Significant changes in pKa between bulk aqueous solution and surface immobilized species: ortho-hydroquinones

Lee, P. T.; Harfield, John C.; Crossley, Alison; Pilgrim, Ben S.; Compton, Richard G.

doi:10.1039/c3ra00164d

Cited by 17 publications

(20 citation statements)

References 44 publications

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“…The above-described dependence of mid-peak potentials of cyclic voltammograms of the menaquinone spiked DMPC films on pH is in general agreement with the observations made by other authors in case of immobilized dibasic acids (Masheter et al 2007;Lee et al 2013). As discussed before, these authors interpreted their behavior using the common model of two deprotonation steps characterized by the two constants pK a1 and pK a2 , and finding that these constants are equal, i.e., pK a1 = pK a2 .…”

Section: Resultssupporting

confidence: 90%

“…Although the above mentioned identical values of pK a1 and pK a2 , resulting from the least-square fitting, cannot be taken as strictly proven, this would not be surprising: the phenomenon of identical pK a1 and pK a2 data of immobilized quinoide compounds is well known (Ksenzhek et al 1977;Masheter et al 2007;Lee et al 2013). Identical pK a,i values have been observed for drop casted films on graphite electrodes, adsorbed quinones, as well as for covalently bond hydroquinones.…”

Section: Resultsmentioning

confidence: 99%

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The acid–base and redox properties of menaquinone MK-4, MK-7, and MK-9 (vitamin K2) in DMPC monolayers on mercury

et al. 2020

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The acid-base and redox properties of the menaquinones MK-4, MK-7, and MK-9 (vitamin K 2) have been studied in DMPC monolayers on mercury electrodes. The monolayers were prepared by adhesion-spreading of menaquinone-spiked DMPC liposomes on a stationary mercury drop electrode. All three menaquinones possess pK a constants outside the experimentally accessible range, i.e., they are higher than about 12. The standard potentials of MK-4, MK-7, and MK-9 in the DMPC monolayers are very similar, i.e., 0.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

The acid–base and redox properties of menaquinone MK-4, MK-7, and MK-9 (vitamin K2) in DMPC monolayers on mercury

et al. 2020

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“…The possible interaction of C−OH groups (reduced form of HQ) and of C=O groups (oxidized form of HQ) with the oxo‐surface groups may modify the voltammetric response of HQ. HQ is oxidized by a slow electron transfer process involving a two‐electron/two‐proton mechanism and its oxidized form can be reduced back . The heterogeneous rate constant for HQ oxidation is quite sensitive to the interface structure and hence the voltammetric profile depends on the nature of the electrode.…”

Section: Resultsmentioning

confidence: 99%

“…HQ is oxidizedb yaslow electron transfer process involving at woelectron/two-proton mechanism and its oxidized form can be reduced back. [22,51] The heterogeneous rate constant for HQ oxidationi sq uite sensitive to the interface structure and hence the voltammetric profile depends on the nature of the electrode.…”

Section: The Role Of Cf On the Voltammetric Properties Of Cntmentioning

confidence: 99%

Role of Carbonaceous Fragments on the Functionalization and Electrochemistry of Carbon Materials

et al. 2016

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Carbonaceous fragments (CF) formed by acid treatment of carbon materials have important properties that are not completely understood. In this work, CF were produced by oxidation of CNT by using mineral acid followed by treatment with NaOH. The role of CF on CNT voltammetric properties was studied by using different materials: oxidized CNT (a‐CNT), a‐CNT refluxed in NaOH and neutralized with HCl (b‐CNT), pristine CNT exposed to a CF suspension (c‐CNT), and b‐CNT exposed to a CF suspension (r‐CNT). The extension of functionalization of these materials was evaluated by thermogravimetric analysis (TGA). The spectroscopic characterization (UV/Vis, fluorescence, FTIR, Raman and NMR) of CF indicates the presence of graphene‐type conjugated aromatic rings with highly oxidized moieties. In this work we demonstrate that CF are responsible for the ameliorated voltammetric properties of oxidized CNT. Adsorption of CF on oxidized and non‐oxidized CNT showed that CF provide active sites for hydroquinone (HQ) adsorption, enhancing current responses. The interaction of CF with carbon materials depended on both the surface oxidation degree and the surface roughness. Voltammograms from CF adsorbed on oxidized CNT indicate the presence of labile supramolecular structures with a voltammetric response typical of quinoid units. Carbon materials functionalized with CF displayed lower peak potentials and higher currents (30 to 180 %) than the unmodified electrodes, demonstrating that CF is a promising material for sensors design.

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“…45,46 The pKa1, pKa2, and pKa3 values of caffeic acid in aqueous solution are 4.4, 8.6 and 12.6 at 25 C, corresponding to the carboxylic acid group and the two phenolic hydroxyl groups of caffeic acid, respectively. 50,51 Thus, one proton is dissociated from the carboxylic group of caffeic acid at pH 7.0 and 8.0. One pair of electrochemical oxidation and reduction peaks are exhibited at pH 7.0 -10.0, corresponding to the two-electron transfer process between caffeic acid and ortho-quinone derivative (Fig.…”

Section: Electrochemistry Of Caffeic Acidmentioning

confidence: 99%

Sensitive Detection of Caffeic Acid and Rutin via the Enhanced Anodic Electrochemiluminescence Signal of Luminol

et al. 2019

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The electrooxidation of phenolic groups of caffeic acid and rutin promote anodic electrochemiluminescence (ECL) luminol substantially. A sensitive, and cost-effective ECL method has thus been developed to detect caffeic acid, ranging from 0.1 to 5.0 μM, with a detection limit of 0.1 μM and rutin ranging from 0.2 to 25 μM with a detection limit of 0.12 μM. Contrarily, phenolic compounds quench the weak cathodic ECL of luminol. Both of anodic and cathodic ECL mechanisms of luminol in the presence of phenolic compounds are analyzed. The method based on the boomed anodic ECL of luminol is comparable to those based on Ru(bpy)3 2+ and S2O8 2-/O2 systems. A lower onset potential and price than the other ECL reagents would realize its widely applications in the detection of phenolic compounds in food and medicine.

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Significant changes in pKa between bulk aqueous solution and surface immobilized species: ortho-hydroquinones

Cited by 17 publications

References 44 publications

The acid–base and redox properties of menaquinone MK-4, MK-7, and MK-9 (vitamin K2) in DMPC monolayers on mercury

The acid–base and redox properties of menaquinone MK-4, MK-7, and MK-9 (vitamin K2) in DMPC monolayers on mercury

Role of Carbonaceous Fragments on the Functionalization and Electrochemistry of Carbon Materials

Sensitive Detection of Caffeic Acid and Rutin via the Enhanced Anodic Electrochemiluminescence Signal of Luminol

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