bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxidation‐Induced Structural Changes in Sub‐Nanometer Platinum Supported on Alumina
Authors: Moses‐DeBusk Melanie , Allard Lawrence F. , Blom Douglas A. , Narula Chaitanya K. 
Published: June 2015

AbstractPt supported on alumina is an essential component of emission treatment catalysts used in transportation. Theoretical, experimental, and mechanistic aspects of Pt particles supported on a variety of supports have been studied extensively; however, available experimental information on the behavior of single versus sub‐nanometer Pt is extremely limited. To bridge the knowledge gap between single supported Pt and well‐formed supported Pt nanoparticles, we have performed the synthesis, characterization, and CO and NO oxidation studies of sub‐nanometer Pt supported on α‐, θ‐, and γ‐Al2O3 and monitored the changes in structure upon exposure to CO and NO oxidation conditions. We find that sub‐nanometer Pt is highly effective for CO oxidation because of the high Pt dispersion, but it is not very efficient as a NO oxidation catalyst. Furthermore, sub‐nanometer Pt agglomerates rapidly under CO or NO oxidation conditions to form nanoparticles.
Preferential Oxidation of CO in H2 on Pure Co3O4−x and Pt/Co3O4−x
Authors: Nguyen Luan , Zhang Shiran , Yoon Seog Joon , Tao Franklin (Feng) 
Published: June 2015

AbstractDriven by the development of a catalyst made of earth‐abundant elements for on‐board purification of H2 of this energy conversion technology, preferential oxidation (PROX) on pure Co3O4 nanorods and Co3O4 nanorods with supported Pt nanoparticles was explored with the aid of in situ studies. This catalyst remains its 100 % conversion of CO in H2 at a gas hourly space velocity of 42 857 mL h−1 g−1 at 120 °C for at least 96 h. In situ studies showed that the active surface phase during PROX is nonstoichiometric Co3O4−x. A correlation between density of surface oxygen vacancies and conversion of CO to CO2 suggest that oxygen vacancy is a necessary component of a catalytic site for PROX on Co3O4−x. Compared to pure Co3O4 nanorods, anchoring Pt nanoparticles on Co3O4 nanorods unfortunately increases selectivity for oxidation of H2 owing to the low dissociation barrier of molecular H2 on Pt. Co3O4−x exhibits much higher selectivity for CO oxidation in PROX than Pt/Co3O4−x at a temperature lower than 140 °C.
Functionalized Magnetic Mesoporous Silica Nanoparticle‐Supported Palladium Catalysts for Carbonylative Sonogashira Coupling Reactions of Aryl Iodides
Authors: Natour Suzana , Abu‐Reziq Raed 
Published: June 2015

AbstractMagnetic mesoporous silica nanoparticles (MMSN) were prepared and used as a support for palladium catalysts. MMSN with a surface area of 1909 m2 g−1 were synthesized by a nanoemulsification process involving the dispersion of hydrophobic magnetite nanoparticles in chloroform in the presence of cetyltrimethylammonium bromide, followed by the addition of tetraethoxysilane and its polycondensation by a sol–gel route. The MMSN were modified with phosphine and N‐heterocyclic carbene‐based ligands, which provided coordination sites for conjugation with a palladium catalyst. These modified particles were fully characterized and employed as catalyst nanosupports. The palladium catalyst was immobilized on the surface and within the pores of MMSN and applied in copper‐free carbonylative Sonogashira coupling reactions of aryl iodides with terminal alkynes.
Diarylethene Self‐Assembled Monolayers: Cocrystallization and Mixing‐Induced Cooperativity Highlighted by Scanning Tunneling Microscopy at the Liquid/Solid Interface
Authors: Frath Denis , Sakano Takeshi , Imaizumi Yohei , Yokoyama Soichi , Hirose Takashi , Matsuda Kenji 
Published: June 2015

