Polyelectrolytes

Macromolecules, such as polylysine (see here), carry multiples of only positive or negative charge. Such molecules are called polyelectrolytes. They have many like charges to be in close proximity and this causes the pK a of each group to be influenced by the state of ionization of the others - widening the range of ionization beyond that of the simple range of a single such group. In a molecule like polylysine, the first protons are more easily removed than the last, because the strong positive charge on the fully protonated molecule helps drive protons away.

Nucleic acids are polyelectrolytes (negatively charged) and are ionized over a wide pH range for the reason given above.

See also: Ampholytes, Polyampholytes, pK a, Nucleic Acids