Efficient Electron Transfer Mediator Research Articles

Thymoquinone as an electron transfer mediator to convert Type II photosensitizers to Type I photosensitizers

The development of Type I photosensitizers (PSs) is of great importance due to the inherent hypoxic intolerance of photodynamic therapy (PDT) in the hypoxic microenvironment. Compared to Type II PSs, Type I PSs are less reported due to the absence of a general molecular design strategy. Herein, we report that the combination of typical Type II PS and natural substrate carvacrol (CA) can significantly facilitate the Type I pathway to efficiently generate superoxide radical (O2–•). Detailed mechanism study suggests that CA is activated into thymoquinone (TQ) by local singlet oxygen generated from the PS upon light irradiation. With TQ as an efficient electron transfer mediator, it promotes the conversion of O2 to O2–• by PS via electron transfer-based Type I pathway. Notably, three classical Type II PSs are employed to demonstrate the universality of the proposed approach. The Type I PDT against S. aureus has been demonstrated under hypoxic conditions in vitro. Furthermore, this coupled photodynamic agent exhibits significant bactericidal activity with an antibacterial rate of 99.6% for the bacterial-infection female mice in the in vivo experiments. Here, we show a simple, effective, and universal method to endow traditional Type II PSs with hypoxic tolerance.

A Novel Viologen‐Derived Covalent Organic Framework Based Metal Free Catalyst for Nitrophenol Reduction

AbstractIt is highly desirable to develop new metal free catalysts to reduction of toxic organic pollutants such as 4‐nitrophenol (4‐NP). Viologens are efficient electron‐transfer mediators (ETMs) for reduction reactions with NaBH4 as an effective hydrogen source. NaBH4‐assisted reduction of 4‐NP via a novel viologen‐based covalent organic framework as metal free catalyst has been reported. The butyl bridge between the pyridine moieties at viologen based COF‐TPCBP structure provides flexibility to the framework and gives the structure and amorphous character according to SEM, TEM and XRD results. The flexible 3D structure was also demonstrated by the geometric optimization. The structure without any metal moiety was fully completed to 4‐NP reduction in only 12 minutes and have 88 % efficiency after 5 catalytic cycles because of the porous surface of the COF‐TPCBP powder.

Unexpected Insulating Polymer Maneuvered Solar CO2‐to‐Syngas Conversion

AbstractCO2 reduction to carbon feedstocks using heterogeneous photocatalysis technique has been deemed as an attractive means of addressing both deteriorating greenhouse effect and depletion of fossil fuels. Nevertheless, deficiency of accessible active sites on the catalyst surface, low CO2 adsorption rate, and short carrier lifetime retard the photocatalytic CO2 conversion into hydrocarbon fuels. In this study, the controllable construction of spatially separated directional charge transport pathways over multilayered heterostructured transition metal chalcogenides (TMCs) based photosystems for high‐performance photocatalytic CO2‐to‐syngas conversion are shown. In this scenario, ultrathin non‐conjugated insulating poly(diallyl‐dimethyl‐ammonium chloride) (PDDA) layer are intercalated in‐between TMCs and layered double hydroxide (LDH) and serve as an efficient electron transfer mediator, whilst LDH functions as a hole‐withdrawing regulator, both of which synergistically foster the spatial vectorial charge migration/separation over TMCs, thus endowing the TMCs/PDDA/LDH heterostructures with significantly boosted visible‐light‐driven photoactivity toward CO2 conversion into syngas. This study can inspire sparkling new ideas to realize fine tuning of charge motion for stimulating solar‐to‐fuel conversion.

Inner-Membrane-Bound Gold Nanoparticles as Efficient Electron Transfer Mediators for Enhanced Mitochondrial Electron Transport Chain Activity.

