bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contributions of wildland fire to terrestrial ecosystem carbon dynamics in North America from 1990 to 2012
Authors: Chen Guangsheng , Hayes Daniel J. , David McGuire A. 
Published: May 2017

AbstractBurn area and the frequency of extreme fire events have been increasing during recent decades in North America, and this trend is expected to continue over the 21st century. While many aspects of the North American carbon budget have been intensively studied, the net contribution of fire disturbance to the overall net carbon flux at the continental scale remains uncertain. Based on national scale, spatially explicit and long‐term fire data, along with the improved model parameterization in a process‐based ecosystem model, we simulated the impact of fire disturbance on both direct carbon emissions and net terrestrial ecosystem carbon balance in North America. Fire‐caused direct carbon emissions were 106.55 ± 15.98 Tg C/yr during 1990–2012; however, the net ecosystem carbon balance associated with fire was −26.09 ± 5.22 Tg C/yr, indicating that most of the emitted carbon was resequestered by the terrestrial ecosystem. Direct carbon emissions showed an increase in Alaska and Canada during 1990–2012 as compared to prior periods due to more extreme fire events, resulting in a large carbon source from these two regions. Among biomes, the largest carbon source was found to be from the boreal forest, primarily due to large reductions in soil organic matter during, and with slower recovery after, fire events. The interactions between fire and environmental factors reduced the fire‐caused ecosystem carbon source. Fire disturbance only caused a weak carbon source as compared to the best estimate terrestrial carbon sink in North America owing to the long‐term legacy effects of historical burn area coupled with fast ecosystem recovery during 1990–2012.
Precessional variability of87Sr/86Sr in the late Miocene Sorbas Basin: An interdisciplinary study of drivers of interbasin exchange
Authors: Modestou Sevasti , Simon Dirk , Gutjahr Marcus , Marzocchi Alice , Kouwenhoven Tanja J. , Ellam Rob M. , Flecker Rachel 
Published: May 2017

AbstractWe present the first subprecessional record of seawater87Sr/86Sr isotope ratios for a marginal Mediterranean subbasin. The sediments contained in this interval (three precessional cycles between 6.60 and 6.55 Ma) are important because they record conditions during the transition to the Messinian Salinity Crisis (MSC; 5.97 to 5.33 Ma), an event for which many details are still poorly understood. The record, derived from planktic foraminifera of the late Miocene Sorbas Basin (SE Spain), shows brief excursions with precessional cyclicity to87Sr/86Sr ratios higher than coeval ocean87Sr/86Sr. The hydrologic conditions required to generate the observed record are investigated using box modeling, constrained using a new paleodepth estimate (150 to 250 m) based on benthic foraminiferal assemblages. The box model results highlight the role of climate‐driven interbasin density contrast as a significant driver of, or impediment to, exchange. The results are particularly significant in the context of the MSC, where87Sr/86Sr excursions have been interpreted purely as a consequence of physical restriction. To replicate the observed temporal patterns of lithological variations and87Sr/86Sr isotope excursions, the Sorbas Basin “box” must have a mainly positive hydrologic budget, in contrast with the Mediterranean's negative budget during the late Miocene. This result has implications for the assumption of synchronous deposition of specific sedimentary layers (sapropels) between marginal and open Mediterranean settings at subprecessional resolution. A net positive hydrologic budget in marginal Mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits.
Thick‐skinned tectonics within the intracontinental easternmost Atlas foreland‐and‐thrust belt (Tunisia): Meso‐Cenozoic kinematics and implications for regional geodynamics
Authors: Belkhiria W. , Boussiga H. , Inoubli M. H. 
Published: May 2017

