Intrinsic Redox Potentials Research Articles

A Contactless Method for Measuring the Redox Potentials of Metal Nanoparticles.

The standard redox potentials of metal nanoparticles are important for understanding their chemical properties. Traditionally, these redox potentials are measured by using voltammetry. Although voltammetry is fast and cost-effective, loading or landing the nanoparticles on electrodes alters their electrochemical properties, posing a challenge for accurately determining their intrinsic redox potentials. Here, a contactless method was developed utilizing chemical assays and the Nernst equation to measure the standard reduction potentials of gold nanoparticles in their colloidal state. To showcase the versatility and accuracy of this Nernstian approach, the reduction potentials were measured for a size range of 5.0-73 nm, revealing their scaling law and dependence on the nanoparticle surface energy.

Catalytic Asymmetric Redox-Neutral [3+2] Photocycloadditions of Cyclopropyl Ketones with Vinylazaarenes Enabled by Consecutive Photoinduced Electron Transfer.

Consecutive photoinduced electron transfer (ConPET) is a powerful and atom-economical protocol to overcome the limitations of the intrinsic redox potential of visible light-absorbing photosensitizers, thereby considerably improving the substrate and reaction types. Likely because such an exothermic single-electron transfer (SET) process usually does not require the aid of chiral catalysts, resulting in an inevitable racemic background reaction, notably, no enantioselective manifolds have been reported. Herein, we report on the viability of cooperative ConPET and chiral hydrogen-bonding catalysis for the [3+2] photocycloaddition of cyclopropyl ketones with vinylazaarenes. In addition to enabling the first use of olefins that preferentially interact with chiral catalysts, this catalysis platform paves the way for the efficient synthesis of pharmaceutically and synthetically important cyclopentyl ketones functionalized by azaarenes with high yields, ees and dr. The robust capacity of the method can be further highlighted by the low loading of the chiral catalyst (1.0 mol %), the good compatibility of both 2-azaarene and 3-pyridine-based olefins, and the successful concurrent construction of three stereocenters on cyclopentane rings involving an elusive but important all-carbon quaternary.

Catalytic Asymmetric Redox‐Neutral [3+2] Photocycloadditions of Cyclopropyl Ketones with Vinylazaarenes Enabled by Consecutive Photoinduced Electron Transfer

AbstractConsecutive photoinduced electron transfer (ConPET) is a powerful and atom‐economical protocol to overcome the limitations of the intrinsic redox potential of visible light‐absorbing photosensitizers, thereby considerably improving the substrate and reaction types. Likely because such an exothermic single‐electron transfer (SET) process usually does not require the aid of chiral catalysts, resulting in an inevitable racemic background reaction, notably, no enantioselective manifolds have been reported. Herein, we report on the viability of cooperative ConPET and chiral hydrogen‐bonding catalysis for the [3+2] photocycloaddition of cyclopropyl ketones with vinylazaarenes. In addition to enabling the first use of olefins that preferentially interact with chiral catalysts, this catalysis platform paves the way for the efficient synthesis of pharmaceutically and synthetically important cyclopentyl ketones functionalized by azaarenes with high yields, ees and dr. The robust capacity of the method can be further highlighted by the low loading of the chiral catalyst (1.0 mol %), the good compatibility of both 2‐azaarene and 3‐pyridine‐based olefins, and the successful concurrent construction of three stereocenters on cyclopentane rings involving an elusive but important all‐carbon quaternary.

Switchable Design of Redox-Enhanced Nonaromatic Quinones Enabled by Conjugation Recovery.

An innovative switchable design strategy for modulating the electronic structures of quinones is proposed herein, leading to remarkably enhanced intrinsic redox potentials by restoring conjugated but nonaromatic backbone architectures. Computational validation of two fundamental hypotheses confirms the recovery of backbone conjugation and optimal utilization of the inductive effect in switched quinones, which affords significantly improved redox chemistry and overall performance compared to reference quinones. Geometric and electronic analyses provide strong evidence for the restored backbone conjugation and nonaromaticity in the switched quinones, while highlighting the reinforcement of the inductive effect and suppression of the resonance effect. This strategic approach facilitates the development of an exceptional quinone, viz. 2,6-naphthoquinone, with outstanding performance parameters (338.9 mAh g-1 and 912.9 mWh g-1). Furthermore, 2,6-anthraquinone with superior cyclic stability, demonstrates comparable performance (257.4 mAh g-1 and 702.8 mWh g-1). These findings offer valuable insights into the design of organic cathode materials with favorable redox chemistry in secondary batteries.

