JP5673769B2 - Molecular element, single molecule optical switch element, functional element, molecular wire and electronic device - Google Patents

Description

  The present invention relates to a molecular element, a monomolecular optical switch element, a functional element, a molecular wire, and an electronic device, and in particular, a molecular element using an electron transfer protein such as zinc cytochrome c, a single molecular optical switch element, a functional element, and various types The present invention relates to a molecular wire suitable for element wiring and an electronic device using the functional element.

The world of electronic devices using semiconductors in the fields of information communication and computer has developed miniaturization technology to improve its performance. However, the physical limits are approaching that point, and breakthroughs with new technological innovations are desired. One of them is an electronic circuit using molecules and molecular element technology. A molecular element functions in an angstrom order size and can improve the integration degree by 10 ³ to 10 ⁶ times as compared with a semiconductor device (see, for example, Non-Patent Document 1).

Several proposals have been made regarding the driving principles and models of molecular devices.
Batlogg et al. Obtained the knowledge that conductivity or superconductivity is expressed in organic crystals by using a field effect transistor (FET) technique (see Non-Patent Document 2). This property has also been found in fullerenes and metal complexes, and has attracted attention as being capable of imparting a switching function to various compound molecules by carrier doping by an electric field.
Wada et al. Have proposed a model of a molecular single-electron transistor having fullerenes as quantum dots as a possibility of a single molecule device (see Patent Document 1). This is a technique in which the potential of a quantum dot is changed by tunneling an electrode to the quantum dot and applying a gate voltage across an insulating layer to develop a function as a transistor.

Furthermore, there are attempts to apply supramolecules that exhibit various structural and functional properties and apply their molecular recognition functions to switching. This supramolecule has a variety of structural features that are impossible in a single state by organizing multiple molecules using non-covalent interactions such as coordination bonds, hydrogen bonds, and intermolecular forces.・ A functional property has been acquired. Balzani et al. Have proposed a molecular switch whose behavior is changed by an external field such as pH or light using a supramolecular compound having a molecular recognition function such as catenane or rotaxane (see Non-Patent Document 3).
On the other hand, with regard to the wiring technology in molecular devices, attempts have been made to introduce a functional group such as thiol at the terminal of a conductive polymer and perform wiring connection using chemical adsorption to gold or ITO electrode.

As described above, although much research has been conducted on molecular devices so far, no technology has yet been provided that enables construction of practical molecular devices or circuits using them. .
In the design or construction of molecular elements or circuits using them, the arrangement and arrangement of individual molecules, the recognition of individual molecules, access to individual molecules, and connections between specific molecular elements are precisely formed to form a circuit. The problem is how to perform wiring and addressing. For example, regarding the arrangement and arrangement of the individual molecules described above, although technology for arranging atoms one by one using a scanning probe microscope (SPM) has been developed, as a design or construction of a nanoscale device, Not realistic. In addition, for the above-mentioned wiring, when designing the molecular device described above, it is considered realistic to drive it by an electrical signal in a solid as in the case of a semiconductor device, but it is macroscopic compared to a device at the molecular level. Connecting scale conductors is extremely difficult.

  On the other hand, in the design or construction of the molecular device or the circuit using the molecular device, a molecular wire formed by a single chain polymer or a one-dimensionally integrated molecule is used as a conductive path or itself. Is considered to be an important element in molecular devices having a switching function and has been studied. However, in the case of molecular wires currently being studied, the current state is that none of the conduction mechanisms have been fully elucidated. In general, a simple one-dimensional substance has a problem that it is not easy to form a molecular wire because conductivity is impaired due to properties unique to a one-dimensional system such as Peierls transition.

In addition, for metal complex chains expected as molecular wires, especially ladder-type metal complexes, the theoretical study on their properties was started by Rice et al., Which is called a spin ladder with an even number of antiferromagnetic metal chains. In the case of a ladder structure, it is expected that superconductivity is exhibited by carrier doping (see Non-Patent Document 4), and the possibility of functioning as an element is also conceivable. As an experimental example, a double-stranded ladder compound using copper oxide has been synthesized, and a superconducting phenomenon has been found under high pressure (see Non-Patent Document 5). In addition, the formation of molecular wires by dispersing a halogen-bridged metal complex coated with an organic counter anion in a solvent was studied by Kimizuka et al. (See Non-Patent Document 6), and metal by p-EPYNN and Ni (dmit) ₂ Ladder type compounds using complexes have also been studied (see Non-Patent Document 7). Furthermore, so-called crossbar switches that control switching at the intersection of nanowires orthogonally with inputs from the nanowires have been actively studied in recent years as candidates for nanodevices that do not require complex processing (for example, non-crossover switches). If it can construct | assemble the array by said nanowire by a molecular level and bottom-up, it is anticipated by the point which can implement | achieve an extremely high-density device comparatively easily.

  However, any of the molecular wires and nanowires described above is only a prediction and an experimental view, and lacks practicality and concreteness. It is difficult to achieve these with existing technology, and a new method is desired that enables molecular-level wiring and the like to be realized in a bottom-up manner at the molecular level. On the other hand, a synthesis example of a metal complex integrated structure has also been reported (see Non-Patent Document 9). However, in many cases, there is a problem that packing control is difficult because molecules are merely arranged in a ladder shape by a weak interaction such as intermolecular force. In addition, the molecular arrangement in the resulting metal complex chain greatly depends on the molecular shape, the effect of substituents, subtle interactions between molecules, etc., and even if it is chemically modified, it can take a ladder structure. Since the probability is low, there is a problem that it cannot function sufficiently as a single wire.

In a sample in which zinc cytochrome c is randomly adsorbed on a nanoporous titanium oxide (TiO ₂ ) electrode, electrons excited by light irradiation to the zinc cytochrome c are injected into the conduction band of TiO _2. It has been reported that a photocurrent is generated (see Non-Patent Document 10).
Further, in a monolayer film having a two-layer structure of iron cytochrome c and green fluorescent protein (GFP) immobilized on a gold substrate, photocurrent may be generated by light irradiation. It has been reported (see Non-Patent Document 11).
In addition, it has been reported that a photocurrent is generated by light irradiation in a monomolecular film of a peptide immobilized on a gold substrate (see Non-Patent Document 12). In this Non-Patent Document 12, two types of peptides having different photoresponsiveness are immobilized on a single gold substrate via a monomolecular film of a disulfide that is a sulfur compound, whereby the polarity of the photocurrent is determined by the irradiation light. Controlled by wavelength.
In addition, a method for synthesizing zinc cytochrome c has been reported (see Non-Patent Document 13).
In addition, a method for producing a gold electrode in which a single molecule of iron cytochrome c is adsorbed has been reported (see Non-Patent Document 14).

JP-A-11-266007

Kazumi Matsushige, Kazuyoshi Tanaka “Molecular Nanotechnology: Utilizing Molecular Capabilities for Device Development” J.H.Schon, Ch.Kolc, B.Batlogg, Nature, 406, 702 (2000) V. Balzani, A. Credi, and M. Venturi, Coord. Chem. Rev., 171, 3 (1998) T. M. Rice, S. Gopalan and M. Sigrist, Europhys. Lett., 23,445 (1993) M. Uehara, T. Nagata, J. Akimitsu, H. Takahashi, H. Mori and K. Kinoshita, J. Phys. Soc. Jpn., 65, 2764 (1996) N. Kimizuka, N. Oda, T. Kunitake, Inorg. Chem. 39, 2684 (2000) H. Imai, T. Inabe, T. Otsuka, T. Okuno, and K. Agawa, Phys. Rev. B 54, R6838 (1996) James R. Heath, Philip J. Kuekes, Gregory S. Snider, R. Stanley Williams, Science Vol. 280 (1998) W. Huang, S. Gou, D. Hu, S. Chantrapromma, H. Fun, and Q. Meng, Inorg. Chem., 40, 1712 (2001) Emmanuel Topoglidis, Colin J. Campbell, Emilio Palomares, and James R. Durrant, Chem. Commun. 2002, 1518-1519 Jeong-Woo Choi and Masamichi Fujihira, Appl. Phys. Lett. 84, 2187-2189 (2004) Shiro Yasutomi, Tomoyuki Morita, Yukio Imanishi, ShunsakuKimura, Science 304, 1944-1947 (2004) Martin Braun, Stefan Atalick, Dirk M. Guldi, Harald Lanig, Michael Brettreich, Stephan Burghardt, Maria Hatzimarinaki, Elena Ravanelli, Maurizio Prato, Rudi van Eldik, and Andreas Hirsch, Chem. Eur. J. 9, 3867-3875 (2003 ) Ryutaro Tanimura, Michael G. Hill, Emanuel Margoliash, Katsumi Niki, Hiroyuki Ohno, and Harry Gray, Electrochem.Solid-State Lett. 5, E67-E70 (2002)

The problem to be solved by the present invention is a molecular device and a single-molecule optical switch device that can be easily configured without using complicated chemical synthesis, can operate at ultra-high speed, and can be integrated at ultra-high density And providing a functional element.
Another problem to be solved by the present invention is to provide a molecular wire suitable for use in the wiring of various devices including the above-described molecular device, monomolecular optical switch device and functional device.
Still another problem to be solved by the present invention is to provide various electronic devices using the above functional elements.

