Bimetallic Cu–Pt/nanoporous carbon composite as an efficient catalyst for methanol oxidation

A novel bimetallic Cu–Pt nanoparticle supported onto Cu/indirectly carbonized nanoporous carbon composite (Cu–Pt/ICNPCC) was prepared through a two-step process: first, carbonization of furfuryl alcohol-infiltrated MOF-199 [metal–organic framework Cu₃(BTC)₂ (BTC?=?1,3,5-benzene tricarboxylate)], without removing the Cu metal with HF aqueous solution; second, the partial galvanic replacement reaction (GRR) of Cu nanoparticles by Pt^IV upon immersion in a platinum(IV) chloride solution. The synthesized materials characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electrochemical methods. The EDS result revealed that part of Cu nanoparticles have been substituted by Pt nanoparticles after GRR. The methanol oxidation at the surface of Cu–Pt/ICNPCC was investigated by cyclic voltammetry method in 0.5 M H₂SO₄ and indicated good electro-catalytic activity towards methanol oxidation (E_p?=?0.85 V vs. NHE and j_f?=?1.00 mA cm^?2). It is suggested that this improvement is attributed to the effect of proper Cu/ICNPCC for fine dispersion, efficient adhesion, and prevention of Pt coalescing.     

Gravitational luminosity of a hot plasma in $$R^{2}$$ gravity

The \(R^{2}\)-gravity contribution to the energy loss of a hot plasma due to gravitational bremsstrahlung is calculated in the linearized theory on the basis of classical Coulomb scattering of plasma constituents in small-angle scattering approximation. The explicit dependence of the gravitational luminosity on the plasma temperature is derived and its relevance to the Einstein gravity is demonstrated. The result, when applied to the Sun as a hot plasma, shows very good agreement with available data.     

Poly(ortho‐toluidine) Modified Carbon Paste Electrode: A Sensor for Electrocatalytic Reduction of Nitrite

The electrocatalytic reduction of nitrite has been studied by poly(ortho‐toluidine) films modified carbon paste electrode (P‐OT/MCPE). Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of poly(ortho‐toluidine) as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the reduction of nitrite occurs at a potential about 600 mV more positive than unmodified carbon paste electrode. The catalytic reaction rate constant, (k_h), was calculated 8.68×10² M^?1 s^?1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00×10^?4 M–1.90×10^?2 M. Detection limit has been found to be 3.38×10^?4 M (2σ). This method has been successfully employed for quantification of nitrite in real sample.     

Spectrophotometric study of the effects of surfactants and ethanol on the acidity constants of fluorescein

In the present paper, a sensitive, fast and suitable method for the calculation of pK(a) values of fluorescein is proposed. The effects of sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100) as a surface-active agent on the acidic and basic forms, and the spectral properties of fluorescein were studied by the spectrophotometric method. The study was performed in sub-micelle surfactant concentration, and absorption spectra at 300-550 nm intervals were recorded. Stepwise acidity constants of fluorescein at pH range 1.50-10.00 and at constant ionic strength 0.1M and 25 degrees C were determined using DATAN program using pH-spectrophotometric titration data. The method is efficient, however the component spectra showed intensive overlapping. The calculated acidity constants of fluorescein in water at ionic strength 0.1 are pK(a1)=2.20, pK(a2)=4.30 and pK(a3)=6.43. The acidity constants of the dye in ethanol-water solution were studied by the same procedure. Effect of surfactants and ethanol on acidity constants and pure spectrum of each component are also discussed.     

New unsymmetrical cyanine dyes for real-time thermal cycling

Asymmetric cyanine dyes bind to the minor groove of double stranded DNA (dsDNA) owing to their crescent configuration; therefore, these dyes are widely used as a dsDNA probes. BOXTO-MEE is derived from BOXTO by adding the polar methoxyethoxyethyl tail in order to increase solubility, dissociation rate kinetics, and stability. As a result, BOXTO-MEE showed significant reduction in nonspecific amplification (primer dimers) without significant effect on target sequence amplification, PCR efficiency, and standard curve correlation coefficient. BETIBO is another example of an asymmetric cyanine dye that can binds to dsDNA but is less efficient than BOXTO-MEE for use in real-time PCR. Statistical analysis of reproducibility results shows that BETIBO is not strong enough to be used for quantifying low nucleic acid quantities. Statistical analysis for BOXTO-MEE results shows that there is no significant difference between the efficiency and correlation coefficient achieved by BOXTO-MEE and SYBR Green I, but a significant difference in the dynamic range is observed because BOXTO-MEE has a wider dynamic range. BOXTO-MEE stock solution was stable at −20 °C for more than 1 year and 40 μM solution was stable for 45 days (at least) at 4 °C.     

