A MOLECULAR MECHANICS AND SEMIEMPIRICAL CONFORMATIONAL-ANALYSIS OF THE HERBICIDE DIURON INHIBITOR OF PHOTOSYSTEM-II

The potential energy surface (PES) for the herbicide diuron (DCMU), a photosystem II inhibitor, has been extensively investigated using the quantum-mechanical semiempirical molecular orbital methods AM1 and PM3 and molecular mechanics method. A detailed conformational search has been carried out which revealed the occurrence of four genuine minimum energy structures. The relative stability of the conformers and rotat ional barriers to conformational interconversion were evaluated using distinct theoretical approaches. The results showed that the trans for m of the diuron molecule is more stable than the cis form in all metho ds, and so it may possibly be the biologically active isomer.