58,929 results match your criteria Journal of the American Chemical Society [Journal]


Towards an atomic-scale understanding of electrochemical interface structure and dynamics.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

For the knowledged-based development of electrochemical processes, a better fundamental understanding of the interfaces between electrodes and electrolytes is necessary. This requires insight into the interface structure and dynamics on the atomic-scale, including that of the liquid electrolyte in the near-surface region, i.e. Read More

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http://dx.doi.org/10.1021/jacs.8b13188DOI Listing
February 2019

1,2-Diazacyclopentane-3,5-diyl Diradicals: Electronic Structure and Reactivity.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Localized singlet diradicals are key intermediates in bond-homolyses. A thorough study of the reactive species is needed to clarify the mechanisms of the homolytic bond-cleavage and formation processes. In general the singlet diradicals are quite short-lived due to the fast radical-radical coupling reactions. Read More

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http://dx.doi.org/10.1021/jacs.8b12254DOI Listing
February 2019
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Mitigation of Hydrophobicity-Induced Immunotoxicity by Sugar Poly(orthoesters).

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Polymeric nanoparticles (NPs) derived from self-assemblies of amphiphilic polymers have demonstrated great potentials in clinical applications. However, there are challenges ahead. Notably, immunotoxicity remains as a major roadblock that deters the NPs further applications. Read More

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http://dx.doi.org/10.1021/jacs.8b12205DOI Listing
February 2019

Strong and Confined Acids Enable a Catalytic Asymmetric Nazarov Cyclization of Simple Divinyl Ketones.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1 , 45470 Mülheim an der Ruhr , Germany.

We report a catalytic asymmetric Nazarov cyclization of simple, acylic, alkyl-substituted divinyl ketones using our recently disclosed strong and confined imidodiphosphorimidate Brønsted acids. The corresponding monocyclic cyclopentenones are formed in good yields and excellent regio-, diastereo-, and enantioselectivities. Further, the chemical utility of the obtained enantiopure cyclopentenones is demonstrated. Read More

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http://dx.doi.org/10.1021/jacs.8b13899DOI Listing
February 2019

MACROCYCLIC PEPTIDES AS DRUG CANDIDATES: RECENT PROGRESS AND REMAINING CHALLENGES.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Peptides as a therapeutic modality attract much attention due to their synthetic accessibility, high degree of specific binding, and the ability to target protein surfaces traditionally considered "undruggable". Unfortunately, at the same time, other pharmacological properties of a generic peptide, such as metabolic stability and cell permeability, are quite poor, which limits the success of de novo discovered biologically active peptides as drug candidates. Here, we review how macrocyclization as well as the incorporation of non-proteogenic amino acids and various conjugation strategies may be utilized to improve on these characteristics to create better drug candidates. Read More

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http://dx.doi.org/10.1021/jacs.8b13178DOI Listing
February 2019
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Highly Efficient Photo- and Electroluminescence from Two-Coordinate Cu(I) Complexes Featuring Nonconventional N-Heterocyclic Carbenes.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

A series of six luminescent two-coordinate Cu(I) complexes were investigated bearing nonconventional N-heterocyclic carbene ligands, monoamido-aminocarbene (MAC*) and diamidocarbene (DAC*), along with carbazolyl (Cz) as well as mono- and dicyano-substituted Cz derivatives. The emission color can be systematically varied over 270 nm, from violet to red, through proper choice of the acceptor (carbene) and donor (carbazolyl) groups. The compounds exhibit photoluminescent quantum efficiencies up to 100% in fluid solution and polystyrene films with short decay lifetimes (τ ≈ 1 μs). Read More

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http://dx.doi.org/10.1021/jacs.8b12397DOI Listing
February 2019

Rational reprogramming O-methylation regioselectivity for combinatorial biosynthetic tailoring of benzenediol lactone scaffolds.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

O-Methylation modulates the pharmacokinetic and pharmacodynamic (PK/PD) properties of small molecule natural products affecting their bioavailability, stability, and binding to targets. Diversity-oriented combinatorial biosynthesis of new chemical entities for drug discovery, and optimization of known bioactive scaffolds during drug development both demand efficient O-methyltransferase (OMT) biocatalysts with considerable substrate promiscuity and tunable regioselectivity that can be deployed in a scalable and sustainable manner. Here we demonstrate efficient total biosynthetic and biocatalytic platforms that use a pair of fungal OMTs with orthogonal regiospecificity to produce unnatural O-methylated benzenediol lactone (BDL) polyketides. Read More

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http://dx.doi.org/10.1021/jacs.8b12967DOI Listing
February 2019

