1,721,312 research outputs found
Implementing inherent chirality in ionic liquids and supporting electrolytes: design strategies, electrochemical properties, enantioselectivity
No full textThe interest for Chiral Ionic Liquids (CILs) has been steadily increasing in the last years. Although their application to electrochemical processes is a field still requiring exploration, they should have a huge impact for instance in asymmetric electropolymerizations and in regioregular electrochemically activated polymerizations, as well as in preparative electrosynthetic processes of chiral compounds.
Our group has recently presented a new class of heterocycle-based "inherently chiral" electroactive materials of unprecedented chirality manifestations and enantiorecognition ability [1-3]. The "inherent chirality" concept implies that both the stereogenic element and the electroactivity source coincide with the whole conjugated molecular backbone, which features a tailored torsion induced by an atropisomeric bithiophene scaffold. Now we are applying the same "inherent chirality" approach to the development of inherently chiral ionic liquids (ICILs) and/or supporting electrolytes, hopefully endowed with high enantioselectivity, like the formerly developed inherently chiral electrodes. In particular, we are working on two molecule families, 1,1'-bibenzimidazolium dialkyl salts [4] and 3,3'-bicollidinium dialkyl salts. In fact both the 1,1'-bibenzimidazole scaffold (unlike the 2,2' one) and the 3,3'-bicollidine one consist of two moieties separated by very high torsional barriers; therefore they exist into two stable enantiomers that can be separated and stored. The high torsional barriers also result in low overall conjugation efficiency, with first oxidation and reduction located near or beyond the background, ensuring a very wide potential window (a desirable feature for use as electrochemical reaction medium) albeit becoming narrower on the cathodic side upon conversion of the scaffolds into the corresponding alkyl salts. The number and length of the alkyl chains, as well as the anion choice, modulate the melting points. According to the latter being higher or lower than room temperature, the new salts can be used as chiral ionic liquids or/and chiral supporting electrolytes, to which. The 3,3'-bicollidine case is particularly interesting because (a) its enantiopure antipodes can be obtained by fractional crystallization of diastereoisomeric salts, without requiring expensive preparative HPLC, and (b) all the salts liquid at room temperature so far obtained belong to this family.
The electrochemical properties of the new inherently chiral media will be presented, as well as the promising preliminary results concerning their enantioselection capability.
With the contribution of Fondazione Cariplo, grant no. 2011-1851
References
[1] F. Sannicolò, S. Arnaboldi, P.R. Mussini et al. Angew. Chem. Int. Ed. 2014, 53, 2623-2627.
[2] F. Sannicolò, P.R. Mussini, S. Arnaboldi et al. Chem. Eur. J. 2014, 20, 15298-15302.
[3] S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P.R. Mussini, K. Noworyta, F. Sannicolò, Chemical Science 2015, DOI: 10.1039/C4SC03713H
[4] S. Arnaboldi, R. Cirilli, A. Forni, A. Gennaro, A.A. Isse, V. Mihali, P.R. Mussini, M. Pierini, S. Rizzo, F. Sannicolò, Electrochimica Acta 2015 doi:10.1016/j.electacta.2015.03.17
"Inherently Chiral" electrodes: tools for chiral voltammetry
Full text linkThe development of artificial "intelligent" electrodes, capable to discriminate and quantify the enantiomers of chiral analytes is a quite attractive target in electroanalysis, and many approaches have been so far proposed, none of them however resolutive. An effective solution is now provided from a new class, which we have recently presented1-3 and patented, of "inherently chiral" molecular semiconductors, whose stereogenic element is a tailored torsion in the electroactive conductive backbone. The coincidence of the element granting both electroactivity and chirality with the
entire molecular backbone results in extraordinary chirality manifestations (such as circularly polarized luminescence), finely and reversibly tuned by the electric potential. Above all, enantiopure electrode surfaces can be easily prepared e.g. by fast electrooligomerization, mostly consisting of cyclic oligomers, highly electroactive and chiral, idealizing conducting polymers without ends and of high complexing ability; they are able to discriminate enantiomers of chiral molecules in terms of large peak potential differences (80-200 mV and more), with linear dynamic ranges for peak currents, thus affording enantiomeric ratio evaluation. The same spectacular enantioselectivity is obtained on chemically different surfaces of the same structural concept, which demonstrates the general validity of our proposed strategy. A simple reconditioning protocol affords performing more experiments on a single electrode. The new electrodes have been tested with very good results on chiral probes even very different and of applicative interest3 (Dopa and methyl-Dopa, ofloxacin, norepinephrine, tyrosine, naproxen, catechines, ascorbic acid...), on different supports, including commercial screen
printed ones, and in different media (aqueous and nonaqueous ones, as well as ionic liquid drops on screen printed electrodes). This work was supported by Fondazione Cariplo (Grant no. 2011-0417)
[1] F. Sannicolò, S. Arnaboldi, P.R. Mussini et al. Angew. Chem. 2014, 53, 2623. [2] F. Sannicolò, P.R. Mussini, S. Arnaboldi et al. Chem. Eur. J. 2014, 20, 15296.
