INTERFACIAL PHOTOREACTIONS AT THE PHOTOSYNTHETIC MEMBRANE INTERFACE - AN UPPER LIMIT FOR THE NUMBER OF PLATINUM ATOMS REQUIRED TO FORM A HYDROGEN-EVOLVING PLATINUM METAL CATALYST

A new interfacial photochemical reaction at the photosynthetic membrane interface in which hexachloroplatinate is converted to metallic platinum is reported. The reductive precipitation of zerovalent platinum from a hexachloroplatinate ion requires four reducing equivalents. In situ photochemical reductive precipitation of hexachloroplatinate has been performed using the photochemical apparatus of isolated spinach chloroplasts illuminated with single-turnover, saturating flashes of lights. By continuously monitoring for the onset of photoevolved hydrogen, it is possible to set an upper limit for the minimum number of platinum atoms required to form catalytically active platinum. The key results of the experiments are that the onset of catalytic hydrogen evolution during the creation of platinum metal catalyst can be observed with 50 atoms or fewer and that a stable metal catalyst is created at about 500 atoms or fewer.