Relationship between Molecular Properties of some Photosystem II Inhibitors and their Activity on Triazine-Resistant and -Susceptible Chloroplasts

T he conform ations and electronic p roperties of several u rea/am ide, uracil, s-triazine and m ethylth iopyrim idine inhibitors of photosystem II were determ ined using m olecular m echanics (C H A R M M , SY BYL) or quan tum sem i-em pirical (M N D O , A M I) m ethods. Spectroscopic m easu rem en ts o f the in vitro hydrogen bonding capacity of these com pounds w ere also carried ou t. T he validity of the calculated values was estim ated from experim ental m easurem ents. The conform ationa l and electronic p roperties of the inhibitors studied are then discussed in term s of their m echanism of action on the D1 site and its m odification by triazine resistance.