Ferricyanide Reduction Research Articles

Enhanced Photogenerated Electron Transfer in a Semiartificial Photosynthesis System Based on Highly Dispersed Titanium Oxide Nanoparticles.

In this study, a hybrid semiartificial photosynthesis system based on chloroplast (CLP) and titanium oxide nanoparticles (TiO2 NPs) was constructed. 2,6-Dichlorophenolindophenol (DCPIP) reduction by TiO2/CLP complex and methylene blue (MB) reduction by TiO2 were used to determine enhanced photogenerated electron transfer in this hybrid system. The DCPIP reduction by the TiO2/CLP complex showed the same trend as MB reduction by TiO2 as a function of concentration of TiO2 NPs, indicating interception of photogenerated electrons in TiO2 by CLP that leads to enhanced photosynthesis efficiency. Decreased photoluminescence intensity and shortened excited-state lifetime of the TiO2/CLP complex compared to that of pure TiO2 also support electron transfer from TiO2 to CLP. Longer visible light absorption wavelength and increasing valence band edges reveal the narrower band gap of TiO2/CLP, which finally results in the enhanced electron transfer from TiO2 to CLP. Higher ferricyanide reduction and enhanced ATP formation with the TiO2/CLP complex demonstrate the accelerated electron-transfer rate of the electron-transfer chain. This study reveals the mechanism of how TiO2 interacts with CLP to enhance the photosynthesis via constructing a semiartificial photosynthesis system.

The Effect of a Conical Inner Electrode on the Mass-transfer Behavior in a Cylindrical Electrochemical Reactor under Single-Phase and Two-Phase (Gas-Liquid) Swirling Flow

The influence of a continuous change in the cross-section area on mass-transfer performance is analyzed in an electrochemical reactor under swirling flow. Thus, a conical frustum is used as an inner electrode in a cylindrical arrangement. A convergent flow is obtained by placing the conical frustum with its smaller base at the bottom of the reactor, or conversely, it produces a divergent flow. Experimental local mass-transfer coefficients along the electrode length are reported using the reduction of ferricyanide as a test reaction. The mass-transfer distribution as well as the global mass-transfer coefficient are both discussed in three geometric arrangements, i.e. constant interelectrode gap, convergent and divergent cases under single-phase and two-phase (gas-liquid) flow. The highest global mass-transfer coefficients are obtained for the convergent arrangement in the middle range of volumetric flow rates, giving out values 7.6% higher than those for the constant interelectrode gap case. Divergent geometry presents, as its main asset, the most uniform mass-transfer distribution in comparison with the other two configurations. The presence of the gas phase also has little influence on the mass-transfer performance of the reactor. Computational fluid dynamics calculations are in good agreement with experimental measurements.

Variability in Loss of Multiple Enzyme Activities Due to the Human Genetic Variation P284T Located in the Flexible Hinge Region of NADPH Cytochrome P450 Oxidoreductase.

Cytochromes P450 located in the endoplasmic reticulum require NADPH cytochrome P450 oxidoreductase (POR) for their catalytic activities. Mutations in POR cause multiple disorders in humans related to the biosynthesis of steroid hormones and also affect drug-metabolizing cytochrome P450 activities. Electron transfer in POR occurs from NADH to FAD to FMN, and the flexible hinge region in POR is essential for domain movements to bring the FAD and FMN close together for electron transfer. We tested the effect of variations in the hinge region of POR to check if the effects would be similar across all redox partners or there will be differences in activities. Here we are reporting the effects of a POR genetic variant P284T located in the hinge region of POR that is necessary for the domain movements and internal electron transfer between co-factors. Human wild-type and P284T mutant of POR and cytochrome P450 proteins were expressed in bacteria, purified, and reconstituted for enzyme assays. We found that for the P284T variant of POR, the cytochrome c reduction activity was reduced to 47% of the WT and MTT reduction was reduced to only 15% of the WT. No impact on ferricyanide reduction activity was observed, indicating intact direct electron transfer from FAD to ferricyanide, but a severe loss of CYP19A1 (aromatase) activity was observed (9% of WT). In the assays of drug-metabolizing cytochrome P450 enzymes, the P284T variant of POR showed 26% activity for CYP2C9, 44% activity for CYP2C19, 23% activity for CYP3A4, and 44% activity in CYP3A5 assays compared to the WT POR. These results indicate a severe effect on several cytochrome P450 activities due to the P284T variation in POR, which suggests a negative impact on both the steroid as well as drug metabolism in the individuals carrying this variation. The negative impact of P284T mutation in the hinge region of POR seems to be due to disruption of FAD to FMN electron transfer. These results further emphasize the importance of hinge region in POR for protein flexibility and electron transfer within POR as well as the interaction of POR with different redox partners.

