5 - A Note on Molecular Modelling of Piperonyl Butoxide Using a Computational Chemistry Program for the IBM Personal Computer PC

Abstract

This chapter describes molecular modeling of piperonyl butoxide (PBO) using a computational chemistry program for the IBM computer. Most of the fragments encountered during metabolism and degradation studies of PBO pointed to a progressive chain shortening of the polyethoxy side chain. The usual pattern of chain shortening would be the formation of a preoxidative state followed by cleavage and formation of a hydroxyl group. Following this, a progressive cascade oxidation of the hydroxy carbon through aldehyde to a final carboxylic acid would follow. Some partial oxidation of the n-propyl side chain could also be detected in certain studies. In no studies were less polar substances such as dihydrosafrole formed. Ethers with the oxygen adjacent to a methylene group are prone to peroxidation at the adjacent carbon and are then likely to undergo fission, particularly in the presence of light. The computer simulation showed partial charges calculated as a modified Del Re charge on all the ether oxygens in the range –0.23 to –0.27, which is in line with their electronegative character. A slightly higher partial charge of –0.31 was noted on the first oxygen interruption from the ring. The computer simulation also colored the atoms by lipophilicity and hydrophilicity.