A method for controlling multi electrons spin selective reactions and a coating therefor

Abstract

The present disclosure relates to a method for controlling multi electrons spin selective reactions, a coating and an electrode. The attachment between the chiral coating surface layer and the electrode is configured for causing charge rearrangement, spin polarization of the electrode surface, controllably affecting coherent and entangled properties of the multi-electrons being injected from or to the electrode surface thereby modifying the rate of the multi electrons spin selective reactions and product selectivity.

Description

[0001] A METHOD FOR CONTROLLING MULTI ELECTRONS SPIN SELECTIVE REACTIONS AND A COATING THEREFOR

[0002] TECHNOLOGICAL FIELD

[0003] The presently disclosed subject matter relates to multi-electrons spin selective reactions and to a method for controlling them as well as a coating and an electrode thereof.

[0004] BACKGROUND ART

[0005] References considered to be relevant as background to the presently disclosed subject matter are listed below:

[0006] 1. Kulkarni, S. Siahrostami, A. Patel, J. K. Norskov, Understanding catalytic activity trends in the oxygen reduction reaction. Chem. Rev. 118, 2302-2312 (2018).

[0007] 2. M. Shao, Q. Chang, J. P. Dofrlry, R. Chenitz, Recent advances in electrocatalysts for oxygen reduction reaction. Chem. Rev. 115, 3594-3657 (2016).

[0008] 3. C. Biz, M. Fianchini and J. Gracia, Catalysis Meets Spintronics; Spin Potentials Associated with Open-Shell Orbital Configurations Enhance the Activity of Pt3Co Nanostructures for Oxygen Reduction: A Density Functional Theory Study, ACS Appl. Nano Mater., 2020, 3(1), 506-515.

[0009] 4. Y. Sang, F. Tassinaria, K. Santra, W. Zhang, C. Fontanesi, B. P. Bloom, D. H. Waldeck, J. Fransson, R. Naaman, Chirality enhances oxygen reduction, PNAS 119 e2202650119 (2022).

[0010] 5. A. Gupta, Y. Sang, C. Fontanesi, L. Turin, R. Naaman, The Effect of Anesthesia Gases on the Oxygen Reduction Reaction, J. Phys. Chem. Lett. 14, 1756-1761 (2023)

[0011] 6. D. K. Bhowmick, T. K. Das, K. Santra, A. K. Mondal, F. Tassinari, R. Schwarz, C. E. Diesendruck, R. Naaman, Spin-Induced Asymmetry Reaction - The Formation of Asymmetric Carbon by Electropolymerization, Science Adv. 8, eabq2727 (2022). 7. S. Mishra, S. Pirbadian, A. K. Mondal, M. Y. El-Naggar, R. Naaman, Spin- Dependent Electron Transport through Bacterial Cell Surface Multiheme Electron Conduits, J. Am. Chem. Soc. 141, 19198-19202 (2019).

[0012] 8. Y. Sang, S. Mishra, F. Tassinari, K. S. Kumar, R. Carmieli, R. D. Teo, A. Migliore, D. N. Beratan, H. B. Gray, I. Pecht, J. Fransson, D. H. Waldeck, R Naaman, Temperature Dependence of Charge and Spin Transfer in Azurin, J. Phys. Chem. C 125, 9875-9883 (2021).

[0013] 9. Mtangi W ., Kiran V., Fontanesi C., Naaman R., The Role of the Electron Spin Polarization in Water Splitting, J. Phys. Chem. Lett., 6, 4916-4922 (2015).

[0014] 10. Xiang, L., Palma, J. L.; Bruot, C., Mujica, V., Ratner, M. A., Tao, N., Intermediate Tunnelling-Hopping Regime in DNA Charge Transport, Nat. Chem. 2015, 7, 221- 226.

[0015] 11. Mishra, S., Mondal, A. K., Pal, S., Das, T. K., Smolinsky, E. Z. B., Siligardi, G., Naaman, R., Length-Dependent Electron Spin Polarization in Oligopeptides and DNA. J. Phys. Chem. C 2020, 124, 10776-10782.

[0016] 12. Valdiviezo, J., Clever, C., Beall, E., Pearse, A., Bae, Y., Zhang, P., Achim, C., Beratan, D. N., Waldeck, D. H., Delocalization- Assisted Transport through Nucleic Acids in Molecular Junctions. Biochemistry 2021, 60, 1368-1378.

[0017] Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.

[0018] BACKGROUND

[0019] The concept of applying the coherent properties of electrons to control chemical reactions has fascinated the chemical community for several decades. Two electrons are considered entangled when they can be described by a state that conserves the phase between them. This state is established due to exchange interaction and may persist as long as there are no other interactions affecting the electrons’ state.

[0020] If the electrons leaving the surface collide with other molecules, their entanglement may be destroyed. Consequently, the electrons are not interacting with the molecule as a pair, but instead each one of them interacts separately. In such cases, for example, during oxygen reduction, it has been demonstrated that the resulting product does not stem directly from the reduction of the oxygen, but instead proceeds in stages with hydrogen peroxide formed as a byproduct.

