N[C@@H](CCCCNC(=O)CCCC[C@@H]1SC[C@H]2NC(=O)N[C@@H]21)C(=O)O
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?