O=C(N/C(=C\c1ccc([N+](=O)[O-])cc1)c1nc2c(O)nc(S)nc2[nH]1)c1ccccc1
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?