[0021] Typically, the injection or removal of subsequent electrons from an already partially reduced / oxidized system requires overcoming an electrostatic barrier. In the case of reduction, this barrier results from the repulsion between the partially reduced system and the additional electron, while for oxidation, it is a consequence of the Coulomb attraction between the partially oxidized species and the electron that needs to be removed. However, there are cases in which the injection or removal of the second electron encounters a very low barrier, and in some cases, these processes are even favorable in a situation referred to as “potential inversion.” Namely, the two-electron process is more energetically favorable than the single electron one. It is commonly assumed that in these cases, following the transfer of the first electron, the system undergoes a structural change that enables the transfer of the second electron. However, there are cases in which the single electron process generates another product, due to spin restriction for example. Therefore, the transfer of two electrons is expected to occur simultaneously. It is well established that in the oxygen reduction reaction (ORR), four electrons are transferred as two pairs [1,2]. The reaction is spin-forbidden because the oxygen ground state is triplet, while the products are all singlets. The interaction between the two electrons in each pair determines the potential for the reaction and affects the reaction mechanism.

[0022] GENERAL DESCRIPTION

[0023] As described above, two electrons are considered entangled when they can be described by a state that conserves the phase between them. This state is established due to exchange interaction which may be of short range (a few angstroms), resulting in an oxygen molecule attached to the surface having a size of maximum 3 angstroms. The transfer of two electrons to a ground state oxygen molecule depends on their spins being parallel to each other. This spin can either arrive as an entangled pair or as a separate step process. In the first case, the direct overlap between the entangled pair and the triplet state controls the rate, enhancing reaction efficiency.

[0024] The ORR yields water as the lower energy product and hydrogen peroxide as a higher-energy byproduct. However, it was found that the water production itself has a high barrier due to the need to overcome the spin restriction in the reaction [3], It was demonstrated that by having the two electrons in the same spin state, the reaction rate is enhanced, since the spin restriction is removed, and the reaction can occur on a triplet potential energy surface to produce water. If the spins are not co-aligned, the hydrogen peroxide production is enhanced [4], It was also observed that by adding various gases, which can affect the spin alignment of the transferred electrons, the reaction rate for direct reduction efficiency is reduced while the formation of hydrogen peroxide is enhanced [5], The technique of the present disclosure enables to control the spin coherent properties of the electrons in multi electrons spin selective reactions, for increasing reaction rate and product selectivity. The inventors found that the coherent properties of a pair of electrons used for reducing or oxidizing a system, upon their transmission to oxygen during oxygen reduction, affect the reaction yield, its rate and the distribution of products using a dense nanometric layer of chiral coating. Because the oxygen molecule has a triplet ground state, both its formation in the oxygen evolution reaction (OER) and its decomposition in the oxygen reduction reaction (ORR) involve transmission of pairs of electrons. The inventors found that the phase relation between these electrons in the pair has an important effect on the reaction rate and on the production of byproducts and explored the role of entanglement in multi-electrons oxygen spin-polarized electrons electron transfer process. Since multiple electrons redox processes are common in chemistry and specifically in biology, the inventors found that room temperature coherent effects can be of importance. The coating of the presently disclosed subject matter can be implemented by utilizing electrons ejected from an electrode, and the reduction of oxygen, which is a process occurring in respiration and in fuel cells.

[0025] Thus, according to one broad aspect of the disclosure there is provided a method for controlling multi electrons spin selective reactions comprising: selecting a nanometric thickness of a chiral coating surface layer to provide spin-polarized coupled electrons, wherein the thickness of the chiral coating surface layer is below twenty nanometers; attaching the chiral coating surface layer of the selected thickness to an electrode surface; applying a potential difference between the electrode carrying the chiral coating surface layer and a counter-electrode so as to create transfer of charges between the electrodes and to provide spin-polarized coupled electrons. The attachment between the chiral coating surface layer and the electrode is configured for causing charge rearrangement, spin polarization of the electrode surface, controllably affecting coherent and entangled properties of the multi-electrons being injected from or to the electrode surface thereby modifying the rate of the multi electrons spin selective reactions and product selectivity.

[0026] Attaching the chiral coating surface layer to the electrode surface may comprise at least one of depositing, growing, adsorbing, or coating electrode surface.

[0027] In some embodiments, attaching the chiral coating surface layer to the electrode surface comprises adsorbing a thin layer of chiral polymer on an electrode.

[0028] In some embodiments, the method for controlling multi electrons spin selective reactions further comprises interacting between the electrode carrying the chiral coating surface layer on the electrode’s surface and oxygen dissolved in an electrolyte solution for producing water and hydrogen peroxide.

[0029] Selecting the thickness of the chiral coating surface layer may comprise determining a particular length of chiral molecules, chiral monolayers or chiral structures (e.g., metal structure or chiral oxide) or a specific thickness of the chiral layer.

