8,198 research outputs found
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
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
Ultrafast energy transfer in chlorosome probed by femtosecond pump-probe polarization anisotropy
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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
Proline-rich tyrosine kinase 2 mediates gonadotropin-releasing hormone signaling to a specific extracellularly regulated kinase-sensitive transcriptional locus in the luteinizing hormone beta-subunit gene
No full textG protein-coupled receptor regulation of gene transcription primarily occurs through the phosphorylation of transcription factors by MAPKs. This requires transduction of an activating signal via scaffold proteins that can ultimately determine the outcome by binding signaling kinases and adapter proteins with effects on the target transcription factor and locus of activation. By investigating these mechanisms, we have elucidated how pituitary gonadotrope cells decode an input GnRH signal into coherent transcriptional output from the LH beta-subunit gene promoter. We show that GnRH activates c-Src and multiple members of the MAPK family, c-Jun NH2-terminal kinase 1/2, p38MAPK, and ERK1/2. Using dominant-negative point mutations and chemical inhibitors, we identified that calcium-dependent proline-rich tyrosine kinase 2 specifically acts as a scaffold for a focal adhesion/cytoskeleton-dependent complex comprised of c-Src, Grb2, and mSos that translocates an ERK-activating signal to the nucleus. The locus of action of ERK was specifically mapped to early growth response-1 (Egr-1) DNA binding sites within the LH beta-subunit gene proximal promoter, which was also activated by p38MAPK, but not c-Jun NH2-terminal kinase 1/2. Egr-1 was confirmed as the transcription factor target of ERK and p38MAPK by blockade of protein expression, transcriptional activity, and DNA binding. We have identified a novel GnRH-activated proline-rich tyrosine kinase 2-dependent ERK-mediated signal transduction pathway that specifically regulates Egr-1 activation of the LH beta-subunit proximal gene promoter, and thus provide insight into the molecular mechanisms required for differential regulation of gonadotropin gene expression
Enhancement of Energy Transfer Efficiency with Structural Control of Multichromophore Light‐Harvesting Assembly
No full text© 2020 The Authors. Published by Wiley-VCH GmbH. Multichromophore systems (MCSs) are envisioned as building blocks of molecular optoelectronic devices. While it is important to understand the characteristics of energy transfer in MCSs, the effect of multiple donors on energy transfer has not been understood completely, mainly due to the lack of a platform to investigate such an effect systematically. Here, a systematic study on how the number of donors (n(D)) and interchromophore distances affect the efficiency of energy transfer (eta(FRET)) is presented. Specifically,eta(FRET)is calculated for a series of model MCSs using simulations, a series of multiporphyrin dendrimers with systematic variation ofn(D)and interdonor distances is synthesized, and eta(FRET)s of those dendrimers using transient absorption spectroscopy are measured. The simulations predict eta(FRET)in the multiporphyrin dendrimers well. In particular, it is found that eta(FRET)is enhanced by donor-to-donor energy transfer only when structural heterogeneity exists in an MCS, and the relationships between the eta(FRET)enhancement and the structural parameters of the MCS are revealed11sciescopu
author
No full textauthorIn other places [Old Joe, the trapper] pointed out otter (or, as he pronounced it, "author") slidesPRINTED ITEM G.M.Story April 1959Not UsedNot UsedWithdrawn[see 'otter']Checked by Jordyn Hughes on Thu 09 Jun 201
Jia ru ju he wu dui jun yun tuan liu ji jun yun tuan liu dui liu de ying xiang
No full textWong, Chai Kwok = 加入聚合物對均勻湍流及均勻湍流對流的影響 / 黃濟國.Thesis M.Phil. Chinese University of Hong Kong 2013.Includes bibliographical references (leaves 89-91).Abstracts also in Chinese.Title from PDF title page (viewed on 01, November, 2016).Wong, Chai Kwok = Jia ru ju he wu dui jun yun tuan liu ji jun yun tuan liu dui liu de ying xiang / Huang Jiguo
Combined probes of X-ray scattering and optical spectroscopy reveal how global conformational change is temporally and spatially linked to local structural perturbation in photoactive yellow protein
No full textReal-time probing of structural transitions of a photoactive protein is challenging owing to the lack of a universal time-resolved technique that can probe the changes in both global conformation and light-absorbing chromophores of the protein. In this work, we combine time-resolved X-ray solution scattering (TRXSS) and transient absorption (TA) spectroscopy to investigate how the global conformational changes involved in the photoinduced signal transduction of photoactive yellow protein (PYP) is temporally and spatially related to the local structural change around the light-absorbing chromophore. In particular, we examine the role of internal proton transfer in developing a signaling state of PYP by employing its E46Q mutant (E46Q-PYP), where the internal proton transfer is inhibited by the replacement of a proton donor. The comparison of TRXSS and TA spectroscopy data directly reveals that the global conformational change of the protein, which is probed by TRXSS, is temporally delayed by tens of microseconds from the local structural change of the chromophore, which is probed by TA spectroscopy. The molecular shape of the signaling state reconstructed from the TRXSS curves directly visualizes the three-dimensional conformations of protein intermediates and reveals that the smaller structural change in E46Q-PYP than in wild-type PYP suggested by previous studies is manifested in terms of much smaller protrusion, confirming that the signaling state of E46Q-PYP is only partially developed compared with that of wild-type PYP. This finding provides direct evidence of how the environmental change in the vicinity of the chromophore alters the conformational change of the entire protein matrix. © the Owner Societies 201619101sciescopu
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