COc1ccc(Nc2sc(C(=O)Nc3cccc(Cl)c3)c(N)c2C(=O)Nc2ccccc2OC)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?