Molecular Ionic Probes:  A New Class of Hill Reagents and Their Potential for Nanofabrication and Biometallocatalysis

We report the results of an extensive experimental survey and characterization of over 20 species of transition-metal compounds for their activity in the Hill reaction and photoprecipitation of metal at the lipid−water interface of photosynthetic thylakoid membranes. Four new Hill reagents were identified: PtCl 4, OsCl 3, [RuCl 6 ] 2-, and [RuCl 6 ] 3- . Each can be photosynthetically reduced to form a metallic catalyst at the reducing site of photosystem I (PSI) in the thylakoid membranes. Negative charge of the metal-compound species is apparently essential for their interaction with the reducing site of PSI. When PtCl 4 and OsCl 3 are dissolved in water, they combine with water molecules to form H 2 [PtCl 4 (OH) 2 ] and H 3 [OsCl 3 (OH) 3 ], which can dissociate to negatively charged species [PtCl 4 (OH) 2 ] 2- and [OsCl 3 (OH) 3 ] 3- at neutral pH. Metallic ruthenium can also catalyze reduction of protons for H 2 production, in addition to its known catalytic ability to fix CO 2 . These findings could have important implications for nanofabrication and biometallocatalysis to harness the power of photosynthetic systems.