An "inherently chiral" 1,1′-bibenzimidazolium additive for enantioselective voltammetry in ionic liquid media

A dialkyl-1,1′-bibenzimidazolium salt, consisting of an atropisomeric dication (i.e. featuring a stereogenic axis and thus "inherently chiral") and an achiral counteranion, is employed as a chiral additive in three commercial ionic liquids, providing successful enantiodiscrimination in voltammetry experiments on screen-printed electrodes (SPEs) with the enantiomers of N,N′-dimethyl-1-ferrocenyl-ethylamine as model chiral probes. Significant differences in redox potentials are observed for the probe enantiomers despite the low concentration (0.01 M) of the chiral additive. The nature of the achiral ionic liquid in which the additive is employed significantly affects the peak potentials and potential differences, but does not alter the enantiomer sequence. Keywords: Chiral electrochemistry and electroanalysis, Ionic liquids, Chiral additives, Inherent chirality, Enantiorecognitio

Electrocatalytic reduction of bromothiophenes on gold and silver electrodes: An example of synergy in electrocatalysis

The electroreduction of bromothiophenes on Au and Ag provides a striking model of synergy in electrocatalysis, when a second group specifically interacting with the catalytic surface is present besides the reacting one, providing an auxiliary anchoring effect. The high catalytic activity of Ag for bromobenzene reduction is enhanced in the bromothiophene case. Moreover, Au, having for bromobenzene a much lower and less reproducible catalytic effect than Ag on account of the repulsive effect of its very negative surface charge in the working potential range, approaches Ag activity in the case of 2-bromothiophene, where the anchoring S group is adjacent to the Br group to be cleaved. The beneficial anchoring effect is lower when it has to be shared between two Br leaving groups adjacent to the S group, and becomes negligible in the case of a bromide leaving group in 3-position. Keywords: Molecular electrocatalysis, Dissociative electron transfer, Anchoring groups, Bromothiophenes, Gold electrodes, Silver electrode

The effect of dwarf galaxies disruption in semi-analytic models

We present results for a galaxy formation model that includes a simple treatment for the disruption of dwarf galaxies by gravitational forces and galaxy encounters within galaxy clusters. This is implemented a posteriori in a semi-analytic model by considering the stability of cluster dark matter sub-haloes at z=0. We assume that a galaxy whose dark matter substructure has been disrupted will itself disperse, while its stars become part of the population of intracluster stars responsible for the observed intracluster light. Despite the simplicity of this assumption, our results show a substantial improvement over previous models and indicate that the inclusion of galaxy disruption is indeed a necessary ingredient of galaxy formation models. We find that galaxy disruption suppresses the number density of dwarf galaxies by about a factor of two. This makes the slope of the faint end of the galaxy luminosity function shallower, in agreement with observations. In particular, the abundance of faint, red galaxies is strongly suppressed. As a result, the luminosity function of red galaxies and the distinction between the red and the blue galaxy populations in colour-magnitude relationships are correctly predicted. Finally, we estimate a fraction of intracluster light comparable to that found in clusters of galaxies.Comment: 7 pages, 6 figures, accepted for publication in MNRAS, 2 figures changed and references adde

Theoretical insights into the Electronic and Structural Properties of New, Low-band Gap Inherently Chiral Ethylendioxythiophene-based Oligothiophene

In the last years, conjugated oligothiophene macrocycles have attracted increasing scientific interest due to some peculiar properties related to their cyclic structure [1-3]. T. Benincori et al. synthesized the 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene nicknamed BT2T4 (Figure 1) that represents the first member of a new class of chiral oligothiophenes in which chirality results from a tailored torsion produced in the polyconjugated backbone and not from the presence of stereogenic centres, external to it. Interestingly, the FeCl3 oxidation of the enantiopure BT2T4 produce a mixture of chiral macrocycles, like dimers and trimers. [4] Recently, also thanks to DFT and TD-DFT calculations, we have studied the new monomer BT2E4 in order to investigate the role of the insertion of 3,4-ethylenedioxythiophene (EDOT) units on the electronic and molecular properties of neutral and charged monomer and oligomer species. Furthermore, the electroactive films were evaluated by cyclic voltammetry (CV), UV/vis spectroelectrochemistry and CV coupled with in-situ conductance measurements. [5]Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Controlled Patterning of Complex Resistance Gradients in Conducting Polymers with Bipolar Electrochemistry