[0030] In some embodiments, determining a particular length of chiral molecules, chiral monolayers or chiral structures comprises increasing a molecular length beyond the particular length of the chiral material to increase a threshold potential, decrease a reaction yield and to provide an enhanced production of hydrogen peroxide.

[0031] In some embodiments, selecting a thickness of a chiral coating surface layer comprises determining a particular length of chiral material enabling enhanced four- electron reduction of oxygen to produce water and reduced production of hydrogen peroxide.

[0032] In some other embodiments, interacting between the electrode carrying the chiral coating surface layer on the electrode’s surface and oxygen dissolved in an electrolyte solution further comprises interacting between the electrode carrying the chiral coating surface layer and anesthetic gases for enhancing formation of hydrogen peroxide.

[0033] According to some other broad aspect of the disclosure there is provided a coating for electrodes for use in multi electrons spin selective reactions comprising a chiral coating surface layer, configured with a thickness being selected to provide spin-polarized coupled electrons, control coherent and entangled properties of the multi spin-polarized electrons, thereby increasing reaction rate and product selectivity.

[0034] In some embodiments, the thickness of the chiral coating surface layer is in the range of about 3 nm to 20 nm.

[0035] In some embodiments, the chiral coating surface layer comprises a chiral polymer. In some embodiments, an interaction between an electrode coated with the coating and oxygen dissolved in an electrolyte solution produces water and hydrogen peroxide.

[0036] In some embodiments, the thickness of the chiral coating surface layer is selected by determining a particular length of chiral molecules, chiral monolayers or chiral structures enabling enhanced four-electron reduction of oxygen to produce water and reduced production of hydrogen peroxide, while in other embodiments, the thickness of the chiral coating surface layer is selected by determining a particular length of chiral molecules, chiral monolayers or chiral structures beyond which an enhanced production of hydrogen peroxide is provided.

[0037] The chiral coating surface layer of the coating of the disclosure includes at least one chiral layer being composed for example of the following: oligopeptides, amino acids, DNA, helicenes, and chiral conductive polymer chiral oxides, chiral metals, and is either chemically bound to an electrode or physically adsorbed on it.

[0038] In yet another broad aspect of the disclosure, there is provided an electrode for controlling multi electrons spin selective reactions comprising a chiral coating surface layer attached on an electrode surface, wherein the chiral coating surface layer has a thickness being selected to cause charge rearrangement and spin polarization of the electrode surface, to thereby controllably affect coherent properties of the multi-electrons being injected from or to the electrode surface thereby modifying the rate of the multi electrons spin selective reactions and product selectivity.

[0039] In some embodiments the thickness of the chiral coating surface layer on top of the electrode is in the range of about 3 nm to 20 nm.

[0040] In some embodiments the thickness of the chiral coating surface layer is selected by determining a particular length of chiral molecules, chiral monolayers or chiral structures, which may be in the range of about 1.5 nm-6 nm.

[0041] In some embodiments the chiral coating surface layer of the electrode is either chemically bound to the electrode surface or physically adsorbed on it.

[0042] In some embodiments the thickness of the chiral coating surface layer of the electrode is selected to cause alignment of the spins of transferred electrons released to oxygen from the electrode during oxygen reduction reaction to thereby create a spin specificity of the electrons transferred through the chiral system to oxygen, decreasing an overpotential of the oxygen reduction reaction and thereby enhancing a multielectron reduction of diatomic oxygen to produce water. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0044] Fig- 1 is a flow chart exemplifying the main steps for controlling multi electrons spin selective reactions according to some embodiments of the presently disclosed subject-matter;

[0045] Fig- 2 is a flow chart exemplifying a method being specifically related to the oxygen reduction reaction (ORR) according to some embodiments of the presently disclosed subject-matter;

[0046] Fig- 3 shows Linear Voltammetry Curve (LVC), i.e., the current versus the potential, measured in an electrochemical system for magnetic (M-solid lines) and nonmagnetic (NM-dotted lines) electrodes for pure oxygen and when addition gas, CCL is added;

[0047] Figs. 4A and 4B show the effect of a thin layer of chiral polymer (e.g., polymer of 2-vinyl pyridine) adsorbed on an electrode on the oxygen reduction reaction (ORR), wherein Fig. 4A shows the relative rate of reduction of the oxygen as a function of the polymer thickness (presented as time of polymerization), and Fig. 4B shows the amount of hydrogen peroxide produced as a function of the chiral film thickness;

[0048] Fig. 5A shows the current through a polymer layer of 2-vynil pyridine, as a function of the layer thickness, measured by mc-AFM with the magnetic north pole of the substrate pointing towards (Mag up) or away (Mag down) from the polymer film, respectively;

[0049] Fig. 5B shows the difference in the currents for the two orientations of the magnetic field, Iup-Idown, as a function of the polymer thickness;

