Search results for "Chemical physics"
showing 10 items of 2553 documents
Multiple interactions between molecular and supramolecular ordering
1999
We report studies of the interplay among processes of molecular conformational changes, spinodal demixing of the solution, and molecular crosslinking involved in the physical gelation of a biopolysaccharide-water system. Multiple interactions and kinetic competition among these processes were studied under largely different absolute and relative values of their individual rates by appropriate choices of the quenching temperature at constant polymer concentration. Quenching temperature strongly affects the rate of growth but not the final value of the fractal dimension of the gel. Kinetic competition plays a central role in determining the final conformation of individual molecules and the s…
HACANCOi : a new Hα-detected experiment for backbone resonance assignment of intrinsically disordered proteins
2020
AbstractUnidirectional coherence transfer is highly efficient in intrinsically disordered proteins (IDPs). Their elevated ps-ns timescale dynamics ensures long transverse (T2) relaxation times allowing sophisticated coherence transfer pathway selection in comparison to folded proteins. 1Hα-detection ensures non-susceptibility to chemical exchange with the solvent and enables chemical shift assignment of consecutive proline residues, typically abundant in IDPs. However, many IDPs undergo a disorder-to-order transition upon interaction with their target protein, which leads to the loss of the favorable relaxation properties. Long coherence transfer routes now result in prohibitively large dec…
Structure and Dynamics of NaCl in Methanol. A Molecular Dynamics Study
1991
Abstract A recently developed flexible three-site model for methanol was employed to perform a Molecular Dynamics simulation of a 0.6 molal NaCl solution. The ion-methanol and ion-ion potential functions were derived from ab initio calculations. The structural properties of the solution are discussed on the basis of radial and angular distribution functions, the orientation of the methanol molecules, and their geometrical arrangement in the solvation shells of the ions. The dynamical properties of the solution - like self-diffusion coefficients, hindered translations, librations, and internal vibrations of the methanol molecules - are calculated from various autocorrelation functions.
Monolayers of Bolaform Amphiphiles: Influence of Alkyl Chain Length and Counterions
1994
We have prepared self-assembled monolayers of novel cationic bolaform amphiphiles on negatively charged substrates. Most of these amphiphiles form smooth, defect-free monolayers which can be used to reverse the substrate surface charge and thus allow subsequent adsorption of anionic molecules and construction of multilayers. Atomic force microscopy, surface force measurement, and surface plasmon spectroscopy were combined to probe the molecular orientation and ordering, mechanical properties, and surface electrical properties of the monolayers. In addition, the amphiphile aggregation behavior at an air-water interface was studied by surface tension measurement, and lyotropic phase behavior …
Hydrogenation of light hydrocarbons on palladium: theoretical study of the local surface arrangements
2001
Abstract Quantum mechanical calculations at HF, MP2 and DFT levels were used to rationalise the surface effects of the hydrocarbon lateral interactions occurring on single planar metal surfaces or on different adjacent surfaces during the hydrogenation on palladium catalyst. The different values of electronic charge, found in the different atoms of palladium clusters, were suggested as a possible explanation of the non-homogeneous behaviour already inferred for catalyst surface sites having non-isotropic local arrangement.
Impact of the reaction pathway on the final product in on-surface synthesis
2020
International audience; On-surface synthesis provides a very promising strategy for creating stable functional structures on surfaces. In the past, classical reactions known from solution synthesis have been successfully transferred onto a surface. Due to the presence of the surface, on-surface synthesis provides the potential of directing the reaction pathway in a manner that might not be accessible in classical solution synthesis. In this work, we present evidence for an acetylene polymerization from a terminal alkyne monomer deposited onto calcite (10.4). Strikingly, although the dimer forms on the surface as well, we find no indication for diacetylene polymerization. This is in sharp co…
Impact of surface state on polyethylene glycol conformation confined inside a nanopore.
2021
Solid-state nanopores are a promising platform for characterizing proteins. In order to improve their lifetime and prevent fouling, Polyethylene Glycol (PEG) grafting is one of the most efficient and low-cost solutions. Different models to calculate the PEG thickness do not consider their interaction with the nanopore inner surface nor the effect of confinement. Here, we investigate by molecular dynamic simulation the PEG conformation inside a nanopore in the case of hydrophobic and hydrophilic nanopores. Our results reveal that the nanopore inner surface plays a role in the PEG organization and, thus, in the speed of the salt constituent. The resulting pair interaction between PEG and its …
Chain linear dimensions in the surface-enriched layer of polymer mixtures
1992
We calculate the mean-square end-to-end distances and mean-square gyration radii using the bond fluctuation model for a binary polymer blend in the presence of a wall by Monte Carlo simulation. In the bulk, the size of the minority, low-concentration polymer species is compressed compared to the majority one. In the vicinity of the wall, where the minority polymer concentration is enriched due to attraction from the wall, the dimensions of the two types of polymers are approximately equal and are essentially the same as in an athermal polymer melt. Thus, the geometric constraint is more important to the structure of the polymers than the polymer-polymer and polymer-wall interactions.
Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)
1994
The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by …
Concentration-dependent switch between chain association and dissociation of oppositely charged weak polyelectrolytes in solution
2019
Abstract Joint solutions of oppositely charged weak polyelectrolytes are considerably less studied than their strong counterparts; as a result, their thermodynamic understanding is still unsatisfactory. This shortcoming hampers the development of a general picture about the physical properties of these mixtures, which further hampers their use to design new materials. To close this gap, we investigate the ternary system ethanol/polyacid/polybase (polyacid: methacrylic acid containing copolymer; polybase: N,N-dimethylaminoethyl methacrylate containing terpolymer) with respect to its demixing and viscometric behavior. Complete homogeneity can only be reached if the total polymer concentration…