PubMed Journal Database | Angewandte Chemie (International ed. in English) 
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Showing PubMed Articles 1–25 of 5,500+ from Angewandte Chemie (International ed. in English)
Improving Hydrothermal Carbonization by Using Poly(ionic liquid)s.
Pores for thought: Porous nitrogen-doped carbon materials (HTC Carbon with PILs) composed of spherical nanoparticles, and also those with Au-Pd core-shell nanoparticles embedded (Au-Pd@N-Carbon) were synthesized. These materials can be prepared from sugars by hydrothermal carbonization (160-200 °C) in the presence of poly(ionic liquid)s (PILs), which act as a stabilizer, pore-generating agent, and nitrogen source.
A simple and straightforward method for the stereocontrolled synthesis of β-linked N-glycosides uses alkyl and aryl azides as the nitrogen source. The N-glycosides are formed in high yields and with high β selectivities (typically >70 % yield, >15:1 β:α selectivity). This approach is also amenable to the synthesis of N-glycosylated amino acids and peptides (see example, Fmoc=9-fluorenylmethoxycarbonyl).
Nanoscale chemical imaging using tip-enhanced Raman spectroscopy: a critical review.
Methods for chemical analysis at the nanometer scale are crucial for understanding and characterizing nanostructures of modern materials and biological systems. Tip-enhanced Raman spectroscopy (TERS) combines the chemical information provided by Raman spectroscopy with the signal enhancement known from surface-enhanced Raman scattering (SERS) and the high spatial resolution of atomic force microscopy (AFM) or scanning tunneling microscopy (STM). A metallic or metallized tip is illuminated by a focused laser...
Iridium-catalyzed enantioselective hydrogenation of unsaturated heterocyclic acids.
Spiral binding: A highly enantioselective hydrogenation of unsaturated heterocyclic acids has been developed by using chiral iridium/spirophosphino oxazoline catalysts (see scheme; BArF (-) =tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, Boc=tert-butoxycarbonyl). This reaction provided an efficient method for the preparation of optically active heterocyclic acids with excellent enantioselectivities.
Silicon swallows up boron: The novel open tetrahedral framework structure (OTF) of the Zintl phase LiBSi2 was made by applying high pressure to a mixture of LiB and elemental silicon. The compound represents a new topology in the B-Si net (called tum), which hosts Li atoms in the channels. LiBSi2 is the first example where B and Si atoms form an ordered common framework structure with B engaged exclusively in heteronuclear BSi contacts.
A 100 % atom-efficient synthesis of ketones from electron-deficient internal olefins was achieved using O2 as a "green" oxidant (see scheme, DMA=N,N-dimethylacetamide, EWG=electron-withdrawing group). Various electron-deficient olefins were oxidized to the corresponding ketones with over 99 % selectivity and without the formation of olefin isomers or their oxidized products.
An aptamer-based strategy was developed for the high-throughput analysis of protein biomarkers, such as lysozyme, by on-target MALDI-TOF MS. The aptamers were immobilized on the target plate through formation of covalent bonds with a stable and porous gold layer. An infrared laser was subsequently applied for fast proteolysis. High sensitivities were observed both in standard solutions and human urine.
General entry to aspidosperma alkaloids: enantioselective total synthesis of (-)-aspidophytine.
A general approach toward the asymmetric total synthesis of various aspidosperma alkaloids includes the combination of a CH bond activation with a Heck-type coupling, and the stereo-controlled formation of piperidine and pyrrolidine rings as key steps. The feasibility of this approach was demonstrated with the total synthesis of aspidophytine in 18 steps from 4,4-disubstituted cyclohexanedione and 2,3-dimethoxyaniline.
Parallel-stacked gold nanowires (NWs) in a ring conformation are induced to coalesce, forming solid seamless rings. The axial lattice orientation of the original Au NWs is preserved in the coalesced rings (see picture; scale bars 2 nm, insets 50 nm). A zipper mechanism is proposed to reconcile the three major events in coalescing nanocrystals: ligand loss, lattice alignment, and coalescence.
Directed amination of non-acidic arene ch bonds by a copper-silver catalytic system.
Amine meets arene: A method for direct amination of β-C(sp(2) )H bonds of benzoic acid derivatives and γ-C(sp(2) )H bonds of benzylamine derivatives has been developed. The reaction is catalyzed by Cu(OAc)2 and a Ag2 CO3 cocatalyst, and shows high generality and functional-group tolerance, as well as providing a straightforward means for the preparation of ortho-aminobenzoic acid derivatives.
The Absolute Configuration of (+)- and (-)-erythro-Mefloquine.
The controversy over the absolute configuration of (+)-erythro-mefloquine, the less psychosis-causing enantiomer of the anti-malarial drug Lariam, has been resolved by Mosher ester crystallization. The configuration determined previously by physical methods is correct, whereas the configuration determined by three enantioselective syntheses is wrong.
The T-helper epitope peptide P30 (green in the scheme) from tetanus toxoid was used as the immunostimulant in MUC1 glycopeptide antitumor vaccines and apparently also acts as a built-in adjuvant. P30-conjugated glycopeptide vaccines containing three glycans in the immunodominant motifs PDTRP and GSTAP induced much stronger immune responses and complement dependent cytotoxicity mediated killing of tumor cells when applied in plain PBS solution without complete Freund's adjuvant.
Mechanical carbohydrate sensors based on soft hydrogel particles.