Electron transfer through the mitochondrial electron transport chain (ETC) can be critically blocked by the dysfunction of protein complexes. Redox-active molecules have been used to mediate the electron transfer in place of the dysfunctional complexes; however, they are limited to replacing complex I and are known to be toxic. Here we report artificial mitochondrial electron transfer pathways that enhance ETC activity by exploiting inner-membrane-bound gold nanoparticles (GNPs) as efficient electron transfer mediators. The hybridization of mitochondria with GNPs, driven by electrostatic interaction, is successfully visualized in real time at the level of a single mitochondrion. By observing quantized quenching dips via plasmon resonance energy transfer, we reveal that the hybridized GNPs are bound to the inner membrane of mitochondria irrespective of the presence of the outer membrane. The ETC activity of mitochondria with GNPs such as membrane potential, oxygen consumption, and ATP production is remarkably increased in vitro.

Z-scheme K-C3N4/Ag/Ag3PMo12O40 heterojunction with improved visible light photodegradation of formaldehyde

Photocatalytic degradation of formaldehyde is an ideal way to solve indoor air pollution. The development of Z-scheme heterojunction photocatalysts is economic and effective way in eliminating formaldehyde pollution. Herein, a ternary heterojunction photocatalyst K-C3N4/Ag/Ag3PMo12O40 (abbreviated as K-C3N4/Ag/APM) was synthesized by self-assembly of PMo12O403- with Ag+ and K-C3N4 followed by in-situ photoreduction. The Ag/Ag3PMo12O40 (APM) hetero-nanoparticles obtained by photoreduction are uniformly loaded on K-C3N4 nanosheets. The structure, morphology, optical and photoelectrochemical properties etc. of K-C3N4/Ag/APM were characterized and explored. The photocatalytic activity of K-C3N4/Ag/APM was assessed on the degradation of HCHO. K-C3N4/Ag/APM showed remarkably improved photocatalytic activity than the g-C3N4, K-C3N4 and K-C3N4/Ag in the degradation of HCHO under visible light irradiation. The K-C3N4/Ag/APM heterojunction can degrade 60% gaseous HCHO (0.16 mg L-1) in 60 min (λ > 400 nm). The optimum experimental parameters were temperature 20 ℃, RH 70%, catalyst amount 20 mg and initial HCHO concentration 0.16 mg L-1. The enhanced photocatalytic efficiency of K-C3N4/Ag/APM is attributed to the synergistic effect of improved light harvesting, excellent interface contact and accelerated transmission and separation of photogenerated carriers in the Z-scheme structure with Ag as efficient electron transfer mediators. Free radical trapping and electron spin resonance (ESR) experiments confirmed the Z-scheme charge transfer mechanism, and proved that •O2– and h+ were the main active species in HCHO oxidation reaction. The intermediate species in the HCHO photocatalytic degradation process were tested by in situ DRIFTS technology. The construction of g-C3N4 based Z-scheme photocatalyst may provide an insight for the design of new and efficient photocatalysts for environmental applications.

Enhancing the Photoelectrochemical Water Oxidation Activity of α‐Fe2O3 Thin Film Photoanode by Employing rGO as Electron Transfer Mediator and NiFe‐LDH as Cocatalyst

AbstractThe shortcomings of poor charge transfer ability and slow surface water oxidation kinetics in the single component photoanode limit the performances of photocatalytic water splitting. Herein, a α‐Fe2O3/rGO/NiFe‐LDH composite photoanode was designed for enhancing photoelectrochemical (PEC) water oxidation activity. The rGO nanosheets serve as an efficient electron transfer mediator for promoting charge transport and separation. The NiFe‐LDH is well anchored on rGO nanosheets and provides additional active sites for accelerating water oxidation reaction kinetics. By the virtue of synergistic effect between rGO and NiFe‐LDH, the composite photoanode achieves a pronounced photocurrent density of 1.46 mA/cm2 at 1.23 VRHE (V vs. reversible hydrogen electrode), which is 2.86 times of α‐Fe2O3. Moreover, the onset potential exhibits a significant cathodic shift of 230 mV. This work provides a valuable strategy for the design of photoanode with light absorber, rGO electron transfer mediator and other cocatalysts to achieve efficient and stable PEC water splitting.

