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United States Patent Application 20170335474
Kind Code A1
FLECHSIG; Gerd-Uwe November 23, 2017

ELECTROCHEMICAL SYNTHESIS METHOD AND DEVICE

Abstract

The present invention relates to a method for producing at least one product by electrochemical synthesis on a directly electrically-heated working electrode (1), in which at least one educt reacts on the heated working electrode (1) to the at least one product. The invention also relates to the use of a directly electrically-heated working electrode (1) for the electrochemical synthesis of at least one product. The invention relates in particular to a working electrode (1), particularly in the form of a three-dimensional, preferably conical spiral, designed for the electrochemical synthesis. Another object of the invention is the synthesis/regeneration of an enzymatic cofactor on a working electrode (1) according to the invention.


Inventors: FLECHSIG; Gerd-Uwe; (East Greenbush, NY)
Applicant:
Name City State Country Type

UNIVERSITAT ROSTOCK

Rostock

DE
Assignee: ; UNIVERSITAT ROSTOCK
Rostock
DE

Family ID: 1000002819715
Appl. No.: 15/514233
Filed: September 25, 2015
PCT Filed: September 25, 2015
PCT NO: PCT/DE2015/100403
371 Date: March 24, 2017


Current U.S. Class: 1/1
Current CPC Class: C25B 11/02 20130101; C25B 3/00 20130101; C25B 1/00 20130101
International Class: C25B 11/02 20060101 C25B011/02; C25B 3/00 20060101 C25B003/00; C25B 1/00 20060101 C25B001/00

Foreign Application Data

DateCodeApplication Number
Sep 26, 2014DE10 2014 114 047.8

Claims



1. A process for producing at least one product by electrochemical synthesis on a directly electrically heated working electrode (1) in which at least one educt reacts on the heated working electrode (1) to the at least one product.

2. The use of a directly electrically heated working electrode (1) for the electrochemical synthesis of at least one product, in which at least one educt reacts on the heated working electrode (1) to the at least one product.

3. The process of claim 1, wherein the working electrode (1) is directly heated by means of a symmetrical arrangement with a heating current in the form of an alternating current, wherein the symmetrical contacting preferably occurs via a bridge circuit (2).

4. The process of claim 1, wherein the electrochemically active surface area of the working electrode (1) comprises at least 1.times.10.sup.-6 m.sup.2, preferably 1.times.10.sup.-5 m.sup.2 or 1.times.10.sup.-4 m.sup.2.

5. The process of claim 1, wherein the reaction is selected from the group consisting of oxidation, reduction, protonation, deprotonation, substitution, hydrogenation, dehydrogenation, condensation, hydrolysis, addition, cleavage, cyclization, dimerization, polymerization and elimination.

6. The process of claim 1, wherein the product is selected from the group consisting of a protein comprising a nitro group, gluconic acid, sorbitol, D-arabinose, adiponitrile, a regenerated cofactor such as NAD+ or NADP+ and a product which is unstable at the reaction temperature on the working electrode (1).

7. The process of claim 1, wherein the reaction of the at least one educt to the at least one product is enzymatically catalyzed, wherein optionally the enzyme and/or a cofactor is immobilized on the heated working electrode (1).

8. The process according to claim 1, wherein a heating current in the form of an alternating current with a frequency of at least 1 kHz, preferably at least 20 kHz, more preferably at least 50 kHz or at least 100 kHz is used for heating the working electrode (1), and/or wherein the temperature of the working electrode (1) is increased pulse-like for up to 250 ms above the boiling point of the electrolytes surrounding the electrode.

9. A device comprising two insulated conductors (3) which are connected to one another via a working electrode (1) which is thinner in relation to the conductors, wherein the working electrode is a wire of an electrode material selected from the group comprising gold, platinum, copper, nickel, stainless steel, lead, Hg-amalgams, indium-doped tin oxide and carbon, wherein the working electrode (1) has the form of a three-dimensional spiral.

10. The device according to claim 9, wherein the spiral forms a conical spiral, preferably a conical Archimedean spiral or an Archimedean spiral coil, a loxodrome or a section of such a spiral.