AbstractStimulus control over 2D multicomponent molecular ordering on surfaces is a key technique for realizing advanced materials with stimuli‐responsive surface properties. The formation of 2D molecular ordering along with photoisomerization was monitored by scanning tunneling microscopy at the octanoic acid/highly oriented pyrolytic graphite interface for a synthesized amide‐containing diarylethene, which underwent photoisomerization between the open‐ and closed‐ring isomers and also a side‐reaction to give the annulated isomer. The nucleation (Kn) and elongation (Ke) equilibrium constants were determined by analysis of the concentration dependence of the surface coverage by using a cooperative model at the liquid/solid interface. It was found that the annulated isomer has a very large equilibrium constant, which explains the predominantly observed ordering of the annulated isomer. It was also found that the presence of the closed‐ring isomer induces cooperativity into the formation of molecular ordering composed of the open‐ring isomer. A quantitative analysis of the formation of ordering by using the cooperative model has provided a new view of the formation of 2D multicomponent molecular ordering.
Anion‐, Solvent‐, Temperature‐, and Mechano‐Responsive Photoluminescence in Gold(I) Diphosphine‐Based Dimers
Authors: Deák Andrea , Jobbágy Csaba , Marsi Gábor , Molnár Miklós , Szakács Zoltán , Baranyai Péter 
Published: June 2015

AbstractA series of [Au2(nixantphos)2](X)2 (nixantphos=4,6‐bis(diphenylphosphino)‐phenoxazine; X=NO3, 1; CF3COO, 2; CF3SO3, 3; [Au(CN)2], 4; and BF4, 5) complexes that exhibit intriguing anion‐switchable and stimuli‐responsive luminescent photophysical properties have been synthesized and characterized. Depending on their anions, these complexes display yellow (3), orange (4 and 5), and red (1 and 2) emission colors. They exhibit reversible thermo‐, mechano‐, and vapochromic luminescence changes readily perceivable by the naked eye. Single‐crystal X‐ray studies show that the [Au2(nixantphos)2]2+ cations with short intramolecular Au⋅⋅⋅Au interactions are involved as donors in an infinite NH⋅⋅⋅X (X=O and N) hydrogen‐bonded chain formation with CF3COO− (2 C) and aurophilically linked [Au(CN)2]− counterions (4 C). Both crystals show thermochromic luminescence; their room temperature red (2 C) and orange (4 C) emission turns into yellow upon cooling to 77 K. They also exhibit reversible mechanochromic luminescence by changing their emission color from red to dark (2 C), and orange to red (4 C). Compounds 1–5 also display reversible mechanochromic luminescence, altering their emission colors between orange (1) or red (2) to dark, as well as between yellow (3) or orange (4 and 5) to red. Detailed photophysical investigations and correlation with solid‐state structural data established the significant role of NH⋅⋅⋅X interactions in the stimuli‐responsive luminescent behavior.
Calcium Hydride Catalyzed Highly 1,2‐Selective Pyridine Hydrosilylation
Authors: Intemann Julia , Bauer Heiko , Pahl Jürgen , Maron Laurent , Harder Sjoerd 
Published: June 2015

AbstractReaction of the calcium hydride complex (DIPPnacnac‐CaH⋅THF)2 with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6‐iPr2C6H3)NC(Me)]2CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2‐position is observed and also at higher temperatures no 1,2→1,4 isomerization is found. The heteroleptic product DIPPnacnac‐Ca(1,2‐dihydropyridide)⋅(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well‐defined homoleptic products which could be characterized by X‐ray diffraction: Ca(1,2‐dihydroisoquinolide)2⋅(isoquinoline)4 and Ca3(1,2‐dihydroisoquinolide)6⋅(isoquinoline)6. The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH3 yields exclusively 1,2‐dihydropyridine and 1,2‐dihydroquinoline silanes with 80–90 % conversion. Similar results can be achieved with the catalyst Ca[N(SiMe3)2]2⋅(THF)2. These calcium complexes represent the first catalysts for the 1,2‐selective hydrosilylation of pyridines.
Mechanistic Insights into the Post‐Cyclization Isomerization in Gold‐Catalyzed 7‐exo‐dig‐Hydroarylations
Authors: Pflästerer Daniel , Schumacher Sören , Rudolph Matthias , Hashmi A. Stephen K. 
Published: June 2015

AbstractThe subsequent double‐bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron‐rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold‐catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species.
Hydroboration of Alkynes with Zwitterionic Ruthenium–Borate Complexes: Novel Vinylborane Complexes
Authors: Anju R. S. , Mondal Bijan , Saha Koushik , Panja Subir , Varghese Babu , Ghosh Sundargopal 
Published: June 2015

