Specific Ionic Effects

We have studied the electrochemical behavior and redox-driven mass changes for PAH-Os/PVS films immersed in solutions of salts with a common anion and different cations and a common cation and different anions [148]. The electrochemical and 

Qdx CV anodic peak charge, Eip - average peak potential, peak separation, Am/Aq  

QdX CV anodic peak charge, E1/2 average peak potential, E[ x-E]fd peak separation, Am/Aq exchanged mass to redox charge ratio for complete film oxidation, Am/Amol exchanged mass per mole of electrons and Dapp apparent diffusion coefficient measured by EIS. 

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One of the main shortcomings of the traditional DLVO theory is its inability to predict specific ionic effects. These effects are sometimes much stronger than what the excluded volume effects (examined in the previous chapter) can explain. It was recently suggested by Ninham and his group that the van der Waals interactions between ions and the rest of the system might be responsible for the ionic specificity [M. Bostrom, D.M.R. Williams, B.W. Ninham, Phys. Rev. Lett. 87 (2001) 168103]. However, these ion-dispersion forces lead to qualitatively incorrect results, namely that the cations are attracted toward the air/water interface and the anions are repelled by that interface. Experiment shows that the opposite is actually true. 

We showed previously that a simple model for the ion-hydration interactions, which separates the ion-hydration forces in a long-range term due to the behavior of water as a continuous dielectric (the screened image force) and a short-range term due to the discreetness of the water molecules (SM/SB), can explain almost quantitatively a number of phenomena related to the electrolyte interfaces.6 In this article, we examined the limitations of the model in predicting the distributions of ions near the air/water interface, by comparison with molecular dynamics simulations. It is clear that the real ion-hydration forces are more complicated than the simple model employed here however, the interfacia] phenomena (including specific ionic effects) can be understood, at least qualitatively, in terms of this simple approach. 

An important issue is whether the structure of the adsorbed protein is modified by the addition of electrolyte. The electrolyte is added only at the beginning of the light scattering experiment,1 and one might expect that during the experiment (about 2 min), and at low electrolyte concentrations, not much modification in the structure of the adsorbed layer can occur. This expectation, however, is probably not accurate. The strong specific ionic effects... 

Despite the fact that main focus has always been on ion channels, the influence of physiologically most relevant ions (such as Na", K", Cl , Ca, or Mg" ) on model lipid membranes was also studied in considerable detail [21-24]. Additionally, other ions, such as Li", Cs", NH4, Ba" ", La" ", F , Br , I , NO3, and SCN , were also investigated [24-26] in order to elucidate the factors influencing the specific ionic effects observed. This specificity has been known from measurements to be more pronounced for anions than for cations consequently, more experimental data are available for the former ions [26-29]. Computer simulations are, however, typically more focused on cations, since a proper description of the effects of larger anions often requires the use of resource-consuming polarizable force... 

The understanding of equilibrium, thermodynamical and strnctural properties in colloidal and interfacial systems, especially that of specific ionic effects in charged systems, can be attacked from the theoretical point of view using different levels of description and different, more or less approximated approaches. 

D. di Caprio, J. Stafiej, J. P. Badiah. A field theory study of the effect of specific ionic interactions in ionic systems. J Chem Phys 705 8572-8583, 1998. 

In the meantime, we believe that the best prediction of the toxicity of an ionic liquid of type [cation] [anion] can be derived from the often well known toxicity data for the salts [cation]Cl and Na[anion]. Since almost all chemistry in nature takes place in aqueous media, the ions of the ionic liquid can be assumed to be present in dissociated form. Therefore, a reliable prediction of ionic liquids HSE data should be possible from a combination of the loiown effects of the alkali metal and chloride salts. Already from these, very preliminary, studies, it is clear that HSE considerations will be an important criterion in selection and exclusion of specific ionic liquid candidates for future large-scale, technical applications. 

The derivation of the equations of the Debye-Huckel theory did not require differentiation between a solution of a single electrolyte and an electrolyte mixture provided that the limiting law approximation Eq. (1.3.24), was used, which does not contain any specific ionic parameter. If, however, approximation (1.3.29) is to be used, containing the effective ionic diameter ay it must be recalled that this quantity was introduced as the minimal mean distance of approach of both positive and negative ions to the central ion. Thus, this quantity a is in a certain sense an average of effects of all the ions but, at the same time, a characteristic value for the given central... 

In this case, the anion being hard and with a high charge density, the reactions are concerned with tight ion pairs. During the course of the reaction, ionic dissociation is increased and hence polarity is enhanced from the GS towards the TS. Specific microwave effects should be expected. 

Polycarbonyl and polyamino compounds include chelates, which are manmade compounds, and siderophores, which are biologically derived and more specialized. They can help dissolve inorganic ions, keep ions in one specific ionic state, and maintain them in biologically available forms. Because of their ability to bring ions into solution, they are often used to extract specific ions in specific forms from soil. Cationic micronutrients, particularly iron and zinc, are often applied in chelated form as a foliar spray to alleviate nutrient deficiencies. This is particularly true of plants growing in basic soil and is done even when plants do not show micronutrient deficiencies. Typically, both foliar and soil applications are effective in this regard. 

Keywords Asymmetric synthesis, Chiral ionic liquids, Ion pairing, Local structure. Nuclear Overhauser effect. Task-specific ionic liquids... 

Let us consider now the case of a specific ionic polysaccharide. The unique properties of complexes of the cationic chitosan with non-ionic sorbitan esters provides an interesting example. Grant and co-workers (2006) have established that mixtures of chitosan and surfactant form emulsion-like solutions and/or creams, where the surfactant component is present as droplets or micelle-like particles and the chitosan solution acts as the system s continuous phase. It was established that the length and the degree of saturation of the surfactant hydrocarbon chain have a significant impact on the development of the chitosan-surfactant complexes. Moreover, an optimal distance between the chitosan s protonated amine groups is required for effective interactions to occur between the polysaccharide and the sorbitan esters. 

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