A bioorganic view of the chemistry of vision: H.T.-n and B.P.-m,n mechanisms for reactions of confined, anchored polyenes

Liu, Robert S. H.; Browne, Douglas T.

doi:10.1021/ar00122a003

Cited by 85 publications

(38 citation statements)

References 73 publications

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“…Furthermore, calculations have shown that inversion is the preferred pathway for the ground-state isomerization in the gas phase. [15] We also exclude the socalled hula-twist pathway, which has been suggested for the cis-trans isomerization of the retinal chromophore within its limited volume [16] and observed recently for stilbene, [17] because this necessitates an energetically unfavorable vertical displacement of a phenyl group. We thus interpret the observed isomerization as an inversion of one of the NÀC bonds with the lone pair of the nitrogen.…”

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confidence: 91%

Reversible cis–trans Isomerization of a Single Azobenzene Molecule

et al. 2006

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mentioning

confidence: 91%

Reversible cis–trans Isomerization of a Single Azobenzene Molecule

et al. 2006

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“…postulated HT-10 and HT-11 as the respective primary photochemical processes for these pigments (17). However, because of subsequent observation of photoreactivity of the rhodopsin analog 22 (49)(50)(51), the new mode of HT-12 was invoked (49). Ishiguro (31) recently demonstrated by molecular modeling that HT-12 is the preferred photoisomerization process of rhodopsin giving 12-S-cis intermediate 23.…”

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confidence: 99%

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

Liu

Hammond²

2000

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

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170

130

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This paper critically reviews examples in the literature of photochemical cis-trans isomerization paying particular attention to the medium effect and accompanied conformational changes. A case is made that the Hula-Twist mechanism, postulated in 1985 as a photochemical reaction pathway for a polyene chromophore imbedded in a protein binding cavity such as those of rhodopsin and bacteriorhodopsin, is also a dominant reaction pathway for a diene, or a longer polyene confined in a rigid (relative to isomerization rate) medium. The conventional one-bond-flip process is the preferred reaction pathway in a fluid medium. While defining experiments are proposed, this dual mechanistic approach successfully accounts for all examples in the literature on photoisomerization reactions whether involving conformational changes or not.

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“…This is an ambiguous position with respect to the two TICT channels. It corresponds to either a concerted-or "hula-" twisted geometry 70 .…”

Section: Discussionmentioning

confidence: 99%

Valence-bond non-equilibrium solvation model for a twisting monomethine cyanine

McConnell

McKenzie

Olsen

2015

The Journal of Chemical Physics

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We propose and analyze a two-state valence-bond model of non-equilibrium solvation effects on the excited-state twisting reaction of monomethine cyanines. Suppression of this reaction is thought responsible for environment-dependent fluorescence yield enhancement in these dyes. Fluorescence is quenched because twisting is accompanied via the formation of dark twisted intramolecular charge-transfer (TICT) states. For monomethine cyanines, where the ground state is a superposition of structures with different bond and charge localization, there are two possible twisting pathways with different charge localization in the excited state. For parameters corresponding to symmetric monomethines, the model predicts two low-energy twisting channels on the excited-state surface that lead to a manifold of twisted intramolecular charge-transfer (TICT) states. For typical monomethines, twisting on the excited state surface will occur with a small barrier or no barrier. Changes in the solvation configuration can differentially stabilize TICT states in channels corresponding to different bonds, and that the position of a conical intersection between adiabatic states moves in response to solvation to stabilize either one channel or the other. There is a conical intersection seam that grows along the bottom of the excited-state potential with increasing solvent polarity. For monomethine cyanines with modest-sized terminal groups in moderately polar solution, the bottom of the excited-state potential surface is completely spanned by a conical intersection seam.

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A bioorganic view of the chemistry of vision: H.T.-n and B.P.-m,n mechanisms for reactions of confined, anchored polyenes

Cited by 85 publications

References 73 publications

Reversible cis–trans Isomerization of a Single Azobenzene Molecule

Reversible cis–trans Isomerization of a Single Azobenzene Molecule

The case of medium-dependent dual mechanisms for photoisomerization: One-bond-flip and Hula-Twist

Valence-bond non-equilibrium solvation model for a twisting monomethine cyanine

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