AbstractBuilding upon previous studies on the synthesis of bis(sigma)borate and agostic complexes of ruthenium, the chemistry of nido‐[(Cp*Ru)2B3H9] (1) with other ligand systems was explored. In this regard, mild thermolysis of nido‐1 with 2‐mercaptobenzothiazole (2‐mbzt), 2‐mercaptobenzoxazole (2‐mbzo) and 2‐mercaptobenzimidazole (2‐mbzi) ligands were performed which led to the isolation of bis(sigma)borate complexes [Cp*RuBH3L] (2 a–c) and β‐agostic complexes [Cp*RuBH2L2] (3 a–c; 2 a, 3 a: L=C7H4NS2; 2 b, 3 b: L=C7H4NSO; 2 c, 3 c: L=C7H5N2S). Further, the chemistry of these novel complexes towards various diphosphine ligands was investigated. Room temperature treatment of 3 a with [PPh2(CH2)nPPh2] (n=1–3) yielded [Cp*Ru(PPh2(CH2)nPPh2)‐BH2(L2)] (4 a–c; 4 a: n=1; 4 b: n=2; 4 c: n=3; L=C7H4NS2). Mild thermolysis of 2 a with [PPh2(CH2)nPPh2] (n=1–3) led to the isolation of [Cp*Ru(PPh2(CH2)nPPh2)(L)] (L=C7H4NS2 5 a–c; 5 a: n=1; 5 b: n=2; 5 c: n=3). Treatment of 4 a with terminal alkynes causes a hydroboration reaction to generate vinylborane complexes [Cp*Ru(RCCH2)BH(L2)] (6 and 7; 6: R=Ph; 7: R=COOCH3; L=C7H4NS2). Complexes 6 and 7 can also be viewed as η‐alkene complexes of ruthenium that feature a dative bond to the ruthenium centre from the vinylinic double bond. In addition, DFT computations were performed to shed light on the bonding and electronic structures of the new compounds.
A Reversible Proton Relay Process Mediated by Hydrogen‐Bonding Interactions in [FeFe]Hydrogenase Modeling
Authors: Chu Kai‐Ti , Liu Yu‐Chiao , Huang Yi‐Lan , Hsu Cheng‐Huey , Lee Gene‐Hsiang , Chiang Ming‐Hsi 
Published: June 2015

AbstractA reversible and temperature‐dependent proton‐relay process is demonstrated for a Fe2 complex possessing a terminal thiolate in the presence of nitrogen‐based acids. The terminal sulfur site (St) of the complex forms a hydrogen‐bond interaction with N,N‐dimethylanilinium acid at 183 K. The Fe2 core, instead, is protonated to generate a bridging hydride at 298 K. Reversibility is observed for the tautomerization between the hydrogen‐bonded pair and the Fe–hydride species. X‐ray structural analysis of the hydrogen‐bonded species at 193 K reveals a short N(H)⋅⋅⋅St contact. Employment of pyridinium acid also results in similar behavior, with reversible proton–hydride interconversion. DFT investigation of the proton‐transfer pathways indicates that the pKa value of the hydrogen‐bonded species is enhanced by 3.2 pKa units when the temperature is decreased from 298 K to 183 K.
Direct Evidence for a [4+2] Cycloaddition Mechanism of Alkynes to Tantallacyclopentadiene on Dinuclear Tantalum Complexes as a Model of Alkyne Cyclotrimerization
Authors: Yamamoto Keishi , Tsurugi Hayato , Mashima Kazushi 
Published: June 2015

AbstractA dinuclear tantalum complex, [Ta2Cl6(μ‐C4Et4)] (2), bearing a tantallacyclopentadiene moiety, was synthesized by treating [(η2‐EtCCEt)TaCl3(DME)] (1) with AlCl3. Complex 2 and its Lewis base adducts, [Ta2Cl6(μ‐C4Et4)L] (L=THF (3 a), pyridine (3 b), THT (3 c)), served as more active catalysts for cyclotrimerization of internal alkynes than 1. During the reaction of 3 a with 3‐hexyne, we isolated [Ta2Cl4(μ‐η4:η4‐C6Et6)(μ‐η2:η2‐EtCCEt)] (4), sandwiched by a two‐electron reduced μ‐η4:η4‐hexaethylbenzene and a μ‐η2:η2‐3‐hexyne ligand, as a product of an intermolecular cyclization between the metallacyclopentadiene moiety and 3‐hexyne. The formation of arene complexes [Ta2Cl4(μ‐η4:η4‐C6Et4Me2)(μ‐η2:η2‐Me3SiCCSiMe3)] (7 b) and [Ta2Cl4(μ‐η4:η4‐C6Et4RH)(μ‐η2:η2‐Me3SiCCSiMe3)] (R=nBu (8 a), p‐tolyl (8 b)) by treating [Ta2Cl4(μ‐C4Et4)(μ‐η2:η2‐Me3SiCCSiMe3)] (6) with 2‐butyne, 1‐hexyne, and p‐tolylacetylene without any isomers, at room temperature or low temperature were key for clarifying the [4+2] cycloaddition mechanism because of the restricted rotation behavior of the two‐electron reduced arene ligands without dissociation from the dinuclear tantalum center.
Indachlorins: Nonplanar Indanone‐Annulated Chlorin Analogues with Panchromatic Absorption Spectra between 300 and 900 nm
Authors: Samankumara Lalith P. , Dorazio Sarina J. , Akhigbe Joshua , Li Ruoshi , Nimthong‐Roldán Arunpatcha , Zeller Matthias , Brückner Christian 
Published: June 2015