A semiconductor/molecular catalyst hybrid photoanode with FeOOH as an electron transfer relay

A Fe2 O3 /FeOOH/poly-Ru(bda)(vpy) (bda = 2,2'-bipyridine-6,6'-dicarboxylate,vpy = 4-vinylpyridine) photoanode has been fabricated by electropolymerization of molecular Ru(bda)(vpy) catalyst on FeOOH modified Fe2 O3 , in which a thin layer of FeOOH replicates the role of tyrosine residue in PSII as an efficient electron transfer mediator. The ternary hybrid photoanode produced a 2.4 times higher photocurrent density than that of previously reported Fe2 O3 /poly-Ru(bda)(vpy) under AM 1.5 G illumination and displayed a negative shift on the onset potential by 100 mV. In addition, the Fe2 O3 /FeOOH/poly-Ru(bda)(vpy) exhibited long-term stability for at least 10 h with a Faraday efficiency of ∼96%. The high performance shown here was attributed to the improved charge separation between excited semiconductor and the catalyst caused by FeOOH mediated electron transfer on the electrode surface.

Z-scheme heterojunction g-C3N4@PDA/BiOBr with biomimetic polydopamine as electron transfer mediators for enhanced visible-light driven degradation of sulfamethoxazole

Visible-light photocatalysis boosted by Z-scheme photocatalysts has been deemed as an economic and effective way in eliminating emerging antibiotics pollution. A Z-scheme heterojunction photocatalyst g-C3N4@PDA/BiOBr (CNPB) was hereby facilely constructed through polydopamine (PDA) modification of g-C3N4 followed by deposition of BiOBr component via a solvothermal reaction. The structure, morphology, optical and photoelectrochemical properties etc. of CNPB were characterized and explored. The photocatalytic activity of CNPB was assessed on the degradation of sulfamethoxazole (SMX). CNPB manifested remarkably improved photocatalytic performance than the as-prepared g-C3N4, BiOBr and g-C3N4/BiOBr heterojunction in the degradation of SMX under visible light irradiation. SMX could be nearly completely degraded in 60 mins by CNPB, while the degradation rate of SMX under g-C3N4, BiOBr, g-C3N4/BiOBr heterojunction, and the “g-C3N4@PDA + BiOBr” mixture were 30%, 42%, 71%, and 47%, respectively. The highly enhanced photocatalytic efficiency of CNPB was attributed to the synergistic effect of improved light harvesting and accelerated transport and separation of photo-generated carriers in the Z-scheme structure with PDA as efficient electron transfer mediators. A Z-scheme charge transfer mechanism was confirmed by experiments on radical scavenging and electron spin resonance (ESR) signals trapping, which demonstrated that the h+ and O2− were the major reactive species in oxidizing SMX. The degradation mechanism, main intermediates and reaction pathways were further explored. Besides, CNPB exhibited good stability and reusability in multiple uses. The construction of Z-scheme photocatalyst using biomimetic polydopamine as electron transfer mediators may provide an insight into designing new and efficient photocatalysts for environmental applications.

Mediator BOD Biosensor Based on Cells of Microorganisms Isolated from Activated Sludge

Three bacterial strains (SPB1, SPB2, and SPB3) isolated from the activated sludge of treatment facilities most efficiently oxidized (as compared to other strains) a model solution based on glucose and glutamic acid in the presence of a ferrocene mediator. The possible use of isolated strains as a basis for a mediator-type amperometric BOD biosensor was studied. Analysis of 16S rRNA genes demonstrated that the SPB1, SPB2, and SPB3 strains are 99.79–100% similar to the Paracoccus yeei BAA-599T, Pseudomonas veronii DSM 11331T, and Bacillus proteolyticus TD42T strains, respectively. It was established that the bioreceptor element based on the P. yeei SPB1 strain possessed the best characteristics. It was stable in storage at 4°С for 22 days, and the lower limit of detectable concentrations was 1.3 mg О2/dm3. In order to search for the most efficient electron transfer mediator for this strain, nine compounds, including ferrocene, thionine, methylene blue, potassium hexacyanoferrate(III), and 2,6-dichlorophenolindophenol, were screened. The mediator electron transfer signals were obtained for each of them. Ferrocene was the most efficient in terms of sensitivity and the amount of substrate oxidation that can be registered in the presence of the mediator. An analysis of ten samples of wastewater (before and after purification) and the rivers of Tula oblast demonstrated that the use of ferrocene and P. yeei SPB1 strain cells made it possible to obtain data with a high correlation (R = 0.9934) with the results of the standard method.

