Autoprotolysis constants in nonaqueous solvents and aqueous organic solvent mixtures

The recent IUPAC document on standardization of pH measurements in nonaqueous solvents and aqueous-organic solvent mixtures (P.A.C. 57 865 (1985)) underlines the importance of the autoprotolysis constant, K, which defines the normal range of pH in the relevant solvent. The recommended e.m.f. method of determination and the standard states implied by different K definitions are duly focused. This compilation is articulated in two Tables the first of which reports K data for 100% pure solvents mostly at 298.15 K and the other concerns binary aqueous-organic mixtures of different compositions and at various temperatures

Reference value standards and primary standards for pH measurements in organic solvents and water + organic solvent mixtures of moderate to high permittivities

Ref. value stds. (pHRVS) and primary stds. (pHS) for pH measurements detd. prior to 1985, the aggregation of new stds. freshly detd. in the light of IUPAC rules and procedures, and the compilation of recommended data were reexamd. The pHRVS data (the RVS material is the 0.05 m K H phthalate buffer) now available cover the following solvents and/or their mixts. with H2O: MeOH, EtOH, 2-PrOH, 1,4-dioxane, MeCN, DMSO, and D2O. The various pHS now available cover MeOH, EtOH, DMSO and D2O

Electroactive chiral oligo- and polymer layers for electrochemical enantiorecognition

Electronically conducting polymer (ECP) and oligomer films are one of the most popular classes of artificial materials for electrode surface modification and nanostructured electroactive film preparation for use as active layers in advanced sensing electrochemical devices. They can act as both receptors and transducers on account of their electroactivity and easy derivatization in a virtually unlimited structure range, and typically have low cost and easy processability. The tailoring possibilities of ECP films also make them attractive selector candidates to achieve the superior level of molecular recognition represented by enantioselective electroanalysis, implying to discriminate between specular images of a chiral molecule . This superior recognition level requires to endow them with chirality and to employ them as enantiopure films, which can be made along different strategies, with different implications in terms of enantioselectivity, kind of transduction of the recognition event, specificity vs general applicability, preparation difficulty, robustness, etc. In this context an outstanding tool is provided by the \u201cinherent chirality\u201dstrategy

The solvent effect on the electrocatalytic cleavage of carbon-halogen bonds on Ag and Au

In recent years it has been shown in detail how the electrocatalytic cleavage of carbonhalogen bonds is modulated by (a) the stepwise or concerted nature of the dissociative electrontransfer mechanism, which is influenced by the nature of the electrode surface, the type of halogen atom and the molecular structure of RX as a whole, and (b) the double-layer structure (as a function of the nature and bulkiness of the supporting electrolyte ions). In order to both complete and support the interpretative scheme thus developed, this work is focused on the solvent role. When one compares aprotic with protic organic solvents after appropriate intersolvental normalization, interesting peculiarities emerge, especially concerning protic media. Solvent proticity deeply affects both the reaction mechanism (on both non-catalytic and catalytic electrodes) and the extent of the catalytic effects. These items are discussed on the basis of a complete investigation carried out with a carefully controlled experimental protocol on two chloride and bromide couples, one aromatic and one aliphatic, representative of stepwise and concerted mechanisms, respectively, in four aprotic and four protic solvents, on both non-catalytic GC and catalytic Ag and Au electrodes. The results are discussed in the framework of a recently developed interpretative scheme of the carbon-halogen cleavage mechanism

"Egg of Columbus": single-step complete removal of chloride impurities from ionic liquids by AgCl deposition on silver electrode

Chloride impurities in ionic liquids (ILs), which can be present even in huge amounts depending on the IL synthetic route, are particularly critical for electrochemical processes; thus, their abatement is often mandatory. However, while their analytical quantification has been the subject of many studies involving a variety of techniques, the so far available processes for their abatement are still unsatisfactory, having low efficiency, and/or involving multiple steps, and/or being far from mild and easily scalable. In this context, like an "egg of Columbus", a quite simple and safe process for chloride abatement in ILs is proposed, practically coinciding with the electrolytic preparation of a Ag|AgCl electrode. It proceeds in a single step, at room temperature, at very low potentials, with nearly ideal current efficiencies, and with negligible side effects on the electrolyzed IL. The chloride impurities are quantitatively captured and accumulated on the silver wire and eliminated by simply removing the resulting Ag|AgCl electrode from the solution, with no need of subsequent treatments

Electrochemistry of cyclic triimidazoles and their halo derivatives: A casebook for multiple equivalent centers and electrocatalysis

