Solution dielectric constant

Another interface that needs to be mentioned in the context of polarized interfaces is the interface between the insulator and the electrolyte. It has been proposed as a means for realization of adsorption-based potentiometric sensors using Teflon, polyethylene, and other hydrophobic polymers of low dielectric constant Z>2, which can serve as the substrates for immobilized charged biomolecules. This type of interface happens also to be the largest area interface on this planet the interface between air (insulator) and sea water (electrolyte). This interface behaves differently from the one found in a typical metal-electrolyte electrode. When an ion approaches such an interface from an aqueous solution (dielectric constant Di) an image charge is formed in the insulator. In other words, the interface acts as an electrostatic mirror. The two charges repel each other, due to the low dielectric constant (Williams, 1975). This repulsion is called the Born repulsion H, and it is given by (5.10). 

A few analytical formulae to compute the GB radii in the above two models were proposed. Recently Wojciechowski and Lesyng81 proposed a generalization of this model mapping the exponents of 6 and 1/3 into n and l/(n-3), respectively. In their model, the parameter n depends on the ratio of the solvent and solute dielectric constant. At present, this model reproduces the PB energy in the best way. 

It is also possible to combine the supermolecule and continuum approaches by using specific solvent molecules to capture the short-range effects (i.e., those involving specific noncovalent interactions between solute and solvent) and a reaction field to treat longer range effects.33-35 Alternatively, structures along the gas phase reaction coordinate can be immersed in a box of hundreds (or more) of explicit solvent molecules that are treated using force field approaches.36,37 Each type of method - the SCRF, solvent box, and supermolecule approaches - tests the importance of particular features of the solvent on the reactivity of the solute dielectric constant, multiple specific classical electrostatic interactions, and specific local directional noncovalent interactions, respectively. 

S]. Another explanation could be changes in the dielectric constant in the region of the film, since the dielectric constant has an effect on conductivity responses for APM devices (see Section 3.3.4) [16,34]. In another study, a TSM was used with a conductivity electrode to make a sensitive probe of conductivity that had little dependence on solution viscosity and density [36]. In addition, the parasitic contribution to the static capacitance in TSM devices has been correlated with solution dielectric constant [11,12]. 

Reference system contribution, indicated by the tilde, to the binding energy of a distinguished molecule of type a to the solution. Dielectric constant. 

No experimental results are available for the nucleic acids, with or without methyl substitution, to test the theories, but we can compare the results for thymine to three theoretical estimates based on the linearized Poisson-Boltzmann equation. The AM1-SM2 and PM3-SM3 values are —16.5 and -20.1 kcal/mol, respectively. Using charges and force field parameters from the AMBER,347 CHARMM, and OPLS molecular mechanics force fields and a solute dielectric constant of 1, Mohan et al.i calculated solvation energies of -19.1, -10.4, and -8.4 kcal/mol. The wide variation is disconcerting. In light of such wide variations with off-the-shelf parameters, the SMx approach based on parameters specifically adjusted to solvation energies appears to be more reliable. 

The free ions and ion pairs play a distinct role in the dielectric properties of electrolyte solutions. Due to the saturation of the dipole orientation near free ions, the dielectric constant of the system decreases with the increase of free ion concentration. Ion pairs possess the dipole moments and produce an additional contribution to the dielectric properties. Due to the new polarization effect, the dielectric constant of the entire system increases with the increase of the ion pair concentration. It is generally accepted to distinguish the solvent dielectric constant, es, and the solution dielectric constant, e [3], The dielectric constant of the solvent describes the polarization effect of the solvent molecules in the presence of ions es decreases with the increase of ion concentration. The dielectric constant of the solution also includes the polarization effect from the ion pairs that can increase or decrease with the increase of ion concentration. Due to this, e > es, and only for a completely dissociated electrolyte, (a = 1) e = es. 

The polarization effect on the ion pair is important in describing the dielectric constant e of the solution. For this purpose it is possible to use the modified version of the MSA-MAL theory in which ion pairs are included as new polar entities with the density 1 / 2- pt( — a) and with the dipole moment Pi = eRi. Correspondingly, the ion density should be changed to the density of free ions api. Such ion-dipole mixture being taken into consideration, again leads to the form (123) for the solution dielectric constant. However, in the considered case ys should be changed to... 

The system of equations for the parameter 62 should be also slightly modified. If we assume for the simplification that ion pairs have the same sizes as the solvent molecules, the system of equations for the parameter 62 reduces to the system that is similar to that obtained in the MSA theory for ion- dipole mixture [65, 66]. The proposed theory includes two opposite tendencies. Due to the change of m to na, the solution dielectric constant, e, decreases slower with the increase of ion concentration. Due to the change of ys to y, the dielectric constant e can increase with the increase of ion concentration. For the low ion... 

An ion in solution has a repulsive interaction from the surface when the solution dielectric constant is higher than that of the substrate. This effect can lead to desorption for highly charged PE chains. On the contrary, when the substrate is a metal, there is a possibility to induce PE adsorption on noncharged substrates or on substrates bearing charges of the same sign as the PE. See Ref. [84] for more details. 

The experiments described above have led to the conclusion that the chiral-induced equilibrium shift could be induced in the lanthanide (III) complex by a combination of electrostatic and hydrophobic interactions. Hydrogen bonding effects appear to be less important as suggested by experiments carried out under variable pH, temperature, concentration, solvent type, and solution dielectric constant conditions. By analogy to the associated/dissociated equilibrium shift models of Schipper (1978) in which the source of the equilibrium perturbation is attributed to a free energy of mixing, Brittain (1981) and Wu et al. (1989) attempted to ascertain the complex mechanism responsible for this type of Pfeiffer effect. However, their conclusions were opposite as they concluded that the [Tb(DPA)3] complex interacted with the... 

The maximum change of n of the protein solution affected by theTC reached the value of An = 2x10-4, which is an order of magnitude larger than the temperature changes of n. Thus, the numerical estimates and the experimental data show that changes of n caused by the influence of the TC have been conditioned by nonthermal changes of the solution dielectric constant, which may be described as the total contribution of electronic, vibrational and orientational components. 

The thylakoid membranes are represented by plane sheets of a dielectric with constant D. The charges are considered as smeared over the surface thus yielding a charge density a. The space in and outside the thylakoids contains an aqueous solution (dielectric constant D ) of a 1,1-electrolyte. With a reference point for the electric potential in the bulk phase. 

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