bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chiral Salen Complexes for Asymmetric Heterogeneous Catalysis: Recent Examples for Recycling and Cooperativity
Authors: Abd El Sater Mariam , Jaber Nada , Schulz Emmanuelle 
Published: May 2019

AbstractChiral salen complexes are privileged and versatile catalysts used in a wide variety of enantioselective transformations. Researches for their use in multicatalysis, including cooperative as well as tandem processes, are more recent, but many reports already highlight the important effect of the salen ligand structure on reaction rates and/or selectivities. This review article thus outlines the literature covering last five years, on the current developments of chiral polymetallic salen complexes used in asymmetric heterogeneous catalysis; their preparation, their efficiency as catalysts in various reactions and their recyclability are highlighted according to the immobilization procedures involved for their heterogenization. These methods include grafting on organic or inorganic supports insuring easy recovery by simple filtration. Polymerization processes are also part of recent research, leading to high densities of catalytic sites to favor their cooperativity. Combination of salen complexes via non covalent interactions or their introduction on MOFs and COFs networks is currently in full expansion, with examples of highly functionalized and enantioenriched products issued from tandem catalysis.
Specific Residues Expand the Substrate Scope and Enhance the Regioselectivity of a Plant O‐Methyltransferase
Authors: Tang Qingyun , Bornscheuer Uwe T. , Pavlidis Ioannis V. 
Published: May 2019

AbstractAn isoeugenol 4‐O‐methyltransferase (IeOMT), isolated from the plant Clarkia breweri, can be engineered to a caffeic acid 3‐O‐methyltransferase (CaOMT) by replacing three consecutive residues. Here we further investigated functions of these residues by constructing the triple mutant T133M/A134N/T135Q as well as single mutants of each residue. Phenolics with different chain lengths and different functional groups were investigated. The variant T133M improves the enzymatic activities against all tested substrates by providing beneficial interactions to residues which directly interact with the substrate. Mutant A134N significantly enhanced the regioselectivity. It is meta‐selective or even specific against most of the tested substrates but para‐specific towards 3,4‐dihydroxybenzoic acid. The triple mutant T133M/A134N/T135Q benefits from these two mutations, which not only expand the substrate scope but also enhance the regioselectivity of IeOMT. On the basis of our work, regiospecific methylated phenolics can be produced in high purity by different IeOMT variants.
Cyclization of Terphenyl‐Bisfluorenols: A Mechanistic Study of the Regioselectvity
Authors: Poriel Cyril , Barrière Frédéric , Rault‐Berthelot Joëlle , Thirion Damien 
Published: May 2019

AbstractThe mechanism of the bicyclization reaction of a series of terphenyl‐bisfluorenols into dispiro[fluorene‐9,6′‐indeno[1,2‐b]fluorene‐12′,9′′‐fluorene] and dispiro[fluorene‐9,6′‐indeno[2,1‐a]fluorene‐12′,9′′‐fluorene] is reported. Through a combined experimental and theoretical study, the different parameters that drive the regioselectivity of this cyclization reaction have been studied and are presented.
α‐Branched Ketone Dienolates: Base‐Catalysed Generation and Regio‐ and Enantioselective Addition Reactions
Authors: Urruzuno Iñaki , Mugica Odei , Zanella Giovanna , Vera Silvia , Gómez‐Bengoa Enrique , Oiarbide Mikel , Palomo Claudio 
Published: May 2019

AbstractIn this study, the unique capacity of bifunctional Brønsted bases to generate α‐branched ketone dienolates and control both site‐ and stereoselectivity of their addition reactions to representative classes of carbon electrophiles (i.e., vinyl sulfones, nitroolefins, formaldehyde) is documented. We demonstrate that by using selected chiral tertiary amine/squaramide catalysts, the reactions of β,γ‐unsaturated cycloalkanones proceed through the dienolate Cα almost exclusively and provide all‐carbon quaternary cyclic ketone adducts in good yields with very high enantioselectivities. A minor amount (<5 %) of γ‐addition is observed when nitroolefins are used as electrophiles. The parent acyclic ketone dienolates proved to be less reactive under these conditions, and thus still constitute a challenging class of substrates. Quantum chemical calculations correctly predict these differences in reactivity and explain the observed site‐specificity and enantioselectivity.
Synthesis, Characterization, and Properties of Tetraphenylethylene‐Based Tetrakis‐NHC Ligands and Their Metal Complexes
Authors: Sun Li‐Ying , Feng Ting , Das Rajorshi , Hahn F. Ekkehardt , Han Ying‐Feng 
Published: May 2019

