NC(Cc1ccc(S(=O)(=O)O)cc1)C(=O)NC(Cc1ccc(S(=O)(=O)O)cc1)C(=O)NC(Cc1ccc(S(=O)(=O)O)cc1)C(=O)[O-].[Na+]
A higher negative pKa value denotes a less powerful acid. What is this molecule's negative pKa value?