Stock material or miscellaneous articles – Composite
Reexamination Certificate
1998-10-27
2001-05-15
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
C428S446000, C428S457000, C428S910000, C257S040000, C257S642000
Reexamination Certificate
active
06231983
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates, in general, to methods of forming molecular devices capable of converting light energy into chemical energy. More specifically, the present invention is directed to methods of chemically modifying the surface of a substrate such that Photosystem I reaction centers may be oriented in a preselected orientation.
BACKGROUND OF THE INVENTION
Green plants and photosynthetic bacteria capture and utilize sunlight by means of molecular electronic complexes, reaction centers, that are embedded in their membranes. In oxygenic plants, photon capture and conversion of light energy into chemical energy take place in pigment-protein complexes known as Photosystem I (“PSI”) and Photosystem II (“PSII”) reaction centers. As explained in
Nature,
R. Hill and F. Bendall (London) 186, 136 (1960), photosynthesis requires PSII and PSI working in sequence, using water as the source of electrons and CO
2
as the terminal electron acceptor. The two reaction centers use a special pair of chlorophyll molecules as the primary electron donor and chlorophyll or pheophytin as the primary electron acceptor. Following excitation, transfer of an electron from the excited primary donor to the primary acceptor occurs within picoseconds, a process characterized by high quantum efficiency and minimal side reactions. For the PSI reaction center, the midpoint oxidization potential generated by the primary electron donor (P700) is about +0.4 V and the corresponding reduction potential generated by the electron acceptor (4Fe-4S center) is about −0.7 V. The PSI reaction center, therefore, is a photodiode (unidirectional electron flow) and nanometer-sized (~6 nm) solar battery.
Additionally, since the PSI reaction center is one of the pigment-protein complexes that is responsible for the photosynthetic conversion of light energy to chemical energy, these reaction centers may be used as an electronic component in a variety of different devices. These possible devices include, but are not limited to, spatial imaging devices, solar batteries, optical computing and logic gates, optoelectronic switches, photonic A/D converters, and thin film “flexible” photovoltaic structures. However, in order to make these PSI reaction centers into a molecular device it is very important to use a method to selectively immobilize the PSI reaction centers onto a substrate without denaturation of the PSI.
The prior art has attempted to replicate this photochemical reaction by using PSI reaction centers on a metal surface. The prior art has shown that platinum may be precipitated on the surface of photosynthetic membranes, thereby making direct electrical contact with the acceptor side of PSI, where it can either catalyze hydrogen evolution or drive photocurrent through an external circuit. Additionally, the prior art has recently shown that isolated PSI reaction centers can be platinized without altering their intrinsic excitation dynamics and initial electron transfer reactions. Additionally, the prior art has shown that a two-dimensional spatial array of isolated PSIs may be anchored onto a metal surface by PSI-platinum-gold bonding at a biological temperature and pH. However, these prior art methods were not capable of orienting the PSI reaction centers on the surface of the substrate. PSI reaction centers which are not oriented will cancel each other out, which, therefore, would not permit the PSI-immobilized devices to be used in photoelectric devices such as solar batteries or logic gates.
The present invention provides a solution to the orientation problem. The present invention provides a method for controlling the orientation of two-dimensional spatial arrays of isolated reaction centers on derivatized surfaces. By controlling the orientation of the reaction centers, these arrays may be used in the construction of biomolecular electronic devices.
SUMMARY OF THE INVENTION
The present invention is directed to methods of forming molecular devices that are capable of converting light energy into chemical energy. The devices convert the light energy to chemical energy through the use of Photosystem I (“PSI”) reaction centers. More specifically, the present invention is directed to methods of chemically modifying the surface of a substrate such that PSI reaction centers may be oriented in a preselected orientation. The methods orient and immobilize PSI reaction centers onto a substrate without denaturation of the PSI.
The methods of the present invention orient and immobilize the PSI reaction centers by chemically modifying the surface of the substrate and then immersing the chemically-modified substrate within a PSI solution such that the PSI reaction centers are immobilized on the surface of the substrate. The chemical compound may be selected to modify the substrate such that the PSI reaction centers are oriented in a preselected orientation. Preferably, the chemical compound is a sulfur-organic compound. Depending on the chemical compound used, the PSI reaction centers may be immobilized and oriented in a direction parallel to the surface of the substrate, perpendicular to the surface in the “up” position, or perpendicular to the surface in the “down” position. Each of these directions provides different characteristics to the device.
Accordingly it is an object of the present invention to provide methods useful for forming molecular devices.
It is another object of the present invention to provide methods of selectively immobilizing Photosystem I reaction centers onto a substrate without denaturation of the PSI.
It is still another object of the present invention to provide methods of selectively immobilizing Photosystem I reaction centers onto a substrate in a preselected orientation.
These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
REFERENCES:
patent: 4399044 (1983-08-01), Buckley et al.
patent: 5585646 (1996-12-01), Kossovsky et al.
Lee, Ida et al., “Biomolecular Electronics: Vectorial Arrays of Photosynthetic Reaction Centers,”Physical Review Letters, vol. 79, No. 17, pp. 3294-3297 (Oct. 27, 1997).
Reeves, S.G. et al., “Higher Plant Chloroplasts and Grana: General Preparative Procedures (Excluding High Carbon Dioxide Fixation Ability Chloroplasts),”Methods in Enzymology, vol. 69, pp. 85-94 (1980).
Hill, R. et al., “Function of the Two Cytchrome Components in Chloroplasts: A Working Hypothesis,”Nature, vol. 186, pp. 136-137 (Apr. 9, 1960).
Greenbaum Elias
Lee Ida
Lee James W.
Kilpatric Stockton LLP
Thibodeau Paul
UT-Battelle
Zacharia Ramsey
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