AbstractThe transition zone between western and central Mediterranean domains presents a key area to investigate kinematic interactions within the adjacent orogen systems such as the easternmost Atlas foreland‐and‐thrust belt. Gravity and seismic data revealed a highly structured basement, characterizing a series of structural highs and lows delimited by high‐angle N‐S, E‐W, and NW‐SE extensional faults. This basement architecture is inherited from successive extensional events related to the openings of the Triassic‐Early Cretaceous Tethys oceans (i.e., Alpine Tethys, Ligurian Tethys, and Mesogea). Throughout this period, this mosaic of continental blocks significantly controlled the thickness and facies distributions. Early stages of diapirism took place along these basement faults and allowed maximum subsidence in minibasins revealed by the development of growth strata. In response to the Late Cretaceous‐Eocene shortenings, these extensional faults have been reactivated as trasnpressional shear zones, giving rise to narrow pop‐up structures. In addition, gravity modeling indicates crustal thinning and deep‐rooted faults affecting the crust south of the Zaghouan Thrust and along E‐W transfer zones. From the late Miocene, a drastic change in the stress regime is attributed to the effect of the adjacent Sicily channel on the study area. This promotes crustal thinning, basin subsidence, and channeling up of mantle‐derived helium along lithospheric‐scale weak zones. Our results give rise to new insights into the reactivation of inherited weakness zones of southern Tethys margin in response to the complex interaction between African and Eurasian plates accommodated by subduction, rollback, collision, and slab segmentation.
Tectonic drivers of the Wrangell block: Insights on fore‐arc sliver processes from 3‐D geodynamic models of Alaska
Authors: Haynie K. L. , Jadamec M. A. 
Published: May 2017

AbstractIntracontinental shear zones can play a key role in understanding how plate convergence is manifested in the upper plate in regions of oblique subduction. However, the relative role of the driving forces from the subducting plate and the resisting force from within intracontinental shear zones is not well understood. Results from high‐resolution, geographically referenced, instantaneous 3‐D geodynamic models of flat slab subduction at the oblique convergent margin of Alaska are presented. These models investigate how viscosity and length of the Denali fault intracontinental shear zone as well as coupling along the plate boundary interface modulate motion of the Wrangell block fore‐arc sliver and slip across the Denali fault. Models with a weak Denali fault (1017 Pa s) and strong plate coupling (1021 Pa s) were found to produce the fastest motions of the Wrangell block (∼10 mm/yr). The 3‐D models predict along‐strike variation in motion along the Denali fault, changing from dextral strike‐slip motion in the eastern segment to oblique convergence toward the fault apex. Models further show that the flat slab drives oblique motion of the Wrangell block and contributes to 20% (models with a short fault) and 28% (models with a long fault) of the observed Quaternary slip rates along the Denali fault. The 3‐D models provide insight into the general processes of fore‐arc sliver mechanics and also offer a 3‐D framework for interpreting hazards in regions of flat slab subduction.
Changing patterns of exhumation and denudation in front of an advancing crustal indenter, Tauern Window (Eastern Alps)
Authors: Favaro S. , Handy M. R. , Scharf A. , Schuster R. 
Published: May 2017

AbstractThe changing shape of indenting crustal blocks during northward motion of the Adriatic microplate induced migration of Miocene doming and orogen‐parallel extension of orogenic crust in the Tauern Window. New structural and kinematic data indicate that initial shortening of the Penninic nappe pile in the Tauern Window by upright folding and strike‐slip faulting was transitional to coeval north‐south shortening and east‐west extension; the latter was accommodated by normal faulting at the eastern and western margins of the window. Retrodeforming these post‐nappe structures in map view yields a map‐view reconstruction of the orogenic crust back to 30 Ma, including the onset of pronounced indentation at ~21 Ma. This model supports the notion that indentation involved approximately equal amounts of north‐south shortening and orogen‐parallel stretching and extrusion toward the Pannonian Basin, as measured from the indenter tip to the European foreland in the north and Austroalpine units in the east. Comparison of areal denudation of the orogenic crust before and after indentation indicates that erosion associated with upright folding was the primary agent of denudation, whereas extensional unroofing and limited erosion along normal faults at the eastern and western ends of the Tauern Window accounted for only about a third of the total denudation.
The polyphased tectonic evolution of the Anegada Passage in the northern Lesser Antilles subduction zone
Authors: Laurencin M. , Marcaillou B. , Graindorge D. , Klingelhoefer F. , Lallemand S. , Laigle M. , Lebrun J.‐F. 
Published: May 2017

