Electrochemical behavior of the bis(2,2'-bipyridyl)copper(II) complex immobilized on a self-assembled monolayer modified electrode for L-ascorbic acid detection

Supramolecular Memristor Based on Bistable [2]Catenanes: Toward High-Density and Non-Volatile Memory Devices

The ever-increasing demand for data storage and neuromorphic computing calls for innovative, high-density solutions, such as resistive random-access memory (RRAM). However, the integration of resistive switching and rectification at the nanoscale remains a formidable challenge. In this study, we introduce a bistable [2]catenane-based supramolecular junction that simultaneously functions as a resistive switch and a diode. All supramolecular junctions are highly stable and reproducible over thousands of resistive switching cycles, because the nano-confinement of two mechanically interlocked rings can stabilize the radical states of pyridinium moieties under ambient conditions. The successful realization of supramolecular junctions in functionality with a thickness of approximately 2 nm presents a promising avenue for the development of molecule-scale based RRAM for a better solution to high density and energy efficiency.

Rectification in Molecular Tunneling Junctions Based on Alkanethiolates with Bipyridine-Metal Complexes

This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure Au^TS-S(CH₂)₁₁BIPY-MCl₂ (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, Au^TS-S(CH₂)₁₁BIPY is a self-assembled monolayer (SAM) of an alkanethiolate with 4-methyl-2,2'-bipyridine (BIPY) head groups, on template-stripped gold (Au^TS). When the SAM is exposed to cobalt(II) chloride, SAMs of the form Au^TS-S(CH₂)₁₁BIPY-CoCl₂ rectify current with a rectification ratio of r⁺ = 82.0 at ±1.0 V. The rectification, however, disappears (r⁺ = 1.0) when the SAM is exposed to copper(II) chloride instead of cobalt. We draw the following conclusions from our experimental results: (i) Au^TS-S(CH₂)₁₁BIPY-CoCl₂ junctions rectify current because only at positive bias (+1.0 V) is there an accessible molecular orbital (the LUMO) on the BIPY-CoCl₂ moiety, while at negative bias (-1.0 V), neither the energy level of the HOMO or the LUMO lies between the Fermi levels of the electrodes. (ii) Au^TS-S(CH₂)₁₁BIPY-CuCl₂ junctions do not rectify current because there is an accessible molecular orbital on the BIPY-CuCl₂ moiety at both negative and positive bias (the HOMO is accessible at negative bias, and the LUMO is accessible at positive bias). The difference in accessibility of the HOMO levels at -1.0 V causes charge transfer-at negative bias-to take place via Fowler-Nordheim tunneling in BIPY-CoCl₂ junctions, and via direct tunneling in BIPY-CuCl₂ junctions. This difference in tunneling mechanism at negative bias is the origin of the difference in rectification ratio between BIPY-CoCl₂ and BIPY-CuCl₂ junctions.

A novel dinuclear Schiff-base copper(II) complex modified electrode for ascorbic acid catalytic oxidation and determination

A new dinuclear copper salicylaldehyde-glycine Schiff-base complex [Cu(2)(Sal-Gly)(2)(H(2)O)(2)] was synthesized and structurally characterized. [Cu(2)(Sal-Gly)(2)(H(2)O)(2)] crystallized in the monoclinic system in the P2(1)/c space group. The molecule is a dinuclear complex, formed by two [Cu(Sal-Gly)(H(2)O)] units. The electropolymerization properties of the copper complex on a glass carbon electrode were studied at different potential ranges. The electropolymerization occurred when the high scan potential reached 1.4 V. The modified electrode exhibited good electrocatalytic oxidation properties to ascorbic acid and showed a sensitivity of 22.9 nA μM(-1) (r(2) = 0.9998) and detection limit of 0.39 μM (S/N = 3) in the amperometric determination of ascorbic acid. The designed determination method can be used to analyze vitamin C tablets.

Manganese Dioxide Graphite Composite Electrodes: Application to the Electroanalysis of Hydrogen Peroxide, Ascorbic Acid and Nitrite

The modification of carbon powder with manganese dioxide using a wet impregnation procedure with electrochemical characterisation of the modified powder is described. The process involves saturation of the carbon powder with manganese(II) nitrate followed by thermal treatment at ca. 773 K leading to formation of manganese(IV) oxide on the surface of the carbon powder. The construction of composite electrodes based on manganese dioxide modified carbon powder and epoxy resin is also described, including optimisation of the percentage of the modified carbon powder. Composite electrodes showed attractive performances for electroanalytical applications, proving to be suitable for the electrochemical detection of hydrogen peroxide, ascorbic acid and nitrite ions with limits of detection comparable to the detection limits achieved by other analytical techniques. The results obtained for detection of these analytes, together with composite electrodes flexible design and low cost offers potential application of composite electrodes in biosensors.