AbstractThe development of highly emissive dinuclear AgI or AuI complexes [M2L](PF6)2 (L=2 a, 2 b; M=Ag, Au) derived from tetraphenylethylene (TPE)‐based tetrabenzimidazolin‐2‐ylidene ligands is reported. The new complexes exhibit a remarkable fluorescence enhancement compared to their parent benzimidazolium salts. The quantum yield (ΦF) value for salt H4‐2 a(PF6)4 in dilute solution (c=10−5 m) was found to be less than 1 %, whereas its metal complexes show ΦF values up to 55 % at similar solution concentration. This observation can be attributed to the rigidification of the TPE skeleton upon metalation resulting in a restriction of the intramolecular rotation of the phenyl groups. Functionalization of the complexes [M22 b](PF6)2 (M=Ag, Au) with terminal coumarin groups and subsequent photoirradiation yielded the complexes [M23 b](PF6)2 (M=Ag, Au) bearing a new type of ligand with an unaffected TPE moiety.
A Brief History of Chemical Reactor and Reaction Technology
Authors: Kockmann Norbert 
Published: May 2019

AbstractThe term “chemical reactor” appears for the first time in open literature at the end of First World War, while in Germany the term “reaction technology” was coined in the 1950s, although chemical reactions and processes have been known for thousands of years. In the early days, reactors were furnaces and pots, which specialized further over the centuries. With the Industrial Revolution many reactor types were already known, and industrialization brought an enormous innovation thrust in the field of products as well as technologies. The diversity of reactors today is almost uncomprehensive and so efforts to standardize apparatus are understandable.
Cover Picture: Facile Synthesis and in situ TEM Observation of Nanoporous Pd for Enhanced Catalytic Applications (Chin. J. Chem. 6/2019)
Authors: Liu Haiyang , Ke Kai , Li Chang , Chen Xin , Wu Yulian 
Published: May 2019

The cover picture shows facile photochemical synthesis, direct in situ TEM characterization, and effective catalytical applications of sponge‐like porous Pd nano particles. In situ liquid cell TEM observation not only confirms the actual existence of the sponge‐like Pd in a liquid solution, but also shows such Pd nanostructure is in a dynamic stable state, which is beneficial for the material exchange and the catalytic performance improvement. The expected catalytic activity improvement is supported by such as the 4‐nitrophenol reduction reactions, which is important both for the environment and the industry. More details are discussed in the article by Chen et al. on page 565–569.
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Definitive Conditions on Maxwell's Tangential E or H for Solutions to His Equations Inside a Bounded Region
Authors: Cappell Sylvain E. , Miller Edward Y. 
Published: May 2019

AbstractLet U be a connected, closed, bounded region in ℝ3 with smooth boundary 𝛛U. Consider Maxwell's equations on U for smooth fields and smooth sources, which are time harmonic, i.e., the fields E,B,H,D and the current density J and charge density ρ on U temporally varying as e−iωt. We assume ω ≠ 0; when it is real, ω is the frequency of the pure oscillation; when ω is not real, one has exponentially decreasing or increasing oscillatory fields. We treat very general electric permittivity ɛω and magnetic permeability μω, which may both depend upon ω. Both can be arbitrary, time‐independent, smoothly varying with position and described by complex Hermitian tensors subject only to weak positivity conditions specified below at each point of U.In this paper necessary and sufficient conditions are found for the tangential components, ET or HT on 𝛛U, to be realized by solutions of Maxwell's equations on all of U with these given sources J, ρ in the time‐harmonic realm with ω ≠ 0. Also, all solutions E,H on U with specified ET, HT, respectively, satisfying the necessary finite‐dimensional conditions are derived by an effective natural algorithm.In the electric ET case, the positivity condition is this: the complex Hermitian matrix μω(p) is to be positive definite while only the real part of ɛω(p), i.e., Re(ɛω(p)), necessarily real symmetric, need be positive definite. In the magnetic‐type HT case, the two roles are reversed. These positivity conditions are more general than those commonly considered. In the final section Maxwell's equations and all the present results are reformulated yet more generally in a context of compact, smooth, Riemannian manifolds with boundary. Sample examples include periodic lattices and wave guides. © 2019 Wiley Periodicals, Inc.
Homoleptic and Heteroleptic Copper Complexes as Redox Couples in Dye‐Sensitized Solar Cells
Authors: Lennert Annkatrin , Guldi Dirk M. 
Published: May 2019

