The dissertation investigates the behavior of one of the key parameters of aqueous
solutions – the hydrogen index – under variations in temperature and concentrations of
salts and proteins in solution. The hydrogen index (pH value) is determined by the
concentration of free hydrogen ions in a solution and plays a crucial role in the
formation of the physicochemical properties of the system. Investigation of pH
behavior is highly relevant, since the acid–base balance affects the electrophysical
properties of proteins, the structural organization of the aqueous medium, the stability
of colloidal systems, and the course of biochemical processes in living organisms.
It is known [1] that the pH value of human blood is a strict physiological constant
ranging from 7.36 to 7.44. Deviations beyond this interval lead to disturbances in
homeostasis, while changes in normal pH values by 0.4–0.5 units may cause
irreversible alterations incompatible with life. Variations in the acid–base state of blood
influence the functioning of enzymatic systems, the permeability of cellular
membranes, the transport of oxygen and carbon dioxide, as well as the electrokinetic
properties of blood plasma proteins. Furthermore, a decrease in sodium chloride
concentration in blood causes water transport from the bloodstream into the
intercellular space, resulting in blood thickening, disorders of the nervous and
cardiovascular systems, and disturbances of the body’s water–salt balance. Therefore,
investigation of the mechanisms governing acid–base balance formation is important
from both fundamental and applied perspectives.
A considerable number of scientific studies have been devoted to determining the
hydrogen index of solutions and investigating the temperature and concentration
dependences of pH. Traditional approaches to describing the acid–base properties of
aqueous systems are based on thermodynamic concepts, the theory of electrolytic
dissociation, ion activity models, and the concept of water autoprotolysis. Most
existing models assume structural homogeneity of water and independence of proton
transfer processes from the local organization of hydrogen bonds. However, such
approaches do not always adequately explain the behavior of pH in concentrated salt
and protein systems, where collective effects, hydration processes, and structural
rearrangements of the aqueous medium play a significant role.
Modern investigations also actively employ statistical and molecular dynamics
approaches for describing water structure and proton transfer mechanisms.
Nevertheless, the considerable complexity of intermolecular interactions in water and
protein solutions prevents the development of a universal model capable of
simultaneously accounting for the influence of temperature, electrolyte concentration,
protein macromolecules, dielectric permittivity, and the hydrogen-bond network on
acid–base balance. The relationship between pH and the zeta potential of protein
solutions also remains insufficiently studied, despite the fact that these parameters
largely determine the stability of biocolloidal systems and the characteristics of
intermolecular interactions.
