Search results for "Surfaces"
showing 10 items of 2837 documents
Evidence that steric factors modulate reactivity of tautomeric iron-oxo species in stereospecific alkane C-H hydroxylation
2014
A new iron complex mediates stereospecific hydroxylation of alkyl C-H bonds with hydrogen peroxide, exhibiting excellent efficiency. Isotope labelling studies provide evidence that the relative reactivity of tautomerically related oxo-iron species responsible for the C-H hydroxylation reaction is dominated by steric factors This work has been supported by the European Union (the Erasmus Mundus program), the International Research Training Group Metal Sites in Biomolecules: Structures, Regulation and Mechanisms (www.biometals.eu), and COST Action CM1003. M.C. acknowledges ERC-29910, MINECO of Spain for CTQ2012- 37420-C02-01/BQU and CSD2010-00065, catalan DIUE (2009SGR637) and an ICREA academ…
Steric vs. electronic stereocontrol in syndio- or iso-selective ROP of functional chiral β-lactones mediated by achiral yttrium-bisphenolate complexes
2018
International audience; Origins of stereoselectivity in ROP of racemic chiral cyclic esters promoted by achiral yttrium complexes, resulting in the formation of highly heterotactic polylactide, and highly syndiotactic or, more uniquely, highly isotactic poly(3-hydroxybutyrate)s, are discussed. A close interplay between the nature of the cyclic ester, most particularly of the exocyclic functional chain installed on the chiral center of β-lactones, and the ortho-substituents installed on the phenolate rings of the ligand, results in various determining secondary interactions of steric and also electronic nature.
Study of Confined 5-Aza[5]helicene in Ytterbium(III) Bis(2-ethylhexyl) Sulfosuccinate Reversed Micelles
2007
Some relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Mor…
Molecular Recognition via Hydrogen Bonding at the Air−Water Interface: An Isotherm and Fourier Transform Infrared Reflection Spectroscopy Study
1997
Molecular recognition in Langmuir monolayers at the air−water interface as a function of headgroup orientation and substrate using isotherms and in-situ Fourier transform infrared (FT-IR) reflection spectroscopy has been investigated. Isotherm measurements show that urea and 2,4,6-triaminopyrimidine (TAP) are specifically bound to barbituric acid lipid monolayers. As expected, TAP causes a larger shift in the limiting area of the isotherms than urea due to steric requirements. The peak positions of the CH stretching vibrations of the barbituric acid lipids indicate that the alkyl chains of barbituric acid lipids 1−3 are in a close-packed all-trans conformation both before and after the reco…
Ligand effects on the dimensionality of oxamato-bridged mixed-metal open-framework magnets
2012
Increasing dimensionality [from 2D (1) to 3D (2)] and T(C) [from 10 (1) to 20 K (2)] in two new oxamato-bridged heterobimetallic Mn(II)(2)Cu(II)(3) open-frameworks result from the steric hindrance provided by the different alkyl substituents of the N-phenyloxamate bridging ligands.
A spatially resolved investigation of oxygen adsorption on polycrystalline copper and titanium by means of photoemission electron microscopy
2004
Abstract The interaction of oxygen with polycrystalline copper and titanium surfaces was studied by means of photoemission electron microscopy. Variations in the image brightness were used to determine the work function of different Cu crystallites. The change of the work function was monitored during oxygen adsorption on both, Cu and Ti. Those changes are smooth for Cu whereas different Ti crystallites exhibit a rather complicated behavior during oxygen adsorption. The transformation of brightness versus exposure curves into work function versus coverage curves allows to determine the initial dipole moment of the adsorbed oxygen atoms. A value of about 20 mD was found for O on Cu(1 1 0). V…
Sticking Probability on Zeolites
2006
The sticking coefficient, i.e., the probability that, on hitting the surface of a nanoporous particle (zeolite), a molecule shall be able to enter the intracrystalline space, is a key quantity for the application of such materials in heterogeneous catalysis and molecular sieving. On the basis of pulsed field gradient NMR diffusion measurements and molecular dynamics simulations, typical values of this probability are found to be close to one. They exceed previous estimates on the basis of IR uptake measurements by many orders of magnitude.
Competition between the buckling-driven delamination and wrinkling in compressed thin coatings
2012
Abstract The competition between two common failure modes of a thin coating under in-plane compression, the surface wrinkling and the buckling-driven delamination, is studied to assess the critical strain when the mechanical instability may occur at given geometrical and material parameters. A buckling map is constructed based on results of a finite element analysis, which relates the critical applied strain for the onset of instability to the interface adhesion and elastic properties of materials. An approximate scaling relation is derived for the energy release rate of buckling-driven delamination of a coating deposited on a compliant substrate.
Enantioselective synthesis of pyrazolone α-aminonitrile derivatives via an organocatalytic Strecker reaction
2017
A new organocatalytic enantioselective Strecker reaction of pyrazolone-derived ketimine electrophiles has been developed. Using pseudo-enantiomeric squaramide catalysts the nucleophilic 1,2-addition of trimethylsilyl cyanide to the ketimines efficiently provides a direct entry to both enantiomers of pyrazolone α- aminonitrile derivatives at will in good yields and high enantioselectivities for a wide variety of substrates. peerReviewed
Real time optical immunosensing with flow-through porous alumina membranes
2014
Through the presentation of analytical data from bioassay experiments, measured by polarimetry, we demonstrate for the first time a real time immunoassay within a free standing macroporous alumina membrane. The 200 nm nominal pore diameter of the membrane enables flow-through, thereby providing an ideal fluidic platform for the targeted delivery of analytes to bioreceptors immobilized on the pore walls, enabling fast sensing response times and the use of small sample volumes (<100 mu L). For the immunoassay, the pore walls were first coated with the functional copolymer, copoly(DMA-NAS) using a novel coupling process, before immobilization of the allergen protein, beta-lactoglobulin, by spo…