Polyion interactions

For the electrostatic term, there is a lack of reliable data and predictions dealing with the variation of the ions -polyion interactions with temperature. If one considers the relation (8), the product D T is a decreasing function of temperature but the term 7 decreases for the high values of and increases for the low values of . Nervertheless, these variations are negligeable and we have considered, in a first approximation, that the electrostatic term remains constant for 20 < T < 80°C. 

The low adsorbance and the high thickness at low salt concentration are due to the electrostatic repulsion, i.e., the excluded volume between the charged groups of adsorbed polyions. As the ionic strength is increased, the intra- and inter-polyion interactions of adsorbed NaPSS chains diminish so that a larger adsorbance and smaller thickness should be obtained. 

Despite the inherent weaknesses of the Poission-Boltzmann (PB) equation that includes neglect of polyion-polyion interactions and the size of mobile ions, it has nevertheless played an important role in elucidating the characteristics of electrostatic interactions and ion atmopshere in nucleic acids [12]. Two salient results have emerged from such an analysis. First, for cylindrical-shaped molecule of infinite length, there is a critical linear charge density beyond which counterion condensation takes place [33, 34]. Second, the phenomenon of counterion condensation takes place in one and two dimensions only [33, 35], An... 

The effect of simple salt on the surfactant binding confirms the electrostatic nature of the surfactant ion-polyion interactions (step 1, Scheme 1). Any increase in the ionic strength of solution shifts the onset of binding toward higher free surfactant concentrations (compare isotherms in water, 0.01 M, and 0.1 M NaCl, Figure 6) and decreases the amount of bound surfactant. These observations can be related to the screening influence of the simple salt, which acts to diminish the electrostatic interactions between surfactant cations and polyanions. This is also well documented in the literature for a variety of polyelectrolyte-surfactant pairs [26-29],... 

Transport parameters of the polyion itself will be affected by two types of ion-polyion interactions ... 

From the experimental results that we have just presented, which were obtained by various independant techniques, it is obvious that electrostatic interactions have a predominant influence on ion-polyion interactions in aqueous solutions. This influence is exerted at three different levels ... 

The acceleration of the Hg(II)-induced aquation of [Co(NH3)5X] (X = Cl or Br) by the mucopolysaccharides chondroitin sulfate A and C has been studied as a function of the concentration of polyion and Hg(II), of pH, and the ionic strength. Inhibition of this reaction by a number of divalent ions emphasizes the electrostatic character of the metal-polyion interactions when sulfate groups are involved. 

Large spherical polyions are usually treated as an effective one-component system where the interaction between the polyions is given by a hard sphere potential plus a repulsive screened Coulomb potential (DLVO model) [31]. The screening of the polyion interactions is entirely due to the charges and concentrations of counterions and salt ions. As a result, the polyions interact via an effective charge Zeff or an effective surface potential. The value of z f depends on how the correlations between the polyions themselves and between polyions and counterions are theoretically formulated. All models discussed so far lead to an effective interaction in terms of screening arguments. A more detailed theory is required to consider the small ions in the system explicitly. Different approaches... 

Chemical transformations corresponding to schemes I and II, in terms of traditional classification represent ion exchange and neutralization reactions, respectively. However, with respect to polyion interaction these processes can be considered as polyion addition reactions. 

The variation of reduced increments versus the concentration is probably a consequence of the polyion-polyion interactions which reduce the extension of polyions and their ionic atmosphere. 

This result is strictly valid in the limit of infinite polyion dilutions, a situation for which polyion-polyion interactions are vanishing. For more concentrated solutions one has to take into account isotopic interactions fss when flux equations for both labelled and unlabelled particles are developed. For this point see References [3] and [4]. 

Although not directly contained within the framework of this paper, before finishing, I should like to mention the case when it is the ion or the small molecule that is optically active instead of the macromolecule because this case offers an interesting approach to ion-polyion interactions through the optical activity. One can mention for example the variations of the ORD of complex Com ions in the presence of sodium... 

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