Anion exchangers bind negatively charged solute ions (anions); therefore, the stationary matrix itself carries a permanent or positive charge (e.g., diethylaminoethyl or quaternary amine groups).

Quaternary amine (Q-type) is the classic strong anion exchanger (fully ionized across the entire working pH range). Hydroxyapatite acts as a mixed-mode crystalline calcium phosphate matrix exhibiting strong phosphate/anion exchange binding. DEAE is a weak anion exchanger, and sulphonate is a strong cation exchanger.

SDS denatures proteins and binds at a constant ratio of approximately $1.4\text{ g SDS/g protein}$, conferring a uniform negative charge density and identical charge-to-mass ratio. Consequently, separation in the polyacrylamide gel occurs exclusively based on molecular size through the molecular sieving effect of the gel pores.

Thermodynamics of globular protein folding in water:

• Glutamic acid carries a negatively charged carboxylate side chain (hydrophilic) that interacts favorably with surrounding water molecules on the protein exterior surface.
• Aspartic acid is similarly a charged, polar hydrophilic residue that segregates to the outer surface.
• Lysine carries a positively charged ammonium side chain (hydrophilic) exposed on the external solvent interface.
• Phenylalanine possesses a bulky nonpolar aromatic benzyl side chain that is hydrophobic and buries within the interior core of the folded protein away from water.