O=C(Nc1nc2ncn(CCNCCn3cnc4nc(NC(=O)c5ccccc5)[nH]c(=O)c43)c2c(=O)[nH]1)c1ccccc1
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?