11. A device comprising two insulated conductors (3) which are connected to one another via a plurality of working electrodes which are thinner in relation to the insulated conductors, wherein the working electrodes (1) are composed of an electrode material selected from the group comprising gold, platinum, copper, nickel, noble steel, lead, Hg-amalgams, indium doped tin oxide and carbon, wherein the working electrodes (1) are arranged so that no vertical superimposition takes place and that they (a) are preferably essentially parallel to one another, and/or (b) preferably extend from a lower contact point (5) with one of the insulated conductors (3) to an upper contact point (6) offset vertically and optionally horizontally with the other insulated conductor (3), wherein the working electrodes (1) extend outwardly from the lower contact point (5), extend obliquely upwards in an intermediate section and extend inwards in an upper section towards the upper contact point (6), wherein the inclination in the middle section is arranged so that no vertical superimposition of the working electrode sections (1) or the working electrodes (1) occurs.

12. The device according to claim 9, wherein the working electrode (1) is stabilized by an insulating carrier (7), wherein the insulating carrier (7) is preferably a cage or a grid, and/or wherein the insulating carrier (7) is preferably made of an insulating material selected from the group comprising glass, ceramic or plastic, e.g. Polytetrafluoroethylene (PTFE).

13. The device according to claim 9, wherein the working electrode has a surface area of at least 1.times.10.sup.-5m.sup.2, preferably 5.times.10.sup.-5m.sup.2 or 7.times.10.sup.-5m.sup.2, and/or a diameter of 0.1-5 mm and/or a length of 2.5-100 mm and/or a resistance of 0.5-20 Ohm.

14. The device according to claim 9, wherein the working electrode (1) is directly heated by means of a symmetrical arrangement with a heating current in the form of an alternating current, wherein the symmetrical contacting preferably occurs via a bridge circuit (2).

15. The device according to claim 9, wherein the counterelectrode is arranged with a distance of at least 1 mm, preferably at least 5 mm, relative to the working electrode, such that the thermal convection around and above the working electrode does not lead to a mixing of the space around the counterelectrode, preferably the counterelectrode is located under the working electrode.

16. The process of claim 1, wherein the reaction proceeds at the directly heated working electrode of a device comprising two insulated conductors (3) which are connected to one another via a working electrode (1) which is thinner in relation to the conductors, wherein the working electrode is a wire of an electrode material selected from the group comprising gold, platinum, copper, nickel, stainless steel, lead, Hg-amalgams, indium-doped tin oxide and carbon, wherein the working electrode (1) has the form of a three-dimensional spiral.

17. A process for the synthesis or regeneration of a cofactor of an enzymatic reaction, wherein the synthesis or regeneration takes place on a directly electrically heatable working electrode, preferably on the directly heated working electrode of a device according to claim 9.

18. The use of claim 2, wherein the working electrode (1) is directly heated by means of a symmetrical arrangement with a heating current in the form of an alternating current, wherein the symmetrical contacting preferably occurs via a bridge circuit (2).

19. The use of claim 2, wherein the electrochemically active surface area of the working electrode (1) comprises at least 1.times.10.sup.-6 m.sup.2, preferably 1.times.10.sup.-5 m.sup.2 or 1.times.10.sup.-4 m.sup.2.

20. The use of claim 2, wherein the reaction is selected from the group consisting of oxidation, reduction, protonation, deprotonation, substitution, hydrogenation, dehydrogenation, condensation, hydrolysis, addition, cleavage, cyclization, dimerization, polymerization and elimination.

21. The use of claim 2, wherein the product is selected from the group consisting of a protein comprising a nitro group, gluconic acid, sorbitol, D-arabinose, adiponitrile, a regenerated cofactor such as NAD+ or NADP+ and a product which is unstable at the reaction temperature on the working electrode (1).

22. The use of claim 2, wherein the reaction of the at least one educt to the at least one product is enzymatically catalyzed, wherein optionally the enzyme and/or a cofactor is immobilized on the heated working electrode (1).

23. The use according to claim 2, wherein a heating current in the form of an alternating current with a frequency of at least 1 kHz, preferably at least 20 kHz, more preferably at least 50 kHz or at least 100 kHz is used for heating the working electrode (1), and/or wherein the temperature of the working electrode (1) is increased pulse-like for up to 250 ms above the boiling point of the electrolytes surrounding the electrode.