Editors' Choice—Coupling k Convection-Diffusion and Laplace Equations in an Open-Source CFD Model for Tertiary Current Distribution Calculations

A mathematical model to calculate tertiary current distributions in electrochemical reactors is presented taking into account the potential and concentration fields together with the hydrodynamics under laminar or turbulent conditions. Multiple reactions with different kinetic controls are considered at both electrodes. The computational algorithm solving the model was implemented in OpenFOAM. It allows the calculations for a given local potential at the working electrode, potentiostatic control, or for a fixed cell potential difference and also for a current flowing through the cell, galvanostatic operation. The model was validated by using the reduction of ferricyanide and the oxidation of ferrocyanide from dilute solutions as main test reactions and hydrogen and oxygen evolution as secondary ones, in a modified hydrocyclone. A close agreement between experimental and predicted current distributions was obtained. The hydrocyclone presents a promising electrochemical performance being the mass-transfer conditions in its cylindrical part better than in the conical region. The computational tool developed in this paper can be employed to optimize both cells stack design and system operation conditions. Likewise, the algorithm can also be used to check, when limiting current studies are needed, whether the desired reaction is under mass-transfer or charge-transfer control for a given geometric configuration.

Hexacyano Ferrate (III) Reduction by Electron Transfer Induced by Plasmonic Catalysis on Gold Nanoparticles.

Redox reactions are of great importance in environmental catalysis. Gold nanoparticles (Au-NPs) have attracted much attention because of their catalytic activity and their localized surface plasmon resonance (LSPR). In the present study, we investigated, in detail, the reduction of ferricyanide (III) ion into a ferrocyanide (II) ion catalyzed by spherical gold nanoparticles of two different sizes, 15 nm and 30 nm, and excited at their LSPR band. Experiments were conducted in the presence (or absence) of sodium thiosulfate. This catalysis is enhanced in the presence of Au- NPs under visible light excitation. This reduction also takes place even without sodium thiosulfate. Our results demonstrate the implication of hot electrons in this reduction.

Enzymatic synthesis, antioxidant ability and oil-water distribution coefficient of troxerutin fatty acid esters

Abstract Troxerutin fatty acid esters were prepared using troxerutin and fatty acid vinyl esters as substrates in pyridine through enzymatic route. The structures of as-prepared compounds were identified by FT-TR, NMR, and ESI-HRMS. Using alkaline protease (≥30 mg/mL) as enzyme, maximum yields reached 58% at 3:1 (vinyl hexanoate to troxerutin) in pyridine (water content ≤1%). The yields gradually declined as chain length of acyl donors rose. The antioxidation abilities of the as-obtained compounds were confirmed by both DPPH free radical scavenging and potassium ferricyanide reduction methods. The antioxidation ability of troxerutin fatty acid esters was found lower than that of troxerutin. However, the logP values of troxerutin fatty acid esters varied from 0.15 to 1.94, suggesting that troxerutin fatty acid esters had better lipophilicity than troxerutin (logP = −2.12) when compared to their oil-water distribution coefficients. Overall, these findings look promising as reference for further development of future troxerutin.

The strain- and impurity-dependent electron states and catalytic activity of graphene in a static magnetic field

Harnessing the full potential of graphene for optoelectronic and electrochemical devices requires tunning and goal-directed control of its electronic properties. We report a computational study of the electron density of states and catalytic activity of graphene in the perpendicular magnetic field. We focus on the influence of uniaxial strain, covalently bonded moieties, charged ions at graphene surface, and positively charged impurities located between graphene layer and substrate, on the Landau levels (LL) observed on density of states and the resulting catalytic activity. For this study, the reduction of ferricyanide to ferrocyanide serves as a benchmark electrochemical reaction. Results show that LLs strongly affect the shape of the cathodic reaction rate curve. Armchair strain and covalently bonded moieties do not affect the intensity of LLs. On the other hand, zigzag strain, charged ions represented by Gaussian-like potential, and positively charged impurities represented by Coulomb-like potential, give rise to a gradual disappearance of the LLs. Positively charged Coulomb-like impurities cause a shift of the density of states towards higher energy which results in an extraordinary increase of the standard rate constant by one order of magnitude at the impurities concentration of 0.1%.

