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Choline chloride (ChCl) based binary and ternary deep eutectic solvents (DES) were evaluated for methylene green electropolymerization with oxalic acid (OA) and ethylene glycol (EG) as hydrogen bond donors. Binary DES ChCl : OA in molar ratios 1 : 1 and 2 : 1 and ChCl : EG 1 : 2 and ternary DES (tDES) in different molar ratios and percentages of water were evaluated. The highest polymer growth was in ChCl : OA : EG‐tDES with 13% added water, that had a lower viscosity and higher ionic conductivity when associated with HCl as dopant. This enhanced the formation of more cation radicals and, consequently, more polymer formation. The PMG/MWCNT/GCE‐tDES sensor was successfully applied to the simultaneous determination of 5‐aminosalicylic acid (5‐ASA) and acetaminophen (APAP) by differential pulse voltammetry in the concentration range 1 μM–200 μM, with detection limits of 0.37 μM and 0.49 μM for 5‐ASA and APAP, respectively. The sensor demonstrated good repeatability, reproducibility and stability, and was successfully applied in pharmaceutical formulations. [ABSTRACT FROM AUTHOR]

Pulsed underwater direct current discharge is considered as a tool for a one-step process for ferrite synthesis and organic dye removal. The formation of cobalt, nickel and titanium ferrites during the discharge firing process was confirmed by methods of dynamic light scattering and X-ray phase analysis. The transformation of dye molecules (fluorescein, methylene green) during the combined action of plasma and ferrites was detected by UV absorption spectroscopy. The contributions of the separate action of plasma and ferrites to the process of dye removal from the solution were investigated. It was found that the synthesized structures have a high sorption capacity. It was found that fluorescein can be used as an indicator for the presence of nickel ferrites. [ABSTRACT FROM AUTHOR]

Victoria blue and methylene green dyes have both been extensively studied due to their numerous applications, including their ability to bind to DNA. Dyes are very important in everyday life with applications in textile, cosmetics, food and pharmaceutical industries. It has been found that some of them adversely affect human health causing severe abnormalities. Among these abnormalities, cancer is of great concern due to its fatal and almost non-recoverable nature. In this work we have studied the binding of two dyes namely Victoria blue B (VBB) and Methylene green (MG) with double stranded DNA (Salmon sperm). The interactions were studied in the presence of different concentrations of buffer solutions at a constant pH. The selected dyes showed interactions with double-stranded DNA through intercalation and electrostatic modes. Upon increasing ionic strength of the buffer the binding constant (Kb) value for MG was decreased whereas increased for VBB, which conclude that, at higher ionic strength (0.5 M) the DNA–MG interactions is lower and DNA–VVB interactions is maximum. The carcinogenicity of a given dye is indicated from its binding constants in the current study. Based on the recorded Kb values of the selected dyes it was concluded that proper disposing and precautions should be taken while utilizing/dealing these dyes in order to minimize/avoid their impact on environment and human health. [ABSTRACT FROM AUTHOR]

This investigation focuses on dyes that differ only in the nitro substituent. The NO2 group leads to a strong hardening of the fluorescence at 298 K. In methylene green (MG) the excitation energy migrates to the system of triplet states. This non-radiative process causes the MG fuorescence absent or too low compared to methylene blue (MB). Moreover, laser-induced fluorescence is completely absent for MG in the investigated solvents. However, at liquid nitrogen temperature, we recorded fluorescence for MG in ethanol 250 times higher than at room temperature and phosphorescence too. The intensity of the MB fluorescence band in ethanol at 77 K is 6 times higher than at room temperature. According to the results of this study, the lifetime in the excited state decreases in the following order: isopropanol > acetonitrile≈ethanol≈dimethyl sulfoxide > > water for MG and chloroform > acetonitrile≈ethanol≈dimethyl sulfoxide > > water≈isopropanol for MB. In addition, MG has phosphorescence in ethanol at 780 nm (12,800 cm−1) and in chloroform at 810 nm (12,300 cm−1). [ABSTRACT FROM AUTHOR]

