Search results for "Electrostatics"
showing 10 items of 67 documents
Effect of Cholesterol on Electrostatics in Lipid−Protein Films of a Pulmonary Surfactant
2010
We report the changes in the electrical properties of the lipid-protein film of pulmonary surfactant produced by excess cholesterol. Pulmonary surfactant (PS) is a complex lipid-protein mixture that forms a molecular film at the interface of the lung's epithelia. The defined molecular arrangement of the lipids and proteins of the surfactant film gives rise to the locally highly variable electrical surface potential of the interface, which becomes considerably altered in the presence of cholesterol. With frequency modulation Kelvin probe force microscopy (FM-KPFM) and force measurements, complemented by theoretical analysis, we showed that excess cholesterol significantly changes the electri…
Molecular recognition of naphthalene diimide ligands by telomeric quadruplex-DNA: the importance of the protonation state and mediated hydrogen bonds.
2016
In depth Monte Carlo conformational scans in combination with molecular dynamics (MD) simulations and electronic structure calculations were applied in order to study the molecular recognition process between tetrasubstituted naphthalene diimide (ND) guests and G-quadruplex (G4) DNA receptors. ND guests are a promising class of telomere stabilizers due to which they are used in novel anticancer therapeutics. Though several ND guests have been studied experimentally in the past, the protonation state under physiological conditions is still unclear. Based on chemical intuition, in the case of N-methyl-piperazine substitution, different protonation states are possible and might play a crucial …
Local control of antibody binding to hapten-presenting interfaces: Steric and electrostatic interaction
1991
The binding of labeled antibodies to hapten substituted monolayers at the air/water interface has been studied by means of fluorescence microscopy. Haptens with various spacer lengths between the epitope and a hydrocarbon chain, anchoring the molecule to the interface, have been synthesized. With DMPC,a unspecific binding has been shown to predominate over specific binding due to electrostatic interactions. At high surface pressures the bound antibody is detached because of steric interference with the lipid head groups. Due to a reduction of electrostatic interactions, no unspecific binding is observed to monolayers of cholesterol, which carries a small dipole moment. Mixed monolayers of c…
Vectorized ‘‘TOPO’’ Program for the Theoretical Simulation of Molecular Shape
1991
The TOPO program for theoretical simulation of molecular shape is presented here. Molecular shape is characterized by a set of electrostatic and geometrical descriptors and topological indices including the fractal dimension of the accessible surface. An atom-atom analysis of all descriptors has been implemented. The program has been adapted for the realization of high-performance computing. Results are reported for porphine and phthalocyanine molecules.
Experimental and theoretical evidence of overcharging of calcium silicate hydrate
2007
International audience; Electrokinetic measurements such as electrophoresis may show an inversion of the effective surface charge of colloidal particle called overcharging. This phenomenon has been studied by various theoretical approaches but up to now very few attempts of confrontation between theory and experiment have been conducted. In this work we report electrophoretic measurements as well as Monte Carlo simulations of the electrokinetic potential for the surface of calcium silicate hydrate (Csingle bondSsingle bondH), which is the major constituent of hydrated cement. In the simulations, the surface charge of Csingle bondSsingle bondH nanoparticles in equilibrium with the ionic solu…
Generic nature of long-range repulsion mechanism on a bulk insulator?
2017
Dynamic atomic force microscopy measurements are reported that provide evidence for the presence of long-range repulsion in molecular self-assembly on a bulk insulator surface. We present the structures formed from four different benzoic acid derivatives on the (10.4) cleavage plane of calcite kept in ultra-high vacuum. These molecules have in common that they self-assemble into molecular stripes when deposited onto the surface held at room temperature. For all molecules tested, a detailed analysis of the stripe-to-stripe distance distribution reveals a clear deviation from what would be expected for randomly placed, non-interacting stripes (i.e., geometric distribution). When excluding kin…
N ‐Annulated Perylene Bisimides to Bias the Differentiation of Metastable Supramolecular Assemblies into J‐ and H‐Aggregates
2020
The unique self-assembling features of N-annulated perylene bisimides (PBIs) 1 and 2 are reported. The stability of the aggregates of diester 1, in which no H-bonding interactions are operative, corroborates the significance of long-range van der Waals and dipole-dipole electrostatic interactions in the construction of stable supramolecular assemblies. The incorporation of amide functional groups within the N-annulated PBI in 2 stimulates pathway differentiation to achieve up to three J-type aggregates and a fourth H-type aggregate depending on the experimental conditions. The results presented demonstrate unprecedented levels of control over synthetic supramolecular self-assembly and the r…
Solution properties of polyelectrolytes
1993
Abstract Aqueous size-exclusion chromatography was used to analyse the elution behaviour of several standard ionic polymers, including poly( l -glutamic acid), sodium poly(styrene sulphonate) and poly(acrylic acid), different in nature and chain flexibility, as a function of the pH and ionic strength of the eluent. Two organic-based hydrophilic packings, Spherogel TSK PW4000 and Ultrahydrogel 250, were tested in order to select the optimal conditions of macromolecular separation, and the results obtained for each column were compared. A set of calibration graphs for the above polyions as a function of eluent pH and ionic strength were obtained and compared with those obtained for uncharged …
Solution properties of polyelectrolytes XII. Semi-quantitative approach to mixed electrostatic and hydrophobic polymer-gel interactions
1996
Abstract Aqueous size-exclusion chromatography of polyanions, where secondary effects affect the total separation mechanism, was investigated. For elution of polyelectrolytes on inorganic silica-based supports, the electrostatic polymer-gel repulsive interactions were evaluated through the values for a hypothetical repulsion layer, X e , according to the model developed by other workers. Using a similar procedure, the existence of an effective barrier defined as X e − X h is proposed for those systems in which electrostatic repulsion and hydrophobic interactions take place simultaneously as secondary mechanisms. X h can be viewed as a measure of the “enlargement” of the geometrical pore rad…
Ionic transport characteristics of negatively and positively charged conical nanopores in 1:1, 2:1, 3:1, 2:2, 1:2, and 1:3 electrolytes
2019
We study experimentally the current (I)-voltage (V) curves of 1:1, 2:1, 3:1, 2:2, 1:2, and 1:3 electrolytes in positively and negatively charged conically-shaped pores of nanoscale dimensions. The positive charges are poly(allylamine hydrochloride) chains functionalized on the pore surface by electrostatic interactions while the negative charges are carboxylic acid groups. Under physiological conditions, these fixed-charge groups are ionized and strongly interact with the different monovalent, divalent, and trivalent ions in the pore solution. The current rectification of the I-V curves and the membrane potentials provide fundamental information on the interaction of the pore charge groups …