O=C(CC1N=C2c3ccccc3N=C(SCc3ccc(Cl)cc3)N2C1=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?