Theoretical modeling of changes in the vibronic absorption and fluorescence spectra in the molecules of two dyes of the thiazine series – methylene blue and methylene green – during the transition from an acidic to an alkaline medium has been carried out by the time dependent density functional theory (TDDFT) method. It is shown that the introduction of the NO2 group leads to more resolved vibronic spectra in the case of low pH values and to the opposite effect at high pH values. This effect can be explained by the intramolecular interaction of functional groups that make up the corresponding molecules. [ABSTRACT FROM AUTHOR]

A voltammetric DNA sensor based on the polyelectrolyte complexes of polyethylenimine and DNA obtained by self-assembly from solutions of components on a glassy carbon electrode has been developed. Cyclic voltammetry was used to study the preparation conditions and characterize the permeability of the complex for low-molecular-weight redox indicators differing in the mechanism of interaction with DNA (methylene blue and methylene green). The formation of the polyelectrolyte complex was independently confirmed by surface plasmon resonance measurements. The redox peak currents of methylene blue and methylene green varied differently depending on the number of layers of the complex and the nature of the outer layer due to different mechanisms of binding the indicators to DNA molecules and varied assembly density of the complex polyelectrolytes. An increase in the concentration of polyions from 0.1 to 10 μg/mL suppressed the effect of the charge of the outer layer on the indicator currents. Polyelectrolyte coatings were tested to detect specific DNA interactions including intercalation with the anticancer drug doxorubicin and the thermal and chemical denaturation of DNA. It was found that the introduction of decacarboxylated pillar[5]arene into the layer increased the sensitivity of the methylene blue signal to the thermal denaturation of DNA. A comparison between changes in the peak currents of methylene blue and methylene green makes it possible to distinguish the mechanism of DNA damage and separately take into account the contribution of the considered chemical and physical damaging factors. The developed DNA sensor makes it possible to semiquantitatively evaluate the protective effect of antioxidants, which decrease the effect of reactive oxygen species on DNA in the biosensor. [ABSTRACT FROM AUTHOR]

In this research, a novel adsorbent, tin sulfide nanoparticles coated on activated carbon [SnS-NP-C] was synthesized by a simple, low cost and efficient procedure for the removal of methylene green from aqueous solutions. Subsequently, this novel material characterization and identification has been completed by different techniques such as TEM, FT-IR, and UV-Vis spectrometry analysis. In the batch experimental set-up, optimum conditions for quantitative removal of Methylene green by [SnS-NP-C] was attained following searching effect of variables such as adsorbent dosage (0.05-0.35 g), contact time (10-120 min), solution pH (6-10), and initial concentration of dye (10–60 mg/L) on the adsorption process was investigated. Optimum values were set at pH of 8.0, 0.25 g of [SnS-NP-C] at removal time of 50 min. Kinetic studies at the various adsorbent dosage and initial methylene green concentration show that maximum dye was sequestered within 10 min as a sort time. The adsorption of methylene green follows the pseudo-second-order rate equation in addition to the interparticle diffusion model (with the removal of more than 99%) at all conditions. Equilibrium data fitted well with the Langmuir model at all amount of adsorbent, while maximum adsorption capacity was 14.22 mg/g for 0.2 g of [SnS-NP-C]. The present procedure is green and offers advantages such as shorter reaction time, simple workup, and high percentage removal.

