The size and charge state of each of these test cases are summarized in Table . In four cases (1ABA, 1STP, 1TOW, 2IFB), the ligands are deprotonated acids with a single negative charge, while for 2PK4, the ligand is a zwitterion. For 1AAL and 1A6F, the ligands are phosphate and sulfate ions with a negative charge of -3 and -2, respectively.