Valence Tautomerism in Chromium Half-Sandwich Triarylmethylium Dyads

Valence tautomerism (VT) may occur if a molecule contains two chemically different redox-active units, which differ only slightly in their intrinsic redox potential. Herein, we present three new half-sandwich complexes [(η6-arene)Cr(CO)2L]+ with a triarylmethylium substituent appended to the π-coordinated arene and different coligands L (L = CO, P(OPh)3, PPh3, 1+–3+) at the chromium atom. Ligand substitution purposefully lowers the half-wave potential for chromium oxidation and thereby the redox potential difference towards tritylium reduction. For the PPh3-substituted complex 3+, cyclic voltammetry measurements indicate that chromium oxidation and tritylium reduction occur at (almost) the same potential. This renders the diamagnetic Cr(0)-C6H4-CAr2+ form 3+, and its paramagnetic diradical Cr(I)+•-C6H4-CAr2• valence tautomer 3+•• energetically nearly degenerate. Temperature-dependent IR spectroscopy indeed shows two pairs of carbonyl bands that are assignable to a Cr(0) and a Cr(I) species, coexisting in a T-dependent equilibrium with almost equal quantities for both at −70 °C. The diradical form with one unpaired spin at the trityl unit engages in a monomer ⇌ dimer equilibrium, which was investigated by means of quantitative EPR spectroscopy. The diradical species 1+••–3+•• were found to be highly reactive, leading to several identified reaction products, which presumably result from hydrogen atom abstraction via the trityl C atom, e.g., from the solvent.

Different peroxymonosulfate activation and utilization pathways of typical cobalt oxides, cobalt-carbon and carbonaceous composites derived from metal-organic frameworks for pollutant oxidation in wastewater

Cobalt-based persulfate activation system has attracted increasing interests in recent years. However, few studies have focused on the corresponding relationship between different types of catalysts and peroxymonosulfate (PMS) utilization pathway in PMS activation process. To unravel this, three typical cobalt-based catalysts derived from ZIF materials (metal oxides ZMs, metal–carbon composite ZMCs, and etching metal–carbon composite ZCs) were applied in PMS activation system, and acetaminophen (APAP) was used as target contaminant. Quenching experiments and electron paramagnetic resonance (EPR) investigation testified that SO4·− were considered as the dominant reactive oxygen species (ROS) in the ZMs/PMS system, whereas non-radical pathway was dominant in the ZMCs/PMS and ZCs/PMS system. More Co-N species in ZMCs promoted the adsorption of PMS molecules and the formation of metastable PMS-catalyst complex. Electrochemical analysis proved that the improved intrinsic redox potential of metastable PMS-catalyst complex was due to the strong combination of PMS with positively charged Co-N species, resulting in the mass consumption of PMS. In addition, the CoⅣ=O species were mainly generated from single atomic Co or encapsulated Co sites in ZMCs and ZCs. Major degradation intermediates of APAP were detected by liquid chromatograph mass spectrometer (LC-MS) and differences in degradation pathway in three reaction systems were proposed. This study provides new insight into the PMS utilization mechanism during PMS activation process and offered environmentally friendly catalytic process for the degradation of pharmaceutical contaminants in wastewater.

Electrodeposition of Alkali Metals in Nonaqueous Electrolytes: Classical and Nonclassical Phenomena

The electrodeposition of metals in aqueous electrolytes is an important technology for corrosion protection, surface beautification, complex pattern formation, and many other applications. In most cases, a smooth surface finish is desired and achieved, thanks to the precision understanding of the nucleation and growth mechanisms. However, the electrodeposition of alkali metals in nonaqueous electrolytes, which is critical for anode-free alkali-ion batteries to achieve the highest possible energy density, is still poorly understood. During battery recharge, alkali ions stored in the positive electrode of the battery would move toward the negative electrode to deposit on the current collector. However, due to the very low intrinsic redox potentials of alkali metals (Li, Na, and K for battery applications), even nonaqueous electrolytes would spontaneously react with the metal deposits to form a solid-electrolyte interphase (SEI) layer composed of organic and inorganic reduction products that allow ions to pass through but not electrons. The SEI layer, which is heterogeneous in nature, not only undermines the uniformity of incoming ion flux but also impedes the surface diffusion of adatoms, leading to undesired localized nucleation and growths that pose short-circuiting risks. In this presentation, we will introduce our latest results on the operando characterization and mathematical modeling of electrodeposition of alkali metals in various nonaqueous electrolytes, yet against a porous separator. Our analyses in three different dynamic regimes will facilitate the precision understanding of the nonclassical electrodeposition behaviors and reveal the remaining challenge that the electrodeposition community can contribute toward achieving revolutionary stable metal electrodes.

