Reduction Of MB Research Articles

Highly efficient visible light active ZnO/Cu-DPA composite photocatalysts for the treatment of wastewater contaminated with organic dye

Industrial effluents are a leading major threat for water contamination, subsequently which results in severe health associated risks. Hence, purifying wastewater before releasing into the water resources is essential to avoid contamination. In this study, ZnO/Cu-DPA nano-composites were prepared by altering the percentage of Cu-DPA (20%, 30%, 40%, and 50% which are denoted to be ZnO/20%Cu-DPA, ZnO/30%Cu-DPA, ZnO/40%Cu-DPA and ZnO/50%Cu-DPA) using a simple mechanical grinding process. Several spectroscopic studies were employed such as electron paramagnetic analysis (EPR), powdered X-ray diffractometer (PXRD), UV–Vis absorbance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscope to characterize these nano-composites. The photo-catalytic activities of the prepared nano-composites were studied by degrading MB under visible light irradiation. ZnO, ZnO/20%Cu-DPA, ZnO/30%Cu-DPA, ZnO/40%Cu-DPA and ZnO/50%Cu-DPA degradation efficiencies were determined to be 71.8, 78.5, 77.1, and 66.1%, respectively. Among the composite catalysts, the ZnO/20%Cu-DPA coupled system are demonstrated the best efficiency (87%) for photo-degradation of MB within 80 min when exposed to visible light. The ZnO/Cu-DPA nano-composites had a greater MB photodegradation efficiency than pristine ZnO owing to p-n heterojunction in the linked system. Under visible light irradiation, the ZnO/20%Cu-DPA catalysed the conversion of dissolved O2 to hydroxyl radicals (OH·), triggering the reduction of MB. This suggests that ·OH is the primary specific active radical involved in the photo-catalytic decomposition of MB. Furthermore, EPR analysis indicates the existence of ·OH in the photo-catalytic system. The proposed nano-composites (ZnO/20%Cu-DPA) reusability was investigated across three cycles as the most efficient photo-catalyst. The results show that, the ZnO/Cu-DPA nano-catalyst is a potential candidate for the remediation of dirty water.

Synergistic effect of silver NPs immobilized on Fe3O4@L-proline magnetic nanocomposite toward the photocatalytic degradation of Victoria blue and reduction of organic pollutants.

The surface of magnetite (Fe3O4) nanoparticles was subject to modification through the incorporation of L-proline (LP) by simple co-precipitation method in which silver nanoparticles were deposited by in situ method, thereby yielding the Fe3O4@LP-Ag nanocatalyst. The fabricated nanocatalyst was characterized using an array of techniques including Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET), and UV-Vis spectroscopy. The results evince that the immobilization of LP on the Fe3O4 magnetic support facilitated the dispersion and stabilization of Ag NPs. The SPION@LP-Ag nanophotocatalyst exhibited exceptional catalytic efficiency facilitating the reduction of MO, MB, p-NP, p-NA, NB, and CR in the presence of NaBH4. The rate constants obtained from the pseudo-first-order equation were 0.78, 0.41, 0.34, 0.27, 0.45, 0.44, and 0.34 min-1 for CR, p-NP, NB, MB, MO, and p-NA, respectively. Additionally, the Langmuir-Hinshelwood model was deemed the most probable mechanism for catalytic reduction. The novelty of this study lies in the use of L-proline immobilized on Fe3O4 MNPs as a stabilizing agent for the in-situ deposition of silver nanoparticles, resulting in the synthesis of Fe3O4@LP-Ag nanocatalyst. This nanocatalyst exhibits high catalytic efficacy for the reduction of multiple organic pollutants and azo dyes, which can be attributed to the synergistic effects between the magnetic support and the catalytic activity of the silver nanoparticles. The easy recyclability and low cost of the Fe3O4@LP-Ag nanocatalyst further enhance its potential application in environmental remediation.

Catalytic Reduction of Dyes and Antibacterial Activity of AgNPs@Zn@Alginate Composite Aerogel Beads.

