bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclization of 2‐Ethynylphenyl Vinyl Ether Catalyzed by a Ruthenium Complex: Mechanism of Catalytic Cyclization and Stoichiometric Cycloisomerization
Authors: Chen Chi‐Ren , Lai Ying‐Xuan , Wu Rong‐Yu , Liu Yi‐Hung , Lin Ying‐Chih 
Published: June 2016

AbstractCatalytic cyclization reactions and new stoichiometric skeletal rearrangement cycloisomerizations of 2‐ethynylphenyl vinyl ethers containing methyl substituents on the vinyl groups by using [Ru]Cl {[Ru]=Cp(PPh3)2Ru, Cp=η5‐cyclopentadienyl} were observed in MeOH and CH2Cl2, respectively. In MeOH, the catalytic cyclization of three different enynes gave the corresponding benzoxepine derivatives in high yields in each case. Interestingly, in the stoichiometric reactions of [Ru]Cl with enynes, two unprecedented rearrangements of enynes were observed in CH2Cl2. The presence of a methyl group in the vinyl unit plays a critical role in choosing one of the double bonds of the vinylidene ligand, that is, the Ru=Cα or the Cα=Cβ bond, for the [2+2] cycloaddition in the cycloisomerization processes. Structure determination by single‐crystal X‐ray diffraction analysis along with various isotope studies corroborated the proposed mechanisms.
Design, Synthesis, EPR‐Studies and Conformational Bias of Novel Spin‐Labeled DCC‐Analogues for the Highly Regioselective Labeling of Aliphatic and Aromatic Carboxylic Acids
Authors: Gölz Jan Philipp , NejatyJahromy Yaser , Bauer Mirko , Muhammad Ashraf , Schnakenburg Gregor , Grimme Stefan , Schiemann Olav , Menche Dirk 
Published: June 2016

AbstractNovel types of spin‐labeled N,N′‐dicyclohexylcarbodiimides (DCC) are reported that bear a 2,2,6,6‐tetramethylpiperidinyloxyl (TEMPO) residue on one side and different aromatic and aliphatic cyclohexyl analogues on the other side of the diimide core. These readily available novel reagents add efficiently to aliphatic and aromatic carboxylic acids, forming two possible spin‐labeled amide derivatives with different radical distances of the resulting amide. The addition of aromatic DCC analogues proceeds with excellent selectivity, giving amides where the carboxylic acid is exclusively connected to the aromatic residue, while little or no selectivity was observed for the aliphatic congeners. The usefulness of these adducts in structural studies was demonstrated by EPR (electron paramagnetic resonance) measurements of biradical adducts of biphenyl‐4,4′‐dicarboxylic acids. These analyses also reveal high degrees of conformational bias for aromatic DCC derivatives, which further underlines the powerfulness of these novel reagents. This observation was further corroborated by quantum chemical calculations, giving a detailed understanding of the structural dynamics, while detailed information on the solid state structure of all novel reagents was obtained by X‐ray structure analyses.
The Mechanism of Phosphonium Ylide Alcoholysis and Hydrolysis: Concerted Addition of the O−H Bond Across the P=C Bond
Authors: Byrne Peter A. , Gilheany Declan G. 
Published: June 2016

AbstractThe previous work on the hydrolysis and alcoholysis reactions of phosphonium ylides is summarized and reviewed in the context of their currently accepted mechanisms. Several experimental facts relating to ylide hydrolysis and to salt and ylide alcoholysis are shown to conflict with those mechanisms. In particular, we demonstrate that the pKa values of water and alcohols are too high in organic media to bring about protonation of ylide. Therefore, we propose concerted addition of the water or alcohol O−H bond across the ylide P=C bond. In support of this, we provide NMR spectroscopic evidence for equilibrium between ylide and aclohol that does not require the involvement of phosphonium hydroxide. We report the first P‐alkoxyphosphorane to be characterised by NMR spectroscopy that does not undergo exchange on an NMR timescale. Two‐dimensional NMR spectroscopic techniques have been applied to the characterisation to P‐alkoxyphosphoranes for the first time.
First Atroposelective Total Synthesis of Enantiomerically Pure Ancistrocladidine and Ancistrotectorine
Authors: Bringmann Gerhard , Manchala Narasimhulu , Büttner Tobias , Hertlein‐Amslinger Barbara , Seupel Raina 
Published: June 2016

