Nanoscale photosynthesis: Photocatalytic production of hydrogen by platinized photosystem I reaction centers

A study of the photocatalytic production of molecular hydrogen from platini zed photosystem I (PSI) reaction centers is reported. At pH 7 and room temp erature metallic platinum was photoprecipitated at the reducing end of PSI according to the reaction, [PtCl6](2-) + 4e(-) + hv --> Pt down arrow + 6Cl ,where it interacted with photogenerated PSI electrons and catalyzed the ev olution of molecular hydrogen. The reaction mixture included purified spina ch PSI reaction centers, sodium ascorbate and spinach plastocyanin, Experim ental data on real-time catalytic platinum formation as measured by the ons et and rates of hydrogen photoevolution as a function of time are presented . The key objective of the experiments was demonstration of functional nano scale surface metalization at the reducing end of isolated PSI by substitut ing negatively charged [PtCl6](2-) for negatively charged ferredoxin, the n aturally occurring water-soluble electron carrier in photosynthesis. The da ta are interpreted in terms of electrostatic interactions between [PtCl6](2 -) and the positively charged surface of psaD, the ferredoxin docking site situated at the stromal interface of the photosynthetic membrane and which is presumably retained in our PSI preparation. A discussion of the rates of hydrogen evolution in terms of the structural components of the various PS I preparations as well as of those of the intact thylakoid membranes is pre sented.