The inventors of the present invention have intensively studied to solve the above problems. The outline will be described as follows.
In general, organic molecules are used for the structure of the molecular device, and a device formation method using a synthesis technique and a bottom-up method such as self-assembly is used. However, in order to express the function of a molecular device, it is difficult to actually put it into practical use, since a single device can be finally obtained by designing a molecule and making full use of multi-step complex synthesis techniques. In addition, in order to form a single molecule device, it becomes necessary to manipulate one molecule using SPM technology such as atomic force microscope and optical tweezer technology. The size is too small and technically difficult. There are fullerenes typified by C ₆₀ as molecules of nanometer scale to solve this problem. However, the function of fullerene is limited, and if a molecular transistor is made of C ₆₀ , it will eventually be necessary to carry out complex organic synthesis.
In addition, carbon nanotubes have been proposed as molecular elements as wires for passing electrons, but there are many problems such as the difficulty of aligning the length and manipulating in a directional manner for adjustment. . As described above, the production of a molecular device using ordinary organic molecules or fullerenes involves many difficulties and is unrealistic.

  On the other hand, looking at proteins, it can be seen that many of the above problems have already been solved from the beginning. Proteins are amino acid polymers, some of which incorporate functional molecules (for example, metal ions, metal complexes, coenzymes, etc.). The structure is extremely complex, and a structure optimized for each protein to express its function is created. Among functional proteins, there is a group of proteins that transfer electrons, called electron transfer proteins. Although this electron transfer protein is an insulating substance called protein, it has the ability to transfer electrons on the nanometer scale very efficiently from its skillful structure. This means that it already has the ideal properties of a molecular wire that is difficult to achieve. Previously, it was difficult to physically interpret the correlation between protein function and structure, and for example, there was little knowledge about the electron transfer mechanism of electron transfer proteins. However, due to recent advances in molecular biology and protein engineering, as well as advances in physical chemistry including quantum chemistry, the electron transfer mechanism has become clear and protein functional modification can be easily performed. It has become. In other words, the functions already possessed by proteins themselves can be used as molecular elements. For example, it is possible to change a certain amino acid residue of a protein, insert or delete it at a certain place, and replace a partial structure such as an α helix or β sheet. Has become relatively easy to do. In other words, at present, it is much easier and more realistic to modify nanometer-sized single molecules as desired and to have the desired functions, rather than assembling from organic molecules. In the first place, it is impossible at present to make a polymer molecule that is complex and highly functional like a protein and has a uniform molecular weight by a synthetic method.

  Instability may be pointed out as a problem in making molecular elements using proteins, but in this respect as well, the progress of protein engineering and the fact that thermophile-derived proteins are very stable in the first place. Even so, it is a problem that can be solved sufficiently, and it is closer to the realization of a molecular device to modify the protein itself so that the very high function of the protein can be used.

  Therefore, the present inventors have intensively studied to solve the above-mentioned problems of the prior art at once by realizing a molecular element using a protein. As a result, the present inventors are a kind of electron transfer protein. As a result of the first successful observation of bidirectional photocurrent associated with photoexcitation in zinc cytochrome c, the mechanism was almost elucidated, and further studies were made based on this finding, and as a result, the present invention was devised.

That is, in order to solve the above problem, the first invention
The molecular device has at least one molecule of zinc cytochrome c, and moves electrons or holes in the zinc cytochrome c by utilizing electron transition between molecular orbitals of the zinc cytochrome c.
Here, the molecular orbitals involved in the electron transition are basically as long as the electrons or holes move from one position in the zinc cytochrome c to another position away from this position as a result of the transition. Any molecular orbital may be used. Specifically, this molecular orbital is, for example, localized to the first molecular orbital that localizes to the first amino acid residue of zinc cytochrome c and the second amino acid residue of zinc cytochrome c, and This is the second molecular orbital having the maximum transition probability per unit time for one molecular orbital. In this case, electrons or holes move between the first amino acid residue and the second amino acid residue. . At this time, the first amino acid residue and the second amino acid residue constitute the starting point and the ending point of the movement of electrons or holes. Typically, electrons or holes are generated by photoexcitation in one of the first molecular orbital and the second molecular orbital, but other methods, for example, an electron or hole may be generated by applying an electric field. Good. In addition, this molecular orbital is localized, for example, in an amino acid residue of zinc cytochrome c and a molecular orbital localized in zinc porphyrin and other amino acid residues, and per unit time with respect to the former molecular orbital. The molecular orbital has the maximum transition probability. In this case, electrons or holes move between the former amino acid residue and the latter amino acid residue. Furthermore, this molecular orbital is localized in, for example, a molecular orbital localized in zinc porphyrin of zinc cytochrome c and other amino acid residues, and has a maximum transition probability per unit time with respect to the former molecular orbital. In this case, an electron or hole moves between the former zinc porphyrin and the latter amino acid residue.

  The rate of electron transfer associated with the transition of electrons from one molecular orbital to another is described by the following Fermi's golden rule (Dirac, PAM (1927) Proc. Roy. Soc. (London ) A 114: 243-265 and Fermi, E. (1950) Nuclear Physics. University of Chicago Press.

However, in the expression (1), | <f | H ′ | i> | transitions from the initial state | i> (molecular orbital i) to the final state | f> (molecular orbital f) by the interaction H ′. The magnitude of the transition integral (Transfer Integral), ρ (E _fi ) is the density of states when electrons transition to the molecular orbital f, and E _fi is the energy difference between the molecular orbital f and the molecular orbital i. Further writing | <f | H '| i> | and replacing ρ (E _fi ) with an approximate expression,

It becomes. The first term in equation (2) is the Franck-Condon term (effect of the vibration part), the second term is the transition integral (effect of the electron part), the third item is an approximation of the state density, and Dirac ( Dirac) delta function.
The zinc cytochrome c constituting this molecular element can be fixed as at least one molecule, a monomolecular film or a polymolecular film on an electrode made of a conductive material, for example, by electrostatic bonding or chemical bonding. can do. A plurality of first electrodes may be separately provided on the substrate, and one or more zinc cytochromes c may be fixed to each of them. The zinc cytochrome c may be fixed directly on the electrode or indirectly through an intermediate layer made of an organic compound having a hetero atom such as a sulfur atom. This intermediate layer has a phenomenon in which, after electrons generated by photoexcitation of zinc cytochrome c move to the electrode, this electron can return to zinc cytochrome c again, that is, reverse electron transfer can be prevented. It is preferable to use what has. As such an intermediate layer, for example, a monomolecular film of a disulfide that is a sulfur compound is used (see Non-Patent Document 12). It is desirable that the conductive material used for the electrode is excellent in fixing ability when zinc cytochrome c is directly fixed on the electrode, and fixing the intermediate layer when fixing via the intermediate layer. It is desirable that it is excellent in chemical ability. Specifically, examples of the conductive material include metals such as gold, platinum, and silver, ITO (indium-tin composite oxide), FTO (fluorine-doped tin oxide), and nesa glass (SnO ₂ glass). In addition to inorganic materials such as metal oxide or glass, conductive polymers (polythiophene, polypyrrole, polyacetylene, polydiacetylene, polyparaphenylene, polyparaphenylene sulfide, etc.), tetrathiafulvalene derivatives (TTF, TMTSF, BEDT) A charge transfer complex (e.g., TTF-TCNQ) including -TTF and the like can be used. The surface shape of the electrode may be an arbitrary shape such as a concave surface, a convex surface, or an uneven surface, and zinc cytochrome c can be easily fixed to any surface. Zinc cytochrome c may be sandwiched between this electrode and another electrode. As the conductive material of the other electrode, the same conductive material as that used for the above electrode can be used. When light is incident through at least one of these electrodes, at least one of these electrodes is configured to be transparent to visible light. A structure in which zinc cytochrome c is sandwiched between these electrodes can be used as, for example, a photoelectric conversion element.

This photoelectric conversion element can be operated in a solution (electrolyte solution) or in a dry environment as long as the photoelectric conversion function and the electron transfer function of zinc cytochrome c are not impaired. For example, when operating in an electrolyte solution, typically, other electrodes are provided so as to face the zinc cytochrome c fixed on the electrodes with a space therebetween, and these electrodes are connected to the electrolyte solution. Soaked in. As the electrolyte (or redox species) of this electrolyte solution, one that undergoes an oxidation reaction at one electrode and undergoes a reduction reaction at the other electrode is used. Specifically, for example, K ₄ [Fe (CN) ₆ ] or [Co (NH ₃ ) ₆ ] Cl ₃ is used as the electrolyte (or redox species). When operating in a dry environment, typically, for example, a solid electrolyte that does not adsorb zinc cytochrome c, specifically a wet solid electrolyte such as agar or polyacrylamide gel, is on one electrode. Between the fixed zinc cytochrome c and the other electrode, a sealing wall for preventing the drying of the solid electrolyte is preferably provided around the solid electrolyte. In these cases, a photocurrent can be obtained when light is received by a light receiving portion made of zinc cytochrome c with a polarity based on the difference in natural electrode potential between these electrodes.