Persulfate activation with rice husk-based magnetic biochar for degrading PAEs in marine sediments.

Phthalate esters (PAEs) can interfere with the endocrine systems of humans and wildlife. The main objective of this study was to evaluate the suitability of a composite for remediating marine sediments contaminated with PAEs. The composite was synthesized with magnetite nanoparticles (Fe3O4) and rice husk biochar (RHB) by using chemical co-precipitation. Fe3O4, RHB, and Fe3O4-RHB substantially activated sodium persulfate (Na2S2O8, PS) oxidation to form SO4-• and thus degrade PAEs in marine sediments in a slurry system. The morphology and structural composition of the magnetic composites were examined using XRD, FTIR, environmental scanning electron microscopy-energy-dispersive X-ray spectrometry, and superconducting quantum interference device. The Fe3O4-RHB composites were confirmed to be prepared successfully. The influences of various parameters, including the PS concentration, composite loading, and initial pH, were investigated. The concentration of high-molecular-weight PAEs (HPAEs) in sediment was much higher than that of low-molecular-weight PAEs (LPAEs); di-(2-ethylhexyl) phthalate (DEHP) was an especially salient marker of PAE contamination in sediments. Furthermore, increasing the PS and Fe3O4-RHB doses accelerated PAE oxidation at pH3.0; 83% degradation of PAEs was achieved when the PS and Fe3O4-RHB concentrations were increased to 2.3 × 10-2mM and 1.67g/L, respectively. LPAEs such as dibutyl phthalate (DnBP) are easier to degrade than HPAEs such as DEHP, diisononyl phthalate (DINP), and diisodecyl phthalate (DIDP). In addition, possible activation mechanisms of the interactions between S2O82- and Fe2+/Fe3+ on the Fe3O4 surface, which involve an efficient electron transfer mediator of the RHB oxygen functional groups promoting the generation of SO4-• in the Fe3O4-RHB/PS system, were clarified. Thus, the Fe3O4-RHB/PS oxidation process is expected to be a viable method for remediating PAE-contaminated marine sediment.

A new electron transfer mediator actuated non-enzymatic nitrite sensor based on the voltammetry synthetic composites of 1-(2-pyridylazo)-2-naphthol nanostructures coated electrochemical reduced graphene oxide nanosheets

As efficient electron transfer mediator, various nanomaterials with smart performance have been explored in non-enzymatic sensor fabrication. We herein present an electron transfer mediator actuated electrochemical non-enzymatic sensor to assay nitrite, enabled by electrochemical reduced graphene oxide (ERGO) and 1-(2-pyridylazo)-2-naphthol (PAN). The composites of PAN-ERGO coating on electrode surface were successfully fabricated through a facile and green cyclic voltammetry technique. With the aid of ERGO nanosheets on the electrode surface, the electron transfer mediator of PAN nanostructures was easily immobilized and hybridized with ERGO, resulting in a remarkably synergistic effect between ERGO sensing substrate and the electrodeposited PAN coating for target electron transfer. The results demonstrated that the electrocatalytic current increased linearly with the nitrite concentration in the range of 7.49–1752.6 μM and 1752.6–3500 μM, with a good detection limit of 0.67 μM and 1.44 μM (signal-to-noise ratio, S/N = 3), respectively. The present work provide some new insights for the smart design of high efficiency electrocatalytic materials that based on the composites of electrochemical reduced graphene oxide and other substances.

