Conjugated QSPR models: application to simultaneous prediction of tautomeric equilibrium constants and acidity of molecules

Here, we describe a concept of conjugated models for several properties (activities) linked by a strict mathematical relationship. This relationship can be directly integrated analytically into the Ridge Regression (RR) algorithm or accounted for in a special case of “twin” neural networks (NN). Developed approaches were applied to the modelling of the logarithm of the prototropic tautomeric constant (logKT) which can be expressed as the difference between the acidity constants (pKa) of two related tautomers. Both conjugated and individual RR and NN models for logKT and pKa were developed. The modelling set included 639 tautomeric constants and 2371 acidity constants of organic molecules in various solvents. Descriptors vector for each reaction resulted from the concatenation of structural descriptors and some parameters for reaction conditions. As a former, atom-centered substructural fragments describing acid sites in tautomer molecules were used. The latter were automatically identified using the Conde...