O=C(O)c1ccc(C2Nc3ccccc3-c3nnc(SCc4ccc(Cl)cc4)nc3O2)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?