- Email: [email protected]
Surface chirality effects induced by magnetic fields
Accepted Manuscript
Surface chirality effects induced by magnetic fields I. Mogi , R. Morimoto , R. Aogaki PII: DOI: Reference:
S2451-9103(17)30137-0 10.1016/j.coelec.2017.09.029 COELEC 134
To appear in:
Current Opinion in Electrochemistry
Received date: Revised date: Accepted date:
18 August 2017 26 September 2017 26 September 2017
Please cite this article as: I. Mogi , R. Morimoto , R. Aogaki , Surface chirality effects induced by magnetic fields, Current Opinion in Electrochemistry (2017), doi: 10.1016/j.coelec.2017.09.029
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Highlights Magnetohydrodynamic (MHD) effects in electrodeposition under magnetic fields
Macroscopic spiral and helical structures in magnetoelectrodeposition
Micro-MHD vortices induce surface chirality on electrodeposit films
Chiral symmetry in rotational magnetoelectrodeposition
AC
CE
PT
ED
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Review Article Surface chirality effects induced by magnetic fields I. Mogi1,*, R. Morimoto2 and R. Aogaki3
The most striking effect of magnetic field on electrochemical systems is the magnetohydrodynamic
CR IP T
(MHD) one. The MHD convections produced spiral and helical structures in electroless and electrodeposition. Thereafter, chiral surface formation has been explored in the electrodeposition of metal films under magnetic fields, and the chiral surfaces were found in silver and copper films, which could recognize the enantiomers of chiral molecules such as glucose and amino acids. Considering the mechanisms of such chiral surface formation would lead to a clue for the homochiral molecular evolution.
AN US
Address 1
Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan,
2
Saitama Waterworks Bureau, Misato 341-0028, Japan,
3
M
Polytechnic University, Sumida-ku Tokyo 130-0026, Japan
Corresponding author: Mogi, I. ([email protected])
ED
Introduction
Surfaces of metals and minerals are often used as catalysts in many kinds of chemical reactions. When
PT
such surfaces have chirality, they could serve as enantioselective catalysts [1-4], which are significant in pharmaceutical processes. In the viewpoint of molecular evolution towards the birth of life, the mineral
CE
surfaces played crucial catalytic roles in the formation reactions of amino acids under oceans on the early earth [5,6]. If such catalytic surfaces were chiral, the amino acids would be no longer racemic. Hence, the
AC
studies on chiral surface formation are significant not only for the development of chiral catalysts but also for the origin of homochirality in biochemistry.
In the past two decades, electrodeposition under magnetic fields (magnetoelectrodeposition; MED) has been found to produce chiral structures in metal deposits and deposit surfaces. The first part of this review describes the brief history of the findings of chiral structures in the MED processes, and the second part focuses on the chiral surface formation of metals.
Macroscopic chiral structures in magnetoelectrodeposition
ACCEPTED MANUSCRIPT
In MED processes, the Lorentz force acting on ionic currents causes magnetohydrodynamic (MHD) convections in the electrolytic solutions [7-9]. The MHD convections produce spiral structures in the zinc dendrites in a thin-layer electrolytic cell [10-12]. The spiral patterns were observed even in the electroless deposition of silver [13, 14], where the Lorentz force acting on the currents in the growing branches forces to tilt the branches. A similar spiral structure was observed in the magneto-electropolymerization
CR IP T
(MEP) of a conducting polymer polypyrrole [15]. In the three-dimensional growth of metal-silicate membrane tubes, so-called ‘chemical garden’, the MHD flow produces two types of helical growth; the membrane tube itself is twisted helically, and such a twisted tube grows helically along the inner wall of tube vessel [16,17]. These spiral and helical structures are in macroscopic scales of mm – cm, and the chirality of each growth definitely depends on the magnetic field polarity. These facts demonstrate that
AN US
the MED has the potential to induce chirality in the electrodeposits.
The next target of chiral structures spontaneously shifted to the induction of molecular-scale chirality. The first attempt was conducted in the MEP of a conducting polymer polyaniline [18,19]. Polyaniline tends to form a helical structure [20-22], however, the chirality of each helical chain cannot be controlled
M
without chiral dopants or templates. In the electropolymerization processes the electrons transport from the front to the substrate electrode within the chain. Under magnetic fields, the Lorentz force is expected to act on the currents and induce the unbalanced distribution between the right- and left-handed helical
ED
chains. To examine the chirality of polyaniline films, the MEP films were employed as a modified electrode, and the voltammograms of the enantiomers of ascorbic acid were measured. The MEP film
PT
electrodes showed different oxidation currents between the enantiomers, and the films prepared under the reverse magnetic fields exhibited the opposite chirality [18]. This fact means that the MEP polyaniline
CE
films possess chirality and recognize the molecular chirality of ascorbic acid.
AC
Micro-MHD effect
The finding of chirality in the MEP polyaniline films encouraged the exploration of surface chirality in the MED of metal films. In general, one of typical growth mechanisms of deposit films is screw dislocation growth [23]. The screw dislocation is a chiral site, and the distributions of the right- and left-handed sites are usually the same. If the MHD convections could affect the formation of screw dislocation, the surface chirality would be induced.
When magnetic fields are imposed perpendicularly to the electrode surface, two types of MHD flows are excited [24,25], as shown in Fig. 1. The one is the macroscopic MHD flow around the electrode edge,
ACCEPTED MANUSCRIPT
where the ionic currents are not parallel to the magnetic fields. This is termed as vertical MHD flow. Another is a micro-MHD vortex around local bumps and dents formed by non-equilibrium fluctuation in electrodeposition. The surface morphologies of the MED films exhibited micro-circular and network structures [24, 26-29], suggesting the existence of micro-MHD vortices. Recently, the micro-MHD vortices were visualized in the MED of silver, using light-reflective guanine micro-crystals as a fluid
CR IP T
tracer [30].
The self-organized state of micro-MHD vortices consist of both clockwise and anticlockwise flows such that the adjoining flows never conflict with each other. Such a symmetric state produces racemic chiral sites, leading to achiral surfaces. Aogaki and Morimoto proposed that the micro-MHD vortices could affect the formation of screw dislocations [25]. To produce chiral surfaces, some symmetry breaking is
AN US
necessary in the micro-MHD vortices. Fortunately, the vertical MHD flow could make considerable influence on the micro-MHD vortices: The micro-MHD vortices are stable if the vorticity has the same sign as the vertical MHD flow, whereas anticyclonic vortices become unstable [31, 32]. Thereby, the
M
symmetry in the micro-MHD vortices is broken, and then the chiral surface could be formed.
