In situ nanostructure formation of (micro-hydroxo)bis(micro-carboxylato) diruthenium units in nafion membrane and its utilization for selective reduction of nitrosonium ion in aqueous medium

In Situ Immobilized Sesamol-Quinone/Carbon Nanoblack-Based Electrochemical Redox Platform for Efficient Bioelectrocatalytic and Immunosensor Applications

Most of the common redox mediators such as organic dyes and cyanide ligand-associated metal complex systems that have been used for various electrochemical applications are hazardous nature. Sesamol, a vital nutrient that exists in natural products like sesame seeds and oil, shows several therapeutic benefits including anticancer, antidiabetic, cardiovascular protective properties, etc. Herein, we introduce a new electrochemical redox platform based on a sesamol derivative, sesamol-quinone (Ses-Qn; oxidized sesamol), prepared by the in situ electrochemical oxidation method on a carbon nanoblack chemically modified glassy carbon electrode surface (GCE/CB@Ses-Qn) in pH 7 phosphate buffer solution, for nontoxic and sustainable electrochemical, electroanalytical, and bioelectroanalytical applications. The new Ses-Qn-modified electrode showed a well-defined redox peak at E ^o = 0.1 V vs Ag/AgCl without any surface-fouling behavior. Following three representative applications were demonstrated with this new redox system: (i) simple and quick estimation of sesamol content in the natural herbal products by electrochemical oxidation on GCE/CB followed by analyzing the oxidation current signal. (ii) Utilization of the GCE/CB@Ses-Qn as a transducer, bioelectrocatalytic reduction, and sensing of H₂O₂ after absorbing the horseradish peroxidase (HRP)-based enzymatic system on the underlying surface. The biosensor showed a highly selective H₂O₂ signal with current sensitivity and detection limit values 0.1303 μA μM^-1 and 990 nM, respectively, with tolerable interference from the common biochemicals like dissolved oxygen, cysteine, ascorbic acid, glucose, xanthine, hypoxanthine, uric acid, and hydrazine. (iii) Electrochemical immunosensing of white spot syndrome virus by sequentially modifying primary antibody, antigen, secondary antibody (HRP-linked), and bovine serum albumin on the redox electrode, followed by selective bioelectrochemical detection of H₂O₂.

A dinuclear [{(p-cym)Ru(II)Cl}2(μ-bpytz˙(-))](+) complex bridged by a radical anion: synthesis, spectroelectrochemical, EPR and theoretical investigation (bpytz = 3,6-bis(3,5-dimethylpyrazolyl)1,2,4,5-tetrazine; p-cym = p-cymene)

The reaction of the chloro-bridged dimeric precursor [{(p-cym)Ru(II)Cl}(μ-Cl)]2 (p-cym = p-cymene) with the bridging ligand 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine (bpytz) in ethanol results in the formation of the dinuclear complex [{(p-cym)Ru(II)Cl}2(μ-bpytz˙(-))](+), [1](+). The bridging tetrazine ligand is reduced to the anion radical (bpytz˙(-)) which connects the two Ru(II) centres. Compound [1](PF6) has been characterised by an array of spectroscopic and electrochemical techniques. The radical anion character has been confirmed by magnetic moment (corresponding to one electron paramagnetism) measurement, EPR spectroscopic investigation (tetrazine radical anion based EPR spectrum) as well as density functional theory based calculations. Complex [1](+) displays two successive one electron oxidation processes at 0.66 and 1.56 V versus Ag/AgCl which can be attributed to [{(p-cym)Ru(II)C}2(μ-bpytz˙(-))](+)/[{(p-cym)Ru(II)Cl}2(μ-bpytz)](2+) and [{(p-cym)Ru(II)Cl}2(μ-bpytz)](+)/[{(p-cym)Ru(III)Cl}2(μ-bpytz)](2+) processes (couples I and II), respectively. The reduction processes (couple III-couple V), which are irreversible, likely involve the successive reduction of the bridging ligand and the metal centres together with loss of the coordinated chloride ligands. UV-Vis-NIR spectroelectrochemical investigation reveals typical tetrazine radical anion containing bands for [1](+) and a strong absorption in the visible region for the oxidized form [1](2+), which can be assigned to a Ru(II) → π* (tetrazine) MLCT transition. The assignment of spectroscopic bands was confirmed by theoretical calculations.

Chemically modified electrode with a film of nano ruthenium oxides stabilizing high valent RuO(4)(-) species and its redox-selective sequential transformation to polynuclear ruthenium oxide-metallocyanates

High-valent Ru(VII)O(4)(-) (perruthenate) is a short-lived species in aqueous solutions (pH 1-14) and has scarcely been studied through electrochemistry. By a potential-controlled oxidative deposition method at 1 V vs Ag/AgCl using RuCl(3) in a pH 2 KCl-HCl buffer solution, chemically modified glassy carbon (GCE) and indium tin oxide (ITO) electrodes were successfully prepared with a film of hydrous nano ruthenium oxides RuO(2) and RuO(3), stabilizing the high-valent perruthenate anion (Ru(VII)-RuO(x)-CME, x = 2 and 3, CME = chemically modified electrode). The electrodes showed three distinct redox peaks corresponding to Ru(2)O(3)/RuO(2), RuO(2)/RuO(3), and RuO(4)(2-)/RuO(4)(-) redox processes at pH 2, like the classical RuO(2) electrodes in alkaline conditions. Solid state UV-visible spectra of the ITO/Ru(VII)-RuO(x)-CME showed characteristic absorption very close to chemically generated authentic RuO(4)(-) species in alkaline solution. Further, redox-controlled sequential procedures yielded polynuclear ruthenium oxide-hexacyanometallate films (RuO-MCN-CME, M = Fe and Ru), in which Ru(VII)-RuO(x)-CME acted as a specific template. A controlled-potential activation (>1 V) of Ru(VII)-RuO(x)-CME, stabilizing the key RuO(4)(-) species, in a solution of [Fe(CN)(6)](3-) or [Ru(CN)(6)](4-), should be a critical step for the formation of polynuclear RuO-MCN matrix.