Scalable Total Synthesis of (-)-Vinigrol.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Vinigrol is a structurally and stereochemically complex natural product that displays various potent pharmacological activities, including the capability to modulate TNF-α. A new and efficient synthetic route towards this natural product has been developed to complete the asymmetric synthesis of (-)-vinigrol and provide over 600 mg material, manifesting the power of macrocyclic stereocontrol and transannular Diels-Alder reaction. Read More

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http://dx.doi.org/10.1021/jacs.9b00621DOI Listing
February 2019

Length-selective synthesis of acylglycerol-phosphates through energy-dissipative cycling.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

The main aim of origins of life research is to find a plausible sequence of transitions from prebiotic chemistry to nascent biolo-gy. In this context, understanding how and when phospholipid membranes appeared on early Earth is critical to elucidating the prebiotic pathways that led to the emergence of primitive cells. Here we show that exposing glycerol-2-phosphate to acylating agents leads to the formation of a library of acylglycerol-phosphates. Read More

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http://dx.doi.org/10.1021/jacs.8b12331DOI Listing
February 2019

1,1-Digoldallylium Complexes: Diaurated Allylic Carbocations Indicate New Prospects of the Coordination Chemistry of Carbon.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Reacting (NHC)(cyclopropenyl)gold(I) complexes with cationic gold complexes [(IPr)AuX] afforded extremely reactive allylium-1,1-diido-bridged digold intermediates. We prove the existence and constitution of this structure with FT-ICR-MS/MS, NMR, and UV-Vis-NIR experiments and isolated the nucleophilic addi-tion product [(Me)(Ph)(CCHC){Au(IPr)}2(SOMe2)]NTf2 with DMSO. Our computational investigation unveiled that the bond-ing situation of this -allylium-1,1-diido digold domain was best described as a three-center four electron bond with -backbond. Read More

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http://dx.doi.org/10.1021/jacs.8b13395DOI Listing
February 2019

Cobalt in Nitrogen-Doped Graphene as Single-Atom Catalyst for High-Sulphur Content Lithium-Sulphur Batteries.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Due to their high theoretical energy density and low cost, lithium-sulphur (Li-S) batteries are promising next-generation energy storage devices. The electrochemical performance of Li-S batteries largely depends on the efficient reversible conversion of Li polysulphides to LiS in discharge, and to elemental S during charging. Here, we report on our discovery that monodisperse cobalt atoms embedded in nitrogen-doped graphene (Co-N/G) can trigger the surface-mediated reaction of Li polysulphides. Read More

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http://dx.doi.org/10.1021/jacs.8b12973DOI Listing
February 2019

A KAS-III Heterodimer in Lipstatin Biosynthesis Nondecarboxylatively Condenses C and C Fatty Acyl-CoA Substrates by a Variable Mechanism during the Establishment of a C Aliphatic Skeleton.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

β-Ketoacyl-acyl carrier protein (ACP) synthase-III (KAS-III) and its homologs are thiolase-fold proteins that typically behave as homodimers functioning in diverse thioester-based reactions for C-C, C-O or C-N bond formation. Here, we report an exception observed in the biosynthesis of lipstatin. During the establishment of the C aliphatic skeleton of this β-lactone lipase inhibitor, LstA and LstB, which both are KAS-III homologs but phylogenetically distinct from each other, function together by forming an unusual heterodimer to catalyze a nondecarboxylating Claisen condensation of C and C fatty acyl-CoA substrates. Read More

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http://dx.doi.org/10.1021/jacs.8b12843DOI Listing
February 2019

A Two-Enzyme Pathway Links L-Arginine to Nitric Oxide in N-Nitroso Biosynthesis.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Nitric oxide (NO) has wide-ranging roles in biology, but less is known about its role in building chemical diversity. Here we report a new route to NO from the biosynthetic pathway to the N-nitroso compound streptozocin. We show that the N-nitroso of streptozocin comes from biosynthetic reassembly of L-arginine, with the guanidino nitrogens forming a nitrogen-nitrogen bond. Read More

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http://dx.doi.org/10.1021/jacs.8b13049DOI Listing
February 2019

Zeolitic Intermetallics: LnNiSi (Ln = La-Nd).

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Materials Research Center for Element Strategy , Tokyo Institute of Technology , 4259 Nagatsuta , Midori-ku , Yokohama 226-8503 , Japan.