Herein, the flower-like mixed Cu-Ni cobaltite spinels Cu 1−x Ni x Co 2 O 4 (x = 0, 0.05, 0.15, and 0.25) were successfully synthesized via simple hydrothermal approach followed by annealing process. Copper cobaltite flowers were characterized using XPS, XRD, FT-IR, SEM, TEM, EDAX, BET, and UV–Vis analysis. The photodegradation efficiency (PDE) of the cobaltite photocatalysts was determined by the degradation of rhodamine 6 G (Rh6G), methylene green (MG), and mixed dye effluents (Rh6G+MG, 1:1 v/v) upon visible-light radiation. The PDE of the CNC 3 catalyst was found to be 90%, 83%, and 86% for degradation of Rh6G, MG, and mixed dye effluents, respectively, and it retained 87% of photocatalytic efficiency even after four cycles. The phytotoxic analysis of control, untreated, and treated Rh6G dye solutions was examined in Phaseolus vulgaris for real-time applications. The electrochemical characteristic was investigated by CV, GCD, and EIS. The CNC 3 electrode showed excellent electrochemical performance (315 Fg−1 at 0.5 Ag−1), and the capacity reached 93% of its initial capacitance after 3000 cycles. The b values of oxidative and reductive currents were determined to be 0.67 and 0.68, respectively. The capacitance contribution was 56% at 10 mVs−1, indicating a mixture of surface capacitive and diffusion controlled behavior in charge/discharge processes. The two-electrode symmetric cell was fabricated using CNC 3 as the positive and negative electrodes for real-life applications. CNC 3 cell delivered a significant energy density (13.47 Wh/kg) and a power density (251.01 W/kg) at 0.5 Ag−1. [Display omitted] • The flower-like mixed Cu-Ni cobaltite spinels (Cu 1 - x Ni x Co 2 O 4) were synthesized via simple hydrothermal approach. • The PDE of the CNC 3 catalyst was found to be good for the degradation of Rh6G, MG, and mixed dye effluents, respectively. • The phytotoxic analysis of control, untreated, and treated Rh6G dye solutions was examined in Phaseolus vulgaris. • The CNC 3 electrode showed excellent electrochemical performance (315 Fg-1 at 0.5 Ag-1). • The two-electrode symmetric cell was tested with CNC 3 as the positive and negative electrodes for real-life applications. [ABSTRACT FROM AUTHOR]

In this work, we investigated aggregation of native DNA and thiacalix[4]arene derivative bearing eight terminal amino groups in cone configuration using various redox probes on the glassy carbon electrode. It was shown that sorption transfer of the aggregates on the surface of the electrode covered with carbon black resulted in changes in electrostatic interactions and diffusional permeability of the surface layer. Such changes alter the signals of ferricyanide ion, methylene green and hydroquinone as redox probes to a degree depending on their specific interactions with DNA and own charge. Inclusion of DNA in the surface layer was independently confirmed by scanning electron microscopy, electrochemical impedance spectroscopy and experiments with doxorubicin as a model intercalator. Thermal denaturing of DNA affected the charge separation on the electrode interface and the signals of redox probes. Using hydroquinone, less sensitive to electrostatic interactions, made it possible to determine from 10 pM to 1.0 nM doxorubicin (limit of detection 3 pM) after 10 min incubation. Stabilizers present in the commercial medications did not alter the signal. The DNA sensors developed can find future application in the assessment of the complexes formed by DNA and macrocycles as delivery agents for small chemical species.

The hybrid multilevel approach based on molecular dynamics, quantum mechanics, and statistical theory has been applied to profiles of electronic absorption bands of a number of thiazine dyes (phenothiazine, methylene blue, and methylene green), whose photochemical and biological properties depend on the external medium. The effect of single fragments of the methylene green (MG) molecule on its spectral-luminescent properties is studied. The most preferred geometry for the MG molecule is identified, and its relations with the spectral properties and the solvent nature are established. The energies of the electron states are calculated, and their nature is revealed. The electrostatic potential is analyzed, and the places of the most probable interaction of the molecule with the medium are found. Conclusions on the mechanism of forming the MG absorption spectrum are made based on the observations and calculations performed within the framework of the present work. It is established that the formation of the N-H bonds leads to the formation of an inactive lower excited singlet state and delocalization of the electron charge upon excitation. The position of the maximum of the long-wavelength absorption band of the MG correlates with the donor number of solvents in the series acetonitrile < water < ethanol < isopropanol < dimethyl sulfoxide. The position of the MG electron transition in the region of 630 nm is determined by the interaction of nitrogen and sulfur atoms of the central ring rather than by the increased number of substituents in the structure of the molecule. [ABSTRACT FROM AUTHOR]

