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PubMed Journal Database | Journal of the American Chemical Society RSS

23:14 EDT 22nd May 2019 | BioPortfolio

The US National Library of Medicine and National Institutes of Health manage PubMed.gov which comprises of more than 29 million records, papers, reports for biomedical literature, including MEDLINE, life science and medical journals, articles, reviews, reports and  books.

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For example view all recent relevant publications on Epigenetics and associated publications and clincial trials.

Showing PubMed Articles 1–25 of 3,200+ from Journal of the American Chemical Society

Formation of Giant and Small Cyclic Complexes from a Flexible Tripeptide Ligand Controlled by Metal Coordination and Hydrogen Bonds.

Formation of giant cyclic complexes by the assembly of small, flexible units is demonstrated by connecting 14 artificial tripeptides (1) with 14 Ni(II) ions. Although tripeptide 1 is very flexible because of the presence of three CH groups in the main chain, it formed a tetradecanuclear cyclic complex ([1Ni]) with a large cavity (diameter: ca. 2 nm). In this structure, three tripeptides are coordinated to each Ni(II) center by three different coordination sites in 1, forming a mesh-like structure. Crystal s...

Excimer-Mediated Intermolecular Charge Transfer in Self-Assembled Donor-Acceptor Dyes on Metal Oxides.

When conjugate molecules are self-assembled on the surface of semiconductors, emergent properties resulting from the electronic coupling between the conjugate moieties are of importance in the interfacial electron transfer dynamics for photoelectrochemical and optoelectronics devices. In this work, we investigate the self-assembly of the triphenylamine-oligothiophene-perylenemonoimide (PMI) molecules, denoted as BH4, on metal oxide surfaces via UV-Vis absorption, photoluminescence, transient near-infrared a...

A Robust Squarate-Based Metal-Organic Framework Demonstrates Record High Affinity and Selectivity for Xenon over Krypton.

The efficient separation of xenon (Xe) and krypton (Kr) is one of industrially important processes. While adsorptive separation of these two species is considered as an energy efficient process, developing highly selective adsorbent remains challenging. Herein, a rigid squarate-based MOF, having a perfect pore size (4.1 Å  4.3 Å) comparable with the kinetic diameter of Xe (4.047 Å) as well as pore surface decorated with very polar hydroxyl groups, is able to effectively discriminate Xe atoms, affordin...

Traceless Photolabile Linker Expedites Chemical Synthesis of Complex Oligosaccharides by Automated Glycan Assembly.

Automated glycan assembly (AGA) aims at accelerating access to synthetic oligosaccharides to meet the demand for defined glycans as tools for molecular glycobiology. The linkers used to connect the growing glycan chain to the solid support play a pivotal role for the synthetic strategy as they determine all chemical conditions used during the synthe-sis and the form of the glycan obtained at the end of it. Here, we describe a traceless photolabile linker to prepare car-bohydrates with a free reducing end. M...

Microporous 3D Covalent Organic Frameworks for Liquid Chromatographic Separation of Xylene Isomers and Ethylbenzene.

Microporous covalent organic frameworks (COFs) hold great potential for small molecule separation, but are yet challenging to design and synthesize. Here we report a framework interpenetration strategy to make microporous COFs for efficient separations of C8 alkyl-aromatic isomers. Two pairs of microporous three-dimensional (3D) salen- and Zn(salen)-based COFs are prepared by Schiff-base condensation of ethanediamine with tetrahedral tetra(salicylaldehyde)-silane or -methane derivatives in the presence or a...

Bacterial cell wall modification with a glycolipid substrate.

Despite the ubiquity and importance of glycans in biology, methods to probe their structures in cells are limited. Mammalian glycans can be modulated using metabolic incorporation, a process in which non-natural sugars are taken up by cells, converted to nucleotide-sugar intermediates, and incorporated into glycans via biosynthetic pathways. Applying this process to bacteria is problematic, as bacteria can acquire and use monosaccharides as carbon sources. Therefore, we sought to develop a strategy that cir...

Charge disproportionation triggers bipolar doping in FeSb2-xSnxSe4 ferromagnetic semiconductors enabling temperature-induced Lifshitz transition.

Ferromagnetic semiconductors (FMSs) featuring high Curie transition temperature (Tc) and strong correlation between itinerant carriers and localized magnetic moments are of tremendous importance for the development of practical spintronic devices. The realization of such materials hinges on the ability to generate and manipulate a high density of itinerant spin-polarized carriers and the understanding of their responses to external stimuli. In this study, we demonstrate the ability to tune magnetic ordering...

The Calyciphylline B-type Alkaloids: Total Syntheses of (-)-Daphlongamine H and (-)-Isodaphlongamine H.

The first total synthesis of the complex hexacylic Daphni-phyllum alkaloid (-)-daphlongamine H has been accom-plished. Key to the success of the strategy are a complexity-building Mannich reaction, efficient cyclizations, and a highly diastereoselective hydrogenation to assemble multigram quan-tities of the tricyclic core bearing four contiguous stereocen-ters. Following construction of the hydro-indene substructure by means of a Pauson-Khand reaction, endgame redox manip-ulations delivered the natural prod...

