11-cz.s-Retinal

The reaction sequence of Eq. 23-37 can be slowed by lowering the temperature. Thus, at 70K illumination of rhodopsin leads to a photostationary state in which only rhodopsin, bathorhodopsin, and a third form, isorhodopsin, are present in a constant ratio.510 Isorhodopsin (maximum absorption at 483 nm)513 contains 9-ds-retinal and is not on the pathway of Eq. 23-37. Resonance Raman spectroscopy at low temperature supports a distorted all-frans structure for the retinal Schiff base in bathorhodopsin.510 The same technique suggests the trans geometry of the C = N bond shown in Eqs. 23-38 and 23-39. Simple Schiff bases of 11-cz s-retinal undergo isomerization just as rapidly as does rhodopsin.514... 

---