A Novel Electrochemical Sensor Based on Plastic Antibodies for Vitamin D3 Detection in Real Samples

A highly sensitive voltammetric sensor for vitamin D3 is designed and build by the electropolymerization of molecularly imprinted polymer (MIP). Vitamin D3 selective MIP is synthesized by the electropolymerization of p-phenylenediamine–resorcinol mixture on the screen-printed carbon electrode (SPCE) surface in the presence of the vitamin D3 molecules. The electropolymerization of monomers made a film deposition on electrode surface which absolutely suppressed the reduction of ferricyanide. The removal of the vitamin D3 creates the cavities which caused noticeably increased ferricyanide signal, which was again suppressed after the rebinding of vitamin D3. It was shown that the decrease of the ferricyanide peak of the MIP electrode was affected linearly by vitamin D3 concentration. Various factors, by which the response current of the electrode is mainly affected, were studied and optimized. This sensor shows a linear response range of $1 \times 10^{-11}$ – $2 \times 10^{-9}$ M and lower detection limit of $1 \times 10^{\mathbf {-12}}$ M. The sensor was successfully applied for the detection of vitamin D3 in human plasma samples.

Electrocatalysis of ferricyanide reduction mediated by electron transfer through the DNA duplex: Kinetic analysis by thin layer voltammetry

DNA-mediated electron transfer (ET) underlies a variety of bioelectronics applications, and, thus, simple approaches for its kinetic analysis are required. Here, electrocatalysis of a ferricyanide reduction catalyzed by methylene blue (MB) bound to either (dGdC)20 or (dAdT)25 duplexes tethered to gold via an alkanethiol linker was voltammetrically studied at stationary electrodes, and its kinetics was analyzed by two theoretical models. A thin layer voltammetry analysis, assuming that the reaction occurs within the l-nm thick layer formed by the DNA duplexes of the length l, yielded the electrocatalytic rate constant k1 of (2.1 ± 0.4)105 and (2.4 ± 0.5)106 M−1 s−1, for (dGdC)20 and (dAdT)25. The sequence-specific k1 values were consistent with structural differences of (dGdC)20 or (dAdT)25 at the negatively polarized interface and approached the k1 previously reported for the rotating disk electrode system (Angew. Chemie Int. Ed. 58 (2019) 3048). These results offer new tools for immediate kinetic analysis of electrocatalytic reactions involving long-range ET along the DNA duplexes, the tools that allow differentiating electrical properties of nucleic acids in the most convenient and simple way.

Effect of Macromolecular Crowding on the FMN-Heme Intraprotein Electron Transfer in Inducible NO Synthase.

Previous biochemical studies of nitric oxide synthase enzymes (NOSs) were conducted in diluted solutions. However, the intracellular milieu where the proteins perform their biological functions is crowded with macromolecules. The effect of crowding on the electron transfer kinetics of multidomain proteins is much less understood. Herein, we investigated the effect of macromolecular crowding on the FMN-heme intraprotein interdomain electron transfer (IET), an obligatory step in NOS catalysis. A noticeable increase in the IET rate in the bidomain oxygenase/FMN (oxyFMN) and the holoprotein of human inducible NOS (iNOS) was observed upon addition of Ficoll 70 in a nonsaturable manner. Additionally, the magnitude of IET enhancement for the holoenzyme is much higher than that that of the oxyFMN construct. The crowding effect is also evident at different ionic strengths. Importantly, the enhancing extent is similar for the iNOS oxyFMN protein with added Ficoll 70 and Dextran 70 that give the same solution viscosity, showing that specific interactions do not exist between the NOS protein and the crowder. Moreover, the population of the docked FMN-heme state is significantly increased upon addition of Ficoll 70 and the fluorescence lifetime values do not correspond to those in the absence of Ficoll 70. The steady-state cytochrome c reduction by the holoenzyme is noticeably enhanced by the crowder, while the ferricyanide reduction is unchanged. The NO production activity of the iNOS holoenzyme is stimulated by Ficoll 70. The effect of macromolecular crowding on the kinetics can be rationalized on the basis of the excluded volume effect, with an entropic origin. The intraprotein electron transfer kinetics, fluorescence lifetime, and steady-state enzymatic activity results indicate that macromolecular crowding modulates the NOS electron transfer through multiple pathways. Such a mechanism should be applicable to electron transfer in other multidomain redox proteins.

