Life‐history traits from four geographical populations (tropical Ledong population [LD], subtropical Guangzhou [GZ] and Yongxiu populations, and temperate Langfang population [LF]) of the Asian corn borer, Ostrinia furnacalis were investigated at a wide range of temperatures (20–32°C). The larval and pupal times were significantly decreased with increasing rearing temperature, and growth rate was positively correlated with temperature. The relationship between body weight and rearing temperature in O. furnacalis did not follow the temperature–size rule (TSR); all populations exhibited the highest pupal and adult weights at high temperatures or intermediate temperatures. However, development time, growth rate, and body weight did not show a constant latitudinal gradient. Across all populations at each temperature, female were significantly bigger than males, showing a female‐biased sexual size dimorphism (SSD). Contrary to Rensch's rule, the SSD tended to increase with rising temperature. The subtropical GZ population exhibited the largest degree of dimorphism while the temperate LF exhibited the smallest. Male pupae lose significantly more weight at metamorphosis compared to females. The proportionate weight losses of different populations were significantly different. Adult longevity was significantly decreased with increasing temperature. Between sexes, all populations exhibit a rather female‐biased adult longevity. Finally, we discuss the adaptive significance of higher temperature‐inducing high body weight in the moth's life history and why the moth exhibits the reverse TSR.
One‐Pot Synthesis of Phosphanylbis(N‐arylglycines) and Spontaneous Diastereoselective Lactamization of P‐Alkyl Derivatives To Form Five‐Membered P,N‐Heterocyclic Amino Acids
Authors: Lach Joanna , Palm Gottfried J. , Jones Peter G. , Heinicke Joachim W.
Published: June 2016

The one‐pot, three‐component reaction of phenylphosphane with two equivalents each of 4‐acetylaniline and glyoxylic acid hydrate (GAH) in diethyl ether at room temperature furnished phosphanyl‐bis(glycine) 1 as a rac/meso mixture (molar ratio 7:3) whereas condensation of primary alkylphosphanes (cHexPH2, iBuPH2) with p‐toluidine and GAH was followed by additional spontaneous and highly diastereoselective lactamization to form five‐membered P,N‐heterocyclic racemic amino acids 2 and 3. Compound 2, with three centres of asymmetry, displayed only one set of NMR signals, whereas for compound 3 one set was strongly preferred. Crystal structure analysis of 2 confirmed the presence of a racemate, with the asymmetric unit consisting of the 2R,3R,4R isomer; the molecules are linked by hydrogen bonds. The trans(eq‐eq)‐position of the P‐cyclohexyl group towards the substituents at the adjacent C2 and C4 atoms is maintained in [D8]THF solution, as shown by small 2JPH coupling constants. Large 2JPH couplings in compound 3 hint at the opposite preference, i.e. cis orientation, of the less spatially demanding isobutyl group at phosphorus towards the C2 and C4 substituents. The trans isomers of 3 were detected only in trace amounts on the basis of characteristic PCH proton doublets with small 2JPH values. This facile route to novel trialkylphosphane‐type hybrid ligands 2 and 3 may pave the way for further studies of their properties and use as ligands in transition metal compounds and catalysis.
Thiamine‐Diphosphate‐Dependent Enzymes as Catalytic Tools for the Asymmetric Benzoin‐Type Reaction
Authors: Giovannini Pier Paolo , Bortolini Olga , Massi Alessandro
Published: June 2016

Benzoin‐type reactions allow the generation of α‐hydroxy ketones through the (formal) carboligation of two aldehyde reactants. The synthetic relevance of the products and the wide distribution of the α‐hydroxy ketone functionality in bioactive natural compounds have provided the motivation for intensive research efforts directed towards the development of ever more efficient and selective catalysts for reactions of this class. As in many other areas of study, the solution developed in nature – that is, the utilization of thiamine‐diphosphate‐dependent (ThDP‐dependent) enzymes – also in this case allows levels of chemo‐ and stereoselectivity currently unattainable by biomimetic organocatalysts to be achieved. Here we present an overview of the structural diversity of the α‐hydroxy ketone motif achievable through ThDP‐dependent enzyme catalysis. Details relating to structure–activity relationships and to rational mutagenesis approaches for improving the catalytic performances of wild‐type enzymes are also illustrated.
Selectivity Modulation of the Ley–Griffith TPAP Oxidation with N‐Oxide Salts
Authors: Moore Peter W. , Jiao Yanxiao , Mirzayans Paul M. , Sheng Lexter Ng Qi , Hooker Jordan P. , Williams Craig M.
Published: June 2016