24. The use of claim 2, wherein the reaction proceeds at the directly heated working electrode of a device comprising two insulated conductors (3) which are connected to one another via a working electrode (1) which is thinner in relation to the conductors, wherein the working electrode is a wire of an electrode material selected from the group comprising gold, platinum, copper, nickel, stainless steel, lead, Hg-amalgams, indium-doped tin oxide and carbon, wherein the working electrode (1) has the form of a three-dimensional spiral.
Description



[0001] The present invention relates to a method for producing at least one product by electrochemical synthesis on a directly electrically-heated working electrode (1), in which at least one educt reacts on the heated working electrode (1) to the at least one product. The invention also relates to the use of a directly electrically-heated working electrode (1) for the electrochemical synthesis of at least one product. The invention relates in particular to a working electrode (1), particularly in the form of a three-dimensional, preferably conical spiral, designed for the electrochemical synthesis. Another object of the invention is the synthesis/regeneration of an enzymatic cofactor on a working electrode (1) according to the invention.

[0002] In the prior art, heated working electrodes are used for trace analysis in voltammetry, amperometry/coulometry and potentiometry, and they can, for example, be directly heated by means of alternating current or indirectly by means of alternating current or direct current.

[0003] In the case of indirect heating, the working electrode can be constructed from several concentric or parallel layers, which are galvanically separated from one another, the outermost layer serving as an electrode and an inner layer serving as a heating element. Indirect heating by means of heaters galvanically separated from the electrode is disadvantageous, because the construction of the sensors is more complicated, the temperature changes are generally slower because of the thermal inertia (due to the heat capacity) of the different layers, and the possibilities for miniaturization are limited.

[0004] Various directly-heatable working electrodes, in which the heating current as well as the electrolysis current, i.e., the current for the electrochemical measurement signal, flow together through the same conductor, are known from the prior art.

[0005] Direct electrical heating of the working electrode and simultaneous interference-free electrochemical measurement can be performed according to the prior art by a so-called symmetrical arrangement or special filter circuits. One variant of the directly-heated working electrode has a third contact for connection to the electrochemical measuring device, situated precisely in the middle between the two contacts which supply the heating current. This arrangement prevents interfering influences of the heating current on the measuring signals. A disadvantage is the complex design with three contacts per working electrode, the thermal disturbance due to the heat-dissipating third contact and the complicated miniaturization. In a preferred embodiment according to the invention, therefore, a symmetrical contacting is effected by means of a bridge circuit, which allows direct heating (Wachholz et al., 2007, Electroanalysis 19, 535-540, in particular FIG. 3; Dissertation Wachsholz 2009). Thereby, the working electrode can be arranged so that the temperature distribution on the surface of the working electrode is uniform (DE 10 2004 017 750). DE 10 2006 006 347 discloses advantageous directly electrically heatable electrodes.

[0006] According to the prior art, there are various kinds of directly heated working electrodes and arrays. The oldest variant of a single electrode is based on circuit boards which have corresponding recesses (wide slots) and an electrical insulation with a paraffin-PE mixture. Here, wire electrodes of gold or platinum are typically soldered. The wire diameter is usually 25 micrometers (P. Grundler et al., Chem. Phys. Chem. 10 (2009) 559).

[0007] In addition, layered electrodes and arrays have been proposed. Printed circuit boards, glass, and plastic were specified as substrates.

[0008] In all layered constructions, there is the disadvantage that the electrolyte solution cannot circulate freely around the electrode (limited micro-stirring effect, temperature and diffusion field are deformed) and that a considerable portion of the heat is used for heating the substrate and so is lost. This also leads to slowed heating and cooling of the working electrode due to the heat capacity of the substrate.

[0009] The disadvantage of the previous wire electrodes was, above all, that either no microliter droplets could be deposited on them or that a construction with an additional plastic bar was used in which the electrode construction (with respect to the printed circuit board) had to be vertical. (Flechsig et al., Langmuir 21 (2005) 7848). An array construction in this way was hardly conceivable.

[0010] It was also disadvantageous that previous electrode arrays of layered working electrodes always consisted of identical electrode material in each case. A design consisting of a plurality of different electrode materials (for example, gold, silver and platinum working electrodes on an array) would have involved high production costs (sputtering, evaporation, screen printing with many changing masks).

[0011] According to the state of the art, there are also array-like devices with a plurality of wire-shaped working electrodes which are to be independently heated, and which enable interference-free electrochemical measurement while simultaneously electrically-heating the electrodes, whereby the electrolyte solution can circulate freely around the electrodes. The materials of the working electrodes can vary within an array. Similar to a conventional flat array, microliter drops can be deposited on the electrodes and surround them (WO 2013/017635).