Antioxidant activity and lipid oxidation in milk from cows with soybean oil and propolis extract added to their feed

Abstract The presence of PUFA (polyunsaturated fatty acids) in cow milk, including conjugated linoleic acids (CLA) isomers, makes milk susceptible to lipid oxidation, and may lead to the formation of volatile products responsible for a rancid smell. Consequently, including natural antioxidants in the diet of dairy cattle can assist in preventing lipid oxidation. In this study, soybean oil (a source of PUFA) and different ethanolic extracts of Brazilian propolis were included in the cows' feed, and the antioxidant activity and lipid oxidation of the animals' milk was assessed. Antioxidant activity was analyzed using the DPPH method, potassium ferricyanide reduction and chelating ability. Total phenolic compounds and flavonoids were also determined. Lipid oxidation was assessed by determining conjugated dienes and the production of aldehydes (propanal, pentanal, hexanal and octanal). Increased antioxidant activity was seen in the samples of milk from cows receiving propolis. Similarly, the addition of ethanolic extract of propolis to the diet of dairy cattle increased milk protection for two treatments with propolis against lipid oxidation in terms of production of propanal and hexanal. These results confirm the positive effect of applying this natural additive to the diet of lactating cows, improving the nutritional quality of the milk produced.

A Novel Flow Electrochemical Reactor for Intensifying Diffusion-Limited Electrochemical Processes

Electrochemical processing is attracting renewed interest in industry for synthesis of chemicals or for the removal of a range of contaminants because it is cleaner than most alternatives. Redox reactions that are controlled by applying a potential between two electrodes avoid the use of potentially harmful auxiliary chemicals, an increasingly important advantage that offsets the electrical energy that is required. However, electrochemical processing is still limited in many applications by electrochemical engineering issues such as electrode material selection and construction, efficiency losses caused by mass transfer limitations and batch mode of operation. The CSIRO flow electrochemical cell aims to address these issues by using advanced computational fluid dynamics (CFD) to design, manufacture and optimize an electrode that can maximize mixing within an axial flow cell. The static mixer working electrode is made using additive manufacturing techniques that allows complex designs to be realised using a range of different metals with different surface roughnesses. The current design of the CSIRO electrochemical flow cell employs an additively manufactured, high surface area static mixer as a central working electrode that fits snugly within a tubular porous polymeric separator which defines a working compartment. Two ports at either end of the electrode, manufactured as an integral part of the design provide connections for fluid flow. As with all static mixers, the momentum of the solution induces mixing as it flows past the electrode surface. In the current version of the cell, an inert tubular counter electrode surrounds the working compartment at a small distance from the separator, creating a low volume counter compartment and formed the outside casing of the cell. Separate ports provide fluid flow into this latter compartment. Figure 1 shows a schematic drawing of one configuration of the electrochemical cell with the arrangement of the electrodes, the fluidic setup including the peristaltic pump(s) used to control the solution flow into and out of the cell and the power supply connection to the cell. The efficiency with which the cell works may be evaluated by comparing the limiting current measured at various flow rates with results from a Rotating disk electrode (RDE) in the same solution. These comparisons are useful indicators of performance only, and are not used to draw any conclusions about the hydrodynamic conditions at the static mixer surface. The CSIRO flow electrochemical cell has been characterized using the reduction of Ferricyanide, [Fe(CN)6]3+) at three different reactant concentrations and seven different flow rates. Results show that the cell can accelerate the rate of the reduction reaction by nearly forty-five times. As expected, the rate of this acceleration is highest when the reaction is diffusion limited, so the impact is seen most clearly in dilute solutions. By comparison, results obtained with an RDE were not as promising confirming the effectiveness of the CSIRO designed flow electrochemical cell. Exhaustive electrolysis experiments were also undertaken to show how effectively the cell can remove contaminants from a fixed volume of a contaminated aqueous solution. A two Litre solution of copper contaminated water (i.e. 100 pm CuSO4.4H2O in 0.01M H2SO4) was processed using the flow cell at a constant flow rate of 100 mL/min for 5 hours. SEM/EDS results confirmed the deposition of copper ions onto the static mixer working electrode. ICP results showed that a 50% reduction in the copper concentration from 100 ppm to 51 ppm was achieved in 5 hours which is encouraging. Figure 1

