Some rules for the definition of dielectric constants in proteins.

Definition	Value	Comments
Polar = ε large	ε = large	Protein sites are always polar near small radii ions.
Nonpolar = ε small
	ε(r) > 10 often ε(r) ≥ 40	The value of ε is large for charge–charge interactions.
	ε B > 10	Proteins can provide as much solvation as water for ionised groups with small radii.
	ε ≥ 4	For functionally important charge–dipole interactions, the value of ε could be as small as 4. Such a low value, however, requires relatively fixed dipoles with little energy for reorganisation.