[3] S. Arnaboldi, P.R. Mussini, F. Sannicolò et al. Chemical Science, 2015, 6, 2041
"Inherently Chiral" electrodes: tools for chiral voltammetry and enantiomeric excess evaluation
No full textThe development of artificial "intelligent" electrodes, capable to discriminate and quantify the enantiomers of chiral analytes, particularly of biological and pharmaceutical interest, is a quite attractive issue in electroanalysis. Obviously, selectivity towards specular molecules can only be achieved on enantiopure chiral electrodes. For this aim, many approaches have been proposed in the last years. However, even the most successful attempts at chiral discimination almost invariably resulted in the detection of a difference in current intensity between the signals of the two antipodes of a chiral probe, without differentiation of their redox potentials; the chiral enantioselective layer is in many instances not of general use, but tailored for a given probe; many preparation procedures are very sophisticated and/or the active films fragile. A winning solution comes from a new class, which we have recently presented1‐3 and patented4, of "inherently chiral" molecular semiconductors, whose stereogenic element is a tailored torsion in the electroactive conductive backbone. The coincidence of the element granting both electroactivity and chirality with the entire molecular backbone results in extraordinary chirality manifestations (such as circularly polarized luminescence), that can be finely and reversibly tuned by the electric potential. Above all, enantiopure electrode surfaces can be easily prepared e.g. by fast electrooligomerization, mostly consisting of cyclic oligomers, highly electroactive and chiral, idealizing conducting polymers without ends and of high complexing ability; they are able to discriminate enantiomers of chiral molecules in terms of large peak potential differences (80‐200 mV and more), with linear dynamic ranges for peak currents, thus affording enantiomeric
ratio evaluation. The same spectacular enantioselectivity is obtained on chemically different surfaces of the same structural concept, which demonstrates the general validity of our proposed strategy. A simple reconditioning protocol affords performing more experiments on a single electrode. The new electrodes have been tested with very good results on chiral probes even very different and of applicative interest3 (Dopa and methyl‐Dopa [see our parallel presentation] ofloxacin, norepinephrine, tyrosine, naproxen, catechines, ascorbic acid...), on different supports, including commercial screen printed ones, and in different media (aqueous and nonaqueous ones, as well as small ionic liquid drops on SPEs).
This work was supported by Fondazione Cariplo (Grant no. 2011‐0417)
References
1. F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P.R. Mussini, M.
Panigati, M. Pierino, S. Rizzo, Angew. Chem. Int. Ed. 2014, 53, 2623.
2. F. Sannicolò, P.R. Mussini, T. Benincori, R. Cirilli, S. Abbate, S. Arnaboldi, S. Casolo, E. Castiglioni, G. Longhi, R.
Martinazzo, M. Panigati, M. Pappini, E. Quartapelle Procopio, S. Rizzo, Chem. Eur. J. 2014, 20, 15296..