The photo-kinetics of photoinduced transformation reaction of methylene green and titanium trichloride was investigated in water and different aqueous-alcoholic solvents. The reaction is pseudo-first order, dependent only on the concentration of titanium trichloride at fixed concentration of methylene green. The effect of water and aqueous-alcoholic solvents was studied in the acidic range from 4 to 7. It was observed that the quantum yield (φ) of reaction increased with increase in polarity of the solvent. The quantum yield (φ) was high in acidic condition and decreased with further increase in acidity. The quantum yield (φ) increased sharply with increase in concentration of titanium trichloride while it almost remained unaffected by change in concentration of methylene green. The addition of ions increased the quantum yield (φ) of reaction. The increase in temperature decreased the rate and quantum yield (φ) of reaction. An electron transfer mechanism for the reaction has been proposed in accordance with the kinetics of reaction. The absence of any reaction intermediate was confirmed by spectroscopic investigations. Activation energy ( E ) was calculated by Arrhenius relation. Thermodynamic parameters such as activation energy ( E ), enthalpy change (Δ H), free energy change (Δ G) and entropy change (Δ S) were also evaluated. [ABSTRACT FROM AUTHOR]

Thermal stability, direct current electrical conductivity ( σ ), alternating current electrical conductivity ( σ ) and dielectric properties of bulk methylene green (MG) have been investigated. The thermal stability of MG was studied by differential scanning calorimetry and thermogravimetry techniques. Temperature dependence of σ showed that the MG has semiconductor behavior with two activation energies determined as 0.12 eV and 0.31 eV in the temperature range 303-343 K and 363-463 K, respectively. The σ of bulk MG was performed in the frequency range 150 Hz-5 MHz and temperature range 303-463 K. The dependence of AC conductivity on frequency for MG is found to satisfy Jonscher's\ universal power law, especially at high frequencies. The correlated barrier hopping model is found to be applicable in which the density of localized states is determined. The σ is thermally activated and the activation energy decreases with the increases in frequency. The variation of the real and imaginary parts of the dielectric constant with the frequency and temperature is explained. [ABSTRACT FROM AUTHOR]

This study demonstrates the exploitation of carbon nanotubes (CNTs) combined with mesoporous metal-organic frameworks (Tb@mesoMOFs) to form a novel nanocomposite as the platform to construct electrochemical biosensors for glucose detection. Energy-dispersive X-ray spectroscopy, UV/Vis spectroscopy, scanning electron microscopy, and electrochemical techniques were used to characterize the Tb@mesoMOFs-CNT nanocomposites. The results showed that a thin layer of Tb@mesoMOFs uniformly covered the surface of CNTs. The Tb@mesoMOFs-CNT nanocomposites served as a supporting matrix to load both methylene green (MG) as electron mediators and glucose dehydrogenases (GDH) as electrocatalysts on a glassy carbon electrode (GCE) for constructing an electrochemical glucose biosensor, owing to the large number of micropores of Tb@mesoMOFs and excellent electrical conductivity of the CNTs together with ultrahigh surface area of the nanocomposites. GDH/MG−Tb@MOF-CNTs/GCE showed good performance for glucose detection with a wide linear range of approximately 25 μM to 17 mM and a low detection limit of 8 μM ( R=0.998, n=10). The work also provided a novel idea to prepare excellent MOFs/CNT-based materials for electrochemical sensing. [ABSTRACT FROM AUTHOR]

The kinetics of the electron transfer reaction of methylene green and titanium trichloride was investigated in different solvents by spectrophotometry at different temperatures. The the reaction rate was determined by monitoring the absorbance as a function of time at λ 655 nm. The reaction is pseudo-first order, dependent only on the concentration of titanium trichloride at a fixed concentration of methylene green. The effect of an aqueous alcoholic solvent was studied in the acidic range of pH from 4 to 7. It was observed that the reaction rate increased with an increase in polarity of the reaction medium. The the reaction rate was high in acidic conditions and decreased with a further increase in acidity. The increase in temperature increased the rate of the electron transfer reaction of methylene green and titanium trichloride. The activation energy ( E ) was calculated by the Arrhenius relation. The absence of any reaction intermediate was confirmed by spectroscopic and kinetic investigations. A plausible mechanism for the reaction in line with outer-sphere reaction pathway has been proposed. Thermodynamic parameters such as the activation energy ( E ), enthalpy change (Δ H), free energy change (Δ G), and entropy change (Δ S) were also evaluated [ABSTRACT FROM AUTHOR]

