Hydration and Ion Binding of Small Biologically Active Molecules: The Case of Neurotransmitters

Despite the emergence of many different techniques to study the solvation of various solutes during the last decades, fundamental rules and guidelines for the description of the hydration structure and dynamics are still lacking. It seems that despite recent advances in these felds, many questions are still open and fnding answers to at least some of these matters could be of crucial importance for chemistry, biochemistry and chemical engineering. However, in order not to get hopelessly lost in its complexity of this issues, it is instructive to focus on a certain class molecules. Thorough investigations of their physico-chemical behaviour in aqueous solution could infer information on the solute-solute and solvent-solvent interactions. These data, in the case of biologically relevant solutes, could shed some light on their biological activity and, on the other hand, could potentially be used for the construction of models for other solutes. This work presents an in-depth investigation of the structure, solvation and dynamics of aqueous solutions of some selected neurotransmitters and other chemically-related, biologically relevant molecules by the means of dielectric relaxation spectroscopy (DRS) in the megahertz to gigahertz frequency range. A special focus of this thesis is the interpretation of the DRS results on a microscopic level with the aid of quantum chemical calculation of the investigated molecules. Comparisons of these results with other theoretical and experimental approaches will be drawn, with the aim to provide a coherent picture and thus to build a bridge between the different techniques. Furthermore, new mathematical approaches for the analysis of the DR spectra were developed and utilized in this work