pinecone/core-2020-05-10-deduplication huggingface dataset:
Enzyme activity by design : an artificial rhodium hydroformylase for linear aldehydes

Funding: Marie Curie Individual Fellowship project ArtOxiZymes to AGJ (contract no. H2020-MSCA-IF-2014-657755), EPSRC Critical mass grant ‘Clean catalysis for sustainable development’ (EP/J018139/1) and Sasol (CASE studentship to P.J.D.), EPSRC (EP/K014854/1).Artificial metalloenzymes (ArMs) are hybrid catalysts that offer a unique opportunity to combine the superior performance of natural protein structures with the unnatural reactivity of transition-metal catalytic centers. Therefore, they provide the prospect of highly selective and active catalytic chemical conversions for which natural enzymes are unavailable. Herein, we show how by rationally combining robust site-specific phosphine bioconjugation methods and a lipid-binding protein (SCP-2L), an artificial rhodium hydroformylase was developed that displays remarkable activities and selectivities for the biphasic production of long-chain linear aldehydes under benign aqueous conditions. Overall, this study demonstrates that judiciously chosen protein-binding scaffolds can be adapted to obtain metalloenzymes that provide the reactivity of the introduced metal center combined with specifically intended product selectivity.Publisher PDFPeer reviewe
Aryloxide-facilitated catalyst turnover in enantioselective α,β-unsaturated acyl ammonium catalysis

The authors thank the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) ERC grant agreement no. 279850 (A.D.S) and the EPSRC (EP/J018139/1, A.M.) for funding. A.D.S. thanks the Royal Society for a Wolfson Research Merit Award.A new general concept for α,β-unsaturated acyl ammonium catalysis is reported that uses p-nitrophenoxide release from an α,β-unsaturated p-nitrophenyl ester substrate to facilitate catalyst turnover. This method was used for the enantioselective isothiourea-catalyzed Michael addition of nitroalkanes to α,β-unsaturated p-nitrophenyl esters in generally good yield and with excellent enantioselectivity (27 examples, up to 79% yield, 99:1 er). Mechanistic studies identified rapid and reversible catalyst acylation by the α,β-unsaturated p-nitrophenyl ester, and a recently-reported variable time normalization kinetic analysis method was used to delineate the complex reaction kinetics.Publisher PDFPeer reviewe
Layered nano-TiO2 based treatments for the maintenance of natural stones in historical architecture

Layered treatments of natural stones based on dispersions of experimental nano-TiO2 and commercial TEOS, showing photocatalytic and self-cleaning properties have been set-up and tested. To enhance nano-TiO2 efficacy, a surface pre-treatment with tetraethyl orthosilicate has been proposed to avoid the penetration of NPs into the crystalline porous substrates and to improve their adhesion to the stone. Two treatment applications - wet-on-wet and wet-on-dry -have been compared, showing different results. A strong interaction Si-O-Ti has proved to be the key factor for the successful treatment, leaving the bandgap and relevant properties of nano-TiO2 unaltered. The layered treatments have been tested on a porous calcarenite (Noto stone) and a very compact marble (Carrara marble). The combined SiO2-nano-TiO2 treatments can find application in suitable cases where a surface consolidation is needed, ensuring a depolluting and self-cleaning durable activit
Spectral imaging and archival data in analyzing the Madonna of the Rabbit painting by Manet and Titian

A concise insight into the outputs provided by the latest prototype of visible-near infrared (VIS-NIR) multispectral scanner (National Research Council-National Institute of Optics, CNR-INO, Italy) is presented. The analytical data acquired on an oil painting Madonna of the Rabbit by É. Manet are described. In this work, the VIS-NIR was complemented with X-ray fluorescence (XRF) mapping for the chemical and spatial characterization of several pigments. The spatially registered VIS-NIR data facilitated their processing by spectral correlation mapping (SCM) and artificial neural network (ANN) algorithm respectively for pigment mapping and improved visibility of pentimenti and of underdrawing style. The data provided several key elements for the comparison with a homonymous original work by Titian studied within the ARCHive LABoratory (ARCHLAB) transnational access project
Synthesis, Structure and Reactivity of Sulfur-Rich Cyclopentadienyl-Transition Metal Complexes: Sulfur Chemistry from an Organometallic Point of View

