pinecone/core-2020-05-10-deduplication huggingface dataset:
Catalytic transfer hydrogenation by a trivalent phosphorus compound: phosphorus-ligand cooperation pathway or P(III) /P(V) redox pathway?

Main-group-element catalysts are a desirable alternative to transition-metal catalysts because of natural abundance and cost. However, the examples are very limited. Catalytic cycles involving a redox process and E-ligand cooperation (E=main-group element), which are often found in catalytic cycles of transition-metal catalysts, have not been reported. Herein theoretical investigations of a catalytic hydrogenation of azobenzene with ammonia-borane using a trivalent phosphorus compound, which was experimentally proposed to occur through P(III) /P(V) redox processes via an unusual pentavalent dihydridophosphorane, were performed. DFT and ONIOM(CCSD(T):MP2) calculations disclosed that this catalytic reaction occurs through a P-O cooperation mechanism, which resembles the metal-ligand cooperation mechanism of transition-metal catalysts
The potent oxidant anticancer activity of organoiridium catalysts

YesPlatinum complexes are the most widely used anticancer drugs; however, new generations of agents are needed. The organoiridium(III) complex [(η5-Cpxbiph)Ir(phpy)(Cl)] (1-Cl), which contains π-bonded biphenyltetramethylcyclopentadienyl (Cpxbiph) and C^N-chelated phenylpyridine (phpy) ligands, undergoes rapid hydrolysis of the chlorido ligand. In contrast, the pyridine complex [(η5-Cpxbiph)Ir(phpy)(py)]+ (1-py) aquates slowly, and is more potent (in nanomolar amounts) than both 1-Cl and cisplatin towards a wide range of cancer cells. The pyridine ligand protects 1-py from rapid reaction with intracellular glutathione. The high potency of 1-py correlates with its ability to increase substantially the level of reactive oxygen species (ROS) in cancer cells. The unprecedented ability of these iridium complexes to generate H2O2 by catalytic hydride transfer from the coenzyme NADH to oxygen is demonstrated. Such organoiridium complexes are promising as a new generation of anticancer drugs for effective oxidant therapy.We thank the ERC (247450), SNSF (PA00P2_145308 for N.P.E.B.), IAS (for I.R.C.), BBSRC (for J.M.H.), Science City (AWM and ERDF), and the EPSRC for support, and Prof. Timothy Bugg and members of EC COST Action CM1105 for stimulating discussions. We also thank Professor Pat Unwin, Mike Snowden, and Rob Lazenby for their help with the electrochemical experiments and the National Cancer Institute for NCI-60 human tumor cell panel screening.Gol
Modeling Heat Dissipation at the Nanoscale: An Embedding Approach for
  Chemical Reaction Dynamics on Metal Surfaces

We present an embedding technique for metallic systems that makes it possible
to model energy dissipation into substrate phonons during surface chemical
reactions from first principles. The separation of chemical and elastic
contributions to the interaction potential provides a quantitative description
of both electronic and phononic band structure. Application to the dissociation
of O$_2$ at Pd(100) predicts translationally "hot" oxygen adsorbates as a
consequence of the released adsorption energy (ca. 2.6 eV). This finding
questions the instant thermalization of reaction enthalpies generally assumed
in models of heterogeneous catalysis.Comment: 6 pages, 2 figure
On-top π-stacking of quasiplanar molecules in hole-transporting materials: inducing anisotropic carrier mobility in amorphous films.

Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top π-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the π-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on π-stacking, thus facilitating an out-of-plane carrier mobility
Introducing deep eutectic solvents to polar organometallic chemistry : chemoselective addition of organolithium and grignard reagents to ketones in air

Despite their enormous synthetic relevance, the use of polar organolithium and Grignard reagents is greatly limited by their requirements of low temperatures in order to control their reactivity as well as the need of dry organic solvents and inert atmosphere protocols to avoid their fast decomposition. Breaking new ground on the applications of these commodity organometallics in synthesis under more environmentally friendly conditions, this work introduces deep eutetic solvents (DESs) as a green alternative media to carry out chemoselective additions of ketones in air at room temperature. Comparing their reactivities in DES with those observed in pure water suggest that a kinetic activation of the alkylating reagents is taking place, favoring nucleophilic addition over the competitive hydrolysis, which can be rationalized through formation of halide-rich magnesiate or lithiate species
Total Synthesis of (+)-Madangamine D

Madangamines are a group of bioactive marine sponge alkaloids, embodying an unprecedented diazapentacyclic skeletal type. The enantioselective total synthesis of madangamine D has been accomplished, and represents the first total synthesis of an alkaloid of the madangamine group. It involves the stereoselective construction of the diazatricyclic ABC core using a phenylglycinol-derived lactam as the starting enantiomeric scaffold and the subsequent assembly of the peripheral macrocyclic rings. The synthesis provides, for the first time, a pure sample of madangamine D and confirms the absolute configuration of this alkaloid family
In situ observation of surface species on iridium oxide nanoparticles during the oxygen evolution reaction

An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient-pressure X-ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from Ir-IV to Ir-V that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH-mediated deprotonation mechanism
Laboratory real-time and in situ monitoring of mechanochemical milling reactions using Raman spectroscopy

Mechanistic understanding of mechanochemical reactions is sparse and has been acquired mostly by stepwise ex situ analysis. We describe here an unprecedented laboratory technique to monitor the course of mechanochemical transformations at the molecular level in situ and in real time by using Raman spectroscopy. The technique, which employs translucent milling vessels that allow collecting a Raman scattering signal from the sample as it is being milled, was validated on mechanochemical reactions forming coordination polymers and organic cocrystals. The technique enabled assessing reaction dynamics and course under different reaction conditions as well as, for the first time, direct insight in the behaviour of liquid additives during liquid-assisted grinding
Fast Prediction of Adsorption Properties for Platinum Nanocatalysts with Generalized Coordination Numbers

International audiencePlatinum is a prominent catalyst for a multiplicity of reactions because of its high activity and stability. As Pt nanoparticles are normally used to maximize catalyst utilization and to minimize catalyst loading, it is important to rationalize and predict catalytic activity trends in nanoparticles in simple terms, while being able to compare these trends with those of extended surfaces. The trends in the adsorption energies of small oxygen- and hydrogen-containing adsorbates on Pt nanoparticles of various sizes and on extended surfaces were analyzed through DFT calculations by making use of the generalized coordination numbers of the surface sites. This simple and predictive descriptor links the geometric arrangement of a surface to its adsorption properties. It generates linear adsorption-energy trends, captures finite-size effects, and provides more accurate descriptions than d-band centers and usual coordination numbers. Unlike electronic-structure descriptors, which require knowledge of the densities of states, it is calculated manually. Finally, it was shown that an approximate equivalence exists between generalized coordination numbers and d-band centers
Classification framework for graphene-based materials

Graphene is the enabling material of the 21st century and there are high expectations for its potential applications. A clear and consistent system describing the various derivatives of graphene promotes a precise vocabulary for the family of graphene-based materials. This will be a prerequisite, for example, to understand structure–activity relationships in the context of human health and safety and to avoid generalizations about the capabilities and limitations of graphenebased materials. Within the European Union's GRAPHENE Flagship project, three physical-chemical descriptors specific for graphene were defined to assist in the classification of graphene-based materials
A localised tolerance in the substrate specificity of the fluorinase enzyme enables "last step" 18F fluorination of a RGD peptide under ambient aqueous conditions