[0012] In order to carry out electrochemical analyses in the trace range, microelectrodes heated as in the prior art can be used. The working electrode must therefore be small in order to keep the mass conversion negligibly small, thus avoiding changes in the analytical solution, which is a prerequisite in analytical voltammetry and amperometry, and also in order to comply with the working range of the potentiostat-galvanostat.

[0013] In order to be able to carry out electrochemical syntheses at elevated temperatures, electrochemical cells are generally used which are brought to the desired temperature by means of a thermostat with water as heat exchanger. The entire quantity of electrolyte is heated in the process. A platinum electrode is generally used as the working electrode, as a cylinder of 3 cm in diameter and 5 cm in length.

[0014] In electrochemical syntheses, the problem arises for the skilled worker that firstly, a large amount of energy is needed to heat the entire solution, secondly, the temperature changes are very slow, and thirdly, sensitive substances can be affected in the electrolyte solution. It is therefore an object of the invention to provide a device and a method to enable an electrochemical synthesis with a large conversion of material which reduces or at least partially overcomes the above-mentioned problems.

[0015] This object is achieved by the present invention, in particular by the subject matter of the claims.

[0016] The invention provides a process for producing at least one product by electrochemical synthesis on a directly electrically-heated working electrode (1), in which at least one educt reacts on the heated working electrode (1) to the at least one product. The invention also provides the use of a directly electrically-heated working electrode (1) for the electrochemical synthesis of at least one product, in which at least one educt reacts on the heated working electrode (1) to the at least one product.

[0017] The working electrode (1) can be directly heated by means of a symmetrical arrangement with a heating current in the form of an alternating current, wherein the use of a bridge circuit, as described above, is particularly advantageous. The symmetrical contacting and direct heating of the working electrode (1) can therefore be effected by means of, for example, the bridge circuit disclosed in Wachholz et al., 2007, Electroanalysis 19, 535-540, in particular FIG. 3. In particular, the working electrode (1) can have a first and a second contact for supplying the heating current, wherein the working electrode (1) is connected to a potentiostat via a third contact, wherein the connection of the third contact to the working electrode (1) is formed via a bridge circuit (2), which is connected to the first and second contact. Suitable circuits are disclosed, for example, in DE 2006 006 347.

[0018] In order to heat the working electrode, a heating current in the form of an alternating current can be used, in particular with a frequency of at least 1 kHz, preferably at least 20 kHz, more preferably at least 50 kHz or at least 100 kHz.

[0019] The electrochemically active surface of the working electrode (1) preferably comprises at least 1.times.10.sup.-6 m.sup.2, applicable for instance for syntheses on a micro-scale, preferably 1.times.10.sup.-5 m.sup.2 for instance on the half-micron scale or 1.times.10.sup.-4 m.sup.2 for instance on the larger laboratory scale. Electrochemically-active surfaces up to an area of one or several square meters are also possible.

[0020] The fact that the volume elements of the electrolyte solution are heated only very briefly when they come into contact with the working electrode (1) is particularly advantageous in the process according to the invention, the educts being converted electrochemically at the desired elevated temperature. Even undesired subsequent reactions at high temperature can be minimized by the rapid cooling of each volume element due to thermal convection. Thus, only the electrochemical reaction takes place at elevated temperature. There is a method for chemical reaction in the gas phase in a very limited, very hot zone: see air combustion in the electrical arc according to the Birkeland-Eyde method (1904, U.S. Pat. No. 775,123), which describes similar considerations.

[0021] A process according to the invention can be used advantageously for various electrochemical syntheses, for example for oxidation, reduction, substitution, dehydrogenation, addition, cleavage, cyclization, dimerization, polymerisation, protonation, deprotonation or elimination.

[0022] The at least one product of the reaction may be, for example, a protein comprising a nitroso group, gluconic acid, sorbitol, D-arabinose, adipodinitrile, a regenerated cofactor such as NAD+ or NADP+. It is particularly advantageous if the product of the synthesis is a product which is unstable at the reaction temperature at the working electrode (1), since in this case the product is exposed to this temperature only for a minimal time. After synthesis on the heated working electrode, the product diffuses into the electrolyte, which itself is not heated to the reaction temperature. Unstable in this context means that the stability at the reaction temperature is lower than the stability at a lower temperature (e.g., room temperature or 4.degree. C.), especially for an, e.g. three- or ten-fold, lower stability relative to the difference in the reaction rate. The stability may be analyzed by, e.g. half-life. It is possible to cool the electrolyte solution if this promotes the stability of the educt or product or the course of the reaction.

