Differential selectivity in electrochemical oxidation of ascorbic acid and hydrogen peroxide at the surface of functionalized ormosil-modified electrodes

Functionalized ormosil-modified electrodes have been developed for electroanalytical applications. The functionalized ormosil-modified electrodes are made by encapsulating potassium ferricyanide/potassium ferrocyanide within ormosil film derived from an optimum composition of 3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium in absence of Nafion/crown ether (system 1), in the presence of Nafion (system 2) and in the presence of dibenzo-18-crown-6 (system 3). Another modified electrode (system 4) is also developed using the reaction product of potassium ferricyanide, 3-aminopropyltrimethoxysilane and either tetrahydrofuran (THF) or cyclohexanone followed by ormosil formation in the presence of 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium. The electrochemical oxidation of hydrogen peroxide and ascorbic acid conducted at the surface of these four types of functionalized electrodes shows very interesting observations on the selective sensing of ascorbic acid and peroxide. The results based on cyclic voltammetry justify the relative performances on the kinetics of hydrogen peroxide oxidation and reduction. System 3 shows relatively much better oxidation kinetics of hydrogen peroxide as compared to other three systems with relatively weak reduction kinetics whereas system 4 shows relatively faster reduction kinetics of hydrogen peroxide as compared to other three systems. Similarly system 4 shows excellent response to ascorbic acid whereas system 3 shows insensitivity to ascorbic acid under similar experimental conditions. Typical response curve for the analysis of hydrogen peroxide and ascorbic acid using system 3 and system 4 respectively are reported. The results show that system 3 is the best for probing hydrogen peroxide with lowest detection limit of 0.5 μM without any interference from ascorbic acid as commonly encountered using many conventional and chemically modified electrodes.     

Bayes estimation of reliability in stress-strength model of Weibull distribution with equal scale parameters

The paper provides a Bayesian approach to inference about the reliability in a multicomponent stress-strength system. We consider Bayes' estimator of the system reliability from data consisting of a random sample from the stress distribution and one from the strength distribution when the two distributions are Weibull with equal and known scale parameters. The estimator of λ, ratio of two shape parameters, is also considered. The proposed estimators can be compared with the maximum likelihood estimators (mles). However, the comparison is carried out for single component stress-strength system and the Monte Carlo efficiencies are obtained. It is found that the proposed estimators are better than the corresponding mles.     

A New Solid-State pH Sensor and Its Application in the Construction of all Solid-State Urea Biosensor

A new solid-state pH sensor is developed using neutral poly(3-cyclohexyl thiophene) assembled over a Pt disk electrode. The new sensor is developed following two different approaches; 1) the neutral poly(3-cyclohexyl thiophene) dissolved in chloroform and subsequent coating on to a Pt disk electrode; 2) the neutral polymer is incorporated into plasticized poly(vinyl chloride) matrix membrane. In both cases the polymer modified electrode is sensitive to pH and a reversible super Nernstian behavior is observed. The typical response of the pH sensor and its reversibility are reported. The polymer coated electrode is subsequently used to construct an all solid-state urea sensor. The construction of this new urea sensor involves the following two major steps; a) 20 µL of urease solution (40 mg /mL) is allowed to assemble overnight at 4 °C over neutral poly (3-cyclohexyl thiophene) modified electrode; b) an organically modified sol-gel layer is allowed to form over the urease adsorbed polymer modified electrode. The new solid-state urea sensor provides excellent reproducibility of the measurements and is stable for 3 months when stored at 4 °C under dry condition. The typical response of the solid-state urea sensor and the calibration plot of urea analysis are reported.     

An ab initio study of microsolvation of LiF in water: structures and properties of LiF-Wn,n = 1-9 complexes

Geometries of clusters of water molecules (W(n)) and those of the LiF-W(n) (n = 1-9) complexes were optimized using the B3LYP/6-31+G** method. Geometries of the complexes up to n = 7 were also optimized using the MP2/6-31+G** approach. Only one structure of each of W(n), n = 1-5 was considered to generate the complexes with LiF while two structures, one of a cage type and the other of a prism type, were considered for n = 6-9. The LiF-W(2) complex is found to be most stable among the various complexes. The LiF-W(6) complex, where W(6) is of a cage type, is predicted to be substantially less stable than that where W(6) is of a prism type. Certain existing ambiguities regarding the most stable structures of the LiF-W(n) (n = 1-3) complexes have been resolved. The LiF molecule seems to divide the W(n) clusters in the LiF-W(n) (n = 3-6) complexes into different fragments where at least one W(2)-like fragment is present. In LiF-W(6) (cage), there is one W(2)-like fragment while in LiF-W(6) (prism), there are three W(2)-like fragments. The LiF bond length is substantially increased in going from the gas phase to the different complexes, this increase being most prominent in LiF-W(6), where W(6) is of the cage or prism type. The LiF molecule, however, does not acquire the ionic structure Li(+)F(-) in any of the complexes studied here. An appreciable amount of electronic charge is transferred from LiF to the water molecules involved in the different complexes. In this process, the Li atom gains electronic charge in some cases, while the F atom considered separately, as well as the Li and F atoms taken together, lose the same in most cases.     

