• Predicting the solubility of hydrogen bonding aromatics

      Yalkowsky, Samuel H.; Miller, Allan Harvey, 1968- (The University of Arizona., 1993)
      The AQUAFAC (Aqueous Functional Group Activity Coefficients) method for predicting aqueous activity coefficients proposed by Myrdal et al. (1992) is expanded to include for hydrogen bonding groups: hydroxy, carboxy, nitro and amino. Activity coefficients can be used to estimate aqueous solubility. Using aqueous solubility data, from a number of sources, for a set of subsituted aromatic compounds, group or q values are derived. Group values have been generated for a number of substituents, none have included hydrogen bonding groups (Myrdal et al., 1992,1993). Q values are related to activity coefficients through the following relationship: log gammaw = Sigmaniqi where log gammaw is the log of the activity coefficient, qi is the group value subtituent i and ni is the group frequency. Ortho effects between hydrogen bonding groups is also examined. Intramoleculat hydrogen bonding involving carboxy substituted compounds, in this research, does appear to affect aqueous solubility.
    • Solubility of quinoline in aqueous systems: Effect of pH and ionic strength

      Yalkowsky, Samuel H.; Carvajal-Figueroa, Maria Teresa, 1959- (The University of Arizona., 1989)
      Nitrogen-heterocyclic compounds are commonly found in gas waste and coal cleaning residue. Within this general compound class, quinoline is especially important because it has the potential to induce liver carcinoma and it also has a high solubility in water. The pH-solubility profile of quinoline was determined in citrate-phosphate buffer at different ionic strengths. The pKa was observed to change with ionic strength. The intrinsic solubility is always reported as a constant. However, in this study the intrinsic solubility was observed to vary with ionic strength. The solubility of quinoline is dependent on pH as well as the ionic strength. At pH values lower than the pKa (4.96), quinoline is in the protonated form (QH⁺), and enhanced solubility was observed. At pH values higher than the pKa, quinoline is in the neutral form (Q) which is the form that determines intrinsic solubility (So). So decreased with increasing ionic strength. This observation can be explained as a salting out effect. From the solubility data the apparent ionization constant, pKa, of quinoline was obtained for the different systems.