AbstractThe first regio‐ and stereoselective total synthesis of the axially chiral 7,3′‐coupled naphthylisoquinoline alkaloids ancistrocladidine (1) and ancistrotectorine (2) has been described. Both possess a 7,3′‐coupled axis, which before now, was difficult to attain synthetically. Moreover, target 2 has a sensitive relative cis‐array of the two methyl groups at C1 and C3 in the tetrahydroisoquinoline part. The key step in the chosen strategy was the construction of the biaryl axis in accordance with the “lactone method”: the two molecular halves, which were activated in an “inverse‐halogenated” form, were prefixed by an ester bridge, followed by intramolecular coupling, and atroposelective cleavage of the lactone auxiliary bridge delivered the desired biaryl scaffold.
Experiment‐Driven Modeling of Crystalline Phosphorus Nitride P3N5: Wide‐Ranging Implications from a Unique Structure
Authors: Tolhurst Thomas M. , Braun Cordula , Boyko Teak D. , Schnick Wolfgang , Moewes Alexander 
Published: June 2016

AbstractNitridophosphates have emerged as advanced materials due to their structural variability and broad technical applicability. Their binary parent compound P3N5, a polymeric network of corner‐ and edge‐sharing PN4 tetrahedra with N and N sites, is a particularly interesting example. We present a study of the band gap and electronic structure of α‐P3N5 by using soft X‐ray spectroscopy measurements and DFT calculations. The band gap, which is crucial for all applications, is measured to be 5.87±0.20 eV. This agrees well with the calculated, indirect band gap of 5.21 eV. The density of states are found to show dramatic variation between the nonequivalent N sites and a high degree of covalency. Coupled to these results is what is, to our knowledge, the largest core hole shift reported to date for a soft X‐ray absorption spectrum. We propose an intuitive bonding scheme for α‐P3N5 that explains the observed band gap and unique density of states, while providing a framework for predicting these properties in known and yet to be discovered PN compounds. We briefly consider the implications of these results for new low‐dimensional P and PN materials, which alongside graphene, could become important materials for nanoelectronics.
Towards Safer Rocket Fuels: Hypergolic Imidazolylidene‐Borane Compounds as Replacements for Hydrazine Derivatives
Authors: Huang Shi , Qi Xiujuan , Liu Tianlin , Wang Kangcai , Zhang Wenquan , Li Jianlin , Zhang Qinghua 
Published: June 2016

AbstractCurrently, toxic and volatile hydrazine derivatives are still the main fuel choices for liquid bipropellants, especially in some traditional rocket propulsion systems. Therefore, the search for safer hypergolic fuels as replacements for hydrazine derivatives has been one of the most challenging tasks. In this study, six imidazolylidene‐borane compounds with zwitterionic structure have been synthesized and characterized, and their hypergolic reactivity has been studied. As expected, these compounds exhibited fast spontaneous combustion upon contact with white fuming nitric acid (WFNA). Among them, compound 5 showed excellent integrated properties including wide liquid operating range (−70–160 °C), superior loading density (0.99 g cm−3), ultrafast ignition delay times with WFNA (15 ms), and high specific impulse (303.5 s), suggesting promising application potential as safer hypergolic fuels in liquid bipropellant formulations.
[40]π Fused and Nonfused Core‐Modified Nonaphyrins: Syntheses and Structural Diversity
Authors: Ghosh Arindam , Srinivasan A. , Suresh Cherumuttathu H. , Chandrashekar Tavarekere K. 
Published: June 2016

AbstractThe synthesis of fused and nonfused core‐modified 40π nonaphyrins are reported. Spectroscopic and X‐ray structural studies reveal a twisted figure‐eight conformation in the freebase form that is nonaromatic. Structural changes occur, from figure‐eight to open extended conformation, upon protonation, thereby adopting 4nπ Hückel antiaromatic character, which is reflected in spectroscopic and theoretical studies. Such a structural change also induces ring inversions of specific heterocyclic rings by 180°.
Noncovalent Substrate‐Directed Enantioselective Heck Reactions: Synthesis of S‐ and P‐Stereogenic Heterocycles
Authors: de Azambuja Francisco , Carmona Rafaela C. , Chorro Tomaz H. D. , Heerdt Gabriel , Correia Carlos Roque D. 
Published: June 2016