Breaking the intrinsic activity barriers of perovskite oxides photocatalysts for catalytic CO2 reduction via piezoelectric polarization

Breaking the limitations of the intrinsic redox potential of perovskite oxides photocatalysts for catalytic CO2 reduction remains a big challenge. Here we report a new process to achieve the durability yet efficient CO2 reduction activity of various perovskite oxides (BiFeO3, LaFeO3 and LaNiO3) with an inactive CO2 photo-reduction ability via piezoelectrically polarization. Taking BiFeO3 (BFO) as a representative sample, the band tilting and structure compression of BFO reach the redox potential of CO2 reduction and build a piezoelectric field for CO2 adsorption and activation by introducing vibration energy, inducing a piezoelectric catalytic CO2 reduction process. Continued ultrasonic vibration with BFO achieves durability CO2 reduction to high production rates of CH4 (17.9 µmol g−1 h−1) and CO (28.7 µmol g−1 h−1), respectively. This crucial feature highlights the feasibility of piezoelectric catalysis for CO2 conversion by utilizing mechanical energy, which can break the limitation of intrinsic redox properties of the perovskite oxides.

Effective Nitrogen Incorporation for High‐Potential Anthracene Cathodes with Conjugated Frameworks

AbstractTo design high‐potential cathode materials for Li‐ion batteries through doping architecture, a well‐known anthracene framework is used as the basis for a broad array of nitrogen‐incorporated derivatives. A computational investigation of these derivatives clarifies that introduction of electron‐withdrawing nitrogen atoms improves the intrinsic redox potential at fully charged states, exhibiting a linear correlation between redox potential and electron affinity. However, this linear relationship between the redox potential and the density of nitrogen dopants is not fully followed during the discharging process. Consequently, it is found that doping one to three nitrogen atoms into anthracene is detrimental to the Li‐storage capacity, while doping four to ten nitrogen atoms is suggested as a suitable approach to improve the redox properties. At the end of the discharging process, electron affinity no longer plays a critical role in determining the redox potential. Each derivative is cathodically deactivated with the binding of the last Li atom, primarily owing to a sudden increase in the solvation energy, despite a negligible change in the electron affinity. These analyses assist to establish a promising approach for designing nitrogen‐incorporated anthracene derivatives for high‐performance cathode applications.

The sole tryptophan of amicyanin enhances its thermal stability but does not influence the electronic properties of the type 1 copper site

The cupredoxin amicyanin possesses a single tryptophan residue, Trp45. Its fluorescence is quenched when copper is bound even though it is separated by 10.1Å. Mutation of Trp45 to Ala, Phe, Leu and Lys resulted in undetectable protein expression. A W45Y amicyanin variant was isolated. The W45Y mutation did not alter the spectroscopic properties or intrinsic redox potential of amicyanin, but increased the pKa value for the pH-dependent redox potential by 0.5units. This is due to a hydrogen-bond involving the His95 copper ligand which is present in reduced W45Y amicyanin but not in native amicyanin. The W45Y mutation significantly decreased the thermal stability of amicyanin, as determined by changes in the visible absorbance of oxidized amicyanin and in the circular dichroism spectra for oxidized, reduced and apo forms of amicyanin. Comparison of the crystal structures suggests that the decreased stability of W45Y amicyanin may be attributed to the loss of a strong interior hydrogen bond between Trp45 and Tyr90 in native amicyanin which links two of the β-sheets that comprise the overall structure of amicyanin. Thus, Trp45 is critical for stabilizing the structure of amicyanin but it does not influence the electronic properties of the copper which quenches its fluorescence.

