pinecone/core-2020-05-10-deduplication huggingface dataset:
Isolation and Characterization of Precise Dye/Dendrimer Ratios

Fluorescent dyes are commonly conjugated to nanomaterials for imaging applications using stochastic synthesis conditions that result in a Poisson distribution of dye/particle ratios and therefore a broad range of photophysical and biodistribution properties. We report the isolation and characterization of generation 5 poly(amidoamine) (G5 PAMAM) dendrimer samples containing 1, 2, 3, and 4 fluorescein (FC) or 6‐carboxytetramethylrhodamine succinimidyl ester (TAMRA) dyes per polymer particle. For the fluorescein case, this was achieved by stochastically functionalizing dendrimer with a cyclooctyne “click” ligand, separation into sample containing precisely defined “click” ligand/particle ratios using reverse‐phase high performance liquid chromatography (RP‐HPLC), followed by reaction with excess azide‐functionalized fluorescein dye. For the TAMRA samples, stochastically functionalized dendrimer was directly separated into precise dye/particle ratios using RP‐HPLC. These materials were characterized using  1 H and  19 F NMR spectroscopy, RP‐HPLC, UV/Vis and fluorescence spectroscopy, lifetime measurements, and MALDI.     High definition : Two approaches for the formation of generation 5 PAMAM samples containing precise dye/dendrimer ratios are presented. The first approach, using direct separation based on dye hydrophobicity, generated a set of TAMRA‐containing dendrimers, and the second, using click chemistry, generated a set of fluorescein‐containing dendrimer (see figure)
Catalyst-free photoredox addition–cyclisations : exploitation of natural synergy between aryl acetic acids and maleimide

This work was funded by EPSRC Grant Numbers: EP/I003479/1, EP/I003800/2. The paper was made open accees through RCUK block grant funds.Suitably functionalised carboxylic acids undergo a previously unknown photoredox reaction when irradiated with UVA in the presence of maleimide. Maleimide was found to synergistically act as a radical generating photoxidant and as a radical acceptor, negating the need for an extrinsic photoredox catalyst. Modest to excellent yields of the product chromenopyrroledione, thiochromenopyrroledione and pyrroloquinolinedione derivatives were obtained in thirteen preparative photolyses. In situ NMR spectroscopy was used to study each reaction. Reactant decay and product build-up were monitored, enabling reaction profiles to be plotted. A plausible mechanism, whereby photo-excited maleimide acts as an oxidant to generate a radical ion pair, has been postulated and is supported by UV/Vis. spectroscopy and DFT computations. The radical-cation reactive intermediates were also characterised in solution by EPR spectroscopy.Publisher PDFPeer reviewe
Mixed-valence ruthenium complexes rotating through a conformational Robin–Day continuum.

The conformational energy landscape and the associated electronic structure and spectroscopic properties (UV/Vis/near-infrared (NIR) and IR) of three formally d5/d6 mixed-valence diruthenium complex cations, [{Ru(dppe)Cp*}2(μ-C≡CC6H4C≡C)]+, [1]+, [trans-{RuCl(dppe)2}2(μ-C≡CC6H4C≡C)]+, [2]+, and the Creutz–Taube ion, [{Ru(NH3)5}2(μ-pz)]5+, [3]5+ (Cp=cyclopentadienyl; dppe=1,2-bis(diphenylphosphino)ethane; pz=pyrazine), have been studied using a nonstandard hybrid density functional BLYP35 with 35 % exact exchange and continuum solvent models. For the closely related monocations [1]+ and [2]+, the calculations indicated that the lowest-energy conformers exhibited delocalized electronic structures (or class III mixed-valence character). However, these minima alone explained neither the presence of shoulder(s) in the NIR absorption envelope nor the presence of features in the observed vibrational spectra characteristic of both delocalized and valence-trapped electronic structures. A series of computational models have been used to demonstrate that the mutual conformation of the metal fragments—and even more importantly the orientation of the bridging ligand relative to those metal centers—influences the electronic coupling sufficiently to afford valence-trapped conformations, which are of sufficiently low energy to be thermally populated. Areas in the conformational phase space with variable degrees of symmetry breaking of structures and spin-density distributions are shown to be responsible for the characteristic spectroscopic features of these two complexes. The Creutz–Taube ion [3]5+ also exhibits low-lying valence-trapped conformational areas, but the electronic transitions that characterize these conformations with valence-localized electronic structures have low intensities and do not influence the observed spectroscopic characteristics to any notable extent
Carbamoyl radical-mediated synthesis and semipinacol rearrangement of β-lactam diols.