Considering the solution viscosity and the friction against the film surface, there remains a question that it is impossible to excite nanometer-scale vortices. Aogaki proposed a breakthrough mechanism with a
ED
concept of ionic vacancy [33,34]: The electrodeposition process generates ionic vacancies with sizes smaller than 1 nm, which extremely decrease the viscosity and the friction, leading to the excitation of
PT
nanometer-scale MHD vortices. The existence of ionic vacancies was supported by the observation of
CE
micro-bubbles arising from the aggregation of ionic vacancies [35, 36].
Surface chirality in magnetoelectrodeposited metal films
AC
Chiral surface formation was explored in the potentiostatic MED of silver [37] and copper [29,38]. The surface chirality of the MED films was examined by the voltammetric measurements of enantiomers of chiral molecules. The silver MED films exhibited chiral behavior for the oxidation reaction of glucose enantiomers [37]. In the copper MED, the film thickness dependence of surface chirality was studied for the oxidation reaction of an amino acid alanine [38]. The surface chirality could be detected at the film thickness of 100 – 400 nm. In the thinner film formation, the non-equilibrium fluctuation does not develop sufficiently, causing no micro-MHD effects. On the other hand, in the thicker film formation, the non-equilibrium fluctuation becomes dominant, preventing the formation of self-organization of micro-MHD vortices.
ACCEPTED MANUSCRIPT
The enantioselective recognition of copper MED films was examined for several kinds of amino acids [38]: The chiral behavior was observed for alanine, aspartic acid and glutamic acid, and it was not detected for phenylalanine, lysine and arginine. These facts imply that the capability of chiral recognition could depend on the specific adsorption, steric effects and the number of reaction sites in the amino acids.
CR IP T
The chiral recognition mechanism was studied in the copper MED film electrodes by varying potential sweep rate in the voltammetric measurements of tartaric acid [39]. Clear current difference between the enantiomers was observed at the sweep rates of 40 – 100 mV s-1, but it was not observed at lower sweep rates of 5 – 30 mV s-1. This indicates that the enantioselective recognition is performed as the difference in the electron-transfer rate of the enantiomers at the chiral sites on the film surfaces.
AN US
The galvanostatic MED of copper films provided new aspects of chiral surface formation [40]. It was found that the surface chirality considerably depends on the deposition current. Fig. 2a shows the voltammograms of alanine enantiomers on the copper MED film electrode prepared with the deposition current of 20 mA cm-2 in the magnetic field of +5 T, where the + and – signs of magnetic field represent
M
the directions parallel and antiparallel to the ionic currents in the solution, respectively. The peak current of L-alanine is greater than that of D-alanine, thus this MED film shows L-activity. The deposition current dependence of chiral activity was examined for the +5T- and –5T-films, and the results are shown
ED
in Figs. 2b and 2c, where the chirality is evaluated by the enantiomeric excess (ee) ratio. In the
PT
voltammograms of enantiomers, the ee ratio can be defined as
CE
ee = (ipL – ipD) / (ipL + ipD),
where ipL and ipD represent the peak currents of L- and D-alanines, respectively. The positive sign of the ee ratio represents L-activity, and the negative one represents D-activity. The ee profile of +5T-film
AC
exhibits D-activity in the small current region around –11 mA cm-2, and then L-activity around –20 mA cm-2. On the contrary, the ee profile of –5T-film exhibits L-activity in the small current region and D-activity in the larger one. These results demonstrate that the surface chirality depends on both the deposition current and the magnetic field polarity.
The magnetic-field-polarity dependence of chiral sign is easily understood by considering the direction of vertical MHD flow. The vertical MHD flow makes the cyclonic micro-MHD vortices stable, and it makes the anticyclonic ones unstable. The magnetic field polarity fixes the direction of vertical MHD flow,
ACCEPTED MANUSCRIPT
thereby being responsible for the chiral sign. On the other hand, the current dependence of chiral sign is a new aspect. This suggests that the effects of micro-MHD vortex on the screw dislocation growth depend on the rate-limiting step of MED processes: The surface chirality (chiral sign and ee ratio) is different between the kinetic-controlled and mass-transfer-controlled MED processes.
CR IP T
The chirality induction was found in magnetoelectrochemical etching of copper [41]. The ee profile of the etching films showed that the chiral sign was fixed by the magnetic field polarity. A similar vortex scheme like Fig. 1 can be depicted for the etching processes.
Chiral symmetry breaking for magnetic field polarity
The surface chirality can be affected by specific adsorption of additives on the electrodeposit surfaces.
AN US
The chloride (Cl-) additive effects on the surface chirality were examined in the MED of copper [40]. Figs. 2d and 2e show the ee profiles for the +5T-film and –5T-film electrodes, respectively, where small amount of chloride ions (0.13 mM (M = mol cm-3) were added into the deposition bath (50 mM CuSO4 + 0.5 M H2SO4). It is surprising that both +5T-film and –5T-film electrodes exhibit L-activity in the middle
M
current region. This fact means that the chiral symmetry is broken for the polarity of magnetic field. The specific adsorption of chloride ions on the deposit surface could disturb the self-organized state of micro-MHD vortices. Similar chiral symmetry breaking was observed in the MED on micro-electrodes
ED
with diameters of 25 ~ 100 µm [42]. The mechanism of such chiral symmetry breaking is of great interest
PT
in connection with the homochiral molecular evolution on the early earth.
Rotational magnetoelectrodeposition
CE
The rotation of electrochemical system under magnetic fields could break the symmetry of micro-MHD vortices through the Coriolis force, inducing the surface chirality [25, 43]. The experimental system of
AC
rotational MED is schemed in Fig. 3. The electrochemical cell is rotated in the bore of a cryocooled superconducting magnet, and the magnetic field is imposed perpendicularly to the working electrode, which is embedded in a tube to suppress the influence of the vertical MHD flow (see the right part of Fig. 3). The experimental result of rotational MED of copper films showed that the system rotation induces the surface chirality and the rotational direction allows control of the chiral sign in a frequency of 2 Hz in a magnetic field of 5T [43].
Fig. 4 shows the effects of rotational direction on the surface chirality of the MED films [44]. The rotational condition is at 4 Hz with clockwise (CW) and anticlockwise (ACW) directions.
ACCEPTED MANUSCRIPT
Assuming that the peak current is proportional to the number of chiral site, Fig. 4 represents the comparison of chiral sites between the CW- and ACW-films. In the case of the +5T-films, while the rotational direction exhibits no influence on the L-active site formation (Fig. 4a), it considerably affects the D-active site formation; the CW rotation enriches the D-active sites (Fig. 4b). In the case of –5T-films, on the contrary, the ACW rotation enriches the L-active sites
CR IP T
(Fig. 4c), while the rotational direction exhibits no influence on the D-active site formation (Fig. 4d). This result demonstrates the perfect symmetry among the magnetic field polarity, the rotational direction and the surface chirality. In such a beautiful condition, the system rotation could allow control of the formation of L- and D-active sites independently. Hence, the
AN US
rotational MED could be one of the most useful method to control surface chirality.