LnNiSi (Ln = La-Nd) comprising a three-dimensional NiSi framework has electrons in the crystallographic cavity space. In the temperature region 473-773 K, it accepts the insertion/de-insertion of hydrogen topotactically without a change in unitcell volume. The insertion of hydrogens into the cavity space is accompanied by a redox reaction with the orbitals of atoms constituting the cavity wall. Read More

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http://pubs.acs.org/doi/10.1021/jacs.8b12784
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http://dx.doi.org/10.1021/jacs.8b12784DOI Listing
February 2019
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Solution NMR Analysis of Ligand Environment in Quaternary Ammonium-Terminated Self-Assembled Monolayers on Gold Nanoparticles: The Effect of Surface Curvature and Ligand Structure.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

We report a solution NMR-based analysis of (16-mercaptohexadecyl)trimethylammonium bromide (MTAB) self-assembled monolayers (SAMs) on colloidal gold nanospheres (AuNSs) with diameters from 1.2 nm to 25 nm, and gold nanorods (AuNRs) with aspect ratios from 1.4 to 3. Read More

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http://dx.doi.org/10.1021/jacs.8b11445DOI Listing
February 2019

C3N5: A Low Bandgap Semiconductor Containing an Azo-linked Carbon Nitride Framework for Photocatalytic, Photovoltaic and Adsorbent Applications.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of melem hydrazine precursor. Read More

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http://dx.doi.org/10.1021/jacs.9b00144DOI Listing
February 2019

Oxidatively Induced Reductive Elimination: Exploring the Scope and Catalyst Systems with Ir, Rh, and Ru Complexes.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Direct conversion of C-H bonds into C-C bonds is a promising alternative to the conventional cross-coupling reactions, thus giving rise to a wide range of efficient catalytic C-H functionalization reactions. Among the elementary stages in the catalytic C-C bond formation, reductive elimination constitutes a key step of the catalytic cycle, and, therefore, extensive studies have been made to facilitate this process. In this regard, oxidation on the metal center of a post-transmetalation intermediate would be an appealing approach. Read More

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http://dx.doi.org/10.1021/jacs.9b00364DOI Listing
February 2019

Bioinspired Syntheses of Herqulines B and C from Cyclodipeptide Mycocyclosin.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

A bioinspired approach for the syntheses of herqulines B and C is reported that takes advantage of an L-tyrosine-derived diketopiperazine, a mycocyclosin analog, as a synthetic precursor. The strategy relies on a series of consecutive reductions to adjust the mycocyclosin oxidation state to that observed in the herquline class of natural products. The strained and distorted L-tyrosine-based biaryl system characteristic for mycocyclosin is selectively converted to the 1,4-diketone structural motif common to the herqulines via initial hypervalent iodine-mediated dearomatization and a subsequent directed Birch reduction, enabled by an intramolecular H-source. Read More

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http://dx.doi.org/10.1021/jacs.8b13849DOI Listing
February 2019

Measurement of Electric Fields Experienced by Urea Guest Molecules in the 18-Crown-6:Urea (1:5) Host-Guest Complex: An Experimental Reference Point for Electric-Field-Assisted Catalysis.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

High resolution synchrotron and neutron single crystal diffraction data of 18-crown-6:(pentakis)urea measured at 30 K are combined, with the aim to better appreciate the electrostatics associated with intermolecular interactions in condensed matter. With two 18-crown-6 molecules and five different urea molecules in the crystal, this represents the most ambitious combined X-ray/synchrotron and neu-tron experimental charge density analysis to date on a co-crystal or host-guest system incorporating such a large number of unique mole-cules. Dipole moments of the five urea guest molecules in the crystal are enhanced considerably compared with values determined for isolated molecules, and 2D maps of the electrostatic potential and electric field show clearly how the urea molecules are oriented with dipole moments aligned along the electric field exerted by their molecular neighbors. Read More

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http://dx.doi.org/10.1021/jacs.8b12927DOI Listing
February 2019

Machine Learning Identifies Chemical Characteristics that Promote Enzyme Catalysis.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Despite tremendous progress in understanding and engineering enzymes, knowledge of how enzyme structures and their dynamics induce observed catalytic properties is incomplete, and capabilities to engineer enzymes fall far short of industrial needs. Here we investigate the structural and dynamic drivers of enzyme catalysis for the rate-limiting step of the industrially important enzyme ketol-acid reductoisomerase (KARI) and identify a region of the conformational space of the bound enzyme-substrate complex that, when populated, leads to large increases in reactivity. We apply computational statistical mechanical methods that implement transition interface sampling to simulate the kinetics of the reaction and combine this with machine learning techniques from artificial intelligence to select features relevant to reactivity and to build predictive models for reactive trajectories. Read More