The authors thank the ERC, EPSRC and the Scottish Imaging Network (SINAPSE) for grants, and the John and Kathleen Watson Scholarship (S.T.) for financial support.A strategy for last-step 18F fluorination of bioconjugated peptides is reported that exploits an “Achilles heel” in the substrate specificity of the fluorinase enzyme. An acetylene functionality at the C-2 position of the adenosine substrate projects from the active site into the solvent. The fluorinase catalyzes a transhalogenation of 5′-chlorodeoxy-2-ethynyladenosine (ClDEA) to 5′-fluorodeoxy-2-ethynyladenosine (FDEA). Extending a polyethylene glycol linker from the terminus of the acetylene allows the presentation of bioconjugation cargo to the enzyme for 18F labelling. The method uses an aqueous solution (H218O) of [18F]fluoride generated by the cyclotron and has the capacity to isotopically label peptides of choice for positron emission tomography (PET).PostprintPeer reviewe
Metal-Size Influence in Iso-Selective Lactide Polymerization

Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a Pi value of 0.81–0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (Ps=0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La>Y>Lu
Using the population-shift mechanism to rationally introduce "hill-type" cooperativity into a normally non-cooperative receptor

Allosteric cooperativity, which nature uses to improve the sensitivity with which biomolecular receptors respond to small changes in ligand concentration, could likewise be of use in improving the responsiveness of artificial biosystems. Thus motivated, we demonstrate here the rational design of cooperative molecular beacons, a widely employed DNA sensor, using a generalizable population-shift approach in which we engineer receptors that equilibrate between a low-affinity state and a high-affinity state exposing two binding sites. Doing so we achieve cooperativity within error of ideal behavior, greatly steepening the beacon's binding curve relative to that of the parent receptor. The ability to rationally engineer cooperativity should prove useful in applications such as biosensors, synthetic biology and "smart" biomaterials, in which improved responsiveness is of value
Collisional and Coulombic Unfolding of Gas‐Phase Proteins: High Correlation to Their Domain Structures in Solution

The three‐dimensional structures adopted by proteins are predicated by their many biological functions. Mass spectrometry has played a rapidly expanding role in protein structure discovery, enabling the generation of models for both proteins and their higher‐order assemblies. While important coursed‐grained insights have been generated, relatively few examples exist where mass spectrometry has been successfully applied to the characterization of protein tertiary structure. Here, we demonstrate that gas‐phase unfolding can be used to determine the number of autonomously folded domains within monomeric proteins. Our ion mobility‐mass spectrometry data highlight a strong, positive correlation between the number of protein unfolding transitions observed in the gas phase and the number of known domains within a group of sixteen proteins ranging from 8–78 kDa. This correlation and its potential uses for structural biology is discussed.     Gas‐phase unfolding  is used as a means to determine the number of autonomously folded domains within monomeric proteins. Ion‐mobility mass spectrometry data show a strong, positive correlation between the number of protein unfolding transitions observed in the gas phase and the number of known domains within a group of sixteen proteins ranging from 8–78 kDa. CCS=collision cross‐section
Total Synthesis of Jiadifenolide

As a potent neurotrophic agent, the sesquiterpenoid jiadifenolide represents a valuable small-molecule lead for the potential therapeutic treatment of neurodegenerative diseases. A stereocontrolled total synthesis of this densely functionalized natural product is reported, central to which is an adventurous samarium-mediated cyclization reaction to establish the tricyclic core and the adjacent C5 and C6 quaternary stereocenters.We thank Clare College Cambridge (Fellowship to S.M.D.) and the
EPSRC UK National Mass Spectrometry Facility at Swansea.This is the final published version. It's also available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/anie.201404224/abstract
Palladium-catalyzed amination of aryl sulfides with anilines.