AbstractTo gather a comprehensive understanding of copper complexes as redox couples in dye‐sensitized solar cells (DSSCs), a series of copper complexes were synthesized and thoroughly characterized. Characterization was undertaken using an arsenal of spectroscopic techniques, including steady‐state spectroscopy, electrochemical and spectroelectrochemical assays, current‐voltage measurements, electrochemical impedance spectroscopy (EIS), and transient absorption spectroscopy (TAS). Starting from a homoleptic copper complex featuring two bathocuproine ligands and replacing one of them by either another N‐ or a P‐coordinating ligand, a clear relationship between ligand size, on one hand, and charge transport, recombination as well as effective regeneration of the sensitizer, on the other hand, was established. With this information in hand, the future targeted synthesis of copper complexes to achieve maximum device performance may be achieved.
Preferential Orientation of Crystals and its Influence on the Emission Wavelength of Acrylonitrile Derivatives Treated with Polar Solvents
Authors: Percino Maria Judith , Cerón Margarita , Pérez‐Gutiérrez Enrique , Perumal Venkatesan , Siegler Maxime A. , Subbiah Thamotharan , Ceballos Paulina , Gordillo‐Guerra Paola , Bonilla‐Cruz José , Longoria Francisco Enrique , Lara Tania 
Published: May 2019

AbstractPhotoluminescence properties in solid state and its relationship with structural features of prop‐2‐enenitrile derivatives containing any of functional groups 4‐halogenphenyl, phenyl, 4‐dimethylamino, or 4‐diphenylamino are investigated. The compounds show change in color from yellow to orange after treatment with dimethyl sulfoxide or dimethyl formamide. Nevertheless, the single‐crystal X‐ray diffraction for both, the original yellow and the treated orange crystals, does not display any major structural differences. The optical properties are related to the crystal packing and intermolecular interactions such as edge‐to‐face through the vertices of aromatic rings. The last is supported by the behavior of the presence of functional group. The absorption spectrum in solution for all compounds shows two absorption bands with wavelength of maximum absorption around 390–430 nm and at 290–300 nm. Regardless of the crystal type, the maximum emission in solution was between 450–570 nm. In solid state, yellow crystals exhibit an emission in the 500–530 nm range and in the 580–630 nm range for orange crystals. Results suggest that optical properties are strongly dependent on morphology and habit. Powder X‐ray characterization shows a preferential orientation for orange crystals. All compounds are characterized by common spectroscopy techniques, fluorescence, atomic force microscopy and X‐ray diffraction.
Simulation of positronium plasma by the molecular dynamics method
Authors: Kodanova Sandugash K. , Issanova Moldir K. , Ramazanov Tlekkabul S. , Khikmetov Askar K. , Maiorov Sergey A. 
Published: May 2019

AbstractIn this paper, the relaxation properties of a fully ionized, hot, ideal plasma have been studied using the molecular dynamics method. As an example, the classical problem of equalization of the electron and ion temperatures for various mass ratios is considered, the relaxation times for temperatures is determined, and the influence of the number of particles and the type of boundary conditions on the simulation results is studied. The simulation results are compared with the available theoretical results.
Dust‐acoustic envelope solitons in super‐thermal plasmas
Authors: Noman A.A. , Chowdhury N.A. , Mannan A. , Mamun A.A. 
Published: May 2019

AbstractThe modulational instability (MI) of the dust‐acoustic waves (DAWs) in an electron‐positron‐ion‐dust plasma (containing super‐thermal electrons, positrons, and ions along with negatively charged adiabatic dust grains) is investigated by the analysis of the non‐linear Schrödinger equation (NLSE). To derive the NLSE, the reductive perturbation method was employed. Two different parametric regions for stable and unstable DAWs are observed. The presence of super‐thermal electrons, positrons, and ions significantly modifies both the stable and unstable regions. The critical wave number kc (at which MI sets in) depends on the super‐thermal electron, positron, and ion, and adiabatic dust concentrations.
Primary adrenal gland epithelioid sarcoma: A case report and literature review
Authors: Huang Xiao , Nayar Ritu , Zhou Haijun 
Published: May 2019

