O=[N+]([O-])c1c(/C=N/Nc2ccccc2)oc(-c2ccc3c(c2)OCO3)c1-c1ccc2c(c1)OCO2
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?