AbstractIndaphyrins, pyrrole‐modified porphyrins containing a cleaved pyrrole β,β′‐bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π‐expanded chromophores. The parent free base indaphyrin has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. It was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring‐cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin‐based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper‐ and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid‐state conformations were analyzed.
Synthesis of Polysubstituted γ‐Butenolides via a Radical Pathway: Cyclization of α‐Bromo Aluminium Acetals and Comparison with the Cyclization of α‐Bromoesters at High Temperature
Authors: Bénéteau Romain , Despiau Carole F. , Rouaud Jean‐Christophe , Boussonnière Anne , Silvestre Virginie , Lebreton Jacques , Dénès Fabrice 
Published: June 2015

AbstractPolysubstituted butenolides were obtained in good to high yields from α‐bromoesters derived from propargyl alcohols by a one‐pot reaction involving the radical cyclization of α‐bromo aluminium acetals, followed by the oxidation of the resulting cyclic aluminium acetals in an Oppenauer‐type process and migration of the exocyclic CC bond into the α,β‐position. Comparison with the direct cyclization of α‐bromoesters at high temperature and under high dilution conditions is described. Deuterium‐labelling experiments allowed us to uncover “invisible” 1,5‐hydrogen atom transfers (1,5‐HATs) that occur during these cyclization processes, together with the consequences of the latter in the epimerization of stereogenic centres. Compared to the classical approach, the cyclization of aluminium acetals proved to be highly chemoselective and its efficiency was illustrated by the short total syntheses of optically enriched γ‐butenolides isolated from Plagiomnium undulatum and from Kyrtuhrix maculans.
Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations
Authors: Vidal‐Ferran Anton , Mon Ignasi , Bauzá Antonio , Frontera Antonio , Rovira Laura 
Published: June 2015

AbstractHerein we report the use of polyether binders as regulation agents (RAs) to enhance the enantioselectivity of rhodium‐catalyzed transformations. For reactions of diverse substrates mediated by rhodium complexes of the α,ω‐bisphosphite‐polyether ligands 1–5,a–d, the enantiomeric excess (ee) of hydroformylations was increased by up to 82 % (substrate: vinyl benzoate, 96 % ee), and the ee value of hydrogenations was increased by up to 5 % (substrate: N‐(1‐(naphthalene‐1‐yl)vinyl)acetamide, 78 % ee). The ligand design enabled the regulation of enantioselectivity by generation of an array of catalysts that simultaneously preserve the advantages of a privileged structure in asymmetric catalysis and offer geometrically close catalytic sites. The highest enantioselectivities in the hydroformylation of vinyl acetate with ligand 4 b were achieved by using the Rb[B(3,5‐(CF3)2C6H3)4] (RbBArF) as the RA. The enantioselective hydrogenation of the substrates 10 required the rhodium catalysts derived from bisphosphites 3 a or 4 a, either alone or in combination with different RAs (sodium, cesium, or (R,R)‐bis(1‐phenylethyl)ammonium salts). This design approach was supported by results from computational studies.
Crystal Engineering of Energetic Materials: Co‐crystals of Ethylenedinitramine (EDNA) with Modified Performance and Improved Chemical Stability
Authors: Aakeröy Christer B. , Wijethunga Tharanga K. , Desper John 
Published: June 2015

