A bioinspired copper 2,2-bipyridyl complex immobilized MWCNT modified electrode prepared by a new strategy for elegant electrocatalytic reduction and sensing of hydrogen peroxide

Electrical Wiring of Malarial Parasite Intermediate Hematin on a Tailored N-Doped Carbon Nanomaterial Surface and Its Bioelectrocatalytic Hydrogen Peroxide Reduction and Sensing

Hematin, an iron-containing porphyrin compound, plays a crucial role in various biological processes, including oxygen transport, storage, and functionality of the malarial parasite. Specifically, hematin-Fe interacts with the nitrogen atom of antimalarial drugs, forming an intermediate step crucial for their function. The electron transfer functionality of hematin in biological systems has been scarcely investigated. In this study, we developed a biomimicking electrical wiring of hematin-Fe with a model N-drug system, represented as {hematin-Fe---N-drug}. We achieved this by immobilizing hematin on a multiwalled carbon nanotube (MWCNT)/N-graphene quantum dot (N-GQD) modified electrode (MWCNT/N-GQD@Hemat). N-GQD serves as a model molecular drug system containing nitrogen atoms to mimic the {hematin-Fe---N-drug} interaction. The prepared bioelectrode exhibited a distinct redox peak at a measured potential (E1/2) of -0.410 V vs Ag/AgCl, accompanied by a surface excess value of 3.54 × 10-9 mol cm-2. This observation contrasts significantly with the weak or electroinactive electrochemical responses documented in literature-based hematin systems. We performed a comprehensive set of physicochemical and electrochemical characterizations on the MWCNT/N-GQD@Hemat system, employing techniques including FESEM, TEM, Raman spectroscopy, IR spectroscopy, and AFM. To evaluate the biomimetic electrode's electroactivity, we investigated the selective-mediated reduction of H2O2 as a model system. As an important aspect of our research, we demonstrated the use of scanning electrochemical microscopy to visualize the in situ electron transfer reaction of the biomimicking electrode. In an independent study, we showed enzyme-less electrocatalytic reduction and selective electrocatalytic sensing of H2O2 with a detection limit of 319 nM. We achieved this using a batch injection analysis-coupled disposable screen-printed electrode system in physiological solution.

Bimetallic Cu-Zn Zeolitic Imidazolate Frameworks as Peroxidase Mimics for the Detection of Hydrogen Peroxide: Electrochemical and Spectrophotometric Evaluation

A copper incorporated zeolitic imidazolate framework-8 (ZIF-8) has been synthesized and demonstrated to be a potential material for a peroxidase mimic. The resultant bimetallic Cu-Zn incorporated MOF is used for the dual mode sensing of hydrogen peroxide by following electrochemical as well as spectrophotometric methods. Using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate, spectrophotometric studies are carried out, and the steady state kinetic parameters are determined for two different concentrations of Cu incorporated ZIF-8 (viz Cu@ZIF-8-1 and Cu@ZIF-8-2). It is found that both Cu@ZIF-8-1 and Cu@ZIF-8-2 exhibit more affinity toward the TMB substrate than the horseradish peroxidase (HRP) enzyme as indicated by the low Km values obtained for the substrate. Also, as the concentration of incorporated Cu increases, Vmax values are also found to be enhanced. Electrochemically, the Cu@ZIF-8 modified glassy carbon electrode (GCE) showed a good response for peroxide detection in the concentration range from 0.5 mM to 5 mM at a working potential of -0.25 V in PBS (pH 7.0) with a limit of detection (LOD) value of 0.46 mM and a sensitivity of 20.25 μA/mM. Further, the chromogenic substrate TMB is successfully immobilized on the electrode surface and subsequently used for the peroxide detection along with Cu@ZIF-8. Here, TMB acts as a mediator and shifted the working potential to 0.1 V in acetate buffer (pH 5.0) in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.499 mM and a sensitivity of 0.097 μA/mM. Interestingly, the same electrode in PBS of pH 7.0 showed a response to peroxide at a working potential of -0.1 V in the concentration range from 0.5 mM to 5 mM with an LOD value of 0.143 mM and a sensitivity of 0.33 μA/mM. Moreover, the applicability of this material for peroxide sensing is evaluated using milk samples, and the proposed material is able to recover the peroxide present in milk. Thus, the bimetallic Cu-Zn MOF can be utilized for the dual mode sensing of peroxide and can be extended for various real time applications.

A web of poly(bisbenzimidazolatocopper(ii)) around multiwalled carbon nanotubes for the electrochemical detection of hydrogen peroxide

The present work focuses on the electrochemical determination of hydrogen peroxide (H2O2), using a poly(bisbenzimidazolatocopper(ii)) coordinated multiwalled carbon nanotube modified glassy carbon electrode (MWCNT/(BIM–Cu2+)n@GCE).