[0050] Fig. 5C shows the current versus voltage (CV) curves obtained for working electrodes coated with various thicknesses of the polymer, wherein zero thickness refers to magnetic electrode with its magnetic field pointing up with no polymer coating;

[0051] Figs. 6A-6D show the dependence of the characteristic parameters of the CV curves shown in Fig. 5C on the thickness of the chiral polymer film, wherein Fig. 6A shows the dependence of the peak potential; Fig. 6B shows the onset potential; Fig. 6C shows the current at the peak of the curve; and Fig. 6D shows the current at -0.5V; Fig 7 shows hydrogen peroxide production in the ORR, as a function of the thickness of the chiral polymer film coating the working electrode;

[0052] Figs. 8A-8C show results from the ORR reaction obtained for working electrode coated with monolayer of double stranded DNA of various lengths, wherein Fig. 8A shows the rising of the CV curve for 20,30,50, and 70 base pairs (bp) long DNA; Fig. 8B shows the current density at a potential of -0.45 V for all 5 lengths of the DNA; and Fig. 8C shows the onset potential, defined as the potential for which the current density is 0. ImA / cm2, for the 5 different lengths of DNA;

[0053] Figs. 9A-9C show CV plots and the spin-dependent current obtained for electrodes coated with monolayers of a-helices of oligopeptides, wherein Fig. 9A shows the electrochemical CV curves for oligopeptides of two lengths (A15 and A136, respectively); Figs. 9B and 9C show the current versus voltage (IV) curves measured for the two oligopeptide lengths (A15 and A136, respectively). The spin polarization (SP) values measured are shown in the figures;

[0054] Figs. 10A-10C show a schematic presentation of the ORR with its two paths, wherein Fig. 10A shows that when the two electrons in each pair interact and form a coherent pair, the reaction is efficient and water is produced; Fig. 10B shows that when the two electrons are not coherent (presented as some delay in their approach), the reaction product is hydrogen peroxide; and Fig. 10C shows that the production of hydrogen peroxide is the high energy path that results from the two electrons not inserted coherently into the oxygen.

[0055] DETAILED DESCRIPTION OF EMBODIMENTS

[0056] Reference is made to Fig. 1 showing, by way of a flow diagram, the principal steps of the method 100 of the present disclosure. The method 100 starts by selecting a nanometric thickness of a chiral coating surface layer to provide spin-polarized coupled electrons, wherein the thickness of the chiral coating surface layer is below twenty nanometers as shown in 101). In 102, an attachment is provided between the chiral coating surface layer of the selected thickness and an electrode. This attachment may comprise at least one of depositing, growing, adsorbing, or coating electrode surface. Selecting a nanometric thickness of a chiral coating surface layer may comprise determining a particular length of chiral molecules, chiral monolayers or chiral structures and the attachment in 102 may comprise adsorbing a thin layer of chiral polymer on an electrode.

[0057] In the 103, a potential difference is applied between the electrode carrying the chiral coating surface layer and a counter-electrode so as to create transfer of charges between the electrodes and to provide spin-polarized coupled electrons. The attachment between the chiral coating surface layer and the electrode is configured for causing charge rearrangement and the spin polarization of the electrode surface, controllably affecting coherent and entangled properties of the multi-electrons being injected from or to the electrode surface, thereby modifying the rate of the multi electrons spin selective reactions and product selectivity.

[0058] Fig. 2 exemplifies the main steps of another method 200 of the present disclosure specifically related to the oxygen reduction reaction (ORR). In 201, a particular nanometric length of a chiral polymer is determined to provide spin-polarized coupled electrons, wherein the length of the chiral polymer is below twenty nanometers. Then in 202, a thin layer of the chiral polymer is adsorbed on an electrode’s surface. In 203, a potential difference is applied between the electrode carrying the chiral polymer layer and a counter-electrode, such that the oxygen dissolved in an electrolyte solution may produce water and hydrogen peroxide (through the oxygen reduction reaction (ORR)).

[0059] The particular length of the chiral polymer may be determined in 201 to enable enhanced four-electron reduction of oxygen to produce water and reduced production of hydrogen peroxide.

[0060] Additionally or alternatively, the length of the chiral polymer may be increased in 204 beyond a particular length to increase the threshold potential, decrease the reaction yield and to provide an enhanced production of hydrogen peroxide.

[0061] In some embodiments, the electrode carrying the chiral polymer layer may be interacted in 206 with anesthetic gases for enhancing formation of hydrogen peroxide.

[0062] Fig- 3 shows the Linear Voltammetry Curve (LVC) plot of oxygen reduction when pure oxygen is introduced to the solution versus the case that chloroform is added. The current versus the potential was measured in an electrochemical system for magnetic (M-solid lines) and non-magnetic (NM-dotted lines) electrodes for pure oxygen and when addition gas, CCL , is added. The clear decrease in the signal and a shift to higher potential when the addition gas, CCL , is added indicate that chloroform dramatically reduces the rate of the oxygen reduction process, the reaction changes from being a two electrons process to a single electron one, and the amount of hydrogen peroxide produced increases.