Changes in Drug Metabolizing Enzyme Cytochrome P450 CYP3A4 Activities Due to Polymorphisms in Human Cytochrome P450 Oxidoreductase

BackgroundCytochromes P450 proteins are responsible for the metabolism of drugs and xenobiotics. All cytochromes P450s in the endoplasmic reticulum rely on P450 oxidoreductase (POR) for their catalytic activities. Previously it has been shown that mutations in POR cause metabolic disorders of steroid hormone biosynthesis but less attention has been paid to drug metabolizing P450 activities. Considering the critical role of POR in activities of drug metabolizing P450 enzymes it is likely that polymorphisms and mutations in POR also affect drug metabolism. We aimed to characterize the variations identified in nonclinical individuals to access their effects on drug metabolizing cytochrome P450 CYP3A4. The variant P284T of POR (rs72557937, NM_000941.2:c.850C>A) is exclusively present in the African population, while A503V allele of POR is found in about 25% of alleles across different populations.MethodsWT and mutant POR proteins, as well as cytochrome P450s, were expressed in recombinant form in bacteria and purified. We used liposomes to embed the P450 and POR proteins and created a functional P450 metabolic system. Metabolism of Testosterone, small molecule dyes, and tracer compounds was evaluated by radioactive ligand metabolism, fluorescent substrate metabolism and colorimetric assays using chromogenic substrates. Enzyme kinetic analysis was performed using Prizm.ResultsTo study the effect of the P284T variant on POR activity, we first measured the ability of WT and P284T variant to transfer electrons from NADPH to cytochrome c, MTT or ferricyanide. Compared to WT POR, the P284T variant had ~50% activity to reduce cytochrome c and 15 % activity to reduce MTT. However, the ferricyanide reduction activity was not affected by the P284T mutation. As compared to WT POR, both FMN and FAD binding was affected due to the P284T mutation. The FMN content of POR‐P284T was 64% as compared to WT while the FAD content was reduced by 35% suggesting that these mutations do affect FMN and FAD binding to POR. The PORvariant P284T had severe loss of CYP3A4 activity with only 22.8% residual activity as compared to WT indicating a potential impact on drug metabolism. The POR common polymorphism A503V which is found in around 25% of all alleles across different genetic populations showed increased activities of drug metabolizing enzyme CYP3A4.ConclusionsThese results indicate that effects of mutations on activities of individual cytochromes P450 can be variable and a detailed analysis of each variant with different partner proteins is necessary to determine the genotype‐phenotype correlations of POR variants accurately. These results further affirm the critical role of POR in drug metabolism and suggest that variations in POR should also be considered during the evaluation of abnormal drug‐metabolizing cytochrome P450 activities.Support or Funding InformationThis research was supported by grants to Amit V Pandey from the Swiss National Science Foundation, Novartis Foundation for Medical Biological Research and BurgerGemeinde Bern, Switzerland.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Controlling the morphological and redox properties of the CuTCNQ catalyst through solvent engineering