Metal-sulfur centers play an important role in the activity of metalloproteins in enzymatic catalysis and the activity of metal sulfides as heterogeneous catalysts. The systematic search for M[BOND]S model compounds led to the discovery of an interesting and novel structural chemistry, which stems from the numerous coordination possibilities of sulfur ligands. The intention of this review article is to present and outline new approaches to sulfur chemistry from the organometallic point of view. Reactive cyclopentadienyl-transition metal fragments incorporate elemental sulfur to give polynuclear sulfur-rich complexes, which can contain either mono-, di- or polysulfido ligands or several such ligands in combined form. The versatile structural chemistry of the complexes formed and their reactivity towards organic, inorganic and organometallic compounds are discussed, and examples of some simple and rational procedures for their synthesis starting from cyclopentadienylcarbonyl- and cyclopentadienylhydrido-complexes are outlined. Their reactivity is manifested in numerous metal- and ligandcentered reactions. Finally the, albeit far less extensive, complex chemistry of the other chalcogens (O, Se, Te) is also considered for comparison, thus providing a more detailed survey of particular aspects of this area of chemistry
Solid-State Chemistry with Nonmetal Nitrides

Among the nonmetal nitrides, the polymeric binary compounds BN and Si3N4are of particular interest for the development of materials for high-performance applications. The outstanding features of both substances are their thermal, mechanical, and chemical stability, coupled with their low density. Because of their extremely low reactivity, boron and silicon nitride are hardly ever used as starting materials for the preparation of ternary nitrides, but are used primarily in the manufacture of crucibles or other vessels or as insulation materials. The chemistry of ternary and higher nonmetal nitrides that contain electropositive elements and are thus analogous with the oxo compounds such as borates, silicates, phosphates, or sulfates was neglected for many years. Starting from the recent successful preparation of pure P3N5, a further binary nonmetal nitride which shows similarities with Si3N4 with regard to both its structure and properties, this review deals systematically with the solid-state chemistry of ternary and higher phosphorus(V) nitrides and the relationship between the various types of structure found in this class of substance and the resulting properties and possible applications. From the point of view of preparative solid-state chemistry the syntheses, structures, and properties of the binary nonmetal nitrides BN, Si3N4, and P3N5 will be compared and contrasted. The chemistry of the phosphorus(V) nitrides leads us to expect that other nonmetals such as boron, silicon, sulfur, and carbon will also participate in a rich nitride chemistry, as initial reports indeed indicate.
Energy Barrier Enhancement by Ligand Substitution in Tetrairon(III) Single Molecule Magnets

A dramatic increase of the energy barrier (Ueff) in tetrairon(III) single-mol. magnets can be achieved by simple chem. modification.  Site-specific replacement of the six methoxide bridges in [Fe4(OMe)6(dpm)6] (Hdpm = dipivaloylmethane; Ueff/kB = 3.5 K) with two tripodal 1,1,1-tris(hydroxymethyl)ethane (H3thme) ligands affords [Fe4(thme)2(dpm)6] with Ueff/kB = 15.6(2) K and a magnetic relaxation time exceeding 1000 s at T <0.2 K.  The prepd. complex is trigonal, space group R-3c, Z = 6, R1 = 0.0370, R2 = 0.1089
Azoporphyrin : the porphyrin analogue of azobenzene

Azobenzenes (1,2-diaryldiazenes) are very important organic\ud
pigments, and they have a unique place in the field of\ud
photoresponsive conjugated molecules due to their (usually)\ud
reversible E/Z photoisomerisation. The current intense interest in\ud
molecular analogues of mechanical components and information\ud
storage and processing elements has stimulated research into\ud
conjugated molecules whose shape and/or optical properties can be\ud
switched electro- or photochemically. Among the classes of\ud
conjugated pigments being explored in these contexts are the\ud
porphyrinoids, which offer advantages of intense light absorption, a\ud
variety of accessible oxidation states, and synthetic control of\ud
properties through peripheral or central substitution. Extension of\ud
porphyrinoid conjugation can be achieved by linking the peripheral\ud
carbons either by three direct bonds (as in the “porphyrin tapes” of\ud
Osuka et al.) or through potentially conjugating bridges such as\ud
alkenes or, even better, alkynes
NMR-guided fragment-based approach for the design of tRNA(Lys3) ligands.

