PubMed Journal Database | Chemistry (Weinheim an der Bergstrasse, Germany) 
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Showing PubMed Articles 1–25 of 4,400+ from Chemistry (Weinheim an der Bergstrasse, Germany)
Noncanonical peptides occur frequently in Nature, and often display high bioactivity. However, the lack of tractable systems for the synthesis of diverse libraries of such peptides has thus far hampered their development as drugs. Genetic reprogramming techniques, in which noncanonical amino acids may be incorporated into peptides, have largely removed this limitation. This Concept article outlines the development of these techniques with an emphasis on drug discovery.
Hierarchical Fe3 O4 @TiO2 Yolk-Shell Microspheres with Enhanced Microwave-Absorption Properties.
A facile and efficient strategy for the synthesis of hierarchical yolk-shell microspheres with magnetic Fe3 O4 cores and dielectric TiO2 shells has been developed. Various Fe3 O4 @TiO2 yolk-shell microspheres with different core sizes, interstitial void volumes, and shell thicknesses have been successfully synthesized by controlling the synthetic parameters. Moreover, the microwave absorption properties of these yolk-shell microspheres, such as the complex permittivity and permeability, were investigated. T...
The local symmetry and local magnetic properties of 6 nm-sized, bimetallic, cyanide-bridged CsNiCr(CN)6 coordination nanoparticles 1 and 8 nm-sized, trimetallic, CsNiCr(CN)6 @CsCoCr(CN)6 core-shell nanoparticles 2 were studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The measurements were performed at the Ni(II) , Co(II) , and Cr(III) L2,3 edges. This study revealed the presence of distorted Ni(II) sites located on the particle surface of 1 that account for th...
Novel bay-functionalized perylene diimides with additional substitution sites close to the perylene core have been prepared by the reaction between 1,7(6)-dibromoperylene diimide 6 (dibromo-PDI) and 2-(benzyloxymethyl)pyrrolidine 5. Distinct differences in the chemical behaviors of the 1,7- and 1,6-regioisomers have been discerned. While the 1,6-dibromo-PDI produced the corresponding 1,6-bis-substituted derivative more efficiently, the 1,7-dibromo-PDI underwent predominant mono-debromination, yielding a mon...
We report herein a simple and efficient approach to the synthesis of a variety of meso-substituted purpurinimides. The reaction of meso-substituted purpurinimide with N-bromosuccinimide regioselectively introduced a bromo functionality at the 20-position, which on further reaction with a variety of boronic acids under Suzuki reaction conditions yielded the corresponding meso-substituted analogues. Interestingly, the free base and the metalated analogues showed remarkable differences in photosensitizing effi...
Properties of a tunable multinuclear nickel polyoxotungstate platform.
A series of hybrid nickel bisphosphonate (BP) polyoxometalates (POMs) has been isolated. The complexes NaK-Ni7 -Ale2 (Ale=[H2 O3 PC(C3 H6 NH2 )(OH)PO3 H2 ]) and NaNH4 -Ni7 -Ale2 are both made of two {PW9 O34 } fragments enclosing a heptanuclear Ni(II) core connected to two alendronate ligands. By pre-functionalising the alendronate moiety through the amino group, the naphthalene (napht) derivative Ni7 -(AleNapht)2 and the compounds Ni7 -(AlePy2 Ni)2 (py=pyridyl) and Ni7 -(AleAc2 Ni)2 (Ac=acyl) have been obt...
The synthesis of six new [2+2] metallarectangles through the coordination-driven self-assembly of octahedral Ru(II) -based acceptors with ambidentate pyridyl-carboxylate donors is described. These molecular rectangles are fully characterized by (1) H NMR spectroscopy, high-resolution electrospray mass spectrometry, and single-crystal X-ray diffraction. In each case, despite the possible formation of multiple isomers, based on the relative orientation of the pyridyl and carboxylate groups (head-to-head ver...
Crystals of MIL-88B-Fe and NH2 -MIL-88B-Fe were prepared by a new rapid microwave-assisted solvothermal method. High-purity, spindle-shaped crystals of MIL-88B-Fe with a length of about 2 μm and a diameter of 1 μm and needle-shaped crystals of NH2 -MIL-88B-Fe with a length of about 1.5 μm and a diameter of 300 nm were produced with uniform size and excellent crystallinity. The possibility to reduce the as-prepared frameworks and the chemical capture of carbon monoxide in these materials was studi...
