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Probing electrostatic interactions in solution by EPR


Shi,  Feng
MPI for Polymer Research, Max Planck Society;

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Shi, F. (2003). Probing electrostatic interactions in solution by EPR. Master Thesis, Johannes Gutenberg-Universität, Mainz.

Most chemical reactions are carried out in solutions and those encountered between charged particles are known to be influenced by electrostatic interaction between them. Electrostatic interactions are important for the selforganization of synthetic supramolecular systems and for the function of biomacromolecules such as DNA and proteins. The theory of such interactions is usually based on Coulomb’s law, thus considering the space between the ions as a dielectric continuum. At short distances between ions this is unlikely to be a good approximation – it may be necessary to include salvation explicitly in the model. The theoretical calculation of the electrostatic interaction is still difficult because many factors have to be taken into account. These are the spatial distribution of the charge over the reagents (in nonspheric particles), the possibility of the association of reagents with a counterion and reliable data on the microscopic dielectric constant of the medium in the vicinity of ions, etc. [5] As to the experimental research on the role of electrostatic interaction in ionic reactions, the most complicated thing is that the reaction rate depends on a great number of factors each of which is difficult to estimate a priori. The spin exchange between charged particles is influenced by a much smaller number of factors. The study of spin exchange is therefore a convenient method to investigate the influence of electrostatic interactions on the efficiency of various processes in liquids. In our short time work, we use this method to probe the electrostatic interactions in solutions and try to obtain some useful information on the properties by varying the solution components. Firstly in the theoretical part we will give a short introduction of the background of the electrostatic interaction in solutions and the principle of EPR, secondly in the experimental part we will study the various factors influencing the electrostatic interactions by varying the solvent/solvent mixtures for the oppositely charged spin probes, Cat1 and Fs, via EPR spectroscopy to quantify exchange interaction. In the discussion part, we consider whether the experimental results can be explained by simple theories on electrostatic interaction and exchange coupling in solution.