arXiv subjects

Ryuji Itakura

Publications and source records attributed to Ryuji Itakura.

5 recordsLinked to original sources

arXiv2026

Roles of individual pigments in ultrafast excitation dynamics of light-harvesting phycobiliproteins revealed by recombinant techniques and two-dimensional electronic spectroscopy

Phycobiliproteins serve as highly efficient light-harvesting antennae in cyanobacteria, yet the molecular factors governing their ultrafast energy relaxation and coherence dynamics remain incompletely understood. In this study, we investigate the role of pigment arrangement and pigment-protein interactions by combining recombinant protein engineering with two-dimensional electronic spectroscopy (2D-ES). In addition to wild-type allophycocyanin (APC) and C-phycocyanin (CPC), we artificially synthesized a {\beta}153 phycocyanobilin (PCB)-deficient CPC mutant, enabling direct experimental isolation of the contribution of this peripheral pigment. The absorption and fluorescence spectra show that removal of the {\beta}153 pigment primarily eliminates its spectral contribution without significantly altering the excitonic coupling between the {\alpha}84 and {\beta}84 pigments. Time-resolved 2D-ES reveals the close similarity between the dynamics of wild-type and {\beta}153-deficient CPCs, which demonstrates that the \b{eta}153 pigment plays a minor role in ultrafast relaxation dynamics. Instead, the differences between APC and CPC arise primarily from pigment-protein interactions that modulate pigment structure and vibronic states. These results highlight the critical importance of local protein environments in controlling energy relaxation and coherence in photosynthetic light-harvesting proteins.

physics.bio-ph↗

arXiv2025

Dependence of energy relaxation and vibrational coherence on the location of light-harvesting chromoproteins in photosynthetic antenna protein complexes

Phycobilisomes are antenna protein complexes in cyanobacteria and red algae. In phycobilisomes, energy transfer is unidirectional with an extremely high quantum efficiency close to unity. We investigate intraprotein energy relaxation and quantum coherence of constituent chromoproteins of allophycocyanin (APC) and two kinds of C-phycocyanin (CPC) in phycobilisomes using two-dimensional electronic spectroscopy (2D-ES). These chromoproteins have similar adjacent pairs of pigments $\alpha$84 and $\beta$84, which are excited to delocalized exciton states. However, the kinetics and coherence of exciton states are significantly different from each other. Even CPCs with almost the same molecular structure display significantly different spectra and kinetics when the locations in the phycobilisome are different. This difference may be one of the key mechanisms for the efficient and unidirectional energy transfer in phycobilisomes. We observe low-frequency coherent vibrational motion of approximately 200 cm$^{-1}$ with large amplitude and a decay time of 200 fs. The wave packet motion involving energy relaxation and oscillatory motions on the potential energy surface of the exciton state is clearly visualized using beat-frequency-resolved 2D-ES.

physics.chem-ph↗

arXiv2024

Electron recollisional excitation of OCS$^+$ in phase-locked $\omega + 2\omega$ intense laser fields

Photoelectron-photoion coincidence momentum imaging has been performed to investigate excitation processes on dissociative ionization of OCS, OCS $\to$ OCS$^+$ + e$^-$ $\to$ OC + S$^+$ + e$^-$, in phase-locked $\omega + 2\omega$ intense laser fields. The electron kinetic energy spectra depend on coincidentally produced ion species, OCS$^+$ or S$^+$. The observed electron momentum distribution shows clear asymmetry along the laser polarization direction with a 2$\pi$-oscillation period as a function of the phase difference between the $\omega$ and $2\omega$ laser fields. The asymmetry of electron emission in the OCS$^+$ channel flips at the electron kinetic energy of 8.2 eV where the dominant scattering direction switches from forward to backward. In the S$^+$ channel, the asymmetry flips at the lower kinetic energy of 4.2 eV. In comparison with a classical trajectory Monte Carlo simulation, it has been clarified that this energy shift between the OCS$^+$ and S$^+$ channels corresponds to the excitation energy of the parent ion and that electron recollisional excitation takes place to form the fragment ion in intense laser fields.

physics.atom-ph↗

arXiv2022

Beat-frequency-resolved two-dimensional electronic spectroscopy: disentangling vibrational coherences in artificial fluorescent proteins with sub-10-fs visible laser pulses

We perform a beat-frequency-resolved analysis for two-dimensional electronic spectroscopy using a high-speed and stable 2D electronic spectrometer and few-cycle visible laser pulses to disentangle the vibrational coherences in an artificial fluorescent protein. We develop a highly stable ultrashort light source that generates 5.3-fs visible pulses with a pulse energy of 4.7 uJ at a repetition rate of 10 kHz using multi-plate pulse compression and laser filamentation in a gas cell. The above-5.3-fs laser pulses together with a high-speed multichannel detector enable us to measure a series of 2D electronic spectra, which are resolved in terms of beat frequency related to vibrational coherence. We successfully extract the discrete vibrational peaks behind the inhomogeneous broadening in the absorption spectra and the vibrational quantum beats of the excited electronic state behind the strong stationary signal in the typical 2D electronic spectra.

physics.chem-ph↗

arXiv2018

Deformation of an inner valence molecular orbital in ethanol by an intense laser field

Valence molecular orbitals play a crucial role in chemical reactions. Here we reveal that an intense laser field deforms an inner valence orbital (10a') in the ethanol molecule. We measure the recoil-frame photoelectron angular distribution (RFPAD), which corresponds to the orientation dependence of the ionization probability of the orbital, using photoelectron-photoion coincidence momentum imaging with a circularly polarized laser pulse. Ab initio simulations show that the orbital deformation depends strongly on the laser field direction, and that the measured RFPAD cannot be reproduced without taking the orbital deformation into account. Our findings suggest that the laser-induced orbital deformation occurs prior to electron emission on a sub-optical-cycle time scale.

physics.chem-ph↗