The E-state as the basis for molecular structure space definition and structure similarity

The electrotopological state (E-state) is presented as a representation of molecular structure useful for definition of a space for chemical structures. This E-state representation provides the basis for chemical database management. The E-state formalism is presented along with its extension to the atom-type E-state. An approach to database organization, using polychlorobiphenyls (PCBs) as examples, reveals the descriptive power of the E-state paradigm. A well-organized chemical database, as described here, may be searched to find structures similar to a target structure with the expectation that such structures may exhibit properties similar to the target. Searches using the atom-type E-state indices are demonstrated with two example drug molecules.