AbstractS‐ and P‐Stereogenic heterocycles were synthesized by a remarkably simple enantioselective Heck desymmetrization reaction based on the unprecedented noncovalent directing effect of S=O and P=O functionalities. Selected prochiral symmetric substrates were efficiently arylated using the recently disclosed chiral PyraBOx ligand under mild and open‐flask reaction conditions. Several five‐membered aryl‐ sulfones, sulfoxides, and phosphine oxides were synthesized in good to excellent yields, in good to high diastereoselectivity, and enantiomeric ratios up to 98:2. Theoretical calculations also support the noncovalent directing effect of the S=O and P=O functionalities during the arylation process.
Nickel‐Catalyzed Cross‐Electrophile Coupling with Organic Reductants in Non‐Amide Solvents
Authors: Anka‐Lufford Lukiana L. , Huihui Kierra M. M. , Gower Nicholas J. , Ackerman Laura K. G. , Weix Daniel J. 
Published: June 2016

AbstractCross‐electrophile coupling of aryl halides with alkyl halides has thus far been primarily conducted with stoichiometric metallic reductants in amide solvents. This report demonstrates that the use of tetrakis(dimethylamino)ethylene (TDAE) as an organic reductant enables the use of non‐amide solvents, such as acetonitrile or propylene oxide, for the coupling of benzyl chlorides and alkyl iodides with aryl halides. Furthermore, these conditions work for several electron‐poor heterocycles that are easily reduced by manganese. Finally, we demonstrate that TDAE addition can be used as a control element to ‘hold’ a reaction without diminishing yield or catalyst activity.
Chiral HPLC Separation, Absolute Structural Elucidation, and Determination of Stereochemical Stability of trans‐Bis[2‐(2‐pyridinyl)aminophenolato] Cyclotriphosphazene
Authors: Kajiyama Kazumasa , Setone Yuki , Aoyagi Kouki , Yuge Hidetaka 
Published: June 2016

AbstractChiral high‐performance liquid chromatography (HPLC) separation of trans‐bis[2‐(2‐pyridyl)aminophenolato] dichlorocyclotriphosphazene 1 was achieved and the absolute configuration of (+)-1 was assigned to be S,S by single‐crystal X‐ray structural analysis. The optically pure 1,2‐diphenyl‐1,2‐ethanediolate derivatives (+)‐2a and (−)‐2b were synthesized by the reactions of (+)-1 and (-)-1 with (R,R)‐hydrobenzoin, respectively, in refluxing toluene in the presence of an excess amount of triethylamine and a catalytic amount of 4‐(dimethylamino)pyridine. The racemization of the enantiomers of 1 and the epimerization of diastereomers of 2 were not observed in refluxing toluene neither under acidic nor basic conditions. The stereochemistry of (+)-1 was confirmed by the crystal structure of (+)‐2a and bis[(4‐methyl‐2‐pyridyl)oxy]cyclotriphosphazene (+)-3 derived from (+)-1. Chirality 28:556–561, 2016. © 2016 Wiley Periodicals, Inc.
Imaging the Bonds of Dehalogenated Benzene Radicals on Cu(111) and Au(111)
Authors: Simic‐Milosevic Violeta , Mehlhorn Michael , Morgenstern Karina 
Published: June 2016

AbstractDissociative adsorption of doubly substituted benzene molecules leads to formation of benzyne radicals. In this study, co‐adsorbed hydrogen molecules are used in scanning tunneling hydrogen microscopy to enhance the contrast of the meta‐ and the para‐isomers of these radicals on Cu(111) and Au(111). Up to three hydrogen molecules are attached to one radical. One hydrogen molecule reveals the orientation of the carbon ring and its adsorption site, allowing discrimination between the two radicals. Two hydrogen molecules reflect the bond picture of the carbon skeleton and reveals that adsorption on Cu(111) distorts the meta‐ isomer differently from its gas‐phase distortion. Three hydrogen molecules allow us to determine the bond picture of a minor species.
Gadolinium(III)‐Based Porous Luminescent Metal–Organic Frameworks for Bimodal Imaging
Authors: Kundu Tanay , Mitra Shouvik , Díaz Díaz David , Banerjee Rahul 
Published: June 2016