Heptametallic, octupolar nonlinear optical chromophores with six ferrocenyl substituents.
New complexes with six ferrocenyl (Fc) groups connected to Zn(II) or Cd(II) tris(2,2'-bipyridyl) cores are described. A thorough characterisation of their BPh4 (-) salts includes two single-crystal X-ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(Fe(II) )→π* metal-to-ligand charge-transfer (MLCT) bands accompany the π→π* intraligand charge-transfer absorptions in the near UV region. Each complex shows a single, fully reversible Fe(III/II) wave...
Glycerol is converted to a mixture of butyric and isobutyric acid by rhodium- or iridium-catalysed carbonylation using HI as the co-catalyst. The initial reaction of glycerol with HI results in several intermediates that lead to isopropyl iodide, which upon carbonylation forms butyric and isobutyric acid. At low HI concentration, the intermediate allyl iodide undergoes carbonylation to give vinyl acetic acid and crotonic acid. Higher polyols Cn Hn+2 (OH)n are carbonylated to the corresponding Cn+1 mono-carb...
A detailed mechanistic study of the hydroxylation of alkane CH bonds using H2 O2 by a family of mononuclear non heme iron catalysts with the formula [Fe(II) (CF3 SO3 )2 (L)] is described, in which L is a tetradentate ligand containing a triazacyclononane tripod and a pyridine ring bearing different substituents at the α and γ positions, which tune the electronic or steric properties of the corresponding iron complexes. Two inequivalent cis-labile exchangeable sites, occupied by triflate ions, complete...
Translation initiation is a dynamic and complicated process requiring the building a 70S initiation complex (70S-IC) composed of a ribosome, mRNA, and an initiator tRNA. During the formation of the 70S-IC, initiation factors (IFs: IF1, IF2, and IF3) interact with a ribosome to form a 30S initiation complex (30S-IC) and a 70S-IC. Although some spectroscopic analyses have been performed, the mechanism of binding and dissociation of IFs remains unclear. Here, we employed a 27 MHz quartz crystal microbalance...
Herein, we report a unique structural property of 2,4,6-tri-tert-butylanilide, which can be separated into its amide rotamers at room temperature. Interconversion between the rotamers of anilide enolates occurs readily at room temperature and their reaction with electrophiles gives mixtures of the rotamers in a ratio that depends on the reactivity of the corresponding electrophile. That is, the reaction of the 2,4,6-tri-tert-butylacetanilide enolate with reactive electrophiles, such as allyl bromide or prot...
The syntheses of the transition metal complexes cis-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)2 MX2 ] (1, M=Pd, X=Cl; 2, M=Pd, X=Br; 3, M=Pd, X=I; 4, M=Pt, X=Cl), cis-[{2,6-(Me2 NCH2 )2 C6 H3 SnCl}2 MX2 ] (5, M=Pd, X=I; 6, M=Pt, X=Cl), trans-[{2,6-(Me2 NCH2 )2 C6 H3 SnI}2 PtI2 ] (7) and trans-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)PdI2 ]2 (8) are reported. Also reported is the serendipitous formation of the unprecedented complexes trans-[(4-tBu-2,6-{P(O)(OiPr)2 }2 C6 H2 SnCl)2 Pt(SnCl3 )2 ] (10) and [(4-tBu-2,...
Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless "click-chemistry" reaction, two series of sulfonyl-based high-generation NLO dendrimers were conveniently prepared with high purity and in satisfactory yields. Thanks to the perfect three-dimensional (3D) spatial isolation from the highly branched structure and the isolation effect of the exterior benzene moieties and the interior triazole rings, these dendrimers exhibited large second...
Total synthesis and biological evaluation of grassypeptolide a.
Herein, we describe in full our investigations into the synthesis of grassypeptolide A (1) in 17 linear steps with an overall yield of 11.3 %. In particular, this work features the late-stage introduction of sensitive bis(thiazoline) heterocycles and 31-membered macrocyclization conducted at the sterically congested secondary amide site in superb conversion (72 % yield). Biological evaluation indicated that grassypeptolide A significantly inhibited cancer cell proliferation in a dose-dependent manner....