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http://dx.doi.org/10.1021/jacs.8b13879DOI Listing
February 2019

Repurposing non-heme iron hydroxylases to enable catalytic nitrile installation through an azido group assistance.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Three mononuclear non-heme iron dependent enzymes, L-Ile 4-hydroxylase, L-Leu 5-hydroxylase and polyoxin dihydroxylase, are reported to catalyze the hydroxylation of L-isoleucine, L-leucine and L-α-amino-δ-carbamoylhydroxyvaleric acid (ACV). In this study we showed that these enzymes can accommodate various leucine isomers and catalyze regiospecific hydroxylation. Based on these results, as a proof-of-concept, we demonstrated that the outcome of the reaction can be redirected by installation of an assisting group within the substrate. Read More

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http://dx.doi.org/10.1021/jacs.8b13906DOI Listing
February 2019

A Catalytic Strategy for Regioselective Arylethylamine Synthesis.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

A mild, modular, and practical catalytic system for synthesis of the highly privileged phenethylamine pharmacophore is reported. Using a unique combi-nation of organic catalysts to promote the transfer of electrons and hydrogen atoms, this system per-forms direct hydroarylation of vinyl amine deriva-tives with a wide range of aryl halides (including aryl chlorides). This general and highly chemose-lective protocol delivers a broad range of arylethyl-amine products with complete regiocontrol. Read More

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http://dx.doi.org/10.1021/jacs.9b01077DOI Listing
February 2019

Caged Nitric Oxide-Thiyl Radical Pairs.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

S-Nitrosothiols (RSNO) are exogenous and endogenous sources of nitric oxide in biological systems due to facile homolytic cleavage of the S-N bonds. By following the photolytic decomposition of prototypical RSNO (R = Me and Et) in Ne, Ar, and N2 matrices (< 10 K), elusive caged radical pairs (RPs) con-sisting of nitric oxide (NO•) and thiyl radicals (RS•), bridged by O···S and H···N connections, have been identified with IR and UV/Vis spectroscopy. Upon red-light irradiation, both caged radical pairs (RS•···•ON) vanish and reform RSNO. Read More

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http://dx.doi.org/10.1021/jacs.8b12746DOI Listing
February 2019

Cysteine-Aminoethylation-Assisted Chemical Ubiquitination of Recombinant Histones.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Tsinghua-Peking Center for Life Sciences, Ministry of Education Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Center for Synthetic and Systems Biology, State Key Laboratory of Chemical Oncogenomics (Shenzhen), Department of Chemistry , Tsinghua University , Beijing 100084 , China.

Histone ubiquitination affects the structure and function of nucleosomes through tightly regulated dynamic reversible processes. The efficient preparation of ubiquitinated histones and their analogs is important for biochemical and biophysical studies on histone ubiquitination. Here, we report the CAACU (cysteine-aminoethylation assisted chemical ubiquitination) strategy for the efficient synthesis of ubiquitinated histone analogs. Read More

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http://dx.doi.org/10.1021/jacs.8b13213DOI Listing
February 2019

13-Step Total Synthesis of Atropurpuran.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Herein, we report a concise total synthesis of atropurpuran, a unique and synthetically challenging pentacyclic diterpene that bears a tetracyclo[5.3.3. Read More

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http://dx.doi.org/10.1021/jacs.9b00391DOI Listing
February 2019

Computationally-Assisted Discovery and Assignment of a Highly Strained and PANC-1 Selective Alkaloid from Alaska's Deep Ocean.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Aleutianamine represents the first in a new class of pyrroloimino-quinone alkaloids possessing a highly strained multi-bridged ring system, discovered from Latrunculia (Latrunculia) austini Samaai, Kelly & Gibbons, 2006 (class Demospongiae, order Poeciloscle-rida, family Latrunculiidae) recovered during a NOAA deep-water exploration of the Aleutian Islands. The molecule was identified with the guidance of MS, NMR, and Molecular Ion Networking (MoIN) analysis. The structure of aleutianamine was determined using extensive spectroscopic analysis in conjunction with compu-tationally-assisted quantitative structure elucidation tools. Read More

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http://dx.doi.org/10.1021/jacs.8b11403DOI Listing
February 2019

Reactivity Profiles of Diazo Amides, Esters, and Ketones in Transition-Metal-Free C-H Insertion Reactions.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Department of Chemistry , The University of Vermont , Burlington , Vermont 05405 , United States.