The solution-based synthesis of the coordination polymer, CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane), which exists in two phases, has predominately used acetonitrile (MeCN) as the solvent. However, our knowledge on the growth and properties of CuTCNQ in other solvents remains limited. In this work, the synthesis of CuTCNQ on Cu foil in two protic (MeOH, EtOH) as well as four aprotic (MeCN, DMSO, DMF, THF) solvents has allowed us to obtain new insights into the important role of the reaction medium in the spontaneous crystallization of CuTCNQ in discrete morphologies and phases. A new electrochemical method for phase identification also has been developed to support this study. Findings reveal that (i) the solvents with higher dielectric constants favor CuTCNQ crystallization; (ii) irrespective of the solvent, use of high temperature (60 °C vs. 25 °C in conventional synthesis) promotes CuTCNQ crystallization and facilitate conversion of phase I to phase II; (iii) phase I CuTCNQ possess enhanced redox catalysis (ferricyanide reduction by thiosulfate) performance over phase II CuTCNQ; and (iv) the amount of catalyst is not necessarily the most important factor for driving catalytic reactions, and other factors, such as, morphology, redox characteristics and solvent in which the CuTCNQ is synthesized may dictate the overall catalytic performance. These findings emphasize the importance of understanding the influence of parameters, such as, solvent and temperature in CuTCNQ synthesis as a means of providing materials with improved catalytic activity.

Progress, Mechanisms and Applications of Liquid-Metal Catalyst Systems.

Among the significant growths of liquid metal (LM) research achieved over the past few years, the field of LM as catalysts offers promising opportunities for material scientists to exploit, and thus, burgeoning progress has been made. This article presents an overview of recent progress in developing LM catalysis, which spans from liquid-phase catalysts, photocatalysts, heterogeneous catalysts, and bimetallic catalysts, to catalysts based on liquid-metal/metal-oxide (LM/MO) frameworks. The different types, preparation methods, and typical applications of LM catalysts are classified and reviewed. Typical catalytic applications of LM systems discussed include the growth of graphene films/nanoribbons/carbon nanotube, photocatalytic degradation of CR or PFOA/splitting of H2 O/reduction of CO2 , and catalytic reactions like butane or acetylene dehydrogenation, methanol steam reforming, and reduction of potassium ferricyanide. The prospects, future trends, and challenges of LM catalysts are also mentioned.

Enhanced Bacterial Growth and Gene Expression of D-Amino Acid Dehydrogenase With D-Glutamate as the Sole Carbon Source.

In a search for life-supporting, not life-assisting, D-amino acid metabolism, an environmental strain that grows better with D-glutamate as the sole carbon source was isolated from an ordinary river. The strain, designated as A25, exhibited a faster growth rate and greater cell yield with D-glutamate than with L-glutamate. Conversely, the D/L ratio of total cellular glutamate was as low as 4/96, which suggests that D-glutamate is more likely catabolized than anabolized. Strain A25 was phylogenetically most closely related to the gamma-proteobacterial species Raoultella ornithinolytica, with a 16S rRNA gene sequence similarity of 100%. A standard strain, R. ornithinolytica JCM 6096T, also showed similarly enhanced growth with D-glutamate, which was proven for the first time. Gene expression of the enzymes involved in D-amino acid metabolism was assayed by reverse-transcription quantitative PCR (RT-qPCR) using specifically designed primers. The targets were the genes encoding D-amino acid dehydrogenase (DAD; EC 1.4.99.1), glutamate racemase (EC 5.1.1.3), D-glutamate oxidase (EC 1.4.3.7 or EC 1.4.3.15), and UDP-N-acetyl-α-D-muramoyl-L-alanyl-D-glutamate ligase (EC 6.3.2.9). As a result, the growth of strains A25 and R. ornithinolytica JCM 6096T on D-glutamate was conspicuously associated with the enhanced expression of the DAD gene (dadA) in the exponential phase compared with the other enzyme genes. Pseudomonas aeruginosa is also known to grow on D-glutamate as the sole carbon source but to a lesser degree than with L-glutamate. A standard strain of P. aeruginosa, JCM 5962T, was tested for gene expression of the relevant enzymes by RT-qPCR and also showed enhanced dadA expression, but in the stationary phase. Reduction of ferricyanide with D-glutamate was detected in cell extracts of the tested strains, implying probable involvement of DAD in the D-glutamate catabolizing activity. DAD-mediated catalysis may have advantages in the one-step production of α-keto acids and non-production of H2O2 over other enzymes such as racemase and D-amino acid oxidase. The physiological and biochemical importance of DAD in D-amino acid metabolism is discussed.

