Search results for "bond"
showing 10 items of 3527 documents
Chiroptical Phenomena in Reverse Micelles: The Case of (1R,2S)- Dodecyl (2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium Bromide (DMEB)
2014
(1R,2S)-Dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) aggregates dispersed in carbon tetrachloride have been investigated by Fourier transform infrared (FT-IR), vibrational circular dichroism (VCD) and 1H nuclear magnetic resonance (NMR) spectroscopy at various surfactant concentration and water-to-surfactant molar ratio. Experimental data indicate that, even at the lowest investigated concentration and in absence of added water, DMEBmolecules associate in supramolecular assemblies. At higherDMEBconcentration the aggregates can confine watermolecules,making it plausible to think thatDMEB form reverse micelles and that watermolecules are quite uniformly distributed…
Increased conformational rigidity of humic substances by oxidative biomimetic catalysis
2005
A synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials. High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS-(13)C NMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mw(a)) occurred invariably for all humic substances with the oxidative polymerization catalyzed …
Conformational investigation of α,β‐dehydropeptides. XV: N‐acetyl‐α,β‐dehydroamino acid N ′N ′‐dimethylamides: conformational properties from infrare…
2005
The FTIR spectra were analysed in the region of the nu(s)(N-H), AI(C=O) and nu(s)(Calpha=Cbeta) bands for a series of Ac-DeltaXaa-NMe2, where DeltaXaa = DeltaAla, (Z)-DeltaAbu, (Z)-DeltaLeu, (Z)-DeltaPhe and DeltaVal, to determine a predominant solution conformation of these alpha,beta-dehydropeptide-related molecules. Measurements were taken in CCl4, DCM and MeCN solutions. In the same way, spectra of saturated analogues Ac-Xaa-NMe2, where Xaa = Ala, Abu, Leu, Phe and Val, were investigated. To help interpret the spectroscopic results, conformational maps were calculated by the B3LYP/6-31+G** method. Also, the relative energies of all conformers of the dehydro compounds in vacuo as well as…
Crystal structure of (E)-4-methyl-N-{2-[2-(4-nitrobenzylidene)hydrazin-1-yl]-2-oxoethyl}benzenesulfonamideN,N-dimethylformamide monosolvate
2017
The molecule of the title Schiff base compound, C16H16N4O5S·C3H7NO, displays atransconformation with respect to the C=N double bond. The C—N and N—N bonds are relatively short compared to their normal bond lengths, indicating some degree of delocalization in the molecule. The molecule is bent at the S atom, with an S—N—C—C torsion angle of 164.48 (11)°. The dihedral angle between the two aromatic rings is 84.594 (7)°. Intermolecular N—H...O and C —H...O hydrogen bonds connect centrosymmetrically related molecules into dimers forming rings ofR33(11) andR22(10) graph-set motif stacked along theaaxis into a columnar arrangement. The molecular columns are further linked into a three-dimensional…
Crystal structure of the tripeptideN-(benzyloxycarbonyl)glycylglycyl-L-norvaline
2015
The title tripeptide, C17H23N3O6, contains a nonproteinogenic C-terminal amino acid residue, norvaline, which is an isomer of the amino acid valine. Norvaline, unlike valine, has an unbranched side chain. The molecule has a Gly–Gly segment which adopts an extended conformation. The norvaline residue also adopts an extended backbone conformation while its side chain has ag+tconformation. In the crystal lattice, N—H...O and O—H...O hydrogen bonds stabilize the packing. Molecules translated along the crystallographicaaxis associate through an N—H...O hydrogen bond. The remaining three hydrogen bonds are between molecules related by a21screw axis.
Conformational investigation of α,β‐dehydropeptides Part VI. Molecular and crystal structure of benzyloxycarbonylglycyl‐(Z )‐dehydrophenylalanine
1994
The structure of a peptide containing C-terminal dehydrophenylalanine, Z-Gly-(Z)-delta Phe (C19H18N2O5, MW = 354) was determined from single-crystal X-ray diffraction data. Needle-shaped crystals were grown from a 1:1 mixture of methanol-acetone in the monoclinic space group P2(1) with a = 14.717(4), b = 4.941(2), c = 12.073(4) A, beta = 103.72(4) degrees; V = 852.86(8) A3, Z = 2 and Dc = 1.32 g cm-3. The structure was solved by direct methods using SHELXS-86 and refined to a final R-index of 0.032 for 1714 observed reflections. The peptide adopts a conformation folded at the glycine residue, and principal torsion angles are omega 0 = -167.6(2) degrees, phi 1 = -71.8(3) degrees, psi 1 = -31…
Cytotoxicity investigations of plasma sprayed calcium phosphate coatings
1994
One potential alternative material to replace hydroxyapatite (HAp) as a coating material for plasma-sprayed coatings on implants for hip replacement is fluorapatite (FAp). FAp has advantages over HAp regarding the capability of being chemically stable during the coating process. This leads to surface coatings containing high apatite rates with a mechanical stability (bond strength, microhardness) comparable to HAp. From the technical point of view the production of FAp coatings is well investigated, although studies on biocompatibility of FAp coatings are fewer. This paper reports the production of HAp and FAp coatings with varying solubilities by plasma spraying and their in vitro cytotoxi…
Reactivity of bis(cyclohexylammonium) 4-nitrophenylphosphate with SnMe3 Cl. X-ray structure of 4-NO2 C6 H4 PO4(SnMe3)2·H2 O
2014
The reaction of bis(cyclohexylammonium) 4-nitrophenylphosphate with Me3 SnCl (1:2) under reflux in ethanol yielded the title compound 4-NO2 C6 H4 PO4(SnMe3)2H2 O (1). The X-ray crystallographic analysis achieved on single crystals obtained by slow evaporation at room temperature revealed the formation of an unexpected supramolecular coordination network. The elementary building block can be viewed as two Me3 Sn moieties linked by a bridging 4-nitrophenylphosphate ligand. The two tin atoms are five-coordinated and describe a trans-Me3 SnO2 geometry in a trigonal bipyramidal arrangement. However, the Sn atoms are distinct, exhibiting two different environments. Thus, one is linked to two axia…
The first catalytic method for Heck alkynylation of unactivated aryl bromides (copper-free Sonogashira) in an ionic liquid: 1 mol-percent palladium/t…
2007
Herein we report the studies of Heck alkynylation (copper-free Sonogashira) with aryl halides (I, Br, Cl) employing various metallic precursors, tertiary phosphanes and bases in [BMIM][BF4] as the solvent. As a result, we provide the first method that allows the coupling of a large array of substrates, either activated or deactivated bromides in an ionic liquid. Furthermore, the system of highest efficiency is unexpectedly the simplest and cheaper combination that employs [Pd(η3-C3H5)Cl]2/PPh3 at only a 1 mol-% loading with pyrrolidine as the base and in the absence of a copper salt. The coupling of sterically and electronically deactivated bromides bearing different functional groups to ar…
Uzņēmējdarbības un vadības dažādi aspekti / Different Aspects of Entrepreneurship and Management: Report of Abstracts
2022
LU Biznesa, vadības un ekonomikas fakultāte