Vinyl cations derived from diazo ketones participate in transition-metal-free C-H insertion reactions, but the corresponding amide and ester analog exhibit divergent reactivity profiles. Whereas cations formed from diazo ketones undergo a rearrangement and C-H insertion sequence, those from diazo amides do so less efficiently and tend to be competitively trapped before the insertion step occurs. Diazo esters undergo several rearrangement steps and fail to insert. Read More

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http://dx.doi.org/10.1021/jacs.8b12420DOI Listing
February 2019

3d-Metal Induced Magnetic Ordering on U(IV) Atoms as a Route toward U(IV) Magnetic Materials.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Department of Chemistry and Biochemistry , University of South Carolina , Columbia , South Carolina 29208 , United States.

Uranium(IV) 5f magnetism is dominated by a transition from a triplet to a singlet ground state at low temperatures. For the first time, we achieved magnetic ordering of U(IV) atoms in a complex fluoride through the incorporation of 3 d transition metal cations. This new route allowed us to obtain an unprecedented series of U(IV) ferrimagnetic materials of the new composition CsMUF (M = Mn, Co, and Ni), which were comprehensively characterized with respect to their structural and magnetic properties. Read More

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http://dx.doi.org/10.1021/jacs.9b00345DOI Listing
February 2019

Designing solid materials from their solute state: a shift in paradigms towards a holistic approach in functional materials chemistry.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

"Non-classical" notions consider formation pathways of crystalline materials where larger species than monomeric chemical constituents, i.e., ions or single molecules, play crucial roles, which are not covered by the classical theories dating back to the 1870s and 1920s. Read More

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http://dx.doi.org/10.1021/jacs.8b13231DOI Listing
February 2019

Open-Air Alkylation Reactions in Photoredox-Catalyzed DNA-Encoded Library Synthesis.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

Roy and Diana Vagelos Laboratories, Department of Chemistry , University of Pennsylvania , 231 South 34th Street , Philadelphia , Pennsylvania 19104-6323 , United States.

DNA-encoded library (DEL) technology is a powerful tool commonly used by the pharmaceutical industry for the identification of compounds with affinity to biomolecular targets. Success in this endeavor lies in sampling diverse chemical libraries. However, current DELs tend to be deficient in C(sp) carbon counts. Read More

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http://pubs.acs.org/doi/10.1021/jacs.9b00669
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http://dx.doi.org/10.1021/jacs.9b00669DOI Listing
February 2019
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Mechanistic Insights into Ruthenium-Pincer-Catalyzed Amine-Assisted Homogeneous Hydrogenation of CO to Methanol.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

Loker Hydrocarbon Research Institute and Department of Chemistry , University of Southern California , University Park, Los Angeles , California 90089-1661 , United States.

Amine-assisted homogeneous hydrogenation of CO to methanol is one of the most effective approaches to integrate CO capture with its subsequent conversion to CHOH. The hydrogenation typically proceeds in two steps. In the first step the amine is formylated via an in situ formed alkylammonium formate salt (with consumption of 1 equiv of H). Read More

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http://dx.doi.org/10.1021/jacs.8b12763DOI Listing
February 2019

KLi(HCNO)·2HO: Solvent-drop Grinding Method toward the Hydro-isocyanurate Nonlinear Optical Crystal.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

Key Laboratory of Optoelectronic Materials Chemistry and Physics , Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences , Fuzhou , Fujian 350002 , China.

A novel mixed alkali hydro-isocyanurate, KLi(HCNO)·2HO was first prepared in AOH-BOH-HCNO (A/B = Li/Na/K/Rb/Cs) system via a solvent-drop grinding method. KLi(HCNO)·2HO shows a large second harmonic generation response (5.3 × KHPO) with an ultraviolet cutoff edge of 237 nm. Read More

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http://pubs.acs.org/doi/10.1021/jacs.8b13280
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http://dx.doi.org/10.1021/jacs.8b13280DOI Listing
February 2019
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Spatially Selective and Density-Controlled Activation of Interfacial Mechanophores.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

Mechanically sensitive molecules known as mechanophores have recently attracted much interest due to the need for mechanoresponsive materials. Maleimide-anthracene mechanophores located at the interface between poly(glycidyl methacrylate) (PGMA) polymer brushes and Si wafer surfaces were activated locally using atomic force microscopy (AFM) probes to deliver mechanical stimulation. Each individual maleimide-anthracene mechanophore exhibits binary behavior: undergoing a retro [4+2] cycloaddition reaction under high load to form a surface-bound anthracene moiety and free PGMA, or remaining unchanged if the load falls below the activation threshold. Read More

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http://dx.doi.org/10.1021/jacs.8b10257DOI Listing
February 2019

Catalytic Enantioselective Hetero-[6+4] and -[6+2] Cycloadditions for the Construction of Condensed Polycyclic Pyrroles, Imidazoles, and Pyrazoles.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

Department of Chemistry , Aarhus University , DK-8000 Aarhus C , Denmark.