[0023] Within the scope of the present invention, the indefinite article "an/a" also includes "two/more", unless it is clearly understood from the context to be otherwise. In particular, an electrochemical synthesis can for example proceed via a reaction of two educts to form one or two product(s) or via a reaction of one educt to form two products.

[0024] In a further advantageous embodiment, the reaction of the at least one educt to the at least one product can also be enzymatically catalyzed, wherein optionally the enzyme and/or a necessary cofactor is immobilized on the heated working electrode (1). However, the educt(s), enzyme and/or cofactor can also be homogeneously distributed in the electrolyte solution. In one embodiment, a synthesis reaction takes place from at least one product catalyzed by an enzyme that requires a cofactor such as NAD+ or NADP+. The regeneration of the cofactor, which is necessary for a continuation of the reaction, takes place at the working electrode. In the case of enzymatic catalysis it is, of course, also possible to synthesize a product which is unstable at the reaction temperature.

[0025] In an embodiment which is particularly suitable for reactions concerning thermally highly sensitive substances or in which reaction products otherwise deposit on the working electrode, the temperature of the working electrode can be pulse-like for up to 300 ms, e.g. about 5-250 ms, 50-200 ms or 100-150 ms, but preferably less than 100 ms, above the boiling point of the electrolytes surrounding the electrode. This has the advantage that only a small portion of the solution is heated for a short period of time. The thermal convection occurring briefly after the heating pulse makes stirring of the solution unnecessary. In addition, the short period of heating is beneficial for the stability of educts and products and, if applicable, of enzymes which catalyze the reaction. In the case of unstable educts or products, this advantage plays an important role. Furthermore, any deposits on the working electrode are removed so that the latter cleans itself.

[0026] The process according to the invention makes it possible to monitor the material conversion of the reaction coulometrically. In particular, coulometric tracking of the faraday mass conversion of a synthesis reaction is possible by measuring the electrolyte current strength and calculating the charge quantity/substance quantity as an integral of the current over time.

[0027] The invention also relates to a device which comprises two insulated conductors (3) which are connected to one another via a working electrode (1) which is thinner in relation to the conductors, the working electrode (1) being formed as an anode from an electrode material such as a wire of noble metal, in particular gold or platinum; or a rod of carbon, for example graphite, boron-doped diamond or glass-carbon; or optically transparent conductive material, such as ITO (indium-doped tin oxide) (an electrode material), preferably gold or platinum, wherein the working electrode (1) is preferably in the form of a spiral, more preferably a three-dimensional spiral. In addition to the materials mentioned, less noble metals such as copper, stainless steel or nickel can also be used as the cathode material.

[0028] The insulated conductors (3) can be, e.g. copper rods or other good electrical conductors, which are insulated, e.g. by a glass tube or by a plastic sheath, as is known in the art.

[0029] In a circular cylinder, a flat Archimedian spiral can be placed on the ground and a screw (or helix) can be fitted into the shell as a curve. The overlap curve of the spiral and screw is referred to as a conical spiral or cone-shaped space spiral. In an Archimedian spiral, the distance to the center increases linearly to the increasing angle of its orbit. If this distance is projected as an angular distance to a pole on a spherical surface, an Archimedian spherical spiral is created. It is a line of finite length, and is not identical with the loxodrome, which by its construction method resembles the logarithmic spiral (Source: Wikipedia, see also FIG. 1). A central axis can be thought of through the center of the spiral.

[0030] These spiral shapes can be used in the context of the invention. Advantageously, the spiral is a conical spiral, in particular a conical Archimedeal spiral or an Archimedean spherical spiral or a loxodrome. A section of such a spiral is sufficient, in particular in the case of spherical spirals, it is even preferred to use only a section which increases or decreases (i.e. not increases and then decreases) in diameter. Irregular spiral shapes are also possible. A particularly advantageous embodiment is shown in FIG. 2.