Elastic sensors: A simple method is presented for the measurement of specific biomolecular interactions with soft colloidal hydrogel particles (SCPs) as sensors. Carbohydrate/lectin interactions (see picture; green: carbohydrate molecules) were studied by optical detection of the mechanical deformation of the particles on a lectin surface. The affinity of various carbohydrate inhibitors could also be readily determined.
A method based on plasmon resonance Rayleigh scattering (PRRS) spectroscopy and dark-field microscopy (DFM) was established for the real-time monitoring of a click reaction at the single-nanoparticle level. Click reactions on the surface of single gold nanoparticles (GNPs) result in interparticle coupling, which leads to a red-shift of the λmax (Δλmax =43 nm) in the PRRS spectra and a color change of the single gold nanoparticles in DFM (from green to orange).
An orientational change from homeotropic to planar of liquid crystal (LC) mesogens and the microphase separation (MPS) domains is attained by the segregated skin layer at the free surface. This allows for an efficient in-plane photoalignment of the cylindrical domains. The surface segregation strategy is very simple and is therefore expected to open up new possibilities for the orientation control of various types of LC materials.
Give it a tweak: A novel oxidizing directing group was developed for a rhodium(III)-catalyzed CH functionalization of N-phenoxyacetamides with alkynes. A small change in the reaction conditions leads to either ortho-hydroxyphenyl-substituted enamides or cyclization to deliver benzofurans with high selectivity (see scheme; Cp*=C5 Me5 ).
Direct growth of a single to a few layers of graphene on a germanium nanowire (Gr/Ge NW; see picture) was achieved by a metal-catalyst-free chemical vapor deposition (CVD) process. The Gr/Ge NW was used as anode in a lithium ion battery. This material has a specific capacity of 1059 mA h g(-1) at 4.0 C, a long cycle life over 200 cycles, and a high capacity retention of 90 %.
Plasmonic and Catalytic AuPd Nanowheels for the Efficient Conversion of Light into Chemical Energy.
Reinventing the wheel: Bimetallic AuPd nanowheels, a freestanding form of 2D AuPd nanostructures, were synthesized in a one-pot process. The well-defined and tunable surface plasmon resonance displayed by these nanowheels was exploited in a unique catalytic process in which light energy was used to drive catalytic reactions, such as the Suzuki coupling, with much higher efficiency than that of the conventional heating process.
Manganese-catalyzed oxidative benzylic C-h fluorination by fluoride ions.
An efficient protocol for the selective fluorination of benzylic CH bonds is described. The process is catalyzed by manganese salen complexes and uses nucleophilic fluorine sources, such as triethylamine trihydrofluoride and KF. Reaction rates are sufficiently high (30 min) to allow adoption for the incorporation of (18) F fluoride sources for PET imaging applications.
Palladium-catalyzed direct ch alkylation of electron-deficient pyrrole derivatives.
The apparent and the real: What looks like a Friedel-Crafts alkylation reaction of electron-deficient pyrroles is actually a Pd(II) -catalyzed, norbornene-mediated CH activation reaction, in which the alkylation of the pyrrole core occurs by reductive elimination. As well as ethyl-1H-pyrrole-2-carboxylate, several other 2,3-disubstituted pyrroles underwent the selective C5 alkylation in good yield.
Prevention of self-quenching in fluorescent silica nanoparticles by efficient energy transfer.
Stars that shine bright: A high local dye concentration in doped silica-based core-shell nanoparticles causes self-quenching and spectral broadening (top images). This phenomenon jeopardizes the potential advantages of heavily doped systems. Förster resonance energy transfer (FRET) to an acceptor co-included in the silica led to ultrabright nanoparticles (bottom images) with a preselected narrow-band emission and a pseudo-Stokes shift of 129 nm.
About phase: The coexistence of rhombohedral LiTMO2 (TM=Ni, Co, or Mn) and monoclinic Li2 MnO3 -like structures inside Li1.2 Mn0.567 Ni0.166 Co0.067 O2 is revealed directly at atomic resolution. The hetero-interface along the [001]rh /[103]mon zone axis direction is demonstrated, indicating the two-phase nature of these lithium-rich cathode materials (green Li, blue Mn, red O, cyan TM).
Fluid catalytic cracking (FCC) is the main conversion process used in oil refineries. An X-ray microscopy method is used to show that metal poisoning and related structural changes in the zeolite active material lead to a non-uniform core-shell deactivation of FCC catalyst particles. The study links the detrimental effect of V and Ni poisoning with zeolite destruction and dealumination in a spatial manner within a single FCC catalyst particle.
A unifying bonding concept for metal hydrosilane complexes.
Experimental and theoretical charge density studies and molecular orbital analyses suggest that the complexes [Cp2 Ti(PMe3 )SiH2 Ph2 ] (1) and [Cp2 Ti(PMe3 )SiHCl3 ] (2) display virtually the same electronic structures. No evidence for a significant interligand hypervalent interaction could be identified for 2. A bonding concept for transition-metal hydrosilane complexes aims to identify the true key parameters for a selective activation of the individual MSi and SiH bonds.
Helical Oligomers of Thiazole-Based γ-Amino Acids: Synthesis and Structural Studies.
9-Helix: 4-Amino(methyl)-1,3-thiazole-5-carboxylic acids (ATCs) were synthesized as new γ-amino acid building blocks. The structures of various ATC oligomers were analyzed in solution by CD and NMR spectroscopy and in the solid state by X-ray crystallography. The ATC sequences adopted a well-defined 9-helix structure in the solid state and in aprotic and protic organic solvents as well as in aqueous solution.