Perspectives
Recently the measurements of redox potentials of mineral surfaces demonstrated the existence of redox and electrochemical reactions in hydrothermal fields in deep seas [45], implying that electrochemical reactions could contribute to molecular evolution of prebiotic molecules on the early earth. In such
M
situations, the chiral surface formation of minerals is a crucial point for the elucidation of homochirality in biomolecules. The studies of surface chirality in the MED processes have demonstrated that the chiral surfaces could be formed by the combination of local vortices and large flows or system rotation. This
ED
could lead to a hint for the formation of chiral reaction fields. Furthermore, the MED can provide a novel method for the tailoring of chiral surfaces without chiral chemicals. This is of great significance in a
PT
viewpoint of green chemistry.
CE
Acknowledgement
This work was partially supported by JSPS KAKENHI Grant-in-Aid for Scientific Research (C) No.
AC
16K04913.
ACCEPTED MANUSCRIPT
References and recommended regarding Paper of particular interest, published within the period of review, have been highlighted as *Paper of special interest
1.
CR IP T
**Paper of outstanding interest
Ahmadi A, Attard G, Feliu J, Rodes A: Surface reactivity at “chiral” platinum surfaces. Langmuir 1999, 15: 2420-2424.
2.
Attard G, Harris C, Herrero E, Feliu J: The influence of anions and kink structure on the enantioselective electro-oxidation of glucose. Faraday Discuss 2002, 121: 253-266. doi: 10.1039/b110764j
Gellman AJ, Horvath JD, Buelow MT: Chiral single crystal surface chemistry. J. Molecular Catalysis A: Chemical 2001, 167: 3-11.
4.
AN US
3.
Switzer JA, Kotharl HM, Nakanishi S, Bohannan EW: Enantiospecific electrodeposition of a chiral catalyst. Nature 2003, 425: 490-493.
Wachtershauser G: Before enzymes and templates: Theory of surface metabolism. Microbiol Rev
M
5.
1988, 52: 452-484.
Lazcano A, Miller L: On the origin of metabolic pathways. J Mol Evol 1999, 49: 424-431.
7.
Aogaki R, Fueki K, Mukaibo T: Application of magnetohydrodynamic effect to the analysis of
ED
6.
electrochemical reaction. Electrochemistry 1975, 43: 504-514. Fahidy TZ: Magnetoelectrolysis, J Appl Electrochem 1983, 13: 553-563.
9.
Monzon LMA, Coey LMD: Magnetic fields in electrochemistry: The Lorentz force. Electrochem
PT
8.
CE
Commun 2014, 42: 38-41. http://dx.doi.org/10.1016/j.elecom.2014.02.006 10. Mogi I, Kamiko M, Okubo S, Kido G: Pattern formation of electrodeposit of zinc in magnetic
AC
fields. Physica B, 1994, 201: 606-610. 11. Ni Mhiochain TR, Coey JMD: Chirality of electrodeposits grown in a magnetic field. Phys Rev E 2004, 69: 06140.
12.
Heresanu V, Ballou R, Molho P: Electrochemical growth of Zn and Fe arborescences under
normal magnetic field. Magnetohydrodynamics 2003, 39: 461-468. 13. Mogi I, Okubo S, Nakagawa Y: Dense radial growth of silver metal leaves in a high magnetic field. J Phys Soc Jpn 1991, 60: 3200-3202. 14. Hirota N, Hara H, Uetake H, Nakamura H, Kitazawa K: In situ microscopic observations of an electroless silver deposition process under high magnetic fields. J Cryst Growth 2006, 286:
ACCEPTED MANUSCRIPT
465-469. doi:10.1016/j.jcrysgro.2005.10.122 15. Mogi I, Kamiko M:
Pattern Formation in Magneto-electropolymerization of pyrrole.
Electrochemistry 1996, 64: 842-844. 16. Duan W, Kitamura S, Uechi I, Katsuki A, Tanimoto Y: Three-dimensional morphological chirality induction using high magnetic fields in membrane tubes prepared by a silicate garden
CR IP T
reaction. J Phys Chem B 2005, 109: 13445-13450. *The findings of beautiful helical growth of silicate tube in magnetic fields.
17. Yokoi H, Kuroda N, Kakudate Y: Magnetic field induced helical structure in freestanding metal silicate tubes. J Appl Phys 2005, 97: 10R513. http://dx.doi.org/10.1063/1.1861394
18. Mogi I, Watanabe K: Chirality of magnetoelectropolymerized polyaniline electrodes. Jpn J Appl Phys 2005, 44: L199-L201.
AN US
19. Mogi I, Watanabe K: Electrocatalytic chirality on magneto-electropolymerized polyaniline electrodes. J Solid State Electrochem 2007, 11: 751-756.
20. Yang Y, Wan M: Chiral nanotubes of polyaniline synthesized by a template-free method. J Mater Chem 2002, 12: 897-901. doi: 10.1039/b107384m
M
21. Yuan G-L, Kuramoto N: Helical polyaniline induced by specific interaction with biomolecules in neutral solution. Polymer 2003, 44: 5501-5504. doi: 10.1016/S0032-3861(03)00503-2 22. Kessick R, Tepper G: Microscale polymeric helical structures produced by electrospinning. Appl
ED
Phys Lett 2004, 84: 4807-4809. doi:10.1063/1.1762704 23. Yanson YI, Rost MJ: Structural accelerating effect of chloride on copper electrodeposition.
PT
Angew. Chem. Int. Ed. 2013, 52: 2454-2458. http://dx.doi.org/10.1002/anie.201207342 **In-situ observation of screw dislocations on electrodeposit film surfaces.
CE
24. Aogaki R: Micro-MHD effect on electrodeposition in the vertical magnetic field. Magnetohydrodynamics 2003, 4: 453-460.
AC
* The first study of the micro-MHD effect. 25. Aogaki R, Morimoto R: Nonequilibrium fluctuations in micro-MHD effects on electrodeposition. Heat and Mass Transfer: Modeling and Simulation, ed. by M. Hossain, InTech, Croatia, 2011, pp. 189-216.