Generalizable Protein Biosensors Based on Synthetic Switch Modules.

Allosteric protein switches are key controllers of information and energy processing in living organisms and are desirable engineered control tools in synthetic systems. Here we present a generally applicable strategy for construction of allosteric signaling systems with inputs and outputs of choice. We demonstrate conversion of constitutively active enzymes into peptide-operated synthetic allosteric ON switches by insertion of a calmodulin domain into rationally selected sites. Switches based on EGFP, gluc...

The Interplay Between n→π* Interaction and Dynamic Covalent Bond: Quantification and Modulation by Solvent Effects.

Orbital donor-acceptor interactions play critical roles throughout chemistry, and hence, their regulation and functionalization are of great significance. Herein we demonstrate for the first time the investigation of n→π* interaction through the strategy of dynamic covalent chemistry (DCC), and further showcase its use in the stabilization of imine. The n→π* interaction between donor X and acceptor aldehyde/imine within 2-X-2'-formylbiphenyl derivatives was found to significantly influence the thermod...

Direct Intermolecular Anti-Markovnikov Hydroazidation of Unactivated Olefins.

We herein report a direct intermolecular anti-Markovnikov hydroazidation method for unactivated olefins, which is promoted by a catalytic amount of bench-stable benziodoxole at ambient temperature. This method facilitates previously difficult, direct addition of hydrazoic acid across a wide variety of unactivated olefins in both complex molecules and unfunctionalized commodity chemicals. It conveniently fills a gap of existing olefin hydroazidation procedures and thereby provides a valuable tool for azido-g...

Preparation of Chiral Allenes through Pd-Catalyzed Intermolecular Hydroamination of Conjugated Enynes: Enantioselective Synthesis Enabled by Catalyst Design.

In this study, we establish that conjugated enynes undergo selective 1,4-hydroamination under Pd catalysis to deliver chiral allenes with pendant allylic amines. Several primary and secondary aliphatic and aryl-substituted amines couple with a wide range of mono- and disubstituted enynes in a non-enantioselective reaction where DPEphos serves as the ligand for Pd. Benzophenone imine acts as an ammonia surrogate to afford primary amines in a two-step/one-pot process. Examination of chiral catalysts revealed ...

Interfacial construction of plasmonic nanostructures for the utilization of the plasmon-excited electrons and holes.

Surface plasmons (SPs) are able to promote chemical reactions through the participation of the energetic charge carriers produced following plasmons decay. Us-ing p-aminothiophenol (PATP) as a probe molecule, we used surface-enhanced Raman spectroscopy (SERS) to follow the progress of its transformation, in situ, to sys-tematically investigate the role of hot electrons and holes. The energetic carrier mediated PATP oxidation was found to occur even in the absence of oxygen, and was greatly influenced by the...

Directed Evolution of a Cytochrome P450 Carbene Transferase for Selective Functionalization of Cyclic Compounds.

Transfers of carbene moieties to heterocycles or cyclic alkenes to obtain C(sp2)‒H alkylation or cyclopropane products are valuable transformations for synthesis of pharmacophores and chemical building blocks. Through their readily tunable active site geometries, hemoprotein "carbene transferases" could provide an alternative to traditional transition metal catalysts by enabling heterocycle functionalizations with high chemo-, regio- and stereocontrol. However, carbene transferases accepting heterocyclic ...

Palladium/XuPhos-Catalyzed Enantioselective Carboiodination of Olefin-tethered Aryl Iodides.

highly enantioselective palladium-catalyzed iodine atom transfer cycloisomerization of unactivated alkenes has been developed. This represents the first example of highly enantioselective carboio-dination of olefin-tethered aryl iodides, which provides a perfect atom economy method to construct a series of optically active 2,3-dihydrobenzofuran, indolines and chromane bearing an alkyl iodide group in moderate to good yields. Moreover, the use of readily available starting materials, a broad substrate scope,...

Total Synthesis of Caprazamycin A: Practical and Scalable Synthesis of syn-β-Hydroxyamino Acids and Introduction of a Fatty Acid Side Chain to 1,4-Diazepanone.

The first total synthesis of caprazamycin A (1), a representative liponucleoside antibiotic, is described. Diastereoselective aldol reactions of aldehydes 12 and 25-27, derived from uridine, with diethyl isocyanomalonate 13 and phenylcarbamate 21 were investigated using thiourea catalysts 14 or bases to synthesize syn-β-hydroxyamino acid derivatives. The 1,4-diazepanone core of 1 was constructed using a Mitsunobu reaction, and the fatty acid side chain was introduced using a stepwise sequence based on mode...

Hydrogen Bonding Assisted Exogenous Nucleophilic Reagent Effect for β-Selective Glycosylation of Rare 3-Amino Sugars.

