O=C(Nc1ccc(Oc2ccccc2)cc1)c1ccc(Cn2c(=O)[nH]c3ccsc3c2=O)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?