In an approach to the biologically important 6-azabicyclo[3.2.1]octane ring system, the scope of the tandem 4-exo-trig carbamoyl radical cyclization—dithiocarbamate group transfer reaction to ring-fused β-lactams is evaluated. β-Lactams fused to five-, six-, and seven-membered rings are prepared in good to excellent yield, and with moderate to complete control at the newly formed dithiocarbamate stereocentre. No cyclization is observed with an additional methyl substituent on the terminus of the double bond. Elimination of the dithiocarbamate group gives α,β- or β,γ-unsaturated lactams depending on both the methodology employed (base-mediated or thermal) and the nature of the carbocycle fused to the β-lactam. Fused β-lactam diols, obtained from catalytic OsO4-mediated dihydroxylation of α,β-unsaturated β-lactams, undergo semipinacol rearrangement via the corresponding cyclic sulfite or phosphorane to give keto-bridged bicyclic amides by exclusive N-acyl group migration. A monocyclic β-lactam diol undergoes Appel reaction at a primary alcohol in preference to semipinacol rearrangement. Preliminary investigations into the chemo- and stereoselective manipulation of the two carbonyl groups present in a representative 7,8-dioxo-6-azabicyclo[3.2.1]octane rearrangement product are also reported
Designed Single-Step Synthesis, Structure, and Derivative Textural Properties of Well-Ordered Layered Penta-coordinate Silicon Alcoholate Complexes

The controllable synthesis of well-ordered layered materials with specific nanoarchitecture poses a grand challenge in materials chemistry. Here the solvothermal synthesis of two structurally analogous 5-coordinate organosilicate complexes through a novel transesterification mechanism is reported. Since the polycrystalline nature of the intrinsic hypervalent Si complex thwarts the endeavor in determining its structure, a novel strategy concerning the elegant addition of a small fraction of B species as an effective crystal growth mediator and a sacrificial agent is proposed to directly prepare diffraction-quality single crystals without disrupting the intrinsic elemental type. In the determined crystal structure, two monomeric primary building units (PBUs) self-assemble into a dimeric asymmetric secondary BU via strong Na+[BOND]O2− ionic bonds. The designed one-pot synthesis is straightforward, robust, and efficient, leading to a well-ordered (10ī)-parallel layered Si complex with its principal interlayers intercalated with extensive van der Waals gaps in spite of the presence of substantial Na+ counter-ions as a result of unique atomic arrangement in its structure. However, upon fast pyrolysis, followed by acid leaching, both complexes are converted into two SiO2 composites bearing BET surface areas of 163.3 and 254.7 m2 g−1 for the pyrolyzed intrinsic and B-assisted Si complexes, respectively. The transesterification methodology merely involving alcoholysis but without any hydrolysis side reaction is designed to have generalized applicability for use in synthesizing new layered metal–organic compounds with tailored PBUs and corresponding metal oxide particles with hierarchical porosity.United States. Defense Advanced Research Projects Agency (control No. 0471-1627)National Institute for Biomedical Imaging and Bioengineering (U.S.) (award No. EB-001960)National Institutes of Health (U.S.) (NIBIB award No. EB-002026)National Science Foundation (U.S.) (Grant No. CHE-0946721
Influence of Catalyst Structure and Reaction Conditions on  anti ‐ versus  syn ‐Aminopalladation Pathways in Pd‐Catalyzed Alkene Carboamination Reactions of  N ‐Allylsulfamides

The Pd‐catalyzed coupling of  N ‐allylsulfamides with aryl and alkenyl triflates to afford cyclic sulfamide products is described. In contrast to other known Pd‐catalyzed alkene carboamination reactions, these transformations may be selectively induced to occur by way of either  anti ‐ or  syn ‐aminopalladation mechanistic pathways by modifying the catalyst structure and reaction conditions.     A constructive approach : A concise, efficient approach has led to the synthesis of cyclic sulfamides by using Pd‐catalyzed alkene carboamination reactions of  N ‐allylsulfamides (see picture; OTf=triflate, RuPhos=2‐dicyclohexylphosphino‐2′,6′‐diisopropoxybiphenyl, X‐phos=2‐dicyclohexylphosphino‐2′,4′,6′‐triisopropylbiphenyl). The mechanism of these transformations is highly dependent on the catalyst structure and reaction conditions. The reactions can be induced to proceed selectively through either  syn ‐ or  anti ‐aminopalladation pathways under appropriate conditions
Exploiting molecular self-assembly: from urea-based organocatalysts to multifunctional supramolecular gels