G-C3N4 Hydrogen-Bonding Viologen for Significantly Enhanced Visible-Light Photocatalytic H2 Evolution

Graphitic carbon nitride (g-C3N4) has recently emerged as a promising metal-free photocatalytic material for the conversion of solar energy into chemical energy under visible-light irradiation. Unfortunately, the photocatalytic activity of g-C3N4 is still unsatisfactory due to the serious recombination of photogenerated electron–hole pairs. Here, we develop a strategy to construct a type of g-C3N4-based composite photocatalyst (C3N4/CBV2+), a g-C3N4 surface coupled with a viologen redox mediator (1,1′-bis(4-carboxylatobenzyl)-4,4′-bipyridinium dichloride, denoted as CBV2+) through hydrogen bonds, for enhanced H2 production from water under visible-light irradiation. The CBV2+ molecules not only provide sites for metal particle formation but also act as an efficient electron transfer mediator to transfer the photoinduced electrons from g-C3N4 to platinum nanoparticles (Pt NPs). The vectorial charge transfer results in an efficient spatial separation of electrons and holes in the C3N4/CBV2+ composite photoc...

A Novel Chemical Sensor Based on Sb2S3 Film for Highly Sensitive Detection of Hydrazine

AbstractThe Sb2S3 film on indium‐tin oxide (ITO) substrate has been used as an efficient electron transfer mediator for the fabrication of novel chemical sensor towards hydrazine, which is a diamine known as neurotoxin and carcinogen. Sb2S3 film is deposited on ITO substrate by drop‐casting process using Sb2S3 solution as precursor and possesses reticular structure with the morphology of uniform hollow hemispheres. The fabricated chemical sensor for selective detection of hydrazine displays a high sensitivity of 106.25 μA/(mM cm2) with a low detection limit of 0.5 μM and it also exhibits excellent reproducibility and stability in hydrazine detection.

Trilayer CdS/carbon nanofiber (CNF) mat/Pt-TiO2 composite structures for solar hydrogen production: Effects of CNF mat thickness

Solar H2 production by photocatalytic water splitting is a promising technology that permits direct H2 production from the clean and abundant resources of water and solar light. We successfully fabricated trilayer heterostructures of CdS/carbon nanofiber (CNF) mat/Pt-deposited TiO2 (Pt-TiO2) for solar H2 production. The CNF mat was prepared by electrospinning and carbonization. CdS and Pt-TiO2 were coated on the front and back of the CNF mat by doctor blading. Under visible-light irradiation on the CdS side, the addition of the Pt-TiO2 coating improved the H2 production by a factor of 3.4. This suggests that the H2 production reaction could occur on Pt-TiO2, which is not active under visible irradiation; therefore, the CNF mat could act as an efficient photogenerated electron-transfer mediator from CdS to Pt-TiO2. The H2 production rates of the trilayer CdS/CNF/Pt-TiO2 heterostructures were strongly affected by the thickness of the CNF mat and the carbonization temperatures used in production, which affect the resistance of the CNF mat between the CdS and Pt-TiO2 sides. The results clearly demonstrated that the CNF acted as an efficient electron-transfer mediator as well as a support material.

Electron-transfer catalyzed cycloaddition reactions of unactivated cyclic olefins in weakly coordinating anion electrolyte