Despite recent breakthroughs, the de novo design of new compounds that specifically bind to structured RNAs is still a standing challenge. The aim of this study was to find molecules that bind to tRNALys3 and serve as leads for inhibitors of the formation of the HIV-1 reverse transcription initiation complex. We used NMR screening to identify ligands from spectral changes induced by their binding on the target. Using a fragment-based approach, a selective ligand of tRNALys3 with micromolar dissociation constant has been synthesised for the first time
Superoxide does react with peroxides : direct observation of the haber-weiss reaction in the gas phase

The fact that nature provides specific enzymes to selectively remove superoxide (O2.−) from aerobic organisms, namely, the superoxide dismutase enzymes,1 has led to the suggestion that this radical ion may cause the oxidative damage associated with degradative disease and aging.2 Intriguingly, however, superoxide itself is relatively unreactive toward most cellular components, which suggests that dismutase enzymes may ultimately protect the cell against more pernicious oxidants formed from superoxide. As such, there is increasing interest in the endogenous chemistry of superoxide and the pathways by which it might beget more reactive oxygen species. Protonation of superoxide to form the hydroperoxyl radical (HOO.) and dismutation of the same species to hydrogen peroxide (HOOH), with subsequent metal-catalyzed reduction to the hydroxyl radical (HO.), are well-characterized processes in which both the HOO. and HO. radicals are significantly more reactive than their common progenitor.2 Recent examples, however, have also linked superoxide to the putative production of singlet oxygen3 and ozone,4, 5 although the definitive characterization of these chemistries in the cellular milieu has proved challengin
Dynamics and Infrared Spectroscopy of the Protonated Water Dimer

The dynamics and infrared absorption spectrum of the protonated water dimer
are reported by full quantum simulation. Strong couplings between the
spectroscopically active proton-transfer motion and low-frequency,
large-amplitude torsional modes are clearly identified and their role in the
cluster dynamics is explained. These couplings are responsible for the
characteristic doublet-peak around 1000 cm-1, which was not understood and
subject of debate. This spectral feature is reproduced, assigned and explained.Comment: 7 pages, 5 figures, accepted version in Angewandte Chemie. The
  content is the same as in older versions, the style was adapted to match the
  requirements of Ange. Che
A Biomimetic Enantioselective Approach to the Decahydroquinoline Class of Dendrobatid Alkaloids

Frogs of the neotropical family Dendrobatidae produce a remarkably diverse array of biologically active alkaloids. One of the major classes of these amphibian alkaloids[1] are the decahydroquinolines, which have been isolated not only from skin extracts of dendrobatid and mantelline frogs,[2] but also from bufonid toads,[3] tunicates,[4] marine flatworms,[4b] and myrmicine ants.[5] They possess either a cis or trans decahydroquinoline ring fusion, with a side-chain substituent at both the C2 and C5 positions and, in the lepadin series,[4] an acylated hydroxy group at the C3 position. The most representative decahydroquinoline alkaloid is cis-195A (formerly called pumiliotoxin C), first isolated in 1969 from a Panamanian population of Dendrobates pumilio. [6] The source of amphibian alkaloids remains an unresolved and challenging question,[1] in particular after the discovery that some of these alkaloids also occur in ants, thus strengthening a dietary hypothesis for their origin in frogs.[5] Although there are no conclusive studies concerning the biosynthesis of these toxins and, consequently, little is known about the biosynthetic pathways, there has been speculation as to possible derivation from the polyketide route by aminocyclization of polycarbonyl intermediates (A), leading to either 2,5-disubstituted decahydroquinolines (C) or spiropiperidines (histrionicotoxins).[1a,b, 7] In accordance with this hypothesis, a plausible biosynthetic pathway to the decahydroquinoline class of dendrobatid alkaloids is depicted i
Cyclic peptides bearing a side-chain tail: A tool to model the structure and reactivity of protein zinc sites.

