O=C(Nc1ccc(N2C(=O)C3C4C=CC(C4)C3C2=O)cc1Cl)c1cccs1
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?