A novel chemosensor for Methylene Green (MG) based on naphthalene-appended calix[4]arene (NAC4) clicking surface has been reported. Multisignaling changes were observed through fluorescence spectroscopy (FL), electrochemical impedance spectroscopy (EIS) and contact angle (CA). The impedance reduced and contact angle changes from hydrophobic to hydrophilic when the NAC4 functional interface treated with MG. Meanwhile, FL intensity of NAC4 was decreased obviously. The proposed optical-electrochemical-wettability sensing devices display a remarkable specificity, intuitive and convenient method for MG detection, which provided a new opportunity for the production of MG recognition chips that can be used in the fields of biology and environmental monitoring. [ABSTRACT FROM AUTHOR]

Novel,water-soluble CdTe quantum dots (QDs) capped with β-cyclodextrin (β-CD) and ~ 4.0 nm in diameter were synthesized in aqueous solution, and characterized using transmission electron microscopy (TEM). A fluorescence-sensing system based on the photoinduced electron transfer (PET) of (mono-6-thio-β-CD)-CdTe QDs was then designed to measure the interaction of phenothiazine dyes [methylene blue (MB) and methylene green (MG)]with herring sperm DNA (hsDNA). This fluorescence-sensing system was based on a fluorescence "OFF-ON" mode. First,MB/MG adsorbed on the surface of (mono-6-thio-β-CD)-CdTe QDs effectively quenches the fluorescence of (mono-6-thio-β-CD)-CdTe QDs through PET. Then, addition of hsDNA restores the fluorescence intensity of (mono-6-thio-β-CD)-CdTe QDs, because hsDNA can bind with MB/MG and remove it from the as prepared (mono-6-thio-β-CD)-CdTe QDs. In addition, detailed reaction mechanisms of the (mono-6-thio-β-CD)-CdTe QDs-MB/ MG-hsDNA solution system were studied using optical methods, by comparison with the TGA-CdTe QDs-MB/MG-hsDNA solution system. [ABSTRACT FROM AUTHOR]

We prepared and characterized electrocatalysts based on multiwalled carbon nanotubes (MWCNTs) coated with methylene green (MG). These electrocatalysts can regenerate nicotinamide adenine dinucleotide (NAD+), so they are potentially applicable in the field of bioelectronics. NADH oxidation occurs between 0.14±0.002 and 0.16±0.002 V vs. Ag/AgCl. The most efficient bioanode furnishes 88±7 µW cm−2 and 500 µA cm−2 and an open circuit voltage of 590±22 mV. In conclusion, we obtained a reliable and easy-to-prepare electrocatalyst that can regenerate NAD+ and may be applicable in biosensors and bioelectronic devices that use a wide range of NAD+-dependent enzymes. [ABSTRACT FROM AUTHOR]

Carbon papers are frequent current collectors in fuel cells, but recently carbon nanotube papers have been introduced as new types of carbon paper. They have varying thickness, surface area, density, gas permeability, and conductivity. This paper studies the effect of these properties on electrochemical performance. Electropolymerizing methylene green on each carbon nanotube papers was performed to study the papers' ability to oxidize NADH. Secondly, glucose bioanodes were formed with carbon nanotube papers to study glucose bioelectrocatalysis. The optimal carbon nanotube paper had a high surface area, low gas permeability, and low sheet resistance. Our results showed a greater than three-fold increase in sensitivity over commercially available Toray carbon paper. [ABSTRACT FROM AUTHOR]