[0063] The degree of coupling between electrons participating in the oxygen reduction reaction can be controlled, for example, by deposition of a thin film of chiral molecules on the electrode. Fig- 4 shows the degree of oxygen reduction as a function of the thickness of a chiral film (normalized to the current), consisting of a polymer of 2-vinyl pyridine, and the amount of hydrogen peroxide produced as a function of the film thickness. Clearly there is correlation between the two phenomena, i.e., the amount of hydrogen peroxide is increasing (i.e., the efficiency of the oxygen reduction reaction is decreased) with an increase in the thickness of the chiral film. It is important to note that spin polarization grows with the increase in chiral film thickness, however the oxygen reduction efficiency is reduced due to the loss of the coherence effect, i.e., breaking of the coupling between the electrons by the thicker chiral polymer layer.

[0064] It should be noted that there are a large number of chemical reactions in which multiple electrons are transferred so as to reduce or oxidize a reagent. Some exemplary reduction processes involve the electrodeposition of metals from their ions (like Fe+2, Cu+2, Ni+2). In numerous numbers of metallo-organic systems, controlling the spin and the entanglement and coherent coupling between electrons may affect the production of high or low spin states, that will result in different products.

[0065] For determining the importance of the interaction between the electrons, the electrochemical ORR was further investigated by the inventors either with a magnetic working electrode for reference or with working electrode coated with chiral polymer film of 2-vinyl pyridine of various selected thicknesses. The chiral polymer film was produced by electrochemical reaction as described before [6], The selected thickness of the film depends on the time of electropolymerization, and it was calibrated using atomic force microscopy (AFM). The spin-dependent current for the films as a function of their selected thickness was determined by magnetic contact AFM (mcAFM) and is shown in Fig. 5A. The spin polarization (SP, in %) is shown, SP~J“p Idownwhen Iupand Idown are lup+Idown the current with the magnet north pole pointing up or down, respectively. The current is measured at +3 V.

[0066] By varying the magnetic orientation of the magnetic substrate, the current was measured for each spin and for 7 samples of different selected thicknesses. Clearly, the ratio between the two currents measured when the north pole of the magnet is pointing either towards the adsorbed layer, Iup, or away from it, Idown, increases with increasing thickness. At a selected thickness of 4 nm, the ratio is about 3:2 while at 20 nm it is 2: 1. Hence the spin polarization, SP~J“p Idownincreases with increasing film thickness, lup Idown while the current itself decreases with increasing film thickness.

[0067] Fig. 5B shows the difference between the currents, Iup- Idown, when the magnetic direction of the substrate, from which the electrons are injected, is switched. The figure illustrates clearly that the absolute magnitude of the spin polarized current decays with increasing the thickness, despite the increase in the spin polarization at higher thicknesses.

[0068] The ORR was investigated using electrochemistry with a three-electrode cell configuration. An Hg / Hg2C12 / saturated KC1 (saturated calomel electrode, SCE), a Pt wire was used as the reference electrode (RE) and counter electrode (CE), respectively. A 0.1 M KOH solution was used as electrolyte with pH = 12.6. The working electrode was fixed to the bottom of a teflon cell through an O-ring of 0.76 cm2area. Current versus voltage, C V curves were obtained either for gold coated Ni working electrode that was magnetized out of plan (Zero thickness), or with the gold electrode coated with different selected thickness of chiral polymer. Fig. 5C shows the CV curves obtained and Table 1 below summarizes the parameters obtained from the electrochemical studies of the ORR for electrode coated with chiral polymer of different selected thicknesses of each curve. The efficiency of the reaction can be evaluated from the threshold potential in the curve, from the peak potential, and from the current.

[0069] Table 1

[0070] It can be clearly seen in Fig. 5C and Table 1 above that as the chiral polymer film on the electrode becomes thicker, both the threshold potential and the peak potential are shifting to higher potential, indicating a higher barrier for the reaction. Since the ORR reaction is much more efficient for spin polarized electrons, as described in [9], one would expect that the reaction efficiency would decrease slowly with the thickness of the chiral polymer, namely with the decrease of the current of the spin preferred electrons (Mag up in Fig. 5A).

[0071] Figs. 6A-6D and Table 1 above (the onset potential is defined as the potential at a current of 0.1 mA) show the dependence of the characteristic parameters of the CV curves shown in Fig. 5C on the thickness of the chiral polymer film. Fig. 6A shows the current obtained at the peak of the reduction current as a function of the film thickness. It clearly shows that the reaction rate decreases sharply for polymer films with a thickness above about 6 nm. Similar results are obtained for the onset potential (Fig. 6B), for the current at the peak of the CV (Fig. 6C) and for the current at -0.5 V which is near the peak of the CV for the bare electrode (Fig. 6D). Table 1 above summarizes all these relevant parameters.