AbstractThe influence of the highly oblique plate convergence at the northern Lesser Antilles onto the margin strain partitioning and deformation pattern, although frequently invoked, has never been clearly imaged. The Anegada Passage is a set of basins and deep valleys, regularly related to the southern boundary of the Puerto Rico‐Virgin Islands (PRVI) microplate. Despite the publications of various tectonic models mostly based on bathymetric data, the tectonic origin and deformation of this Passage remains unconstrained in the absence of deep structure imaging. During cruises Antithesis 1 and 3 (2013–2016), we recorded the first deep multichannel seismic images and new multibeam data in the northern Lesser Antilles margin segment in order to shed a new light on the structure and tectonic pattern of the Anegada Passage. We image the northeastern extent of the Anegada Passage, from the Sombrero Basin to the Lesser Antilles margin front. Our results reveal that this northeastern segment is an EW trending left‐stepping en échelon strike‐slip system that consists of the Sombrero and Malliwana pull‐apart basins, the Malliwana and Anguilla left‐lateral faults, and the NE‐SW compressional restraining bend at the Malliwana Hill. Reviewing the structure of the Anegada Passage, from the south of Puerto Rico to the Lesser Antilles margin front, reveals a polyphased tectonic history. The Anegada Passage is formed by a NW‐SE extension, possibly related to the rotation or escape of PRVI block due to collision of the Bahamas Bank. Currently, it is deformed by an active WNW‐ESE strike‐slip deformation associated to the shear component of the strain partitioning resulting from the subduction obliquity.
N‐Heterocyclic Carbene‐Catalyzed Mannich Reaction for the Synthesis of β‐Amino Ketones: N,N‐Dimethylformamide as Carbon Source
Authors: Alanthadka Anitha , Devi E. Sankari , Selvi A. Tamil , Nagarajan Subbiah , Sridharan Vellaisamy , Maheswari C. Uma 
Published: May 2017

AbstractThe efficiency of N,N‐dimethylformamide (DMF) in the N‐heterocyclic carbene‐catalyzed Mannich reaction for the synthesis of β‐amino ketones has been demonstrated. This strategy involves oxidative coupling of aryl methyl ketones and 2‐aminopyridines in the presence of DMF. The reaction does not require pre‐functionalization of the substrates, thus making it a practically applicable approach for the generation of β‐amino ketones. The reaction requires the use of tin(II) chloride dihydrate (SnCl2⋅2 H2O) as Lewis acid in the presence of tert‐butyl hydroperoxide (TBHP) as the oxidant. The reaction was tolerant to several aryl methyl ketones, including 2‐acetylnaphthalene and acetylthiophene. Various substituted 2‐aminopyridines react with acetophenone to give the desired β‐amino ketones in good yields.magnified image
Synthesis of Nitrogen‐Containing Heterocycles and Cyclopentenone Derivatives via Phosphine‐Catalyzed Michael Addition/Intramolecular Wittig Reaction
Authors: Saleh Nidal , Blanchard Florent , Voituriez Arnaud 
Published: May 2017

AbstractThe phosphine‐catalyzed Michael addition/intramolecular Wittig reaction between dialkyl acetylenedicarboxylate and amino‐carbaldehyde or amino ester derivatives has been developped. This reaction can be rendered catalytic in phosphine by the in situ chemoselective reduction of the phosphine oxide with silane. This methodology enables rapid access to a variety of nitrogen‐containing heterocycles, which are present in numerous natural products and/or bioactive compounds. Either classical heating or microwave conditions give access to the desired products in good yields (15 examples, 60–99% yields). This catalytic methodology is further applicable to the synthesis of enantioenriched 1H‐pyrrole derivatives, with the use of chiral phosphines. Finally, we successfully extended the reaction to the synthesis of a polysubstituted cyclopentenone, starting from butane‐2,3‐dione as substrate.magnified image
Exploring Multistep Continuous‐Flow Hydrosilylation Reactions Catalyzed by Tris(pentafluorophenyl)borane
Authors: Wilkins Lewis C. , Howard Joseph L. , Burger Stefan , Frentzel‐Beyme Louis , Browne Duncan L. , Melen Rebecca L. 
Published: May 2017

AbstractExploring the combination of continuous‐flow processes with the boron Lewis acid catalyzed hydrosilylation of aldehydes and ketones has delivered a robust and generally applicable reaction protocol. Notably this approach permits ready access to high temperatures and pressures and thus allows improved reactivity of substrates that were previously recalcitrant under the traditional approach. Efforts to quench the output from the flow reactor with water showed surprising tolerance leading to the application of continuous‐flow systems in multistep imine formation/hydrosilylation processes to generate the corresponding secondary amines from their aldehyde and aniline precursors.magnified image
Organocatalyzed Deracemization of Δ2‐Pyrrolin‐4‐ones
Authors: Ričko Sebastijan , Meden Anže , Ivančič Anže , Perdih Andrej , Štefane Bogdan , Svete Jurij , Grošelj Uroš 
Published: May 2017