3. S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P.R. Mussini, K. Noworyta, F. Sannicolò, Chemical
Science, 2015, 6, 2041.
4. F. Sannicolò, P.R. Mussini, S. Arnaboldi, T. Benincori, R. Cirilli et al., Patent appl. MI2014A000948 (2014
Powerful, Versatile Inherent Chirality at Electrochemical Interphases
No full textChirality can make electrochemistry even smarter, endowing it with a superior level of selectivity. In fact, chiral electrochemistry implies the ability to discriminate and possibly also quantify enantiomers of chiral molecules, in situ and with no preliminary separation steps, for analytical purposes; and to selectively activate or obtain the desired enantiomer of a chiral molecule, for synthetic purposes; moreover, a chiral electrochemical interphase can act as a spin filter, since electrons in rototranslational motion to/from the electrode surface are truly chiral objects.
Thus chiral electrochemistry represents an attractive area with a huge applicative potential, although mostly unexploited so far, in spite of many proposed approaches. [1]
In this context, the inherent chirality concept can provide the breakthrough. In fact, it implies chirality and key functional properties, like electroactivity, to originate from the same structural element, which can coincide with the whole backbone of the chiral selector, featuring a tailored torsion. Such unique threefold identity can endow the selector with extraordinary chirality manifestations.
Unprecedented enantiorecognition in terms of large potential differences was indeed recently observed in voltammetry experiments, implementing inherent chirality in electrochemical interphases in terms of either (a) enantiopure electrode surfaces based on inherently chiral heterocycle-based electroactive oligomer films [2-5] or (b) highly ordered enantiopure media based on inherently chiral molecular salts (either as bulk ionic liquids or as additives in achiral ionic liquids)[6,7] The property appears of general character, a given selector being effective with quite different chiral probes, and viceversa.
But such enantioselectivity has an even more wider character than that. In fact, the features of inherently chiral molecular materials can also make them outstandingly selective towards the two specular circular components of plane polarized light, resulting in outstanding chiroptical properties in both adsorption (circular dichroism) and emission (circularly polarized luminescence), even electrochemically modulable.[2,4,5] Furthermore, they could discriminate a vs b electrons in rototranslational motion to/from the electrode surface, which they are truly chiral objects; and impressive features have been recently observed in magnetoelectrochemistry experiments.[8]
Such first thrilling evidences suggest fascinating correlations worthy to be explored among chiral electrochemistry, polarized light and spin magnetic moments.
Dedicated to professor Armando Gennaro, an outstanding teacher in science and in life
Support by Regione Lombardia, Fondazione Cariplo and Università degli Studi di Milano is gratefully acknowledged.
[1] S. Arnaboldi, M. Magni, P. R. Mussini, Curr. Opin. Electrochem., 2018, 8, 60–72.
[2] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P.R. Mussini, M. Panigati, M. Pierini, S. Rizzo, Angew. Chem. Int. Ed. 2014, 53, 2623-2627.
[3] S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P.R. Mussini, K. Noworyta, F. Sannicolò, Chem. Science 2015, 6, 1706-1711.
[4] S.Arnaboldi, T. Benincori, A. Penoni, L. Vaghi, R. Cirilli, S. Abbate, G. Longhi, G. Mazzeo, S. Grecchi, M. Panigati, P. R. Mussini, Chem. Sci. 2019, 2708-2717
[5] S. Arnaboldi, S. Cauteruccio, S. Grecchi, T. Benincori, M. Marcaccio, A. Orbelli Biroli, G. Longhi, E. Licandro, P.R. Mussini, Chem.Sci. 6, 2019, 1706-1711
[6] S. Rizzo, S. Arnaboldi, V. Mihali, R. Cirilli, A. Forni, A. Gennaro, A.A. Isse, M. Pierini, P.R. Mussini, F. Sannicolò, Angew. Chem. Int. Ed. 2017, 56, 2079-2082.
