Electrochimica Colloquia

Dean of the Department and Division Deputies Introduction

With a Little Help From My Friends: The New Era of High Throughput Electrochemical Multimicroscopy

Patrick R. Unwin

Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK

Email: p.r.unwin@warwick.ac.uk

Electrochemistry is a beautiful, as well as important, subject! It is at the heart of living systems, on the one hand, and the often-quoted applications in batteries, fuel cells and electrolyzers, on the other. Electrochemical devices are also widely-used in diagnostic and sensor platforms, from measuring glucose in blood to trace gases in the air. All of this makes electrochemistry one of the most fascinating scientific areas to explore, and the key to solving some of the most pressing problems facing the planet.

From the earliest days of electrochemistry, scientists have sought to visualise processes at electrochemical interfaces, and this aspiration has never been more important than today. In this lecture, I shall explain why we invented scanning electrochemical cell microscopy (SECCM) and how we use it at the centre of a multimicroscopy strategy in order to understand structure-activity at the nanoscale.

I will show how SECCM multimicroscopy can be used to solve a range of important problems in electrochemical and interfacial science, spanning energy storage materials, (electro)catalysis and membranes. In essence, the electrochemistry of complex interfaces is studied with SECCM as a set of “single entities”, inter alia, individual steps, terraces, defects, crystal facets, grain boundaries, and single particles can be targeted and analysed. Moreover, SECCM facilitates high throughput combinatorial experiments, because parameters can be varied from spot to spot. This aspect of SECCM is further enhanced with in-situ (or operando) optical microscopy techniques to enable smart scanning and visualisation of the SECCM meniscus in real time.    

With sincere gratitude to members of the Warwick Electrochemistry & Interfaces Group and collaborators who have contributed to our work in this area.

Enlightening electrochemiluminescence: new insights in coreactant ECL mechanism

Francesco Paolucci, Claudio I. Santo, Chiara Mariani, Alessandro Fracassa, Massimo Marcaccio, Giovanni Valenti

Dipartimento di Chimica Giacomo Ciamician, Alma Mater Studiorum - Università di Bologna

Via Selmi 2, 40126 Bologna, Italy

francesco.paolucci@unibo.it

The accurate and reproducible detection of diagnostic biomarkers serves to predice relevant clinical outcomes or diseases across a variety of populations and their detection, identification and quantification gave rise to the development of sophisticated analytical methods and instrumentations as powerful aids to clinical diagnostic and therapeutic monitoring. Electrochemiluminescence (ECL) appears, in such a context, as a leading transduction technique thanks to the optimal combination of electrochemical and spectroscopic methods, and it has received enormous attention as a powerful tool in the biosensing field [1,2].

The ECL process is intrinsically surface-confined with concomitant steps involved in the generation of the analytical signal. Rate determining factors, affecting the overall ECL efficiency, include the heterogeneous electron transfer kinetics, the electrogenerated radicals stability and the spatial luminophores distribution and the optimization of the ECL signal has largely been focused on materials, either luminophores, coreactants or electrodes, aiming at identifying the best candidates for an ultra-bright ECL emission [3-5].  To a lesser extent, the interest has been directed to the investigation of the fundamental mechanisms at the basis of the ECL phenomenon, clearly aware that a real comprehension of those can only be the sound basis for a substantial improvement of ECL analytical power.

In such a context, the use of ECL microscopy has proved a powerful technique potentially able to obtain a great insight in the functioning of, .e.g., living cells at either the diffraction-limited or super-resolved levels [6,7], and was successfully employed to obtain new insights into the ECL mechanisms operating under either homogeneous or heterogeneneous conditions as those realized, e.g., on the surface of microbeads, typically used in commercial immunoassay [8,9].

References

1.        C. Ma, Y. Cao, X. Gou and J.-J. Zhu Anal. Chem., 92, 431−45 (2020)

2.        X. Ma, W. Gao, F. Du, F. Yuan, J. Yu, Y. Guan, N. Sojic and G. Xu Acc. Chem. Res., 54, 2936−2945 (2021)

3.        L. Hu, Y. Wu, M. Xu, W. Gu and C. Zhu  Chem. Commun., 56, 10989—10999 (2020)

4.        A. Fiorani, G. Valenti, F. Paolucci and Y. Einaga Chem Commun., 59, 7900-7910 (2023)

5.        A Fracassa, C Mariani, M Marcaccio, G Xu, N Sojic, G Valenti and F Paolucci Current Opinion in Electrochemistry, 41, 101375 (2023)

