O=C(Nc1ccccc1-c1nnn(CC(=O)N2CCN(c3ccccc3)CC2)n1)c1cccs1
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?