A wide variety of novel non‐hygroscopic N‐oxide tetraphenylborate salts were synthesized and evaluated as co‐oxidants in the Ley–Griffith (TPAP) oxidation of benzylic and allylic alcohols under non‐anhydrous conditions. The novel DABCOO·TPB (2:1) salt was herein unearthed as a viable competitor to the first‐generation NMO·TPB (2:1) salt, but more importantly gave increased performance under oxidative competition. X‐ray crystal structure analysis and NMR spectroscopy revealed that depending on the crystallization conditions 1:1, 2:1 or 3:2 N‐oxide–tetraphenylborate salts could be formed.
Selective Synthesis of 5‐Substituted N‐Aryloxazolidinones by Cycloaddition Reaction of Epoxides with Arylcarbamates Catalyzed by the Ionic Liquid BmimOAc
Authors: Elageed Elnazeer H. M. , Chen Bihua , Wang Binshen , Zhang Yongya , Wu Shi , Liu Xiuli , Gao Guohua
Published: June 2016

A selective procedure for the synthesis of 5‐substituted N‐aryloxazolidinones by the coupling of epoxides with arylcarbamates catalyzed by ionic liquids has been developed. The effects of reaction time, reactant molar ratio, amount of catalyst, and temperature were investigated. Under the optimal reaction conditions, BmimOAc exhibited efficient catalytic activity compared with other ionic liquids leading to the formation of 5‐substituted N‐aryloxazolidinones in excellent yields. In addition, chiral 5‐substituted oxazolidinones were synthesized by this procedure in good‐to‐excellent yields with enantiomeric excesses in excess of 99.9 % starting from chiral terminal epoxides. A possible reaction mechanism is discussed in accord with the results obtained by 1H NMR spectroscopy and DFT calculations, which indicate the cooperative activation by BmimOAc through the formation of hydrogen bonds with the substrates.
Peptide Mechanosynthesis by Direct Coupling of N‐Protected α‐Amino Acids with Amino Esters
Authors: Porte Vincent , Thioloy Marion , Pigoux Titouan , Métro Thomas‐Xavier , Martinez Jean , Lamaty Frédéric
Published: June 2016

In view of developing alternatives to classical peptide synthesis strategies that suffer from low efficacy and negative environmental impact, the reactivity of N‐protected α‐amino acids, amino esters, and N‐ethyl‐N′‐(3‐dimethylaminopropyl)carbodiimide was studied under liquid‐assisted grinding (LAG) conditions. The optimal reaction conditions enabled the intensive and environmentally benign mechanosynthesis of a wide range of dipeptides that could be produced up to the multigram scale. The critical influence of the nature of the liquid additive on the course of the reaction was revealed. Combined with solvent‐free tert‐butoxycarbonyl deprotection steps, this approach was applied to the synthesis of tri‐ and tetrapeptides, thus opening the way to the synthesis of much longer peptides.
Nanoporous Gold Electrodes with Tuneable Pore Sizes for Bioelectrochemical Applications
Authors: Siepenkoetter Till , Salaj‐Kosla Urszula , Xiao Xinxin , Belochapkine Serguei , Magner Edmond
Published: June 2016

Nanoporous gold (NPG) fabricated by sputtering is a material of versatile morphology with pores whose size can be tailored to accommodate enzymes. The process of pore formation and the size of the pores in NPG are influenced by the composition of Au and Ag in the alloy used to prepare the electrodes together with the temperature and time period of the dealloying process. On increasing the time from 1 to 60 min and the temperature from 0.5 °C to 60.5 °C in concentrated HNO3, significant increases in the average pore diameters from 4.4 to 78 nm were observed with simultaneous decreases in the roughness factor (Rf). The pores of NPG were fully addressable regardless of the diameter, with Rf increasing linearly up to an alloy thickness of 500 nm. The influence of the pore size on the bioelectrochemical response of redox proteins was evaluated using cytochrome c as a model system. The highest current densities of ca. 30 µA cm−2 were observed at cytochrome c modified NPG electrodes with an average pore size of ca. 10 nm. The pores in NPG were also tuned for the mediatorless immobilization of Myrothecium verrucaria bilirubin oxidase. High current densities of ca. 65 µA cm−2 were observed at MvBOD modified NPG electrodes prepared by dealloying at 0.5 °C for 5 min with an average pore size of 8 nm, which is too small to accommodate the enzyme into the pores, indicating that the response was from enzyme adsorbed on the electrode surface.
Capillary electrophoresis coupled with in‐column fiber‐optic laser‐induced fluorescence detection for the rapid separation of neodymium
Authors: Cheng Changming , Jiang Tao , Han Jun , Lv Kai , Hu Sheng , Wang Xiaolin
Published: June 2016