6.        W. Zhao, H.-Y. Chen and J.-J. Xu Chem. Sci., 12, 5720 (2021)

7.        J. Feng Current Opinion in Electrochemistry, 34, 101000 (2022)

8.        A. Zanut, A. Fiorani, S. Canola, T. Saito, N. Ziebart, S. Rapino, S. Rebeccani, A. Barbon, T. Irie, H. P. Josel, F. Negri, M. Marcaccio, M. Windfuhr, K. Imai, G. Valenti and F. Paolucci, Nat. Commun., 11 2668 (2020)

9.        S. Knežević, E. Kerr,  B. Goudeau, G. Valenti, F. Paolucci, P. S. Francis, F. Kanoufi and  N. Sojic, Anal. Chem. 95, 7372–7378 (2023)

A molecular approach to enhance the efficiency of coreactant ECL of bifunctional organic dyes

Federico Polo

Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Via Torino 155, 30172 Venezia, Italy European Centre for Living Technology (ECLT), Ca' Bottacin 30124, Venice, Italy

federico.polo@unive.it

Electrogenerated chemiluminescence (ECL) of a luminophore can be conveniently attained with a single potential step or by one-directional scanning the electrode potential in the presence of a compound known as the coreactant. Depending on the HOMO-LUMO band gap of the luminophore, the stability of its radical ions in the given solvent, and the potential window of choice, specific coreactants can be employed to trigger ECL in either the positive- or negative-going scan direction. Both the luminophore and co-reactant undergo oxidation or reduction at the electrode to form radicals. Typically, electrogenerated radicals of the coreactants decompose to provide powerful reducing or oxidizing agent that undergo highly energetic electron transfer (ET) reactions with the electrooxidized or electroreduced luminophore, thereby providing the excited state species that emits light. When highly reducing species are generated upon electrooxidation or highly oxidating species are generated upon electroreduction of the coreactants, ECL reactions can be referred to as “oxidative-reduction” ECL or “reductive-oxidation” ECL, respectively.

Therefore, attaining efficient ECL requires fulfilling the energetic requirements of both the luminophore and the reducing or oxidizing derived from the coreactant, while carefully choosing the solvent-electrolyte system and electrode material. So far, whenever a coreactant proved unsuitable toward a given luminophore, a different molecule was chosen. Indeed, very little work has been done to improve the physicochemical properties of a specific coreactant type. Here we will describe our latest findings concerning a series of dibenzoyl peroxide derivatives that allowed us to finely control the oxidation potential of the ensuing radicals to match the energetic criteria, resulting in efficient ECL of bifunctional organic dyes.

Electrifying Organic Synthesis

Siegfried R. Waldvogel

Department of Chemistry, Johannes Gutenberg University

Mainz/Germany and Max-Planck Institute for Chemical Energy Conversion Mülheim/Germany

siegfried.waldvogel(at)cec.mpg.de

The direct use of electrochemistry for the generation of reactive intermediates can have major advantages towards conventional synthetic strategies. Compared to the action other sustainable approaches such as photochemistry, the overall energetic balance is superior and allows easily scalable conversions. Less or no regent waste is generated and new reaction pathways are accessible. In order to exploit the electricity driven conversions for synthetic purposes and to install unique selectivity two modern approaches will be outlined:

1. For reaching larger scale in electrochemical conversions, the formation of high-performance oxidizers is an option. By the given versatility a broad applicability is targeted.

2. Several unique molecular entities require for their installation large amounts of reagents, when using electrochemical tools this can be achieved almost waste-free. This is of particular interest when complex molecules are desired.

The working horse to identify suitable electrolytic conditions is the electrosynthetic screening approach. This strategy gives also rise to fast optimization and subsequent scale-up. For technical realization of electrosyntheses carbon electrodes play a crucial role ranging from diamond to highly isostatic graphite carbon allotropes.

Some references:

Angew. Chem. Int. Ed. 2023, e202219217; Eur. J. Org. Chem. 2023, e202300220;

Angew. Chem. Int. Ed. 2023, 62, e202214820; JACS Au 2023, 3, 575; Angew.

Chem. Int. Ed. 2023, 62, e202213630; Science 2021, 371, 507.

