O=C(N/C(=C\NC1=NCCS1)C(=O)N1CSC[C@@H]1C(=O)O)c1ccccc1
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?