19 research outputs found
Demonstration of a Light-Driven SO42- Transporter and Its Spectroscopic Characteristics.
In organisms, ion transporters play essential roles in the generation and dissipation of ion gradients across cell membranes. Microbial rhodopsins selectively transport cognate ions using solar energy, in which the substrate ions identified to date have been confined to monovalent ions such as H+, Na+, and Cl-. Here we report a novel rhodopsin from the cyanobacterium Synechocystis sp. PCC 7509, which inwardly transports a polyatomic divalent sulfate ion, SO42-, with changes of its spectroscopic properties in both unphotolyzed and photolyzed states. Upon illumination, cells expressing the novel rhodopsin, named Synechocystis halorhodopsin (SyHR), showed alkalization of the medium only in the presence of Cl- or SO42-. That alkalization signal was enhanced by addition of a protonophore, indicating an inward transport of Cl- and SO42- with a subsequent secondary inward H+ movement across the membrane. The anion binding to SyHR was suggested by absorption spectral shifts from 542 to 536 nm for Cl- and from 542 to 556 nm for SO42-, and the affinities of Cl- and SO42- were estimated as 0.112 and 5.81 mM, respectively. We then performed time-resolved spectroscopic measurements ranging from femtosecond to millisecond time domains to elucidate the structure and structural changes of SyHR during the photoreaction. Based on the results, we propose a photocycle model for SyHR in the absence or presence of substrate ions with the timing of their uptake and release. Thus, we demonstrate SyHR as the first light-driven polyatomic divalent anion (SO42-) transporter and report its spectroscopic characteristics
Fifth-order impulsive stimulated Raman spectroscopy for visualizing vibrational coupling in reactive excited states
Chemical reactions proceed on the complex potential energy surface (PES), which consists of a vast degree of freedom of nuclear coordinates for polyatomic molecular systems. For unraveling (and manipulating) the reaction coordinate and molecular mechanisms that underlie the reaction, it is desirable to map out the PES, which has been a long-lasting central subject in both experimental and theoretical chemistries. In this quest, understanding of the vibrational coupling between normal mode coordinates is essential, since it actually characterizes the complex shape of the PES. Here, we report fifth-order time-domain Raman spectroscopy of a bacterial photoreceptor, photoactive yellow protein (PYP), with the aim to visualize vibrational coupling in its reactive excited state.Published versio
Environment-sensitive fluorescence of COT-fused perylene bisimide based on symmetry-breaking charge separation
Flexible and aromatic photofunctional system (FLAP) is composed of flapping rigid aromatic wings fused with a flexible 8π ring at the center such as cyclooctatetraene (COT). A series of FLAP have been actively studied for the interesting dynamic behaviors. Here, we synthesized a new flapping molecule bearing naphtho-perylenebisimide wings (NPBI-FLAP), in which two perylene units are arranged side by side. As a reference compound, we also prepared COT-fused NPBI (NPBI-COT) that contains only single perylene unit. In both compounds, inherent strong fluorescence of the NPBI moiety is almost quenched and the FL lifetime becomes much shortened in highly polar solvents (acetone and DMF). Through the analyses of environment-sensitive fluorescence, electrochemical reduction/oxidation, and femtosecond transient absorption, the fluorescence quenching behavior was attributed to rapid symmetry-breaking charge separation (SB-CS) for NPBI-FLAP and to intramolecular charge transfer (ICT) for NPBI-COT. Most of the excited species of these compounds decay with the bent geometry, which is in contrast with the excited-state planarization behavior of a previously reported COT-fused peryleneimides with the double-headed arrangement of the perylene moieties. These results indicate that changing the fusion manners between COT and other skeletons offers new functional molecules with distinct dynamics
Ultrafast Structural Evolution of Photoactive Yellow Protein Chromophore Revealed by Ultraviolet Resonance Femtosecond Stimulated Raman Spectroscopy
We studied ultrafast structural dynamics of the chromophore
of photoactive yellow protein, <i>trans</i>-<i>p</i>-coumaric acid (pCA), using newly developed ultraviolet resonance
femtosecond stimulated Raman spectroscopy (UV-FSRS). The UV-FSRS data
of the anionic form (pCA<sup>–</sup>) in a buffer solution
showed clear spectral changes within 1 ps, followed by a spectrally
uniform decay with a time constant of 2.4 ps. The observed spectral
change indicates that the structural change occurs in excited pCA<sup>–</sup> from the Franck–Condon state to the S<sub>1</sub> potential minimum in the femtosecond time region. The S<sub>1</sub> Raman spectra exhibit spectral patterns that are similar to the
ground-state spectrum, suggesting that pCA<sup>–</sup> yet
retains a planar-trans conformation throughout the S<sub>1</sub> lifetime.
