Electrochemical Behaviour of Methylene Blue in Non-Aqueous Solvents

Caram, José Alberto; Suárez, Jaime; Gennaro, Ana María; Mirífico, María Virginia

doi:10.1016/j.electacta.2015.01.196

Cited by 12 publications

(10 citation statements)

References 32 publications

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“…The validity of eqs 23 and 24 is supported by previously reported results from the work of Caram and colleagues 38 on voltammetric measurements of methylene blue performed in aprotic media in the presence and absence of proton donors (see, e.g., Scheme 2 in ref 38). Using this assumption, we compared the voltammetric response of a new batch of DNAfunctionalized electrodes at pH = 4.0 (Figure 7A), 7.0 (Figure 7B), and 9.0 (Figure 7C) versus the output of our model.…”

Section: ■ Results and Discussionsupporting

confidence: 80%

Chemical Equilibrium-Based Mechanism for the Electrochemical Reduction of DNA-Bound Methylene Blue Explains Double Redox Waves in Voltammetry

2021

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Methylene blue is widely used as a redox reporter in DNA-based electrochemical sensors and, in particular, it is the benchmark DNA-bound reporter used in electrochemical, aptamer-based sensors (E-ABs). Our group recently published an approach to interrogate E-ABs via cyclic voltammetry, which uses the cathodic to anodic peak-to-peak voltage separation (ΔE P) from methylene blue to report on the electron-transfer kinetics and binding state of these sensors. Although effective at scanning rates ≤10 V·s–1, the method is limited at faster scanning rates because cyclic voltammograms of methylene blue-modified, electrode-bound DNA present double faradaic waves that prevent the accurate estimation of ΔE P. These double waves have been observed in previous works, but their origin was unknown. In response, here we investigated the origin of these redox waves by developing a numerical model that incorporates methylene blue’s chemical equilibria in phosphate buffer to predict the shape and magnitude of cyclic voltammograms with 85% or better accuracy from single- and double-stranded DNA. Our model confirms that the peak splitting observed at scanning rates >10 V·s–1 originates from the protonation equilibrium of the radical intermediate species formed after methylene blue receives the first electron. Moreover, the model reveals a strong interaction between the proton transferred during the reduction of methylene blue and the chemical make of blocking self-assembled monolayers typically used in the fabrication of E-ABs. This interaction affects the apparent rate of the first electron-transfer step, accelerating or decelerating it depending on the hydrophobicity and polarity of the blocking monolayer. By expanding our understanding of the effect that monolayer chemistries have on methylene blue’s protonation rates and E-AB signaling, this work may serve the rational design of future sensors with tunable electron-transfer kinetics.

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Section: ■ Results and Discussionsupporting

confidence: 80%

Chemical Equilibrium-Based Mechanism for the Electrochemical Reduction of DNA-Bound Methylene Blue Explains Double Redox Waves in Voltammetry

2021

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“…Figure shows the case of MB. The reduction of MB produces the colorless radical form (MB • ), or leucomethylene blue (LMB), − resulting in the diminishing of absorption at around 650 nm. The absorption spectra of these phenothiazine dyes recovered within several minutes under dark conditions.…”

Section: Resultsmentioning

confidence: 99%

Phenothiazine Dyes Induce NADH Photooxidation through Electron Transfer: Kinetics and the Effect of Copper Ions

Hirakawa

Mori

2021

ACS Omega

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Phenothiazine dyes, methylene blue, new methylene blue, azure A, and azure B, photosensitized the oxidation of nicotinamide adenine dinucleotide (NADH), an important coenzyme in the living cells, through electron transfer. The reduced forms of these phenothiazine dyes, which were produced through electron extraction from NADH, underwent reoxidation to the original cationic forms, leading to the construction of a photoredox cycle. This reoxidation process was the rate-determining step in the photoredox cycle. The electron extraction from NADH using phenothiazine dyes can trigger the chain reaction of the NADH oxidation. Copper ions enhanced the photoredox cycle through reoxidation of the reduced forms of phenothiazine dyes. New methylene blue demonstrated the highest photooxidative activity in this experiment due to the fast reoxidation process. Electron-transfer-mediated oxidation and the role of endogenous metal ions may be important elements in the photosterilization mechanism.

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“…In this implementation, the PVDF film acts as an electron “pump”, moving electrons into the impact site from ground, or from the impact site to ground. Although the PVDF film is quite thin, the potential required for methylene blue reduction is −660 to −760 mV in a non-aqueous medium, 32 which is easily achievable given the impact forces realized in the vial. The open-circuit potential realized by the application of force is given by eqn (3).…”

Section: Resultsmentioning

confidence: 99%

“…This reaction has been thoroughly studied in aqueous and non-aqueous systems. 32 Fully oxidized methylene blue has an absorption maximum near 665 nm and a high molar extinction coefficient, while the reduced form is nearly colourless. The high extinction coefficient of the oxidized form allows the measurement of very small concentrations using simple instrumentation.…”

Section: Introductionmentioning

confidence: 99%