[0031] In any case, a sufficient distance between sections of the working electrode (1) should be ensured in order to prevent short circuits. A distance of about 1 to about 20 mm, preferably about 5 to about 15 mm or about 8 to about 10 mm, is useful. The spacing is preferably uniform within the spiral. The electrical contact points between the working electrode (1) and the insulated conductors (3) can be located approximately in the middle, i.e. on or near the central axis of the spiral. In this case, the lower and upper contact points (5, 6) are preferably slightly laterally offset from one another. The contact point, which is connected to the outermost side of the spiral most remote from the axis, can also be situated along the outer side of the spiral. If the connection of this contact point is situated within the spiral, an isolation up to the contact point on the outermost side of the spiral most remote from the axis can lead to an even more uniform temperature, above all at the nearest lowest turn. Preferably, the three-dimensional spherical working electrode is oriented with respect to the insulated conductors and, as the case may be, the further structure of the device, such that the diameter of the spiral decreases from the bottom to the top.

[0032] When the spiral working electrode is vertically aligned along its central axis in the preferred three-dimensional spiral shape, and the device is used for electrochemical synthesis, the working electrode is hardly, or at best is not, vertically superimposed. Therefore, through heating of the working electrode the heated electrolyte solution does not meet overlying sections of the working electrode and additionally heat them. This ensures a uniform temperature of the working electrode, which is important for the course of the synthesis.

[0033] The same effect can be achieved with a further device according to the invention which comprises two insulated conductors (3) which are connected to one another via a plurality of working electrodes (1) which are thinner in relation to the insulated conductors, wherein the working electrodes (1) are formed as an anode of a wire of noble metal, in particular gold or platinum; or a rod of carbon, for example graphite, boron-doped diamond or glass-carbon; or optically transparent conductive material such as ITO (indium-doped tin oxide) (an electrode material). In addition to the materials mentioned, less noble metals such as copper, stainless steel or nickel can also be used as the cathode.

[0034] The working electrodes (1) are arranged so that no vertical superimposition of the working electrodes (1) takes place and that they

[0035] (a) are preferably essentially parallel to one another, and/or

[0036] (b) preferably extend from a lower contact point (5) with one of the insulated conductors (3) to an upper contact point (6) offset vertically and optionally horizontally with the other insulated conductor (3), wherein the working electrodes (1) extend outwardly from the lower contact point (5), extend obliquely upwards in an intermediate section and extend inwards in an upper section towards the upper contact point (6), wherein the inclination in the middle section is arranged so that no vertical superimposition of the working electrode sections (1) or the working electrodes (1) occurs.

[0037] One embodiment is particularly advantageous when carbon is used as the electrode material, e.g. glass carbon or graphite, for example in the form of a rod. In this case, the working electrode essentially has a stepladder-like shape, as in the case of a rung wall, the struts of which form the insulated conductors (3) and which are set obliquely in order to prevent a vertical superposition of the working electrodes (rungs). For example, parallel glass charcoal or graphite rods, which are arranged ladder-like, but obliquely. These parallel rods are connected by insulated conductors, resulting in a grid-shaped working electrode. The rods can be fixed, e.g. by attachment to an insulating grid or cage. The grid or cage can be a stretched, e.g. a flat or e.g. cylindrical, shape. Also, the use of screen printing electrodes e.g. of carbon in parallel form, is possible.

[0038] It may be useful in an apparatus according to the invention to stabilize the working electrodes (1) by means of an insulating carrier (7). The insulating carrier (7) can, for example, be a cage or a grid. Preferably, free circulation of the electrolyte by the support (7) is not severely restricted. The insulating support preferably consists of or comprises an insulating material, the material being glass, ceramic or plastic, e.g. Polytetrafluoroethylene (PTFE, Teflon.RTM.). If sufficient stability is ensured by the material and the shape of the electrode (1), the use of a carrier is not necessary.

[0039] The use of a two-dimensional working electrode in the method of the invention is also possible. No vertical superposition occurs here either, so that a uniform temperature distribution is possible.

[0040] Preferably, the working electrode (1) has a surface area of at least 1.times.10.sup.-6 m.sup.2, preferably 1.times.10.sup.-5 m.sup.2 or 1.times.10.sup.-4 m.sup.2. The diameter may be e.g. about 0.05-5 mm, preferably 0.1-1 mm. The length may be about 2.5-100 cm, preferably 5-50 cm, 10-40 cm, 15-30 cm or 20-25 cm. The length depends on the cross-sectional area and the specific resistance of the electrode material, so that a reasonable resistance range is maintained: the resistance between the two heating current contacts (5) and (6) should be determined, e.g. approximately 0.5 to 20 Ohm, preferably 1 to 10 Ohm. In this way, the voltage drop between the contacts is on the one hand not too great, on the other hand, the resistance can still be easily measured by means of electronics, and thus the heating power can be automatically regulated (Flechsig, Grundner, Wang, 2004, EP 1743173, DE 10 2004 017 750 B4).