This work focuses on the preparation of aerogel composite beads based on Zn(II)-crosslinked alginate and loaded with different percentages of AgNPs using a simple approach. The obtained samples were evaluated in two different applications: the first application consists in their use as catalysts for the reduction of MB, MO, OG and CR dyes in a simple and binary system under the presence of NaBH4. For this, several parameters affecting the catalytic behavior of these catalysts have been investigated and discussed such as the catalyst mass, AgNPs content, dye nature, and the selectivity of the catalyst in a binary system. The second application concerns their antibacterial activities towards two Gram-negative bacteria Escherichia coli (ATCC 25922), and Pseudomonas aeruginosa (ATCC 27853), and a Gram-positive bacteria Staphylococcus aureus (ATCC 25923). The physico-chemical properties of different samples were characterized by XRD, FTIR, SEM/EDS, and TGA analysis. The obtained results confirmed the presence of AgNPs on a highly porous alginate structure. The dispersion of a high percentage of AgNPs leads to the formation of nanoparticles on the outer surface of the alginate which led to their leaching after the catalytic test, while the composite having a low percentage of AgNPs showed good results through all dyes without leaching of AgNPs. For the antibacterial application of the different samples, it was shown that a composite with a higher percentage of AgNPs was the most effective against all bacteria.

Ag NPs decorated on the magnetic Fe3O4@PDA as efficient catalyst for organic pollutants removal and as effective antimicrobial agent for microbial inhibition

In this paper, Ag NPs-decorated magnetic Fe3O4 @PDA nanocomposites have been successfully prepared. The spherical Fe3O4 nanoparticles with an average size approximately 340 nm were modified by dopamine under mild conditions. Dopamine was self-polymerized surrounding Fe3O4 nanoparticles and transformed into poly dopamine (PDA) layers. The PDA-encapsulated magnetic (Fe3O4 @PDA) nanoparticles could in-situ reduce silver ammonium ions by the catechol groups in PDA layers. The Ag NPs with an average size ranging from 20 nm to 36 nm were densely decorated on the thin PDA shell. The resultant Fe3O4 @PDA-Ag nanocomposites were employed as highly efficient catalysts for the reduction of different organic pollutants in the appearance of sodium borohydride. The Fe3O4 @PDA-Ag nanocomposites also demonstrated extraordinary cycling stability when the catalyst was recycled several times for the reduction of MB. The antimicrobial tests indicated Fe3O4 @PDA-Ag nanocomposites could efficiently prohibit the growth of microorganism, including various bacteria and fungi. The minimal inhibitory concentrations (MIC) for Fe3O4 @PDA-Ag nanocomposites against different bacteria and fungi were also determined. The excellent catalytic activity, magnetic recyclability, and antimicrobial performance make Fe3O4@PDA-Ag a feasible candidate for the remediation of wastewater which contains multiple water soluble organic pollutants and pathogenic microorganism.

Catalytic reduction of 4-nitrophenol and methylene blue pollutants in water by copper and nickel nanoparticles decorated polymer sponges

In the present study, two catalysts based-on copper and nickel nanoparticles anchored on agarose-coated sponge (Cu-AG-sponge and Ni-AG-sponge) were prepared, respectively. Both catalysts were characterized by analytical techniques of thermogravimetric analysis energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). Spherical Cu and Ni nanoparticles on struts of AG-coated sponge were observed by FESEM and the samples’ elemental composition was confirmed by EDX technique. After characterization, the Cu-AG-sponge and Ni-AG-sponge catalysts were tested in 4-nitrophenol (4-NP) and methylene blue dye (MB) reduction in an aqueous medium. The reduction of the 4-NP to 4-aminophenol (4-AP) was achieved up to 95% using the NaBH4 reductant and Cu-AG-sponge and Ni-AG-sponge catalysts, respectively. Similarly, the rate of reduction of MB was faster for the Cu-AG-sponge as compared to the Ni-AG-sponge which was discussed based-on the catalyst morphology and other factors. The high rate of reactions for the 4-NP and MB reduction suggests that the Cu-AG-sponge and Ni-AG-sponge catalyst possess high catalytic efficiency, low cost and good reusability having the potential to be used in similar other reactions.