In this photoelectric conversion element, light flowing inside the element is adjusted by adjusting at least one of the potential difference between these electrodes, the intensity of the light irradiated to the zinc cytochrome c, and the wavelength of the light irradiated to the zinc cytochrome c. The magnitude and / or polarity of the current can be changed. Here, the potential difference between these electrodes includes both the meaning of a bias voltage artificially generated by voltage application and the difference in natural electrode potential between the first electrode and the second electrode.
This photoelectric conversion element can be used for, for example, a photodetector (photosensor), and a photocurrent amplifier circuit or the like can be used together as necessary. The photodetector can be used for various purposes such as detection of an optical signal, and can also be applied to an artificial retina. This photoelectric conversion element can also be used as a solar cell.
This photoelectric conversion element can be used for various devices and devices using photoelectric conversion, and specifically, for example, can be used for an electronic device having a light receiving portion.

  You may use this photoelectric conversion element for a semiconductor device. In this semiconductor device, the photoelectric conversion element is fixed on a semiconductor substrate. On this semiconductor substrate, typically, a semiconductor element or an electronic circuit that amplifies a photocurrent extracted from the photoelectric conversion element is formed by a conventionally known semiconductor technology. The semiconductor substrate may be a semiconductor substrate made of an elemental semiconductor such as Si or a semiconductor substrate made of a compound semiconductor such as GaAs. This semiconductor device can be configured as an optoelectronic integrated circuit device, for example. In this optoelectronic integrated circuit device, for example, in addition to a photoelectric conversion element, a light emitting element such as a semiconductor laser or a light emitting diode, an electronic circuit, or the like is formed on a semiconductor substrate. In this case, light from the light emitting element may be incident on the photoelectric conversion element. There are no particular restrictions on the function or application of the semiconductor device, but specific examples include a photodetector, an optical signal processing device, and an imaging device (such as a MOS image sensor or a charge transfer device (CCD)).

The second invention is
A single-molecule optical switching device having a single molecule of zinc cytochrome c and utilizing the movement of electrons or holes in the zinc cytochrome c using the transition of electrons between molecular orbitals of the zinc cytochrome c. ,
A wiring is connected to each of a plurality of different amino acid residues of the zinc cytochrome c,
A first molecular orbital and a second molecular orbital are localized in a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues, respectively, and the second molecular orbital is The transition probability per unit time is maximum with respect to the first molecular orbital.
Here, the wiring connected to the amino acid residue may be a conventionally known molecular wire, a molecular wire using zinc cytochrome c described later, or other conductive molecules such as DNA, if necessary, using an appropriate linker. Connecting.
In the second invention, what has been described in relation to the first invention is valid as long as it is not against the nature thereof.

The third invention is
The functional element has at least one molecule of zinc cytochrome c, and moves electrons or holes in the zinc cytochrome c by utilizing electron transition between molecular orbitals of the zinc cytochrome c.
Here, the functional element may be basically any one as long as it performs a certain function by utilizing the conductivity of zinc cytochrome c generated by the transition of electrons between molecular orbitals. . This functional element includes a switch element such as a single molecular optical switch that switches by irradiation of light, an integrated circuit element, a matrix circuit, a molecular functional device, a logic circuit, and a circuit element that is formed by spreading zinc cytochrome c on a substrate. It is suitable for construction of circuits and the like, and can be applied to miniaturization and refinement of various elements and devices such as arithmetic devices, displays, and memories in the information communication field.
In the third invention, what has been described in relation to the first and second inventions is valid as long as it is not contrary to the nature.

The fourth invention is:
This molecular wire has at least one molecule of zinc cytochrome c, and moves electrons or holes in the zinc cytochrome c by utilizing electron transition between molecular orbitals of the zinc cytochrome c.
Here, the molecular wire is typically formed by connecting a plurality of molecules of zinc cytochrome c in series so as to have a length corresponding to the wiring distance and a wiring routing shape. It may contain other electron transfer proteins such as sex substances such as iron cytochrome c. In this way, for example, electrons generated by photoexcitation in zinc cytochrome c at one end of the molecular wire can be moved sequentially between these electron transfer proteins to move to the other end. A DNA wiring may be provided in the middle of the molecular wire.
In the fourth invention, what has been described in relation to the first invention is valid as long as it is not contrary to the nature thereof.

The fifth invention is:
In an electronic device having one or more functional elements,
A functional element having at least one molecule of zinc cytochrome c as at least one of the functional elements, and moving electrons or holes in the zinc cytochrome c using the transition of electrons between molecular orbitals of the zinc cytochrome c. It is characterized by being used.
The functions and applications of this electronic device are not particularly limited, and may be various electronic devices, including both portable and stationary types. Specific examples include digital cameras and camera-integrated VTRs. (Video tape recorder).
In the fifth invention, what has been described in relation to the first and fourth inventions is valid as long as it is not contrary to the nature thereof.

The sixth invention is:
It is a molecular device characterized in that it has at least one molecule of an electron transfer protein and moves electrons or holes in the electron transfer protein by utilizing an electron transition between molecular orbitals of the electron transfer protein.

The seventh invention
A single-molecule optical switching device having a single molecule of an electron transfer protein and utilizing the movement of electrons or holes in the electron transfer protein using the transition of electrons between the molecular orbitals of the electron transfer protein. ,
A wire is connected to each of a plurality of different amino acid residues of the electron transfer protein,
A first molecular orbital and a second molecular orbital are localized in a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues, respectively, and the second molecular orbital is The transition probability per unit time is maximum with respect to the first molecular orbital.

The eighth invention
A functional device having at least one molecule of an electron transfer protein and moving electrons or holes in the electron transfer protein by utilizing an electron transition between molecular orbitals of the electron transfer protein.

The ninth invention
It is a molecular wire characterized by having at least one molecule of an electron transfer protein and moving electrons or holes in the electron transfer protein by utilizing an electron transition between molecular orbitals of the electron transfer protein.

The tenth invention is
In an electronic device having one or more functional elements,
A functional element having at least one molecule of an electron transfer protein as at least one of the functional elements and moving electrons or holes in the electron transfer protein by utilizing an electron transition between molecular orbitals of the electron transfer protein. It is characterized by being used.

  In the sixth to tenth inventions, the electron transfer protein is generally an electron transfer protein containing a metal. This metal is preferably a transition metal (for example, zinc or iron) having electrons in a high-energy orbit higher than the d orbit. This electron transfer protein includes iron-sulfur proteins (for example, rubredoxin, diiron ferredoxin, triiron ferredoxin, tetrairon ferredoxin, etc.), blue copper proteins (for example, plastocyanin, azurin, pseudoazurin, plantacyanin, stellacyanin) ), Cytochromes (eg, cytochrome c (zinc cytochrome c), cytochrome b, cytochrome b5, cytochrome c1, cytochrome a, cytochrome a3, cytochrome f, cytochrome b6, etc.), but are not limited thereto. It is not a thing. For example, derivatives of these electron transfer proteins (the amino acid residues of the backbone are chemically modified) or mutants thereof (a portion of the backbone amino acid residues are substituted with other amino acid residues).

  In the present invention configured as described above, zinc cytochrome c, which is a protein, and electron transfer protein are nanometer-sized, and therefore, ultra-high density integration is possible. In addition, these proteins are nanometer-sized, uniform functional polymers. By using naturally derived proteins as raw materials, the necessary synthesis reactions can be minimized, and complex chemistry such as organic semiconductors can be achieved. Not only can it be easily obtained without using synthesis, but single molecule manipulation can also be handled more easily than angstrom-sized organic molecules using SPM technology. In addition, these proteins can obtain high-speed photocurrent response characteristics by photoexcitation. Moreover, in these proteins, since the periphery of the electron transfer path is covered with an amino acid residue which is an insulator, mixing of noise can be suppressed. Furthermore, since the start and end points of the movement of electrons or holes are determined, an integrated circuit can be formed by connecting the part with a bulk electrode such as another functional molecule, functional protein or metal. Can do. In addition, proteins are good at specific molecular recognition, and if designed using the molecular recognition ability of proteins, nanometer-sized functional molecules (proteins) can be self-assembled as desired. It will be concise.

  According to the present invention, a molecular device, a single-molecule optical switch device, and a functional device that can be easily configured without using complicated chemical synthesis, can operate at high speed, and can be integrated at an ultra-high density. Can be realized. In addition, a molecular wire suitable for use in wiring of various elements including a molecular element, a monomolecular optical switch element, and a functional element can be realized. In addition, a high-performance electronic device using this functional element can be realized.