The development of the first chemo-, regio-, and stereoselective hetero-[6+4] and -[6+2] cycloadditions of heteroaromatic compounds via amino aza- and diazafulvenes is presented. Pyrroles, imidazoles, and pyrazoles substituted with a formyl group react with an aminocatalyst to generate an electron-rich hetero-6π-component that reacts in a chemo-, regio-, and stereoselective manner with electron-deficient dienes and olefins. For the hetero-[6+4] cycloaddition of the pyrrole system with dienes, a wide variation of both reaction partners is possible, providing attractive pyrrolo-azepine products in high yields and excellent enantioselectivities (99% ee). Read More

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http://dx.doi.org/10.1021/jacs.8b13659DOI Listing
February 2019

Mechanosensitive Fluorescent Probes to Image Membrane Tension in Mitochondria, Endoplasmic Reticulum, and Lysosomes.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

School of Chemistry and Biochemistry and ‡National Centre of Competence in Research (NCCR) Chemical Biology , University of Geneva , CH-1211 Geneva , Switzerland.

Measuring forces inside cells is particularly challenging. With the development of quantitative microscopy, fluorophores which allow the measurement of forces became highly desirable. We have previously introduced a mechanosensitive flipper probe, which responds to the change of plasma membrane tension by changing its fluorescence lifetime and thus allows tension imaging by FLIM. Read More

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http://dx.doi.org/10.1021/jacs.8b13189DOI Listing
February 2019

Coordination Chemistry of a Molecular Pentafoil Knot.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

The binding of Zn(II) cations to a pentafoil (51) knotted ligand allows the synthesis of otherwise inaccessible metallated molecular pentafoil knots via transmetallation, affording the corresponding 'first sphere' coordination Co(II), Ni(II) and Cu(II) pentanuclear knots in good yields (≥85 %). Each of the knot complexes was characterized by mass spectrometry, the diamagnetic (zinc) knot complex was characterized by 1H and 13C NMR spectroscopy, and the zinc, cobalt and nickel pentafoil knots afforded single crystals whose structures were determined by X-ray crystallography. Lehn-type circular helicates generally only form with tris-bipy ligand strands and Fe(II) (and, in some cases, Ni(II) and Zn(II)) salts, so such architectures become accessible for other metal cations only through the use of knotted ligands. Read More

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http://dx.doi.org/10.1021/jacs.8b12548DOI Listing
February 2019

Direct Quantification of Rapid and Efficient Single-Stroke Actuation by a Martensitic Transition in a Thermosalient Crystal.

J Am Chem Soc 2019 Feb 14. Epub 2019 Feb 14.

New York University Abu Dhabi , P.O. Box 129188, Abu Dhabi , United Arab Emirates.

Molecular dynamic crystals conveniently combine flexibility required for mechanical reconfiguration, strength for effective translation of elastic energy, and long-range order of mechanically coupled molecules for rapid conversion of disordered motion (heat) or photons (light) into ordered motion (work). By direct measurement of the actuation force generated by crystals of a thermosalient solid, here we describe the first direct quantification of the work performed and energy conversion that can be accomplished by using dynamic crystals as supramolecular actuators. Upon reversible α-to-γ phase transition, crystals of (phenylazophenyl)palladium hexafluoroacetylacetonate of submillimeter to millimeter size exert forces in the range of 1-100 mN upon longitudinal and lateral expansion. Read More

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http://dx.doi.org/10.1021/jacs.8b12752DOI Listing
February 2019

Solvent-Free Secondary Growth of Highly b-Oriented MFI Zeolite Films from Anhydrous Synthetic Powder.

J Am Chem Soc 2019 Feb 12. Epub 2019 Feb 12.

Zhejiang Provincial Key Laboratory of Advanced Chemical Engineering Manufacture Technology, College of Chemical and Biological Engineering , Zhejiang University , Hangzhou 310027 , P. R. China.

