Photosystem I-Based Applications for the Photo-catalyzed Production of Hydrogen and Electricity

The aim of this dissertation was to optimize systems integrating the photosystem I (PSI) redox protein, which is involved in photosynthesis, with noble metals for electron transfer to show its versatility: 1) in solution coupled with platinum to mediate hydrogen evolution and 2) on a planar gold surface for electricity production.

Response surface methodology was utilized to study variables that affect hydrogen (H₂) yield from platinized-PSI. Light intensity, temperature, and platinum concentration were varied during the platinum-photo-reduction process. Analysis of the effects of the variables on H₂ yield allowed for determination of a condition for optimized hydrogen production: 240 μE/m²/s [micro-Einsteins per square meter per second] light intensity, 638 μM [micro-molar] platinum, and 31°C [degrees Celsius] temperature. A model was developed from an experimental solution space and predicted an optimum H₂ yield of ~8.17 µmol H₂/mg chl a/h [micro-mole hydrogen per milligram chlorophyll a per hour]. The model was validated by an 8.02 µmol H₂/mg chl a/h value determined experimentally and platinum concentration had the greatest influence on H₂ yield.

Small-angle neutron scattering was used to investigate the solution structure of trimeric PSI from Thermosynechococcus elongatus in n-dodecyl-beta-D-maltoside (DDM) detergent to determine the orientation of the detergent molecules around PSI. The resulting PSI-DDM reconstruction structure showed the detergent oriented around the hydrophobic and interstitial periphery of the trimer in a non-uniform manner and did not agglomerate on the stromal or lumenal surfaces. Therefore, linkages to these faces are unlikely to be hindered by the presence of detergent.

Photo-activity has been observed from techniques attaching PSI to conductive surfaces. These techniques allow for dense deposition of the protein, but fail to control the orientation of PSI on the surface. The highly selective sortase-mediated ligation (SML) reaction was used to covalently attach PSI on tri-glycine functionalized gold surfaces. The exposed C-termini of PSI subunits from Synechocystis sp. PCC 6803 were targeted to study SML to control the orientation of PSI on gold for enhanced electron transfer, which yielded a 50% increase in current production from less than 100 nA/cm² [nanoampere per square centimeter] to approximately 150 nA/cm² compared to other monolayers.