It is a basic diagram which shows the molecular structure of zinc cytochrome c. It is a drawing substitute photograph which shows a zinc cytochrome c carrying | support drop-shaped gold electrode. It is a basic diagram which shows a three-electrode measurement system. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a basic diagram which shows the evaluation result by the three-electrode measurement system shown in FIG. It is a stereogram of apo-zinc cytochrome c. It is a conceptual diagram of the frame division | segmentation in the case of calculating using proteinDF. It is a basic diagram which shows the model molecule | numerator of His18 and Met80. It is a basic diagram which shows a zinc porphyrin model. It is a basic diagram which shows a zinc porphyrin expansion model. It is a basic diagram which shows the zinc porphyrin expansion model 2. FIG. It is a basic diagram which shows the side chain model molecule | numerator of zinc porphyrin. It is a basic diagram which shows the zinc porphyrin expansion model 3. FIG. It is a basic diagram which shows the whole structure of the zinc cytochrome c finally calculated. It is a basic diagram which shows the molecular orbital energy of zinc cytochrome c. It is a basic diagram which shows the density of states of zinc cytochrome c. It is an approximate line figure showing a model molecule used for excited state calculation. It is a top view which shows a zinc porphyrin model molecule. It is a side view which shows the 144th and 145th molecular orbital of a zinc porphyrin model molecule. FIG. 6 is a schematic diagram showing molecular orbital energy in the vicinity of the Fermi level of zinc cytochrome c and isosurfaces of molecular orbitals involved in photoexcitation. It is a basic diagram which shows the molecular orbital of zinc cytochrome c. It is a basic diagram which shows the molecular orbital of zinc cytochrome c. It is a basic diagram which shows the molecular orbital of zinc cytochrome c. It is a basic diagram which shows the adsorption | suction state to the electrode of zinc cytochrome c. It is a basic diagram which shows the movement path | route of the hole produced by the photoexcitation of the zinc cytochrome c on an electrode. It is a basic diagram which shows the movement path | route of the electron produced by the photoexcitation of the zinc cytochrome c on an electrode. It is a basic diagram which shows the transition probability of the electronic transition between MO3272 and other molecular orbitals of zinc cytochrome c. It is a basic diagram which shows the transition probability of the electronic transition between MO3268 of zinc cytochrome c and another molecular orbital. It is a basic diagram which shows the transition probability of the electronic transition between MO3297 of zinc cytochrome c and another molecular orbital. It is a basic diagram which shows the transition probability of the electronic transition between MO3299 of zinc cytochrome c and another molecular orbital. 1 is a schematic diagram showing a single molecule optical switch according to a first embodiment of the present invention. It is a basic diagram which shows the molecular wire by 2nd Embodiment of this invention. It is a basic diagram which shows the molecular wire by 3rd Embodiment of this invention. It is a basic diagram which shows the photoelectric conversion element by 4th Embodiment of this invention. It is a circuit diagram which shows the photodetector by 5th Embodiment of this invention. It is a top view which shows the structural example of the photodetector by 5th Embodiment of this invention. It is sectional drawing which shows the structural example of the photodetector by 5th Embodiment of this invention. It is sectional drawing which shows the structural example of the photodetector by 5th Embodiment of this invention. It is sectional drawing which shows the CCD image sensor by the 6th Embodiment of this invention. It is a circuit diagram which shows the inverter circuit by 7th Embodiment of this invention. It is a circuit diagram which shows the structural example of the inverter circuit by 7th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the results of an experiment conducted using zinc cytochrome c as an example of an electron transfer protein will be described.
FIGS. 1A and B show ribbon model diagrams of zinc cytochrome c. FIG. 1A also shows amino acid side chains, and FIG. 1B omits amino acid side chains. The number of amino acid residues of zinc cytochrome c is 104. Zinc is coordinated as a central metal to the porphyrin at the center of this zinc cytochrome c, and becomes the center of light absorption and photoinduced electron transfer reaction. The protein part surrounding porphyrin in this zinc cytochrome c is an insulator. Zinc cytochrome c has characteristic absorption peaks called a soret band and a Q band in the visible light region, and can be photoexcited by visible light.

<Experiment 1>
1. Preparation of Sample A high-purity gold wire was melted with a burner into a drop shape having a diameter of several mm, and used as an electrode. The drop-like gold is immersed in an ethanol solution of 10-carboxy-1-decanethiol (HS (CH ₂ ) ₁₀ COOH) to thereby form a self-assembled monolayer of HS (CH ₂ ) ₁₀ COOH. , SAM) as an intermediate layer was formed on a drop-like gold surface. By immersing the SAM electrode thus obtained in a 10 mM Tris-HCl buffer solution (pH 8.0) of zinc cytochrome c, HS (CH ₂ ) ₁₀ COOH and zinc cytochrome c were adsorbed on the drop-shaped gold surface. A SAM electrode having a layer structure was produced. Hereinafter, this SAM electrode having a two-layer structure is referred to as a zinc cytochrome c electrode. This zinc cytochrome c electrode is shown in FIG. The synthesis of zinc cytochrome c followed Non-Patent Document 4. Moreover, the production of the zinc cytochrome c electrode followed the method for producing the iron cytochrome c electrode in Non-Patent Document 2.

2. Preparation for measurement An optical experimental system was prepared so that the surface of the zinc cytochrome c electrode could be uniformly irradiated with monochromatic light, and the timing of light irradiation could be controlled by opening and closing the shutter. Then, a zinc cytochrome c electrode is connected to a potentiostat with a working electrode, a silver wire as a reference electrode, and a platinum wire as a counter electrode, and these electrodes are connected to a 10 mM phosphate buffer aqueous solution containing 2.5 mM K ₄ [Fe (CN) ₆ ]. Soaked in (pH 7.0). This experimental system is shown in FIG. In FIG. 3, reference numeral 21 denotes an Xe lamp (150 W) as a light source, 22 denotes a cold filter that efficiently transmits visible light in the emission spectrum of the Xe lamp 21 and reflects heat rays, and 23 denotes a condensing light. Lens, 24 is a shutter (0.5 Hz) for controlling transmission / non-transmission of light, 25 is a condensing lens, 26 is a monochromator for monochromating light having passed through the shutter 24 to a desired wavelength, and 27 is a condensing lens , 28 is a container, 29 is a phosphate buffer aqueous solution containing K ₄ [Fe (CN) ₆ ], 30 is a zinc cytochrome c electrode as a working electrode, 31 is a silver wire as a reference electrode, and 32 is a platinum wire as a counter electrode , 33 is an Al mirror that reflects light monochromatized by the monochromator 26, and 34 is a potentiostat. The computer 35 can control the opening / closing of the shutter 24 and the wavelength of the light monochromatized by the monochromator 26. The entire condenser lens 27 and the container 28 are covered with a metal shield 36 for blocking outside light, except for the light inlet monochromatized by the monochromator 26. This shield 36 is grounded.

3. Observation of Photocurrent While the shutter 24 was closed, a bias voltage of +313 mV was applied to the zinc cytochrome c electrode 30 with respect to the silver wire 31 and left in that state for 60 seconds. At this time, the dark current gradually decreased. Next, the shutter 24 was opened and irradiated with light having a wavelength of 380 nm for 1 second, and the shutter 24 was closed again and rested for 1 second. After that, light of wavelength 381 nm is irradiated for 1 second, light is paused for 1 second, light of wavelength 382 nm is lighted for 1 second, and light is paused for 1 second. Swept one by one. As a result of measuring the time change of the current value in the process of such intermittent light irradiation, a pulsed current change synchronized with the on / off of the irradiation light, that is, a photocurrent was observed. The result is shown in FIG.
In each pulse obtained by the above measurement, the average value of the rising width and the falling width was obtained, and this was used as a photocurrent value, and the photocurrent value at each wavelength was plotted to obtain a photocurrent action spectrum. (FIG. 5). The obtained photocurrent action spectrum is similar to the absorption spectrum of zinc cytochrome c. From this, it was confirmed that this photocurrent was accompanied by photoexcitation of zinc cytochrome c.
FIG. 6 shows the obtained photocurrent action spectrum corrected with the incident light intensity constant, and FIG. 7 shows the obtained photocurrent action spectrum corrected with the incident photon number constant.

4). Control of the direction and magnitude of the photocurrent As shown in FIG. 8, by adjusting the bias voltage applied to the zinc cytochrome c electrode 30, it is possible to control both the polarity (flow direction) and magnitude of the photocurrent. It was possible.
5. Reversal of steady current direction by light irradiation As shown in FIG. 9, the bias voltage applied to the zinc cytochrome c electrode 30 is a bias voltage (here, +23 mV vs. Ag) that can obtain a very weak negative current in a dark place. ), The polarity of this current could be reversed by light irradiation.

  Experiment 1 shows that a bidirectional photocurrent can be obtained at the zinc cytochrome c electrode 30. Next, the bias voltage dependency of the photocurrent was measured. The result is shown in FIG. When the bias voltage was changed while irradiating light with a wavelength of 420 nm, it was found that the photocurrent showed a linear response to the bias voltage, and that the zinc cytochrome c electrode 30 worked as a photoconductor.