Hydrotalcite catalysis in ionic liquid medium: a recyclable reaction system for heterogeneous Knoevenagel and nitroaldol condensation

Knoevenagel condensation proceeds efficiently in recyclable [bmim]PF₆ and [bmim]BF₄ without any catalyst, and hydrotalcites in ionic liquid serve as a safe and recyclable reaction system for both Knoevenagel as well as nitroaldol condensations.     

Performance of CeO2–TiO2-admixed photoelectrode for natural dye-sensitized solar cell

Extracts from roots of Beta vulgaris were used as natural sensitizers of a wide-bandgap semiconductor (CeO₂–TiO₂) in photoelectrochemical solar cells. The natural dye, adsorbed onto the semiconductor surface, absorbs visible light and promotes electron transfer across the dye/semiconductor interface. We have applied CeO₂–TiO₂ to natural dye sensitizer solar cells as a photoelectrode to reduce the charge recombination rate by providing energy barrier at the interface between the photoanode and electrolyte which offers an improvement of photovoltaic efficiency. Short-circuit current density (J _sc) and open-circuit voltages (V _oc) of 9.0 mA cm^?2 and 680 mV, respectively, were obtained, and an effective energy conversion efficiency of 3.5?% was achieved. This simple and cheap technique of cell preparation opens up a perspective of commercial feasibility for inexpensive and environment-friendly dye cells.     

Evaluation of the Antioxidant and Hepatoprotective Effect of Phyllanthus fraternus Against a Chemotherapeutic Drug Cyclophosphamide

In the present study, hepatoprotective and antioxidant properties of aqueous extract of Phyllanthus fraternus (AEPF 200, 300, and 400 mg/kg body weight (bw), orally) were investigated against cyclophosphamide (CPA 200 mg/kg, bw, intraperitoneally administered) induced liver damage in mice. Histopathological studies of CPA administration cause liver injury, featuring substantial increase in serum glutamic oxaloacetic transaminase, serum glutamate pyruvate transaminase, lactate dehydrogenase, alkaline phosphatase, acid phosphatase, and total bilirubin. Moreover, CPA intoxication also causes strong oxidative stress, which is evident from significant increase in lipid peroxide level. These changes were coupled with a decline in superoxide dismutase and catalase as well as albumin, cholesterol level, red blood cell (RBC), and white blood cell (WBC) count. AEPF-treated mice displayed a significant inhibition of lipid peroxidation and augmentation of endogenous antioxidants. The study emphasizes the hepatoprotective effect of AEPF against CPA-induced oxidative liver injury, which may serve as a promising medicinal herb in complementary chemotherapeutic modalities.     

Platinum(IV) complexes of reducing sugars in an alkaline medium and their resistance to reaction with N-bromosuccinimide. A kinetic study

Spectrophotometric studies support the formation of { Pt^IV–S} (where S = glucose, galactose and fructose) complexes in an alkaline medium. The resistance of these complexes to reaction with N-bromosuccinimide (NBS) has been observed. The kinetic data also support the formation of { Pt^IV –S} complexes.     

Base-catalyzed cyclization reaction of 2-chloroquinoline-3-carbonitriles and guanidine hydrochloride: a rapid synthesis of 2-amino-3H-pyrimido[4,5-b]quinolin-4-ones

t-BuOK-catalyzed cyclization of 2-chloroquinoline-3-carbonitriles with guanidine hydrochloride provided simple and rapid synthesis of 2-amino-3H-pyrimido[4,5-b]quinolin-4-ones in very short reaction time with good yield. Other 1,3-binucleophiles are found to react at the same rate. This methodology could be extended with their 3-formyl and 3-ester derivatives for the synthesis of pyrimido annulated quinolines.     

Synthesis of 1D β-MnO2 for high-performance supercapacitor application

Journal of Solid State Electrochemistry - Electrochemical supercapacitors (ESs) still need to overcome development obstacles in order to realize their full potential while being acknowledged as a...