O=C(Nc1ccc(Oc2ccc3c(c2)C(=O)N(c2ccc(O)cc2)C3=O)cc1)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?