Abstract
Femtosecond transient absorption was used to study excitation decay in monomeric and trimeric cyanobacterial Photosystem I (PSI) being prepared in three states: (1) in aqueous solution, (2) deposited and dried on glass surface (either conducting or non-conducting), and (3) deposited on glass (conducting) surface but being in contact with aqueous solvent. The main goal of this contribution was to determine the reason of the acceleration of the excitation decay in dried PSI deposited on the conducting surface relative to PSI in solution observed previously using time-resolved fluorescence (Szewczyk et al., Photysnth Res 132(2):111–126, 2017). We formulated two alternative working hypotheses: (1) the acceleration results from electron injection from PSI to the conducting surface; (2) the acceleration is caused by dehydration and/or crowding of PSI proteins deposited on the glass substrate. Excitation dynamics of PSI in all three types of samples can be described by three main components of subpicosecond, 3–5, and 20–26 ps lifetimes of different relative contributions in solution than in PSI-substrate systems. The presence of similar kinetic components for all the samples indicates intactness of PSI proteins after their deposition onto the substrates. The kinetic traces for all systems with PSI deposited on substrates are almost identical and they decay significantly faster than the kinetic traces of PSI in solution. We conclude that the accelerated excitation decay in PSI-substrate systems is caused mostly by dense packing of proteins.
Highlights
In recent years, photosynthetic pigment–protein complexes gained great attention in fabrication of bio-inorganic devices
We reported that immobilization of Photosystem I (PSI) on inorganic substrate, FTO conductive glass, modifies the spectral characteristics of some chlorophyll pools and accelerates the decay of PSI antenna excitation: from mean lifetime of tav = 16 ps for PSI in solution to 11 ps for PSI deposited on FTO glass (Szewczyk et al 2017)
For time-resolved absorption measurements of PSI in solution, both trimeric and monomeric forms were diluted in buffer A to O D680 nm, 1 cm = 0.4 and placed in the 2-mm quartz cuvette
Summary
Photosynthetic pigment–protein complexes gained great attention in fabrication of bio-inorganic devices. The usefulness of PSI complex in various bio-hybrid devices has been previously demonstrated in many studies These include different substrates (for working electrodes) such as gold, TiO2, ZnO, graphene, and conductive polymer systems (for instance, Ciesielski et al 2010; Mershin et al 2012; Feifel et al 2015; Carter et al 2016; Robinson et al 2017). Acceleration of the dye-excited state quenching was generally correlated with more efficient electron injection into a particular substrate (Koops et al 2009; Sobuś et al 2014) Another considered cause of accelerated excitation dynamics in immobilized PSI (Szewczyk et al 2017) was radical disparity in environmental conditions (PSI in water + detergent solution vs PSI dialyzed in order to get rid of detergent and deposited onto semiconductor and dried). Experiments described in the aforementioned studies were performed under excitation in the red region (predominantly 660 nm), for trimeric PSI form, in a range of excitation pulse energies
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