O=[N+]([O-])c1ccc(N2N=C(c3ccc(NCc4nc5ccccc5[nH]4)cc3)CC2c2ccco2)cc1
The negative base-10 logarithmic of dissociation constant (pka) for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the pKa value is directly proportional to the standard Gibbs free energy change for the reaction. What is the pka value of this molecule?