Ionization Processes and Proton Binding in Polyprotic Systems: Small Molecules, Proteins, Interfaces, and Polyelectrolytes

Binding of ions to various materials, such as small molecules, proteins, polymers, colloid particles, and membranes, represents a central theme in basic and applied chemistry. Particularly, the case of proton binding to these substances (i.e., their acid-base behavior) has been a focus of research in many branches of chemistry since the turn of the century. One important topic in physical, analytical, and inorganic chemistry is the measurement, compilation, and prediction of acid-base properties of simple molecules or solvated metal ions.(1–8) These topics remain of much relevance for the development of new analytical techniques and tailoring of buffering or complexing agents.(7,9) Accurately known ionization constants also represent a rather stringent testing ground of our ab initio simulation capabilities of simple molecules in water.(10) Acid-base properties of proteins have been also investigated from early on.(11–14) This field has now matured into an active area of modern biochemistry with implications to the current view of protein folding, enzyme action, and photosynthesis.(15–17) Similar studies of weak polyelectrolytes were initiated in polymer science almost simultaneously(18–21) These systems represent an ongoing challenge to our understanding of acid-base equilibria.(22–25) The substantial interest in polyelectrolytes is due to their use as complexing, flocculating, or stabilizing agents, and their importance in various applications in catalysis, material engineering, biochemistry, and water purification.(26–28)