[7] S. Rizzo, S.Arnaboldi, R. Cirilli, A. Gennaro, A. A. Isse, F. Sannicolò, P. R. Mussini, Electrochem. Comm. 2018, 89, 57-61.
[8] T. Benincori, D. Arnaboldi, M.Magni, S. Grecchi, R. Cirilli, C. Fontanesi, P.R. Mussini, Chem. Science 2019, 10, 2750-2757
Achieving chiral electroanalysis on achiral electrodes in innovative "inherently chiral" media
No full textRecently we have presented "inherently chiral" electrodes of unprecedented enantiorecognition ability, able to both discriminate (in terms of large potential differences) and quantify (in terms of linear dynamic ranges for currents) the enantiomers of many chiral probes, without need of prior HPLC separation [1]. The electrode surfaces consist of heterocycle-based "inherently chiral" electroactive oligomers, mostly cyclic, with extraordinary chirality manifestations [2,3]. The "inherent chirality" concept implies that chirality does not originate from localized or external sources, but the stereogenic element responsible for chirality (a tailored torsion induced by atropisomeric biheteroaromatic scaffolds) coincides with the entire main conjugated molecular backbone.
To achieve chiral electroanalysis, an alternative strategy to using chiral electrodes is to work on achiral electrodes but in a chiral medium. Chiral ionic liquids CILs should perform much better than chiral organic solvents, on account of their much higher intrinsic order; and, by analogy with the electrode case, "inherently chiral" ionic liquids ICILs should perform even better than CILs.
To obtain ICILs and test our assumption, we envisaged that the bis-onium salts of atropisomeric biheteroaromatic nitrogen-containing scaffolds could satisfy the “inherent chirality” requirements. The best example we found so far is an alkylated bipyridine scaffold, 3,3'-bicollidine (Fig.1). Consisting of two moieties separated by a very high torsional barrier, it exists in two stable enantiomers that can be separated and stored. The high torsional barrier also results in low overall conjugation efficiency, with first oxidation and reduction located near or beyond the background, ensuring a very wide potential window (a desirable feature for use as electrochemical reaction medium). The bicollidine scaffold can be converted by alkylation into (di)alkyl salts. The number and length of the alkyl chains, as well as the anion choice, modulate the melting points; according to the latter being higher or lower than room T, the new salts can be used as inherently chiral ionic liquids or/and inherently chiral supporting electrolytes. 3,3'-Bicollidine is particularly advantageous also because its enantiopure antipodes can be obtained by fractional crystallization of diastereoisomeric salts, without requiring expensive preparative HPLC; this allows to obtain enantiopure ICILs and inherently chiral supporting electrolytes by an affordable route.
Two bicollidinium ICILs have been already obtained, and we are now scaling their synthesis to achieve suitable quantities for tests as enantioselective media.
However, in the meanwhile, considering that shorter-chained terms in the series, of easier synthesis, could also be of high interest as inherently chiral supporting electrolytes, as well as provide a first proof-of-concept of the family enantioselectivity requiring much smaller amounts of the chiral inductor, we have tested enantiopure (R)- and (S)-3mE2BF4 antipodes as low-concentration chiral additives in achiral ionic liquid BMIMPF6. The test was performed on commercial SPEs, with the same commercial (R)- and (S)- ferrocenyl-based probes previously used for analogous tests of inherently chiral surfaces. The result was an outstanding enantiomer separation (Fig. 2, about 250 mV with 0.01 M chiral additive in BMIMPF6). We also observed that enantiomer separation is modulated by the additive concentration, and that the medium enantioselectivity holds even changing the nature of the chiral probe, or in the simultaneous presence of different probes.
Such an extraordinary result, beyond our own expectations, points to the possibility to obtain outstanding enantiodiscrimination on achiral electrodes employing the new compounds even as minority components in a commercial achiral medium.
References
[1] F. Sannicolò, S. Arnaboldi, P.R. Mussini et al. Angew. Chem. Int. Ed. 53, 2014, pp 2623-2627.