Kinetics of an alkaline reduction of the methylene green with ethylenediaminetetraaceticacid (EDTA) as a role of dielectric constant of the medium with anecdotal ionic strength in a diverse solvent system (aqueous mixtures of methanol) (10-30%) was studied by measuring the specific rate constant of the reaction spectrophotometrically at λmax = 660nm. An effort has been made to give an elucidation of vital role of dielectric constant of the medium captivating into reflection of single sphere and double sphere complex in reaction assortment. This investigation leads to disclose that single sphere complex of the dye and reductant was found to be the most suitable complex existed in a varied organic solvent. The deviation of the theoretical values from experimental results for single sphere and double sphere complex model in the presence of an alkali and nitrate ions were justified through HPLC analysis. HPLC analysis recommended that a considerable amount of the dye degrades in the existence of nitrate ion and alkali and additional peaks which may be of by-product were obtained. This leads to confirm the non identical values of single sphere and double sphere model in the occurrence of nitrate and an alkali. Rate of deletion of color showed a linear liaison with respect to water content below 30% and temperature between 20-40°C whereas an increase in the concentration of organic solvent showed the inhibition of dye decoloration at given optimum condition. Therefore study was restricted up to 30% of methanol binary mixtures. A mechanism of reduction of dye has been proposed based on verdict. [ABSTRACT FROM AUTHOR]

Methylene green is a versatile dye that can be used in a wide range of technical applications, most of which require the dye to be pure. Because commercial lots of methylene green are known to be heterogeneous, we report a thin layer chromatographic method for checking purity. We also describe a simple and effective flash chromatographic purification procedure for subsequent purification. The identity and purity of the dye can be checked easily using UV-visible absorption spectrum measurements or by more sophisticated procedures if necessary. [ABSTRACT FROM AUTHOR]

Abstract: The monomer–dimer equilibrium and thermodynamics of ionic dyes were investigated by spectrophotometric and chemometric methods. The dimerization constants of methylene blue, methylene green and thiazole orange have been determined by studying the dependence of their absorption spectra at different concentrations of surfactants, ionic strengths and mixed solvents by means of UV–visible spectroscopy in aqueous solutions. The processing of the data, performed for the quantitative analysis of pure spectral profiles, was based on the simultaneous resolution of the overlapping bands in the whole set of absorption spectra. Utilizing the van’t Hoff relationship, which describes the dependence of the equilibrium constant on temperature, as a constraint we determined the spectral responses of the monomer and dimer species as well as the enthalpy and entropy of the dimerization equilibrium. The exciton theory was used for the elucidation of the angle between the monomer units and the interaction energy between the molecules of the dimers. [Copyright &y& Elsevier]

Abstract: BiOCl was synthesized by hydrolysis method. In order to evaluate their photocatalytic activity, this compound was tested on the degradation reaction of methylene green in aqueous solution. The characterization of the compound included: X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopic image (TEM). MG could be efficiently degraded in aqueous suspension of BiOCl under visible light irradiation. Complete removal of aqueous methylene green (MG) was realized after visible light irradiation for 120min with existing BiOCl as a catalyst. The decrease of the chemical oxygen demand (COD), the formation of inorganic products ( and ) confirmed complete mineralization of aqueous MG during the photocatalytic process. [Copyright &y& Elsevier]

Abstract: Methylene Green (MG) is a cationic phenothiazine dye that can be considered as a nitro derivative of methylene blue (MB). The photophysical and spectroscopical properties of MG were investigated in a wide variety of solvents, including protic and aprotic ones. The absorption and fluorescence maxima, fluorescence quantum yields and emission lifetimes were measured and correlated with the properties of the media by using the Bakhshiev’s model and the empirical solvent parameter . Fairly good linear correlations were obtained in both cases indicating the absence of specific interaction between the dye and the solvents studied. The fluorescence quantum yields were found to be in the range 0.004–0.06. Quantum mechanical calculations at the level of Density Functional Theory (DFT) and its Time-Dependent treatment for excited states (TD-DFT) performed on the ground and singlet excited states of MG (and MB) allowed finding a reasonable interpretation of the solvent effects observed on the photophysical properties of the dyes. The triplet excited state properties of the dye were investigated by laser flash photolysis in both protic and non-protic media. In all cases, the triplet quantum yields measured for MG were very small (<0.01). Triplet–triplet sensitization by duroquinone was required for the spectroscopic characterization of the triplet excited state spectrum of MG and the determination of the in the different media. The triplet state shows important absorptions at 410, 488, and 865 nm. The molar absorption coefficient at 865 nm in acetonitrile, estimated using the depletion method, is ∼30,000 M−1 cm−1. Comparing the calculated values of the deactivation rate constants for the singlet excited states of MG and MB, it is concluded that the incorporation of the nitro group in the thiazine chromophore produces a large (∼30 times) decrease of the intersystem crossing rate constant. With the aid of quantum mechanical calculations it is concluded that the intersystem crossing mechanism in both dyes differ significantly. [Copyright &y& Elsevier]