AbstractGdIII‐based metal–organic frameworks, Gd‐pDBI‐1 and Gd‐pDBI‐2, have been synthesized using the linker pDBI (pDBI=1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2yl)benzene). They exhibited structural diversity due to subtle change in reaction constituents. Owing to the judicious choice of the fluorescent linker, the materials could be used for bimodal imaging (fluorescent and magnetic resonance) and displayed a modest T1 relaxivity value.
Somatic growth dynamics of West Atlantic hawksbill sea turtles: a spatio‐temporal perspective
Authors: Bjorndal Karen A. , Chaloupka Milani , Saba Vincent S. , Diez Carlos E. , van Dam Robert P. , Krueger Barry H. , Horrocks Julia A. , Santos Armando J. B. , Bellini Cláudio , Marcovaldi Maria A. G. , Nava Mabel , Willis Sue , Godley Brendan J. , Gore Shannon , Hawkes Lucy A. , McGowan Andrew , Witt Matthew J. , Stringell Thomas B. , Sanghera Amdeep , Richardson Peter B. , Broderick Annette C. , Phillips Quinton , Calosso Marta C. , Claydon John A. B. , Blumenthal Janice , Moncada Felix , Nodarse Gonzalo , Medina Yosvani , Dunbar Stephen G. , Wood Lawrence D. , Lagueux Cynthia J. , Campbell Cathi L. , Meylan Anne B. , Meylan Peter A. , Burns Perez Virginia R. , Coleman Robin A. , Strindberg Samantha , Guzmán‐H. Vicente , Hart Kristen M. , Cherkiss Michael S. , Hillis‐Starr Zandy , Lundgren Ian F. , Boulon Ralf H. , Connett Stephen , Outerbridge Mark E. , Bolten Alan B. 
Published: June 2016

AbstractSomatic growth dynamics are an integrated response to environmental conditions. Hawksbill sea turtles (Eretmochelys imbricata) are long‐lived, major consumers in coral reef habitats that move over broad geographic areas (hundreds to thousands of kilometers). We evaluated spatio‐temporal effects on hawksbill growth dynamics over a 33‐yr period and 24 study sites throughout the West Atlantic and explored relationships between growth dynamics and climate indices. We compiled the largest ever data set on somatic growth rates for hawksbills – 3541 growth increments from 1980 to 2013. Using generalized additive mixed model analyses, we evaluated 10 covariates, including spatial and temporal variation, that could affect growth rates. Growth rates throughout the region responded similarly over space and time. The lack of a spatial effect or spatio‐temporal interaction and the very strong temporal effect reveal that growth rates in West Atlantic hawksbills are likely driven by region‐wide forces. Between 1997 and 2013, mean growth rates declined significantly and steadily by 18%. Regional climate indices have significant relationships with annual growth rates with 0‐ or 1‐yr lags: positive with the Multivariate El Niño Southern Oscillation Index (correlation = 0.99) and negative with Caribbean sea surface temperature (correlation = −0.85). Declines in growth rates between 1997 and 2013 throughout the West Atlantic most likely resulted from warming waters through indirect negative effects on foraging resources of hawksbills. These climatic influences are complex. With increasing temperatures, trajectories of decline of coral cover and availability in reef habitats of major prey species of hawksbills are not parallel. Knowledge of how choice of foraging habitats, prey selection, and prey abundance are affected by warming water temperatures is needed to understand how climate change will affect productivity of consumers that live in association with coral reefs.
Effects of temporal variation in temperature and density dependence on insect population dynamics
Authors: Haridas C. V. , Meinke Lance J. , Hibbard Bruce E. , Siegfried Blair D. , Tenhumberg Brigitte 
Published: June 2016

AbstractUnderstanding the effects of environmental variation on insect populations is important in light of predictions about increasing climatic variability. This paper uses the univoltine western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) as a case study and employs deterministic and stochastic modeling to evaluate how insect population dynamics is shaped by density‐dependent survival and annual variation in temperature, which are key in regulating insect populations. Field data showed that larval survival varied significantly between years but was constant for a range of densities. Survival dropped only beyond a threshold density, a feature resembling generalized Ricker functions used in modeling density‐dependent survival due to scramble competition for resources. We used soil temperature data for 20 yr to model annual variation in developmental time and survival. The deterministic model, where the developmental time was same across years, showed that though survival was high and did not change for a range of densities (i.e., density‐independent survival), predicted densities were large enough that strong density dependence could occur in the field (i.e., predicted densities fall in the region where survival drops sharply) and that populations could exhibit stable equilibrium, cycles, etc. Interestingly, populations with lower density‐independent survival were less likely to produce stable equilibrium compared to populations with higher density‐independent survival. We found that population densities were at stable equilibrium when both mean developmental time and fertility were relatively low or when developmental time and fertility were relatively high. This in turn implies that, in warmer regions, where mean developmental time will be lower, stability is more likely for insect populations with low fertility; species in warmer regions will experience cyclical and unstable dynamics when fertility is high. While increase in the mean developmental time reduces overall survival, increasing variation in developmental time could increase mean survival, a consequence of the Jensen's inequality, since survival was a concave decreasing function of developmental time. Hence, both mean and variability in temperature affect the dynamics of insect populations. Finally, we found that stochastic variation in soil temperature produced large variation in predicted population densities that could potentially enhance or diminish the effect of density dependence.
Mapping for coral reef conservation: comparing the value of participatory and remote sensing approaches
Authors: Selgrath Jennifer C. , Roelfsema Chris , Gergel Sarah E. , Vincent Amanda C. J. 
Published: June 2016