In this study, in‐column fiber‐optic (ICFO) laser‐induced fluorescence (LIF) detection technique is coupled with capillary electrophoresis (CE) for the rapid separation of neodymium for the first time. The effects of buffer concentration, buffer pH, and separation voltage on the CE behaviors, including electrophoretic efficiency and detection sensitivity, are investigated in detail. Under the optimal condition determined in this study (15 mM borate buffer, pH 10.50, separation voltage 24 kV), neodymium could be separated effectively from the neighboring lanthanides (praseodymium and samarium) within several minutes, and the limit of detection for neodymium is estimated to be at the ppt level. The ICFO‐LIF‐CE system assembled in this study exhibits unique performance characteristics such as low cost and flexibility. Meanwhile, the separation efficiency and detection sensitivity of the assembled CE system are comparable to or somewhat better than those obtained in the previous traditional CE systems, indicating the potential of the assembled CE system for practical applications in the fields of spent nuclear fuel analysis, nuclear waste disposal/treatment, and nuclear forensics.
Linking DNA adduct formation and human cancer risk in chemical carcinogenesis
Authors: Poirier Miriam C.
Published: June 2016

Over two centuries ago, Sir Percival Pott, a London surgeon, published a pioneering treatise showing that soot exposure was the cause of high incidences of scrotal cancers occurring in young men who worked as chimney sweeps. Practicing at a time when cellular pathology was not yet recognized, Sir Percival nonetheless observed that the high incidence and short latency of the chimney sweep cancers, was fundamentally different from the rare scrotal cancers typically found in elderly men. Furthermore, his diagnosis that the etiology of these cancers was related to chimney soot exposure, was absolutely accurate, conceptually novel, and initiated the field of “occupational cancer epidemiology.” After many intervening years of research focused on mechanisms of chemical carcinogenesis, briefly described here, it is clear that DNA damage, or DNA adduct formation, is “necessary but not sufficient” for tumor induction, and that many additional factors contribute to carcinogenesis. This review includes a synopsis of carcinogen‐induced DNA adduct formation in experimental models and in the human population, with particular attention paid to molecular dosimetry and molecular cancer epidemiology. Environ. Mol. Mutagen. 57:499–507, 2016. © 2016 Wiley Periodicals, Inc.
Analysis on working performance of the swirl chamber diesel engine with a dual channel and an expansion angle
Authors: Yuan Wenhua , Ma Yi , Fu Jun , Li Yu , Zhang Bin , Huang Qike , Li Guangming
Published: June 2016

Based on the design principles of connecting passage, the article first proposed the idea of dual channel insert with expansion angle and designed three solutions which differed in the expansion angle between channel A and B by 0°& 0°, 5°& 10°, and 10°& 5°. Furthermore, the economic and emission characteristics of the swirl chamber were determined by conducting a bench test. Results indicate that the geometry of dual channel can promote the development of swirl, and a proper increase in the expansion angle of the channel has a positive effect on the development of the swirl in the swirl chamber. When the expansion angles of channel A and B are 10° and 5°, respectively, the swirl characteristic is relatively good, but experimental results show that the oil consumption rates of the Scheme at both the low and heavy load being at their least, which, respectively, are 3% and 3.2% lower than that of the original engine; and the corresponding exhaust transmission coefficients are also 72% and 9.7% lower than that of the original engine, respectively. And the economy and emission characteristics of the other two dual‐channel schemes are also improved in some degree. The research results provide certain reference for the performance improvement of swirl chamber air‐cooled diesel engine and are beneficial to the further design and optimization. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1793–1800, 2016
Trace element storage capacity of sediments in dead Posidonia oceanica mat from a chronically contaminated marine ecosystem
Authors: Di Leonardo Rossella , Mazzola Antonio , Cundy Andrew B. , Tramati Cecilia Doriana , Vizzini Salvatrice
Published: June 2016