Computational Study on the Attack of (.) OH Radicals on Aromatic Amino Acids.
The attack of hydroxyl radicals on aromatic amino acid side chains, namely phenylalanine, tyrosine, and tryptophan, have been studied by using density functional theory. Two reaction mechanisms were considered: 1) Addition reactions onto the aromatic ring atoms and 2) hydrogen abstraction from all of the possible atoms on the side chains. The thermodynamics and kinetics of the attack of a maximum of two hydroxyl radicals were studied, considering the effect of different protein environments at two diffe...
A general procedure for the assembly of hetero-bifunctional cubic silsesquioxanes with diverse functionality and a perfectly controlled distribution of functional groups on the inorganic framework has been developed. The method is based on a two-step sequence of mono- and hepta-functionalization through the ligand-accelerated copper(I)-catalyzed azide-alkyne cycloaddition of a readily available octaazido cubic silsesquioxane. The stoichiometry of the reactants and the law of binomial distribution essentiall...
In Situ Deprotection and Incorporation of Unnatural Amino Acids during Cell-Free Protein Synthesis.
The S30 extract from E. coli BL21 Star (DE3) used for cell-free protein synthesis removes a wide range of α-amino acid protecting groups by cleaving α-carboxyl hydrazides; methyl, benzyl, tert-butyl, and adamantyl esters; tert-butyl and adamantyl carboxamides; α-amino form-, acet-, trifluoroacet-, and benzamides; and side-chain hydrazides and esters. The free amino acids are produced and incorporated into a protein under standard conditions. This approach allows the deprotection of amino acids to be carr...
Acetylcholinesterase (AChE) inhibition is one of the most currently available therapies for the management of Alzheimer's disease (AD) symptoms. In this context, NMR spectroscopy binding studies were accomplished to explain the inhibition of AChE activity by Salvia sclareoides extracts. HPLC-MS analyses of the acetone, butanol and water extracts eluted with methanol and acidified water showed that rosmarinic acid is present in all the studied samples and is a major constituent of butanol and water extracts....
The reactivity of the two diatomic congeneric systems [CO](.+) and [SiO](.+) towards methane has been investigated by means of mass spectrometry and quantum-chemical calculations. While [CO](.+) gives rise to three different reaction channels, [SiO](.+) reacts only by hydrogen-atom transfer (HAT) from methane under thermal conditions. A theoretical analysis of the respective HAT processes reveals two distinctly different mechanistic pathways for [CO](.+) and [SiO](.+) , and a comparison to the higher metal...
An Umpolung approach, in which a phosphorus ylide moiety was introduced to increase the electron density of the double bond, was developed to activate electron-deficient alkenes for reaction with electrophilic iron carbenes. In tandem with the Wittig reaction, the reactions of α,β-unsaturated esters with in situ generated Fecarbene complexes delivered formal CH insertion products through cyclopropanation/ring-opening reactions. DFT calculations and cross-experiments indicate that, in this process, t...
Heparan sulfates (HS) are a class of sulfated polysaccharides that function as dynamic biological regulators of the functions of diverse proteins. The structural basis of these interactions, however, remains elusive, and chemical synthesis of defined structures represents a challenging but powerful approach for unravelling the structure-activity relationships of their complex sulfation patterns. HS has been shown to function as an inhibitor of the β-site cleaving enzyme β-secretase (BACE1), a protease res...
The first catalytic enantioselective 1,3-dipolar cycloaddition of azomethine ylides to α-aminoacrylate catalyzed by a AgOAc/ferrocenyl oxazolinylphosphine (FOXAP) system was developed, which exhibits excellent exo- and enantioselectivity (92-99 % ee). This process provides efficient access to useful 4-aminopyrrolidine-2,4-dicarboxylic acid (APDC)-like compounds containing a unique quaternary α-amino acid unit.
Shine light on your chemistry! Irradiating 3-(4-methoxyphenyl)-3-(trifluoromethyl)-3H-diazirine in the presence of equimolar solutions of phenol and tyrosine derivatives leads to Friedel-Crafts alkylations, which suggests a strategy for the development of "cleaner" diazirines for chemical biology.
