O=C1C2=C(C(c3ccccc3)=NCCN2)C(c2cccc([N+](=O)[O-])c2)N1c1ccccc1
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?