Redox properties of human hemoglobin in complex with fractionated dimeric and polymeric human haptoglobin

Haptoglobin (Hp) is an abundant and conserved plasma glycoprotein, which binds acellular adult hemoglobin (Hb) dimers with high affinity and facilitates their rapid clearance from circulation after hemolysis. Humans possess three main phenotypes of Hp, designated Hp 1-1, Hp 2-1, and Hp 2-2. These variants exhibit diverse structural configurations and have been reported to be functionally nonequivalent. We have investigated the functional and redox properties of Hb–Hp complexes prepared using commercially fractionated Hp and found that all forms exhibit similar behavior. The rate of Hb dimer binding to Hp occurs with bimolecular rate constants of ~0.9μM−1 s−1, irrespective of the type of Hp assayed. Although Hp binding does accelerate the observed rate of HbO2 autoxidation by dissociating Hb tetramers into dimers, the rate observed for these bound dimers is three- to fourfold slower than that of Hb dimers free in solution. Co-incubation of ferric Hb with any form of Hp inhibits heme loss to below detectable levels. Intrinsic redox potentials (E1/2) of the ferric/ferrous pair of each Hb–Hp complex are similar, varying from +54 to +59mV (vs NHE), and are essentially the same as reported by us previously for Hb–Hp complexes prepared from unfractionated Hp. All Hb–Hp complexes generate similar high amounts of ferryl Hb after exposure to hydrogen peroxide. Electron paramagnetic resonance data indicate that the yields of protein-based radicals during this process are approximately 4 to 5% and are unaffected by the variant of Hp assayed. These data indicate that the Hp fractions examined are equivalent to one another with respect to Hb binding and associated stability and redox properties and that this result should be taken into account in the design of phenotype-specific Hp therapeutics aimed at countering Hb-mediated vascular disease.

The INAD Scaffold Is a Dynamic, Redox-Regulated Modulator of Signaling in the Drosophila Eye

INAD is a scaffolding protein that regulates signaling in Drosophila photoreceptors. One of its PDZ domains, PDZ5, cycles between reduced and oxidized forms in response to light, but it is unclear how light affects its redox potential. Through biochemical and structural studies, we show that the redox potential of PDZ5 is allosterically regulated by its interaction with another INAD domain, PDZ4. Whereas isolated PDZ5 is stable in the oxidized state, formation of a PDZ45 "supramodule" locks PDZ5 inthe reduced state by raising the redox potential ofits Cys606/Cys645 disulfide bond by ∼330mV. Acidification, potentially mediated via light and PLCβ-mediated hydrolysis of PIP(2), disrupts the interaction between PDZ4 and PDZ5, leading to PDZ5 oxidation and dissociation from the TRP Ca(2+) channel, a key component of fly visual signaling. These results show that scaffolding proteins can actively modulate the intrinsic redox potentials of their disulfide bonds to exert regulatory roles in signaling.

All-solid-state lithium battery with a three-dimensionally ordered Li 1.5Al 0.5Ti 1.5(PO 4) 3 electrode

To fabricate all-solid-state Li batteries using three-dimensionally ordered macroporous Li 1.5Al 0.5Ti 1.5(PO 4) 3 (3DOM LATP) electrodes, the compatibilities of two anode materials (Li 4Mn 5O 12 and Li 4Ti 5O 12) with a LATP solid electrolyte were tested. Pure Li 4Ti 5O 12 with high crystallinity was not obtained because of the formation of a TiO 2 impurity phase. Li 4Mn 5O 12 with high crystallinity was produced without an impurity phase, suggesting that Li 4Mn 5O 12 is a better anode material for the LATP system. A Li 4Mn 5O 12/3DOM LATP composite anode was fabricated by the colloidal crystal templating method and a sol–gel process. Reversible Li insertion into the fabricated Li 4Mn 5O 12/3DOM LATP anode was observed, and its discharge capacity was measured to be 27 mA h g −1. An all-solid-state battery composed of LiMn 2O 4/3DOM LATP cathode, Li 4Mn 5O 12/3DOM LATP anode, and a polymer electrolyte was fabricated and shown to operate successfully. It had a potential plateau that corresponds to the potential difference expected from the intrinsic redox potentials of LiMn 2O 4 and Li 4Mn 5O 12. The discharge capacity of the all-solid-state battery was 480 μA h cm −2.