Challenges for stereoselective glycosylation of deoxy sugars are notorious in carbohydrate chemistry. We here reported a novel strategy for the construction of the less investigated β-glycosidic bonds of 3,5-trans-3-amino-2,3,6-trideoxysuars (3,5-trans-3-ADSs) which are important components of a few bio-important antibiotics. The strategy took the advantage of the C-3 axial sulfonamide group of 3,5-trans-3-ADSs which served as a hydrogen-bond (H-bond) donor. By introducing sub-stoichiometric amount of phos...

Human DNA Polymerase μ Can Uses a Noncanonical Mechanism for Multiple Mn-mediated Functions.

Recent research on the structure and mechanism of DNA polymerases has continued to generate fundamentally important features, including a noncanonical pathway involving "prebinding" of metal-bound dNTP (MdNTP) in the absence of DNA. While this noncanonical mechanism was shown to be a possible subset for African swine fever DNA polymerase X (Pol X) and human Pol λ it remains unknown whether it could be the primary pathway for a DNA polymerase. Pol μ is a unique member of the X-family with multiple function...

Pd(II) Coordination Sphere Engineering: Pyridine Cages, Quinoline Bowls and Heteroleptic Pills Binding One or Two Fullerenes.

Fullerenes and their derivatives are of tremendous technological relevance. Synthetic access and application are still hampered by tedious purification protocols, peculiar solubility and limited control over regioselective derivatization. We present a modular self-assembly system based on a new low-molecular-weight binding mo-tif, appended by two palladium(II)-coordinating units of different steric demands, to either form a [Pd2L14]4+ cage or unprecedented [Pd2L23(MeCN)2]4+ bowl (with L1 = pyridyl, L2 = qui...

Synthesis and Characterization of Single Phase Metal Dodecaboride Solid Solutions: ZrYB and ZrUB.

Single-phase metal dodecaboride (MB) solid solutions, ZrYB and ZrUB were prepared by arc melting from the pure elements. The phase purity and composition were established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and B and B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to ZrYB were studied and it was found that carbon causes fast cooling and as a result rapid nucleation of grains, as wel...

Ethylenediammonium Based "Hollow" Pb/Sn Perovskites with Ideal-Bandgap Yield Solar Cells with Higher Efficiency and Stability.

The power conversion efficiency (PCE) of halide perovskite solar cells is now comparable to commercial solar cells. These solar cells are generally based on multi-cation mixed-halide perovskite absorbers with non-ideal bandgaps of 1.5 to 1.6 eV. The PCE should be able to rise further if the solar cells could use narrower-bandgap absorbers (1.2-1.4 eV). Reducing the Pb content of the semiconductors without sacrificing performance is also a significant driver in the perovskite solar cell research. Here, we de...

Uniform alignment of non-π-conjugated species enhances deep ultraviolet optical nonlinearity.

The precision of array of laser applications and manipulation on smaller scales are limited by the so-called 200 nm wall, and breakthroughs rely on the discovery of new materials with transparency and phase matchability in the ultraviolet and deep ultraviolet region. Herein, we discover an unprecedented alignment of the asymmetric non-π-conjugated species [PO3F] in NaNH4PO3F·H2O, which allows the best uniform P-F bond orientation that generates a remarkable enhancement of the (010) in-plane anisotropy tha...

Product Selectivity Controlled by Nanoporous Environments in Zeolite Crystals Enveloping Rhodium Nanoparticle Catalysts for CO2 Hydrogenation.

Supported rhodium nanoparticles (NPs) are well known catalyzing methanation in CO2 hydrogenation. Now we have demonstrated that the selectivity in this process can be optimized for CO production by choice of molecular sieve crys-tals as supports. The NPs are enveloped within the crystals with controlled nanopore environments that allow tuning of the catalytic selectivity to minimize methanation and favor the reverse water-gas shift reaction. Pure silica MFI (S-1)-fixed rhodium NPs exhibited maximized CO sel...

Selective acetylene hydrogenation over single-atom alloy nanoparticles by kinetic Monte Carlo.

Single-atom alloys, which are prepared by embedding isolated metal sites in host metals, are promising systems for improved catalyst selectivity. For technical applications, catalysts based on nanoparticles are preferred, thanks to a large surface area. Herein, we investigate acetylene to ethylene hydrogenation using kinetic Monte Carlo simulations based on density functional theory, and compare the performance of Pd/Cu nanoparticles with Pd(111) and Pd/Cu(111). We find that embedding Pd in Cu systems stron...

Tailoring Ultrafast Singlet Fission by Chemical Modification of Phenazinothiadiazoles.

Quantum chemistry and time resolved spectroscopy are applied to rationalize how singlet fission (SF) is affected by systematic chemical modifications introduced in phenazinothiadiazoles (PTD). Substitution of the terminal aromatic ring of TIPS-tetracene by a thiadiazole group leads to a considerable change in the relative energies of its S1 and T1 states. Thus, in contrast to TIPS-tetracene, SF becomes exothermic for various PTD derivatives, which show S1-2T1 energy differences as high as 0.15 eV. This enab...


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