Flow injection amperometric sensing of hydroxylamine at a Cu(ii)–neocuproine-functionalized multiwalled carbon nanotube/screen printed carbon electrode

In the electrocatalytic oxidation mechanism of NH₂OH at modified electrode, firstly NH₂OH reacted with [Cu(Ncp)₂]²⁺ and oxidized to N₂O. The formed [Cu(Ncp)₂]⁺ was reoxidized by giving electrons to electrode resulting in enhancement of anodic current.

Bis(2,2'-bipyridil)Copper(II) Chloride Complex: Tyrosinase Biomimetic Catalyst or Redox Mediator?

In this article, construction of amperometric sensor(s) based on screen-printed carbon electrodes covered by thin layers of two types of carbon nanomaterials serving as amplifiers, and containing [Cu(bipy)₂Cl]Cl∙5H₂O complex is reported. Their performance and biomimetic activity towards two selected neurotransmitters (dopamine and serotonin) was studied mainly using flow injection analysis (FIA). The important parameters of FIA such as working potential, flow rate, and pH were optimized. The mechanism of the catalytic activity is explained and experimentally confirmed. It reveals that presence of hydrogen peroxide plays a crucial role which leads to answer the title question: can presented complex really be considered as a tyrosinase biomimetic catalyst or only as a redox mediator?

Vitamin B12-Immobilized Graphene Oxide for Efficient Electrocatalytic Carbon Dioxide Reduction Reaction

A naturally occurring water-soluble cobalt-complex cyanocobalamin (Vitamin B12) has been identified as a new and efficient electrocatalyst for the CO₂ -to-CO reduction reaction in aqueous solution. Heterogeneous B12-electrocatalysts prepared by a simple electrochemical immobilization technique on graphene-oxide (GO)-modified glassy carbon and carbon paper (CP) electrodes, without any non-degradable polymer-binders, showed a highly stable and well-defined surface-confined redox peak at E'=-0.138 V vs. RHE with a surface-excess value, Γ_B12 =4.28 nmol cm^-2 . This new electrocatalyst exhibits 93 % Faradaic efficiency for CO₂ -to-CO conversion at an electrolysis potential, -0.882 V vs. RHE (an optimal condition) with a high current density, 29.4 mA cm^-2 and turn-over-frequency value, 5.2 s^-1 , without any surface-fouling problem, in 0.5 m KHCO₃ . In further, it follows an eco-friendly, sustainable and water-based approach with the involvement of biodegradable and non-toxic chemicals/materials like B12, GO and CP.

Oxygen sensitive 1-amino-2-naphthol immobilized functionalized-carbon nanotube electrode

Immobilization of 1-amino-2napthol (AN) is enhanced complexing with Cu²⁺ on multiwalled carbon nanotubes (f-MWCNT) surface. Oxygen is reduced at the ligand (AN) site into water, therefore AN–Cu²⁺ immobilized on MWCNT exhibits oxygen sensing.

Elucidation of the Structure of a Thiol Functionalized Cu-tmpa Complex Anchored to Gold via a Self-Assembled Monolayer

The structure of the copper complex of the 6-((1-butanethiol)oxy)-tris(2-pyridylmethyl)amine ligand (Cu-tmpa-O(CH₂)₄SH) anchored to a gold surface has been investigated. To enable covalent attachment of the complex to the gold surface, a heteromolecular self-assembled monolayer (SAM) of butanethiol and a thiol-substituted tmpa ligand was used. Subsequent formation of the immobilized copper complex by cyclic voltammetry in the presence of Cu(OTf)₂ resulted in the formation of the anchored Cu-tmpa-O(CH₂)₄SH system which, according to scanning electron microscopy and X-ray diffraction, did not contain any accumulated copper nanoparticles or crystalline copper material. Electrochemical investigation of the heterogenized system barely showed any redox activity and lacked the typical Cu^II/I redox couple in contrast to the homogeneous complex in solution. The difference between the heterogenized system and the homogeneous complex was confirmed by X-ray photoelectron spectroscopy; the XPS spectrum did not show any satellite features of a Cu^II species but instead showed the presence of a Cu^I ion in a ∼2:3 ratio to nitrogen and a ∼2:7 ratio to sulfur. The +I oxidation state of the copper species was confirmed by the edge position in the X-ray absorption near-edge structure (XANES) region of the X-ray absorption spectrum. These results show that upon immobilization of Cu-tmpa-O(CH₂)₄SH, the resulting structure is not identical to the homogeneous Cu^II-tmpa complex. Upon anchoring, a novel Cu^I species is formed instead. This illustrates the importance of a thorough characterization of heterogenized molecular systems before drawing any conclusions regarding the structure–function relationships.

Both the oxidation state and the structure of the Cu^II complex of tris(2-pyridylmethyl)amine (Cu-tmpa) change upon anchoring it to a gold surface via a self-assembled monolayer. It was shown by XPS and XANES that a Cu^I species is formed upon anchoring instead in which each tmpa ligand contains roughly two to three copper ions.