International audienceA new peptide design has been introduced to model the tetracysteinate zinc sites involving CXXC motifs present in beta-hairpins. It is based on a cyclic peptide incorporating one CXXC motif in addition to a variable CXC motif in a linear chain grafted onto the cycle via a glutamate or a lysine side chain. This 20-amino acid design has been used to model the Zn(Cys)4 sites of the heat shock protein Hsp33. TheZn2+ and Co2+ complexes were characterized by UV/vis, CD and NMR spectroscopy. The structures of two metallated peptides were solved by NMR. An excellent similarly was achieved between the model peptide and the target protein, both at the metal binding site and in the surrounding hydrogen bond network. Preliminary reactivity studies toward H2O2 are reported and show that the best model fit the kinetics observed for Hsp33
Absolute Asymmetric Synthesis

Absolute asymmetric synthesis is the synthesis of optically active products from achiral or racemic precursors only. This has generally been regarded as impossible and is relevant in the discussion of the origins of biomolecular homochirality. A possible route to absolute asymmetric synthesis involves total spontaneous resolution, which is possible for stereochemically labile substances which crystallise as conglomerates (i.e. the enantiomers crystallise in separate crystals).

Using total spontaneous resolution it was, for the first time, possible to prepare bulk-quantities of configurationally labile five-, seven-, and nine-coordinate enantiomers, containing only achiral ligands. Previously, only four- and six-coordinate complexes have been prepared enantiomerically pure in bulk quantities. Spontaneous resolution of eight-coordinate complexes has also been reported. It was also possible to perform total spontaneous resolution of a diaryl sulphide, an octanuclear organo(oxo)zinc complex, and a diindenylzinc complex. In the case of a helical coordination polymer based on copper(I) chloride and triallylamine, it was found that repeated synthesis always yielded an excess of the same enantiomer, possibly due to the influence of cryptochirality.

It has previously been practically impossible to measure enantiomeric excesses in stereochemically labile microcrystalline samples. A method utilising quantitative solid-state CD spectroscopy has been introduced to solve this problem.

In the case of the chiral organometallic reagent di(3-picoline)di(1-indenyl)zinc, it was possible to perform reactions with N-chlorosuccinimide in the presence of methanol and p-benzoquinone yielding optically active stereochemically inert 1-chloroindene in high yield and high enantiomeric excess (up to 89% ee). 

During the cause of theses studies, three cases of concomitant crystallisation of racemic and chiral phases have been discovered. This is a rare phenomenon of considerable interest e.g. in structure prediction.

The first synthetic route to well-defined hydridoalkylzincates is also reported
Rational design of an organometallic glutathione transferase inhibitor

A promising class of ruthenium anticancer drugs are ruthenium(II) arene PTA complexes (RAPTA) which are water-soluble and highly selective for cancer cells. RAPTA-based compounds with ethacrynic acid (EA) ligands have been synthesized, so-called etharapta compounds, and shown to exhibit dual activity of glutathione transferase P1-1 (GST P1-1) inhibition and cancer cell cytotoxicity. The complex was shown to be a more effective GST P1-1 inhibitor than EA alone suggesting that the metal center also is involved in inhibition of the enzyme. Structures of GST P1-1 etharapta complexes derived from crystals of GSTP1-1 incubated with etharapta for varying incubation times reveal that the metal complex binds at the dimer interface first with the metal center bound through Cys-101 residues of opposing monomers and then over time the metal center is released from the protein whilst the EA ligands traverse to the active sites where they bind and inhibit the enzymatic activity. XANES studies demonstrate that that the ruthenium center is reduced from +IV to +II in the process. The intact compound is thought to bind at the dimer interface in a relatively symmetric manner. The compound is then cleaved and the EA moieties transverse to the substrate-binding site while the ruthenium center remains bound to the dimer interface via Cys-101 residues. At some point, the activated metal center is released leading to cell apoptosis. This observation has led to the suggestion that one mode of GST-based resistance might involve sequestering metallodrugs at the subunit interface. Taken together, these results suggest GST inhibitors that block both the dimer interface and active site may prove potent anticancer adjuvants in future drug discovery efforts
Reversible Switching of the Shear Modulus of Photoresponsive Liquid-Crystalline Polymers

