O=C(Cn1c(=O)c2sccc2n(CC(=O)Nc2ccc(Cl)cc2Cl)c1=O)NCCc1ccccc1
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?