A combination of a palladium-NHC catalyst and potassium hexamethyldisilazide enables the amination of aryl sulfides with anilines to afford a wide variety of diarylamines. The reaction conditions are versatile enough for the reaction of even bulky ortho-substituted aryl sulfides. This amination can be applied to the modular synthesis of N-aryl carbazoles from the corresponding ortho-bromothioanisoles. As aryl sulfoxides undergo extended Pummerer reactions to afford ortho-substituted aryl sulfides, the Pummerer products are thus useful substrates for the amination to culminate in efficient syntheses of a 2-anilinobenzothiophene and an indole as proof-of-principle of the utility of the extended Pummerer reaction/amination cascade
Tailoring Intermolecular Interactions for Efficient Room‐Temperature Phosphorescence from Purely Organic Materials in Amorphous Polymer Matrices

Herein we report a rational design strategy for tailoring intermolecular interactions to enhance room‐temperature phosphorescence from purely organic materials in amorphous matrices at ambient conditions. The built‐in strong halogen and hydrogen bonding between the newly developed phosphor G1 and the poly(vinyl alcohol) (PVA) matrix efficiently suppresses vibrational dissipation and thus enables bright room‐temperature phosphorescence (RTP) with quantum yields reaching 24 %. Furthermore, we found that modulation of the strength of halogen and hydrogen bonding in the G1–PVA system by water molecules produced unique reversible phosphorescence‐to‐fluorescence switching behavior. This unique system can be utilized as a ratiometric water sensor.     A bright idea : Rationally designed strong intermolecular hydrogen and halogen bonds between a novel phosphor and a poly(vinyl alcohol) (PVA) matrix led to bright room‐temperature phosphorescence (RTP) with a quantum yield of 24 %. Modulation of the strength of halogen and hydrogen bonding in the purely organic phosphor–PVA system by water enabled reversible switching between phosphorescence (green) and fluorescence (blue)
Enantioselective Assembly of a Ruthenium(II) Polypyridyl Complex into a Double Helix

Evolution can increase the complexity of matter by self-organization into helical architectures, the best example being the DNA double helix. One common aspect, apparently shared by most of these architectures, is the presence of covalent bonds within the helix backbone. Here, we report the unprecedented crystal structures of a metal complex that self-organizes into a continuous double helical structure, assembled by non-covalent building blocks. Built up solely by weak stacking interactions, this alternating tread stairs-like double helical assembly mimics the DNA double helix structure. Starting from a racemic mixture in aqueous solution, the ruthenium(II) polypyridyl complex forms two polymorphic structures of a left-handed double helical assembly of only the Λ-enantiomer. The stacking of the helices is different in both polymorphs: a crossed woodpile structure versus a parallel columnar stacking.status: publishe
A De Novo Designed Metalloenzyme for the Hydration of CO 2

Protein design will ultimately allow for the creation of artificial enzymes with novel functions and unprecedented stability. To test our current mastery of nature’s approach to catalysis, a Zn II  metalloenzyme was prepared using de novo design. α 3 DH 3  folds into a stable single‐stranded three‐helix bundle and binds Zn II  with high affinity using His 3 O coordination. The resulting metalloenzyme catalyzes the hydration of CO 2  better than any small molecule model of carbonic anhydrase and with an efficiency within 1400‐fold of the fastest carbonic anhydrase isoform, CAII, and 11‐fold of CAIII.     Chasing down the cheetah : A synthetic metalloenzyme was created that is capable of catalyzing the hydration of carbon dioxide with an efficiency within 1400‐fold of carbonic anhydrase II, one of the most efficient enzymes known. This designed zinc enzyme performs better than small‐molecule models of carbonic anhydrase. Picture: Zn purple, N dark blue, O red, C cyan
Enantioselective Synthesis of Piperidines through the Formation of Chiral Mixed Phosphoric Acid Acetals: Experimental and Theoretical Studies