Manipulation makes light work: The morphology and rheological properties of a liquid-crystalline system can be dynamically manipulated with UV light by attaching photoresponsive liquid-crystalline moieties to a siloxane-based polymer. Stimulation with UV light induces a conformational change in the molecule, which disrupts the liquid-crystalline mesophase (see picture), and results in a dramatic change in its rheological properties.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (no. DAAD-19-02-D0002)Swiss National Science Foundation (grant PBEZ2-115179)National Science Foundation (U.S.) (award DMR-0225180
Epoxide-Opening Cascades in the Synthesis of Polycyclic Polyether Natural Products

The structural features of polycyclic polyether natural products can, in some cases, be traced to their biosynthetic origin. However in case that are less well understood, only biosynthetic pathways that feature dramatic, yet speculative, epoxide-opening cascades are proposed. We summarize how such epoxide-opening cascade reactions have been used in the synthesis of polycyclic polyethers (see scheme) and related natural products.

The group of polycyclic polyether natural products is of special interest owing to the fascinating structure and biological effects displayed by its members. The latter includes potentially therapeutic antibiotic, antifungal, and anticancer properties, and extreme lethality. The polycyclic structural features of this class of compounds can, in some cases, be traced to their biosynthetic origin, but in others that are less well understood, only to proposed biosynthetic pathways that feature dramatic, yet speculative, epoxide-opening cascades. In this review we summarize how such epoxide-opening cascade reactions have been used in the synthesis of polycyclic polyethers and related natural products
Exploiting the 1,2,3-triazolium motif in anion-templated formation of a bromide-selective rotaxane host assembly

Stimulated by the efficacy of copper (I) catalysed Huisgen-type 1,3-dipolar cycloaddition of terminal alkynes and organic azides to generate 1,4-disubstituted 1,2,3-triazole derivatives, the importance of ‘click’ chemistry in the synthesis of organic and biological molecular systems is ever increasing.[1] The mild reaction conditions have also led to this reaction gaining favour in the construction of interlocked molecular architectures.[2-4] In the majority of cases however, the triazole group simply serves as a covalent linkage with no function in the resulting organic molecular framework. More recently a renewed interest has been shown in the transition metal coordination chemistry of triazole ligands.[3, 5, 6] In addition novel aryl macrocyclic and acyclic triazole based oligomers have been shown to recognise halide anions via cooperative triazole C5-H….anion hydrogen bonds.[7] In light of this it is surprising the potential anion binding affinity of the positively charged triazolium motif has not, with one notable exception,[8] been investigated. With the objective of manipulating the unique topological cavities of mechanically bonded molecules for anion recognition purposes, we have developed general methods of using anions to template the formation of interpenetrated and interlocked structures.[9-13] Herein we report the first examples of exploiting the 1,2,3-triazolium group in the anion templated formation of pseudorotaxane and rotaxane assemblies. In an unprecedented discovery the bromide anion is shown to be a superior templating reagent to chloride in the synthesis of a novel triazolium axle containing [2]rotaxane. Furthermore the resulting rotaxane interlocked host system exhibits the rare selectivity preference for bromide over chloride..
Macrocyclization by Nickel-Catalyzed, Ester-Promoted, Epoxide-Alkyne Reductive Coupling: Total Synthesis of (−)-Gloeosporone

Ringing the changes: The total synthesis of the title compound centers around a novel strategy that employs a nickel(0)–phosphine complex and triethyl borane in an efficient closure of a 14-membered ring through C--C bond formation (see scheme; cod=cyclooctadiene). The synthesis was accomplished in 10 steps and in approximately 9 % overall yield.National Institute of General Medical Sciences (U.S.) (GM-72566)National Science Foundation (U.S.) (CHE-9809061)National Science Foundation (U.S.) (DBI-9729592)National Institutes of Health (U.S.) (1S10RR13866-01
Monitoring Protein Kinases in Cellular Media with Highly Selective Chimeric Reporters

The best of both worlds: Combining a recombinant docking domain (see picture, blue ribbon) with a chemical sensing module (green hexagons) yields a highly selective ERK sensor. This probe exclusively monitors ERK1/2 activity in unfractionated cell lysates without any off-target kinase inhibitors. Good selectivity and biophysical parameters allow high-throughput analysis of ERK1/2 activity without time-consuming enzyme purification.2010 September 13National Institutes of Health (U.S.). Cell Migration Consortium (GM064346)National Science Foundation (U.S.). Biophysical Instrumentation Facility for the Study of Complex Macromolecular Systems (NSF-0070319