Nejvíce citovaný článek - PubMed ID 34551543
Vibronic dynamics resolved by global and target analysis of ultrafast transient absorption spectra
Rhodopsins constitute a broad class of retinal-binding photoreceptors. Microbial rhodopsins are canonically activated through an all-trans to 13-cis photoisomerization, whereas animal rhodopsins are mostly activated through an 11-cis to all-trans isomerization. Bestrhodopsins constitute a special microbial rhodopsin subfamily, with bistable rhodopsin domains that can be photoswitched between a far red-absorbing state D661 and a green-absorbing state P540. Its photochemistry involves a peculiar all-trans to 11-cis isomerization for the D661 to P540 photoreaction and vice versa. Here, we present the P. antarctica bestrhodopsin 11-cis to all-trans photoreaction as determined by femtosecond-to-submillisecond transient absorption, femtosecond stimulated Raman and flash-photolysis spectroscopy. The primary photoreaction involves ultrafast isomerizations in 240 fs from the 11-cis reactant to a mixture of highly distorted all-trans and 13-cis photoproducts. The 13-cis fraction then thermally isomerizes to a distorted all-trans RSB in 120 ps. We propose bicycle pedal models for the branched photoisomerizations with corotation of the C11═C12 and C13═C14 double bonds. One reactant fraction undergoes bicycle pedal motion aborted at the C13═C14 double bond, resulting in all-trans retinal. The other fraction undergoes a full bicycle pedal motion of both C11═C12 and C13═C14, resulting in 13-cis retinal. The primary products are trapped high up the ground-state potential energy surface with a low energetic barrier that facilitates thermal isomerization from 13-cis to all-trans retinal in 120 ps. All-trans retinal then structurally and energetically relaxes with subsequent time constants of 0.7 and 62 μs and 4.4 ms, along with counterion protonation, completing the P540 to D661 photoreaction.
- MeSH
- fotochemické procesy MeSH
- isomerie MeSH
- retinaldehyd * chemie MeSH
- rhodopsiny mikrobiální * chemie MeSH
- stereoizomerie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- retinaldehyd * MeSH
- rhodopsiny mikrobiální * MeSH
Neorhodopsin (NeoR) is a newly discovered fungal bistable rhodopsin that reversibly photoswitches between UV- and near-IR absorbing states denoted NeoR367 and NeoR690, respectively. NeoR367 represents a deprotonated retinal Schiff base (RSB), while NeoR690 represents a protonated RSB. Cryo-EM studies indicate that NeoR forms homodimers with 29 Å center-to-center distance between the retinal chromophores. UV excitation of NeoR367 takes place to an optically allowed S3 state of 1Bu+ symmetry, which rapidly converts to a low-lying optically forbidden S1 state of 2Ag- symmetry in 39 fs, followed by a multiexponential decay to the ground state on the 1-100 ps time scale. A theoretically predicted nπ* (S2) state does not get populated in any appreciable transient concentration during the excited-state relaxation cascade. We observe an intradimer retinal to retinal excitation energy transfer (EET) process from the NeoR367 S1 state to NeoR690, in competition with photoproduct formation. To quantitatively assess the EET mechanism and rate, we experimentally addressed and modeled the EET process under varying NeoR367-NeoR690 photoequilibrium conditions and determined the EET rate at (200 ps)-1. The NeoR367 S1 state shows a weak stimulated emission band in the near-IR around 700 nm, which may result from mixing with an intramolecular charge-transfer (ICT) state, enhancing the transition dipole moment of the S1-S0 transition and possibly facilitating the EET process. We suggest that EET may bear general relevance to the function of bistable multiwavelength rhodopsin oligomers.
Target analysis is employed to resolve the ground and excited state properties from simultaneously measured Femtosecond Stimulated Raman Spectra (FSRS) and Transient Absorption Spectra (TAS). FSRS is a three-pulse technique, involving picosecond Raman pump pulses and femtosecond visible pump and probe pulses. The TAS are needed to precisely estimate the properties of the Instrument Response Function. The prezero "coherent artifact" present during the overlap of the three pulses is described by a damped oscillation with a frequency (ω - ωn) where ωn is a ground state resonance Raman frequency. Simultaneous target analysis of the FSRS and TAS allows the complete excited state dynamics to be resolved with a time resolution better than 100 fs. The model system studied is the carotenoid lycopene in tetrahydrofuran. The lycopene dynamics show a spectral evolution with seven states, including a biphasic cooling process during the S2-S1 internal conversion, multiple S1 lifetimes, and an S* state decaying with a lifetime of 7 ps.
- Publikační typ
- časopisecké články MeSH
