Search results for "Vicinal"
showing 10 items of 37 documents
Organocatalytic Enantioselective Alkylation of Pyrazol-3-ones with Isatin-Derived Ketimines: Stereocontrolled Construction of Vicinal Tetrasubstitute…
2016
A quinine-derived thiourea catalysed the enantioselective addition of 4-substituted pyrazolones to isatin-derived ketimines, providing a variety of aminooxindole-pyrazolone adducts containing congested vicinal tetrasubstituted stereocentres with excellent outcomes (up to 98% yield, >20:1 dr and 98% ee).
Magnetic and structural investigations of ultra-thin Co–Fe alloy films on W(1 1 0)
2004
Abstract We investigated ultra-thin CoxFe1−x films on a flat and vicinal BCC W(1 1 0) surface with thicknesses between 1.8 and 7 monolayers (ML) using longitudinal Kerr magnetometry. We found a transition from magnetic bulk behavior between 3 and 4 ML to the monolayer. The maximum of the remnant Kerr signal that appears for thicker films at x=0.5 turns into a minimum for a sample thickness below 4 ML , while the specific Kerr-rotation per monolayer shows the well known bulk behavior. A similar magnetic behavior on the flat as well as on the stepped part of the substrate indicates that this is an intrinsic property. For x=0.5 the pseudomorphic monolayer is paramagnetic even when it is covere…
Domain structure of epitaxial SrRuO3 thin films
2005
Growth of multidomains in epitaxial thin-film oxides is known to have a detrimental effect on some functional properties, and, thus, efforts are done to suppress them. It is commonly accepted that optimal properties of the metallic and ferromagnetic $\mathrm{SrRu}{\mathrm{O}}_{3}$ (SRO) epitaxies can only be obtained if vicinal $\mathrm{SrTi}{\mathrm{O}}_{3}$ (001) (STO) substrates are used. It is believed that this results from the suppression of multidomain structure in the SRO film. Here we revise this important issue. Nanometric films of SRO have been grown on STO(001) vicinal substrates with miscut $({\ensuremath{\theta}}_{V})$ angles in the $\ensuremath{\sim}0.04\ifmmode^\circ\else\te…
Morphology and magnetism of Fe on vicinal W(110) surfaces with different step orientation
2000
Abstract Nanostructures of monolayer height of single-crystalline Fe(1 1 0) films were grown on stepped W(1 1 0) surfaces. The growth mode strongly depends on the step orientation of the substrate. Continuous stripes are formed at steps along the [1 0 0] direction whereas triangular shaped islands grow on substrates with [1 −1 0]-oriented step edges. No ferromagnetic order was found in submonolayer films grown on [1 −1 0]-steps. The nanostripe array on [1 0 0] steps shows a ferromagnetic phase-transition with a critical behavior different from the Ising-like phase transition observed for submonolayer films grown on smooth W(1 1 0). The magnetic easy axis in the samples is oriented parallel …
Dipolar superferromagnetism in monolayer nanostripes of Fe(110) on vicinal W(110) surfaces
1998
By epitaxial growth of Fe on a vicinal W~110! substrate, densely spaced and continuous monolayer stripes of Fe~110! were prepared, directed along @001#. They exhibit a sharp phase transition to ferromagnetic order, free from relaxations. The magnetic easy axis is in the plane, but along @110# that means across the stripes. This cross magnetization induces ferromagnetic dipolar coupling between the spin blocks in adjacent stripes, which are preformed by exchange interactions. The resulting superferromagnetic phase transition is therefore driven by dipolar interactions. @S0163-1829~98!52002-4#
Type II narrow double barrier quantum well structures : Γ-X coupling and interface effects
1993
Photoluminescence (PL), PL excitation and time resolved PL experiments have been performed on Al0.42Ga0.58As/AlAs/GaAs symmetric double barrier quantum wells (DBQW) with only one or two AlAs monolayers constituting the intermediate barriers. In agreement with the envelope function predictions we show that such DBQW's undergo a type I - type II transition when the GaAs thickness is reduced below 7 and 5 monolayers for 2 and 1 AlAs molecular planes respectively. In type II configuration the PL decay time is found to be strongly dependent on the energy difference between AlAs Xz - and GaAs Γ - electron confined states and the coupling parameter of the Γ and Xz valleys can be deduced (4.2 meV o…
Three nuclei n.m.r. spectroscopy of dimethoate compounds. A large solvent effect on the31PSC1H vicinal coupling
1977
Proton, phosphorus and carbon magnetic resonance spectra of dimethoate, dimethoxon, des-N-methyldimethoate, ω-hydroxydimethoate, trimethyldithiophosphate and O,O-dimethyldithiophosphate in different solvents have been measured. Most of the n.m.r. parameters were characteristic of the structural environment of the corresponding nucleus and solvent-independent. However, in the amide structures dimethoate, dimethoxon, des-N-methyldimethoate and ω-hydroxydimethoate the 31PSC1H vicinal coupling showed an unusually large solvent effect of a 2.3 to 6.5 Hz decrease when CDCI3 was replaced by acetone-d6 or DMSO-d6.
The Nature of Silanol Groups on the Surfaces of Silica, Modified Silica and Some Silica Based Materials
2014
Silica gel, a material that is produced from the condensation polymerisation of silicic acid, contains surface silanol groups formed during the condensation. The silanol groups on the surface are mostly of free and vicinal silanol groups. These silanol groups can be modified in several different ways. Thermal treatment and hydrothermal treatment can be carried out to alter the concentration proportions between free and hydrogen bonded silanol groups on the surface. They can also be chemically treated with suitable chlorosilanes to modify the silanol groups into polar or non polar materials that can be used in separation science.This article explores the chemical nature of silanol groups on …
Binding abilities of dehydropeptides towards Cu(II) and Ni(II) ions. Impact of Z–E isomerization on metal ion binding
2002
The study on the binding ability of dehydro-tri- and tetrapeptides has shown that the alpha,beta-double bond has a critical effect on the peptide coordination to metal ions. It may affect the binding of the vicinal amide nitrogens by the electronic effect and stabilize the complex due to steric effects. The (Z) isomer is the most effective in stabilizing of the complexes formed. The presence of large side chain in the dehydroamino acid residue may also be critical for the coordination mode in the metallopeptide systems.
Informational rigidity in mesitylene-based calix[4]arenes adopting a 1,3-alternate conformation
2000
Abstract Two chiral derivatives of a mesitylene-based calix[4]arene known to exist in the 1,3-alternate conformation were prepared by the attachment of homochiral residues to the four exo -hydroxy groups. Thus, the enantiotopic protons of the central scaffold became diastereotopic, leading to a doubling of their 1 H NMR signals in one example. From the temperature independence of the NMR spectrum, a lower limit of 24.2 kcal/mol could be estimated for the barrier of ring inversion. MM3 calculations confirm the 1,3-alternate conformation as the energy minimum, and estimate a barrier of 25.7 kcal/mol for the 1,3-alternate-to-1,3-alternate* interconversion process. This high barrier is due to t…