**Theoretical review concerning the micro-MHD effect, ionic vacancy and chirality induction. 26. Daltin AL, Chopart JP: Magnetic field effect on electrodeposition of Cu 2O crystals. Magnetohydrodynamics 2009, 45: 267-273. 27. Shinohara K, Hashimoto K, Aogaki R: Hexagonal corrosion pattern upon cleavage of a zinc single crystal under a vertical high magnetic field. Chem Lett 2002, 31: 778-779
ACCEPTED MANUSCRIPT
28. Koza JA, Mogi I, Tschulik IK, Uhleman M, Mickel C, Gebert A, Chultz AL, Electrocrystallisation of metallic films under the influence of an external homogeneous magnetic field – Early stage of the layer growth. Electrochimica Acta, 2010, 55: 6533-6541. 29. Mogi I, Watanabe K Chirality of magnetoelectrodeposited Cu films. Magnetohydrodynamics 2012 48 (2): 251-259.
CR IP T
30. Mogi I, Iwasaka K, Aogaki R, Takahashi K: Visualization of magnetohydrodynamic micro-vortices with guanine micro-cryastals. J Electrochem Soc 2017 164: H584 – H586. doi: 10.1149/2.0711709jes
31. Sommeria J, Meyers SD, Swinney HL: Laboratory simulation of Jupiter’s great red spot. Nature 1988, 331: 689-693.
32. Marcus PS: Numerical simulation of Jupiter’s great red spot. Nature 1988 331: 693-696.
AN US
33. Aogaki R: Theory of stable formation of ionic vacancy in a liquid solution. Electrochemistry 2008, 76: 458-465.
34. Aogaki R, Sugiyama A, Miura M, Oshikiri Y, Miura M, Morimoto R, Takagi S, Mogi I, Yamauchi Y: Origin of Nanobubbles Electrochemically Formed in a Magnetic Field: Ionic Vacancy DOI: 10.1038/srep28927
M
Production in Electrode Reaction. Sci Rep 2016, 6: 28297.
35. Miura M, Aogaki R, Oshikiri Y, Sugiyama A, Morimoto R, Miura M, Mogi I, Yamauchi Y: Microbubble Formation from Ionic Vacancies in Copper Electrodeposition under a High
ED
Magnetic Field. Electrochemistry 2014, 82: 654-657. DOI:10.5796/electrochemistry.82.654 36. Sugiyama A, Morimoto R, Osaka T, Mogi I, Asanuma M, Miura M, Oshikiri Y, Yamauchi Y,
PT
Aogaki R: Lifetime of Ionic Vacancy Created in Redox Electrode Reaction Measured by Cyclotron MHD Electrode. Sci Rep 2016, 6: 19795. DOI: 10.1038/srep19795
CE
37. Mogi I, Watanabe K: Chiral electrode behavior of magneto-electrodeposited silver films. ISIJ Int 2007, 47: 585-587.
AC
*The first study of the chiral surface formation in the MED of metal films. 38. Mogi I, Watanabe K:
Chiral recognition of amino acids by magnetoelectrodeposited Cu film
electrodes. Int J Electrochem 2011: 239637. doi:10.4061/2011/239637
39. Mogi I, Watanabe K: Enantioselective recognition of tartaric acid on magnetoelectrodeposited copper film electrodes. Chem. Lett. 2012, 41: 1439-1441. doi:10.1246/cl.2012.1439 40. Mogi I, Aogaki R, Watanabe K: Tailoring of surface chirality by micro-vortices and specific adsorption
in
magnetoelectrodeposition.
Bull
Chem
Soc
Jpn
2015,
88:
1479-1485.
doi:10.1246/bcsj.20150208 **Noticeable aspects of surface chirality in galvanostatic MED and the chiral symmetry breaking by the
ACCEPTED MANUSCRIPT
specific adsorption. 41. Mogi I,
Aogaki
R,
Watanabe
K:
Chiral
surface
formation
of
copper
films
by
magnetoelectrochemical etching. Magnetohydrodynamics 2015, 51: 361-368. 42. Mogi I, Aogaki R, Takahashi K: Chiral surface formation in magnetoelectrolysis on micro-electrodes, Magnetohydrodynamics, 53 (2017) 321-328.
CR IP T
43. Mogi I, Morimoto R, Aogaki R, Watanabe K: Surface chirality induced by rotational electrodeposition in magnetic fields. Sci Rep 2013, 3: 2574. doi: 10.1038/srep025745 44. Mogi
I,
Iwasaka
M,
Morimoto
R,
Aogaki
R,
Takahashi
K:
Recent
topics
in
magnetoelectrochemical chirality. Poc Int Conf Magneto-Science 2017, (Reims, France, 2017) (in press).
45. Yamamoto M, Nakamura R, Kasaya T, Kumagai H, Suzuki K, Takai K: Spontaneous and
AN US
widespread electricity generation in natural deep-sea hydrothermal fields. Angew Chem Int Ed 2017, 56: 5725-5728. doi: 10.1002/anie.201701768
AC
CE
PT
ED
M
*Significant findings in the molecular evolution and the origin of life.
ACCEPTED MANUSCRIPT
M
AN US
CR IP T
Figure captions
Fig. 1. MHD effects in electrodeposition under vertical magnetic fields: When an applied magnetic field
ED
B is perpendicular to the electrode surface and parallel to the ionic current i, two types MHD flows are caused by the Lorentz force; macroscopic vertical MHD flow around the electrode edge, and micro-MHD
AC
CE
PT
vortices around the non-equilibrium fluctuations (bumps and dents ) on the deposit surface.
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Fig. 2. a: Voltammograms of alanine enantiomers on the Cu +5T-film electrodes prepared with a
ED
deposition current of –20 mA cm-2. b, c: The ee ratios versus deposition currents for the +5T-film and – 5T-film electrodes, respectively. d, e: The ee ratios versus deposition currents for the +5T-film and –
AC
CE
additive.
PT
5T-film electrodes, respectively, where the 5T-films were prepared by the MED with a 0.13 mM Cl-
AN US
CR IP T
ACCEPTED MANUSCRIPT
M
Fig. 3. Schematic of the rotational magnetoelectrodeposition. The electrochemical cell is rotated in a superconducting magnet bore. The applied magnetic field B is parallel or antiparallel to the ioninc current i. A working electrode (WE) is embedded in a tube to suppress the vertical MHD flow. CE and RE
AC
CE
PT
ED
represent counter and reference electrodes, respectively.
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Fig. 4. Effects of rotational directions on the voltammograms of alanine enantiomers on the Cu
rotational-MED film electrodes. The MED films were prepared by rotational MED at 4Hz
ED
frequency with clockwise (CW) and anticlockwise (ACW) directions. a: L-alanine on +5T-film,
AC
CE
PT
b: D-alanine on +5T-film, c: L-alanine on –5T-film, d: D-alanine on –5T-film.