In situ deposition of silver nanoparticles on polydopamine‐coated manganese ferrite nanoparticles: Synthesis, characterization, and application to the degradation of organic dye pollutants as an efficient magnetically recyclable nanocatalyst

The present paper reports a facile in situ synthesis strategy for the production of MnFe2O4@PDA‐Ag magnetically recyclable core–shell nanospheres by the deposition of silver nanoparticles (AgNPs) to the surface of MnFe2O4@PDA nanocomposites through the reduction of silver ions by the outer polydopamine (PDA) layer. The deposition of AgNPs over MnFe2O4@PDA was validated by scanning electron microscopy–energy‐dispersive X‐ray spectroscopy (SEM‐EDX), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and vibrating sample magnetometer (VSM) analysis. The catalytic reduction performance of the obtained MnFe2O4@PDA‐Ag nanospheres were tested over model organic dye pollutants (i.e., methylene blue [MB] and 4‐nitrophenol [4‐NP]) by sodium borohydride. Notably, the as‐prepared MnFe2O4@PDA‐Ag nanocatalyst exhibited significantly enhanced catalytic activity for the reduction of MB (296.52 s−1 g−1) and 4‐NP (92.02 s−1 g−1) compared with the other types of similar Ag‐ and PDA‐based catalytic systems in the recent literature. Moreover, the MnFe2O4@PDA‐Ag nanocatalyst showed excellent recyclability, ease of magnetic separation, and rapid and higher recovery ability with insignificant loss in their catalytic efficiencies even after several cyclic uses. The PDA coating on the surface of MnFe2O4 NPs allocates the surface functionalization for the building of novel catalyst systems. This work presents a simple and practicable for the synthesis of MnFe2O4@PDA‐Ag nanospheres that could have a great potential for the treatment of organic pollutants in wastewater and variety of applications in catalysis.

Radiation-induced synthesis of copper sulfide nanotubes with improved catalytic and antibacterial activities.

In the current paper, copper sulfide nanotubes have been successfully synthesized via the green, simple, and effective gamma-radiolysis method without adding any capping or reducing agents. The structural and morphological characteristics of the as-prepared CuS nanotubes were investigated by X-ray diffraction (XRD), N2 adsorption-desorption measurements at 77K, transmission electron microscopy (TEM), and ultraviolet-visible (UV-vis) spectroscopy, which all demonstrated the formation of pure CuS covellite phase with tubular morphology. The synthesized CuS nanotubes possessed not only high activity towards the reduction of both cationic (methylene blue) and anionic (Congo red) dyes in the presence of NaBH4 but also exhibited excellent reusability. In addition, the pseudo-first-order kinetic model represented the reduction of MB very well, and the value of the normalized rate constant (2.4 × 10-2s-1mg-1) was higher than those of other solid catalysts reported in the literature. Ultimately, CuS nanotubes were found to have a broad-spectrum microbicidal action against the common microbiota, such as Gram-positive (exemplified by Bacillus subtilis and Staphylococcus aureus), Gram-negative bacteria (exemplified by Pseudomonas aeruginosa and Escherichia coli), yeast (exemplified by Candida albicans), and plant pathogenic fungi (exemplified by Aspergillus niger).

Silver nanoparticles decorated g-C3N4: An efficient SERS substrate for monitoring catalytic reduction and selective Hg2+ions detection.

Graphitic carbon nitride supported Ag NPs(AgNPs@g-C3N4) were synthesized by an in-situ chemical reduction using a green reducing agent, tannic acid. They were characterized by UV-Vis, FTIR, XPS, XRD, FESEM, EDAX and HRTEM. They were very much SERS sensitive, and capable of detecting methylene blue and 4-aminothiophenol at 1×10-12M and 1×10-10M, respectively with the corresponding SERS enhancement factor of 1.4×108 and 4.7×107. Apart from its high SERS sensitivity, it exhibited high catalytic activity for the reduction of MB with NaBH4. So, their SERS activity and catalytic activity were combined successfully to monitor catalytic reduction of MB by SERS technique. Further, the SERS activity towards MB was also employed for the detection/quantification of free Hg2+ ions in aqueous solution. The SERS intensity of MB drastically decreased in the presence of Hg2+ ions, and hence it provides novel route to detect and quantify the latter. Presence of Ca2+, Mg2+, Cu2+ and Cd2+ions showed zero interference for it. So, this study proves that Ag NPs@g-C3N4 as a unique substrate for multiple SERS applications.

