Estimation of stability constants of copper(II) and nickel(II) chelates with dipeptides by using topological indices

The estimation of the overall stability constants β₁ of copper(II) and nickel(II) chelates with dipeptides was performed by using the model with the valence connectivity index of the 3rd order (³χ^v). It was done by dividing β₁ to its constituting constants K₁ and K_a, and subsequently by dividing the basic set into subsets or treating the chelate rings as separate units. Altogether 15 copper(II) and eight nickel(II) chelates with dipeptides were investigated. Six models for the estimation of log K₁ and pK_a were checked, most of them by usage of indicator variables (for differentiation of copper(II) and nickel(II) complexes or subclasses of ligands). Estimates of log β₁ gave the range of rms values from 0.19 to 0.27. For the best model, errors of estimates were less than 0.34.