AbstractDetailed habitat maps are critical for conservation planning, yet for many coastal habitats only coarse‐resolution maps are available. As the logistic and technological constraints of habitat mapping become increasingly tractable, habitat map comparisons are warranted. Here we compare two mapping approaches: local environmental knowledge (LEK) obtained from interviews; and remote sensing analysis (RS) of high spatial resolution satellite imagery (2.0 m pixel) using object‐based image analysis. For a coral reef ecosystem, we compare the accuracy of these two approaches for mapping shallow seafloor habitats and contrast their characterization of habitat area and seascape connectivity. We also explore several implications for conservation planning. When evaluated using independent ground verification data, LEK‐derived maps achieved a lower overall accuracy than RS‐derived maps (LEK: 66%; RS: 76%). A comparison of mapped habitats found low overall agreement between LEK and RS maps. The RS map identified 5.4 times more habitat edges (the border between adjacent habitat classes) and 3.7–6.4 times greater seascape connectivity. Since the spatial arrangement of habitats affects many species (e.g., movement, predation risk), such discrepancies in landscape metrics are important to consider in conservation planning. Our results help identify strengths and weakness of both mapping approaches for conservation planning. Because RS provided a more accurate estimate of habitat distributions, it would be better for conservation planning for species sensitive to fine‐spatial scale seascape patterns (e.g., habitat edges), whereas LEK is more cost effective and appropriate for mapping coarse habitat patterns. Goals for maps used in conservation should be identified early in their development.
Metabolic programming in chronically stimulated T cells: Lessons from cancer and viral infections
Authors: Bettonville Marie , D'Aria Stefania , Braun Michel Y. 
Published: June 2016

T‐cell metabolism is central to the shaping of a successful immune response. However, there are pathological situations where T cells are rendered dysfunctional and incapable of eliminating infected or transformed cells. Here, we review the current knowledge on T‐cell metabolism and how persistent antigenic stimulation, in the form of cancer and chronic viral infection, modifies both metabolic and functional pathways in T cells.
Exercise increases pressure pain tolerance but not pressure and heat pain thresholds in healthy young men
Authors: Vaegter H.B. , Hoeger Bement M. , Madsen A.B. , Fridriksson J. , Dasa M. , Graven‐Nielsen T. 
Published: June 2016

AbstractBackgroundExercise causes an acute decrease in the pain sensitivity known as exercise‐induced hypoalgesia (EIH), but the specificity to certain pain modalities remains unknown. This study aimed to compare the effect of isometric exercise on the heat and pressure pain sensitivity.MethodsOn three different days, 20 healthy young men performed two submaximal isometric knee extensions (30% maximal voluntary contraction in 3 min) and a control condition (quiet rest). Before and immediately after exercise and rest, the sensitivity to heat pain and pressure pain was assessed in randomized and counterbalanced order. Cuff pressure pain threshold (cPPT) and pain tolerance (cPTT) were assessed on the ipsilateral lower leg by computer‐controlled cuff algometry. Heat pain threshold (HPT) was recorded on the ipsilateral foot by a computer‐controlled thermal stimulator.ResultsCuff pressure pain tolerance was significantly increased after exercise compared with baseline and rest (p < 0.05). Compared with rest, cPPT and HPT were not significantly increased by exercise. No significant correlation between exercise‐induced changes in HPT and cPPT was found. Test–retest reliability before and after the rest condition was better for cPPT and CPTT (intraclass correlation > 0.77) compared with HPT (intraclass correlation = 0.54).ConclusionsThe results indicate that hypoalgesia after submaximal isometric exercise is primarily affecting tolerance of pressure pain compared with the pain threshold. These data contribute to the understanding of how isometric exercise influences pain perception, which is necessary to optimize the clinical utility of exercise in management of chronic pain.SignificanceThe effect of isometric exercise on pain tolerance may be relevant for patients in chronic musculoskeletal pain as a pain‐coping strategy.What does this study add?

The results indicate that hypoalgesia after submaximal isometric exercise is primarily affecting tolerance of pressure pain compared with the heat and pressure pain threshold.

These data contribute to the understanding of how isometric exercise influences pain perception, which is necessary to optimize the clinical utility of exercise in management of chronic pain.