Search results for "BOND"
showing 10 items of 3527 documents
Solvation chemistry of water-soluble thiol-protected gold nanocluster Au102 from DOSY NMR spectroscopy and DFT calculations
2014
The hydrodynamic diameter of Aum(pMBA)n [(m, n) = (102, 44) and (144, 60)] clusters in aqueous media was determined via DOSY NMR spectroscopy. The apparent size of the same (n, m) cluster depends on the counter ion of the deprotonated pMBA− ligand as explained by the competing ion-pair strength and hydrogen bonding interactions studied in DFT calculations. The choice of the counter ion affects the surface chemistry and molecular structure at the organic/water interface, which is relevant for biological applications.
Synthese sterisch gehinderter Peptide und Depsipeptide nach einem Säurechlorid-Verfahren mit 2-Phosphonioethoxycarbonyl-(Peoc-)Aminosäuren und -Hydro…
1982
2-(Triphenylphosphonio)ethoxycarbonyl-(Peoc-)aminosauren 1 und -hydroxysauren 5 werden mit Oxalylchlorid in bei Raumtemp. stabile Saurechloride 2 bzw. 6 ubergefuhrt. Mit diesen aktivierten Verbindungen werden sterisch gehinderte Amidbindungen — z. B. in den geschutzten Valin-Peptiden 3a—g und in Hydroxyacyl-Dipeptiden 7 — hergestellt. Nach Schutzgruppenabspaltung aus der voll geschutzten Form 7a entsteht so die Sporidesmolsaure B (9a), die in ihren Eigenschaften mit dem Abbauprodukt aus dem Sporidesmolid I ubereinstimmt. Trotz zweimaliger Anwendung der Saurechlorid-Kondensation ist keine Racemisierung eingetreten. Syntheses of Sterically Hindered Peptides and Depsipeptides by Means of an Ac…
Cations mobility and water adsorption in zeolites
2002
As already pointed out [1], dielectric relaxation spectroscopy can be a convenient tool for probing ion dynamic in solids which depends on i) the structure in which ions are embedded and ii) the nature of the interaction ion/network. Consequently, the results obtained from this technique can be used as a data base for theoretical studies which goal is to calculate the ion binding energy and to simulate ionic displacements. Inversely, theoretical calculations are essential for confirming the experimental data and more particularly the method which is used for analysing the dielectric experimental response.
Stable 17-electron Mo(III) complexes containing alkyl ligands
1999
Abstract The alkylation of the half-sandwich complex CpMoCl 2 ( η 4 -diene) (diene=C 4 H 6 , 2,3-Me 2 C 4 H 4 ) affords the first thermally stable 17-electron compounds containing Mo(III)–alkyl bonds.
Synthesis of Trisaccharides by Hetero-Diels–Alder Welding of Two Monosaccharide Units
2012
A new strategy for the synthesis of di- and trisaccharides based on the de novo synthesis of the linking saccharide unit is presented. In this strategy, functionalized monosaccharide building blocks already incorporating the glycosidic linkages are welded together using a metal-catalyzed hetero-Diels–Alder (HDA) reaction to generate a new monosaccharide unit between them. The highest yields and selectivities in the HDA reaction were obtained by using chiral Schiff base chromium complexes. Disaccharide products were accessible by reaction of Danishefsky's diene with acetyl- and benzyl-protected galactoside aldehydes. For the synthesis of trisaccharide products, acetyl-protected glucose or ga…
Synthese von geschützten Asparagin-Glycopeptiden durch N-terminale Peptidketten- Verlängerung. _ Teilsequenzen der Rinder-Desoxyribonuclease A und de…
1983
N-[2-(Triphenylphosphonio)ethoxycarbonyl] -[Peoc-]asparaginsaure-benzylester (8h) und -tert-butylester (8i) werden mit 2-Acetamido-3,4,6-tri-O-acetyl-2-desoxy-β -D-glucopyranosylamin (2) zu den N4-Glycosylasparagin-Derivaten 19 verknupft. Aus diesen kann die Peoc-Gruppe selektiv mit Diethylamin/tert-Butylalkohol oder Morpholin/Methylendichlorid abgespalten werden, wobei in den entstandenen N4-Glycosylasparaginestern 22 alle anderen Schutzgruppen und die glycosidische Bindung erhalten bleiben. Durch Kondensation von 22 mit Peoc-Aminosauren 8 entstehen die voll geschutzten N4-Glycosylasparagin-Dipetide 24 und 30. Bei Kondensation der N2 deblockierten N4-Glycosylasparaginester 22 mit den Peoc-…
A novel photochemical 1,4-acyl migration in enol esters. The photolysis of enol acetates of 3-phenylpropiophenones
1987
Abstract Photolysis of the enol acetates 1a,b gives the 1,4-diketones 4a,b by a mechanism involving a primary homolytic carbonyl—oxygen bond cleavage, followed by 1,2-hydrogen shift and in cage recombination.
Understanding the high reactivity of carbonyl compounds towards nucleophilic carbenoid intermediates generated from carbene isocyanides
2015
The high reactivity of carbonyl compounds towards the carbenoid intermediate cis-IN, generated in situ by the addition of methyl isocyanide to dimethyl acetylenedicarboxylate (DMAD), has been investigated at the MPWB1K/6-311G(d,p) computational level by using Molecular Electron-Density Theory (MEDT). This multicomponent (MC) reaction is a domino process that comprises two sequential reactions: (i) the formation of a nucleophilic carbenoid intermediate trans-IN; and (ii) the nucleophilic attack of cis-IN on the carbonyl compound, resulting in the formation of the final 2-iminofuran derivative. The present MEDT study establishes that the high nucleophilic character and the electronic structur…
Synthesis, crystal structure and molecular conformation of the tBuCO-D,L-Ala-Δz-Phe-NhiPr α,β-unsaturated dipeptide
2009
The crystal structure of the tBuCO-D,L-Ala-delta Z-Phe-NHiPr dipeptide has been solved by X-ray diffraction. The peptide crystallizes in monoclinic space group P2(1)/c with a = 13.445 (3) A, b = 35.088 (4) A, c = 14.755 (3) A, beta = 116.73 (1) degree, Z = 12 and dc = 1.151 g.cm-3. The three independent molecules per asymmetric unit accommodate a beta II-folded conformation, but only one of them contains the typical i + 3----i interaction characterizing a beta-turn. In the other two molecules, the N...O distance exceeds 3.2 A, a value generally considered the upper limit for hydrogen bonds in peptides. In solution, the beta II-turn conformation is largely predominant.
Selektive enzymatische Schutzgruppenabspaltungen: Der n-Heptylester als Carboxylschutzgruppe in der Peptidsynthese
1991
Selective Enzymatic Removal of Protecting Groups: n-Heptyl Esters as Carboxy Protecting Functions in Peptide Synthesis Amino acid heptyl (Hep) esters are accessible as generally crystalline hydro tosylates 3 from the amino acids by azeotropic esterification with 1-heptanol in high yields. They can be condensed with Z-, Boc-, and Aloc-protected amino acids to give the dipeptides 7–9 in the presence of 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). From the fully protected dipeptides the N-terminal protecting groups are cleaved by chemical methods without affecting the Hep esters. On the other hand, the heptyl esters can be hydrolyzed under mild conditions (pH = 7.0, 37°C) and with hi…