THE VISUAL PROCESS: PHOTOPHYSICS and PHOTOISOMERIZATION OF MODEL VISUAL PIGMENTS and THE PRIMARY REACTION

Becker, Ralph S.

doi:10.1111/j.1751-1097.1988.tb02836.x

Cited by 119 publications

(103 citation statements)

References 137 publications

(199 reference statements)

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“…Similarly, irradiation of PSBT in bacteriorhodopsin leads to formation of a 200-fs (4-7) transient and production of the PSB13 within 500 fs. In contrast, the photochemistry of free PSB11 in solution (8) is more than 1 order of magnitude slower: in methanol, PSB11 has a ca. 3-ps fluorescence lifetime and PSBT is formed in 10 ps (9).…”

mentioning

confidence: 96%

Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization

González‐Luque

Garavelli

Bernardi

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

333

339

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In this paper we use ab initio multiconfigurational second-order perturbation theory to establish the intrinsic photoisomerization path model of retinal chromophores. This is accomplished by computing the ground state (S0) and the first two singlet excited-state (S1, S2) energies along the rigorously determined photoisomerization coordinate of the rhodopsin chromophore model 4-cis-␥-methylnona-2,4,6,8-tetraeniminium cation and the bacteriorhodopsin chromophore model all-trans-hepta-2,4,6-trieniminium cation in isolated conditions. The computed S2 and S1 energy profiles do not show any avoided crossing feature along the S1 reaction path and maintain an energy gap >20 kcal⅐mol ؊1 . In addition, the analysis of the charge distribution shows that there is no qualitative change in the S2 and S1 electronic structure along the path. Thus, the S1 state maintains a prevalent ionic (hole-pair) character whereas the S2 state maintains a covalent (dot-dot) character. These results, together with the analysis of the S1 reaction coordinate, support a two-state, two-mode model of the photoisomerization that constitutes a substantial revision of the previously proposed models.T he photoisomerization of the retinal chromophore triggers the conformational changes underlying the activity of rhodopsin proteins (1). In rhodopsin itself (the human retina visual pigment) the retinal molecule is embedded in a cavity where it is covalently bound to a lysine residue via a protonated Schiff base (PSB) linkage. The absorption of a photon of light causes the isomerization (see equation below) of the 11-cis isomer of the retinal PSB (PSB11) to its all-trans isomer (PSBT).Similarly in the bacterial proton-pump bacteriorhodopsin, the photoexcitation causes the isomerization of the PSBT to its 13-cis isomer (PSB13). The photoisomerization of PSB11 and PSBT in the protein environment are among the fastest chemical reactions observed so far. Thus, the photoexcitation of PSB11 in rhodopsin yields a fluorescent transient with a lifetime of ca. 150 fs (2). After this state is left, ground-state PSBT is formed within 200 fs (3). Similarly, irradiation of PSBT in bacteriorhodopsin leads to formation of a 200-fs (4-7) transient and production of the PSB13 within 500 fs. In contrast, the photochemistry of free PSB11 in solution (8) is more than 1 order of magnitude slower: in methanol, PSB11 has a ca. 3-ps fluorescence lifetime and PSBT is formed in 10 ps (9). Similar lifetimes have been reported for PSBT (10-12) and PSB13 (10) in solution.The decrease in excited-state lifetime and the increase in reaction rate of chromophores bound within the protein with respect to the corresponding free forms in solution is a central problem of photobiology. The first step in the quest for a solution to this problem is the detailed understanding of the chromophore photoisomerization path. Recently, Anfinrud and coworkers (13,14) have summarized the experimental evidence in support of a three-electronic state (S 0 , S 1 , and S 2 ) model-the three-state model-of the p...

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mentioning

confidence: 96%

Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization

González‐Luque

Garavelli

Bernardi

et al. 2000

Proc. Natl. Acad. Sci. U.S.A.

333

339

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“…For example, its quantum yield of isomerization is 0.65 (2, 3) (a recently refined value from the long accepted number of 0.67; ref. 4), more than two times higher than that of the same chromophore in solution (0.24, 0.22) (5,6). The rate of isomerization is also much faster in protein (146 fsec) (7) than in solution (1-2 psec) (8).…”

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confidence: 92%

The molecular basis for the high photosensitivity of rhodopsin

Liu

Colmenares

2003

Proc. Natl. Acad. Sci. U.S.A.

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Based on structural information derived from the F NMR data of labeled rhodopsins, rhodopsin crystal structure, and excited-state properties of model polyenes, we propose a molecular mechanism that accounts specifically for the causes of the well-known enhanced photoreactivity of rhodopsin (increased rates and quantum yield of isomerization). Rhodopsin is a heptahelical membrane protein responsible for scotopic vision. It is a photo-receptor protein activated by the 11-cis-retinal (1) (Structure 1) chromophore covalently bonded to Lys-296 through a protonated Schiff base (PSB) linkage. The photoisomerization of the chromophore initiates the vision process (1). The pigment is known to possess unusually high photochemical reactivity. For example, its quantum yield of isomerization is 0.65 (2, 3) (a recently refined value from the long accepted number of 0.67; ref. 4), more than two times higher than that of the same chromophore in solution (0.24, 0.22) (5, 6). The rate of isomerization is also much faster in protein (146 fsec) (7) than in solution (1-2 psec) (8). In this article, we propose a detailed molecular model accounting for the unusual protein assistance to the isomerization process. Background Information

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“…[6][7][8][9][10]. In order to understand the exact nature of the electronically excited state properties of linear polyenes, donor-acceptor molecules based on α,ω-diphenylpolyene [Ar(CH = CH) n Ar] framework, like 1,2-diphenylethene [Ar(CH = CH)Ar, DPE, stilbene], 1,4-diphenylbutadiene [Ar(CH = CH) 2 Ar, DPB], 1,6-diphenylhexatriene [Ar(CH = CH) 3 Ar, DPH] and other longer homologues have been extensively studied as models of photobiologically significant linear polyenes like retinal, carotenoids and their lower homologues [11][12][13][14][15][16][17][18][19][20]. In contrast to the non-fluorescent retinyl polyenes, the fluorescent nature of model α,ω-diphenylpolyenes facilitates study of the electronically excited state properties of linear polyenes.…”

Section: Introductionmentioning

confidence: 99%

Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer, Photoisomerization and Fluorescence Probe Properties

Hota

Singh

2014

J Fluoresc

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Numerous studies of donor-acceptor conjugated linear polyenes have been carried out with the goal to understand the exact nature of the excited state electronic structure and dynamics. In this article we discuss our endeavours with regard to the excited state intramolecular charge transfer, photoisomerization and fluorescence probe properties of various donor-acceptor substituted compounds of diphenylpolyene [Ar(CH = CH) Ar] series and ethenylindoles.

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THE VISUAL PROCESS: PHOTOPHYSICS and PHOTOISOMERIZATION OF MODEL VISUAL PIGMENTS and THE PRIMARY REACTION

Cited by 119 publications

References 137 publications

Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization

Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization

The molecular basis for the high photosensitivity of rhodopsin

Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer, Photoisomerization and Fluorescence Probe Properties

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