Abstract Conducting polymers have gained considerable attention for the possible design of localized electroactive patterns for microelectronics. In this work, the authors take advantage of the properties of polypyrrole, in synergy with a wireless polarization, triggered by bipolar electrochemistry, to produce localized resistance gradient patterns. The physicochemical modification is caused by the reduction and overoxidation of polypyrrole, which produces highly resistive regions at different positions along the conducting substrate at predefined locations. Due to the outstanding flexibility of polypyrrole, U‐, S‐, and E‐shaped bipolar electrodes can be formed for prove‐of‐concept experiments, and electrochemically modified in order to generate well‐defined resistance gradients. Energy‐dispersive X‐ray spectroscopy analysis of the samples confirms the localized physicochemical modifications. This approach presents as main advantages the wireless nature of bipolar electrochemistry and the possible fine‐tuning of the spatial distribution of the electrochemical modification, in comparison with more conventional patterning methods

Electrochemical reduction of organic bromides in 1-butyl-3- methylimidazolium tetrafluoroborate

The electrochemical reduction of a series of aliphatic and aromatic bromides on glassy carbon, silver and copper electrodes has been investigated by cyclic voltammetry in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF4). As in polar aprotic solvents, reductive cleavage of aromatic bromides occurs by a stepwise mechanism with the formation of a transient radical anion. In contrast, concerted electron transfer/bond rupture is the preferred reaction pathway for aliphatic bromides. Both Ag and Cu show remarkable electrocatalytic activities for the activation of the carbon-bromine bond, but the catalytic effect depends on reaction mechanism and molecular structure of RBr. Catalysis is high when reduction occurs by a concerted dissociative electron transfer pathway, which is the case of alkyl bromides. When instead a stepwise mechanism is preferred, i.e., the case of all aromatic bromides, catalysis strongly decreases with the ability of the molecule to delocalize the incoming negative charge. For example, the high positive shift of peak potential (> 0.7 V) observed for bromobenzene on Ag decreases to< 0.1 V for 4-bromobenzonitrile and< 0.02 V for 9-bromoanthracene. Overall, [BMIm]BF4 behaves like molecular solvents such as acetonitrile and dimethylformamide but, in general, both Ag and Cu are less active in the ionic liquid than in polar aprotic solvents

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 carbon-halogen bonds is modulated by (a) the stepwise or concerted nature of the dissociative electron-transfer mechanism, which is in\ufb02 uenced 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 af ter appropriate intersolvental normalization, interesting peculiarities emerge, especially concerning protic media. Solvent proticity deeply affects both the reaction mechanism (on both noncatalytic 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

Bipolar Electrochemical Analysis of Chirality in Complex Media through Miniaturized Stereoselective Light-Emitting Systems

Environmentally relevant contaminants endowed with chirality may include pharmaceutical compounds, flame retardants, perfluoroalkyl chemicals, pesticides, and polychlorinated biphenyls. Despite having similar physicochemical properties, enantiomers may differ in their biochemical interactions with enzymes, receptors, and other chiral molecules leading to different biological responses. In this work, we have designed a wireless miniaturized stereoselective light-emitting system able to qualitatively detect a chiral contaminant (3,4-dihydroxyphenylalanine, DOPA) dissolved in reduced volumes (in the microliters range), through bipolar electrochemistry. The diastereomeric environment was created by mixing the enantiomers of an inherently chiral inductor endowed with helical shape (7,8-dipropyltetrathia[7]helicene) and the chiral probe (DOPA) in micro-solutions of a commercial ionic liquid. The synergy between the inductor, the applied electric field, and the chiral pollutant was transduced by the light emission produced from a miniaturized light-emitting diode (LED) exploited in such an approach as a bipolar electrode

Absolute Chiral Recognition with Hybrid Wireless Electrochemical Actuators

Chiral discrimination is of crucial importance for many applications, including drug cross checking and electronic tongue-type devices. In a typical sensing scheme, an enantiomeric selector is combined with an appropriate transduction mechanism. We propose here a hybrid material composed of an electrically conducting oligomer i.e. oligo-(3,3'-dibenzothio- phene) bearing inherently chiral features and polypyrrole as a support, which can undergo electrochemical actuation. The combination of both leads to a freestanding film that is addressable in a wireless way based on the principle of n bipolar electrochemistry. The induced redox reactions lead to well-pronounced actuation when DOPA with the right chirality is present in solution as a model analyte, whereas absolutely no electromechanical response is measured for the wrong enantiomer. This constitutes a straightforward and absolute read out of chiral information where the amplitude of actuation is correlated with the concentration of the analyte. Optimization of the scheme results in highly efficient bending and thus opens up new directions in the field of chiral technologies