O=C(CSC1=Nc2ccccc2C2=NC(CC(=O)N3CCN(c4ccccc4)CC3)C(=O)N12)NCC1CCCO1
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?