Critical evaluation of electron transfer kinetics in P700–FA/FB, P700–FX, and P700–A1 Photosystem I core complexes in liquid and in trehalose glass

Photovoltaic activity of electrodes based on intact photosystem I electrodeposited on bare conducting glass

“…In this paper, we demonstrate a significant photovoltaic activity of the biohybrid electrodes containing PSI particles which have been proven to be functionally highly intact at the level of ultrafast processes: excitation energy transfer and primary charge separation (Szewczyk et al 2017(Szewczyk et al , 2018. Apparently, the IQE of 0.37% for the OCP is not limited by inefficient charge separation but it may be caused by the internal back electron transfer inside the PSI (both in the fully functional complexes allowing formation of the state P700 + F b − , and in functionally impaired complexes showing charge recombination between P700 + and intermediate PSI electron acceptors (Kurashov et al 2018) or by the external back electron transfer promoted by exogenous redox molecules. Two opposite contributions of the photocurrent were Fig.…”

“…It was demonstrated that at high potentials (+ 650 nm) even the PSI antenna Chls being in the ground state may undergo electrochemical oxidation (Nakamura et al 2004). Therefore, it is justified to expect that the excited Chls (Chls*) which have got very negative midpoint redox potential (− 920 mV) (Zhang et al 2016) will be oxidized by a highpositive potential applied to the FTO despite short excited state lifetime of antenna Chls (of the order of 30 ps; (Gobets et al 2001)), orders of magnitude shorter than the lifetime of F b − (millisecond range; Vassiliev et al 1997;Kurashov et al 2018). This hypothesis is supported by recent observation that excited Chls in the PSII antenna may efficiently donate their electrons to the highly oxidizing acceptor rather than transfer their energy towards the reaction center (Zhang et al 2016).…”

“…As a result, a long-lived chargeseparated state P700 + F b − (or P + F b − ) is formed within < 1 µs (Brettel and Leibl 2001). In isolated PSI, this state may be depopulated either by transferring the electron from F b − and the hole from P700 + to exogenous mediator or electrode, or by a competitive dissipative internal charge recombination occurring on the hundreds of millisecond time scale (Vassiliev et al 1997;Kurashov et al 2018).…”

“…Photocurrent generated from 1 cm 2 of the mentioned above PSIcontaining electrodes ranges from below 1 µA to hundreds of µA, although the intact operation of PSI in these systems is usually assumed rather than demonstrated. In fact, it has been recently demonstrated that in the cyanobacterial PSI immobilized in a trehalose glassy matrix as much as 90% of forward electron transfer was arrested and back electron transfer was observed instead, and only 10% of the electrons excited at the PSI primary donor reached the final PSI electron acceptor (Kurashov et al 2018). Harsh treatment of the PSI in some systems may inactivate even higher percentage of the proteins.…”

Excitation dynamics in Photosystem I trapped in TiO2 mesopores

“…The two branches meet at the F x iron-sulfur cluster, which receives an electron from A 1 and transfers it further to two terminal electron acceptors iron-sulfur clusters, F A and F B . The forward electron transfer events span the lifetimes from ~ 1 ps (primary charge separation or formation of the state P700 + A 0 − ) to ~ 500 ns (formation of the state P700 + F B − ) (Brettel and Leibl 2001) and are much faster than dissipative charge recombination reactions ranging from ~ 10 ns to ~ 100 ms, for the respective charge recombination reactions (Vassiliev et al 1997;Kurashov et al 2018) (~ 10 ns for P700 + A 0 − → P700A 0 , and ~ 100 ms for P700 + F B − → P700F B ). The primary charge separation is preceded by an excitation energy transfer from the antenna Chls to the RC that occurs with apparent/effective lifetime of 20-50 ps in PSI cores from various cyanobacteria (Gobets et al 2001(Gobets et al , 2003 and ~ 20-30 ps in PSI cores from green algae (Gibasiewicz et al 2001;Giera et al 2014), and is usually longer in LHCIcontaining PSI preparations from algae and plants (Giera et al 2014;Melkozernov et al 2004;Le Quiniou et al 2015;Wientjes et al 2011;Slavov et al 2008;Abram et al 2019) due to a relatively slow energy transfer from LHCI to PSI core.…”