Composites beads based on Fe3O4@MCM-41 and calcium alginate for enhanced catalytic reduction of organic dyes

This work concerns the preparation of composite beads based on calcium alginate and Fe3O4@MCM-41. In the first step, the material Fe3O4@MCM-41 was prepared mechanically using several Fe3O4 contents, then was encapsulated by calcium alginate as a cross-linking matrix to give the composites MC@CA(x). The composite beads were used as catalysts for the reduction of MB and OG dyes in a simple system. Several parameters affecting the reduction reaction were investigated such as effect of the shape of composite beads, concentration of NaBH4, Fe3O4 content, catalyst mass and initial concentration of dye. The obtained results showed a higher immobilization of Fe3O4@MCM-41 in the alginate matrix leading to a high porous structure. The results showed that these catalysts have interesting catalytic activities towards the reduction of MB dye in which the reaction was more efficient with the catalyst containing a higher content of Fe3O4. The MC@CA(1) aerogel catalyst was the best in terms of stability compared to its MC@CA(1) hydrogel counterpart. Finally, the MC@CA(1) aerogel composite was reused in five successive cycles, with a slight loss of its activity during the fifth cycle due to the slight leaching of iron in the reaction medium.

Ag nanoparticles encapsulated in carboxyl-functionalized hollow microporous organic nanospheres for highly efficient catalysis applications

In this work, we present a novel synthesis of Ag nanoparticles encapsulated in carboxyl-functionalized hollow microporous organic nanospheres (Ag@COOH-HMONs) by a combination of hyper-cross-linking mediated self-assembly and simply impregnation method, in which the COOH-HMONs supports were prepared via a Friedel-Crafts alkylation reaction by using polylactide-b-poly(tertbutyl acrylate)-b-polystyrene (PLA-b-PtBA-b-PS) triblock copolymer as precursors. Owing to the abundant carboxyl groups in the cavity of COOH-HMONs, highly dispersed silver nanoparticles can be successfully anchored into COOH-HMONs to produce Ag@COOH-HMONs via an ion exchange with AgNO3 following by an in-situ reduction of sodium borohydride (NaBH4). The obtained Ag@COOH-HMONs exhibit the high catalytic activities for the reduction of MB and nitroaromatic compounds as well as selective oxidation of thiol and styrene due to their high surface area, hierarchical porosity and yolk-shell nanostructure. This approach of constructing novel metal@porous organic polymers is expected to open doors for new types of yolk-shell structural catalysts for practical applications.

Study on Optical Properties of Green Synthesized Silver Nanoparticles for Surface Plasmon Resonance

In the present study green, rapid, extracellular synthesis of silver nanoparticles was achieved under alkaline conditions using <i>Penicillium </i>species. The synthesis of silver nanoparticles is greatly influenced by the pH value of the reaction medium and studied visually as well as using UV-visible spectrophotometer. The SPR absorption bands appeared in the range between 408 nm and 415 nm confirm the formation of the silver nanoparticles. Silver nanoparticles prepared at pH value 10 were further characterized using XRD, SEM, TEM, photoluminescence spectroscopy. X-ray diffraction analysis exhibited the crystalline nature of the prepared silver nanoparticles with face centered cubic structure. The prepared silver nanoparticles were spherical in shape as revealed from SEM and TEM images with the sizes in the range between 11 to 19 nm. The emission spectra were recorded at 530 nm when excited at 400 nm in photoluminescence spectroscope. The prepared silver nanoparticles were evaluated for their catalytic activity in the reduction of MB by NaBH₄ and exhibit the excellent results.<div><br></div>

Chemical reduction of methylene blue in the presence of nanocatalysts: a critical review

