Alessandro Agostini , Andrea Calcinoni , Anastasia A. Petrova , Marco Bortolus , Anna Paola Casazza , Donatella Carbonera , Stefano Santabarbara
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Fluorescence Detected Magnetic Resonance (FDMR) allowed resolving four Chl <em>d</em> triplet (<sup>3</sup>Chl <em>d</em>) populations (T<sub>1</sub>-T<sub>4</sub>) both in untreated and illuminated samples in the presence of ascorbate and <em>N</em>,<em>N</em>,<em>N</em>′,<em>N</em>′-tetramethyl-<em>p</em>-phenylenediamine (TMPD). The FDMR signals increased following the pre-illumination treatment, particularly for the T<sub>3</sub> and T<sub>4</sub> populations, which are therefore sensitive to the redox state of PSI cofactors. Microwave-induced Triplet minus Singlet (TmS) spectra were detected in the |D|-|E| resonance window of the T<sub>3</sub> and T<sub>4</sub> triplets. These showed a broad singlet bleaching centred at 740 nm and also displayed complex spectral structure with several derivative-like features, indicating that both the T<sub>3</sub> and T<sub>4</sub> <sup>3</sup>Chl <em>d</em> populations are associated with the PSI reaction centre (RC) triplet, <span><math><msub><mmultiscripts><mi>P</mi><mprescripts></mprescripts><mrow></mrow><mn>3</mn></mmultiscripts><mn>740</mn></msub></math></span>. Parallel measurements by TR-EPR demonstrated that triplet signals observed under all conditions investigated are dominated by an electron spin polarisation (esp), which is typical of intersystem crossing, differently from what expected for recombination triplet states formed from a radical pair precursor. Moreover, stronger reductant conditions obtained by pre-illumination of the samples in the presence of dithionite and 5-methylphenazinium methyl sulfate (PMS) did not lead to a recombination triplet state esp, but rather to a decrease of the whole signal intensity. The energetics of <em>A. marina</em> PSI and the possible occurrence of distributions of cofactors redox properties are discussed in order to address the unexpected <span><math><msub><mmultiscripts><mi>P</mi><mprescripts></mprescripts><mrow></mrow><mn>3</mn></mmultiscripts><mn>740</mn></msub></math></span> esp.</div></div>","PeriodicalId":3,"journal":{"name":"ACS Applied Electronic Materials","volume":null,"pages":null},"PeriodicalIF":4.3000,"publicationDate":"2024-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"An unusual triplet population pathway in the Reaction Centre of the Chlorophyll-d binding Photosystem I of A. marina, as revealed by a combination of TR-EPR and ODMR spectroscopies\",\"authors\":\"Alessandro Agostini , Andrea Calcinoni , Anastasia A. Petrova , Marco Bortolus , Anna Paola Casazza , Donatella Carbonera , Stefano Santabarbara\",\"doi\":\"10.1016/j.bbabio.2024.149515\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>Photo-induced Chlorophyll (Chl) triplet states in the isolated Photosystem I (PSI) of <em>Acaryochloris marina</em>, that harbours Chl <em>d</em> as its main pigment, were investigated by Optically Detected Magnetic Resonance (ODMR) and Time-Resolved Electron Paramagnetic Resonance (TR-EPR), and as a function of pre-illumination of the sample under reducing redox poising. Fluorescence Detected Magnetic Resonance (FDMR) allowed resolving four Chl <em>d</em> triplet (<sup>3</sup>Chl <em>d</em>) populations (T<sub>1</sub>-T<sub>4</sub>) both in untreated and illuminated samples in the presence of ascorbate and <em>N</em>,<em>N</em>,<em>N</em>′,<em>N</em>′-tetramethyl-<em>p</em>-phenylenediamine (TMPD). The FDMR signals increased following the pre-illumination treatment, particularly for the T<sub>3</sub> and T<sub>4</sub> populations, which are therefore sensitive to the redox state of PSI cofactors. Microwave-induced Triplet minus Singlet (TmS) spectra were detected in the |D|-|E| resonance window of the T<sub>3</sub> and T<sub>4</sub> triplets. These showed a broad singlet bleaching centred at 740 nm and also displayed complex spectral structure with several derivative-like features, indicating that both the T<sub>3</sub> and T<sub>4</sub> <sup>3</sup>Chl <em>d</em> populations are associated with the PSI reaction centre (RC) triplet, <span><math><msub><mmultiscripts><mi>P</mi><mprescripts></mprescripts><mrow></mrow><mn>3</mn></mmultiscripts><mn>740</mn></msub></math></span>. Parallel measurements by TR-EPR