<All-electron calculation of zinc cytochrome c by density functional method>
As described above, in the zinc cytochrome c electrode 30, it was confirmed that a bidirectional photocurrent response derived from protein was obtained, and it was found that the generation mechanism of this bidirectional photocurrent is a dye-sensitized type. However, it is expected that the zinc cytochrome c has some special mechanism for the protein as an insulator to generate a photocurrent bidirectionally. In addition, it has been found that zinc cytochrome c itself exhibits the performance as an optical sensor, but in order to design a device while controlling these at the molecular level, it is necessary to know the electronic properties of the protein itself. There is. For that purpose, it is necessary to calculate the electronic state of the protein on the first principle. There is also a method for calculating the electronic state of a protein by a semi-empirical molecular orbital method, but in this method, 1) a metal protein containing a transition metal such as zinc cytochrome c cannot give good results (it cannot be calculated in the first place). ), 2) An error occurs because it is a parameter method, but it cannot be practically used due to problems such as an error that is allowed for low molecules and an allowable range that is too large for calculations of macromolecules such as proteins. Therefore, the electronic state calculation by the density functional theory (DFT) is required, but this method is very expensive, and the convergence condition is severe. It is very important to do. There is a program package called proteinDF as a program that has been devised around this area (Hiroshi Hiroki et al. “Protein Quantum Chemical Computation-Dream and Realization of proteinDF” Advance Software). All the calculations this time are calculations using the proteinDF.

<Construction of calculation model for zinc cytochrome c>
The structure of zinc cytochrome c used for the calculation was 1M60 recorded in the Protein Data Bank (PDB). This structure is determined by NMR, and is different from that obtained by X-ray crystal structure analysis, and the position of the hydrogen atom is determined. The procedure is described below. All pretreatment operations were performed using DS Modeling 1.5.
1) Obtain the structure of zinc cytochrome c from PDB.
2) Molecular mechanics (MM) calculation (RMS condition: 0.00001) by solvent approximation by the Generalized Born method. The force field is CHARMm. At this time, the structure of zinc porphyrin, a heteromolecule, is fixed.
3) Neutralization treatment: Cl ⁺ , lysine (Lys) and arginine (Arg) are added with Cl ⁻ , glutamic acid (Glu) and aspartic acid (Asp) with Na ⁺ . Simple neutralization (adjusted with or without protons) where it cannot be attached.
4) Place TIP3 water.
5) Immobilize the protein part and optimize the other parts with MM.
(RMS condition 0.00001 for vacuum model)
6) Delete TIP3.
7) Zinc porphyrin is deleted, hydrogen is generated in S of Cys14 and Cys17 covalently bonded to zinc porphyrin, and only the two hydrogens are cleaned.
8) Create a PDB type file: At this time, Na ^{+ is set} to +1 and Cl ^{− is set} to −1.
An apo body of zinc cytochrome c is prepared by this method (FIG. 11). Based on this structure, the calculation will proceed according to the following scenario.

<Calculation scenario>
1) DFT calculation of amino acid residues up to 1-104 one by one 2) DFT calculation of amino acid residues up to 1-104 in 3 residues based on the molecular orbital (MO) calculated in 1) : 1-3, 2-4, 3-5, ..., 101-103, 102-104
3) Create a suspicious canonical localization orbit (QCLO) for each fragment (see FIG. 12).
4) Using the QCLO obtained in 3) as the initial MO, DFT calculation of the following amino acid residues is performed. 1-7, 6-14, 13-19, 18-24, 9 to 9 residues, 71-80, 80-86, 85-95, 94-104
5) Create a QCLO for each fragment.
6) Enter into heteromolecular calculation. First, DFT calculations were performed on model molecules of His (histidine) 18 and Met (methionine) 80, respectively, to create QCLO (FIG. 13).
7) DFT calculation with a structure in which zinc and porphyrin skeleton are first made and 8 hydrogen atoms are attached (FIG. 14).
8) Create QCLO. At that time, the fragment definition of QCLO is divided into zinc, porphyrin (Por), and H8. Later, the side chain is bound to the H8 part.
9) DFT calculation with a structure combining 7) and 6). The initial MO is the QCLO created in 6) and 8) (FIG. 15).
10) A structure in which the amino acid residues 13-19 and 78-81 were added to the structure in which zinc and porphyrin skeleton were originally prepared and 8 hydrogen atoms were added thereto was previously prepared. DFT calculation with each QCLO as the initial MO (FIG. 16).
11) DFT calculation using the side chain part of porphyrin as a part. At that time, all the bonds were capped with a methyl group (Me). During the QCLO calculation, the cap methyl group was separated. The part corresponding to Cys14 and Cys17 is subjected to a process of replacing the side chain of each amino acid with the part calculated at this stage (FIG. 17).
12) DFT calculation with zinc and porphyrin skeleton and porphyrin side chain, and amino acid residues 13-19 and 79-81. At this time, the calculation is performed by removing the S—H hydrogen of Cys14 and Cys17. The initial MO uses the QCLO up to the previous stage (FIG. 18).
13) DFT calculation of zinc cytochrome c itself. The initial MO uses the QCLO up to the previous stage.
FIG. 19 shows the overall structure of zinc cytochrome c finally calculated.

<Calculation condition>
Functional: VWN ~
Basis function: DFT type function
H = "O-HYDROGEN (41) DZVP"
C = “O-CARBON (621/41) by FS”
N = “O-NITROGEN (621/41) by FS”
O = “O-OXYGEN (621/41) by FS”
S = "O-SULFUR (6321/521/1 *)"
Auxiliary basis function (Coulomb): DFT type function
H = “A-HYDROGEN (4, 1; 4, 1) from deMon”
C = “A-CARBON (7/2; 7/2) by FS”
N = “A-NITROGEN (7/2; 7/2) by FS”
O = “A-OXYGEN (7/2; 7/2) by FS”
S = “A-SULFUR (5, 4; 5, 4)”
Auxiliary basis function (exchange correlation): DFT type function
H = “A-HYDROGEN (4, 1; 4, 1) from deMon”
C = “A-CARBON (7/2; 7/2) by FS”
N = “A-NITROGEN (7/2; 7/2) by FS”
O = “A-OXYGEN (7/2; 7/2) by FS”
S = “A-SULFUR (5, 4; 5, 4)”

<result>
An energy diagram of molecular orbitals of zinc cytochrome c is shown in FIG. In FIG. 20, the horizontal axis represents the number of SCF (self-consistent field) repeated calculations, the vertical axis represents the energy of molecular orbitals, and the connected line represents the HOMO energy level. Since the HOMO-LUMO gap is about 0.6 eV and the band gap is about 2 to 3 eV, it is a reasonable energy MO diagram. The narrowness of the HOMO-LUMO gap seen in the apo body was eliminated by introducing a hetero molecule. FIG. 21 is a diagram in which FIG. 20 is rewritten to DOS (density of states). In Figure 21, the mountain portion of the low energy side of the Fermi energy E _F is the valence band as referred to Solid State Physics, part of the high energy side is also equivalent to the conduction band.

<Search for molecular orbitals involved in excited states>
Originally, the orbital involved in the excited state is revealed only after the excited state calculation, but the calculation of the excited state of the protein is completely a dream story at present. Therefore, the excited state calculation of the model molecule is performed, and the orbit involved in the excited state of zinc cytochrome c must be inferred therefrom. Fortunately, it is clear from the UV-Vis spectrum shape and various other studies that the excited state in the visible region is derived from the zinc porphyrin moiety. Therefore, zinc porphyrin model molecules are sufficient to investigate the excited states we want to know. In addition, there has been a great deal of research on the excited state of porphyrins in the past, and its properties are almost already known. For these reasons, the excited state calculation was performed here with the structure shown in FIG. Regarding the theory, since the density functional method using VWN to functional is used in ProteinDF, the singlet excited state is calculated using the same functional and the time-dependent density functional method using the same basis function. went. The results are shown in Table 1. The calculation was performed using Gaussian 03.

From the results shown in Table 1, it became clear that the excited states 3 and 4 correspond to the Q band, and the excited states 5 and 6 correspond to the Soret band. Table 1 shows that the four molecular orbitals in the Gouterman four-orbital model are 144, 145, 147, and 148. These molecular orbitals are shown in FIG. 23 (top view). FIG. 24 shows a side view of the molecular orbitals 144 and 145.
From the above, it was found that among the four orbits, the occupied orbitals were large and formed an orbit in which the p orbitals of methionine S and the d orbitals of zinc were mixed. This is a major feature, suggesting that zinc porphyrin, which does not have an axial ligand in ordinary complexes, significantly changes the properties of the porphyrin π orbital when it has an axial ligand. This result is very similar to the mixed state of Fe-S (Cys) bond in P450 and is interesting (Miyahara, T. et al. J. Phys. Chem. B 2001, 105, 7341-7352). In addition, the phenomenon that the axial ligand is dissociated during photoexcitation has been experimentally confirmed, but this phenomenon can be easily explained if the electron is excited from these orbitals (Lampa-Pastirk, S et al. J. Phys. Chem. B 2004, 108, 12602-12607).

<Electronic state of zinc cytochrome c>
The shape of molecular orbitals involved in photoexcitation has been clarified from the calculation of excited states by the zinc porphyrin model molecules described above. Next, the orbital involved in photoexcitation is extracted from the actual molecular orbital of zinc cytochrome c, and what kind of energy and correlation with other molecular orbitals are examined. FIG. 25 shows the molecular orbital energy in the vicinity of the Fermi level and the molecular orbital diagram that is considered to be involved in photoexcitation.