Abstract Methylene blue (MB) (3,7-bis (dimethylamino)-phenothiazin-5-ium chloride) is a harmful pollutant and has been long been known for its detrimental effects on human health. Over the recent years, many strategies including reduction, oxidation, biological and photochemical degradation have been reported for converting this harmful dye into commercially useful products. Among the aforementioned strategies, the nanocatalytic reduction of MB into its reduced counterpart, i.e. leucomethylene blue, is considered more preferable because it has been reported to have numerous applications in various industrial fields in the academic literature. The reduction of MB is the kinetically unfavorable reaction. Henceforth, various nanocatalytic systems utilizing different kinds of stabilization mediums have reportedly been used for speeding up this particular reaction. This article attempts to not only describe the fundamental properties of the reduction reaction of MB but also present the classification of the recently reported nanocatalytic assemblies on the basis of the utilized supporting medium. Various techniques used for the characterization of nanocatalytic systems reported for the reduction of MB have been summarized in this review. The thermodynamics, kinetics and mechanistic studies of this nanocatalytic reaction have also been narrated here. This critical review has been written comprehensively to abridge the recent research progress in the assemblage of nanocatalytic systems used for the reduction of MB and to propose some new ideas for further development in this area.

Direct Electrochemistry of Methanobactin Functionalized Gold Nanoparticles on Au Electrode.

Mathanobatins (Mb, Mbtins) were immobilized successfully on nanometer-sized gold colloid particles associated with β-mercaptoethylamine. The structures of Mb functionalized gold nanoparticles were characterized and confirmed by UV-vis spectroscopy (UV-vis), FTIR spectra and electrochemical analyses. Direct electron transfer between Mb or copper-loading Mbtins and the modified electrode was investigated without the aid of any electron mediator. The copper-loading Mbtins act as a better electrocatalyst for the reduction of H2O2 than Mb. The copper-loading Mb, with which gold nanoparticles were functionalized, as a model enzyme, was immobilized on gold electrode to construct a novel H2O2 biosensor. In pH 6.4 phosphate buffer solution, the reduction and oxidation peak potentials of Mb functionalized gold nanoparticles modified Au electrode (copper-loading Mbtins) were 0.115 and 0.222 V. On the surface, capacitance per unite area (Cd) of Mb functionalized gold nanoparticles modified electrode were 38 μF cm-2. The immobilized Mb displayed the features of a peroxidase and gave an excellent electrocatalytic response to the reduction of H2O2. The detection limit of Mb functionalized gold nanoparticles (copper-loading) were 09 × 10-5 mA/M (S/N = 3). The Michaelis-Menten constant (Km) was 0.787 mM. Good stability and sensitivity were assessed for the biosensor.

Synthesis and characterization of phytochemical fabricated zinc oxide nanoparticles with enhanced antibacterial and catalytic applications

A “green route” to fabricate nanoparticles has emerged as a revolutionary approach. The reported work presents a green approach to synthesize ZnO nanoparticles using Conyza canadensis plant leaves extract. The synthesis of ZnO was conducted at two different temperatures i.e. 30 °C and 80 °C. ZnO nanoparticles prepared at 80 °C were smaller in size and exhibited spherical morphology. The prepared nanomaterials were examined for the reduction of organic dyes i.e. methylene blue and methyl orange. The fabricated ZnO nanoparticles synthesized at 80 °C were found to be highly active for the reduction of aforementioned dyes with 94.5% reduction of MO and 85.3% reduction of MB in 45 min and 20 min respectively. The rate constant (k) for this reduction of MO was found to be 5.781 × 10−3 s−1 in the absence of a catalyst and 5.843 × 10−2 s−1 in the presence of ZnO NPs catalyst. The rate constant (k) for the reduction of MB was found to be 4.7 × 10−3 s−1 in the absence of a catalyst and 9.936 × 10−3 s−1 in the presence of ZnO NPs catalyst. ZnO nanoparticles synthesized at 80 °C were examined for their antibacterial activity. The biogenic ZnO nanoparticles exhibited strong antibacterial activity against E. coli and S. aureus with a zone of inhibition (16 mm) and (14 mm) respectively. This high antibacterial and catalytic activity of biogenic ZnO nanoparticles can be attributed to its small size, good dispersion, and well-defined morphology.