AbstractRacemic pyrrolin‐4‐ones, accessible from α‐amino acids, undergo asymmetric stereoselective organocatalyzed 1,4‐additions to trans‐β‐nitrostyrenes (up to 98 % ee; dr up to 97:3). From a series of typical organocatalysts, the best performance was achieved using (+)‐camphor‐1,3‐diamine‐derived bifunctional organocatalysts. A broad substrate scope and some follow‐up modifications have been demonstrated.magnified image
Molekulare Knoten
Authors: Fielden Stephen D. P. , Leigh David A. , Woltering Steffen L. 
Published: May 2017

AbstractDer erste synthetische Kleeblattknoten wurde in den späten 1980er Jahren hergestellt. Kompliziertere Knotentopologien wurden jedoch erst in den letzten Jahren in molekularer Form erhalten. Die Verknotung molekularer Stränge erzeugt sterische Einschränkungen und kann so wichtige physikalische und chemische Eigenschaften verleihen, unter anderem Chiralität, starkes und selektives Binden von Ionen und katalytische Aktivität. Da die Anzahl und Komplexität molekularer Knoten steigt, wird es für Chemiker immer wichtiger, die Knotennomenklatur anderer Disziplinen zu verwenden. Hier geben wir einen Überblick über die Synthesestrategien für molekulare Knoten und beschreiben die Grundlagen der Knoten‐, Zopf‐ und Tangle‐Theorie in einem für Chemiker und molekulare Strukturen angemessenen Umfang.
Molecular Knots
Authors: Fielden Stephen D. P. , Leigh David A. , Woltering Steffen L. 
Published: May 2017

AbstractThe first synthetic molecular trefoil knot was prepared in the late 1980s. However, it is only in the last few years that more complex small‐molecule knot topologies have been realized through chemical synthesis. The steric restrictions imposed on molecular strands by knotting can impart significant physical and chemical properties, including chirality, strong and selective ion binding, and catalytic activity. As the number and complexity of accessible molecular knot topologies increases, it will become increasingly useful for chemists to adopt the knot terminology employed by other disciplines. Here we give an overview of synthetic strategies towards molecular knots and outline the principles of knot, braid, and tangle theory appropriate to chemistry and molecular structure.
Supported C‐Scorpionate Vanadium(IV) Complexes as Reusable Catalysts for Xylene Oxidation
Authors: Wang Jiawei , Martins Luísa M. D. R. S. , Ribeiro Ana P. C. , Carabineiro Sónia A. C. , Figueiredo José L. , Pombeiro Armando J. L. 
Published: May 2017

AbstractC‐Scorpionate vanadium(IV) [VOxCl3−x{κ3‐RC(pz)3}] [pz=pyrazol‐1‐yl; x=0, R=SO3 (1); x=1, R=CH2OH (2) or CH2OSO2Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V‐scorpionate catalysts used so far for the neat oxidation of o‐, m‐ or p‐xylene, with TBHP (70 % aqueous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably, a p‐toluic acid yield of 43 % (73 % selectivity, TON=1.34×103) was obtained with 2@CNT in a simple microwave‐assisted mild oxidation procedure, using a very low catalyst charge (3.2×10−2 mol % vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of a greener and more sustainable process for oxidation of xylenes. Moreover, reuse of catalysts with preservation of their activity was found for up to six consecutive cycles. The effects of reaction parameters, such as reaction time, temperature, amount of catalyst or type of heating source, on the performance of the above catalytic systems are reported and discussed.
Screening free radical scavengers in Xiexin Tang by HPLC‐ABTS‐DAD‐Q‐TOF/MS
Authors: Wang Yu‐Qing , Li Shu‐Jiao , Zhuang Guo , Geng Rong‐Hui , Jiang Xu 
Published: May 2017