From the results shown in Table 2, it can be seen that the occupied orbital involved in photoexcitation is at a position considerably deeper than the Fermi level (HOMO). On the other hand, it was found that the sky orbit side is at a relatively low position.
<Theoretical study of bidirectional photocurrent phenomenon in zinc cytochrome c electrode>
The fact that the photosensitized current flows in both directions means that there is a path through which excited electrons flow both on the electrode side and on the bulk side, and there is a path on which both the hole, the electrode side, and the bulk side flow. ing. In order to verify whether such a path really exists, we proceeded with a comparison between the molecular orbital isosurface and energy. FIG. 26 to FIG. 28 show isosurface diagrams (−0.0005, 0.0005) of molecular orbitals used for the discussion.

First, it is necessary to consider the direction when zinc cytochrome c is adsorbed on the gold electrode. This has been studied from both recent experimental and theoretical standpoints, and the adsorption state has been clarified (studies on iron cytochrome c) (Li, L. et al., Electroanalysis, 2004, 16, 81). -87). The adsorption state is shown in FIG.
Looking at FIG. 29, it can be imagined that the zinc porphyrin is oriented in the direction of the electrode, and that it is likely that excitation electrons enter the electrode. However, how does electron flow into the bulk occur? In order for electrons to flow to the bulk side, it is necessary to couple with molecular orbitals protruding to the bulk side or to create a path to the bulk side by the large spread of the excited molecular orbitals themselves. The same applies to the hall. Referring to FIG. 25, the orbit involved in the photoexcitation on the occupied orbit side is at a deep position, and there are many orbits that can be coupled at positions near energy. In other words, even if excitation is performed with hem close to the electrode, it is possible to create a path for transporting holes to the bulk via an orbit close to energy. In fact, looking at the molecular orbitals, it can be seen that there are orbits protruding into the bulk coupled with zinc porphyrin (MO3271: Asn54 + Porπ, see FIG. 30).

  From this calculation, it was also found that there is a significant difference between those in which zinc porphyrin is hybridized to other molecular orbital spreads and those that are not (see FIGS. 26 to 28). It is not clear whether or not the zinc porphyrin orbital is affected by the d orbital of zinc, but it has been found that the orbital influence extends to a point where it is considerably separated from the surrounding amino acid orbital. On the other hand, in the orbit that does not involve zinc porphyrin, the orbital is localized on the amino acid residue, and it has been found that it has the property as an insulating original amino acid. This means that when a transition metal is put into a protein, the molecular orbitals show a spread in a form involving amino acids. This is consistent with the fact that electron transfer can be induced artificially just by having zinc porphyrin, even if it is not an electron transfer protein such as myoglobin (Willner, I. & Katz, E. "Bioelectronics" Wiley- VCH (Weinheim), 2005).

The findings obtained above are summarized as follows.
1) First-principles calculation (all-electron calculation) of zinc cytochrome c was performed and the electronic state of the ground state was successfully determined.
2) From the calculation of the excited state of zinc porphyrin, we succeeded in assigning molecular orbitals in zinc cytochrome c related to photocurrent. It is suggested that the reason why the photocurrent is generated in both directions is that the occupied orbit and the empty orbit involved in the photocurrent generation are coupled with the orbit protruding into the bulk.

  Further studies were conducted based on the above findings. From the above knowledge of coupling between molecular orbitals in zinc cytochrome c, for example, from the transfer of electrons from one amino acid residue of zinc cytochrome c to another amino acid residue, from the zinc porphyrin and amino acid residues of zinc cytochrome c It can be seen that electrons can be transferred to other amino acid residues, and electrons can be transferred from zinc porphyrin of zinc cytochrome c to other amino acid residues. For example, when an electron in a molecular orbital localized in a certain amino acid residue is excited and transitions to another molecular orbital localized in another amino acid residue, the electron passes through the zinc cytochrome c in the above amino acid. It has moved from a residue to another amino acid residue. In addition, when electrons in molecular orbitals localized in zinc porphyrin and amino acid residues of zinc cytochrome c are excited and transition to other molecular orbitals localized in other amino acid residues, the electrons are zinc cytochromes. The inside of c was moved from the above zinc porphyrin and amino acid residues to other amino acid residues.

In this case, the speed of electron transfer accompanying the transition between molecular orbitals is described by the equation (1) or (2) as described above. Assuming that the Frank-Condon term of the first term of equation (2) is the maximum value, k _ET was obtained by calculating the second and third terms. The results are shown in FIGS. 32 to 35, the horizontal axis represents the molecular orbital number, and the vertical axis represents _kET . From FIG. 32, for molecular orbitals 3272 (porphyrin π orbitals and Zn-Sπ orbitals), k _ET is maximized by coupling between molecular orbitals 3271 (Asn54 and porphyrin π orbitals), and the maximum value is 1.5. × 10 ¹¹ sec ^-1 From FIG. 33, for molecular orbitals 3268 (porphyrin π orbitals and Zn-Sπ orbitals), k _ET is maximized by coupling with molecular orbitals 3270 (localized in Lys7), and the maximum value is 2.0. × 10 ¹⁰ sec ⁻¹ . As shown in FIG. 34, for molecular orbital 3297 (porphyrin π * orbital), k _ET becomes maximum due to coupling with molecular orbital 3296 (localized in Glu62), and the maximum value is 5.5 × 10 ⁸ sec. ^-1 . In FIG. 34, there are molecular orbitals where k _ET is larger than 5.5 × 10 ⁸ sec ^−1, but the energy of these molecular orbitals is extremely large, and it is impossible to actually participate in photoexcitation. . As shown in FIG. 35, for molecular orbital 3299 (porphyrin π * orbital), k _ET becomes the maximum due to coupling with molecular orbital 3296 (localized in Glu62), and the maximum value is 2.8 × 10 ⁸ sec. ^-1 . In FIG. 35, there are molecular orbitals where k _ET is larger than 2.8 × 10 ⁸ sec ^−1, but the energy of these molecular orbitals is remarkably large, and it is impossible to actually participate in photoexcitation. .

From FIG. 32 to FIG. 35, it can be seen that, for a certain molecular orbital, electron transfer occurs in the zinc cytochrome c with a transition between the molecular orbital with the largest k _ET . That is, among the molecular orbitals in which electron transition can actually occur, electron transition occurs between the molecular orbitals in which k _ET is maximized. The transition between the molecular orbitals having the maximum k _ET causes movement of electrons or holes between the sites where these molecular orbitals are localized in the zinc cytochrome c.

Various devices can be realized by utilizing the movement of electrons or holes in zinc cytochrome c accompanying the transition between molecular orbitals by photoexcitation described above.
FIG. 36 shows a single molecule optical switch according to the first embodiment of the present invention.
As shown in FIG. 36, in this single-molecule optical switch, wirings w _{1 to} w ₄ are connected to four amino acid residues a _{1 to} a ₄ of one molecule of zinc cytochrome c42, respectively. In this case, of these amino acid residues a ₁ ~a ₄ between amino acid residues a _1, a ₄ and between amino acid residues a _2, a _3, the electrons or holes caused by the transition between molecular orbitals by photoexcitation Movement is going to happen. That is, molecular orbitals are localized at amino acid residues a ₁ and a ₄ , respectively, and the other molecular orbital is the molecular orbital with the maximum k _ET with respect to one of the molecular orbitals. Molecular orbitals are localized at the residues a ₂ and a ₃ , respectively, and the molecular orbital of the other molecular orbital is the molecular orbital with the maximum _kET .

The operation method of this single molecule optical switch will be described.
First, for example, light having a wavelength λ ₁ that can selectively excite the molecular orbital MO ₁ localized at the amino acid residue a ₁ is irradiated. As a result, between the molecular orbital MO ₁ and amino acid residues electron transitions between the molecular orbital MO ₄ localized to a ₄ happened, the amino acid residue a ₁ and amino acid residues a ₄ Accordingly As a result, electrons or holes move, and the wirings w ₁ and w ₄ become conductive. At this time, electrons or holes do not move between the amino acid residues a ₂ and a ₃ , and the wirings w ₂ and w ₃ are not conductive. Next, light having a wavelength λ ₂ capable of selectively photoexciting the molecular orbital MO ₂ localized at the amino acid residue a ₂ is irradiated. As a result, between the electron transitions between the molecular orbital MO ₂ and molecular orbital MO ₃ localized to amino acid residues a ₃ happened, the amino acid residue a ₂ amino acid residues a ₃ Accordingly As a result, electrons or holes move, and the wirings w ₂ and w ₃ become conductive. At this time, electrons or holes do not move between the amino acid residues a ₁ and a ₄ , and the wirings w ₁ and w ₄ are not conductive.
As described above, according to the first embodiment, the state where the wirings w ₁ and w ₄ are conductive and the state where the wirings w ₂ and w ₃ are conductive are instantaneously generated by light irradiation. Can be switched to. This single-molecule optical switch can be manufactured very easily using zinc cytochrome c without relying on a complicated chemical synthesis method, and can be integrated at an ultra-high density because of its nanometer size, and Ultra-high speed switching is possible.

