Excited-State Dynamics of a Protonated Retinal Schiff Base in Solution

Logunov, Stephan L.; Li, Song; El‐Sayed, Mostafa A.

doi:10.1021/jp962046d

Cited by 137 publications

(208 citation statements)

References 30 publications

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“…However, this perturbation need not influence the quantum efficiency for photoisomerization. Indeed, mutations that alter the excited state lifetime by more than an order of magnitude were found to have a negligible impact on the quantum efficiency for photoisomerization (14,22). The role of the protein in mediating the all-trans to 13-cis photoisomerization appears be largely as a catalyst along the C 13 AC 14 bond and as an inhibitor along all other double bonds (21).…”

Section: Discussionmentioning

confidence: 99%

“…An implication that emerged from some of the earlier work is that such a bias might facilitate rapid conversion to the 13-cis form and may even be necessary to achieve a high quantum yield for photoisomerization. On the other hand, recent studies of bR mutants revealed quantum efficiencies for photoisomerization that were remarkably constant and similar to the efficiency for native bR, despite excited-state lifetimes that varied by an order of magnitude (14,(20)(21)(22). This suggests that rapid conversion to the 13-cis form might not be necessary to attain a high quantum efficiency for photoisomerization.…”

mentioning

confidence: 92%

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The photoisomerization of retinal in bacteriorhodopsin: Experimental evidence for a three-state model

Hasson

Gai

Anfinrud

1996

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

182

228

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The primary events in the all-trans to 13-cis photoisomerization of retinal in bacteriorhodopsin have been investigated with femtosecond time-resolved absorbance spectroscopy. Spectra measured over a broad range extending from 7000 to 22,400 cm ؊1 reveal features whose dynamics are inconsistent with a model proposed earlier to account for the highly efficient photoisomerization process. Emerging from this work is a new three-state model. Photoexcitation of retinal with visible light accesses a shallow well on the excited state potential energy surface. This well is bounded by a small barrier, arising from an avoided crossing that separates the Franck-Condon region from the nearby reactive region of the photoisomerization coordinate. At ambient temperatures, the reactive region is accessed with a time constant of Ϸ500 fs, whereupon the retinal rapidly twists and encounters a second avoided crossing region. The protein mediates the passage into the second avoided crossing region and thereby exerts control over the quantum yield for forming 13-cis retinal. The driving force for photoisomerization resides in the retinal, not in the surrounding protein. This view contrasts with an earlier model where photoexcitation was thought to access directly a reactive region of the excited-state potential and thereby drive the retinal to a twisted conformation within 100-200 fs.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 92%

The photoisomerization of retinal in bacteriorhodopsin: Experimental evidence for a three-state model

Hasson

Gai

Anfinrud

1996

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

182

228

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“…However, unlike ROHF/AS6 and AS?, there is no explicit barrier, and so the effect on the dynamics can be expected to be less dramatic than for those methods. There is experimental evidence that the excited-state decay of the full retinal chromophore, both in solution [41] and in the protein environment [42][43][44], is multi-exponential. The results in solution have been shown to arise from a barrier on the excited-state surface [41].…”

Section: Ab Initio Excited State Surface Scansmentioning

confidence: 99%

“…There is experimental evidence that the excited-state decay of the full retinal chromophore, both in solution [41] and in the protein environment [42][43][44], is multi-exponential. The results in solution have been shown to arise from a barrier on the excited-state surface [41]. It remains to be seen whether the OM2/GUGA-CI method can model this dynamics accurately, but the results for PSB3 suggest that this approach is promising.…”

Section: Ab Initio Excited State Surface Scansmentioning

confidence: 99%

Assessment of semiempirical methods for the photoisomerisation of a protonated Schiff base

2009

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The potential energy surfaces and non-adiabatic dynamics of the C 5 H 6 NH 2 ? protonated Schiff base (PSB3) have been investigated using the OM2 semiempirical Hamiltonian with GUGA configuration interaction. Three approaches to selecting the GUGA-CI active space are evaluated using closed-shell and open-shell molecular orbitals. Energy minima and minimum energy crossing points (MECPs) have been compared with ab initio CASSCF and CASPT2 results. Only the open-shell calculations give a qualitatively correct MECP. Minimum energy path (MEP) calculations demonstrate that a minimal active space gives a barrierless path from the planar S 1 minimum to the ground state, whereas larger active spaces result in a small barrier to torsional motion. Surface hopping dynamics calculations indicate that this barrier induces bi-exponential dynamics. The comparable CAS-SCF S 1 energy surface is barrierless, but the CASPT2 surface features an energy plateau, which may also lead to more complex dynamics.

