O=C1C(Cl)=C(N2CCN(c3ncccn3)CC2)C(=O)c2c(O)ccc(O)c21
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?