Next explained is a molecular wire according to the second embodiment of the invention.
As shown in FIG. 37, in this molecular wire, a plurality of molecules of zinc cytochrome c42 are linearly bonded in the same orientation. In this case, movement of electrons or holes accompanying the transition between molecular orbitals by photoexcitation occurs between the amino acid residues a ₁ and a _{2 of} each zinc cytochrome c42. That is, molecular orbitals are localized at amino acid residues a ₁ and a ₂ , respectively, and the molecular orbital of the other molecular orbital is the molecular orbital with the maximum k _ET .

The operation method of this molecular wire will be described.
First, light having a wavelength λ ₁ capable of selectively photoexciting the molecular orbital MO ₁ localized at the amino acid residue a ₁ is irradiated. As a result, occurs electron transitions between the molecular orbital MO ₂ localized to the molecular orbital MO ₁ and amino acid residues a _2, between the amino acid residues a ₁ and the amino acid residues a ₂ Accordingly The electron or hole moves. By moving electrons or holes in each zinc cytochrome c42 in this way, a current flows between both ends of the molecular wire.
According to the second embodiment, current can flow instantaneously between both ends of the molecular wire by light irradiation. This molecular wire can be produced very easily using zinc cytochrome c without relying on a complicated chemical synthesis method, and it is nanometer-sized, so that ultrahigh-density wiring is possible.

Next explained is a molecular wire according to the third embodiment of the invention.
As shown in FIG. 38, in this molecular wire, a plurality of molecules of zinc cytochrome c42 are bonded so as to form an L shape. In this case, movement of electrons or holes accompanying the transition between molecular orbitals by photoexcitation occurs between the amino acid residues a ₁ and a ₂ of the zinc cytochrome c42 in the L-shaped straight part. That is, molecular orbitals are localized at amino acid residues a ₁ and a ₂ , respectively, and the molecular orbital of the other molecular orbital is the molecular orbital with the maximum k _ET . On the other hand, in this L-shaped bent portion, movement of electrons or holes accompanying the transition between molecular orbitals due to photoexcitation occurs between amino acid residues a ₁ and a _{3 of} zinc cytochrome c42. That is, molecular orbitals are localized at amino acid residues a ₁ and a ₃ , respectively, and the molecular orbital of the other molecular orbital is the molecular orbital with the maximum k _ET .

The operation method of this molecular wire will be described.
First, light having a wavelength λ ₁ capable of selectively photoexciting the molecular orbital MO ₁ localized at the amino acid residue a ₁ is irradiated. As a result, occurs electron transitions between the molecular orbital MO ₂ localized to the molecular orbital MO ₁ and amino acid residues a _2, between the amino acid residues a ₁ and the amino acid residues a ₂ Accordingly The electron or hole moves. In this way, electrons or holes move in each zinc cytochrome c42 in the L-shaped straight portion. On the other hand, in the L-shaped bent portion, an electron transition occurs between the molecular orbital MO ₁ and the molecular orbital MO ₃ localized at the amino acid residue a ₃ , and accordingly, the amino acid residue a ₁ and the amino acid residue. electrons or holes between a ₃ to move. Thus, current flows between both ends of the molecular wire.
According to the third embodiment, in addition to the same advantages as those of the second embodiment, it is possible to obtain an advantage that a bent molecular wire can be obtained.

Next explained is a photoelectric conversion element according to the fourth embodiment of the invention. FIG. 39 shows this photoelectric conversion element.
As shown in FIG. 39, in this photoelectric conversion element, a monomolecular film or a polymolecular film of zinc cytochrome c42 is fixed directly or indirectly via an intermediate layer on an electrode 43 made of a conductive material. Yes. In FIG. 39, the electrode 43 is drawn so as to have a flat surface shape, but the surface shape of the electrode 43 is arbitrary, and may be any of a concave surface, a convex surface, an uneven surface, and the like. In this case, each zinc cytochrome c42 has an amino acid residue a ₁ on the electrode 43 side and an amino acid residue a ₂ on the opposite side, and a molecular orbital by photoexcitation between these amino acid residues a ₁ and a _2. The movement of electrons or holes accompanying the transition between them occurs. That is, molecular orbitals are localized at amino acid residues a ₁ and a ₂ , respectively, and the molecular orbital of the other molecular orbital is the molecular orbital with the maximum k _ET . An electrode 44 made of a conductive material is provided so as to face a monomolecular film or a polymolecular film of zinc cytochrome c42 fixed on the electrode 43 with a space therebetween. These electrodes 43 and 44 are immersed in an electrolyte solution 46 placed in a container 45. As the electrolyte solution 46, one that does not impair the function of zinc cytochrome c42 is used. The electrolyte (or redox species) of the electrolyte solution 46 is one in which an oxidation reaction occurs at the electrode 43 and a reduction reaction occurs at the electrode 44, or a reduction reaction occurs at the electrode 43 and an oxidation reaction occurs at the electrode 44. Is used.

  In order to perform photoelectric conversion by this photoelectric conversion element, the difference between the natural electrode potentials of the electrodes 43 and 44 is used as a bias voltage, and light is irradiated to the zinc cytochrome c42 fixed to the electrode 43 in this state. This light has a wavelength capable of photoexcitation of zinc cytochrome c42 and is usually visible light. In this case, the magnitude and / or polarity of the photocurrent flowing inside the device is changed by selecting the material of the electrodes 43 and 44, adjusting at least one of the intensity of light to be irradiated and the wavelength of the light to be irradiated. Can be made. The photocurrent is taken out from the terminals 47a and 47b.

  As the conductive materials constituting the electrodes 43 and 44, those already mentioned can be used and are appropriately selected as necessary. Specifically, all or almost all of the zinc cytochrome c42 fixed on the electrode 43 is used. Preferably, at least one of these electrodes 43 and 44 is a conductive material that is transparent to light (usually visible light) used for photoexcitation of zinc cytochrome c42. For example, it is made of ITO, FTO, nesa glass or the like.

  According to the fourth embodiment, a novel photoelectric conversion element using zinc cytochrome c42 as a photoelectric conversion material can be realized. According to this photoelectric conversion element, by selecting at least one of the material of the electrodes 43 and 44, the intensity of the irradiated light, and the wavelength of the irradiated light, the magnitude of the photocurrent flowing through the element and Since the polarity can be changed, various applications are possible. This zinc cytochrome c42 can be easily synthesized, and does not require complicated chemical synthesis such as an organic semiconductor, which is advantageous in producing a photoelectric conversion element. In addition, since the surface shape of the electrode 43 can be arbitrarily selected, the degree of freedom in designing the structure of the photoelectric conversion element is high.

Next explained is a photodetector according to the fifth embodiment of the invention.
FIG. 40 is a circuit diagram showing this photodetector. As shown in FIG. 40, this photodetector is composed of a photodiode 51 composed of a photoelectric conversion element according to the fourth embodiment, and a single electron transistor 52 for amplifying the output of the photodiode 51. Yes. The single electron transistor 52 is composed of a micro tunnel junction J ₁ on the drain side and a micro tunnel junction J ₂ on the source side. The capacitances of these micro tunnel junctions J ₁ and J ₂ are C ₁ and C ₂ , respectively. For example, the electrode 44 of the photodiode 51 is grounded via the load resistor R _L , and the electrode 43 is connected to a positive power supply that supplies a positive voltage V _PD for biasing the photodiode 52. On the other hand, the source of the single electron transistor 52 is grounded, and the drain thereof is connected to a positive power source that supplies a positive voltage _Vcc via an output resistor _Rout . The electrode 44 of the photodiode 51 and the gate of the single electron transistor 52 are connected to each other via a capacitor _Cg .

In the photodetector configured as described above, the capacitance _Cg is charged by the voltage generated at both ends of the load resistance _RL when the photodiode 51 is irradiated with light and a photocurrent flows, and this capacitance is charged. A gate voltage V _g is applied to the gate of the single electron transistor 52 via C _g . Then, the change ΔV _g of the gate voltage V _g is measured by measuring the change ΔQ = C _g ΔV _g of the charge amount accumulated in the capacitor C _g . Here, a single-electron transistor 52 which is used to amplify the output of the photodiode 51, for example also the sensitivity million times the conventional transistor, the capacitance C _g to the charges accumulated amount of change Delta] Q = C _g ΔV _g can be measured. That is, since the single electron transistor 52 can measure a minute change ΔV _g in the gate voltage V _g , the value of the load resistance R _L can be reduced. As a result, the sensitivity and speed of the photodetector can be greatly increased. Further, since thermal noise is suppressed by the charging effect on the single electron transistor 52 side, noise generated on the amplifier circuit side can be suppressed. Further, the single electron transistor 52 uses only one electron tunneling effect in its basic operation, and therefore has extremely low power consumption.
In this photodetector, the photodiode 51 and the single electron transistor 52 are capacitively coupled as described above. Since the voltage gain at this time is given by C _g / C ₁ , the element connected to the next stage of the photodetector is driven by sufficiently reducing the capacitance C ₁ of the minute tunnel junction J _1. Therefore, an output voltage V _out having a sufficient magnitude can be obtained.