ACCEPTED MANUSCRIPT
Graphical abstract
i
Symmetry-breaking MHD flow
AN US
i
CR IP T
Symmetry breaking in magnetohydrodynamic vortices induces surface chirality on electrodeposit films.
i
AC
CE
PT
ED
M
B
Micro-MHD vortex
Electrode
Surface chirality effects induced by magnetic fields I. Mogi , R. Morimoto , R. Aogaki PII: DOI: Reference:
S2451-9103(17)30137-0 10.1016/j.coelec.2017.09.029 COELEC 134
To appear in:
Current Opinion in Electrochemistry
Received date: Revised date: Accepted date:
18 August 2017 26 September 2017 26 September 2017
Please cite this article as: I. Mogi , R. Morimoto , R. Aogaki , Surface chirality effects induced by magnetic fields, Current Opinion in Electrochemistry (2017), doi: 10.1016/j.coelec.2017.09.029
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Highlights Magnetohydrodynamic (MHD) effects in electrodeposition under magnetic fields
Macroscopic spiral and helical structures in magnetoelectrodeposition
Micro-MHD vortices induce surface chirality on electrodeposit films
Chiral symmetry in rotational magnetoelectrodeposition
AC
CE
PT
ED
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Review Article Surface chirality effects induced by magnetic fields I. Mogi1,*, R. Morimoto2 and R. Aogaki3
The most striking effect of magnetic field on electrochemical systems is the magnetohydrodynamic
CR IP T
(MHD) one. The MHD convections produced spiral and helical structures in electroless and electrodeposition. Thereafter, chiral surface formation has been explored in the electrodeposition of metal films under magnetic fields, and the chiral surfaces were found in silver and copper films, which could recognize the enantiomers of chiral molecules such as glucose and amino acids. Considering the mechanisms of such chiral surface formation would lead to a clue for the homochiral molecular evolution.
AN US
Address 1
Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan,
2
Saitama Waterworks Bureau, Misato 341-0028, Japan,
3
M
Polytechnic University, Sumida-ku Tokyo 130-0026, Japan
Corresponding author: Mogi, I. ([email protected])
ED
Introduction
Surfaces of metals and minerals are often used as catalysts in many kinds of chemical reactions. When
PT
such surfaces have chirality, they could serve as enantioselective catalysts [1-4], which are significant in pharmaceutical processes. In the viewpoint of molecular evolution towards the birth of life, the mineral
CE
surfaces played crucial catalytic roles in the formation reactions of amino acids under oceans on the early earth [5,6]. If such catalytic surfaces were chiral, the amino acids would be no longer racemic. Hence, the
AC
studies on chiral surface formation are significant not only for the development of chiral catalysts but also for the origin of homochirality in biochemistry.
In the past two decades, electrodeposition under magnetic fields (magnetoelectrodeposition; MED) has been found to produce chiral structures in metal deposits and deposit surfaces. The first part of this review describes the brief history of the findings of chiral structures in the MED processes, and the second part focuses on the chiral surface formation of metals.
Macroscopic chiral structures in magnetoelectrodeposition
ACCEPTED MANUSCRIPT
In MED processes, the Lorentz force acting on ionic currents causes magnetohydrodynamic (MHD) convections in the electrolytic solutions [7-9]. The MHD convections produce spiral structures in the zinc dendrites in a thin-layer electrolytic cell [10-12]. The spiral patterns were observed even in the electroless deposition of silver [13, 14], where the Lorentz force acting on the currents in the growing branches forces to tilt the branches. A similar spiral structure was observed in the magneto-electropolymerization
CR IP T
(MEP) of a conducting polymer polypyrrole [15]. In the three-dimensional growth of metal-silicate membrane tubes, so-called ‘chemical garden’, the MHD flow produces two types of helical growth; the membrane tube itself is twisted helically, and such a twisted tube grows helically along the inner wall of tube vessel [16,17]. These spiral and helical structures are in macroscopic scales of mm – cm, and the chirality of each growth definitely depends on the magnetic field polarity. These facts demonstrate that
AN US
the MED has the potential to induce chirality in the electrodeposits.
The next target of chiral structures spontaneously shifted to the induction of molecular-scale chirality. The first attempt was conducted in the MEP of a conducting polymer polyaniline [18,19]. Polyaniline tends to form a helical structure [20-22], however, the chirality of each helical chain cannot be controlled
M
without chiral dopants or templates. In the electropolymerization processes the electrons transport from the front to the substrate electrode within the chain. Under magnetic fields, the Lorentz force is expected to act on the currents and induce the unbalanced distribution between the right- and left-handed helical
ED
chains. To examine the chirality of polyaniline films, the MEP films were employed as a modified electrode, and the voltammograms of the enantiomers of ascorbic acid were measured. The MEP film
PT
electrodes showed different oxidation currents between the enantiomers, and the films prepared under the reverse magnetic fields exhibited the opposite chirality [18]. This fact means that the MEP polyaniline
CE
films possess chirality and recognize the molecular chirality of ascorbic acid.
AC
Micro-MHD effect
The finding of chirality in the MEP polyaniline films encouraged the exploration of surface chirality in the MED of metal films. In general, one of typical growth mechanisms of deposit films is screw dislocation growth [23]. The screw dislocation is a chiral site, and the distributions of the right- and left-handed sites are usually the same. If the MHD convections could affect the formation of screw dislocation, the surface chirality would be induced.
When magnetic fields are imposed perpendicularly to the electrode surface, two types of MHD flows are excited [24,25], as shown in Fig. 1. The one is the macroscopic MHD flow around the electrode edge,
ACCEPTED MANUSCRIPT
where the ionic currents are not parallel to the magnetic fields. This is termed as vertical MHD flow. Another is a micro-MHD vortex around local bumps and dents formed by non-equilibrium fluctuation in electrodeposition. The surface morphologies of the MED films exhibited micro-circular and network structures [24, 26-29], suggesting the existence of micro-MHD vortices. Recently, the micro-MHD vortices were visualized in the MED of silver, using light-reflective guanine micro-crystals as a fluid
CR IP T
tracer [30].
The self-organized state of micro-MHD vortices consist of both clockwise and anticlockwise flows such that the adjoining flows never conflict with each other. Such a symmetric state produces racemic chiral sites, leading to achiral surfaces. Aogaki and Morimoto proposed that the micro-MHD vortices could affect the formation of screw dislocations [25]. To produce chiral surfaces, some symmetry breaking is
AN US
necessary in the micro-MHD vortices. Fortunately, the vertical MHD flow could make considerable influence on the micro-MHD vortices: The micro-MHD vortices are stable if the vorticity has the same sign as the vertical MHD flow, whereas anticyclonic vortices become unstable [31, 32]. Thereby, the
M
symmetry in the micro-MHD vortices is broken, and then the chiral surface could be formed.
