A preliminary ab initio investigation of retinal analogs

Abstract

Optimized ab initio STO-3G geometries and various properties are presented for the largest protonated retinal Schiff base analog reported to date for ab initio calculations. The results indicate that completion of the cyclohexene ring has little effect on bonding and other properties of the molecule, but simply causes local torsional distortions. Starting with the four double bond analog, the bonding and net charges of the protonated Schiff base end do not alter upon further addition to the chain. The results also indicate that a conformational change around the C6C7 single bond is accompanied by a small red shift which is important in understanding the opsin shift in bacteriorhodopsin.