Cis-Cyclooctene, C8H14, undergoes an efficient electron-transfer (ET) catalyzed cycloaddition reaction in dichloromethane containing [NBu4][B(C6F5)4] as supporting electrolyte. The reactions were initiated by in-situ anodic generation of catalytic amounts of either [N(2,4-C6H3Br2)3]+ (1+, “magic green”) or [ReCp(CO)3]+ (2+, Cp=(η5-C5H5)). The olefin radical chain reaction induced by ET mediation was complete in less than 10min, some 100–1000times faster than the optimum photochemically induced preparations of cyclobutane derivatives from cyclic olefins. Yields of up to 87% of mixtures of C16H28 isomers were obtained at an electro-synthetic level. Use of the weakly coordinating [B(C6F5)4]− anion, rather than a traditional small anion such as [PF6]− or [ClO4]−, was required to carry out the cyclization reactions. The more easily oxidized trans-cyclooctene, when anodized directly at an electrode, gave a similar isomeric mixture of cyclobutanes. Cycloheptene and cyclohexene underwent similar [2+2] coupling to give cyclobutane products. Cyclopentene gave a [2+2+2] cyclized trimer. The mechanism appears to involve a key radical–substrate propagation step in which an olefin radical cation reacts with a neutral olefin to give a cyclobutyl radical cation, which then accepts an electron, most likely from another olefin, to form the final neutral compound. Although the E1/2 potentials of the ET mediators are 660–900mV lower than the estimated oxidation potentials of the olefins, the endergonic nature of the ET initiation step works to the advantage of the chain process by favoring the radical–substrate propagation step.

Electrical and optical properties of gold nanoparticles: applications in gold nanoparticles-cholesterol oxidase integrated systems for cholesterol sensing

We describe here the application of electrical and optical properties of gold nanoparticles (AuNPs) in conjunction with cholesterol oxidase (ChOx) for cholesterol estimation. The electrocatalytic property of AuNPs was studied with spectrophotometric technique using a redox dye 2,6-dichloroindophenol (DCPIP), where AuNPs found to increase the electron transfer rate between ChOx and DCPIP by ~1.68-fold. This study demonstrated AuNPs as efficient electron transfer mediator for ChOx based electrochemical cholesterol biosensors. Optocatalytic property of AuNPs was used in the AuNPs seed mediated enlargement system to develop an optical detection path for cholesterol. This optical method exhibited a linear detection range of 0.01–0.1 mM and a detection limit of 10 μM cholesterol. The effect of AuNPs size (13–21 nm) on the catalytic properties of AuNPs was also studied. Spectrophotometric analysis of the electron transfer process between ChOx and DCPIP with different sized AuNPs showed highest electron transfer efficiency with smaller (13 nm) AuNPs. The electrochemical bioelectrode fabricated with AuNPs and ChOx gave consensus results. Contrastingly, AuNPs size did not affect its optocatalytic activity and eventually the performance of the optical method based on the growth of AuNPs. The findings of the present study offer useful insight and perspectives for fabricating highly sensitive analytical systems based on AuNPs–ChOx complexes.

Substituted polypyridine complexes of cobalt(II/III) as efficient electron-transfer mediators in dye-sensitized solar cells.

A number of cobalt complexes of substituted polypyridine ligands were synthesized and investigated as possible alternatives to the volatile and corrosive iodide/triiodide redox couple commonly used as an electron-transfer mediator in dye-sensitized solar cells (DSSCs). The extinction coefficients in the visible spectrum are on the order of 10(2) M(-1) cm(-1) for the majority of these complexes, diminishing competition with the light-harvesting dye. Cyclic voltammetric studies revealed a dramatic surface dependence of the heterogeneous electron-transfer rate, which is surprisingly different for gold, carbon, and platinum electrodes. DSSCs were assembled using a mediator that consisted of a mixture of Co(II) and Co(III) complexes in a 10:1 ratio. DSSCs containing these mediators were used to characterize incident photon-to-current conversion efficiency and photoelectrochemical responses. The best performing of these mediators were identified and subjected to further study. As suggested by electrochemical results, gold and carbon are superior cathode materials to platinum, and no evidence of corrosion on any cathode material was observed. Addition of lithium salts to the mediator solution resulted in a dramatic improvement in cell performance. The observed Li(+) effect is explained in terms of the recombination of injected electrons in the photoanode with the oxidized mediator. The best mediator, based on tris(4,4'-di-tert-butyl-2,2'-dipyridyl)cobalt(II/III) perchlorate, resulted in DSSCs exhibiting efficiencies within 80% of that of a comparable iodide/triiodide-mediated DSSC. Due to the commercial availability of the ligand and the simplicity with which the complex can be made, this new mediator represents a nonvolatile, noncorrosive, and practical alternative as an efficient electron-transfer mediator in DSSCs.

