In the present work the thermodynamics of protein adsorption to charged polyelectrolytes is explored. Unravelling interactions of proteins with highly charged polyelectrolytes as e.g. DNA is a central topic in biophysics since many years. It is now well-established that ionic interactions play a major role for the strength of binding as expressed through the thermodynamic binding constant Kb. Moreover, counterion release has been identified as the driving force for binding: Patches of

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... charged amino acid residues located on the surface of the protein act as multivalent counterions that compensate the charge of the polyelectrolyte. In this way a concomitant number of counterions condensed to the polyelectrolyte are released. The first part of this thesis contributes to the understanding of counterion condensation that determines the effective charge of a polyelectrolyte. The interaction between dendritic polyglycerol sulfate (dPGS) and divalent ions (Mg2+ and Ca2+) were analyzed by combination of experiment (isothermal titration calorimetry (ITC)) and theory (non-linear penetrable Poisson-Boltzmann (PPB) model). The discussed lack of ion-specific effects upon adsorption of divalent ions to dPGS and a clear competition between mono- and divalent ions allows a better understanding of the fundamentals of polyelectrolyte-protein (PE-P) interaction that are presented in the following chapters. In the second part, a comprehensive thermodynamic study of the PE-P interaction is presented. Starting form a linear (heparin) and low molecular weight (β cyclodextrin sulfate (β-CD-S)) polyelectrolytes up to a polyelectrolyte brushes - a detailed picture of the binding driving forces is given. A quantitative analysis of the thermodynamic processes involved in the interaction of the model glycosaminoglycan (GAG) - heparin and lysozyme is presented. The binding constant Kb was determined by ITC as the function of temperature and ionic strength adjusted through the concentration cs of added salt. The dependence on salt co [...]