We describe the self-assembly properties of chiral N,N'-disubstituted urea-based organocatalyst 1 that leads to the formation of hierarchical supramolecular gels in organic solvents at low concentrations. The major driving forces for the gelation are hydrogen bonding and pi-pi interactions according to FTIR and H-1 NMR spectroscopy, as well as quantum-mechanical studies. The gelation scope could be interpreted based on Kamlet-Taft solvatochromic parameters. TEM, SEM, and AFM imaging revealed that a variety of morphologies including helical, laths, porous, and lamellar nanostructures could be obtained by varying the solvent. Experimental gelation tests and computational structural analysis of various structurally related compounds proved the existence of a unique set of molecular interactions and an optimal hydrophilic/hydrophobic balance in 1 that drive the formation of stable gels. Responses to thermal, mechanical, optical, and chemical stimuli, as well as multifunctionality were demonstrated in some model gel materials. Specifically, 1 could be used for the phase-selective gelation of organic solvent/water mixtures. The gel prepared in glycerol was found to be thixotropic and provided a sensitive colorimetric method for the detection of Ag-I ions at millimolar concentrations in aqueous solution. Moreover, the gel matrix obtained in toluene served as a nanoreactor for the Friedel-Crafts alkylation of H-1-indole with trans-beta-nitrostyrene.Peer ReviewedPostprint (published version
Rhodium-Catalyzed Intramolecular [3+2+2] Cycloadditions between Alkylidenecyclopropanes, Alkynes, and Alkenes

A Rh-catalyzed intramolecular [3+2+2] cycloaddition is reported. The cycloaddition affords synthetically relevant 5,7,5-fused tricyclic systems of type 2 from readily available dienyne precursors. The transformation takes place with moderate or good yields, high diastereoselectivity, and total chemoselectivitySpanish MINECO. Grant Numbers: SAF2010-20822-C02-01/02, CTQ2010-20714-C02-01/BQU, CSD2007-00006
ERDF
Xunta de Galicia. Grant Numbers: GRC2010/12, GR2013-041, INCITE09 209084PR, EM2013/036
European Research Council. Grant Number: 340055
CAM. Grant Number: S2009/PPQ-1634, AVANCATS
High-Yield Formation of Substituted Tetracyanobutadienes from Reaction of Ynamides with Tetracyanoethylene.

The authors gratefully acknowledge Dr. L. Toupet from Institut de Physique de Rennes for solving X-ray structures, T. C. Nguyen for help in performing DFT calculations and Pr. A. Boucekkine for useful discussions.International audienceA high-yielding sequence of [2+2] cycloaddition-retroelectrocyclization of ynamides with tetracyanoethylene (TCNE) is described. The reaction provided tetracyanobutadiene (TCBD) species, which were characterized by various techniques. DFT and TD-DFT calculations were also performed to complement experimental findings
Stereodivergent organocatalytic intramolecular michael addition/ lactonization for the asymmetric synthesis of substituted dihydrobenzofurans and tetrahydrofurans

The authors thank the Royal Society for a University Research Fellowship (A.D.S.), the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013), ERC Grant Agreement No. 279850 (A.D.L.H. and J.E.T.), and the EPSRC (DTA studentship to D.B.) for funding.A stereodivergent asymmetric Lewis base catalyzed Michael addition/lactonization of enone acids into substituted dihydrobenzofuran and tetrahydrofuran derivatives is reported. Commercially available (S)-(-)-tetramisole hydrochloride gives products with high syn diastereoselectivity in excellent enantioselectivity (up to 99:1 d.r. , 99% ee), whereas using a cinchona alkaloid derived catalyst gives the corresponding anti-diastereoisomers as the major product (up to 10:90 d.r., 99% ee). You can have it both ways! A stereodivergent asymmetric Lewis base catalyzed Michael addition/lactonization of enone acids into substituted dihydrobenzofuran and tetrahydrofuran derivatives is reported, giving products with high d.r. and ee (see scheme).Publisher PDFPeer reviewe
A highly stable zirconium-based metal-organic framework material with high surface area and gas storage capacities