A Natural Isolate Producing Shikimic Acid: Isolation, Identification, and Culture Condition Optimization

Shikimic acid has wide use in pharmaceuticals due to its application in the synthesis of drug Tamiflu used in the treatment of Swine flu. The high cost and limited availability of shikimic acid isolated from plants has impeded the use of this valuable building block of the drug. In this context, fermentation route to produce shikimic acid from renewable resources has become increasingly attractive. The present study was embarked upon isolation of wild-type microorganisms able to produce shikimic acid. Out of the 42 isolates obtained from the soil, isolate GR-21 was selected as the best with initial production of 0.54 g/L shikimic acid and later identified as Citrobacter sp. The process optimization resulted in 14-fold increase in the shikimic acid production, thereby claiming this process to be a sustainable alternative for the production of this important biomolecule. The process was further scaled up to 14 L bioreactor to validate the production of shikimic acid. Further, the product formed is shikimic acid was confirmed by FTIR analysis. The current studies suggest that the selected isolate could be used as a promising agent to fulfill the worldwide demand of shikimic acid.     

A Simple and Efficient Electrochemical Sensor for Electrocatalytic Reduction of Nitrite Based on Poly(4‐aminoacetanilide) Film Using Carbon Paste Electrode

In this study, the electrochemical reduction of nitrite was investigated on poly(4‐aminoacetanilide) (PPAA) forming by cyclic voltammetry at the surface of carbon paste electrode. The electrochemical properties of the modified electrode have been studied by cyclic voltammetry and double potential step chronoamperometry. Results showed that in the optimum condition (pH = 0.00) the reduction of nitrite occurred at a potential about 667 mV more positive than that unmodified carbon paste electrode. This amount of electrocatalytic ability is high compared with other electrocatalysts. Using a chronoamperometric method, the catalytic rate constant (k) was calculated 8.4 × 10⁴ cm³ mol^‐1 s^‐1. Also, the electrocatalytic reduction peak currents was found to be linear with the nitrite concentration in the ranges of 5 × 10^‐4 M to 2.5 × 10^‐2 M and 2 × 10^‐5 M to 7 × 10^‐3 M with detection limits (2σ) were determined as 4.5 × 10^‐4 M and 1 × 10^‐5 M by cyclic voltammetry (CV) and hydrodynamic amperometry methods respectively. Recovery experiments exhibit the satisfactory results.     

Electrocatalytic Oxidation and Determination of Cysteamine by Poly‐N,N‐dimethylaniline/Ferrocyanide Film Modified Carbon Paste Electrode

Functionalized poly‐N,N‐dimethylaniline film was prepared by adsorption of ferrocyanide onto the polymer forming at the surface of carbon paste electrode (CPE) in aqueous solution by using potentiostatic method. The electrocatalytic ability of poly‐N,N‐dimethylaniline/ferrocyanide film modified carbon paste electrode (PDMA/FMCPE) was demonstrated by oxidation of cysteamine. Cyclic voltammetry and chronoamperometry techniques were used to investigate this ability. Results showed that pH 7.00 is the most suitable for this purpose. It is found that the catalytic reaction rate constant, (k_h), is equal to 2.142×10³ M^?1 s^?1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the cysteamine concentration and the linearity range obtained was 8.00×10^?5 M–1.14×10^?2 M. Detection limit was determined 7.97×10^?5 M (2σ). This method has been successfully employed for quantification of cysteamine in real sample.     

Electrocatalytic oxidation of methanol onto platinum particles decorated nanostructured poly (1,5-diaminonaphthalene) film

In this work, platinum particles decorated nanostructured poly (1,5-diaminonaphthalene) modified glassy carbon electrode (Pt/Nano-PDAN/MGCE) is prepared. The composite catalysts are characterized by scanning electron microscopy, energy dispersive spectroscopy, and electrochemical methods. The electrochemical methanol oxidation reaction is studied at the surface of this modified electrode. At same Pt loading, the Pt/Nano-PDAN/MGCE can act as higher efficient catalyst for methanol oxidation than that Pt/MGCE. Then, the influence of some parameters such as potential scan rates, switching potential, and methanol concentration on its oxidation as well as long-term stability of the modified electrode have studied by electrochemical methods. Also, ability of the modified electrode toward electrocatalytic oxidation of formaldehyde as an intermediate in methanol oxidation has been investigated.