O=C(c1ccccc1)c1ccc(N2C(=O)/C(=C/c3ccccc3S)N=C2c2ccccc2)c(N2C(=O)/C(=C/c3ccccc3S)N=C2c2ccccc2)c1
The negative base-10 logarithmic of dissociation constant (pka) for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the pKa value is directly proportional to the standard Gibbs free energy change for the reaction. What is the pka value of this molecule?