Electrochemical Activation of Carbon-Halogen Bonds: From Fundamentals to Applications

Abdirisak Ahmed Isse

Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova

Email: abdirisak.ahmedisse@unipd.it

The injection of one electron into an organic halide, RX, by reduction at an electrode or reaction with an electron donor in homogeneous conditions results in the fragmentation of the molecule into a radical and an anion, by breaking the carbon–halogen σ bond. There are two possible reaction mechanisms for this dissociative electron transfer (DET) process. Electron transfer (ET) and bond breaking can occur either by a stepwise mechanism, with the intermediate formation of a radical anion RX·-, or in a concerted way in which ET and bond breaking occur in a single step. The electrochemical reduction of C–X bonds is among the most studied processes in organic electrochemistry both for fundamental aspects on ET mechanisms and electrocatalysis, and because of various applicative interests in electrosynthesis, analytical chemistry, and environmental remediation.

For more than 25 years Prof. Gennaro has been working on different aspects of the electrochemical activation and utilization of C–X bonds. Besides studies on DET mechanisms and dynamics, his research group developed electrocatalysis on various metals such as Ag and Cu. One of the major applications of C–X activation is its use as the initiating step in atom transfer radical polymerization. In this talk various aspects of the dissociative electron transfer to organic halides will be discussed with major focus on electrocatalysis and the activation step of atom transfer radical polymerization.

Enantiomer discrimination in absorption spectroscopy and in voltammetry: highlighting fascinating similarities and connections

Patrizia Romana Mussini

Department of Chemistry, University of Milano, Via Golgi 19, 20133, Milano

patrizia.mussini@unimi.it 

Absorption spectroscopy and voltammetry, of known analogies and connections, share even more fascinating similarities and connections at a higher complexity level, when “upgrading” them with the ability to discriminate between enantiomers by chiral selector implementation. In both techniques either “molecular” selectors or “electromagnetic” ones (L- versus R- circularly polarized light components for spectroscopy, a- versus b-spin electrons for voltammetry) can be considered; moreover, external magnetic field application can replace a truly chiral actor. A tentative schematization is provided. Analogies and connections also concern molecular features of the enantiodiscrimination actors. In both techniques outstanding performances are obtained with inherently chiral molecules, in which a conjugated backbone with tailored torsion is source of chirality as well as spectroscopic and electrochemical activity, in an attractive three-fold interconnection. Their outstanding effects can be justified by a combination of chemical and electromagnetic properties (excellent potential molecular spin filters), a fascinating challenge for future developments.

Modulation of ferrocene-ferrocene interaction in functional helical peptides induced by different peptide sequences design

Saverio Santi

Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova

saverio.santi@unipd.it

The conjugation of organometallic compounds with biomolecules such as amino acids, peptides, and DNA has provided novel polyfunctional hybrid systems that reflect properties of both ferrocene (Fc) and the biological moieties.

We designed and studied polyfunctional hybrid systems in which the presence of Fc redox "antennas" inserted on peptide scaffolds can allow a realistic modulation of their electronic properties as a function of the applied electrical potential. Firstly, a single terminal Fc group was bound to peptide secondary structural motifs, such as 310-helices with α-amino isobutyric acid (Aib) or L-2,3-diamino propionic (L-Dap) acid, and the 2.05-helix based on Cα,β-didehydroalanine (ΔAla). Bis-ferrocenyl peptides were seldom synthetized.

To our knowledge, the unique examples of end-capped homopeptides were reported by us, namely Fc-CO-(Aib)n-NH-Fc, Fc-CO-(ΔAla)n-NH-Fc, Fc-CO-[L-Dap(Boc)]n-NH-Fc. An intramolecular Fc-N-H---O=C-Fc hydrogen bond (β-turn) is responsible for dipeptide folding. The two terminal, redox-active Fc groups allowed us to study the end-to-end charge transfer across the peptide main chain, deeply influenced by the nature and the length of the peptide secondary structure.

Recently, we prepared and characterized two hexapeptides containing different (Aib)(L-Dap) sequences, first examples of helical peptide containing two Fc moieties laterally appended, in which the L-Dap side chain allowed the introduction of the Fc functionality.

Due to the 310 helical conformation and Fc positions, the Fc groups are expected to be oriented on the same side of the helix 310 in the Z-Aib-Dap(Fc)-Aib-Aib-Dap(Fc)-Aib-NH-iPr (1) sequence, and on the opposite side in Z-Aib-Dap(Fc)-Aib-Dap(Fc)-Aib-Aib-NH-iPr (2).

The metal-metal electronic interaction has been verified by electrochemical studies. Circular dichroism experiments evidenced aggregation for 2 even at lower dilution, suggesting that the presence of Fc-Fc electrostatic interaction is due to intermolecular interaction.