AbstractEpithelioid sarcoma is a malignant mesenchymal neoplasm with morphologic and immunophenotypic epithelioid differentiation, which rarely arises in solid organs. We report a case of primary epithelioid sarcoma in the adrenal gland of a 31‐year‐old female. The patient initially presented with nausea and rectal bleeding, and subsequent imaging studies revealed a 4.4 cm left adrenal gland mass and left retroperitoneal lymphadenopathy. Clinical and radiological studies did not reveal tumor elsewhere in the patient. Histologic features were those of epithelioid sarcoma, proximal type with cohesive clusters of epithelioid tumor cells harboring frequent mitoses, and areas of necrosis. Immunohistochemical stains showed strong, diffuse expression of epithelial markers (pancytokeratin), and CD34 and Fli‐1. Partial and focal positive staining of CK7 was also noted. Nuclear expression of SMARCB1 (INI‐1) protein was lost. ERG was negative in this case. We believe that this is the second‐case report of a primary adrenal gland epithelioid sarcoma. Fli‐1 positivity was seen in our case, and ERG was negative as shown in some recent publications regarding epithelioid sarcomas.
Elimination profile of triamcinolone hexacetonide and its metabolites in human urine and plasma after a single intra‐articular administration
Authors: Coll Sergi , Matabosch Xavier , Llorente‐Onaindia Jone , Carbó Marcel·li , Pérez‐Mañá Clara , Monfort Nuria , Monfort Jordi , Ventura Rosa 
Published: May 2019

AbstractTriamcinolone hexacetonide (THA) is a synthetic glucocorticoid (GC) used by intra‐articular (IA) administration. GCs are prohibited in sports competitions by systemic routes, and they are allowed by other routes considered of local action (IA administration, among others). The aim of the present work was to study the metabolic profile of THA in urine and plasma following IA administration. Eight patients (4 males and 4 females) with knee osteoarthritis received an IA dose of THA (40 mg) in the knee joint. Spot urine and plasma samples were collected before injection and at different time periods up to day 23 and 10 post‐administration, respectively. The samples were analysed by liquid chromatography‐tandem mass spectrometry. Neither THA nor specific THA metabolites were detected in urine. Triamcinolone acetonide (TA) and 6β‐hydroxy‐triamcinolone acetonide were the main urinary metabolites. Maximum concentrations wereobtained between 24 and 48 h after administration. Using the reporting level of 30 ng/mL to distinguish allowed from forbidden administrations of GCs, a large number of false adverse analytical findings would be reported up to day 4. On the other hand, TA was detected in all plasma samples collected up to day 10 after administration. THA was also detected in plasma but at lower concentrations. The detection of plasma THA would be an unequivocal proof to demonstrate IA use of THA. A reversible decrease was observed in plasma concentrations of cortisol in some of the patients, indicating a systemic effect of the drug.
A Chrnb3‐Cre BAC transgenic mouse line for manipulation of gene expression in retinal ganglion cells
Authors: Drayson Lucy E. , Triplett Jason W. 
Published: May 2019

SummaryThe mechanisms by which retinal ganglion cells (RGCs) make specific connections during development is an intense area of research and have served as a model for understanding the general principles of circuit wiring. As such, genetic tools allowing for specific recombination in RGCs are critical to further our understanding of the cell‐specific roles of different genes during these processes. However, many RGC‐specific Cre lines have drawbacks, due to their broad expression in other cell types and/or retinorecipient regions or lack of expression in broad swaths of the retina. Here, we characterize a Cre BAC transgenic line driven by elements of the cholinergic receptor nicotinic beta 3 subunit (Chrnb3). We show that Cre expression is restricted to RGCs in the retina and sparsely expressed in the brain, importantly excluding retinorecipient regions. Furthermore, Chrnb3‐Cre mice label a wide variety of RGCs distributed throughout the retina and Cre activity is detected embryonically, shortly following RGC differentiation. Finally, we find that Chrnb3‐Cre‐labeled RGCs innervate multiple retinorecipient areas that serve both image‐forming and nonimage forming functions. Thus, this genetic tool will be of broad use to investigators studying the RGC‐specific contributions of genes to visual circuit development.
Carbon sequestration and soil restoration potential of grazing lands under exclosure management in a semi‐arid environment of northern Ethiopia
Authors: Gebregergs Tsegay , Tessema Zewdu K. , Solomon Negasi , Birhane Emiru 
Published: May 2019

