O=C(O)COc1ccccc1C1Nc2ccccc2-c2nnc(SCc3ccc(Cl)cc3)nc2O1
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?