Ab initio MO study on the potential energy surfaces for twisting around the C-11=C-12 bond of the protonated Schiff base of retinal

We have calculated potential energy surfaces for the twisting around the C- 11=C-12 bond of the protonated Schiff base of retinal without and with a ne gative point charge or a water molecule in the vicinity of the Schiff base by means of the state-average complete active space self-consistent field ( sa-CASSCF) method. We find that the potential energy surfaces obtained in t his study are qualitatively similar to, but quantitatively different from t hose for the twisting around the C-13=C-14 bond of the protonated Schiff ba se which were obtained previously. (C) 1999 Elsevier Science B.V. All right s reserved.