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Identifier 000458558
Title Μελέτη υπερταχείων φωτοφυσικών διεργασιών των πρωτεϊνών Φουκοξανθίνης Χλωροφύλλης (FCPs) που απομονώνονται από διάτομα μέσω χρονοαναλυόμενης φασματοσκοπίας λέιζερ
Alternative Title Investigation of the ultrafast photophysical processes of Fucoxanthin-Chlorophyll Proteins (FCPs) isolated from diatoms via transient absorption spectroscopy
Author Πολυχρονάκη, Μαρία Ν
Thesis advisor Άγγλος, Δημήτριος
Reviewer Λουκάκος, Παναγιώτης
Βαρώτσης, Κωνσταντίνος
Κουτσολέλος, Αθανάσιος
Παυλίδης, Ιωάννης
Ρίζος, Απόστολος
Δασκαλάκης, Ευάγγελος
Abstract Diatoms are photosynthetic organisms that play a vital role in reducing the concentration of carbon dioxide and increasing the concentration of oxygen in the atmosphere. The organic carbon they generate serves as a food source for various marine organisms. The process of photosynthesis in diatoms is initiated by the involvement of FucoxanthinChlorophyll Proteins (FCPs), which are responsible for the absorption of solar radiation. FCPs include carotenoids, such as Fucoxanthin (Fx), Diadinoxanthin (Ddx) and Diatoxanthin (Dtx), as well as type-a and type-c Chlorophylls (Chl-a, Chl-c). The absorbed radiation is directed towards Chl-a via energy transfer mechanisms and is subsequently directed to the reaction center, where photosynthesis reactions occur. Diadinoxanthin and diatoxanthin play a protective role, shielding FCPs from the potentially damaging intensity of solar radiation. In the context of the present study, we investigated the photophysical and photochemical processes of FCPs isolated from two types of diatoms, Fragilariopsis sp. and Phaeodactylum tricornutum, using Ultrafast Time-Resolved Laser Spectroscopy. The key feature of this technique is the utilization of an ultrashort pump pulse (30×10-15 s) to excite the FCPs. The brief duration of the system's perturbation enables the observation of ultrafast kinetic processes by probing changes in the absorption spectrum. The pump pulse is centered at λ = 395 nm and results in excitation of the FCP chromophores to their second electronically excited state, S2. To investigate the influence of the diatom growth conditions on the composition and function of the FCPs, the FCPs from Fragilariopsis sp. were cultivated with exposure to high- and low-intensity white light, as well as red light. Similarly, the FCPs from Phaeodactylum tricornutum were cultivated under low-intensity white light and red light. The cultivation of diatoms under low-intensity white light simulates the natural growth conditions, while the growth of FCPs under high-intensity white light and red light mimics extreme developmental conditions. Examining the photophysical processes of two FCP types (Fraction 1 and Fraction 3) isolated from the Fragilariopsis sp. cultivated under low-intensity white light revealed two distinct photophysical mechanisms. FCPs of Fraction 3, containing mainly Fx, Chl-a, and Chl-c, exhibit characteristic lifetimes: τ = 1.9 ± 0.05 ps and τ = 61 ± 2 ps. The former corresponds to the hot S1 state of Fx, while the latter corresponds to the S1 state of Fx. Fraction 1 FCPs, comprising Fx, Ddx, and Chlorophyllide a (Chlide-a), demonstrate lifetimes of τ = 0.7 ± 0.02 ps, τ = 13 ± 0.01 ps, and Abstract 15 τ = 77 ± 20.9 ps. The first corresponds to the hot S1 state of Fx and the hot S1 state of Ddx, the second to the S1 state of Ddx, and the third to the energy transfer process tsking place from Fx to Ddx and the S1 state of Fx. The distinction in mechanisms of operation arises from the role the FCPs play in the diatom Fragilariopsis sp. The FCPs of Fraction 1 facilitate energy transfer from Fx to Chlide-a (Protochlorophyllide-a) upon excitation by the pump pulse (λ = 395 nm), whereas the FCPs of Fraction 3 do not engage in this photophysical process. Consequently, it is hypothesized that the FCPs of Fraction 1 contribute to diatom protection against high intensity illumination via conducting energy transfer processes based on the presence of Ddx. The role of the FCPs of Fraction 3 was not elucidated because of inadequate resolution of the spectral-kinetic information that was collected. The FCPs of Fraction 1, isolated from the Phaeodactylum tricornutum diatom, cultivated under low-intensity white light, exhibit a comparable mechanism of operation to that of the FCPs from Fraction 1 isolated from the Fragilariopsis sp diatom. As a result, it is hypothesized that the FCPs of Fraction 1 once again play a role in diatom protection, indicating that the mechanism of operation of FCPs remains independent of the protein's origin. The utilization of high-intensity white light to cultivate Fragilariopsis sp. induces changes in the composition of FCPs Fraction 1 and Fraction 3. FCPs of Fraction 1 were found to contain Fx, Ddx, Chlide-a and Dtx, while FCPs of Fraction 3 contain Fx, Chl-a, Chl-c, Chlide-a, and Ddx. The study of the modified FCPs indicates that the alterations in the composition do not affect their mechanism of operation. The cultivation of Fragilariopsis sp. and Phaeodactylum tricornutum with red light does not disturb the structure of FCPs of Fraction 1, thus the mechanism of operation remains unaffected. In contrast, the configuration of FCPs of Fraction 3 transforms due to the presence of Chlide-a, yet, this does not influence the mechanism of operation of the FCPs. The results of this study have contributed to drawing conclusions regarding the roles of the two types of FCPs isolated from the diatom Fragilariopsis sp. Moreover, insights into the impact of origin and cultivation conditions on the mechanism of operation of FCPs have been obtained. The acquired information requires further investigation, and the technique needs to be optimized to achieve higher quality data. The conclusions drawn from this study are anticipated to make Abstract 16 contributions for further progress in the field of biotechnology, as well as the design of solar systems, as diatoms and FCPs find application in these research domains.
Language Greek
Subject Fragilariopsis sp.
Global Analysis
Phaeodactylum tricornutum
Υπετραχεία Χρονοαναλυόμενη Φασματοσκοπία Λέιζερ
Φωτοφυσικές Διεργασίες
Issue date 2023-09-19
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/a/5/9/metadata-dlib-1694683344-272636-9454.tkl Bookmark and Share
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