Search results for "Surfaces"
showing 10 items of 2837 documents
Regio- and stereo-selectivity in the intramolecular quenching of the excited benzoylthiophene chromophore by tryptophan
2000
Laser flash photolysis studies on the photobehaviour of a series of bichromophoric derivatives bearing benzoylthiophene and tryptophan groups have shown that the efficiency of the intramolecular quenching process depends on both the stereochemistry of the chiral centers and the relative ketone versus tryptophan orientation. Perez Prieto, Julia, Julia.Perez@uv.es
Use of Ambient Ionization High-Resolution Mass Spectrometry for the Kinetic Analysis of Organic Surface Reactions
2016
In contrast to homogeneous systems, studying the kinetics of organic reactions on solid surfaces remains a difficult task due to the limited availability of appropriate analysis techniques that are general, high-throughput, and capable of offering quantitative, structural surface information. Here, we demonstrate how direct analysis in real time mass spectrometry (DART-MS) complies with above considerations and can be used for determining interfacial kinetic parameters. The presented approach is based on the use of a MS tag that - in principle - allows application to other reactions. To show the potential of DART-MS, we selected the widely applied strain-promoted alkyne-azide cycloaddition …
Frictional Forces between Strongly Compressed, Nonentangled Polymer Brushes: Molecular Dynamics Simulations and Scaling Theory
2010
By means of molecular dynamics simulations and scaling theory we study the response of opposing polymer brushes to constant shear motion under good solvent conditions. Model systems that contain explicit solvent molecules (Lennard-Jones dimers) are compared to solvent-free systems while varying of the distance between the grafted layers and their molecular parameters, chain length and grafting density. Our study reveals a power-law dependence of macroscopic transport properties on the Weissenberg number, W, beyond linear response. For instance, we find that the kinetic friction constant scales as μ ∼ W0.57 for large values of W. We develop a scaling theory that describes our data and previo…
Formation Kinetics of Mixed Self-Assembled Monolayers of Alkanethiols on GaAs(100)
2017
International audience; We report on the formation kinetics of mixed self-assembled monolayers (SAMs) comprising 16-mercaptohexadecanoic acid (MHDA) and 11-mercapto-1-undecanol (MUDO) thiols on GaAs(100) substrates. These compounds were selected for their potential in constructing highly selective and efficient architectures for biosensing applications. The molecular composition and quality of one-compound and mixed SAMs were determined by the Fourier transform infrared absorption spectroscopy measurements. The formation of enhanced-quality mixed SAMs was investigated as a function of the molecular composition of the thiol mixture and the proportion of ethanol/water solvent used during thei…
Computing kinetic isotope effects for chorismate mutase with high accuracy. A new DFT/MM strategy.
2006
A novel procedure has been applied to compute experimentally unobserved intrinsic kinetic isotope effects upon the rearrangement of chorismate to prephenate catalyzed by B. subtilis chorismate mutase. In this modified QM/MM approach, the "low-level" QM description of the quantum region is corrected during the optimization procedure by means of a "high-level" calculation in vacuo, keeping the QM-MM interaction contribution at a quantum "low-level". This allows computation of energies, gradients, and Hessians including the polarization of the QM subsystem and its interaction with the MM environment, both terms calculated using the low-level method at a reasonable computational cost. New infor…
A variable charge molecular dynamics study of the initial stage of nickel oxidation
2010
Abstract The oxidation of nickel single crystals is investigated by using variable charge molecular dynamics. The simulations are performed on three nickel low-index surfaces ((1 0 0), (1 1 0) and (1 1 1)) at temperatures between 300 K and 950 K. The results show that the shape of the oxidation kinetics is independent of the crystallographic orientation and the temperature under the present conditions. The oxide thin film grows according to an island growth mode, this initial stage of oxidation can be divided in three steps: (i) the dissociative chemisorption step (ii) the oxide island nucleation and (iii) the lateral growth of the island. The first step is slowdown/speedup by the surface o…
Study of Toner Penetration in Papers by Laser Induced Plasma Spectroscopy and Optical Profilometry
2023
Four major toners are used in the printing industry, cyan, magenta, yellow and black (Key) for making color images on paper. Paper brands suitable for printing have thin mineral/latex coatings, and toners are applied on top of the coating in the printing process. Chemical compositions from toner to toner, as well as from coating to coating, vary according to the needs of the end user. Interactions between the toner and the coating define the final color formation of the images in printing. Hence, it is important to study characteristics and dynamics of toners on coated papers. In this paper, we have used laser-induced plasma spectroscopy (LIBS) to provide information on elemental distributi…
Some factors affecting the removal of lead(II) ions from aqueous solution by porous hydroxyapatite: relationships between surface and adsorption prop…
2006
A porous hydroxyapatite (p-HAp) was prepared and employed for the removal of lead(II) ions at different concentrations from aqueous solution to determine the adsorption properties of p-HAp and compare them with those of a commercial hydroxyapatite (CAp) sample. The kinetic data obtained indicated that the adsorption performances of the adsorbents depended both on their specific surface area and crystallinity. Complexation of the Pb(II) ion on the adsorbent surface favoured the dissolution of hydroxyapatites characterized by a Ca/Pb molar ratio in the 0.85–1.5 range. The maximum adsorption capacity of p-Hap for Pb(II) ions at 30 ± 2°C was 2.30 mmol/g relative to 1.38 mmol/g for the commercia…
Trehalose interacts with phospholipid polar heads in Langmuir monolayers
2000
Surface pressure−area isotherms, surface potential-area isotherms and fluorescence microscopy were employed to study the behavior of phospholipid monolayers at the air/water interface when trehalose was added to the aqueous subphase. In the presence of this sugar, the critical area corresponding to the onset of surface potential increases, indicating that trehalose is participating in the network of hydrogen bonds between the phospholipid polar heads. In addition, it causes an expansion of the isotherm, hindering the formation of the liquid-condensed phase. The collapse area is significantly increased, indicating that trehalose takes part in the monolayer structure without being expelled ev…
Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers.
2007
Abstract In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)2(tmphen)]PF6, (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air–water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as π – A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. B…