O=C(O)CCCCn1c(SCc2cc(=O)n3cc(Cl)ccc3n2)nc2ccsc2c1=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?