O=C(NCc1nnc(S)n1-c1ccc([N+](=O)[O-])cc1)c1ccc(S(=O)(=O)N2CCOCC2)cc1
An acid's negative base-10 logarithmic dissociation constant (pka) follows directly from its underlying thermodynamics; pKa is directly proportional to its standard Gibbs free energy change. What is the pka value of this molecule?