36,110 research outputs found
The time scale of the quaternary structural changes in hemoglobin revealed using the transient grating technique
No full textThe quaternary structural transition between the R and T states of human hemoglobin was investigated using the transient grating technique. The results presented herein reveal that the quaternary structural change accompanied by the R-T transition occurs within a few microseconds. © the Owner Societies 20151331sciescopu
Reply to comment on 'Proton Transfer of Guanine Radical Cations Studied by Time-Resolved Resonance Raman Spectroscopy Combined with Pulse Radiolysis'
No full text[No abstract available1221sciescopu
Coherent oscillations in chlorosome elucidated by two-dimensional electronic spectroscopy
No full textChlorosomes are the most efficient photosynthetic light-harvesting complexes found in nature and consist of many bacteriochlorophyll (BChl) molecules self-assembled into supramolecular aggregates. Here we elucidate the presence and the origin of coherent oscillations in chlorosome at cryogenic temperature using 2D electronic spectroscopy. We observe coherent oscillations of multiple frequencies superimposed on the ultrafast amplitude decay of 2D spectra. Comparison of oscillatory features in the rephasing and nonrephasing 2D spectra suggests that an oscillation of 620 cm-1 frequency arises from electronic coherence. However, this coherent oscillation can be enhanced by vibronic coupling with intermolecular vibrations of BChl aggregate, and thus it might originate from vibronic coherence rather than pure electronic coherence. Although the 620 cm-1 oscillation dephases rapidly, the electronic (or vibronic) coherence may still take part in the initial step of energy transfer in chlorosome, which is comparably fast. © 2014 American Chemical Society.112131sciescopu
Exciton delocalization length in chlorosomes investigated by lineshape dynamics of two-dimensional electronic spectra
No full textA chlorosome, a photosynthetic light-harvesting complex found in green sulfur bacteria, is an aggregate of self-assembled pigments and is optimized for efficient light harvesting and energy transfer under dim-light conditions. In this highly-disordered aggregate, the absorption and transfer of photoexcitation energy are governed by the degree of disorder. To describe the disorder, the number of molecules forming excitons, which is termed exciton delocalization length (EDL), is a relevant parameter because the EDL sensitively changes with the disorder of the constituent molecules. In this work, we determined the EDL in chlorosomes using two-dimensional electronic spectroscopy (2D-ES). Since spectral features correlated with EDL are spread out in the two-dimensional (2D) electronic spectra, we were able to determine the EDL accurately without the effects of homogeneous and inhomogeneous line broadening. In particular, by taking advantage of the multi-dimensionality and the time evolution of 2D spectra, we not only determined the excitation frequency dependence of EDL but also monitored the temporal change of EDL. We found that the EDL is similar to 7 at 77 K and similar to 6 at 298 K and increases with the excitation frequency, with the maximum located well above the maximum of the absorption spectrum of chlorosomes. The spectral profile of EDL changes rapidly within 100 fs and becomes flat over time due to dephasing of initial exciton coherence. From the coherent oscillations superimposed on the decay of EDL, it was learned that high-frequency phonons are more activated at 298 K than at 77 K.11Nsciescopu
Proton Transfer of Guanine Radical Cations Studied by Time-Resolved Resonance Raman Spectroscopy Combined with Pulse Radiolysis
No full textThe oxidation of guanine (G) is studied by
using transient absorption and time-resolved resonance Raman
spectroscopies combined with pulse radiolysis. The transient
absorption spectral change demonstrates that the neutral
radical of G (G•(−H+)), generated by the deprotonation of G
radical cation (G•+), is rapidly converted to other G radical
species. The formation of this species shows the pH
dependence, suggesting that it is the G radical cation (G•+)′
formed from the protonation at the N7 of G•(−H+). On one
hand, most Raman bands of (G•+)′ are up-shifted relative to those of G, indicating the increase in the bonding order of
pyrimidine (Pyr) and imidazole rings. The (G•+)′ exhibits the characteristic CO stretching mode at ∼1266 cm−1 corresponding
