Mariya I. Skvortsova

On a quantum chemical interpretation of molecular connectivity indices for conjugated hydrocarbons

Abstract The topological indices (TIs)—invariants of weighted molecular graphs representing the chemical structures—are widely used as molecular descriptors in quantitative structure-property relationships (QSPR). The essential disadvantage of the TIs-method in QSPR is the absence of any physical-chemical interpretation of the majority of TIs used in QSPR. This leads to problems in the choice of TIs and justification of the obtained correlations, the “TIs-property”. In the present paper a quantum chemical interpretation of connectivity TIs widely used in QSPR for some classes of conjugated hydrocarbons is suggested. The results obtained justify using these TIs in QSPR for such compounds.

Design of topological indices: computer-oriented approach

A novel method is suggested for constructing topological indices (TIs) of molecular graphs which models human logic. This method is described in terms of a block scheme, consisting of the mutually connected elementary blocks. In each block the simple transformations of a molecular graph are fulfilled. A variant of the transformation is selected from the list of possible variants. Every TI is obtained as a result of the sequential execution of a number of operations, corresponding to some ‘walk’ on the block scheme. This walk can be selected both randomly and by the investigator. The suggested method can serve as a basis for the development of the respective computer program which may be used for the automatic construction of any number of TIs of differing nature. By this process one can also obtain the TIs that are unlikely to be constructed manually, due to their complexity. The set of obtained TIs may be used for building the structure–property models. In the case of an unsatisfactory result the obtained set of TIs may be changed using the described generator of TIs. A number of examples of application of the suggested approach for the building QSAR/QSPR models is given.

Investigation of the structure and properties of several endohedral clusters and generalization of the concept of molecular topological form

The problem of structural characterization of nanoparticles and endohedral clusters is discussed. The concept of molecular topological form introduced earlier for the description and classification of stereochemical configurations of organic molecules is generalized. The proposed definition is illustrated taking the Cr(CO)3(C6H6) complex and onion carbon clusters as examples. Topological and geometric characteristics of several multilayer fullerenes are discussed. A basis of invariants for molecular graphs of the icosahedral onion C60@C240@C540 cluster was found. This type of basis can be used for estimations of physicochemical properties of multilayer fullerenes in the topological approximation and for calculations of different topological indices. The results of MNDO/PM3 simulation of molecular and electronic structure of a hypothetical endohedral C20@C60 cluster are reported.