Interfacial electron transfer of flavin coenzymes and riboflavin adsorbed on textured TiO2 films

Shinohara, Hiroaki; Grätzel, Michaël; Vlachopoulos, Nicholas; Aizawa, Masuo

doi:10.1016/0022-0728(91)85604-n

Cited by 14 publications

(6 citation statements)

References 24 publications

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“…This adsorption behavior is indicative of a Langmuir isotherm model, which can be used to obtain the amount adsorbed at full coverage (one monolayer), the equilibrium constant of the adsorption and desorption processes ( K ), and the Gibbs free energy of adsorption (Δ G °). Langmuir behavior for FAD adsorption is in agreement with other reports in the literature, such as FAD adsorption onto TiO 2 , glassy carbon, and Ru-modified glassy carbon . The general expression for the Langmuir adsorption model is shown in eq : normalΓ = normalΓ max ( K c / false( 1 + italicK italicc false) ) where Γ is the surface coverage of adsorbed FAD (mol cm –2 ), Γ max is the maximum amount of FAD that can be adsorbed on the electrode surface as a single monolayer (mol cm –2 ), K is the equilibrium constant for the adsorption and desorption processes (M –1 ), and c is the concentration of FAD in solution (M).…”

Section: Results and Discussionsupporting

confidence: 87%

“…Carbon nanotubes (CNTs) are only one of the many conductive carbon materials available for electrochemical applications, but provide attractive features over traditional carbon electrodes such as increased surface area, high mechanical strength, improved electronic conductivity, and enhanced electrocatalysis. , Their use as an electrode material for chemical sensing is ubiquitous, ,, and is often coupled with enzymes for biosensor and biofuel cell applications. − Flavoenzymes are one of the most common enzymes employed (e.g., glucose oxidase), identified by their use of the enzymatic cofactor flavine adenine dinucleotide (FAD). FAD is electroactive and generally displays a two-electron two-proton redox reaction shown in eq : FAD + 2 normalH + + 2 normale − ↔ FADH 2 Although FAD has been studied on electrode materials such as Hg, − Au, , Ti, TiO 2 , TiO 2 nanoparticles, Ni oxide, Zr oxide, SiO 2 /ZrO 2 /C ceramic electrode, Co oxide, conducting polymers, − poly(FAD) films, , glassy carbon, − and graphite, , its electrochemical behavior on CNTs has only been minimally investigated. The vast majority of studies involving FAD and CNTs have been focused on glucose oxidase (GOx) and an apparent direct electron transfer (DET) between GOx and CNTs. ,,− Thus, subsequent electrochemical characterizations of FAD on CNTs are limited to conditions appropriate for enzymatic activity and ignore inherent electrochemical benefits of FAD as a surface sensitive redox probe.…”

Section: Introductionmentioning

confidence: 99%

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Electrochemical Behavior of Flavin Adenine Dinucleotide Adsorbed onto Carbon Nanotube and Nitrogen-Doped Carbon Nanotube Electrodes

Goran

Stevenson

2013

Langmuir

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Flavin adenine dinucleotide (FAD) is a cofactor for many enzymes, but also an informative redox active surface probe for electrode materials such as carbon nanotubes (CNTs) and nitrogen-doped CNTs (N-CNTs). FAD spontaneously adsorbs onto the surface of CNTs and N-CNTs, displaying Langmuir adsorption characteristics. The Langmuir adsorption model provides a means of calculating the electroactive surface area (ESA), the equilibrium constant for the adsorption and desorption processes (K), and the Gibbs free energy of adsorption (ΔG°). Traditional ESA measurements based on the diffusional flux of a redox active molecule to the electrode surface underestimate the ESA of porous materials because pores are not penetrated. Techniques such as gas adsortion (BET) overestimate the ESA because it includes both electroactive and inactive areas. The ESA determined by extrapolation of the Langmuir adsorption model with the electroactive surface probe FAD will penetrate pores and only include electroactive areas. The redox activity of adsorbed FAD also displays a strong dependency on pH, which provides a means of determining the pKa of the surface confined species. The pKa of FAD decreases as the nitrogen content in the CNTs increases, suggesting a decreased hydrophobicity of the N-CNT surface. FAD desorption at N-CNTs slowly transforms the main FAD surface redox reaction with E1/2 at -0.84 V into two new, reversible, surface confined redox reactions with E1/2 at -0.65 and -0.76 V (vs Hg/Hg2SO4), respectively (1.0 M sodium phosphate buffer pH = 6.75). This is the first time these redox reactions have been observed. The new surface confined redox reactions were not observed during FAD desorption from nondoped CNTs.

