O=C(COc1ccc(OCC(=O)N2C(=O)CC/C2=N\c2ccc(Cl)cc2)cc1)N1C(=O)CS/C1=N\c1ccc(Cl)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?