O=C(CSc1nc(-c2cc(Cl)ccc2Cl)n[nH]1)NCCN1C(=O)CSC1=O
An acid's negative base-10 logarithmic dissociation constant (pKa) follows directly from its underlying thermodynamics; the negative pKa is directly proportional to its standard Gibbs free energy change. What is the negative pKa value of this molecule?