Interactions of glucose oxidase with various metal polypyridine complexes as mediators of glucose oxidation.

The interaction between glucose oxidase (GOx) and a typical metal complex, which is chemically stable in both oxidized and reduced forms, has been investigated by a voltammetric method. The evaluation of an electron-transfer mediator useful for glucose oxidation is discussed from thermodynamic and kinetic points of view, i.e. the redox potentials of various metal complexes and the second-order rate constants for the electron transfer between GOx in reduced form and the metal complexes in oxidized form. No mediation of glucose oxidation by [Co(bpy)(3)](2+) (bpy=2,2'-bipyridine) or [Cu(bpy)(2)](2+) occurred, in spite of their appropriate redox potentials. This was attributed mainly to the lower electron-self-exchange rates of the mediator and the reaction with GOx. All three types of osmium(II) complexes, [Os(PP) (n)](2+) ( n=2 or 3; PP=polypyridine), [OsL(2)(PP)(2)](2+) (L=imidazole and its derivatives), and [OsClL(bpy)(2)](+), acted as excellent electron-transfer mediators for the glucose oxidation. Mixed ligand complexes, [OsL(2)(PP)(2)](2+) and [OsClL(bpy)(2)](+), have been concluded to be more efficient electron-transfer mediators. The electron-transfer rates between the mediator and GOx have been found to be accelerated by intermolecular electrostatic interactions or hydrogen bonds.

Evaluation of osmium(II) complexes as electron transfer mediators accessible for amperometric glucose sensors.

In order to lower the redox potentials of Os(III/II) complexes, the mixed ligand complexes of Os(II) were synthesized. The redox potentials of Os(III/II) complexes could be lowered by the use of 4,4'-dimethyl-2,2'-bipyridine (dmbpy), imidazole (Him) or its derivatives, and chloride ion as ligands, e.g., values of the redox (formal) potentials of 628 mV vs. Ag/AgCl for [Os(bpy)3]3+/2+ (bpy: 2,2'-bipyridine) and -6 mV for [OsCl(Him)(dmbpy)2]2+/+ were given in deaerated 0.1 mol dm-3 phosphate buffer (pH 7.0). The evaluation of Os(II) complexes as electron transfer mediators accessible for amperometric glucose sensors was examined according to the determination of the redox potentials of Os(III/II) complexes and the second-order rate constants for electron transfer between glucose oxidase (GOx) in reduced form and the Os(III) complex. Although the Os(II) complexes with lower redox potentials tended to decrease the second-order rate constants ks, the ks values for the majority of Os(II) complexes synthesized in this study were greater than that for ferrocenecarboxylic acid. Acceleration of the electron-transfer reaction is attributable to the hydrogen bonding and/or the electrostatic interaction between the Os(II) complexes and GOx. It may be consequently concluded that the mixed ligand complexes of Os(II) with bpy (dmbpy), Him (its derivatives), and Cl- can act as more efficient electron transfer mediators for the fabrication of amperometric glucose sensors.

Electrochemical analysis of the coordination sphere of ruthenium(ii) as electron transfer mediator in glucose oxidase catalysis in aqueous solutions

The redox potentials of the cis-[Ru(LL)2XY]n+ complexes (LL = 2,2"-bipyridyl (bpy), 1,10-phenanthroline (phen), and 4,4"-dimethyl-2,2"-bipyridyl (Me2bpy); X, Y = Cl–, Br–, CO32–, NO2–, SCN–, N3–, H2O, and DMSO) in aqueous buffer solutions were measured and analyzed in the framework of the Lever theory on the additivity of contributions of ligands (EL) to the apparent redox potential of the complex (Eo"). The complexes manifest the properties of reversible or quasireversible redox systems, whose formal redox potentials lie in the 0.2—0.5 V range. The complexes are efficient electron transfer mediators between the active center of glucose oxidase (GO) from Aspergillus niger and an electrode.