[0041] Example: the platinum working electrode has a resistance of 2 Ohm and a length of 10 cm. Then the diameter must be 82.2 microns. The electrode surface is then 25.8 mm.sup.2 as a cylinder jacket surface.

[0042] With a diameter of 1 mm, the electrode length would have to be 14.4 m, resulting in an electrode surface of 446 cm.sup.2. That would be pilot plant scale.

[0043] Preferably, the working electrode (1) in the device according to the invention is directly heated by means of a symmetrical arrangement with a heating current in the form of an alternating current. The symmetrical contacting preferably occurs via a bridge circuit (2), as explained above. A symmetrically arranged inductance is provided in the connecting arms of the bridge circuit (7). By means of the bridge circuit, the working electrode (1) can be connected with a galvanostat or a potentiostat, a reference electrode (REF) and a counterelectrode (AUX) which either functions as an anode or a cathode, depending on whether a reduction or an oxidation is running on the working electrode. This galvanostat or potentiostat can also be a simpler power supply device with a two-pole output, on the displays of which only the decomposition voltage between the working electrode and the counterelectrode, as well as the electrolysis current, are indicated.

[0044] Preferably, the counterelectrode (AUX) in the device according to the invention is arranged with a distance to the working electrode of at least 1 mm, preferably at least 5 mm, so that the thermal convection around and above the working electrode does not lead to a mixing of the space around the counterelectrode, preferably it is beneath the working electrode. This avoids the reverse reaction of the product to the educt at the counterelectrode. In addition, unwanted products are prevented from coming from the counterelectrode to the working electrode. Examples include in particular the halogens chlorine and bromine, but also oxygen and others. For example, it may be desirable to carry out a cathodic reduction in a chloride-containing solution at a strongly negative potential. This would result in the oxidation of the chloride to chlorine at the counterelectrode as an anode and, depending on the pH value, also the formation of hypochloride. In this situation, it is advantageous if the two electrode spaces are separated from one another, for which purpose membranes and diaphragms are used. This is also possible within the scope of the invention. However, the use of the limited thermal convection according to the invention makes such a separation by diaphragms or membranes superfluous, so that the device according to the invention preferably does not comprise diaphragms or membranes.

[0045] For support, one can place a cooler at the bottom of the cell, e.g. a cooling Peltier element.

[0046] In an embodiment of the working electrode (1) according to the invention, the device can comprise the components shown in FIG. 2 of the present application. It can also comprise the components shown in DE 10 2006 006 347, FIG. 1, FIG. 2, FIG. 3 or FIG. 4 (preferably FIG. 1) in a corresponding arrangement.

[0047] In a particularly preferred embodiment of the method according to the invention, the reaction proceeds on the directly heated working electrode of a device according to the invention, in particular a device comprising two insulated conductors (3) which are connected to one another via a working electrode (1) which is thinner in relation to the conductors, wherein the working electrode (1) is a wire of an electrode material such as gold, platinum and carbon (e.g. graphite, boron doped diamond or glass carbon) or ITO (as anode or cathode) or even less noble metals such as copper, stainless steel or nickel (as cathode), the working electrode (1) having the form of a spiral, preferably a three-dimensional spiral.

[0048] The invention also relates in particular to a process for the synthesis or regeneration of a cofactor of an enzymatic reaction in which the synthesis or regeneration takes place on a directly electrically heatable working electrode, preferably on the directly heated working electrode of a device according to the invention. It is also preferable to use a device which comprises two insulated conductors (3) which are connected to one another by means of a thinner working electrode (1) in relation to the conductors, the working electrode (1) being a wire of an electrode material such as gold, platinum and carbon (e.g. graphite, boron-doped diamond or glass-carbon) or ITO (as anode or cathode) or even less noble metals such as copper, stainless steel or nickel (as cathode), wherein the working electrode (1) is in the form of a spiral, preferably a three-dimensional spiral.

LEGENDS

[0049] FIG. 1 shows various forms of spirals. (A) conical Archimedean spiral (B) conical logarithmic spiral; in each case viewed obliquely from the side. (C, D) View of a working electrode (1) in the form of a conical Archimedean spiral from above. The insulated conductors (3) are shown as thick dots. (C) shows both insulated conductors (3) in the center of the spiral, (D) shows the insulated conductors (3) with one connected to the outer side of the spiral.