We designed, synthesized and characterized a new Zr-based metal–organic framework material, NU-1100, which exhibits a pore volume of 1.53 cm3/g and Brunauer-Emmett-Teller (BET) surface area of 4020 m2/g; to our knowledge currently the highest published for Zr-based MOFs. CH4/CO2/H2 adsorption isotherms were measured over a broad range of pressures and temperatures and are in excellent agreement with the computational predictions. The total hydrogen adsorption at 65 bar and 77 K is 0.092 g/g which corresponds to 43 g/L. The volumetric and gravimetric methane storage capacities at 65 bar and 298 K are ~180 vSTP/v and 0.27 g/g, respectively.OKF, JTH and RQS thank DOE ARPA-E and the Stanford Global Climate and Energy Project for support of work relevant to methane and CO2, respectively. TY acknowledges support by the U. S. Department of Energy through BES Grant No. DE-FG02-08ER46522. WB acknowledges support from the Foundation for Polish Science through the “Kolumb” Program. DFJ acknowledges the Royal Society (UK) for a University Research Fellowship. This material is based upon work supported by the National Science Foundation (grant CHE-1048773).This is the accepted manuscript. The final version is available as 'Water-Stable Zirconium-Based Metal–Organic Framework Material with High-Surface Area and Gas-Storage Capacities' from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/chem.201402895/abstract
Synthesis of 1,3-Bis(tetracyano-2-azulenyl-3-butadienyl)azulenes by the [2+2] Cycloaddition-Retroelectrocyclization of 1,3-Bis(azulenylethynyl)azulenes with Tetracyanoethylene

1,3-Bis(azulenylethynyl)azulene derivatives 9-14 have been prepared by palladium-catalyzed alkynylation of 1-ethynylazulene 8 with 1,3-diiodoazulene 1 or 1,3-diethynylazulene 2 with the corresponding haloazulenes 3-7 under Sonogashira-Hagihara conditions. Bis(alkynes) 9-14 reacted with tetracyanoethylene (TCNE) in a formal [2+2] cycloaddition-retroelectrocyclization reaction to afford the corresponding new bis(tetracyanobutadiene)s (bis(TCBDs)) 15-20 in excellent yields. The redox behavior of bis(TCBD)s 15-20 was examined by using CV and differential pulse voltammetry (DPV), which revealed their reversible multistage reduction properties under the electrochemical conditions. Moreover, a significant color change of alkynes 9-14 and TCBDs 15-20 was observed by visible spectroscopy under the electrochemical reduction conditions
Diamine Catalyzed Addition of ZnEt2 to PhC(O)CF3: Two Mechanisms and Autocatalytic Asymmetric Enhancement

Producción CientíficaNMR studies of the catalytic addition reaction of ZnEt2 to PhC(O)CF3 in the presence of three very efficient catalysts [TMEDA, tBuBOX, and L; where L is a chiral diamine synthesized from optically pure (R,R)-1,2-diphenylethylenediamine and (S)-2,2'-bis-(bromomethyl)-1,1'-binaphthalene] reveal large differences in their behavior. For the ligands TMEDA and tBuBOX, the catalysis shows no unusual features and proceeds via [(N?N)Zn(Et){OC(CF3 )(Et)Ph}]. For N?N?L, the observation of autocatalytic asymmetric enhancement during the catalysis, and unusual inverse concentration dependence on the reaction rate, indicate the participation of an additional novel catalytic cycle that goes through a dinuclear intermediate containing one ZnEt2 and one ZnEt fragment connected by N?N and OR bridges. Interestingly, the (19) F NMR signals of the main product of the reaction ([Zn(Et){OC*(CF3 )(Et)Ph}]2 ) allowed us to assess the enantioselectivity of the processes in situ without the assistance of chiral chromatography.Ministerio de Economía, Industria y Competitividad (CTQ2013-48406-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. GR169 and VA256U13
Nanoarchitectured Graphene-Based Supercapacitors for Next-Generation Energy-Storage Applications

Tremendous development in the field of portable electronics and hybrid electric vehicles has led to urgent and increasing demand in the field of high‐energy storage devices. In recent years, many research efforts have been made for the development of more efficient energy‐storage devices such as supercapacitors, batteries, and fuel cells. In particular, supercapacitors have great potential to meet the demands of both high energy density and power density in many advanced technologies. For the last half decade, graphene has attracted intense research interest for electrical double‐layer capacitor (EDLC) applications. The unique electronic, thermal, mechanical, and chemical characteristics of graphene, along with the intrinsic benefits of a carbon material, make it a promising candidate for supercapacitor applications. This Review focuses on recent research developments in graphene‐based supercapacitors, including doped graphene, activated graphene, graphene/metal oxide composites, graphene/polymer composites, and graphene‐based asymmetric supercapacitors. The challenges and prospects of graphene‐based supercapacitors are also discussed
Evaluating the thermal vinylcyclopropane rearrangement (VCPR) as a practical method for the synthesis of difluorinated cyclopentenes : experimental and computational studies of rearrangement stereospecificity

