Ionic charge influences

Influence" of ionic charges on second-order diffusion-controlled rate constants in aqueous solution at 25 °C... 

Having discussed ionic screening and its effects on the value of y , we now consider the ionic charge z. When assessing the influence of z, we first define the extent to which a solute promotes association, and thus screening. The preferred parameter is the ionic strength I, as defined by... 

Experimental Rate Constants for Base Protonation Illustrating the Influence of Ionic Charge on Protonation Reactions in Aqueous Solution (25 C, p = 0 M)... 

Equation 32 expresses the influence of the dielectric constant of the medium in the case of infinite dilution of solutions. The first term is attributed to the ionic charge and is of the Born form. Born (11) obtained a corresponding term in A (see Equation 24) in his derivation of the heat of hydration, and Scatchard (12) introduced it in the theory of activities. The second and third terms represent the influence of the dipolar part. Their form is essentially affected by the use of the Onsager model (5). 

The part of the activity coefficients depending on k (Equation 33) can be simplified further if suitable average values are introduced. If the restriction d a is sufficiently well fulfilled, the term in y is small compared with the term in <5. The latter therefore represents the main influence caused by the presence of dipoles since the terms in are from ionic charges. They are identical with terms of corresponding order in the Debye-Hiickel theory. 

Ionic strength influences are well known with respect to the rate and energetics of nucleic acid hybridization [17]. Charge and ionic radius are both important in terms of stabilizing the structure of the duplex as well as stabilizing the stem portion of the molecular beacon [17]. The stem structure stability was increased when a divalent cation was incorporated into the hybridization buffer solution [17]. It was reported that cations were best at stabilizing the duplex formed upon hybridization in the order Ca2+ > Mg2+ K+ > Na+. The ultimate detection limit of the sensor configuration was calculated to be 1.1 nM [17]. 

In contrast to equilibria dominated by chloride complexation, equilibria involving hydrolysis or carbonate complexation are strongly influenced by pH. A cation s tendency towards hydrolysis, and its complexation behaviour in general, can be described in terms of the ratio of its ionic charge squared (z2) to its ionic radius (r) in Angstroms (Turner et al., 1981). Cations with z2/r in the intermediate range, 7 < z/r < 25, have seawater speciation schemes that are strongly influenced by solution pH. Carbonate equilibria of the form... 

Bronsted-Bjerrum equation — The rate constant k of a chemical reaction involving ionic species A and B may be influenced by other ionic species in solution not directly participating in this reaction (i.e., a dissolved salt, thus the associated observation is called primary salt effect). The change of the rate as a function of the ionic charge of the involved species and the - ionic strength of the solution is given by the Bronsted-Bjerrum equation... 

The method of equilibrium foam film allows to study the ( -potential at various aspects by means of the microinterferometric technique (see Chapter 2). For instance, to determine cpo at electrolyte solution/air interface (no surfactant) which is very hard to realise experimentally to find the origin of the surface charge in this case [186,187] to find the isoelectric points at the solution/air interface [173,188] to study the effect of the concentration of various kinds of surfactants [95,100,189,190] ionic effects influence of Na+... 

The time has come to free the treatment of ionic transport from the assumption of the independence of the various ionic fluxes and to consider some phenomena which depend on the fact that the drift of a species i is affected by the flows of other species present in the solution. It is the whole society of ions that displays a transport process, and each individual ionic species takes into account what all the other species are doing. Ions interact with each other through their Coulombic fields and thus it will be seen that the law of electroneutrality that seeks zcto excess charge in any macroscopic volume element plays a fundamental role in phenomena where ionic flows influence each other. 

If a significant change of polarity takes place in the formation of the transition state from the reactants, we have to consider additional contributions to AV which are caused by differences in the electrostriction of the solvent under the influence of partial ionic charges [46]. For a transition state which involves much more charge separation than... 

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