AbstractXiexin Tang (XXT) is a traditional Chinese medicine (TCM) that has been used in herbal clinics for more than 1800 years. Many studies have shown that XXT has therapeutic effects on patients with arteriosclerosis owing to its antioxidant activity. However, there is little information about the relationship between the chemical composition of XXT and its antioxidant activity. In this study, the HPLC‐ABTS‐DAD‐Q‐TOF/MS method, which can simultaneously identify individual components and rapidly screen for antioxidant compounds, was used to screen and identify antioxidant components in XXT. The 15 compounds identified were gluco‐syringic acid, adenine, gallic acid, biflorin, cularine, 6‐C‐arabinose‐8‐C‐glucose‐chrysin, 6‐C‐glucose‐8‐C‐arabinose–chrysin, baicalin, rhein‐8‐O‐β‐d‐glucopyranoside, coptisine, epiberberine, jatrorrhizine, norwogonin, 5,7,2′‐trihydroxy‐6‐ methoxyflavone and baicalein. In addition, the data showed that the antioxidant activity of peaks 4, 6, and 11 was lower in XXT than in its constituent herbs, while the activity of peaks 1, 2, 3, 5, 7, 8, 10, 12, 13, 14 and 15 was higher in XXT. Compound 5 had the strongest antioxidant activity in XXT, while compound 1 showed the strongest antioxidant activity among its constituent herb. The differences between antioxidant activities of major components of XXT and those of its constituent herbs might be due to the interaction of crude drugs that changes the solubility of active components during the decoction process. The results show that the HPLC‐ABTS‐DAD‐Q‐TOF/MS method can successfully combine on‐line mass spectrometry with activity detection system. It is a useful tool for the rapid detection and identification of antioxidants, and for quantitative analysis of individual antioxidants in complex mixtures such as plant extracts. Furthermore, this method does not require extensive extract purification and fraction collection.
Terpenes as Useful Markers in Differentiation of Natural Populations of Relict Pines Pinus heldreichii, P. nigra, and P. peuce
Authors: Mitić Zorica S. , Nikolić Biljana M. , Ristić Mihailo S. , Tešević Vele V. , Bojović Srdjan R. , Marin Petar D. 
Published: May 2017

Comparative analysis of terpene diversity and differentiation of relict pines Pinus heldreichii, P. nigra, and P. peuce from the central Balkans was performed at the population level. Multivariate statistical analyses showed that the composition of needle terpenes reflects clear divergence among the pine species from different subgenera: P. peuce (subgenus Strobus) vs. P. nigra and P. heldreichii (subgenus Pinus). In addition, despite the described morphological similarities and the fact that P. nigra and P. heldreichii may spontaneously hybridize, our results indicated differentiation of their populations naturally growing in the same area. In accordance with recently proposed concept of ‘flavonic evolution’ in the genus Pinus, we assumed that the terpene profile of soft pine P. peuce, defined by high amounts of six monoterpenes, is more basal than those of hard pines P. nigra and P. heldreichii, which were characterized by high content levels of mainly sesquiterpenes. In order to establish precise positions of P. heldreichii, P. nigra and P. peuce within the taxonomic and phylogenetic tree, as well as develop suitable conservation strategies and future breeding efforts, it is necessary to perform additional morphological, biochemical, and genetic studies.
Salvia officinalis L. Essential Oils from Spain: Determination of Composition, Antioxidant Capacity, Antienzymatic, and Antimicrobial Bioactivities
Authors: Cutillas Ana‐Belen , Carrasco Alejandro , Martinez‐Gutierrez Ramiro , Tomas Virginia , Tudela Jose 
Published: May 2017

Four essential oils (EOs) from Salvia officinalis L. cultivated in Spain (Murcia Province) were analyzed by gas chromatography coupled with mass spectrometry (GC/MS) to determine their relative and absolute compositions. The main components were α‐thujone (22.8 – 41.7%), camphor (10.7 – 19.8%), 1,8‐cineole (4.7 – 15.6%), and β‐thujone (6.1 – 15.6%). Enantioselective gas chromatography identified (−)‐α‐thujone and (+)‐camphor as the main enantiomers in all the analyzed EOs. Furthermore, when the EOs were tested to determine their antioxidant activity against free radicals and as ferric reducing and ferrous chelating agents, all were seen to have moderate activity due to the compounds they contained, such as linalool or terpinene. Because of their known relation with inflammatory illnesses and Alzheimer's disease, respectively, the inhibition of lipoxygenase and acetylcholinesterase was studied using the EOs. Some individual compounds also inhibited these enzymes. In addition, the studied EOs were able to inhibit the growth of Escherichia coli, Staphylococcus aureus, and Candida albicans. The characterization carried out increases our awareness of the possible uses of S. officinalis EO as natural additives in food, cosmetics, and pharmaceuticals.