The chemistry of molecular interactions is a matter of shape and electrostatics, but doing electrostatics poorly is worse than doing none at all; accurate charges are required. Even the best charge models are useless if protonation states are wrong. QUACPAC attempts to offer everything necessary to do charges correctly. It includes pKa and tautomer enumeration in order to get correct protonation states, partial charges using multiple models that cover a range of speed and accuracy, and electrostatic potential map construction and storage.
The QUACPAC distribution comprises 4 applications:
Sets the ionization state of input molecules using a rule based system.
Assigns appropriate atomic partial charges, both to small molecule ligands and to biopolymers.
Enumerates the protonation states and assess ligand pKas.
Canonicalizes and enumerates the tautomeric forms of a small molecules.