Considering the solution viscosity and the friction against the film surface, there remains a question that it is impossible to excite nanometer-scale vortices. Aogaki proposed a breakthrough mechanism with a
ED
concept of ionic vacancy [33,34]: The electrodeposition process generates ionic vacancies with sizes smaller than 1 nm, which extremely decrease the viscosity and the friction, leading to the excitation of
PT
nanometer-scale MHD vortices. The existence of ionic vacancies was supported by the observation of
CE
micro-bubbles arising from the aggregation of ionic vacancies [35, 36].
Surface chirality in magnetoelectrodeposited metal films
AC
Chiral surface formation was explored in the potentiostatic MED of silver [37] and copper [29,38]. The surface chirality of the MED films was examined by the voltammetric measurements of enantiomers of chiral molecules. The silver MED films exhibited chiral behavior for the oxidation reaction of glucose enantiomers [37]. In the copper MED, the film thickness dependence of surface chirality was studied for the oxidation reaction of an amino acid alanine [38]. The surface chirality could be detected at the film thickness of 100 – 400 nm. In the thinner film formation, the non-equilibrium fluctuation does not develop sufficiently, causing no micro-MHD effects. On the other hand, in the thicker film formation, the non-equilibrium fluctuation becomes dominant, preventing the formation of self-organization of micro-MHD vortices.
ACCEPTED MANUSCRIPT
The enantioselective recognition of copper MED films was examined for several kinds of amino acids [38]: The chiral behavior was observed for alanine, aspartic acid and glutamic acid, and it was not detected for phenylalanine, lysine and arginine. These facts imply that the capability of chiral recognition could depend on the specific adsorption, steric effects and the number of reaction sites in the amino acids.
CR IP T
The chiral recognition mechanism was studied in the copper MED film electrodes by varying potential sweep rate in the voltammetric measurements of tartaric acid [39]. Clear current difference between the enantiomers was observed at the sweep rates of 40 – 100 mV s-1, but it was not observed at lower sweep rates of 5 – 30 mV s-1. This indicates that the enantioselective recognition is performed as the difference in the electron-transfer rate of the enantiomers at the chiral sites on the film surfaces.
AN US
The galvanostatic MED of copper films provided new aspects of chiral surface formation [40]. It was found that the surface chirality considerably depends on the deposition current. Fig. 2a shows the voltammograms of alanine enantiomers on the copper MED film electrode prepared with the deposition current of 20 mA cm-2 in the magnetic field of +5 T, where the + and – signs of magnetic field represent
M
the directions parallel and antiparallel to the ionic currents in the solution, respectively. The peak current of L-alanine is greater than that of D-alanine, thus this MED film shows L-activity. The deposition current dependence of chiral activity was examined for the +5T- and –5T-films, and the results are shown
ED
in Figs. 2b and 2c, where the chirality is evaluated by the enantiomeric excess (ee) ratio. In the
PT
voltammograms of enantiomers, the ee ratio can be defined as
CE
ee = (ipL – ipD) / (ipL + ipD),
where ipL and ipD represent the peak currents of L- and D-alanines, respectively. The positive sign of the ee ratio represents L-activity, and the negative one represents D-activity. The ee profile of +5T-film
AC
exhibits D-activity in the small current region around –11 mA cm-2, and then L-activity around –20 mA cm-2. On the contrary, the ee profile of –5T-film exhibits L-activity in the small current region and D-activity in the larger one. These results demonstrate that the surface chirality depends on both the deposition current and the magnetic field polarity.
The magnetic-field-polarity dependence of chiral sign is easily understood by considering the direction of vertical MHD flow. The vertical MHD flow makes the cyclonic micro-MHD vortices stable, and it makes the anticyclonic ones unstable. The magnetic field polarity fixes the direction of vertical MHD flow,
ACCEPTED MANUSCRIPT
thereby being responsible for the chiral sign. On the other hand, the current dependence of chiral sign is a new aspect. This suggests that the effects of micro-MHD vortex on the screw dislocation growth depend on the rate-limiting step of MED processes: The surface chirality (chiral sign and ee ratio) is different between the kinetic-controlled and mass-transfer-controlled MED processes.
CR IP T
The chirality induction was found in magnetoelectrochemical etching of copper [41]. The ee profile of the etching films showed that the chiral sign was fixed by the magnetic field polarity. A similar vortex scheme like Fig. 1 can be depicted for the etching processes.
Chiral symmetry breaking for magnetic field polarity
The surface chirality can be affected by specific adsorption of additives on the electrodeposit surfaces.
AN US
The chloride (Cl-) additive effects on the surface chirality were examined in the MED of copper [40]. Figs. 2d and 2e show the ee profiles for the +5T-film and –5T-film electrodes, respectively, where small amount of chloride ions (0.13 mM (M = mol cm-3) were added into the deposition bath (50 mM CuSO4 + 0.5 M H2SO4). It is surprising that both +5T-film and –5T-film electrodes exhibit L-activity in the middle
M
current region. This fact means that the chiral symmetry is broken for the polarity of magnetic field. The specific adsorption of chloride ions on the deposit surface could disturb the self-organized state of micro-MHD vortices. Similar chiral symmetry breaking was observed in the MED on micro-electrodes
ED
with diameters of 25 ~ 100 µm [42]. The mechanism of such chiral symmetry breaking is of great interest
PT
in connection with the homochiral molecular evolution on the early earth.
Rotational magnetoelectrodeposition
CE
The rotation of electrochemical system under magnetic fields could break the symmetry of micro-MHD vortices through the Coriolis force, inducing the surface chirality [25, 43]. The experimental system of
AC
rotational MED is schemed in Fig. 3. The electrochemical cell is rotated in the bore of a cryocooled superconducting magnet, and the magnetic field is imposed perpendicularly to the working electrode, which is embedded in a tube to suppress the influence of the vertical MHD flow (see the right part of Fig. 3). The experimental result of rotational MED of copper films showed that the system rotation induces the surface chirality and the rotational direction allows control of the chiral sign in a frequency of 2 Hz in a magnetic field of 5T [43].
Fig. 4 shows the effects of rotational direction on the surface chirality of the MED films [44]. The rotational condition is at 4 Hz with clockwise (CW) and anticlockwise (ACW) directions.
ACCEPTED MANUSCRIPT
Assuming that the peak current is proportional to the number of chiral site, Fig. 4 represents the comparison of chiral sites between the CW- and ACW-films. In the case of the +5T-films, while the rotational direction exhibits no influence on the L-active site formation (Fig. 4a), it considerably affects the D-active site formation; the CW rotation enriches the D-active sites (Fig. 4b). In the case of –5T-films, on the contrary, the ACW rotation enriches the L-active sites
CR IP T
(Fig. 4c), while the rotational direction exhibits no influence on the D-active site formation (Fig. 4d). This result demonstrates the perfect symmetry among the magnetic field polarity, the rotational direction and the surface chirality. In such a beautiful condition, the system rotation could allow control of the formation of L- and D-active sites independently. Hence, the
AN US
rotational MED could be one of the most useful method to control surface chirality.
