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Nenad Raos and Ante Miličević

Estimation of Stability Constants of Coordination Compounds using Models Based on Topological Indices

The principal aim of our research was to develop theoretical models for estimating stability constants of coordination compounds, focusing on chelates of heavy metals, Cu(II) and Ni(II), with bioligands (amines, amino acids and peptides). We tried to solve the problem using graph-theoretical models. We also encountered a specific problem for coordination compounds - the choice of the constitutional formula, that is graph, of the complex species.

Open access

Ante Miličević and Nenad Raos

Abstract

In order to compare the density functional theory (DFT) and the method with the molecular valence connectivity index of the 3rd order (3χv) in the estimation of stability constants log β2, we used copper(II) complexes with thioflavin-based intercalation compounds designed for application in Alzheimer’s disease. Correlation of ten log β2 values calculated by DFT with 3χv yielded r=0.988 and S.E.=0.85. The correlations of indices ING, HOMA and 3χv with log β2, and the intercorrelations between the indices revealed the crucial influence of 3χv on the prediction of the stability of these complexes.

Open access

Ante Miličević and Nenad Raos

Abstract

Using molecular graph theory we studied the binding of NSFRY-NH2 and 12 related pentapeptide amides to Cu(II) as a model system for atrial natriuretic factor (ANF) peptide interactions with copper. Linear regression models based on the valence connectivity index of the 3rd order (3χv) reproduced experimental stability constants (log β) for 1N, 2N, 3N, and 4N coordinated complexes with the standard error of 0.30-0.39 log β units. We developed separate models for seven tyrosinic (N=28) and five non-tyrosinic peptides (N=20), and a common model for both kinds of peptides (N=48) with an indicator (dummy) variable. The results indicate additional aromatic stabilisation in 4N complexes due to metal cation-π interactions with tyrosine but not with the phenylalanine residue. We have also amended the log K and log K* values to correct miscalculations published by Janicka-Klos et al. in 2013

Open access

Ante Miličević and Nenad Raos

Abstract

Three sets of flavonoid derivatives (N=32, 40, and 74) and logarithms of their dissociation constants (log Kd) that describe flavonoid affinity toward P-glycoprotein were modelled using six connectivity indices. The best results were obtained with the zero-order valence molecular connectivity index (0χv) for all three sets. Standard errors of the calibration models were around 0.3, and of the constants from the test sets even a little lower, 0.22 and 0.24. Despite using only one descriptor, our model proved better in internal (cross-validation) and especially in external (test set) statistics than much more demanding methods used in previous 3D QSAR modelling.