Preparation, characterization and catalytic activity of biomaterial-supported copper nanoparticles

Synthesis of copper nanoparticles was carried out with nanocrystalline cellulose (NCC) as a support by reducing CuSO4·5H2O ions using hydrazine. Ascorbic acid and aqueous NaOH were also used as an antioxidant and pH controller, respectively. The synthesized copper nanoparticles supported on NCC (CuNPs@NCC) were characterized by UV–vis, XRD, TEM, XRF, TGA, DSC, N2 adsorption-desorption method at 77 K and FTIR. The UV–vis confirmed the formation and stability of the CuNPs, which indicated that the maximum absorbance of CuNPs@NCC was at 590 nm due to the surface plasmon absorption of CuNPs. Morphological characterization clearly showed the formation of a spherical structure of the CuNPs with the mean diameter and standard deviation of 2.71 ± 1.12 nm. Similarly, XRD showed that the synthesized CuNPs@NCC was of high purity. The thermal analysis showed that the CuNPs@NCC exhibited better thermal behaviors than NCC. BET surface area revealed that the N2 adsorption–desorption isotherms of CuNPs@NCC featured a type IV isotherm with an H3 hysterisis loop. This chemical method is simple, cost effective, and environmentally friendly. Compared to NCC-supported CuNPs and unsupported CuNPs, the as-prepared CuNPs@NCC exhibit a superior catalytic activity and high sustainability for the reduction of methylene blue with NaBH4 in aqueous solution at room temperature. The CuNPs@NCC achieved complete reduction of MB with completion time, rate constant and correlation coefficient (R 2) of 12 min, 0.7421 min−1 and 0.9922, respectively.

Electrosynthesis and binding properties of molecularly imprinted poly-o-phenylenediamine for selective recognition and direct electrochemical detection of myoglobin

Electrosynthesis of molecularly imprinted polymer (MIP) templated with myoglobin (Mb) and the reference non-imprinted polymer (NIP) was examined with o-phenylenediamine (o-PD) as a monomer. Mass-sensitive quartz crystal microbalance with dissipation monitoring supplied by an electrochemical module (EQCM-D) was applied to characterize and optimize MIP/NIP electrosynthesis. Mb rebinding was detected by direct electrocatalytic reduction of Mb by square wave voltammetry (SWV) or differential pulse voltammetry (DPV). The results obtained showed high specificity of polymeric antibodies to template Mb, with an imprinting factor determined as a ratio Imax(MIP)/Imax(NIP) of 2–4. The prepared MIP sensor is characterized by an apparent dissociation constant of (3.3±0.5)×10−9M and has a broad range of working concentrations of 1nM–1μМ, with the detection limit of 0.5nM (9ng/ml). Mb rebinding was examined in Mb-free diluted human serum spiked with Mb as well as in plasma samples of patients with acute myocardial infarction (AMI) and in control plasma of healthy donors in order to demonstrate the potential medical application of developed MIP sensors.

DNA Electrochemistry with Tethered Methylene Blue

Methylene blue (MB'), covalently attached to DNA through a flexible C(12) alkyl linker, provides a sensitive redox reporter in DNA electrochemistry measurements. Tethered, intercalated MB' is reduced through DNA-mediated charge transport; the incorporation of a single base mismatch at position 3, 10, or 14 of a 17-mer causes an attenuation of the signal to 62 ± 3% of the well-matched DNA, irrespective of position in the duplex. The redox signal intensity for MB'-DNA is found to be least 3-fold larger than that of Nile blue (NB)-DNA, indicating that MB' is even more strongly coupled to the π-stack. The signal attenuation due to an intervening mismatch does, however, depend on DNA film density and the backfilling agent used to passivate the surface. These results highlight two mechanisms for reduction of MB' on the DNA-modified electrode: reduction mediated by the DNA base pair stack and direct surface reduction of MB' at the electrode. These two mechanisms are distinguished by their rates of electron transfer that differ by 20-fold. The extent of direct reduction at the surface can be controlled by assembly and buffer conditions.