Abstract: A rapid, simple, accurate, and highly selective spectrophotometric method is proposed for the determination of periodate in water samples. This method is based on the reaction of methylene green with periodate in the presence of iodide. The decrease in the absorbance of methylene green is used to monitor the reaction spectrophotometrically at 613nm. Under the optimum conditions, periodate could be determined in the concentration range 0.18–6.0μgmL−1. The detection limit for the method is 0.010μgmL−1. The influence of various foreign species was studied, and it was found that iodate did not interfere with the determination even in the presence of 200-fold of periodate. The relative standard deviations for six replicate determinations of 0.30, 0.50, 1.0, 1.5, 4.0, and 5.5μgmL−1 of periodate were 3.33, 2.0, 1.6, 1.33, 0.50, and 0.55%, respectively. The proposed method was applied to the determination of periodate in water samples and indirect determination of ethylene glycol in antifreeze and glycerol in vegetable oil via malaprade reaction, and satisfactory results were obtained. [Copyright &y& Elsevier]

Abstract: A novel amperometric biosensor for the analytical determination of hydrogen peroxide was developed. The fabrication of the biosensor was based on the coimmobilization of horseradish peroxidase (HRP), methylene green (MG) and multiwalled carbon nanotubes within ormosils; 3-aminopropyltrimethoxysilane (APTMOS), 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (ETMOS) and phenyltrimethoxysilane (PHTMOS). APTMOS determined the hydrophilicity/hydrophobicity of the ormosils and PHTMOS and ETMOS increased the physical and mechanical strength of the ormosil matrix. The ormosil modified electrodes were characterized with SEM, UV–vis spectroscopy and electrochemical methods. Cyclic voltammetry and amperometric measurements demonstrated the MG coimmobilized with HRP in this way, displayed good stability and could efficiently shuttle electrons between immobilized enzyme and electrode, and MWCNTs facilitated the electrocatalytic reduction of H2O2 at reduced over potential. The Micheaelis constant of the immobilized HRP was 1.8mM, indicating a high affinity of the HRP to H2O2 without loss of enzymatic activity in ormosil matrix. The prepared biosensor had a fast response of H2O2, less than 10s, and excellent linear range of concentration from 5×10−7 to 2×10−5 M with the detection limit of 0.5μM (S/N=3) under the optimum conditions. At the same time, the influence of solution pH, effect of enzyme amount, steady-state applied potential and temperature on the biosensor were investigated. The enzyme electrode retained about 90% of its initial activity after 30 days of storage in a dry state at 4°C. The preparation of the developed biosensor was convenient and showed high sensitivity with good stability. [Copyright &y& Elsevier]

Two new modified carbon paste electrodes (CPEs) based on two different X type zeolites, a natural zeolitic volcanic tuff (NZ) and a NaX type synthetic zeolite (SZ), modified with methylene green (MG) were developed. Cyclic voltammetry measurements revealed a reasonably fast electron transfer rate and a good stability for both investigated electrodes. The observed differences between the electrochemical behavior of MG-NZ-CPEs and MG-SZ-CPEs (the effect of pH on the formal standard potential, the magnitude of the rate constants for heterogeneous electron transfer and electrode response decay) were explained in terms of zeolites structure. The modified electrodes showed moderate electrocatalytic effect towards H2O2 reduction and a relatively low limit of detection (0.5 m M for MG-NZ-CPEs). [ABSTRACT FROM AUTHOR]