Determination of the intrinsic redox potentials of FeS centers of respiratory complex I from experimental titration curves

Recently, Euro et al. [Biochem. 47, 3185 (2008) ] have reported titration data for seven of nine FeS redox centers of complex I from Escherichia coli. There is a significant uncertainty in the assignment of the titration data. Four of the titration curves were assigned to N1a, N1b, N6b, and N2 centers; one curve either to N3 or N7; one more either to N4 or N5; and the last one denoted Nx could not be assigned at all. In addition, the assignment of the titration data to the N6b/N6a pair is also uncertain. In this paper, using our calculated interaction energies [Couch et al. BBA 1787, 1266 (2009)], we perform statistical analysis of these data, considering a variety of possible assignments, find the best fit, and determine the intrinsic redox potentials of the centers. The intrinsic potentials could be determined with an uncertainty of less than ± 10 mV at a 95% confidence level for best fit assignments. We also find that the best agreement between theoretical and experimental titration curves is obtained with the N6b–N2 interaction equal to 71 ± 14 or 96 ± 26 mV depending on the N6b/N6a titration data assignment, which is stronger than was expected and may indicate a close distance of the N2 center to the membrane surface.

Properties of the Thioredoxin Fold Superfamily Are Modulated by a Single Amino Acid Residue

The ubiquitous thioredoxin fold proteins catalyze oxidation, reduction, or disulfide exchange reactions depending on their redox properties. They also play vital roles in protein folding, redox control, and disease. Here, we have shown that a single residue strongly modifies both the redox properties of thioredoxin fold proteins and their ability to interact with substrates. This residue is adjacent in three-dimensional space to the characteristic CXXC active site motif of thioredoxin fold proteins but distant in sequence. This residue is just N-terminal to the conservative cis-proline. It is isoleucine 75 in the case of thioredoxin. Our findings support the conclusion that a very small percentage of the amino acid residues of thioredoxin-related proteins are capable of dictating the functions of these proteins.

Reactivities of Quinone-free DsbB from Escherichia coli

DsbB is a disulfide oxidoreductase present in the Escherichia coli plasma membrane. Its cysteine pairs, Cys41-Cys44 and Cys104-Cys130, facing the periplasm, as well as the bound quinone molecules play crucial roles in oxidizing DsbA, the protein dithiol oxidant in the periplasm. In this study, we characterized quinone-free forms of DsbB prepared from mutant cells unable to synthesize ubiquinone and menaquinone. While such preparations lacked detectable quinones, previously reported lauroylsarcosine treatment was ineffective in removing DsbB-associated quinones. Moreover, DsbB-bound quinone was shown to contribute to the redox-dependent fluorescence changes observed with DsbB. Now we reconfirmed that redox potentials of cysteine pairs of quinone-free DsbB are lower than that of DsbA, as far as determined in dithiothreitol redox buffer. Nevertheless, the quinone-free DsbB was able to oxidize approximately 40% of DsbA in a 1:1 stoichiometric reaction, in which hemi-oxidized forms of DsbB having either disulfide are generated. It was suggested that the DsbB-DsbA system is designed in such a way that specific interaction of the two components enables the thiol-disulfide exchanges in the "forward" direction. In addition, a minor fraction of quinone-free DsbB formed the DsbA-DsbB disulfide complex stably. Our results show that the rapid and the slow pathways of DsbA oxidation can proceed up to significant points, after which these reactions must be completed and recycled by quinones under physiological conditions. We discuss the significance of having such multiple reaction pathways for the DsbB-dependent DsbA oxidation.

Direct Measurement of the Hydrogen-Bonding Effect on the Intrinsic Redox Potentials of [4Fe−4S] Cubane Complexes

To probe how H-bonding effects the redox potential changes in Fe-S proteins, we produced and studied a series of gaseous cubane-type analogue complexes, [Fe(4)S(4)(SEt)(3)(SC(n)H(2n+1))](2-) and [Fe(4)S(4)(SEt)(3)(SC(n)H(2n)OH)](2-) (n = 4, 6, 11; Et = C(2)H(5)). Intrinsic redox potentials for the [Fe(4)S(4)](2+/3+) redox couple involved in these complexes were measured by photoelectron spectroscopy. The oxidation energies from [Fe(4)S(4)(SEt)(3)(SC(n)H(2n)OH)](2-) to [Fe(4)S(4)(SEt)(3)(SC(n)H(2n)OH)](-) were determined directly from the photoelectron spectra to be approximately 130 meV higher than those for the corresponding [Fe(4)S(4)(SEt)(3)(SC(n)H(2n+1))](2-) systems, because of the OH...S hydrogen bond in the former. Preliminary Monte Carlo and density functional calculations showed that the H-bonding takes place between the -OH group and the S on the terminal ligand in [Fe(4)S(4)(SEt)(3)(SC(6)H(12)OH)](2-). The current data provide a direct experimental measure of a net H-bonding effect on the redox potential of [Fe(4)S(4)] clusters without the perturbation of other environmental effects.

