Search results for "Organic Chemical"
showing 10 items of 733 documents
Impact of α,β-dehydroamino acid residues on the binding abilities of di-, tri- and tetra-peptides
2000
Insertion of a dehydroamino acid residue into a sequence of di-, tri- or tetra-peptide changed considerably the binding abilities of peptide ligands towards copper(II) ions. Potentiometric and spectroscopic (EPR, UV-VIS and CD) data have shown that the amide nitrogen of the dehydroamino acid residue is more effective in co-ordination than its parent analogue. In the case of the bulky ΔPhe residue also the (Z–E) isomerisation has a critical impact on the co-ordination equilibria in the system studied.
THE OCCURRENCE OF CHROMIUM IN RAW MATERIALS AND ITS FATE IN THE BREWING PROCESS
1987
The chromium content of raw materials, intermediate and final products in the brewing process were determined in order to evaluate the contribution of raw materials to the chromium content of beer. The contribution due to beer in the diet is considered in the light of the recommended daily intake of chromium.
IP 3 signalling regulates exogenous RNA i in C aenorhabditis elegans
2015
RNA interference (RNAi) is a widespread and widely exploited phenomenon. Here, we show that changing inositol 1,4,5-trisphosphate (IP3) signalling alters RNAi sensitivity in Caenorhabditis elegans. Reducing IP3 signalling enhances sensitivity to RNAi in a broad range of genes and tissues. Conversely up-regulating IP3 signalling decreases sensitivity. Tissue-specific rescue experiments suggest IP3 functions in the intestine. We also exploit IP3 signalling mutants to further enhance the sensitivity of RNAi hypersensitive strains. These results demonstrate that conserved cell signalling pathways can modify RNAi responses, implying that RNAi responses may be influenced by an animal's physiology…
Halogen bonding and host–guest chemistry between N-alkylammonium resorcinarene halides, diiodoperfluorobutane and neutral guests
2019
Single crystal X-ray structures of halogen-bonded assemblies formed between host N-hexylammonium resorcinarene bromide (1) or N-cyclohexylammonium resorcinarene chloride (2), and 1,4-diiodooctafluorobutane and accompanying small solvent guests (methanol, acetonitrile and water) are presented. The guests’ inclusion affects the geometry of the cavity of the receptors 1 and 2, while the divalent halogen bond donor 1,4-diiodooctafluorobutane determines the overall nature of the halogen bond assembly. The crystal lattice of 1 contains two structurally different dimeric assemblies A and B, formally resulting in the mixture of a capsular dimer and a dimeric pseudo-capsule. 1H and 19F NMR analyses …
ChemInform Abstract: Gold(I)-Catalyzed Intermolecular Oxyarylation of Alkynes: Unexpected Regiochemistry in the Alkylation of Arenes.
2010
The reaction between acetylenes and sulfoxides, studied as a test case for gold-catalyzed intermolecular addition, provides the oxyarylation compounds 3 in good yields. Unpredictably, in all cases a single regioisomer arising from the electrophilic aromatic alkylation at the position adjacent to the sulfur atom is obtained instead of the expected Friedel−Crafts regioisomer. A new concerted mechanism based on DFT calculations is proposed to account for the products in this intermolecular gold(I)-catalyzed reaction.
Efficient ethylene polymerisation catalysis by a cationic benzyl hafnium complex containing pyrrolide-imine ligandsElectronic supplementary informati…
2002
A dibenzyl hafnium(IV) complex containing pyrrolide-imine chelate ligands was synthesized and investigated as an ethylene polymerisation catalyst.
Precatalyst or dosing-device? The [Pd2{μ-(C6H4) PPh2}2{μ-O2C(C6H5)}2] complex anchored on a carboxypolystyrene polymer as an effective supplier of pa…
2020
Abstract A new catalyst has been synthesized from the precursor [Pd2{μ-(C6H4) PPh2}2 {μ-O2C(C6H5)}2] immobilized on a carboxypolystyrene polymer that exhibits an excellent dispersion of the Pd (II) centers, reusability, and catalytic activity in front of phenyl bromides. The activity of this new material was studied in detail for the Suzuki-Miyaura reaction and compared to that of Pd nanoparticles (NPs) supported on UVM-7 (a mesoporous silica), and Pd NPs stabilized with polyvinylpirrolydone. The homogeneous/heterogeneous character of the catalytic process was determined from the results of the hot-filtration, centrifugation, poisoning, three phases tests, and from differential sensitivity …
An unexpected ring carboxylation in the electrocarboxylation of aromatic ketones
2006
The electrocarboxylation of various aromatic ketones, carried out in N-methyl-2-pyrrolidone (NMP) in a diaphragmless cell equipped with a carbon cathode and an aluminium sacrificial anode, yielded, among the products, the target hydroxy acids, the corresponding alcohols and pinacols and, quite surprisingly, detectable amounts of substituted benzoic acids and cycloexene carboxylic acids. These compounds arise from a never reported before electrocarboxylation on the aromatic ring, respectively, for substitution of an aromatic hydrogen and from an addition reaction. For example, the electrocarboxylation of acetophenone gave rise to the substituted benzoic acids in ortho, para and meta position…
Gelation of semiflexible polyelectrolytes by multivalent counterions
2012
Filamentous polyelectrolytes in aqueous solution aggregate into bundles by interactions with multivalent counterions. These effects are well documented by experiment and theory. Theories also predict a gel phase in isotropic rodlike polyelectrolyte solutions caused by multivalent counterion concentrations much lower than those required for filament bundling. We report here the gelation of Pf1 virus, a model semiflexible polyelectrolyte, by the counterions Mg(2+), Mn(2+) and spermine(4+). Gelation can occur at 0.04% Pf1 volume fraction, which is far below the isotropic-nematic transition of 0.7% for Pf1 in monovalent salt. Unlike strongly crosslinked gels of semiflexible polymers, which stif…
A kinetic study of the basic hydrolysis of 2-phenylethyl nitrite in the presence of borate buffer and β-cyclodextrin
2002
The kinetics of the hydrolysis of 2-phenylethyl nitrite have been studied in basic aqueous solutions (borate buffer) in the absence and presence of β-cyclodextrin. The observed kinetic trends show that the hydrolysis reaction consists of at least three subsequent processes. The first is a fast acid-base reaction between the boron atom of boric acid and oxygen atom of the alkyl nitrite. The second one should be the nucleophilic attack of hydroxyl ion on the alkyl nitrite. The last process could be referred to as a combination of transfer of hydrogen acid to a water molecule followed by ruptures of nitrogen-oxygen and boron-oxygen bonds. The effect of β- cyclodextrin on each process is also d…