[0072] Thus, contrary to the expected slow decrease of reaction efficiency with the thickness of the chiral polymer, the results shown in Figs. 6A-6D, and Table 1 above indicate an abrupt drop in the reaction yield following thickness of about 7 nm of the polymer film.

[0073] Another interesting observation is the crossing in the CV curve, observed for the case of zero polymer coating or for the electrode coated with the 4 nm polymer (Fig. 5C). This crossing indicates that the reduction product reacts farther and therefore the CV process is not completely reversible.

[0074] The inventors also probed the production of hydrogen peroxide as a function of the thickness of the chiral polymer layer on the working electrode. The electrolyte solution was exposed to the current for 30 min when the potential in the electrochemical cell was set to -0.5V. The electrolyte was then taken out and the hydrogen peroxide concentration was monitored by addition of o-tolidine as redox indicator. In the presence of H2O2, a yellow color appears with an absorption peak at about 436 nm. This peak is characteristic for the complete two-electron oxidation product of o-tolidine formed by the reaction with hydrogen peroxide. The intensity of the absorption peak divided by the current in the electrochemical cell is shown in Fig. 7, as a function of the film thickness. The data shown in the figure consider, i.e., are corrected for, the reduction of the current when the film thickness increases. It was observed before by the inventors, that decrease in the efficiency of the ORR reaction is accompanied by an increase in the production of hydrogen peroxide, as indeed observed in Fig. 7 showing hydrogen peroxide production in the ORR, as a function of the thickness of the chiral polymer film coating the working electrode. The signal is normalized to the current at -0.5 V. The hydrogen peroxide production increases abruptly with an increased thickness of the polymer to above about 7 nm, the same thickness at which the reaction rate drops, as indicated in Figs. 6A-6D. This increase in hydrogen peroxide concentration cannot be a result of the change in the current since the signal is normalized to the current.

[0075] In the past, it was realized in several studies that the conduction through double stranded DNA [10,11] and peptide nucleic acid (PNA)

[0012] oscillates as a function of the length of the molecule. These oscillations were attributed to the coherent conduction through the systems [10,12], Hence, the inventors explored the efficiency of the ORR reaction as a function of the length of the DNA molecules adsorbed as monolayers on the gold electrode. The DNA sequences used in the experiments: 20bp dsDNA:

[0076] CGC TTC GCT TCG CTT CGC TT / 3ThioMC3-D / AAG CGA AGC GAA GCG AAG CG

[0077] 30bp dsDNA:

[0078] CGC TTC GCT TCG CTT CGC TTC GCT TCG CTT / 3ThioMC3-D / AAG CGA AGC GAA GCG AAG CGA AGC GAA GCG 40bp dsDNA:

[0079] CGC TTC GCT TCG CTT CGC TTC GCT TCG CTT CGC TTC GCT T / 3ThioMC3- D / AAG CGA AGC GAA GCG AAG CGA AGC GAA GCG AAG CGA AGC G 50bp dsDNA: CGC TTC GCT TCG CTT CGC TTC GCT TCG CTT CGC TTC GCT TCG CTT CGC TT / 3ThioMC3-D / AAG CGA AGC GAA GCG AAG CGA AGC GAA GCG AAG CGA AGC GAA GCG AAG CG

[0080] 70bp dsDNA:

[0081] TAC TCT ACC TTC TCA AGA ATC GGC ATT AGC TCA ACT GTC AAC TCC TCT ACC TTC TCA AGA ATC / 3ThioMC3-D / AAA TGC CGA TTC TTG AGA AGG TAG AGG AGT TGA CAG TTG AGC TAA TGC CGA TTC TTG AGA AGG TAG AGT A

[0082] Figs. 8A-8C show results from the ORR reaction obtained for working electrode coated with five DNA double strands of various lengths, containing 20,30,40,50, and 70 base pairs (bp). Fig. 8A shows the rising of the CV curve for 20,30,50, and 70bp long DNA. The results from the 40bp are not presented for clarity since they overlap with the 20 and 30bp signal. Fig. 8B shows the current density at a potential of -0.45V for all 5 lengths of the DNA, and Fig. 8C shows the onset potential, defined as the potential for which the current density is 0. ImA / cm2, for the 5 different lengths of DNA.

[0083] As was shown in

[0011] , while the current through the DNA is generally reduced as the molecule becomes longer, there are oscillations in the current, and the spin polarization tends to increase as a function of length. When the ORR is investigated, it is evident that while the onset of the potential becomes less negative with the length of the DNA, namely lower barrier for the reaction, for the short DNA sequences (20,30,40bp), it becomes much more negative (higher reaction barrier) for the 50bp long DNA, and then for the 70bp the barrier is reduced again (Figs 8A and 8B). When comparing the current density at a potential of -0.45V, in the case of the three short DNA, it is very similar; however, it drops for the 50bp long DNA and increases significantly for the 70bp DNA (Fig. 8C). From the results, it is evident that the ORR reaction characteristics fluctuate as a function of the length of the DNA adsorbed on the electrode. This contrasts with the continuous change in the reaction parameters for electrodes coated with various thicknesses of polymer.