We concluded that S<sub>1</sub> pCA<sup>–</sup> undergoes a
femtosecond in-plane deformation, rather than a substantial C<sub>et</sub>C<sub>et</sub> twist. With these femtosecond vibrational
data, we discuss possible roles of the initial structural evolution
of pCA in triggering the photoreceptive function when embedded in
the protein
Time-Domain Observation of Surface-Enhanced Coherent Raman Scattering with 105106 Enhancement
Quasi-reversible photoinduced displacement of aromatic ligands from semiconductor nanocrystals
Organic-inorganic nanohybrids using semiconductor nanocrystals (NCs) coordinated with aromatic organic molecules have been widely studied in the fields of optoelectronic materials, such as solar cells, photocatalysis, and photon upconversion. In these materials, coordination bonds of ligand molecules are usually assumed to be stable during optical processes. However, this assumption is not always valid. In this study, we demonstrate that the coordination bonds between ligand molecules and NCs by carboxyl groups are displaced quasi-reversibly by light irradiation using zinc sulfide (ZnS) NCs coordinated with perylenebisimide (PBI) as a model system. Ultrafast spectroscopy and density functional theory calculations show that the photoinduced ligand displacement is driven by ultrafast hole transfer from PBI to ZnS NCs, and that the dissociated radical anion of PBI survives over the second timescale. This study opens up a new avenue for advanced photofunctional materials utilizing colloidal NCs, such as photocatalysts that can expose their active facets of NCs on demand, and sub-micropatterning of photoconductive circuits on solid-state NC films
Environment-sensitive fluorescence of COT-fused perylene bisimide based on symmetry-breaking charge separation
Flexible and aromatic photofunctional system (FLAP) is composed of flapping rigid aromatic wings fused with a flexible 8π ring at the center such as cyclooctatetraene (COT). A series of FLAP have been actively studied for the interesting dynamic behaviors. Here, we synthesized a new flapping molecule bearing naphtho-perylenebisimide wings (NPBI-FLAP), in which two perylene units are arranged side by side. As a reference compound, we also prepared COT-fused NPBI (NPBI-COT) that contains only single perylene unit. In both compounds, inherent strong fluorescence of the NPBI moiety is almost quenched and the FL lifetime becomes much shortened in highly polar solvents (acetone and DMF). Through the analyses of environment-sensitive fluorescence, electrochemical reduction/oxidation, and femtosecond transient absorption, the fluorescence quenching behavior was attributed to rapid symmetry-breaking charge separation (SB-CS) for NPBI-FLAP and to intramolecular charge transfer (ICT) for NPBI-COT. Most of the excited species of these compounds decay with the bent geometry, which is in contrast with the excited-state planarization behavior of a previously reported COT-fused peryleneimides with the double-headed arrangement of the perylene moieties. These results indicate that changing the fusion manners between COT and other skeletons offers new functional molecules with distinct dynamics
Role of Coherent Low-Frequency Motion in Excited-State Proton Transfer of Green Fluorescent Protein Studied by Time-Resolved Impulsive Stimulated Raman Spectroscopy
Green
fluorescent protein (GFP) from jellyfish Aequorea
victoria, an essential bioimaging tool, luminesces
via excited-state proton transfer (ESPT) in which the phenolic proton
of the <i>p</i>-hydroxybenzylideneimidazolinone chromophore
is transferred to Glu222 through a hydrogen-bond network. In this
process, the ESPT mediated by the low-frequency motion of the chromophore
has been proposed. We address this issue using femtosecond time-resolved
impulsive stimulated Raman spectroscopy. After coherently exciting
low-frequency modes (<300 cm<sup>–1</sup>) in the excited
state of GFP, we examined the excited-state structural evolution and
the ESPT dynamics within the dephasing time of the low-frequency vibration.
A clear anharmonic vibrational coupling is found between one high-frequency
mode of the chromophore (phenolic CH bend) and a low-frequency mode
at ∼104 cm<sup>–1</sup>. However, the data show that
this low-frequency motion does not substantially affect the ESPT dynamics