O=C(NCCN1C(=O)S/C(=C\c2ccc(Cl)c(Cl)c2)C1=O)c1ccc2c(c1)C(=O)N(Cc1ccncc1)C2=O
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?