[0084] To compare different biologically relevant molecules, the inventors performed similar studies with a gold electrode coated with oligopeptides of different lengths (Figs. 9A-9C, Table 2 below) for comparing with the results obtained with the chiral polymer coated electrode described above. In Table 2 below, the onset potential is defined as the potential at a current of 0.1 mA. These types of molecules were investigated in the past very extensively as spin filters. Specifically here short, SHCH2CH2CO-{Ala-Aib}s- COOH, and long (Ala)4-Lys-(Ala)4-Lys-(Ala)4-Lys-(Ala)4-Lys-(Ala)4-Lys-Ala- COCH2CH2SH oligopeptides (A15 and A136 respectively) were investigated when Ala stands for Alanine, Aib for 2-Aminoisobutyric acid, and Lys for Lysine.

[0085] Figs 9A-9C show the CV plots and the spin dependent current obtained for electrodes coated with monolayers of a-helices of oligopeptides. Fig. 9A shows the electrochemical CV curves for oligopeptides of two lengths, A15 and A136, respectively. For the longer oligomer, the peak in the CV is shifted to lower potential. Figs. 9B-9C show the current versus voltage (IV) curves for the two lengths of the oligopeptides, A15 and A136, respectively. The spin polarization (SP) measured is shown in the figures. The SP does not depend on the voltage, once the voltage is higher than about 0.5 V.

[0086] Table 2

[0087] In the case of oligopeptides, as was observed before, the peak of the current wave is shifted to lower potential with the increasing length and so does the onset potential. This indicates that the reaction is significantly more efficient with the longer oligopeptides. It is important to note that despite the fact that the current is higher for the shorter oligopeptide, the ORR has a higher rate, as indicated by the peak in the CV curve. The results in Figs. 8A-8C and Figs. 9A-9C, clearly show that besides the spin polarization and the current there is another parameter that controls the ORR reaction. This conclusion is consistent with the results in Figs. 6A to 6D and Fig. 7 that point to the importance of an “hidden” factor that affects the reaction rate.

[0088] It is known that in the ORR, there are two separate channels for two different products that can take place. One is the formation of water, which is the lower energy path, and the second is the formation of hydrogen peroxide which is the high energy path. The results in Figs. 6A -6D and Fig. 7 and Table 1 indicate that there is correlation between the peak potential, the threshold potential and the hydrogen peroxide production. The higher the potential, the more hydrogen peroxide is formed. It is important to note that the reaction involves the transfer of two pairs of electrons. As was shown before, the correlation of the two spin directions in those electrons enhances the reaction and eliminates, to a large extent, the formation of hydrogen peroxide. However, there must be another factor that affects the reaction for rationalizing results presented above.

[0089] In the ORR, two pairs of electrons are transferred. The question is if the electrons in each pair interact with each other, and hence form a “triple state” of electrons that is inserted into the oxygen system, or the two electrons can be viewed as separated. In other terms, the question is if the two electrons are in a coherent state thus having a well-defined phase relation between them, or if the two electrons have no well-defined phase relation between them. To gain insight into this question the inventors performed calculations whose conclusions will be described below.

[0090] The model calculations clearly indicated that if the two electrons in each pair are coupled i.e., there is a coherent relation between them and they are entangled, namely form a “triplet state” then the reaction efficiency is larger as compared to two “independent” electrons that have the same spin.

[0091] Figs. 10A-10C show a schematic presentation of the ORR with its two paths and summarize the thickness-dependence of the reaction rate as shown in Figs. 5A-5C and Figs. 6A-6D. Fig. 10A shows that when the two electrons in each pair interact and form a coherent pair, the reaction is efficient as a result of a lowered barrier for the reaction and water is produced. Fig. 10B shows that when the two electrons are not coherent (presented as some delay in their approach), the reaction product is hydrogen peroxide, and Fig. 10C shows that the production of hydrogen peroxide is the high energy path that results from the two electrons not inserted coherently into the oxygen.

[0092] As the thickness of the chiral polymer increases, the spin polarization of the electrons increases, however the electrons undergo more collisions and hence lose their relative coherency. Namely, they reduce the oxygen as independent single electrons. As a result, for polymer thickness exceeding about 7 nm, the ORR rate decreases and hydrogen peroxide production increases.

[0093] If the results obtained with DNA and oligopeptides are compared, it is realized that although the spin polarization is about the same for the two types of molecules, the DNA layer is thicker and indeed one finds that the reaction is less efficient for the DNA than for the oligopeptides (Figs. 8A-8C and Table 2). The comparison between the two types of molecules also indicates that for DNA the longer oligomer shows slightly less efficient reaction, despite the spin polarization being higher. However, for oligopeptides, the reaction efficiency significantly increases with the longer oligomer. It is important to appreciate that while the longer oligopeptide is only 6nm long, in the case of DNA even a short molecule with about 40bp has a length of lOnm. Hence, the better reaction efficiency is clearly related to the fact that for the same spin polarization, the oligopeptides are much shorter and hence the coherency can be maintained.

