COc1ccccc1CNC(=O)CCC1N=C2c3ccccc3N=C(SCc3ccc(C)cc3C)N2C1=O
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?