Quantitative estimates of transferability of the QTAIM descriptors. Case study of the substituted hydropyrimidines

A theoretical study of the quantum-topological properties of three substituted in the positions 4, 5 and 6 hydropyrimidine molecule derivatives in terms of electron density and electronic energy characteristics has been carried out. The uncertainty in the intramolecular QTAIM descriptors obtained within the Kohn-Sham method with B3LYP, BLYP and BHHLYP functionals, as well as the Møller-Plesset second-order perturbation theory using the same 6-311++G** basis set has been considered and the quantitative estimates of transferability of the QTAIM descriptors have been derived. These values might be used as the threshold in the quantitative evaluation of the transferability of the bond or atomic characteristics at the above-mentioned level of approximation. It was found that electron density at the bond critical points, which is the most transferable characteristic, does not allow making a decision concerning the transferability of submolecular moieties in the substituted hydropyrimidines possessing a noticeable flexibility of the heterocyclic ring and side chains. The examinations of the chemical origins of the physiological properties of the substituted hydropyrimidines demands a consideration of maximal set of the QTAIM descriptors. Our results show that changes occurring due to conformational transitions in compounds under investigation regard the bonds and atoms not only of the side chains but also the heterocyclic ring. This observation is useful in the search for new biologically-active substituted hydropyrimidines.