O=C(CSc1nc[nH]n1)N1N=C2/C(=C/c3ccco3)CCCC2C1c1ccco1
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?