to a C−O single bond, indicating that the unpaired electron in (G•+)′ is localized on the oxygen of the Pyr ring. © 2015 American Chemical Society1661sciescopu
Role of thermal excitation in ultrafast energy transfer in chlorosomes revealed by two-dimensional electronic spectroscopy
No full textChlorosomes are the largest light harvesting complexes in nature and consist of many bacteriochlorophyll
pigments forming self-assembled J-aggregates. In this work, we use two-dimensional electronic
spectroscopy (2D-ES) to investigate ultrafast dynamics of excitation energy transfer (EET) in chlorosomes
and their temperature dependence. From time evolution of the measured 2D electronic spectra of
chlorosomes, we directly map out the distribution of the EET rate among the manifold of exciton states in
a 2D energy space. In particular, it is found that the EET rate varies gradually depending on the energies of
energy-donor and energy-acceptor states. In addition, from comparative 2D-ES measurements at 77 K and
room temperature, we show that the EET rate exhibits subtle dependence on both the exciton energy and
temperature, demonstrating the effect of thermal excitation on the EET rate. This observation suggests that
active thermal excitation at room temperature prevents the excitation trapping at low-energy states and
thus promotes efficient exciton diffusion in chlorosomes at ambient temperature.1441sciescopu
Ultrafast energy transfer in chlorosome probed by femtosecond pump-probe polarization anisotropy
No full text1111sciescopuskc
SVD-aided pseudo principal-component analysis: A new method to speed up and improve determination of the optimum kinetic model from time-resolved data
No full textDetermination of the optimum kinetic model is an essential prerequisite for characterizing dynamics and mechanism of a reaction. Here, we propose a simple method, termed as singular value decomposition-aided pseudo principal-component analysis (SAPPA), to facilitate determination of the optimum kinetic model from time-resolved data by bypassing any need to examine candidate kinetic models. We demonstrate the wide applicability of SAPPA by examining three different sets of experimental time-resolved data and show that SAPPA can efficiently determine the optimum kinetic model. In addition, the results of SAPPA for both time-resolved X-ray solution scattering (TRXSS) and transient absorption (TA) data of the same protein reveal that global structural changes of protein, which is probed by TRXSS, may occur more slowly than local structural changes around the chromophore, which is probed by TA spectroscopy
Regulation of protein structural changes by incorporation of a small-molecule linker
No full textProteins have the potential to serve as nanomachines with well-controlled structural movements, and artificial control of their conformational changes is highly desirable for successful applications exploiting their dynamic structural characteristics. Here, we demonstrate an experimental approach for regulating the degree of conformational change in proteins by incorporating a small-molecule linker into a well-known photosensitive protein, photoactive yellow protein (PYP), which is sensitized by blue light and undergoes a photo-induced N-terminal protrusion coupled with chromophore-isomerization-triggered conformational changes. Specifically, we introduced thiol groups into specific sites of PYP through site-directed mutagenesis and then covalently conjugated a small-molecule linker into these sites, with the expectation that the linker is likely to constrain the structural changes associated with the attached positions. To investigate the structural dynamics of PYP incorporated with the small-molecule linker (SML-PYP), we employed the combination of small-angle X-ray scattering (SAXS), transient absorption (TA) spectroscopy and experiment-restrained rigid-body molecular dynamics (MD) simulation. Our results show that SML-PYP exhibits much reduced structural changes during photo-induced signaling as compared to wild-type PYP. This demonstrates that incorporating an external molecular linker can limit photo-induced structural dynamics of the protein and may be used as a strategy for fine control of protein structural dynamics in nanomachines. © 2018 by the authors. Licensee MDPI, Basel, Switzerland11sci
Pump-probe x-ray solution scattering reveals accelerated folding of cytochrome c upon suppression of misligation
No full text1331sciescopuskc
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