Next, a specific structural example of the photodetector will be described.
In this example, the single electron transistor 52 is constituted by a metal / insulator junction, and the photodiode 51 is constituted by a photoelectric conversion element according to the fourth embodiment.
FIG. 41 is a plan view of the photodetector. FIG. 42 is a cross-sectional view of the portion of the photodiode 51 in this photodetector, and FIG. 43 is a cross-sectional view of the portion of the single electron transistor 52 in this photodetector.

As shown in FIGS. 41, 42 and 43, in this photodetector, an insulating film 62 such as a SiO ₂ film, a SiN film or a polyimide film is provided on a substrate 61 such as a semiconductor substrate. ing. An opening 62 a is provided in the insulating film 62 in the photodiode 51 portion. An electrode 43 is provided on the substrate 61 inside the opening 62a, a monomolecular layer of zinc cytochrome c42 is directly or indirectly fixed on the electrode 43, and an electrode 44 is provided thereon. . In this case, since light is transmitted through the electrode 44 and received, the electrode 44 is configured to be transparent to the light used for light excitation of the zinc cytochrome c42.

On the other hand, in the portion of the single electron transistor 52, the source electrode 63 and the drain electrode 64 are provided on the insulating film 62 so as to face each other. A gate electrode 65 is formed so as to partially overlap one end of each of the source electrode 63 and the drain electrode 64. Here, at least the surface of the source electrode 63 and the drain electrode 64 where the gate electrode 65 overlaps has a film thickness of, for example, 0. An insulating film 66 of several nm to several nm is formed. Therefore, the gate electrode 65 partially overlaps one end of each of the source electrode 65 and the drain electrode 66 through the insulating film 66. The size of this overlapping portion is typically several 100 nm × several 100 nm or less. In this case, the portions where the gate electrode 65 and the source electrode 63 overlap through the insulating film 66 correspond to the micro tunnel junctions J ₁ and J ₂ in FIGS. 40 and 41, respectively. The gate electrode 65, the source electrode 63, and the drain electrode 64 are made of a metal such as Al, In, Nb, Au, or Pt.
Although illustration is omitted, if necessary, a passivation film is provided on the entire surface so as to cover the photodiode 51 and the single electron transistor 52.

In this case, one end of the electrode 44 of the photodiode 51 is close to the gate electrode 65 of the single electron transistor 52. When no passivation film is provided, a capacitor having a structure in which an air layer is sandwiched between one end of the electrode 44 and the gate electrode 65 is formed. Are capacitively coupled. When a passivation film is provided, a capacitor having a structure in which the passivation film is sandwiched between one end of the electrode 44 and the gate electrode 65 is formed, whereby the electrode 44 and the gate electrode 65 are connected to each other. Capacitively coupled.
As described above, according to the fifth embodiment, since the output of the photodiode 51 is amplified by the single electron transistor 52, the output of the photodiode is amplified by the conventional normal transistor. Compared with a conventional general photodetector, it is possible to greatly increase the speed, sensitivity, and power consumption of the light detection.

Next, a CCD image sensor according to a sixth embodiment of the present invention is shown. This CCD image sensor is of an interline transfer type having a light receiving portion, a vertical register and a horizontal register.
FIG. 44 shows a cross-sectional structure of the light receiving portion of the CCD image sensor and the vertical register in the vicinity of the light receiving portion. As shown in FIG. 44, a gate insulating film 72 is formed on a p-type Si substrate 71 (or a p-well layer formed on an n-type Si substrate), and a read gate electrode 73 is formed on the gate insulating film 72. ing. An n-type layer 74 and an n-type layer 75 constituting a vertical register are formed in the p-type Si substrate 71 on both sides of the read gate electrode 73. An opening 72 a is formed in a portion of the gate insulating film 72 on the n-type layer 74. For example, the photoelectric conversion element according to the third embodiment is formed as the light receiving portion 76 on the n-type layer 74 inside the opening 72a. The other configuration of the CCD image sensor is the same as that of a conventionally known interline transfer type CCD image sensor.

In this CCD image sensor, the electrode 43 is biased to a positive voltage with respect to the electrode 44 of the photoelectric conversion element. When light enters the zinc cytochrome c 42 in the light receiving portion 76, electrons generated by photoexcitation flow into the n-type layer 74. Next, a positive voltage is applied to the read gate electrode 73 in a state where a voltage higher than that of the n-type layer 74 is applied to the n-type layer 75 constituting the vertical register, whereby the p-type Si substrate 71 immediately below the read gate electrode 73 is applied. An n-type channel is formed in the n-type channel, and electrons in the n-type layer 74 are read out to the n-type layer 75 through the n-type channel. Thereafter, the electric charges read out in this way are transferred in the vertical register and further transferred in the horizontal register, and an electric signal corresponding to the image picked up is taken out from the output terminal.
According to the sixth embodiment, a novel CCD image sensor using zinc cytochrome c42 for the light receiving unit 76 can be realized.

Next explained is an inverter circuit according to the seventh embodiment of the invention.
This inverter circuit is shown in FIG. As shown in FIG. 45, in this inverter circuit, a photoelectric conversion element 81 having a configuration similar to that of the photoelectric conversion element according to the fourth embodiment and a load resistor R _L are connected in series. Here, the load resistance R _L is connected to the electrode 43. A predetermined positive power supply voltage V _DD is applied to one end of the load resistor _RL , and the electrode 44 is grounded. When, for example, visible light is irradiated to the zinc cytochrome c42 of the photoelectric conversion element 81 as a signal light, the photoelectric conversion element 81 is turned on and a photocurrent flows, whereby the output voltage _Vout from the electrode 43 becomes a low level, and the visible light is irradiated. When stopped, the photoelectric conversion element 81 is turned off and the photocurrent does not flow, so that the output voltage _Vout from the electrode 43 becomes high level.

A structural example of this inverter circuit is shown in FIG. As shown in FIG. 46, in this structural example, an n-type layer 92 used as a load resistance R _L is formed in a p-type Si substrate 91 (or a p-well layer formed on an n-type Si substrate). . An insulating film 93 such as a SiO ₂ film is formed on the surface of the p-type Si substrate 91. Openings 93 a and 93 b are formed in the insulating film 93 at one end and the other end of the n-type layer 92. A photoelectric conversion element 81 is formed on the n-type layer 92 inside the opening 93a. The electrode 94 is in ohmic contact with the n-type layer 92 through the opening 93b. On the p-type Si substrate 91, various electronic circuits (amplifier circuits, etc.) driven by the output voltage _Vout can be formed in addition to the inverter circuit as necessary.
According to the seventh embodiment, since the inverter circuit can be configured by the photoelectric conversion element 81 using the zinc cytochrome c42 and the load resistance R _L , various circuits such as a logic circuit can be formed using the inverter circuit. Can be configured.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
For example, the numerical values, structures, configurations, shapes, materials, and the like given in the above-described embodiments are merely examples, and different numerical values, structures, configurations, shapes, materials, and the like may be used as necessary.

  42 ... Zinc cytochrome c, 43 ... electrode, 44 ... electrode, 45 ... container, 46 ... electrolyte solution, 51 ... photodiode, 52 ... single electron transistor, 71 ... p-type Si substrate, 73 ... read gate electrode, 74, 75 ... n-type layer, 76 ... light receiving part, 81 ... photoelectric conversion element, 91 ... p-type Si substrate, 92 ... n-type layer

Claims (9)

It has at least one molecule of electron transfer protein, and wiring is connected to each of a plurality of different amino acid residues of the electron transfer protein,
An electron or a hole moves between a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues,
Molecular element. The electron transfer protein is zinc cytochrome c.
The molecular device according to claim 1. A first molecular orbital and a second molecular orbital are localized in the first amino acid residue and the second amino acid residue, respectively, and the second molecular orbital is unit time with respect to the first molecular orbital. The maximum transition probability per hit,
The molecular device according to claim 1.   Generating electrons or holes by photoexcitation in one of the first molecular orbitals and the second molecular orbitals;
The molecular device according to claim 3.   The first amino acid residue and the second amino acid residue constitute the starting and ending points of electron or hole movement, respectively;
The molecular device according to claim 1. A single-molecule optical switching device having a single molecule of an electron transfer protein and utilizing the movement of electrons or holes in the electron transfer protein using the transition of electrons between the molecular orbitals of the electron transfer protein. ,
A wire is connected to each of a plurality of different amino acid residues of the electron transfer protein,
An electron or a hole moves between a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues,
Single molecule optical switch element. It has at least one molecule of electron transfer protein, and wiring is connected to each of a plurality of different amino acid residues of the electron transfer protein,
A functional element in which electrons or holes move between a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues. It has at least one molecule of electron transfer protein, and wiring is connected to each of a plurality of different amino acid residues of the electron transfer protein,
A molecular wire in which electrons or holes move between a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues. In an electronic device having one or more functional elements,
As at least one functional element, it has at least one molecule of an electron transfer protein, and wiring is connected to each of a plurality of different amino acid residues of the electron transfer protein,
Using a functional element in which electrons or holes move between a first amino acid residue and a second amino acid residue arbitrarily selected from the plurality of amino acid residues,
Electronics.

Images