Perspectives
Recently the measurements of redox potentials of mineral surfaces demonstrated the existence of redox and electrochemical reactions in hydrothermal fields in deep seas [45], implying that electrochemical reactions could contribute to molecular evolution of prebiotic molecules on the early earth. In such
M
situations, the chiral surface formation of minerals is a crucial point for the elucidation of homochirality in biomolecules. The studies of surface chirality in the MED processes have demonstrated that the chiral surfaces could be formed by the combination of local vortices and large flows or system rotation. This
ED
could lead to a hint for the formation of chiral reaction fields. Furthermore, the MED can provide a novel method for the tailoring of chiral surfaces without chiral chemicals. This is of great significance in a
PT
viewpoint of green chemistry.
CE
Acknowledgement
This work was partially supported by JSPS KAKENHI Grant-in-Aid for Scientific Research (C) No.
AC
16K04913.
ACCEPTED MANUSCRIPT
References and recommended regarding Paper of particular interest, published within the period of review, have been highlighted as *Paper of special interest
1.
CR IP T
**Paper of outstanding interest
Ahmadi A, Attard G, Feliu J, Rodes A: Surface reactivity at “chiral” platinum surfaces. Langmuir 1999, 15: 2420-2424.
2.
Attard G, Harris C, Herrero E, Feliu J: The influence of anions and kink structure on the enantioselective electro-oxidation of glucose. Faraday Discuss 2002, 121: 253-266. doi: 10.1039/b110764j
Gellman AJ, Horvath JD, Buelow MT: Chiral single crystal surface chemistry. J. Molecular Catalysis A: Chemical 2001, 167: 3-11.
4.
AN US
3.
Switzer JA, Kotharl HM, Nakanishi S, Bohannan EW: Enantiospecific electrodeposition of a chiral catalyst. Nature 2003, 425: 490-493.
Wachtershauser G: Before enzymes and templates: Theory of surface metabolism. Microbiol Rev
M
5.
1988, 52: 452-484.
Lazcano A, Miller L: On the origin of metabolic pathways. J Mol Evol 1999, 49: 424-431.
7.
Aogaki R, Fueki K, Mukaibo T: Application of magnetohydrodynamic effect to the analysis of
ED
6.
electrochemical reaction. Electrochemistry 1975, 43: 504-514. Fahidy TZ: Magnetoelectrolysis, J Appl Electrochem 1983, 13: 553-563.
9.
Monzon LMA, Coey LMD: Magnetic fields in electrochemistry: The Lorentz force. Electrochem
PT
8.
CE
Commun 2014, 42: 38-41. http://dx.doi.org/10.1016/j.elecom.2014.02.006 10. Mogi I, Kamiko M, Okubo S, Kido G: Pattern formation of electrodeposit of zinc in magnetic
AC
fields. Physica B, 1994, 201: 606-610. 11. Ni Mhiochain TR, Coey JMD: Chirality of electrodeposits grown in a magnetic field. Phys Rev E 2004, 69: 06140.
12.
Heresanu V, Ballou R, Molho P: Electrochemical growth of Zn and Fe arborescences under
normal magnetic field. Magnetohydrodynamics 2003, 39: 461-468. 13. Mogi I, Okubo S, Nakagawa Y: Dense radial growth of silver metal leaves in a high magnetic field. J Phys Soc Jpn 1991, 60: 3200-3202. 14. Hirota N, Hara H, Uetake H, Nakamura H, Kitazawa K: In situ microscopic observations of an electroless silver deposition process under high magnetic fields. J Cryst Growth 2006, 286:
ACCEPTED MANUSCRIPT
465-469. doi:10.1016/j.jcrysgro.2005.10.122 15. Mogi I, Kamiko M:
Pattern Formation in Magneto-electropolymerization of pyrrole.
Electrochemistry 1996, 64: 842-844. 16. Duan W, Kitamura S, Uechi I, Katsuki A, Tanimoto Y: Three-dimensional morphological chirality induction using high magnetic fields in membrane tubes prepared by a silicate garden
CR IP T
reaction. J Phys Chem B 2005, 109: 13445-13450. *The findings of beautiful helical growth of silicate tube in magnetic fields.
17. Yokoi H, Kuroda N, Kakudate Y: Magnetic field induced helical structure in freestanding metal silicate tubes. J Appl Phys 2005, 97: 10R513. http://dx.doi.org/10.1063/1.1861394
18. Mogi I, Watanabe K: Chirality of magnetoelectropolymerized polyaniline electrodes. Jpn J Appl Phys 2005, 44: L199-L201.
AN US
19. Mogi I, Watanabe K: Electrocatalytic chirality on magneto-electropolymerized polyaniline electrodes. J Solid State Electrochem 2007, 11: 751-756.
20. Yang Y, Wan M: Chiral nanotubes of polyaniline synthesized by a template-free method. J Mater Chem 2002, 12: 897-901. doi: 10.1039/b107384m
M
21. Yuan G-L, Kuramoto N: Helical polyaniline induced by specific interaction with biomolecules in neutral solution. Polymer 2003, 44: 5501-5504. doi: 10.1016/S0032-3861(03)00503-2 22. Kessick R, Tepper G: Microscale polymeric helical structures produced by electrospinning. Appl
ED
Phys Lett 2004, 84: 4807-4809. doi:10.1063/1.1762704 23. Yanson YI, Rost MJ: Structural accelerating effect of chloride on copper electrodeposition.
PT
Angew. Chem. Int. Ed. 2013, 52: 2454-2458. http://dx.doi.org/10.1002/anie.201207342 **In-situ observation of screw dislocations on electrodeposit film surfaces.
CE
24. Aogaki R: Micro-MHD effect on electrodeposition in the vertical magnetic field. Magnetohydrodynamics 2003, 4: 453-460.
AC
* The first study of the micro-MHD effect. 25. Aogaki R, Morimoto R: Nonequilibrium fluctuations in micro-MHD effects on electrodeposition. Heat and Mass Transfer: Modeling and Simulation, ed. by M. Hossain, InTech, Croatia, 2011, pp. 189-216.
**Theoretical review concerning the micro-MHD effect, ionic vacancy and chirality induction. 26. Daltin AL, Chopart JP: Magnetic field effect on electrodeposition of Cu 2O crystals. Magnetohydrodynamics 2009, 45: 267-273. 27. Shinohara K, Hashimoto K, Aogaki R: Hexagonal corrosion pattern upon cleavage of a zinc single crystal under a vertical high magnetic field. Chem Lett 2002, 31: 778-779
ACCEPTED MANUSCRIPT
28. Koza JA, Mogi I, Tschulik IK, Uhleman M, Mickel C, Gebert A, Chultz AL, Electrocrystallisation of metallic films under the influence of an external homogeneous magnetic field – Early stage of the layer growth. Electrochimica Acta, 2010, 55: 6533-6541. 29. Mogi I, Watanabe K Chirality of magnetoelectrodeposited Cu films. Magnetohydrodynamics 2012 48 (2): 251-259.