A family of cyclic triazines, based on the triimidazo[1,2-a:1\u2032,2\u2032-c:1\u2033,2\u2033-e][1,3,5]triazine scaffold, has recently caught attention due to its variegated solid state photoluminescent properties (e.g., crystallization induced emission, fluomechanochromism, dual fluorescence, room temperature ultralong phosphorescence), tuned by proper functionalization of the cyclic core. From an electrochemical point of view, this family of heteroaromatic cyclic triazines is unexplored. A cyclic voltammetry study is here performed aiming to clarify structure/electroactivity relationship. The peculiar molecular structure of this class of molecules offers a multi-approach case study, spanning from multiple equivalent redox site interactions in small hoops (due to ideally C3h symmetry) to carbon-halogen bond reactivity in the presence of catalytic metal electrode surfaces (for \u2013Br and \u2013I derivatives). Results point to a poor heteroannular aromaticity along the rigid, planar cyclotrimer, with each equivalent redox site acting quite independently. An unusually higher electrocatalytic performance of gold with respect to silver electrode for the electrocleavage of carbon-halogen bonds (that decreases by increasing number of halo substituents) is tentatively explained in term of a specific interaction between gold and the nitrogen-rich planar cyclotrimer platform

Enantioselective selectors for chiral electrochemistry and electroanalysis : stereogenic elements and enantioselection performance

The ability to select among different electroactive molecules, or among different redox centers on a single molecule, in both analytical and synthetic applications, is a typical asset of electrochemistry, based on fine control of the electrode potential, possibly enhanced by the choice of appropriate electrode surfaces and media. An attractive step further, of great fundamental and applicative interest, is represented by enantioselective electrochemistry, implying the ability to discriminate the enantiomers of chiral molecules (in electroanalysis), or to selectively activate or achieve a given enantiomer of a chiral molecule controlling the electrode potential (in electrosynthesis). Since the enantiomers of a chiral molecule have identical scalar physico-chemical properties and therefore the same electrochemical behavior except when interacting with some other chiral entity, enantioselective electrochemistry necessarily implies the electron transfer process to take place in asymmetric conditions. This can be achieved by the use of a chiral electrode surface or a chiral medium. Artificial selectors are particularly interesting on account of the virtually unlimited range of tailored structures possible as well as the possibility to have both enantiomers of a given selector equally available. Among the many approaches so far proposed for this ambitious target along either of the two above ways, outstanding results have been recently obtained, based on the use of "inherently chiral molecular materials" (either as electrode surfaces or as media) in which the same structural element endows the molecule with both its key functional property and with chirality

A comparative study of electrochemical, spectroscopic and structural properties of phenyl, thienyl and furyl substituted ethylenes

a detailed electrochemical and photophysical comparative study of three parallel series of phenyl, thienyl and furyl substituted ethylenes has been carried out, implemented by the computational calculation of selected terms. Relationships have been highlighted between molecular structure (number and type of aromatic rings) and important functional properties (in particular, electronic features and oligomerization ability). Interestingly, some of the studied heteroaryl-ethylenes show emission in the solid state displaying an aggregation-induced emission behavior

Panoramic Overview on the Enantioselection Performance of Inherently Chiral Surfaces: a Comparison between Systems with Different Atropisomeric Cores and Stereogenic Elements

Enantiorecognition is a key issue in advanced analytical chemistry, particularly concerning the biological and pharmaceutical field. Enantiomeric molecules, being mirror-image structures, have identical physico-chemical scalar properties, but opposite pseudo-scalar ones. When interacting with a racemic probe, chiral molecules are able to recognize the enantiomers through diasteromeric interactions. Similarly, chiral electrodes are required for enantioselective electroanalysis, and the development of "intelligent" electrodes capable of discriminating enantiomers, in particular molecules of biological and pharmaceutical importance, remains as one of the major challenges in electroanalysis. We have recently proposed the first synthetic inherently chiral electrode surfaces able to neatly discriminate as separate peaks (in terms of potential values) the antipodes of model chiral probes, also drugs, both as enantiopure and racemate. [1-2] We have also verified the general validity of the inherently chiral concept, which does not depend from the chemical nature of the atropisomeric scaffold, testing chiral surfaces electrooligomerized from starting monomers with different molecular design (i.e. bithiophene, bibenzothiophene, biindole and paracyclophane cores) and different stereogenic elements (stereogenic axis vs helix vs plane). In order to fully elucidate the enantioselection capability of all of these heteroaromatic systems we propose a detailed comparison (an example in Figure) of our inherently chiral surfaces with different atropisomeric core vs thiahelicene-based films vs \u201ctwo floor\u201d paracyclophanic oligomers. Figure. Enantioselection properties of inherently chiral oligomers with bibenzothiophene and biindole units towards L- and D-DOPA probes. The support of Fondazione Cariplo/Regione Lombardia "Avviso congiunto per l\u2019incremento dell\u2019attrattivit\ue0 del sistema di ricerca lombardo e della competitivit\ue0 dei ricercatori candidati su strumenti ERC - edizione 2016\u201d (Project 2016-0923) is gratefully acknowledged. References: [1] F. Sannicol\uf2, 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., 53 (2014) 2623-2627. [2] S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P. R. Mussini, K. Noworyta, F. Sannicol\uf2, Chem. Sci., 6 (2015) 1706-171

