Surface electrostatic potential

Janssens et al. [38, 40] used photoemission of adsorbed noble gases to measure the electrostatic surface potential on the potassium-promoted (111) surface of rhodium, to estimate the range that is influenced by the promoter. As explained in Chapter 3, UPS of adsorbed Xe measures the local work function, or, equivalently, the electrostatic potential of adsorption sites. The idea of using Kr and Ar in addition to Xe was that by using probe atoms of different sizes one could vary the distance between the potassium and the noble gas atom. Provided the interpretation in terms of Expression (3-13) is permitted, and this is a point the authors checked [38], one thus obtains information about the variation of the electrostatic potential around potassium promoter atoms. 

C. J. Drummond and F. Grieser, Absorption spectra and acid-base dissociation of the 4-alkyl derivatives of 7-hydtoxycoumarin in self-assembled surfactant solution Comments on their use as electrostatic surface potential probes, Photochem. Photobiol. 45, 19-34 (1987). 

Woodle M, et al. Sterically stabilized liposomes. Reduction in electrophoretic mobility but not electrostatic surface potential. Biophys J 1992 61 902. 

One consequence of the molecular asymmetry is that the core particle presents two distinct faces, arbitrarily labeled ventral and dorsal in our images. These two faces have subtle yet distinct dilferences in the electrostatic surface potentials they present. 

An approximate quantum mechanical expressions- that allows one to calculate the electrostatic surface potential around atoms, radicals, ions, and molecules by assuming that the ground-state electron density uniquely specifies the Hamiltonian of the system and thereby all the properties of the ground state. This approach greatly facilitates computational schemes for exact calculation of the ground-state energy and electron density of orbitals. 

Shape descriptor derived from ray traces of the molecule s electrostatic surface potential. 

Reversed-phase chromatography is often used to separate both neutral and ionic organic compounds. In this section, some important aspects for the understanding of the behavior of ionic compounds in reversed-phase chromatography are discussed. The important concepts introduced here are the electrical double layer and the electrostatic surface potential. It will be shown that they are essential for the understanding of the elution profile of ionic compounds. These concepts are further explored in the next section where theoretical models for ion-pair chromatography are discussed. 

For low surface concentrations of charged solutes, the G-C model shows that the electrostatic surface potential created by the adsorbed ions is proportional to the surface concentration of the ion according to the following equation [2,3] ... 

From the previous discussion, it is clear that when an ionic solute adsorbs to the reversed-phase stationary phase, it will create an electrostatic surface potential that will repel ions with the same charge from the surface and that the magnitude of the repulsion is represented by Equation 15.11. With the help of Equations 15.11 and 15.12, the adsorption isotherm for an ionic solute can be derived in the following way ... 

To write down the electrochemical potential for the surface, we must consider that the ionic analyte changes the electrostatic surface potential, i.e.,... 

Equation 15.22 shows that it is the electrostatic surface potential created by the adsorbed pairing ion that is the driving force behind the regulation of retention. The electrostatic surface potential... 

When the electrostatic surface potential becomes high or when the monolayer capacity of the surface is approached. So far the models agree with experiments up to 60-70 mV but the upper limit is probably below 100 mV. 

The Poisson-Boltzmann equation. The slab model is based on a solution of the linearized Poisson-Boltzmann equation that is valid only for low electrostatic surface potentials. As... 

Figure 7.11 A The electrostatic surface potential of trypsin (left) and gamma...

Figure 4. Calculated dependence of the ratio of the surface charge density to the surface excess on the electrostatic surface potential. Curve A is for the infinite flat plate case. Curve B is for a sphere with a 1000 A. radius...

The arrangement of the proteins within the membrane seems to depend to some extent on the electrostatic surface potential and interface permittivity. It is influenced by electrostatic interaction between the proteins, polar head groups of the phospholipid and ions within the aqueous medium of the membrane surface. This can be affected by exogenous molecules such as drugs. Phospholipid-induced conformational change in intestinal calcium-binding protein in the absence and presence of Ca2+ has been described [37]. There is, however, no doubt that hydrophobic interactions between peptides and membrane interfaces play an important role. A general frame-... 

In the case of metallic particles, just this second term dominates the electrostatic potential distribution in the electrolyte solution. As a good approximation in this situation the interaction at a constant electrostatic surface potential may be assumed. However, this approximation does not reflect the actual situation—this latter may slightly depart from the model regime assumed [21]. 

Figure 2.5 (a) Poisson-Boltzmann electrostatic surface potential of chloroperoxidase at pH 7.0 (blue represents areas of positive charge and red, areas of negative charge) and (b) calculated charge on chloroperoxidase as a function of pH. Reprinted with permission from [51], Copyright (2007) American Chemical Society. 

The modulation of analyte retention by the electrostatic surface potential is described by the first term in the numerator of Equation 3.21. If the analyte is oppositely (similarly) charged to the IPR, it experiences an attractive (repulsive) interaction with the stationary phase hence its retention wonld monotonously increase (decrease) with increasing IPR concentration in the absence of other interactions. The second term in the nnmerator of Equation 3.21 is related to ion-pair formation at the stationary phase that may ensue from four interdependent equilibria (1) the simultaneous adsorption of both E and H onto L, (2) the adsorption of E onto LH, (3) the adsorption of H onto LE, and (4) the adsorption of EH onto L. 

Lower electrostatic surface potential according to Equation 3.5 because the fixed surface charges are better shielded by the IM ions in the electrical double layer this promotes analyte elution via a competition between IM and analyte ions for the adsorbed IPR. 

A Donnan effect that prevents self-repulsion of the similarly charged adsorbed IPR ions at higher ionic strength, the higher surface concentration of the IPR ( LH in Equation 3.5) partially compensates for the decreased magnitude of the electrostatic surface potential due to the increased Scoi in Equation 3.5. 

Payne and Glen (105) studied several different aspects of molecular recognition with genetic algorithms. Conformations and orientations were determined which best-fit constraints such as inter- or intramolecular distances, electrostatic surface potentials, or volume overlaps with up to 30 degrees of Ifee-dom. 

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