[0094] This finding is especially interesting, since in proteins a-helices oligomers are one of the most important structural components and electron transport through them is an important feature in Biology and was found to depend on spins [7,8], Hence, one can conclude that the a-helix structure, while being an efficient spin filter, also maintains the electron coherency.

Claims

CLAIMS:

1. A method for controlling multi electrons spin selective reactions comprising: selecting a nanometric thickness of a chiral coating surface layer to provide spin-polarized coupled electrons, wherein the thickness of the chiral coating surface layer is below twenty nanometers; attaching the chiral coating surface layer of the selected thickness to an electrode surface; applying a potential difference between the electrode carrying the chiral coating surface layer and a counter-electrode so as to create transfer of charges between the electrodes and to provide spin-polarized coupled electrons, the attachment between said chiral coating surface layer and the electrode being configured for causing charge rearrangement, spin polarization of the electrode surface, controllably affecting coherent and entangled properties of the multielectrons being injected from or to the electrode surface thereby modifying the rate of the multi electrons spin selective reactions and product selectivity.

2. The method of claim 1, wherein attaching the chiral coating surface layer to the electrode surface comprises at least one of depositing, growing, adsorbing, or coating electrode surface.

3. The method of claim 1 or claim 2, wherein attaching the chiral coating surface layer to the electrode surface comprises adsorbing a thin layer of chiral polymer on an electrode.

4. The method of any one of the preceding claims, further comprising interacting between the electrode carrying the chiral coating surface layer on the electrode’s surface and oxygen dissolved in an electrolyte solution for producing water and hydrogen peroxide.

5. The method of any one of the preceding claims, wherein selecting a thickness of the chiral coating surface layer comprises determining a particular length of chiral molecules, chiral monolayers or chiral structures or specific thickness of the chiral layer.

6. The method of claim 4 or 5, further comprising interacting between the electrode carrying the chiral coating surface layer and anesthetic gases for enhancing formation of hydrogen peroxide.

7. A coating for electrodes for use in multi electrons spin selective reactions comprising a chiral coating surface layer, configured with a thickness being selected toprovide spin-polarized coupled electrons, control coherent and entangled properties of the multi spin-polarized electrons, thereby increasing reaction rate and product selectivity.

8. The coating of claim 7, wherein the thickness of the chiral coating surface layer is in the range of about 3 nm to 20 nm.

9. The coating of claim 7 or claim 8, wherein said chiral coating surface layer comprises a chiral polymer.

10. The coating of any one of claims 7 to claim 9, wherein an interaction between an electrode coated with said coating and oxygen dissolved in an electrolyte solution produces water and hydrogen peroxide.

11. The coating of claim 10, wherein the thickness of the chiral coating surface layer is selected by determining a particular length of chiral molecules, or thickness of the chiral layer enabling enhanced four-electron reduction of oxygen to produce water and reduced production of hydrogen peroxide.

12. The coating of any one of claims 9 to 11, wherein said chiral coating surface layer includes at least one of the following: oligopeptides, amino acids, DNA, helicenes, chiral conductive polymer, chiral oxides, and chiral metals.

13. The coating of any one of claims 7 to 12, wherein said chiral coating surface layer is either chemically bound to an electrode or physically adsorbed on it.

14. An electrode for controlling multi electrons spin selective reactions comprising a chiral coating surface layer attached on an electrode surface, wherein said chiral coating surface layer has a thickness being selected to cause charge rearrangement and spin polarization of the electrode surface, to thereby controllably affect coherent properties of the multi-electrons being injected from or to the electrode surface thereby modifying the rate of the multi electrons spin selective reactions and product selectivity.

15. The electrode of claim 14, wherein the thickness of the chiral coating surface layer on top of the electrode is in the range of about 3 nm to 20 nm.

16. The electrode of any one of claims 14 to 15, wherein the thickness of the chiral coating surface layer is selected by determining a particular length of chiral molecules or the thickness of the chiral layer.

17. The electrode of claim 16, wherein said particular length of chiral molecules is in the range of about 1.5 nm-6 nm.

18. The electrode of any one of claims 14 to 17, wherein said chiral coating surface layer includes at least one of the following: metal structures, oligopeptides, amino acids, DNA, helicenes, chiral oxide and chiral conductive polymer.

19. The electrode of any one of claims 14 to 18, wherein the chiral coating surface layer is either chemically bound to the electrode surface or physically adsorbed on it.

20. The electrode of any one of claims 14 to 19, wherein the thickness of the chiral coating surface layer is selected to cause alignment of the spins of transferred electrons released to oxygen from the electrode during oxygen reduction reaction to thereby create a spin specificity of the electrons transferred through said chiral system to oxygen, decreasing an overpotential of the oxygen reduction reaction and thereby enhancing a multielectron reduction of diatomic oxygen to produce water.

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