Photoisomerization of retinal

The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

Nonadiabatic transitions definitely play crucial roles for molecules to manifest various functions. The theory of nonadiabatic transition is very helpful not only to comprehend the mechanisms, but also to design new molecular functions and enhance their efficiencies. The photochromism that is expected to be applicable to molecular switches and memories is a good example [130]. Photoisomerization of retinal is well known to be a basic mechanism of vision. In these processes, the NT type of nonadiabatic transitions play essential roles. There must be many other similar examples. Utilization of the complete reflection phenomenon can also be another candidate, as discussed in Section V.C. In this section, the following two examples are cosidered (1) photochromism due to photoisomerization between cyclohexadiene (CHD) and hexatriene (HT) as an example of photoswitching molecular functions, and (2) hydrogen transmission through a five-membered carbon ring. 

Migani A, Sinicropi A, Ferr N, Cembran A, Garavelli M, Olivucci M (2004) Structure of the intersection space associated with Z/E photoisomerization of retinal in rhodopsin proteins. Faraday discuss 127 179... 

BR from H. salinarum is a light-driven proton pump, which is triggered by the photoisomerization of retinal covalently linked to its Lys216. It consists of a single polypeptide of 248 amino-acid residues, including seven a-helical TM chains A-G and interconnecting loops, as schematically illustrated in Figure 23. BR is one of the most intensively studied membrane proteins. A variety of experimental techniques have shown it to be... 

The CP MAS NMR spectroscopy has been also extensively used for studies of proteins containing retinylidene chromophore like proteorhodopsin or bacteriorhodopsin. Bacteriorhodopsin is a protein component of purple membrane of Halobacterium salinarium.71 7 This protein contains 248 amino acids residues, forming a 7-helix bundle and a retinal chromophore covalently bound to Lys-216 via a Schiff base linkage. It is a light-driven proton pump that translocates protons from the inside to the outside of the cell. After photoisomerization of retinal, the reaction cycle is described by several intermediate states (J, K, L, M, N, O). Between L and M intermediate states, a proton transfer takes place from the protonated Schiff base to the anionic Asp85 at the central part of the protein. In the M and/or N intermediate states, the global conformational changes of the protein backbone take place. 

The vibronic coupling model has been applied to a number of molecular systems, and used to evaluate the behavior of wavepackets over coupled surfaces [191]. Recent examples are the radical cation of allene [192,193], and benzene [194] (for further examples see references cited therein). It has also been used to explain the lack of structure in the S2 band of the pyrazine absorption spectrum [109,173,174,195], and recently to study the photoisomerization of retinal [196],... 

Takahashi T et al (1991) Photoisomerization of retinal at 13-ene is important for phototaxis of Chlamydomonas reinhardtii - simultaneous measurements of phototactic and photophobic responses. Biochem Biophys Res Com 178 1273-1279... 

Bacteriorhodopsin is the sole membrane protein of seven a-helical transmembrane chains present in the purple membrane of Halobacterium salinarum. This is active as a light-driven proton pump through the photoisomerization of retinal (Fig. 2) from the aW-trans, 15-anti to the 13-cis, 15-anti form covalently linked to Lys216 (helix G) of a single-chain polypeptide of 248 amino acid... 

Photoisomerization of retinal from the all-trans to the 13-ct.v form leads to a cyclic photoreaction with intermediates, bR, K, L, M, N, and O, which are subsequently formed before recovery of the initial state, as schematically illustrated, with the absorption wavelength in the suffix (Fig. 5), together with their individual lifetimes.50 51 The first proton transfer in the photocycle of the all-trans, 15-anti isomer is from the retinal Schiff base to Asp 85 at the central part of the protein. Then, a proton is released from the proton release complex (PRC) consisting of Glu 204, 194 and a bound water molecule at the extracellular surface, as illustrated by arrow A. This is followed by reprotonation of... 

Bacteriorhodopsin is the quintessential transmembrane ion pun ). It consists of a small, seven-helix protein where proton transport across the membrane is driven by photoisomerization of retinal from the all trans to the 13-cis,l5-anti configuration. A number of high-resolution crystal structures of the protein and its photointermediates have been used to propose several competing mechanisms describing proton translocation to fhe extracellular surface. Unresolved issues include understanding how conformational changes couple to proton transfer and the role played by water molecules in the proton transfer process. ... 

Table 2.10 Photoisomerization of Retinal and Azobenzene Derivatives Light-induced changes in rhodopsin...

The photoisomerization of retinal has been studied using super-short light pulses, and the neutral and protonated forms of the retinal analogue (47) have been examined by time-resolved methods.The irradiation of 3-ionone as a complex with P-CD in water leads only to the formation of retro-y-ionone." ... 

Cembran A, Bemardi F, Olivucci M, Garavelli M (2004) Counterion controlled photoisomerization of retinal chromophore models a computational investigation. J Am Chem Soc 126 16018... 

As an apphcation of this approach, it has recently been suggested to use a vibronicaUy coupled two-mode two-state system to model the photoisomerization of retinal in rhodopsin. Due to its importance for the first step in vision, there has been considerable effort to understand this photoreaction. The matrix elements of the molecular Hamiltonian... 

Discuss., 127, 179 (2004). Structure of the Intersection Space Associated with 2/E Photoisomerization of Retinal in Rhodopsin Proteins. 

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