AbstractIn the area of energetic materials, co‐crystallization is emerging as a new technology for modifying or enhancing the properties of existing energetic substances. Ethylenedinitramine (EDNA) is a known energetic material which requires attention partly due to its chemical instability originating with its two highly acidic protons. In order to stabilize EDNA, a co‐crystallization approach targeting the acidic protons using a series of co‐crystallizing agents with suitable hydrogen‐bond acceptors was employed. Fifteen attempted co‐crystallizations resulted in eight successful outcomes and six of these were crystallographically characterized and all showed evidence of hydrogen bonds to the intended protons. Calculated detonation properties and experimental thermal and impact data for the co‐crystals were obtained and compared with those of pure EDNA. The co‐crystal of EDNA and 1,2‐bis(4‐pyridyl)ethylene was recognized as a more thermally stable alternative to EDNA while the co‐crystal of EDNA and pyrazine N,N′‐dioxide showed comparable detonation strengths (and much improved chemical stability) compared with that of EDNA. The co‐crystals EDNA:4,4′‐bipyridine and EDNA:pyrazine N,N′‐dioxide were found to be about 50 % less impact sensitive than EDNA, all of which illustrate how co‐crystallizations can be utilized for successfully modifying specific aspects of energetic materials.
Active Site Mapping of Human Cathepsin F with Dipeptide Nitrile Inhibitors
Authors: Schmitz Janina , Furtmann Norbert , Ponert Moritz , Frizler Maxim , Löser Reik , Bartz Ulrike , Bajorath Jürgen , Gütschow Michael 
Published: June 2015

AbstractCleavage of the invariant chain is the key event in the trafficking pathway of major histocompatibility complex class II. Cathepsin S is the major processing enzyme of the invariant chain, but cathepsin F acts in macrophages as its functional synergist which is as potent as cathepsin S in invariant chain cleavage. Dedicated low‐molecular‐weight inhibitors for cathepsin F have not yet been developed. An active site mapping with 52 dipeptide nitriles, reacting as covalent–reversible inhibitors, was performed to draw structure–activity relationships for the non‐primed binding region of human cathepsin F. In a stepwise process, new compounds with optimized fragment combinations were designed and synthesized. These dipeptide nitriles were evaluated on human cysteine cathepsins F, B, L, K and S. Compounds 10 (N‐(4‐phenylbenzoyl)‐leucylglycine nitrile) and 12 (N‐(4‐phenylbenzoyl)leucylmethionine nitrile) were found to be potent inhibitors of human cathepsin F, with Ki values <10 nM. With all dipeptide nitriles from our study, a 3D activity landscape was generated to visualize structure–activity relationships for this series of cathepsin F inhibitors.
Topographic organization and possible function of the posterior optic tubercles in the brain of the desert locust Schistocerca gregaria
Authors: Beetz M. Jerome , el Jundi Basil , Heinze Stanley , Homberg Uwe 
Published: June 2015

ABSTRACTMigrating desert locusts, Schistocerca gregaria, are able to use the skylight polarization pattern for navigation. They detect polarized light with a specialized dorsal rim area in their compound eye. After multistage processing, polarization signals are transferred to the central complex, a midline‐spanning brain area involved in locomotor control. Polarization‐sensitive tangential neurons (TB‐neurons) of the protocerebral bridge, a part of the central complex, give rise to a topographic arrangement of preferred polarization angles in the bridge, suggesting that the central complex acts as an internal sky compass. TB‐neurons connect the protocerebral bridge with two adjacent brain areas, the posterior optic tubercles. To analyze the polarotopic organization of the central complex further, we investigated the number and morphologies of TB‐neurons and the presence and colocalization of three neuroactive substances in these neurons. Triple immunostaining with antisera against Diploptera punctata allatostatin (Dip‐AST), Manduca sexta allatotropin (Mas‐AT), and serotonin (5HT) raised in the same host species revealed three spatially distinct TB‐neuron clusters, each consisting of 10 neurons per hemisphere: cluster 1 and 3 showed Dip‐AST/5HT immunostaining, whereas cluster 2 showed Dip‐AST/Mas‐AT immunostaining. Five subtypes of TB‐neuron could be distinguished based on ramification patterns. Corresponding to ramification domains in the protocerebral bridge, the neurons invaded distinct but overlapping layers within the posterior optic tubercle. Similarly, neurons interconnecting the tubercles of the two hemispheres also targeted distinct layers of these neuropils. From these data we propose a neuronal circuit that may be suited to stabilize the internal sky compass in the central complex of the locust. J. Comp. Neurol. 523:1589–1607, 2015. © 2015 Wiley Periodicals, Inc.