Probing the intrinsic electronic structure of the cubane [4Fe-4S] cluster: nature's favorite cluster for electron transfer and storage.

The cubane [4Fe-4S] is the most common multinuclear metal center in nature for electron transfer and storage. Using electrospray, we produced a series of gaseous doubly charged cubane-type complexes, [Fe4S4L4]2- (L = -SC2H5, -SH, -Cl, -Br, -I) and the Se-analogues [Fe4Se4L4]2- (L = -SC2H5, -Cl), and probed their electronic structures with photoelectron spectroscopy and density functional calculations. The photoelectron spectral features are similar among all the seven species investigated, revealing a weak threshold feature due to the minority spins on the Fe centers and confirming the low-spin two-layer model for the [4Fe-4S](2+) core and its "inverted level scheme". The measured adiabatic detachment energies, which are sensitive to the terminal ligand substitution, provide the intrinsic oxidation potentials of the [Fe4S4L4]2- complexes. The calculations revealed a simple correlation between the electron donor property of the terminal thiolate as well as the bridging sulfide with the variation of the intrinsic redox potentials. Our data provide intrinsic electronic structure information of the [4Fe-4S] cluster and the molecular basis for understanding the protein and solvent effects on the redox properties of the [4Fe-4S] active sites.

Probing the Electronic Structure of the Di-Iron Subsite of [Fe]-Hydrogenase: A Photoelectron Spectroscopic Study of Fe(I)−Fe(I) Model Complexes

The electronic structures of a series of Fe(I)−Fe(I) model complexes of the di-iron subsite of [Fe]-hydrogenase, [(μ-PDT)Fe2(CO)4(CN)2]2- (I), [Fe2(CO)4{MeSCH2C(Me)(CH2S)2}(CN)2]2- (II), [Fe2(CO)4{PhCH2SCH2C(Me)(CH2S)2}(CN)2]2- (III), [Fe2(CO)4{PhCH2SCH2C(Me) (CH2S)2}(CN)]- (IV), and [Fe2(CO)4{MeSCH2C(Me)(CH2S)2}(CN)]- (V), were investigated in the gas phase using photodetachment photoelectron spectroscopy. The adiabatic electron detachment energy (ADE) of each species and the intramolecular Coulomb repulsion for the doubly charged species were obtained. The ADEs correspond to the intrinsic redox potentials (in vacuo) of reactions involving the Fe(I)−Fe(I)/Fe(I)−Fe(II) couples in these compounds. The photoelectron spectra were understood and qualitatively assigned by comparing with that of Fe2(CO)6S2, which has been well studied previously and exhibits similar valence spectral features as I−V. A “normal level scheme” is suggested for the electronic structure of these low spin di-iron compounds, in which all occupied 3d levels lie above all occupied ligand levels. We also observed subtle differences in the electronic structures of the five di-iron complexes due to the slightly different ligand environments.

Paradoxical redox properties of DsbB and DsbA in the protein disulfide-introducing reaction cascade.

Protein disulfide bond formation in the bacterial periplasm is catalyzed by the Dsb enzymes in conjunction with the respiratory quinone components. Here we characterized redox properties of the redox active sites in DsbB to gain further insights into the catalytic mechanisms of DsbA oxidation. The standard redox potential of DsbB was determined to be -0.21 V for Cys41/Cys44 in the N-terminal periplasmic region (P1) and -0.25 V for Cys104/Cys130 in the C-terminal periplasmic region (P2), while that of Cys30/Cys33 in DsbA was -0.12 V. To our surprise, DsbB, an oxidant for DsbA, is intrinsically more reducing than DsbA. Ubiquinone anomalously affected the apparent redox property of the P1 domain, and mutational alterations of the P1 region significantly lowered the catalytic turnover. It is inferred that ubiquinone, a high redox potential compound, drives the electron flow by interacting with the P1 region with the Cys41/Cys44 active site. Thus, DsbB can mediate electron flow from DsbA to ubiquinone irrespective of the intrinsic redox potential of the Cys residues involved.