CR IP T
30. Mogi I, Iwasaka K, Aogaki R, Takahashi K: Visualization of magnetohydrodynamic micro-vortices with guanine micro-cryastals. J Electrochem Soc 2017 164: H584 – H586. doi: 10.1149/2.0711709jes
31. Sommeria J, Meyers SD, Swinney HL: Laboratory simulation of Jupiter’s great red spot. Nature 1988, 331: 689-693.
32. Marcus PS: Numerical simulation of Jupiter’s great red spot. Nature 1988 331: 693-696.
AN US
33. Aogaki R: Theory of stable formation of ionic vacancy in a liquid solution. Electrochemistry 2008, 76: 458-465.
34. Aogaki R, Sugiyama A, Miura M, Oshikiri Y, Miura M, Morimoto R, Takagi S, Mogi I, Yamauchi Y: Origin of Nanobubbles Electrochemically Formed in a Magnetic Field: Ionic Vacancy DOI: 10.1038/srep28927
M
Production in Electrode Reaction. Sci Rep 2016, 6: 28297.
35. Miura M, Aogaki R, Oshikiri Y, Sugiyama A, Morimoto R, Miura M, Mogi I, Yamauchi Y: Microbubble Formation from Ionic Vacancies in Copper Electrodeposition under a High
ED
Magnetic Field. Electrochemistry 2014, 82: 654-657. DOI:10.5796/electrochemistry.82.654 36. Sugiyama A, Morimoto R, Osaka T, Mogi I, Asanuma M, Miura M, Oshikiri Y, Yamauchi Y,
PT
Aogaki R: Lifetime of Ionic Vacancy Created in Redox Electrode Reaction Measured by Cyclotron MHD Electrode. Sci Rep 2016, 6: 19795. DOI: 10.1038/srep19795
CE
37. Mogi I, Watanabe K: Chiral electrode behavior of magneto-electrodeposited silver films. ISIJ Int 2007, 47: 585-587.
AC
*The first study of the chiral surface formation in the MED of metal films. 38. Mogi I, Watanabe K:
Chiral recognition of amino acids by magnetoelectrodeposited Cu film
electrodes. Int J Electrochem 2011: 239637. doi:10.4061/2011/239637
39. Mogi I, Watanabe K: Enantioselective recognition of tartaric acid on magnetoelectrodeposited copper film electrodes. Chem. Lett. 2012, 41: 1439-1441. doi:10.1246/cl.2012.1439 40. Mogi I, Aogaki R, Watanabe K: Tailoring of surface chirality by micro-vortices and specific adsorption
in
magnetoelectrodeposition.
Bull
Chem
Soc
Jpn
2015,
88:
1479-1485.
doi:10.1246/bcsj.20150208 **Noticeable aspects of surface chirality in galvanostatic MED and the chiral symmetry breaking by the
ACCEPTED MANUSCRIPT
specific adsorption. 41. Mogi I,
Aogaki
R,
Watanabe
K:
Chiral
surface
formation
of
copper
films
by
magnetoelectrochemical etching. Magnetohydrodynamics 2015, 51: 361-368. 42. Mogi I, Aogaki R, Takahashi K: Chiral surface formation in magnetoelectrolysis on micro-electrodes, Magnetohydrodynamics, 53 (2017) 321-328.
CR IP T
43. Mogi I, Morimoto R, Aogaki R, Watanabe K: Surface chirality induced by rotational electrodeposition in magnetic fields. Sci Rep 2013, 3: 2574. doi: 10.1038/srep025745 44. Mogi
I,
Iwasaka
M,
Morimoto
R,
Aogaki
R,
Takahashi
K:
Recent
topics
in
magnetoelectrochemical chirality. Poc Int Conf Magneto-Science 2017, (Reims, France, 2017) (in press).
45. Yamamoto M, Nakamura R, Kasaya T, Kumagai H, Suzuki K, Takai K: Spontaneous and
AN US
widespread electricity generation in natural deep-sea hydrothermal fields. Angew Chem Int Ed 2017, 56: 5725-5728. doi: 10.1002/anie.201701768
AC
CE
PT
ED
M
*Significant findings in the molecular evolution and the origin of life.
ACCEPTED MANUSCRIPT
M
AN US
CR IP T
Figure captions
Fig. 1. MHD effects in electrodeposition under vertical magnetic fields: When an applied magnetic field
ED
B is perpendicular to the electrode surface and parallel to the ionic current i, two types MHD flows are caused by the Lorentz force; macroscopic vertical MHD flow around the electrode edge, and micro-MHD
AC
CE
PT
vortices around the non-equilibrium fluctuations (bumps and dents ) on the deposit surface.
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Fig. 2. a: Voltammograms of alanine enantiomers on the Cu +5T-film electrodes prepared with a
ED
deposition current of –20 mA cm-2. b, c: The ee ratios versus deposition currents for the +5T-film and – 5T-film electrodes, respectively. d, e: The ee ratios versus deposition currents for the +5T-film and –
AC
CE
additive.
PT
5T-film electrodes, respectively, where the 5T-films were prepared by the MED with a 0.13 mM Cl-
AN US
CR IP T
ACCEPTED MANUSCRIPT
M
Fig. 3. Schematic of the rotational magnetoelectrodeposition. The electrochemical cell is rotated in a superconducting magnet bore. The applied magnetic field B is parallel or antiparallel to the ioninc current i. A working electrode (WE) is embedded in a tube to suppress the vertical MHD flow. CE and RE
AC
CE
PT
ED
represent counter and reference electrodes, respectively.
M
AN US
CR IP T
ACCEPTED MANUSCRIPT
Fig. 4. Effects of rotational directions on the voltammograms of alanine enantiomers on the Cu
rotational-MED film electrodes. The MED films were prepared by rotational MED at 4Hz
ED
frequency with clockwise (CW) and anticlockwise (ACW) directions. a: L-alanine on +5T-film,
AC
CE
PT
b: D-alanine on +5T-film, c: L-alanine on –5T-film, d: D-alanine on –5T-film.
ACCEPTED MANUSCRIPT
Graphical abstract
i
Symmetry-breaking MHD flow
AN US
i
CR IP T
Symmetry breaking in magnetohydrodynamic vortices induces surface chirality on electrodeposit films.
i
AC
CE
PT
ED
M
B
Micro-MHD vortex
Electrode