Photobioelectrodes
represent one of the examples where artificial
materials are combined with biological entities to undertake semi-artificial
photosynthesis. Here, an approach is described that uses reduced graphene
oxide (rGO) as an electrode material. This classical 2D material is
used to construct a three-dimensional structure by a template-based
approach combined with a simple spin-coating process during preparation.
Inspired by this novel material and photosystem I (PSI), a biophotovoltaic
electrode is being designed and investigated. Both direct electron
transfer to PSI and mediated electron transfer via cytochrome c from horse heart as redox protein can be confirmed. Electrode preparation and protein
immobilization have been optimized. The performance can be upscaled
by adjusting the thickness of the 3D electrode using different numbers
of spin-coating steps during preparation. Thus, photocurrents up to
∼14 μA/cm2 are measured for 12 spin-coated
layers of rGO corresponding to a turnover frequency of 30 e– PSI–1 s–1 and external quantum
efficiency (EQE) of 0.07% at a thickness of about 15 μm. Operational
stability has been analyzed for several days. Particularly, the performance
at low illumination intensities is very promising (1.39 μA/cm2 at 0.1 mW/cm2 and −0.15 V vs Ag/AgCl; EQE
6.8%).
Photosystems
I (PSI) and II (PSII) are pigment–protein complexes
capable of performing the light-induced charge separation necessary
to convert solar energy into a biochemically storable form, an essential
step in photosynthesis. Small-angle neutron scattering (SANS) is unique
in providing structural information on PSI and PSII in solution under
nearly physiological conditions without the need for crystallization
or temperature decrease. We show that the reliability of the solution
structure critically depends on proper contrast matching of the detergent
belt surrounding the protein. Especially, specifically deuterated
(“invisible”) detergents are shown to be properly matched
out in SANS experiments by a direct, quantitative comparison with
conventional matching strategies. In contrast, protonated detergents
necessarily exhibit incomplete matching so that related SANS results
systematically overestimate the size of the membrane protein under
study. While the solution structures obtained are close to corresponding
high-resolution structures, we show that temperature and solution
state lead to individual structural differences compared with high-resolution
structures. We attribute these differences to the presence of a manifold
of conformational substates accessible by protein dynamics under physiological
conditions.
Photosystem I (PS I) has a symmetric structure with two highly similar branches of pigments at the center that are involved in electron transfer, but shows very different efficiency along the two branches. We have determined the structure of cyanobacterial PS I at room temperature (RT) using femtosecond X-ray pulses from an X-ray free electron laser (XFEL) that shows a clear expansion of the entire protein complex in the direction of the membrane plane, when compared to previous cryogenic structures. This trend was observed by complementary datasets taken at multiple XFEL beamlines. In the RT structure of PS I, we also observe conformational differences between the two branches in the reaction center around the secondary electron acceptors A1A and A1B. The π-stacked Phe residues are rotated with a more parallel orientation in the A-branch and an almost perpendicular confirmation in the B-branch, and the symmetry breaking PsaB-Trp673 is tilted and further away from A1A. These changes increase the asymmetry between the branches and may provide insights into the preferential directionality of electron transfer.
In this paper, we propose novel plasmonic hydrogen sensors based on palladium coated narrow-groove plasmonic nanogratings for sensing of hydrogen gas at visible and near-infrared wavelengths.
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