The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet-Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00216208%3A11320%2F25%3A10507738" target="_blank" >RIV/00216208:11320/25:10507738 - isvavai.cz</a>

Výsledek na webu

<a href="https://verso.is.cuni.cz/pub/verso.fpl?fname=obd_publikace_handle&handle=t5POBhSaKC" target="_blank" >https://verso.is.cuni.cz/pub/verso.fpl?fname=obd_publikace_handle&handle=t5POBhSaKC</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1021/acs.jpcb.5c06284" target="_blank" >10.1021/acs.jpcb.5c06284</a>

Jazyk výsledku

angličtina

Název v původním jazyce

The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet-Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

Popis výsledku v původním jazyce

The light-harvesting 2 (LH2) complex of purple phototrophic bacteria plays a critical role in absorbing solar energy and distributing the excitation energy. Exciton dynamics within LH2 complexes are controlled by the structural arrangement and energy levels of the bacteriochlorophyll (BChl) and carotenoid (Car) pigments. However, there is still debate over the competing light-harvesting versus energy-dissipation pathways. In this work, we compared five variants of the LH2 complex from genetically modified strains of Rhodobacter sphaeroides, all containing the same BChls but different Cars with increasing conjugation: zeta-carotene (N = 7; LH2(Zeta)), neurosporene (N = 9; LH2(Neu)), spheroidene (N = 10; LH2(Spher)), lycopene (N = 11; LH2(Lyco)), and spirilloxanthin (N = 13; LH2(Spir)). Absorption measurements confirmed that the Car excited-state energy decreased with increasing conjugation. Similarly, fluorescence spectra showed that the B850 BChl emission peak had an increasing red shift from LH2(Zeta)-&gt;(LH2(Neu)/LH2(Spher))-&gt; LH2(Lyco)-&gt; LH2(Spir). In contrast, time-resolved fluorescence and ultrafast transient absorption (fs-TA) revealed similar excited-state lifetimes (similar to 1 ns) for all complexes except LH2(Spir) (similar to 0.7 ns). From fs-TA analysis, an additional similar to 7 ps nonradiative dissipation step from B850 BChl was observed for LH2(Zeta). Further, singlet-singlet and singlet-triplet annihilation studies showed a similar to 50% average fluorescence lifetime reduction in LH2(Zeta) at high laser power and high repetition rate, compared to similar to 10-15% reductions in LH2(Neu)/LH2(Spher)/LH2(Lyco) and minimal lifetime change in LH2(Spir). In LH2(Zeta), the fastest decay component (&lt;50 ps) became prominent at high repetition rates, consistent with strong singlet-triplet annihilation. Nanosecond TA measurements revealed long-lived (&gt;40 mu s) BChl triplet states in LH2(Zeta) and signs of damage caused by singlet oxygen, whereas other LH2s showed faster triplet quenching (similar to 18 ns) by Cars. These findings highlight a key design principle of LH2 complexes: the Car triplet energy must be significantly lower than the BChl triplet energy to efficiently quench BChl triplets that otherwise act as potent &quot;trap states,&quot; causing exciton annihilation in laser-based experiments or photodamage in native membranes.

Název v anglickém jazyce

The Impact of Carotenoid Energy Levels on the Exciton Dynamics and Singlet-Triplet Annihilation in Isolated Bacterial Light-Harvesting 2 Complexes

Popis výsledku anglicky

The light-harvesting 2 (LH2) complex of purple phototrophic bacteria plays a critical role in absorbing solar energy and distributing the excitation energy. Exciton dynamics within LH2 complexes are controlled by the structural arrangement and energy levels of the bacteriochlorophyll (BChl) and carotenoid (Car) pigments. However, there is still debate over the competing light-harvesting versus energy-dissipation pathways. In this work, we compared five variants of the LH2 complex from genetically modified strains of Rhodobacter sphaeroides, all containing the same BChls but different Cars with increasing conjugation: zeta-carotene (N = 7; LH2(Zeta)), neurosporene (N = 9; LH2(Neu)), spheroidene (N = 10; LH2(Spher)), lycopene (N = 11; LH2(Lyco)), and spirilloxanthin (N = 13; LH2(Spir)). Absorption measurements confirmed that the Car excited-state energy decreased with increasing conjugation. Similarly, fluorescence spectra showed that the B850 BChl emission peak had an increasing red shift from LH2(Zeta)-&gt;(LH2(Neu)/LH2(Spher))-&gt; LH2(Lyco)-&gt; LH2(Spir). In contrast, time-resolved fluorescence and ultrafast transient absorption (fs-TA) revealed similar excited-state lifetimes (similar to 1 ns) for all complexes except LH2(Spir) (similar to 0.7 ns). From fs-TA analysis, an additional similar to 7 ps nonradiative dissipation step from B850 BChl was observed for LH2(Zeta). Further, singlet-singlet and singlet-triplet annihilation studies showed a similar to 50% average fluorescence lifetime reduction in LH2(Zeta) at high laser power and high repetition rate, compared to similar to 10-15% reductions in LH2(Neu)/LH2(Spher)/LH2(Lyco) and minimal lifetime change in LH2(Spir). In LH2(Zeta), the fastest decay component (&lt;50 ps) became prominent at high repetition rates, consistent with strong singlet-triplet annihilation. Nanosecond TA measurements revealed long-lived (&gt;40 mu s) BChl triplet states in LH2(Zeta) and signs of damage caused by singlet oxygen, whereas other LH2s showed faster triplet quenching (similar to 18 ns) by Cars. These findings highlight a key design principle of LH2 complexes: the Car triplet energy must be significantly lower than the BChl triplet energy to efficiently quench BChl triplets that otherwise act as potent &quot;trap states,&quot; causing exciton annihilation in laser-based experiments or photodamage in native membranes.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10301 - Atomic, molecular and chemical physics (physics of atoms and molecules including collision, interaction with radiation, magnetic resonances, Mössbauer effect)

Projekt

—

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2025

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Journal of Physical Chemistry B

ISSN

1520-6106

e-ISSN

1520-5207

Svazek periodika

129

Číslo periodika v rámci svazku

49

Stát vydavatele periodika

US - Spojené státy americké

Počet stran výsledku

19

Strana od-do

12642-12660

Kód UT WoS článku

001622900900001

EID výsledku v databázi Scopus

2-s2.0-105024725767