An enantioselective intramolecular chiral phosphoric acid‐catalyzed cyclization of unsaturated acetals has been utilized for the synthesis of functionalized chiral piperidines. The chiral enol ether products of these cyclizations undergo subsequent in situ enantioenrichment through acetalization of the minor enantiomer. A new computational reaction exploration method was utilized to elucidate the mechanism and stereoselectivity of this transformation. Rather than confirming the originally postulated cyclization proceeding directly through a vinyl oxocarbenium ion, simulations identified an alternative two‐step mechanism involving the formation of a mixed chiral phosphate acetal, which undergoes a concerted, asynchronous S N 2′‐like displacement to yield the product with stereoselectivity in agreement with experimental observations.     A rich seam : An enantioselective chiral phosphoric acid‐catalyzed cyclization of unsaturated acetals has been utilized for the synthesis of functionalized chiral piperidines. The chiral enol ether products of these cyclizations undergo subsequent in situ enantioenrichment. A new computational method was utilized to elucidate the mechanism and stereoselectivity of this transformation. Cbz=benzyloxycarbonyl;  S =resolution
Towards a Safe Lithium–Sulfur Battery with a Flame‐Inhibiting Electrolyte and a Sulfur‐Based Composite Cathode

Of the various beyond‐lithium‐ion batteries, lithium–sulfur (Li‐S) batteries were recently reported as possibly being the closest to market. However, its theoretically high energy density makes it potentially hazardous under conditions of abuse. Therefore, addressing the safety issues of Li‐S cells is necessary before they can be used in practical applications. Here, we report a concept to build a safe and highly efficient Li‐S battery with a flame‐inhibiting electrolyte and a sulfur‐based composite cathode. The flame retardant not only makes the carbonates nonflammable but also dramatically enhances the electrochemical performance of the sulfur‐based composite cathode, without an apparent capacity decline over 750 cycles, and with a capacity greater than 800 mA h −1  g −1 (sulfur) at a rate of 10 C.     Fire away : A nonflammable sulfur composite cathode has been shown to maintain extremely stable electrochemical activity over 750 cycles and exhibit a discharge capacity greater than 800 mA h −1  g −1 (sulfur) at a high rate of 10 C in a flame‐inhibiting electrolyte. The safe electrolyte was generated from a phosphite additive that participates in interfacial reactions on the cathode and accelerates Li‐ion diffusion more than tenfold
Near-IR-triggered, remote-controlled release of metal ions: A novel strategy for caged ions

A ligand incorporating a dithioethenyl moiety is cleaved into fragments which have a lower metal-ion affinity upon irradiation with low-energy red/near-IR light. The cleavage is a result of singlet oxygen generation which occurs on excitation of the photosensitizer modules. The method has many tunable factors that could make it a satisfactory caging strategy for metal ions. Metal ions on demand: Near-IR irradiation of a designer ligand results in singlet-oxygen-mediated fragmentation with the consequent release of metal ions. The modular nature of the "cage" may herald a new class of agents that could supply chemical effectors on demand. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Metal-Free Dihydrogen Oxidation by a Borenium Cation:A Combined Electrochemical/Frustrated Lewis Pair Approach

In order to use H2 as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H2 into 2 H+ and 2 e−. Herein, we report a metal-free approach to catalyze the oxidation of H2 by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H2 with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC-stabilized borenium cation [(IiPr2)(BC8H14)]+ (IiPr2=C3H2(NiPr)2, NHC=N-heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H2 oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol−1. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C6F5)3, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach
Reversible supramolecular assembly at specific DNA sites: Ni-promoted, bivalent DNA binding with designed peptide and bipyridylbisbenzamidine components

At specific DNA sites, nickel(II) salts promote the assembly of designed components, namely a bis(histidine)-modified peptide that is derived from a bZIP transcription factor and a bis(benzamidine) unit that is equipped with a bipyridine. This programmed supramolecular system with emergent properties reproduces some key characteristics of naturally occurring DNA-binding proteins, such as bivalence, selectivity, responsiveness to external agents, and reversibility.We are thankful for support from Spanish grants (SAF2010-20822-C02 and CTQ2012-31341), Consolider Ingenio 2010 (CSD2007-00006), the Xunta de Galicia (GRC2013-041, INCITE09 209084PR, and PGIDIT08CSA-047209PR), the ERDF, and the European Research Council (Advanced Grant 340055). J.M. and M.I.S. thank the Spanish MCINN for their Ph.D. fellowships.S