Cc1nc(/N=N\c2ccc(S(=O)(=O)[O-])cc2S(=O)(=O)[O-])c(COP(=O)([O-])[O-])c(C=O)c1O.[Na+].[Na+].[Na+].[Na+]
A higher negative pKa value denotes a less powerful acid. What is this molecule's negative pKa value?