The physical nature of catalytic activity due to the molecular environment in terms of intermolecular interaction theory: derivation of simplified models

Abstract

The catalytic or inhibitory activity of a molecular environment has been quantitatively represented as the difference between the interaction energies of the transition complex and the substrate complex with catalyst, and it has been further decomposed into the electrostatic multipole, electrostatic penetration, exchange, induction and dispersion contributions defined within exchange perturbation theory. A sample analysis of catalytic activity of the first hydration shell has been performed for the reaction CO2 + H2O → H2CO3 within the LCAO MO SCF ab initio approach. Results indicate a significant contribution of the electrostatic multipole term in the overall catalytic activity. However, the remaining electrostatic penetration, exchange, induction and dispersion interactions seem to be non-negligible but cancelling each other to a great extent, justifying some intuitively assumed electrostatic hypotheses on the nature of catalytic activity. More approximate models of gradually increasing simplicity have been briefly outlined based on cumulative atomic multipole expansion and nonempirical short range atom-atom potentials, making it possible to deal with much larger molecular systems and to predict the sites of the most effective solvation or the charge distribution of the optimal catalyst for a given reaction.