A Simultaneous Discrimination of Two Different Probes on Achiral Electrodes

A Simultaneous Discrimination of Two Different Probes on Achiral Electrodes S. Grecchia, S. Arnaboldia, S. Rizzob, F. Sannicol\uf2a, P.R. Mussinia a Universit\ue0 degli Studi di Milano, via Golgi 19, 20133 Milano, Italy b Istituto di Scienze e Tecnologie Molecolari, CNR, Via Golgi 19, 20133, Milano, Italy [email protected] In literature few studies have dealt with electrochemistry or electroanalysis on achiral electrodes, the selector being provided by the medium, either having a chiral selector dissolved into it or being itself endowed with chirality. More recently, we have decided to implement the \u201cinherent chirality\u201d concept for the development of media to combine the powerful strategy of inherent chirality with the physico-chemical properties of the ionic liquids. Ionic liquids, organic salts with low melting points, are increasingly popular media on account of many peculiar advantageous properties respect to volatile organic solvents (low vapor pressure, chemical and thermal stability, high solvating ability, non-flammability \u2026). They are even more attractive for electrochemical processes, acting as both solvent and supporting electrolyte, and especially featuring an extremely well-ordered structure at the interface with a charged electrode, expanding for many layers, like a semisolid crystal, even in the presence of significant water traces, and modulated by other species possibly present at the interface. Sometimes, they even border with liquid crystals. A high degree of supramolecular organization can induce significant chirality transfer from the medium to the dissolved species. And, analogously to the electrode case, this attitude could be maximized by the \u201cinherent chirality\u201d strategy, that is, working in inherently chiral ionic liquids, ICILs. To implement inherent chirality in ionic liquids, that are usually based on a heteroaromatic cation with at least one long alkyl chain (to lower the melting point), Sannicol\uf2 et al. proposed to start from biheteroaromatic scaffolds, like bipyridine or bibenzimidazole ones. [1] By dialkylation such inherently chiral scaffolds can be converted into the corresponding double salts. With at least one long alkyl chain and a suitable anion, the melting point can be lowered below room temperature; thus, two ICILs have been very recently obtained as enantiopure antipodes, starting from bicollidine, a very convenient scaffold on account of its low-cost synthesis and possibility to be separated into enantiomers by fractional crystallization, without expensive chiral HPLC. Their enantioselectivity was tested as low-concentration additives in achiral commercial ionic liquids on screen-printed electrodes, with chiral probes already used in tests with electrodes modified with inherently chiral surfaces [2]; large, specular enantiomer peak potential differences were observed. Attractively, the same behavior, as chiral additives, was also shown by family terms solid at room temperature, of faster and easier synthesis. In this context we are studying the effect of the chiral additives on two simultaneously present chiral probes, the first of them giving a chemically reversible ET process. We have to assess the experiments on all possible binary and ternary combinations but evidence of simultaneous discrimination apparently emerges. The inherent chirality research is currently supported by Regione Lombardia and Fondazione Cariplo (Avviso congiunto per l\u2019incremento dell\u2019attrattivit\ue0 del sistema di ricerca lombardo e della competitivit\ue0 dei ricercatori candidati su strumenti ERC-edizione 2016, Project 2016-0923). [1] S. Rizzo, S. Arnaboldi, V. Mihali, R. Cirilli, A. Forni, A. Gennaro, A.A. Isse, M. Pierini, P.R. Mussini, F. Sannicol\uf2 (2017) Angewandte Chemie. International Edition, 56, 2079-2082; S. Arnaboldi, R. Cirilli, A. Forni, A. Gennaro, A. A. Isse, V. Mihali, P. R. Mussini, M. Pierini, S. Rizzo, F. Sannicol\uf2 (2015) Electrochimica Acta, 179, 250-262; S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A. A. Isse, F. Sannicol\uf2, P. R. Mussini (2018) Electrochemistry Communications, 89, 57-61 [2] F. Sannicol\uf2, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P.R. Mussini, M. Panigati, M. Pierini, S. Rizzo (2014) Angewandte Chemie. International Edition, 53, 2623-2627; S. Arnaboldi, T. Benincori, R. Cirilli, S. Grecchi, L. Santagostini, F. Sannicol\uf2, P.R. Mussini (2016) Analytical And Bioanalytical Chemistry, 408, 7243-7254. S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P. R. Mussini, K. Noworyta, F. Sannicol\uf2 (2015) Chemical Science, 6, 1706-171