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“…In contrast, illumination of the all-trans chromophore in solution results in several photoproducts with 11-cis being the most dominant (6)(7)(8). The isomerization quantum yield is greater than 50% in proteins (23), but rarely exceeds 20% in solution (6)(7)(8)(9)(10). Finally, the time scale for isomerization in solution has been measured to be 10 ps (9), while it is faster than 2 ps in protein environments (24,25).…”

mentioning

confidence: 96%

The role of intersection topography in bond selectivity ofcis-transphotoisomerization

Ben‐Nun

Molnár

Schulten

et al. 2002

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

148

146

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Ab initio methods are used to characterize the ground and first excited state of the chromophore in the rhodopsin family of proteins: retinal protonated Schiff base. Retinal protonated Schiff base has five double bonds capable of undergoing isomerization. Upon absorption of light, the chromophore isomerizes and the character of the photoproducts (e.g., 13-cis and 11-cis) depends on the environment, protein vs. solution. Our ab initio calculations show that, in the absence of any specific interactions with the environment (e.g., discrete ordered charges in a protein), energetic considerations cannot explain the observed bond selectivity. We instead attribute the origin of bond selectivity to the shape (topography) of the potential energy surfaces in the vicinity of points of true degeneracy (conical intersections) between the ground and first excited electronic states. This provides a molecular example where a competition between two distinct but nearly isoenergetic photochemical reaction pathways is resolved by a topographical difference between two conical intersections.O ne of the simplest means to convert light into mechanical motion at the atomic scale is cis-trans photoisomerization, and it is widely used in photoactive proteins. Retinal protonated Schiff base (RPSB) is the best known biological chromophore, with five double bonds capable of undergoing photoisomerization. A long-standing question has been the mechanism that selects the isomerizing bond, particularly the role of the protein environment in ''steering'' reactivity. The availability of the structures of rhodopsin (1) and bacteriorhodopsin (2-5), coupled with characterization of RPSB solution-phase photochemistry (6-11), provides a unique opportunity to identify this mechanism. Conical intersections (CIs), geometries where two electronic states are truly degenerate, providing doorways from excited to ground electronic states, are widely believed to be important in photochemistry (12)(13)(14), and their role in photoinduced isomerization has been well documented (14-22). However, their role in bond torsion selectivity has yet to be established. In this paper, we show that the topography, or shape, around CIs determines this selectivity in RPSB. This direct connection between CI topography and photochemical selectivity has significant implications for understanding protein ''steering'' and the rational design of molecular optoelectronic devices.Investigations of the photochemistry of RPSB have established that the protein is not an idle spectator; quantum yield, selectivity, and time scales are all significantly different in solution and protein environments. In the protein environment, isomerization occurs exclusively around a single bond, e.g., 11-cis 3 all-trans in rhodopsin and all-trans 3 13-cis in bacteriorhodopsin. In contrast, illumination of the all-trans chromophore in solution results in several photoproducts with 11-cis being the most dominant (6-8). The isomerization quantum yield is greater than 50% in proteins (23), but rarely excee...

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Excited-State Dynamics of a Protonated Retinal Schiff Base in Solution

Cited by 137 publications

References 30 publications

The photoisomerization of retinal in bacteriorhodopsin: Experimental evidence for a three-state model

The photoisomerization of retinal in bacteriorhodopsin: Experimental evidence for a three-state model

Assessment of semiempirical methods for the photoisomerisation of a protonated Schiff base

The role of intersection topography in bond selectivity ofcis-transphotoisomerization

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