| 研究課題/領域番号 |
23KF0275
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| 研究種目 |
特別研究員奨励費
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| 配分区分 | 基金 |
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| 応募区分 | 外国 |
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| 審査区分 |
小区分32010:基礎物理化学関連
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| 研究機関 | 学習院大学 |
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研究代表者 |
岩田 耕一 学習院大学, 理学部, 教授 (90232678)
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| 研究分担者 |
RAJ ANKIT 学習院大学, 理学部, 外国人特別研究員
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| 研究期間 (年度) |
2023-11-15 – 2026-03-31
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| 研究課題ステータス |
交付 (2023年度)
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| 配分額 *注記 |
2,300千円 (直接経費: 2,300千円)
2025年度: 500千円 (直接経費: 500千円)
2024年度: 1,600千円 (直接経費: 1,600千円)
2023年度: 200千円 (直接経費: 200千円)
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| キーワード | time-resolved / spectroscopy / electron transfer |
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| 研究開始時の研究の概要 |
Photosynthesis is the primary process by which oxygen is produced in Earth’s atmosphere. An important step in this complex reaction is an electron transfer mediated by a molecule called plastoquinone, between two light-absorbing proteins present in the cell-membrane of leaves. We aim to study the structural changes of plastoquinone during the electron transfer process, using vibrational and fluorescence spectroscopy at picosecond time scales under native condition. Information on the dynamics of plastoquinone is crucial to develop better chemical systems for artificial photosynthesis.
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| 研究実績の概要 |
We have started working on the initial aspects of the research project, measurements on ubiquinone (UQ), with present aim at the development of a pico-second time-resolved Raman spectrometer. We aim to measure the structural changes in ubiquinone following the acceptance of an electron in the lipid bilayer membrane using this instrument. Our aim has been the development of the probe laser at 405 nm for observing the transients of UQ (the same transients which are formed after reduction of UQ).
For this, we have used second-harmonic generation using a newly obtained nonlinear crystal providing highly efficient second harmonic conversion. In the process of developing the instrument, we tried two ways to obtain narrow wavelength probe pulses near 400 nm, (a) a grating based 4-f filter, and (b) a narrow band Bragg reflective filter. Testing revealed that with the narrow band Bragg reflective filter worked well and provided good enough throughput for obtaining Raman spectra of high quality. Thus, the notch filter at 405 nm was used to select out narrow wavelength pulses with a temporal bandwidth of about 2 ps. With a Rayleigh rejection filter designed for 405 nm, the Raman measurement instrument was prepared. In preparation for the future experiments, UV-visible absorption spectra have been acquired.
The computer program used to perform measurements has been rewritten to automate Raman spectral acquisition at multiple delay-times. Additionally, since the spectra are affected by laser power fluctuation of probe pulses, simultaneous laser power measurement has been implemented.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
According to the self-review, we are moving in the right direction with regard to the project. The project involves preparation of the spectroscopic instrument for the specific molecules of our interest, quinones, whose transients absorb at wavelength near 400-440 nm. Hence, our first aim was to construct an efficient time-resolved pico-second Raman spectrometer to observe these transients within the specified wavelength region. This involved testing different newly acquired optical components to have probe laser with good enough power, to observe Raman scattering with probe near 400 nm. This development process involved improving the Raman spectrometer and changing the probe wavelength. Optical components were upgraded for the purpose. We tried two ways to have narrow wavelength probe pulse, first with a grating based 4-f filter, and second using a narrow-band Bragg reflective filter. Testing revealed that the narrow band Bragg reflective filter in combination with a narrow band Rayleigh rejection filter performed well. With further improvements to the optical setup, high S/N Raman spectra were obtained. The next aim is to establish appropriate time-delay between probe and pump by observing transient absorption of some reference sample.
Chemical reagents required for executing upcoming experiments have been obtained. Lastly, tests on sample preparation protocols are being done. With these progresses, we believe that the project is on track.
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| 今後の研究の推進方策 |
Our immediate target is to further refine the time-resolved Raman spectrometer. This would involve: (i) correcting the polarization of the probe beam using a half-wave plate, and (ii) obtaining the correct time delays between the pump and probe pulses. A careful examination of the transient absorption (using simple quinone) would give information about the time delay, and whether we need to modify the optical path to adjust the time difference. Spatial overlap between the probe and pump pulses has been already obtained. After these final improvements, we will start with the experiments of ubiquinone in pure solvents and in lipid bilayers. The sample preparation scheme is well established. At first, electron-donor will be added to the sample to observe the target transients. Next, the reduction of quinone molecule (for example, ubiquinone), by electron acceptance will be attempted by photo-ionization of either stilbene (or 3-methyl indole) in the same sample solution. This would involve tests at different concentration to establish the reaction process.
Next, towards the larger goal, we will move to more complex sample system, plastoquinone in active photosynthetic membranes, for which we have prepared the chemical reagents for the sample preparation from green leaves. Regarding the sample preparation, we will start with physical lysis of the plant leaves and centrifugal separation of cellular components and measurement of specific fractions.
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