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Section: Results and Discussionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Electrochemical Behavior of Flavin Adenine Dinucleotide Adsorbed onto Carbon Nanotube and Nitrogen-Doped Carbon Nanotube Electrodes

Goran

Stevenson

2013

Langmuir

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“…From the fit of the experimental data to a Langmuir isotherm, an affinity binding constant and a maximal coverage of 10 5 M –1 and 150 pmol cm –2 was inferred, respectively. The binding constant is similar to the one previously published for FMN adsorbed on TiO 2 powder, i.e., 1.7 × 10 5 M –1 , while the maximal coverage corresponds to ∼30% of the surface coverage expected for a densely packed flavin monolayer (i.e., ∼500 pmol cm –2 ) . At 100 μM FMN, the adsorption kinetic can be fitted to a monoexponential growth, indicative of a pseudo-first-order reaction characterized by an apparent rate constant of 0.77 h –1 .…”

Section: Resultssupporting

confidence: 81%

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

2015

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We report a mild and straightforward one-step chemical surface functionalization of indium tin oxide (ITO) electrodes by redox-active molecules bearing an organophosphoryl anchoring group (i.e., alkyl phosphate or alkyl phosphonate group). The method takes advantage of simple passive adsorption in an aqueous solution at room temperature. We show that organophosphorus compounds can adsorb much more strongly and stably on an ITO surface than analogous redox-active molecules bearing a carboxylate or a boronate moiety. We provide evidence, through quantitative electrochemical characterization (i.e., by cyclic voltammetry) of the adsorbed organophosphoryl redox-active molecules, of the occurrence of three different adsorbate fractions on ITO, exhibiting different stabilities on the surface. Among these three fractions, one is observed to be strongly chemisorbed, exhibiting high stability and resistance to desorption/hydrolysis in a free-redox probe aqueous buffer. We attribute this remarkable stability to the formation of chemical bonds between the organophosphorus anchoring group and the metal oxide surface, likely occurring through a heterocondensation reaction in water. From XPS analysis, we also demonstrate that the surface coverage of the chemisorbed molecules is highly affected by the degree of surface hydroxylation, a parameter that can be tuned by simply preconditioning the freshly cleaned ITO surfaces in water. The lower the relative surface hydroxide density on ITO, the higher was the surface coverage of the chemisorbed species. This behavior is in line with a chemisorption mechanism involving coordination of a deprotonated phosphoryl oxygen atom to the non-hydroxylated acidic metal sites of ITO.

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“…Assuming active microbial metabolism, the value for the back reaction should be negligible, because the concentration of oxidized heme would be markedly lowered by the continuous supply of respiratory electrons to the OmcA-MtrCAB complex (32). We calculated the k f value as a function of the electron-donor potential for both reactions 1 and 2 using plausible α values (α = 0.4, 0.5, and 0.6) and the reported k 0 values for the electrode reaction of flavins, where k 0 (Ox/Sq) = 0.1 and k 0 (Ox/Hq) = 0.15 (33,34) (Fig. S7A).…”

Section: Discussionmentioning

confidence: 99%

Rate enhancement of bacterial extracellular electron transport involves bound flavin semiquinones

Okamoto

Hashimoto

Nealson

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

419

363

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Extracellular redox-active compounds, flavins and other quinones, have been hypothesized to play a major role in the delivery of electrons from cellular metabolic systems to extracellular insoluble substrates by a diffusion-based shuttling two-electron-transfer mechanism. Here we show that flavin molecules secreted by Shewanella oneidensis MR-1 enhance the ability of its outer-membrane c-type cytochromes (OM c-Cyts) to transport electrons as redox cofactors, but not free-form flavins. Whole-cell differential pulse voltammetry revealed that the redox potential of flavin was reversibly shifted more than 100 mV in a positive direction, in good agreement with increasing microbial current generation. Importantly, this flavin/OM c-Cyts interaction was found to facilitate a one-electron redox reaction via a semiquinone, resulting in a 10 3 -to 10 5 -fold faster reaction rate than that of free flavin. These results are not consistent with previously proposed redox-shuttling mechanisms but suggest that the flavin/OM c-Cyts interaction regulates the extent of extracellular electron transport coupled with intracellular metabolic activity.iron-reducing bacteria | electromicrobiology | microbial fuel cell | whole-cell voltammetry | flavin mononucleotide

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Interfacial electron transfer of flavin coenzymes and riboflavin adsorbed on textured TiO2 films

Cited by 14 publications

References 24 publications

Electrochemical Behavior of Flavin Adenine Dinucleotide Adsorbed onto Carbon Nanotube and Nitrogen-Doped Carbon Nanotube Electrodes

Electrochemical Behavior of Flavin Adenine Dinucleotide Adsorbed onto Carbon Nanotube and Nitrogen-Doped Carbon Nanotube Electrodes

Efficient Chemisorption of Organophosphorous Redox Probes on Indium Tin Oxide Surfaces under Mild Conditions

Rate enhancement of bacterial extracellular electron transport involves bound flavin semiquinones

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