[2] F. Sannicolò, P.R. Mussini, S. Arnaboldi et al. Chem. Eur. J. 20, 2014, pp 15298-15302.
[3] S. Arnaboldi, P.R. Mussini, F. Sannicolò et al. Chemical Science 6, 2015 pp. 1706-1711
Wang J., Analytical Electrochemistry, 3rd ed. (2006), Wiley–VCH, New York. A Volume of xvi + 250 pages, ISBN-10: 0-471-67879-1, ISBN-13: 978-0-471-67879-3
No full textElectrochemical investigations of heteroarylethylene class and of related conducting films
No full textWell-known simple molecules such as diphenylethylene (DPE), dithienylethylene
(DTE), and tetraphenylethylene (TPE) show interesting optical properties; for instance,
TPE has been extensively studied because of its tunable luminescent properties and
some of its derivatives show aggregation-induced emission (AIE).
The corresponding thiophene based system: tetra-(2-thienyl)-ethylene (TTE), also giving
AIE, has not been as widely studied as TPE, but it and the peculiar electronic properties of
the thiophene ring make it much more appealing than TPE for applications in photovoltaics
and optoelectronics, both in itself and as building block in wider -conjugated systems.
Moreover, regioselective functionalization of the thiophene rings in TTE could afford a
wide target-oriented modulation of the scaffold properties. A few TTE derivatives had been
reported, but no systematic investigation of the structural and electronic features of the
thienylethylene class was available. Extension of the study to other heteroaromatic rings,
such as the furane based ones, was also overdue. To fill these gaps, we have performed an
electrochemical study, supported by spectroscopic experiments, on the aryl- and
heteroarylethylene molecules shown in Figure, most of them new, synthesized by us
according to an advantageous synthetic pathway. [1]
Our exhaustive investigation now affords a detailed rationalization of the redox properties
and electrooligomerization ability in this promising class of organic semiconductors, to be
exploited for target-oriented molecular design optimization.
[1] A. Bolzoni, L.Viglianti, A. Bossi, P.R. Mussini, S. Cauteruccio, C. Baldoli, E.
Licandro, Eur. J. Org. Chem. 2013, 33, 7489–749
Thermodynamic interpretation of polyionic membrane cell emf's in terms of mixed electrolytes activities
No full textMany applications of ion-exchange membranes involve polyionic transfers between multicomponent electrolyte solns. Polyionic membrane cell potentials are usually interpreted in terms of individual ionic activities, i.e. nonthermodynamic, conventionally established quantities. A new, complete scheme is here described for evaluating emfs. of polyionic membrane cells in terms of thermodn. mean ionic activities in mixed electrolytes together with the relevant ion and solvent transference nos. Applications of the proposed scheme are described for (1) the detn. of transference nos. of ions and solvent across membrane, and (2) the detn. of selectivities of membranes to be used in ion-selective electrodes
Sulfate-sensing electrodes. The lead-amalgam/lead-sulfate electrode
No full textA new, simplified design and a convenient prepn. procedure for the Pb(Hg)|PbSO4|SO42- electrode are proposed. This procedure ensures prepn. of stable amalgams and reproducible electrode potentials, which make this electrode useful and attractive for both thermodn. studies and electroanal. applications. For these purposes, the electrode prepd. according to the proposed procedure was exhaustively characterized both thermodynamically and as a sulfate-sensing electrode, in different sulfate solns., including H2SO4. Also, a practical standardization procedure is proposed. The Pb(Hg)|PbSO4|SO42- electrode can be structured with a built-in concd. Li2SO4 salt bridge for use as a sulfate-based ref. electrode. This electrode can be operated as a ref. electrode alternative to the conventional calomel or Ag|AgCl ref. electrodes in electroanal. practice
Redox potential, rH, and pH: reexamination of the three for a significant use
No full textThe interrelation between the redox potential rH, and pH is analyzed in order to clarify the meaning and help the practical detn. of the redox, potential. Topics discussed include parallelism between the pH and rH metric scales, and procedural and exptl. aspects of the redox potential and rH
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