Mitteionilised

Mitteionilised is an Estonian term used to describe species that have not been ionized and thus carry no net electric charge. In chemistry and biochemistry, many compounds exist in equilibrium between non-ionized and ionized forms depending on conditions such as pH, solvent, and temperature. The relative amounts of each form are described by acid–base equilibria and constants, particularly pKa.

In aqueous solutions, the fraction that remains non-ionized for a weak acid or base is governed by Henderson–Hasselbalch relationships. For a weak acid HA, pH = pKa + log([A-]/[HA]); for a weak base B, pH = pKa + log([BH+]/[B]). Lower pH tends to favor the non-ionized form of acids, while higher pH favors the ionized form; for bases, the opposite.

Non-ionized molecules are typically less polar than their ionized counterparts, with higher lipid solubility and greater ability to cross cell membranes. Ionized species, conversely, are generally more soluble in water and less able to diffuse through lipid barriers. Consequently, the ionization state influences properties such as solubility, permeability, distribution in organisms, and environmental fate. In pharmacology, the non-ionized form often contributes to oral absorption, while in environmental chemistry, speciation affects mobility and bioavailability.

See also: ionization, acid–base equilibrium, pKa, Henderson–Hasselbalch.