Up to date, zeolite films have been mainly fabricated by in situ crystallization, secondary growth in a solution/hydrogel, or occasionally by vapor phase transformation of dry gel. Here we demonstrate for the first time a solvent-free secondary growth method for b-oriented silica MFI zeolite films using the synthetic powder from ground anhydrous raw solids in the presence of NHF. Typically, precisely b-oriented MFI zeolite films are synthesized from seed layers of highly b-oriented MFI zeolite crystals in the synthetic powder of 1SiO:0. Read More

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http://pubs.acs.org/doi/10.1021/jacs.9b00018
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http://dx.doi.org/10.1021/jacs.9b00018DOI Listing
February 2019
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Resonance Theory Reboot.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

What is now called "resonance theory" has a long and conflicted history. We first sketch the early roots of resonance theory, its heritage of diverse physics and chemistry conceptions, and its subsequent rise to reigning chemical bonding paradigm of the mid-20th-century. We then outline the alternative "natural" pathway to localized Lewis- and resonance-structural conceptions that was initiated in the 1950s, given semi-empirical formulation in the 1970s, recast in ab initio form in the 1980s, and successfully generalized to multi-structural "natural resonance theory" (NRT) form in the 1990s. Read More

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http://dx.doi.org/10.1021/jacs.8b12336DOI Listing
February 2019

Nickel-catalyzed Enantioselective Hydroarylation and Hydroalkenylation of Styrenes.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis , Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences , 345 Lingling Lu , Shanghai 200032 , China.

We have developed a Ni-catalyzed enantioselective hydroarylation of styrenes with arylboronic acids using MeOH as the hydrogen source, providing an efficient method to access 1,1-diarylalkanes, which are essential structural units in many biologically active compounds. In addition, Ni-catalyzed enantioselective hydrovinylation of styrenes with vinylboronic acids is also realized with good yields and enantioselectivities. The synthetic utility was demonstrated by the efficient synthesis of ( R)-(-)-ibuprofen. Read More

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http://dx.doi.org/10.1021/jacs.8b13524DOI Listing
February 2019

Photoactivatable Organic Semiconducting Pro-nanoenzymes.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

Therapeutic enzymes hold great promise for cancer therapy; however, in vivo remote control of enzymatic ac-tivity to improve their therapeutic specificity remains challenging. This study reports the development of an organic semiconducting pro-nanoenzyme (OSPE) with a photoactivatable feature for metastasis-inhibited can-cer therapy. Upon near-infrared (NIR) light irradiation, this pro-nanoenzyme not only generates cytotoxic sin-glet oxygen (1O2) for photodynamic therapy (PDT), but also triggers a spontaneous cascade reaction to induce the degradation of ribonucleic acid (RNA) specifically in tumor microenvironment. Read More

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http://pubs.acs.org/doi/10.1021/jacs.8b13507
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http://dx.doi.org/10.1021/jacs.8b13507DOI Listing
February 2019
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Anomalous Halogen-Halogen Interaction Assists Radial Chromophoric Assembly.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

The design of highly efficient supramolecular architectures that mimic competent natural systems requires a comprehensive knowledge of noncovalent interactions. Halogen bonding is an excellent noncovalent interaction that forms halogen-halogen (X) as well as trihalogen interacting synthons. Herein, we report the first observation of a symmetric radial assembly of chromophores ( R-3 c space group) composed of a stable hexabromine interacting synthon (Br) that further push the limits of our understanding on the nature, role and potential of noncovalent halogen bonding. Read More

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http://dx.doi.org/10.1021/jacs.8b13754DOI Listing
February 2019

Stability Effect of Quinary Interactions Reversed by Single Point Mutations.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

In cells, proteins are embedded in a crowded environment that controls their properties via manifold avenues including weak protein-macromolecule interactions. A molecular level understanding of these quinary interactions and their contribution to protein stability, function and localization in the cell is central to modern structural biology. Using a mutational analysis to quantify the energetic contributions of single amino acids to the stability of the ALS related protein superoxide dismutase I (SOD1) in mammalian cells, we show that quinary interactions destabilize SOD1 by a similar energetic offset for most of the mutants, but there are notable exceptions: Mutants that alter its surface properties can even lead to a stabilization of the protein in the cell compared to the test tube. Read More

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http://pubs.acs.org/doi/10.1021/jacs.8b13025
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http://dx.doi.org/10.1021/jacs.8b13025DOI Listing
February 2019
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Selective, Fast-Response, and Regenerable Metal-Organic Framework for Sampling Excess Fluoride Levels in Drinking Water.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

Laboratory of Molecular Simulation (LSMO) and ‡Electronic Workshop, Institut des Sciences et Ingénierie Chimiques (ISIC) , Ecole Polytechnique Fédérale de Lausanne (EPFL Valais) , Rue de l'Industrie 17 , 1951 Sion , Switzerland.

