Wiązanie jonów na granicy faz oraz specyficzne efekty jonowe
Journal Title: Wiadomości Chemiczne - Year 2012, Vol 66, Issue 3
Abstract
Many biological processes taking place across or at membrane surfaces depend on the interaction between interfaces and ions (derived from the background salt) [1]. Binding of ions to surfactant bilayers, nucleic acids, proteins, and biological membranes markedly affects their stability and properties [2–8]. There are different techniques to measure the ion binding to interfaces, including: nuclear magnetic resonance (NMR) spectroscopy [2, 18-20], the method based on measuring of electrophoretic mobility and the so-called zeta potential measurements [4, 21], the method based on measuring of a ratio of acid-to-base forms of the spectrophotometric indicator pyridine- 2-azo-p-dimethylaniline, PADA [12], and the chemical-trapping method [22]. The above-mentioned methods permit investigation of the binding of either cations or anions to interfaces. Many theories and models had been proposed to describe quantitatively the interactions and distribution of ions at a charged surface. The earliest one was proposed by Gouy and Chapman [23, 24]. However, the classical Gouy–Chapman theory was too simplified due to the neglect of the geometrical dimensions of the ions [27]. Other theories have been developed on the basis of the Poisson–Boltzmann theory and the Poisson–Boltzmann equation (equation 3). This equation has been modified by an introduction of different terms [25, 42]. Recently, Radke et al. proposed interesting models of the ion distribution near the interface: the ion binding model [28] (Fig. 1) and the ion image charge interaction model [51] (Fig. 3). Interaction and binding of ions with interfaces is related to the so-called specific ion effects arising at exchanging ions of the same valence. Franz Hofmeister, Professor of Pharmacology at the University of Prague was the first who studied these effects systematically [13, 14]. The specific ion effects play a significant role in a wide range of biological and physicochemical phenomena from the salt solubility, electrolyte activities, the surface tension of electrolyte solutions, values of pH and zeta potentials, the buffer acting, microemulsion microstructure, cloud points of polymers and surfactant solutions to the action of ions on ion-channels in biological membranes (ion transport across membranes), in enzyme activities, in bacterial growth, and in the interaction between membranes [15, 16]. The biological cell activity is also connected to Hofmeister effects. The ion specificity observed is, in fact, a combination of different subtle effects, such as ion size, hydration of ions, ion effect on interfacial water structure, electrostatic and dispersion interactions, thermal motion, and fluctuations [26, 29–31]. Because of a combination of those different effects, Hofmeister effects remain unexplained by the present theories of physical chemistry [16].
Authors and Affiliations
Anna Jakubowska
Keywords
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