[0050] FIG. 2 shows a preferred embodiment of a device according to the invention, with a working electrode (1) shaped as a conical Achimedean spiral. The working electrode (1) is connected to insulated conductors (3) at a lower (5) and an upper (6) contact point. The working electrode (1) is directly electrically heatable via a symmetrical arrangement, with alternating current (AC), preferably at least 50 kHz, being used as the heating current. The symmetrical contacting is effected by means of a bridge circuit (2). A symmetrically arranged inductance is provided in the connection arms of the bridge circuit (7). By means of the bridge circuit, the working electrode (1) is or can be connected with a galvanostat or a potentiostat, a reference electrode (REF) and a counterelectrode (AU/AUX), which functions either as an anode or a cathode, depending on whether a reduction or an oxidation takes place at the working electrode. This galvanostat or potentiostat can also be a simple power supply device with a two-pole output, on whose displays merely the decomposition voltage between the working electrode and the counterelectrode, as well as the electrolytic current, are indicated.

EXAMPLES

Example 1

[0051] According to the invention, a large area of the directly heatable working electrode (1) for electrochemical synthesis can be achieved in that a very long wire e.g. out of platinum or gold, or else parallel thin carbon rods, can be used as working electrodes. The working electrode is contacted at the ends as in the prior art, whereby a heating current of preferably at least 1000 Hz frequency, advantageously at least 20 kHz, more preferably 50 kHz, is used so that a bridge circuit or a choke filter circuit known per se for separating the electrochemical circuit from the heating circuit can be used.

[0052] (A) A Pt wire of, for example, 5 cm in length and 0.1 mm in diameter can be spirally wound onto a cylindrical or preferably conical insulating cage made of glass, plastic or ceramic. Such a working electrode can be used, e.g. in a reagent glass, as a cell for electrochemical synthesis.

[0053] B) A working electrode of platinum has a resistance of 2 ohm and a length of 10 cm. Its diameter is 82.2 microns. The electrode surface area is 25.8 mm.sup.2 as the cylinder surface area.

[0054] C) With a diameter of 1 mm, the electrode length is 14.4 m, resulting in an electrode surface area of 446 cm.sup.2. This already allows for syntheses e.g. in a 10 to 100 L reactor, that is, in pilot-plant scale.

[0055] A wire e.g. of platinum of 1440 cm in length and 1 mm in diameter has an advantageous heating resistance of 1 to 20, preferably 2 to 10 Ohms, and can be used in a larger cell, e.g. in the pilot-plant scale. Advantageously, as the cage and the turns become smaller in diameter (conical rather than cylindrical), the working electrode thus has the shape of a conical spiral. This optimizes thermal convection and achieves a uniform temperature control of the working electrode. The electrochemical contact is located in the center, as shown in FIG. 2.

Example 2

[0056] A device according to the invention is used for

[0057] a) Selective oxidation of free amino groups to nitroso groups in proteins.

[0058] b) Oxidation of aldehyde groups in sugars to gluconic acid by an electrochemically prepared oxidizing agent (e.g., hypobromide of bromide), wherein e.g. heated carbon rod electrodes of graphite or glass-carbon can be used.

[0059] c) Coulometric tracking of the faraday mass conversion of a synthesis reaction by measuring the amount of electrolysis and calculating the charge quantity/substance quantity as an integral of the current over time.

[0060] d) For electrochemical recovery of chlorate from a solution of sodium chloride, the solution must be heated to effect the disproportionation of the primary hypochlorite. Classically, the entire electrolyte solution is heated for this purpose. According to the invention, only the working electrode is heated from directly heated glass carbon rods, wherein simultaneously the solution is thermoconvectively stirred. External stirring and heating are therefore not required. Yield and energy efficiency are improved.

Example 3

[0061] An array of electrolysis cells in combinatorial synthesis or parallel synthesis for the screening of active substances and tests of enzyme variants.

[0062] The electrolysis cells can be structurally separated from one another or can share a common cell space. The latter permits the simultaneous study of immobilized enzymes in biocatalytic electrosynthesis at the respective electrode temperature; the evaluation being carried out by means of the measurement and evaluation of the electrolysis current. Cooling from the outside is particularly important for small cell volumes, in order to keep the electrolyte temperature constant at the desired value. Active cooling by Peltier elements can be helpful. Coolers from above also support thermal convection.

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