Prolonged consumption of water contaminated with fluoride ions (F) at concentrations exceeding 1.5 ppm can lead to considerable health implications, particularly in children and developing embryos. With irreversible and potentially severe forms of fluoride (F) toxicity such as skeletal fluorosis being endemic in at least 25 countries, constructing affordable, remote-access, reliable water-sampling methods for F contamination is an important goal. Read More

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http://dx.doi.org/10.1021/jacs.8b11907DOI Listing
February 2019
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Experimental Evidence for p K-Driven Asynchronicity in C-H Activation by a Terminal Co(III)-Oxo Complex.

J Am Chem Soc 2019 Feb 9. Epub 2019 Feb 9.

C-H activation by transition metal oxo complexes is a fundamental reaction in oxidative reactivity by both biological and synthetic systems. This centrality has motivated efforts to understand the patterns and mechanisms of such reactivity. We have therefore thoroughly examined the C-H activation reactivity of the recently synthesized and characterized late transition metal oxo complex PhB(tBuIm)3CoIIIO. Read More

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http://dx.doi.org/10.1021/jacs.8b13490DOI Listing
February 2019

Superconductivity in BiOSCl with Bi-Cl Planar Layers.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences , Beijing 100190 , People's Republic of China.

A quaternary compound BiOSCl, which consists of novel [BiSCl] layers, is reported. It adopts a layered structure of the space group I4/ mmm (No. 139) with lattice parameters: a = 3. Read More

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http://dx.doi.org/10.1021/jacs.8b13796DOI Listing
February 2019

Self-Assembling Micelles Based on an Intrinsically Disordered Protein Domain.

J Am Chem Soc 2019 Feb 11. Epub 2019 Feb 11.

The self-assembly of micellar structures from di-block polymers that contain hydrophilic and hydrophobic domains has been of great interest for the encapsulation of drugs and other hydrophobic molecules. While most commercially used surfactants are derived from hydrocarbon sources, there have been recent efforts to replace these with biodegradable, non-toxic, biologically synthesized alternatives. Previous examples have primarily examined naturally occurring self-assembling-proteins, such as silk and elastin-like sequences. Read More

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http://dx.doi.org/10.1021/jacs.8b10688DOI Listing
February 2019
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Fluorinated Aromatic Monomers as Building Blocks To Control α-Peptoid Conformation and Structure.

J Am Chem Soc 2019 Feb 15. Epub 2019 Feb 15.

Department of Chemistry , Durham University , South Road , Durham DH1 3LE , U.K.

Peptoids are peptidomimetics of interest in the fields of drug development and biomaterials. However, obtaining stable secondary structures is challenging, and designing these requires effective control of the peptoid tertiary amide cis/trans equilibrium. Herein, we report new fluorine-containing aromatic monomers that can control peptoid conformation. Read More

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http://dx.doi.org/10.1021/jacs.8b13498DOI Listing
February 2019

Ambient Reductive Amination of Levulinic Acid to Pyrrolidones over Pt Nanocatalysts on Porous TiO2 Nanosheets.

J Am Chem Soc 2019 Feb 10. Epub 2019 Feb 10.

Construction of N-substituted pyrrolidones from biomass-derived levulinic acid (LA) via reductive amination is a highly attractive route for biomass valorization. However, realizing this transformation using H2 as the hydrogen source under mild conditions is still very challenging. Herein, we designed porous TiO2 nanosheets supported Pt nanoparticles (Pt/P-TiO2) as the heterogeneous catalyst. Read More

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http://dx.doi.org/10.1021/jacs.8b13024DOI Listing
February 2019

One-Pot Synthesis of High-Quality Bimagnetic Core/Shell Nanocrystals with Diverse Exchange Coupling.

J Am Chem Soc 2019 Feb 13. Epub 2019 Feb 13.

Beijing National Laboratory for Molecular Science , Institute of Chemistry, Chinese Academy of Sciences , CAS Research/Education Center for Excellence in Molecular Sciences, Zhongguancun North First Street 2 , Beijing 100190 , China.

Exchange coupled bimagnetic core/shell nanoparticles are promising for emerging multiferroic and spintronic technologies compared with traditional, single-phase materials, as they deliver numerous appealing effects, such as large exchange bias, tailored coercivities, and tunable blocking temperatures. However, it remains a challenge to manipulate their magnetic properties via exchange coupling due to the lack of a straightforward method that enables the general preparation of desired composites. Here we report a robust and general one-pot approach for the synthesis of different kinds of bimagnetic core/shell nanostructures (BMCS NSs). Read More

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http://dx.doi.org/10.1021/jacs.8b12888DOI Listing
February 2019