Posidonia oceanica mat is considered a long-term bioindicator of contamination. Storage and sequestration of trace elements and organic carbon (Corg) were assessed in dead P. oceanica mat and bare sediments from a highly polluted coastal marine area (Augusta Bay, central Mediterranean). Sediment elemental composition and sources of organic matter have been altered since the 1950s. Dead P. oceanica mat displayed a greater ability to bury and store trace elements and Corg than nearby bare sediments, acting as a long-term contaminant sink over the past 120 yr. Trace elements, probably associated with the mineral fraction, were stabilized and trapped despite die-off of the overlying P. oceanica meadow. Mat deposits registered historic contamination phases well, confirming their role as natural archives for recording trace element trends in marine coastal environments. This sediment typology is enriched with seagrass-derived refractory organic matter, which acts mainly as a diluent of trace elements. Bare sediments showed evidence of inwash of contaminated sediments via reworking; more rapid and irregular sediment accumulation; and, because of the high proportions of labile organic matter, a greater capacity to store trace elements. Through different processes, both sediment typologies represent a repository for chemicals and may pose a risk to the marine ecosystem as a secondary source of contaminants in the case of sediment dredging or erosion. Environ Toxicol Chem 2017;36:49–58. © 2016 SETAC
Discharge estimation under uncertainty using variational methods with application to the full Saint‐Venant hydraulic network model
Authors: Gejadze Igor , Malaterre Pierre‐Olivier
Published: June 2016

Estimating river discharge from in situ and/or remote sensing data is a key issue for evaluation of water balance at local and global scales and for water management. Variational data assimilation (DA) is a powerful approach used in operational weather and ocean forecasting, which can also be used in this context. A distinctive feature of the river discharge estimation problem is the likely presence of significant uncertainty in principal parameters of a hydraulic model, such as bathymetry and friction, which have to be included into the control vector alongside the discharge. However, the conventional variational DA method being used for solving such extended problems often fails. This happens because the control vector iterates (i.e., approximations arising in the course of minimization) result into hydraulic states not supported by the model. In this paper, we suggest a novel version of the variational DA method specially designed for solving estimation‐under‐uncertainty problems, which is based on the ideas of iterative regularization.

The method is implemented with SIC2, which is a full Saint‐Venant based 1D‐network model. The SIC2 software is widely used by research, consultant and industrial communities for modeling river, irrigation canal, and drainage network behavior. The adjoint model required for variational DA is obtained by means of automatic differentiation. This is likely to be the first stable consistent adjoint of the 1D‐network model of a commercial status in existence.

The DA problems considered in this paper are offtake/tributary estimation under uncertainty in the cross‐device parameters and inflow discharge estimation under uncertainty in the bathymetry defining parameters and the friction coefficient. Numerical tests have been designed to understand identifiability of discharge given uncertainty in bathymetry and friction. The developed methodology, and software seems useful in the context of the future Surface Water and Ocean Topography satellite mission. Copyright © 2016 John Wiley & Sons, Ltd.
Final breakup of continental block and opening of oceanic lithosphere: insights from deep crustal structure and tectonic evolution of the ocean–continent transition zone in the northern South China Sea
Authors: Guo L. L. , Li S. Z. , Zhao S. J. , Zhang G. X. , Suo Y. H. , Liu H. , Hui G. G. , Fu S. Y. , Dai L. M. , Cao H. H. , Li X. Y. , Wang P. C. , Wang Q.
Published: June 2016

As an important transition domain between the thinnest continental crust and the initial oceanic crust, the ocean–continent transition zone (OCT) preserves a wealth of information on the processes of lithospheric extension and breakup. The northern margin of the South China Sea (SCS) is a non‐typical, magma‐poor passive continental margin with a particular structural pattern and sedimentary formation. The OCT in the northern margin of the SCS was developed by a series of continental rifting and seafloor spreading. Based on several multi‐channel seismic reflection profiles, crustal‐scale structural profiles extracted from gravity data and ocean‐bottom seismometers (OBS) data, this paper studies the deep crustal structures, deformation and geodynamics of the OCT to further understand the structural patterns and tectonic process from the lithospheric extension to its breakup. The OCT of the northern margin of the SCS is characterized by a crustal thinning and high‐velocity layer (HVL) in the lower crust. The OCT has three structural units: rift depression, volcanic zone and tilted fault blocks. The HVL is mainly limited in the eastern portion of the northern SCS. The HVL is distributed essentially within the OCT but does not clearly develop everywhere in the OCT. We propose a hybrid model of rifting to fit characteristics of the northern margin of the SCS. A crustal‐scale largely symmetric process predominated at the initial rifting stage. The basin‐controlling faults subsequently penetrated the entire crust, resulting in asymmetric tectonic evolution. Then, the OCT occupied this asymmetric location. Copyright © 2016 John Wiley & Sons, Ltd.