Electrochemical sensors for hemoglobin and myoglobin detection based on methylene blue-multiwalled carbon nanotubes nanohybrid-modified glassy carbon electrode

An effective electrochemical sensors for hemoglobin (Hb) and myoglobin (Mb) detection was firstly developed using a simple procedure of self-assembled methylene blue-multiwalled carbon nanotubes (MB-MWNTs) nanohybrid modified on glassy carbon electrode without using any enzymes immobilization. The direct electrochemical and electrocatalytic behaviors of the modified electrode were studied using cyclic voltammetry (CV) and flow injection analysis (FIA) with amperometry. The performance of the sensor was investigated and optimized and the system was evaluated by monitoring Hb and Mb concentrations. The developed MB-MWNTs nanohybrid modified electrode showed excellent electrocatalytic activity for reduction of Hb and Mb with good stability, sensitivity and reproducibility (RSD = 3.05% and 4.5% for 50 successive injections of Hb and Mb, respectively). Under optimal conditions, the catalytic currents are linearly proportional to the concentrations of Hb and Mb in the wide range from 5 nM to 2 μM and 0.1 to 3 μM, and the corresponding detection limits are 1.5 nM and 20 nM (S/N = 3), respectively. This approach provides improved detection limit over other previous works and may provide a novel and efficient platform for the fabrication of sensors for other heme proteins.

Interactions of Methylene Blue with Human Disulfide Reductases and Their Orthologues fromPlasmodium falciparum

Methylene blue (MB) has experienced a renaissance mainly as a component of drug combinations against Plasmodium falciparum malaria. Here, we report biochemically relevant pharmacological data on MB such as rate constants for the uncatalyzed reaction of MB at pH 7.4 with cellular reductants like NAD(P)H (k = 4 M(-1) s(-1)), thioredoxins (k = 8.5 to 26 M(-1) s(-1)), dihydrolipoamide (k = 53 M(-1) s(-1)), and slowly reacting glutathione. As the disulfide reductases are prominent targets of MB, optical tests for enzymes reducing MB at the expense of NAD(P)H under aerobic conditions were developed. The product leucomethylene blue (leucoMB) is auto-oxidized back to MB at pH 7 but can be stabilized by enzymes at pH 5.0, which makes this colorless compound an interesting drug candidate. MB was found to be an inhibitor and/or a redox-cycling substrate of mammalian and P. falciparum disulfide reductases, with the kcat values ranging from 0.03 s(-1) to 10 s(-1) at 25 degrees C. Kinetic spectroscopy of mutagenized glutathione reductase indicates that MB reduction is conducted by enzyme-bound reduced flavin rather than by the active-site dithiol Cys58/Cys63. The enzyme-catalyzed reduction of MB and subsequent auto-oxidation of the product leucoMB mean that MB is a redox-cycling agent which produces H2O2 at the expense of O2 and of NAD(P)H in each cycle, turning the antioxidant disulfide reductases into pro-oxidant enzymes. This explains the terms subversive substrate or turncoat inhibitor for MB. The results are discussed in cell-pathological and clinical contexts.

Sugar-derived Glasses Support Thermal and Photo-initiated Electron Transfer Processes over Macroscopic Distances

Trehalose-derived glasses are shown to support long range electron transfer reactions between spatially well separated donors and protein acceptors. The results indicate that these matrices can be used not only to greatly stabilize protein structures but also to facilitate both thermal and photo-initiated hemeprotein reduction over large macroscopic distances. To date the promise of exciting new protein-based technologies that can harness the exceptional tunability of protein functionality has been significantly thwarted by both intrinsic instability and stringent solvent/environment requirements for the expression of functional properties. The presented results raise the prospect of overcoming these limitations with respect to incorporating redox active proteins into solid state devices such as tunable batteries, switches, and solar cells. The findings also have implications for formulations intended to enhance long term storage of biomaterials, new protein-based synthetic strategies, and biophysical studies of functional intermediates trapped under nonequilibrium conditions. In addition, the study shows that certain sugars such as glucose or tagatose, when added to redox-inactive glassy matrices, can be used as a source of thermal electrons that can be harvested by suitable redox active proteins, raising the prospect of using common sugars as an electron source in solid state thermal fuel cells.