AbstractExclosures are used to regenerate native vegetation as a way to reduce soil erosion, increase rain water infiltration and provide fodder and woody biomass in degraded grazing lands. Therefore, this study assessed the impact of grazing exclosure on carbon sequestration and soil nutrients under 5 and 10 years of grazing exclosures and freely grazed areas in Tigray, northern Ethiopia. Carbon stocks and soil nutrients increased with increasing grazing exclusion. However, open grazing lands and 5 years of grazing exclosure did not differ in above‐ and belowground carbon stocks. Moreover, 10 years of grazing exclosure had a higher (p < 0.01) grass, herb and litter carbon stocks compared to 5 years exclosure and open grazing lands. The total carbon stock was higher for 10 years exclosure (75.65 t C ha‐1) than the 5 years exclosure (55.06 t C ha‐1) and in open grazing areas (51.98 t C ha‐1). Grazing lands closed for 10 years had a higher SOC, organic matter, total N, available P, and exchangeable K + and Na + compared to 5 year's exclosure and open grazing lands. Therefore, establishment of grazing exclosures had a positive effect in restoring degraded grazing lands, thus improving carbon sequestration potentials and soil nutrients.
Species traits shape the relationship between local and regional species abundance distributions
Authors: Dantas de Miranda Murilo , Borda‐de‐Água Luís , Pereira Henrique Miguel , Merckx Thomas 
Published: May 2019

AbstractThe species abundance distribution (SAD) depicts the relative abundance of species within a community, which is a key concept in ecology. Here, we test whether SADs are more likely to either follow a lognormal‐like or follow a logseries‐like distribution and how that may change with spatial scale. Our results show that the shape of SADs changes from logseries‐like at small, plot scales to lognormal‐like at large, landscape scales. However, the rate at which the SAD's shape changes also depends on species traits linked to the spatial distribution of individuals. Specifically, we show for oligophagous and small macro‐moth species that a logseries distribution is more likely at small scales and a lognormal distribution is more likely at large scales, whereas the logseries distribution fits well at both small and large scales for polyphagous and large species. We also show that SAD moments scale as power laws as a function of spatial scale, and we assess the performance of Tchebichef moments and polynomials to reconstruct SADs at the landscape scale from information at local scales. Overall, the method performed well and reproduced the shapes of the empirical distributions.
Cascading influences of grassland degradation on nutrient limitation in a high mountain lake and its inflow streams
Authors: Ren Ze , Niu Decao , Ma Panpan , Wang Ying , Fu Hua , Elser James J. 
Published: May 2019

AbstractNitrogen (N) and phosphorus (P) are key growth‐limiting nutrients for organisms and their absolute and relative supplies regulate the structure and function of ecosystems. Landcover changes lead to modifications of terrestrial biogeochemistry, consequently influencing aquatic nutrient conditions. This study sought to evaluate the potential impacts of grassland degradation on nutrient availability and nutrient limitation in the Qinghai Lake (China) and its inflow streams. We sampled nutrient concentrations and tested stream nutrient limitation by conducting nutrient diffusing substrata (NDS) bioassays in streams flowing through subbasins with different grassland status. To test nutrient limitation and the responses of lake phytoplankton to stream inflows, bioassays were conducted by adding different nutrients (N, P, and joint NP) as well as water from different streams to lake water with phytoplankton, respectively. In general, N concentrations as well as N:P ratios decreased while P concentrations increased with decreased normalized difference vegetation index (NDVI, an index of vegetation status), especially in September, suggesting that grassland degradation (low NDVI) has the potential to differentially decrease N availability and increase P availability in streams. Consistent with this, relative responses (RR) of stream periphyton to P and combined NP enrichments in the NDS bioassays decreased with stream P concentrations while increased with stream water N:P ratios. Lake phytoplankton responded strongly to P and combined NP addition indicating strong P‐limitation of lake phytoplankton. RR of lake phytoplankton to stream water decreased with nitrate concentration and N:P ratios in stream water and increased with the concentrations of ammonium, total phosphorus, and soluble reactive phosphorus, indicating that stream water with higher P but lower N and N:P from degraded subcatchments is associated with increased impact on P‐limited Lake phytoplankton. Overall, this study suggests that grassland degradation has the potential to differentially influence the nutrients delivered to streams with substantial increases in P but decreases in N and N:P, alleviating P limitation of stream periphyton and, ultimately, stimulating P‐limited phytoplankton growth in the lake.