E. Greenbaum*, I. Lee, and J. W. Lee
Chemical Technology Division,Oak Ridge National
This is an abstract
for a presentation given at the
Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is
available on the web.
Photosynthesis is the conversion of electromagnetic energy into stored chemical energy. The process, now well-understood at the molecular level, is schematically illustrated in Fig. 1 where the linear dimension of the membrane is ~5 nm. The primary event of photosynthesis, photon absorption leading to charge separation, occurs in a specialized structure: the photosynthetic reaction center. In higher plants there are two such reaction centers, Photosystems I and II, that have nanometer dimensions, picosecond response times and span a potential difference of one volt or more in their energized charge-separated state. The polarity of the voltage and vectorial nature of the charge separation is indicated in Fig. 1. The scientific focus and work plan of this proposal is on the interfacial physics and chemistry of isolated photosynthetic reaction centers and the construction of molecular logic devices using ORNL's unique experience in PS I self assembly, thin film and surface physics and instrumentation design and development. Fig. 2 is a schematic illustration of the extraction and isolation of Photosystem I reaction centers.
Full size Fig. 1
Figure 1. Schematic illustration of the photosynthetic membrane. The linear dimension of the membrane is approximately 5 nm. © 1998 Oak Ridge National Laboratory.
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Figure 2. The PS I reaction center is a molecular photovoltaic device with nanometer dimensions and picosecond response times. © 1998 Oak Ridge National Laboratory.
This poster presents an overview of the Oak Ridge National Laboratory research program in molecular electronics of photosynthetic reaction centers. We have had initial success in this area by demonstrating direct electrical contact of emergent electrons with the PS I reaction center by nanoparticle precipitation (Greenbaum, 1985; Greenbaum, 1988; J. W. Lee et al., 1998). Moreover, as illustrated in Fig. 3, our recent demonstration of stable diode properties of isolated reaction centers combined with the ability to orient them by self-assembly on a planar surface (I. Lee et al., 1995; I. Lee et al., 1997) make these structures good building blocks for 2-D and potentially 3-D device fabrication. Metallization of isolated PS I centers does not alter their fundamental photophysical properties (J. W. Lee et al., 1995) and they can be bonded to metal surfaces (J. W. Lee et al., 1996). Potential applications of PS I reaction centers for optoelectronic applications as well as molecular logic device construction will be discussed.
Full size Fig. 3
Figure 3. It has been discovered at ORNL that isolated and purified PS I reaction centers are molecular diodes that can be oriented on chemically modified surfaces. It is goal of our research to construct fault-tolerant molecular logic gates capable of all combinatorial logic functions. © 1998 Oak Ridge National Laboratory .
- E. Greenbaum, "Platinized Chloroplasts: A Novel Photocatalytic
Material," Science 230, 1373 1375 (1985).
- E. Greenbaum, "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," J. Phys.
Chem. 92, 4571-4574 (1988).
- I. Lee, J. W. Lee, R. J. Warmack, D. P. Allison, and E. Greenbaum,
"Molecular Electronics of a Single Photosystem I Reaction Center: Studies
with Scanning Tunneling Microscopy and Spectroscopy," Proc. Natl. Acad.
Sci. USA 92, 1965-1969 (1995).
- I. Lee, J. W. Lee, and E. Greenbaum, "Biomolecular Electronics:
Vectorial Arrays of Photosynthetic Reaction Centers," Phys. Rev.
Letters 79, 3294-3297 (1997).
- J. W. Lee, I. Lee, P. D. Laible, T. G. Owens, and E. Greenbaum,
"Chemical Platinization and its Effect on Excitation Transfer Dynamics and
P700 Photooxidation Kinetics in Isolated Photosystem I," Biophys. J.
69, 652-659 (1995).
- J. W. Lee, I. Lee, E. Greenbaum, "Platinization: A Novel Technique to
Anchor Photosystem I Particles onto a Metal Surface at Biological
Temperature and pH," Biosens. Bioelectron. 11, 375 387
- J. W. Lee, R. T. Collins, and E. Greenbaum, "Molecular Ionic Probes: A
New Class of Hill Reagents and their Potential for Nanofabrication and
Biometallocatalysis," J. Phys. Chem. B, 102, 2095-2100
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