Photo-Bioelectrochemistry of Cyanobacteria Lacking Respiratory Terminal Oxidases

In cyanobacteria, the excess electrons produced through photosynthetic electron transport chain at light intensities, are re-oxidized by respiratory terminal oxidases (RTOs) present in the respiratory electron transport chain to minimize photo damage. By knocking out the genes responsible for the RTOs, the organism’s extracellular electron transfer (EET) ability towards the electrode could be further enhanced. In this study, the genes responsible for the RTOs in Synchococcus elongatus (S. elongatus) PCC7942 namely bd-type quinol oxidase, aa3-type cytochrome oxidase and cbb3-type cytochrome oxidase were knocked out individually and in combination to construct single and double mutants. PCR was carried out to confirm the successful construction of mutants. EET ability and photocurrent generation ability of the cyanobacteria in a photo bioelectrochemical cell were investigated through the ferricyanide reduction assay and conventional electrochemical experiments respectively.

Local mass-transfer study in a decaying swirling flow electrochemical reactor under single-phase and two-phase (gas-liquid) flow

Mass transfer was studied at the external electrode of a cylindrical electrochemical reactor with decaying swirling flow using a single phase electrolyte and also a dispersion of a gas phase in the solution. The local mass-transfer coefficients were measured with a segmented cathode using the reduction of ferricyanide as test reaction. Two strategies were used to introduce the gas phase. In the first case the gas was fed by three holes symmetrically drilled at the bottom of the central anode tube and in the second one by means of a tee fitting at the reactor inlet. The best performance was obtained with the single phase electrolyte giving 0.78 as the exponent of the Reynolds number and the mass-transfer distribution along the reactor length is more uniform than that reported for a parallel plate electrochemical reactor under laminar flow conditions. The mass-transfer enhancement factor related to an annular duct with axial developing flow ranges from 8 to 11. This high value is the consequence of two factors: (i) the intensive forced convection produced by the swirling flow at the outer electrode and (ii) the sudden expansion of the flow at the entrance due to the small tangential inlet. The fed of a gas phase in the reactor has scarce influence on the mass-transfer performance. A comparison of mass-transfer results with previous studies is made.

Liquid – Solid mass transfer behaviour of heterogeneous reactor made of a rotating tubular packed bed of spheres

The mass transfer behaviour of a rotating tubular packed bed of spheres was studied using an electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide in a large excess of supporting electrolyte. Variables studied were bed rotation speed, physical properties of the solution, and bed thickness (L). The mass transfer coefficient was found to increase with increasing bed rotation speed and decreases with increasing bed thickness. The mass transfer data were correlated by the equation:Sh=0.126Sc0.33Re0.52LdP-0.8Importance of the present study in the design and operation of high space – time yield heterogeneous reactors such as electrochemical reactors, catalytic reactors, photocatalytic reactors and immobilized enzyme biochemical reactors suitable for conducting diffusion controlled liquid – solid reactions was highlighted. Advantages of the present reactor in conducting small scale production compared to other reactors were pointed out.

Cathodic photoelectrochemical immunoassay based on glucose-oxidase mediated biocatalysis to inhibit the exciton trapping of cupric ions for PbS quantum dots

The integration of photocathodes with enzymatic label tracer for the development of amplified PEC immunoassays is attractive for different diagnosis applications. Herein, we induce a novel strategy for the construction of cathodic PEC immunoassay on the basis of enzymatic reaction inhibited exciton trapping for PbS quantum dots (QDs). The cathodic photocurrent of the PbS QDs sensitized NiO was inhibited by cupric ions due to the formation of exciton trapping centers of CuS on their surface. In the presence the model target of carcinoembryonic antigen (CEA), a sandwich-type immunoreaction occurred with the detection antibody labeled glucose oxidase (GOx) as the signal tracer. The enzymatic reduction of ferricyanide ([Fe(CN)6]3−) by GOx produced ferrocyanide ([Fe(CN)6]4−), which easily combined with cupric ions to form cupric hexacyanoferrate (CuHCF, Cu2[Fe(CN)6]) aggregates, and thus interrupted the formation of the exciton trapping centers of CuS. The enhanced photocurrent of the system was linear with the CEA concentration ranging from 0.5 pg/mL to 30 ng/mL with a detection limit of 0.17 pg/mL. Moreover, the PEC immunosensor also displayed high specificity and good reproducibility toward the target protein. It was also evaluated to analyze CEA in real samples of human serum specimens, which gave well matched results with the commercially available enzyme-linked immunosorbent assay (ELISA) kits.