COc1cc(C(=O)NN2C(=O)/C(=C3\C(=O)Nc4ccccc43)SC2=S)ccc1O
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?