| In the second basic photocycle step, the chromophore is protonated and structural changes take place in the protein. |
| On the other hand, in polar conjugated systems such as protonated Schiff bases the funnel shows a structure with just one twisted double bond. |
| An acetyl group was attached to residue 22 to mimic the preceding peptide bond and the C-terminal carboxylate was protonated. |
| We postulate that this pathway is blocked when both groups are protonated or deprotonated. |
| It can react either as an oxidant or a reducing agent, is a very good nucleophile, and is a base that can be protonated. |
| We present a comparative study of the ultrafast photophysics of all-trans retinal in the protonated Schiff base form in solvents with different polarities and viscosities. |