demonstrated that triplet signals observed under all conditions investigated are dominated by an electron spin polarisation (esp), which is typical of intersystem crossing, differently from what expected for recombination triplet states formed from a radical pair precursor. Moreover, stronger reductant conditions obtained by pre-illumination of the samples in the presence of dithionite and 5-methylphenazinium methyl sulfate (PMS) did not lead to a recombination triplet state esp, but rather to a decrease of the whole signal intensity. The energetics of <em>A. marina</em> PSI and the possible occurrence of distributions of cofactors redox properties are discussed in order to address the unexpected <span><math><msub><mmultiscripts><mi>P</mi><mprescripts></mprescripts><mrow></mrow><mn>3</mn></mmultiscripts><mn>740</mn></msub></math></span> esp.</div></div>\",\"PeriodicalId\":3,\"journal\":{\"name\":\"ACS Applied Electronic Materials\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":4.3000,\"publicationDate\":\"2024-09-28\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"ACS Applied Electronic Materials\",\"FirstCategoryId\":\"99\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0005272824004857\",\"RegionNum\":3,\"RegionCategory\":\"材料科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"ENGINEERING, ELECTRICAL & ELECTRONIC\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Applied Electronic Materials","FirstCategoryId":"99","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0005272824004857","RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, ELECTRICAL & ELECTRONIC","Score":null,"Total":0}
引用次数: 0
摘要
通过光学检测磁共振（ODMR）和时间分辨电子顺磁共振（TR-EPR）研究了以 Chl d 为主要色素的海水藻（Acaryochloris marina）分离光系统 I（PSI）中光诱导的叶绿素（Chl）三重态，并将其作为还原氧化还原条件下样品预照明的函数。在抗坏血酸和 N,N,N',N'-四甲基对苯二胺（TMPD）存在的情况下，荧光检测磁共振（FDMR）可以分辨未经处理和经过光照的样品中的四个 Chl d 三重（3Chl d）群（T1-T4）。 经过光照前处理后，FDMR 信号增加，特别是 T3 和 T4 群，因此它们对 PSI 辅助因子的氧化还原状态很敏感。在 T3 和 T4 三联体的|D|-|E|共振窗口中检测到了微波诱导的三联体减单联体（TmS）光谱。这表明 T3 和 T43Chl d 群体与 PSI 反应中心 (RC) 三重子 P3740 有关。通过 TR-EPR 进行的平行测定表明，在所有研究条件下观察到的三重态信号都以电子自旋极化（esp）为主，这是典型的系统间交叉，不同于由自由基对前体形成的重组三重态。此外，在有连二亚硫酸盐和 5-甲基吩嗪甲基硫酸盐（PMS）存在的情况下对样品进行预照亮而获得的较强还原剂条件并不会导致重组三重态 esp 的出现，反而会导致整个信号强度的下降。为了解决意外的 P3740 esp 问题，我们讨论了 A. marina PSI 的能量学和可能出现的辅助因子氧化还原特性分布。
An unusual triplet population pathway in the Reaction Centre of the Chlorophyll-d binding Photosystem I of A. marina, as revealed by a combination of TR-EPR and ODMR spectroscopies
Photo-induced Chlorophyll (Chl) triplet states in the isolated Photosystem I (PSI) of Acaryochloris marina, that harbours Chl d as its main pigment, were investigated by Optically Detected Magnetic Resonance (ODMR) and Time-Resolved Electron Paramagnetic Resonance (TR-EPR), and as a function of pre-illumination of the sample under reducing redox poising. Fluorescence Detected Magnetic Resonance (FDMR) allowed resolving four Chl d triplet (3Chl d) populations (T1-T4) both in untreated and illuminated samples in the presence of ascorbate and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD). The FDMR signals increased following the pre-illumination treatment, particularly for the T3 and T4 populations, which are therefore sensitive to the redox state of PSI cofactors. Microwave-induced Triplet minus Singlet (TmS) spectra were detected in the |D|-|E| resonance window of the T3 and T4 triplets. These showed a broad singlet bleaching centred at 740 nm and also displayed complex spectral structure with several derivative-like features, indicating that both the T3 and T43Chl d populations are associated with the PSI reaction centre (RC) triplet, . Parallel measurements by TR-EPR demonstrated that triplet signals observed under all conditions investigated are dominated by an electron spin polarisation (esp), which is typical of intersystem crossing, differently from what expected for recombination triplet states formed from a radical pair precursor. Moreover, stronger reductant conditions obtained by pre-illumination of the samples in the presence of dithionite and 5-methylphenazinium methyl sulfate (PMS) did not lead to a recombination triplet state esp, but rather to a decrease of the whole signal intensity. The energetics of A. marina PSI and the possible occurrence of distributions of cofactors redox properties are discussed in order to address the unexpected esp.
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