A study of the photocatalytic production of molecular hydrogen from platinized photosystem I (PSI) reaction centers is reported. At pH 7 and room temperature metallic platinum was photoprecipitated at the reducing end of PSI according to the reaction, [PtCl6]2- + 4e- + hv-->Pt decreases + 6Cl-, where it interacted with photogenerated PSI electrons and catalyzed the evolution of molecular hydrogen. The reaction mixture included purified spinach PSI reaction centers, sodium ascorbate and spinach plastocyanin. Experimental data on real-time catalytic platinum formation as measured by the onset and rates of hydrogen photoevolution as a function of time are presented. The key objective of the experiments was demonstration of functional nanoscale surface metalization at the reducing end of isolated PSI by substituting negatively charged [PtCl6]2- for negatively charged ferredoxin, the naturally occurring water-soluble electron carrier in photosynthesis. The data 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 PSI preparations as well as of those of the intact thylakoid membranes is presented.

A study of the photocatalytic production of molecular hydrogen from platinized photosystem I (PSI) reaction centers is reported. At pH 7 and room temperature metallic platinum was photoprecipitated at the reducing end of PSI according to the reaction, [PtCl6]2−+ 4e−+hν→ Pt↓+ 6Cl−, where it interacted with photogenerated PSI electrons and catalyzed the evolution of molecular hydrogen. The reaction mixture included purified spinach PSI reaction centers, sodium ascorbate and spinach plastocyanin. Experimental data on real‐time catalytic platinum formation as measured by the onset and rates of hydrogen photoevolution as a function of time are presented. The key objective of the experiments was demonstration of functional nanoscale surface metalization at the reducing end of isolated PSI by substituting negatively charged [PtCl6]2− for negatively charged ferredoxin, the naturally occurring water‐soluble electron carrier in photosynthesis. The data 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 PSI preparations as well as of those of the intact thylakoid membranes is presented.

Abstract-Using the technique of Kelvin force microscopy, we have performed the first measurements of photovoltages from single photosynthetic reaction centers [1]. The measured values, typically 1 V or more, are sufficiently large to trigger a neural response. The goal of this project is insertion of purified Photosystem I (PSI) reaction centers or other photoactive agents into retinal cells where they will restore photoreceptor function to people who suffer from age-related macular degeneration (AMD) or retinitis pigmentosa (RP), diseases that are the leading causes of blindness world-wide. Although the neural wiring from eye to brain is intact, these patients lack photoreceptor activity. It is the ultimate goal of this proposal to restore photoreceptor activity to these patients using PSI as the optical trigger. In principle, the approach should work. PSI is a robust integral membrane molecular photovoltaic device. Depending on orientation, it can depolarize or hyperpolarize the cell membrane with sufficient voltage to trigger an action potential. Keywords -artificial sight, photosynthesis, reaction centers I. INTRODUCTIONThis project investigates a new area of multidisciplinary biomedical engineering research that builds on recent advances in nanotechnology of photosynthesis [1,2] and pattern electrical stimulation of the human retina [3] (Fig. 1). The overall goal of the project is restoration of vision to people who are blind owing to outer retinal/photoreceptor degenerations by insertion of purified Photosystem I (PSI) reaction centers into cell membranes of retinal bipolar or ganglion cells. Whereas Fig. 1 illustrates the use of electrodes as the triggering voltage source, this new approach uses PSI reaction centers (Fig. 2). PSI reaction centers are integral membrane pigment-protein complexes. They are also nanometer-scale self-contained portable molecular photovoltaic devices. Using the technique of Kelvin force probe microscopy, we have measured photovoltages from single PSI reaction centers. They span a light-induced electric potential difference of approximately 1 V [1] a value of sufficient magnitude to trigger a neural response. PSI reaction centers self-regenerate via charge recombination, a property that allows them to recycle many times. II. METHODOLOGYHyperpolarization of retinal rod cells occurs when the normally negative interior membrane potential is driven more negative. A single photon absorbed by a dark-adapted rod closes hundreds of cation-specific channels and leads to a hyperpolarization of the membrane [4] which is sensed by the synapse and conveyed to the retinal bipolar and then the retinal ganglion cells of the retina. Since the targeted blind patients lack photoreceptor cells, the specific aim of this project is to properly insert and orient plant membrane pigment-protein complex PS I in a retinal ganglion or bipolar cell membrane, such that photon absorption will trigger an action potential. The basic concept of PSI-assisted generation of an action potential is illustrated schem...