Surface-charge interaction

From the physics point of view, the system that we deal with here—a semiflexible polyelectrolyte that is packaged by protein complexes regularly spaced along its contour—is of a complexity that still allows the application of analytical and numerical models. For quantitative prediction of chromatin properties from such models, certain physical parameters must be known such as the dimensions of the nucleosomes and DNA, their surface charge, interactions, and mechanical flexibility. Current structural research on chromatin, oligonucleosomes, and DNA has brought us into a position where many such elementary physical parameters are known. Thus, our understanding of the components of the chromatin fiber is now at a level where predictions of physical properties of the fiber are possible and can be experimentally tested. 

The adsorption of ionic or polar surfactants on charged or polar surfaces involves coulombic (ion-surface charge interaction), ion-dipole, and/or dipole-dipole interaction. For example, a negatively charged silica surface (at a pH above the isoelectric point of the surface, i.e., pH >2-3)... 

Issues (vi) and (vil) both deal with the nature of the solvent they are also related to (v). Considering water, the spatial distribution of the molecules is in a very complicated way determined by solvent-solvent, solvent-countercharge and solvent-surface charge interactions. A detailed knowledge of this structure is required to quantify ion-ion correlations, ion-ion and ion-surface solvent structure-originated interactions and the local dielectric permittivity. Polarization of the solvent also contributes to the interfacial potential Jump or X POtential (secs. 1.5.5a and 3.9), which does not occur in Poisson-BoltzmEmn theory. 

Figure 7.3 Reflectivity data of the palmitoyl-R-lysine monolayer (see Figure 7.2) in the presence ofS-glutamine in the subphase show that about one quarter of the sites below the lysine head groups are occupied by glutamine. Amide hydrogen bonds cause the enrichment of glutamine on the surface charge interactions between the a-amino acid moieties also stabilize the hydrophilic glutamine layef.

In the above equations, the indices j and 3 range over the source point charges and the surface elements, respectively. In the SC approximation the integral expresses a point charge - surface charge interaction,... 

For two spheres of different radii, R and Rj, and at a constant surface charge interaction, the improved... 

Changes in protein configuration Changes in protein surface charges Interactions between ingredients Competition at oil or air interfaces... 

In the absence of strong attractive interactions induced by charge transfer between adsorbates and surface atoms, weak attractive interactions can be induced in several ways. When a gas atom or molecule with no permanent dipole moment approaches the surface of a metal in which the conduction electrons constitute a mobile, fluctuating electron gas, the surface charge induces a dipole in the approaching species. This attractive induced dipole-surface-charge interaction is similar to that of a gas molecule with a permanent dipole, and the potential energy of interaction is of the form... 

One potentially powerfiil approach to chemical imaging of oxides is to capitalize on the tip-surface interactions caused by the surface charge induced under electrolyte solutions [189]. The sign and the amount of the charge induced on, for example, an oxide surface under an aqueous solution is detenuined by the pH and ionic strength of the solution, as well as by the isoelectric point (lEP) of the sample. At pH values above the lEP, the charge is negative below this value. 

There are two basic physical phenomena which govern atomic collisions in the keV range. First, repulsive interatomic interactions, described by the laws of classical mechanics, control the scattering and recoiling trajectories. Second, electronic transition probabilities, described by the laws of quantum mechanics, control the ion-surface charge exchange process. 

In particular, in polar solvents, the surface of a colloidal particle tends to be charged. As will be discussed in section C2.6.4.2, this has a large influence on particle interactions. A few key concepts are introduced here. For more details, see [32] (eh 13), [33] (eh 7), [36] (eh 4) and [34] (eh 12). The presence of these surface charges gives rise to a number of electrokinetic phenomena, in particular electrophoresis. 

Electrostatic Interaction. Similarly charged particles repel one another. The charges on a particle surface may be due to hydrolysis of surface groups or adsorption of ions from solution. The surface charge density can be converted to an effective surface potential, /, when the potential is <30 mV, using the foUowing equation, where -Np represents the Faraday constant and Ai the gas law constant. 

The size of particles removed by such filters is less than the size of the passages. The mechanism of removal includes adsorption (qv) of the impurities at the interface between the media and the water either by specific chemical or van der Waals attractions or by electrostatic interaction when the medium particles have surface charges opposite to those on the impurities to be removed. 

The first simulation studies of full double layers with molecular models of ions and solvent were performed by Philpott and coworkers [51,54,158] for the NaCl solution, using the fast multipole method for the calculation of Coulomb interactions. The authors studied the screening of a negative surface charge by free ions in several highly concentrated NaCl solutions. A combination of (9-3) LJ potential and image charges was used to describe the metal surface. 

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