Vinyl cyclopropane rearrangement (VCPR) has been utilised to synthesise a difluorinated cyclopentene stereospecifically and under mild thermal conditions. Difluorocyclopropanation chemistry afforded ethyl 3-(1'(2'2'-difluoro-3'-phenyl)cyclopropyl) propenoate as all four stereoisomers (18a, 18b, 22a, 22b) (all racemic). Trans-E isomer (18a), prepared in 70% yield over three steps, underwent near quantitative VCPR to difluorocyclopentene 23 (99%). Rearrangements were followed by 19F NMR (100-180 °C). While cis/trans cyclopropane stereoisomerisation was facile, favouring trans-isomers by a modest margin, no E/Z alkene isomerisation was observed even at higher temperatures. Neither cis nor trans Z-alkenoates underwent VCPR, even up to much higher temperatures (180 oC). Cis-cyclopropanes underwent [3,3]-rearrangement to afford benzocycloheptadiene species. The reaction stereospecificity was explored using electronic structure calculations and UB3LYP/6-31G* methodology allowed the energy barriers for cyclopropane stereoisomerisation, diastereoisomeric VCPR and [3,3]-rearrangement to be ranked in agreement with experiment
Dissymmetrical U-Shaped π-Stacked Supramolecular Assemblies by Using a Dinuclear CuI Clip with Organophosphorus Ligands and Monotopic Fully π-Conjugated Ligands

International audienceReactions between the U-shape binuclear CuI complex A bearing short metal-metal distances and the cyano-capped monotopic π-conjugated ligands 1-5 carrying gradually bulkier polyaromatic terminal fragments lead to the formation of π-stacked supramolecular assemblies 6-10 respectively in  50-80 % yields. These derivatives have been characterized by multinuclear NMR spectroscopy and X-ray diffraction studies. Their solid state structures show the selective formation of  U-shaped supramolecular assemblies in which two monotopic π-conjugated systems present large (6,7,9) or medium (8,10) intramolecular π-overlap revealing π-π interactions. These assemblies self-organize into head-to-tail π-stacked dimers that in turn self-assemble affording infinite columnar π-stacks. The nature, the extentand the complexity of the intermolecular contacts within the head-to-tail π-stacked dimer depends on the nature of  the terminal polyaromatic fragment carried by the cyano-capped monotopic ligand but it does not alter the result of the self-assembling process. These results demonstrate that the dinuclear molecular clip A bearing short metal-metal distance allows selective supramolecular assembling processes driven by the formation of intra- and intermolecular short π-π interactions in the resulting self-assembled structures demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extented π-stacked columns based on dissymmetrical and functionnal π-conjugated systems
Core-shell nanoreactors for efficient aqueous biphasic catalysis

Water-borne phosphine-functionalized core-cross-linked micelles (CCM) consisting of a hydrophobic core and a hydrophilic shell were obtained as stable latexes by reversible addition-fragmentation chain transfer (RAFT) in water in a one-pot, three-step process. Initial homogeneous aqueous-phase copolymerization of methacrylic acid (MAA) and poly(ethylene oxide) methyl ether methacrylate (PEOMA) is followed by copolymerization of styrene (S) and 4-diphenylphosphinostyrene (DPPS), yielding P(MAA-co-PEOMA)-b-P(S-co-DPPS) amphiphilic block copolymer micelles (M) by polymerization-induced self-assembly (PISA), and final micellar cross-linking with a mixture of S and diethylene glycol dimethacrylate. The CCM were characterized by dynamic light scattering and NMR spectroscopy to evaluate size, dispersity, stability, and the swelling ability of various organic substrates. Coordination of [Rh(acac)(CO)2 ] (acac=acetylacetonate) to the core-confined phosphine groups was rapid and quantitative. The CCM and M latexes were then used, in combination with [Rh(acac)(CO)2 ], to catalyze the aqueous biphasic hydroformylation of 1-octene, in which they showed high activity, recyclability, protection of the activated Rh center by the polymer scaffold, and low Rh leaching. The CCM latex gave slightly lower catalytic activity but significantly less Rh leaching than the M latex. A control experiment conducted in the presence of the sulfoxantphos ligand pointed to the action of the CCM as catalytic nanoreactors with substrate and product transport into and out of the polymer core, rather than as a surfactant in interfacial catalysis