O=C(NCCC[N+]1=CC=N[C@H]1c1ccccc1)N1CCCc2nc(-c3ccc(Br)cc3)ccc21
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?