Properties of aromatic ions generated at electrodes

Parker, Vernon D.

doi:10.1351/pac197951051021

Cited by 6 publications

(1 citation statement)

References 25 publications

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“…-250 mV ( Fig. la), which is close to that g = -f3) [5] + ln (kQ 2-jRT [6] EM = E°a nF I. J -anF observed in DMF. At c 5 X 10 M, peak A is small and increases with t, (the time at which the pre-electrolysis potential E, is applied) up to a constant value; this suggests both that lucigenin reaching the electrode by diffusion builds up at it and that only adsorbed molecules are reduced.…”

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confidence: 79%

Electrochemical Reduction of Lucigenin on Mercury in Aqueous Media

Rodríguez‐Amaro¹,

Sánchez²,

Muñoz³

et al. 1996

J. Electrochem. Soc.

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A more comprehensive study than those previously reported in the literature was carried out on the electrochemical reduction of 10,10'-dimethyl-9,9'-baicridinium ion (lucigenin) in aqueous solutions. Lucigenin (L') exhibits one, two, or three irreversible voltammetric reduction peaks, depending on its concentration and the scan rate. The first peak is due to the reduction of the first monolayer of molecules adsorbed on the electrode. This process involves two simultaneous one-electron transfers that yield a molecule (P), also immobilized at the electrode, which undergoes a conformational change to the form F'. In addition, the reagent molecules that reach the electrode by diffusion and the product (P) comproportionate to yield the intermediate radical R. New reactant molecules can displace the product because the monolayer is reversibly adsorbed. The transfer coefficient of the process and the activation energy of the conformational change were determined. The second peak is due to the reduction of a second monolayer of adsorbed lucigenin molecules. This takes place via the first monolayer of product molecules adsorbed on the electrode. Finally, the third peak arises from reduction of lucigenin molecules adsorbed on the previous monolayers. The overvoltage required to reduce lucigenin increases with increasing number of monolayers formed. The formation of new insoluble monolayers blocks the faradaic process altogether in the second scan at more positive potentials than those for the second or third peak. Infroduction 10,10'-Dimethyl-9-9'-biacridinium ion (L'), known as lucigenin and a member of the bipyridine family, has the structure CH3 + N Cl!3 Scheme L where the two tricyclic rings lie at an angle of 90°. There are several papers in the chemical literature dealing with the electrochemical reduction of lucigenin at various types of electrodes.'' However, the most significant contribution to knowledge on the electrochemical reduction of lucigenin in organic media was reported by Ahlberg et at.,' who used a Pt electrode and obtained a two-electron diffusion-controlled voltammetric peak at ca. -300 mV [vs. saturated calomel electrode (SCE)]. Both one-electron transfers take place simultaneously on species L' to yield reduction product P e e L2 P [1]The configuration of intermediate radical R, like that of species L', is such that the two tricyclic rings lie at an angle of 90°. However, the formation of a double bond between these groups in P pushes the molecule to a completely planar configuration, which is impossible owing to steric hindrance between the protons bonded to both rings. The most stable angle in this situation is ca. 45°.Ahlberg et at. found species P to undergo a conformational change to form F' (l0,10'-dimethyl-9,9'-biacridylene) (see Scheme II in Ref. 7), which has a more stable folded structure. The change also implies an alteration of the relative positions of the protons bonded to carbons 1 and 8, * Electrochemical Society Active Member. as well as carbons 1' and 8' in the tricyclic rings. In ...

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supporting

confidence: 79%

Electrochemical Reduction of Lucigenin on Mercury in Aqueous Media

Rodríguez‐Amaro¹,

Sánchez²,

Muñoz³

et al. 1996

J. Electrochem. Soc.

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Adsorption of lucigenin on Ag nanoparticles studied by surface‐enhanced Raman spectroscopy: effect of different anions on the intensification of Raman spectra

Millán

Garcia-Ramos

Sánchez-Cortés

et al. 2003

J Raman Spectroscopy

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The normal Raman and surface-enhanced Raman spectra of acridine derivative lucigenin were analysed on Ag colloid. The effect of different anions on the adsorption mechanism of this molecule was also investigated under different experimental conditions, i.e. excitation wavelength and adsorbate concentration, in order to study the different adsorption of the molecule on the metal under different conditions. The adsorption of lucigenin, which is under the dicationic form, changes depending on the anion added to the surface: in the presence of chloride the molecule forms an ion pair, with a predominant perpendicular orientation, whereas in the presence of sulphate and nitrate, the adsorption is weak and the dication seems to adopt a different orientation with respect to the surface.

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4.2.2.2.1 Radicals containing only C and H atoms

Asmus¹,

Bonifacic²

Carbon-Centered Radicals II

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Properties of aromatic ions generated at electrodes

Cited by 6 publications

References 25 publications

Electrochemical Reduction of Lucigenin on Mercury in Aqueous Media

Electrochemical Reduction of Lucigenin on Mercury in Aqueous Media

Adsorption of lucigenin on Ag nanoparticles studied by surface‐enhanced Raman spectroscopy: effect of different anions on the intensification of Raman spectra

4.2.2.2.1 Radicals containing only C and H atoms

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