Electrostatic bonds are formed when two oppositely charged groups come close together and attract each other.

Example: Divalent cations like Mg²⁺ may form electrostatic bonds with two acidic side chains.

Interaction between acidic and basic groups of amino acid: The R—group of glutamic and aspartic acid contributes negatively charged carboxylate groups, and the basic amino acids (arginine, histidine, and lysine) contain positively charged groups and favour the ionic bonds in between these amino acids.