A conductive crosslinked graphene/cytochrome c networks for the electrochemical and biosensing study

The direct electrochemistry of catalytically active cytochrome C (Cyt c) adsorbed together with a 3-dimensional network of chemically synthesized graphene on glassy carbon electrode has been readily obtained in aqueous phosphate buffer. Direct electrical communication between the redox center of Cyt c and the modified graphene-based electrode was established. The modified electrode was employed as a high-performance hydrogen peroxide (H₂O₂) biosensor. The Cyt c present in modified electrode exhibited a pair of quasi-reversible redox peaks with a midpoint potential of ?0.380 and ?0.2 V, cathodic and anodic, respectively. Investigations into the electrocatalytic activity of the modified electrode upon hydrogen peroxide exposure revealed a rapid amperometric response (5 s). Under optimized conditions, the linear range of response to H₂O₂ concentration ranged from 5 × 10^?7 to 2 × 10^?4 M with a detection limit of 2 × 10^?7 M at a signal-to-noise ratio of 3. The stability, reproducibility, and selectivity of the proposed biosensor are discussed in relation to the morphology and composition of the modified electrode.     

Mesoporous Silica MCM‐41 Supported N‐Heterocyclic Carbene‐Pd Complex for Heck and Sonogashira Coupling Reactions

Heterocyclic carbene‐Pd complex was anchored onto the mesoporous silica MCM‐41 which exhibits high catalytic activity in Heck reaction under phosphine free reaction conditions for the reaction of iodo/bromoarenes with olefinic compounds such as butyl acrylate, isopropyl acrylate and styrene. This catalytic system also showed high activity for Sonogashira coupling reaction of various aryl halides under copper, phosphine and solvent‐free reaction conditions. The air and thermally stable catalyst were reused several times without significant loss of its activity. High efficiency of the catalyst along with its recycling ability and the rather low Pd‐loading demonstrated in both Heck and Sonogashira coupling reactions are the merits of the presented catalyst system.     

Bioactivity-Guided Fractionation and Identification of Antidiabetic Compound of Syzygium polyanthum (Wight.)’s Leaf Extract in Streptozotocin-Induced Diabetic Rat Model

(1) Background: An earlier study on the hypoglycemic activity of S. polyanthum (Wight.) leaf methanol extract identified squalene as the major chemical compound. The present study was conducted to assess the hypoglycemic effect of fractions and subfractions of the methanol extract of S. polyanthum compared to the squalene using a bioassay-guided in vivo study. (2) Methods: The methanol extract was fractionated using the liquid–liquid fractionation method. Streptozotocin-induced type 1 diabetic rat was used to study the hypoglycemic effect. (3) Results: The findings showed that chloroform fraction significantly (p < 0.05) lowered blood glucose levels of diabetic rats as compared to the control. Further fractionation of chloroform fraction yielded subfraction-1 and -2, whereby subfraction-1 exhibited a higher blood-glucose-lowering effect. The lipid profile test showed that the total cholesterol level of subfraction-1 and squalene-treated groups decreased significantly (p < 0.05). An immunohistochemistry study revealed that none of the treatments regenerated pancreatic β-cells. Gas chromatography–mass spectrophotometer analysis identified the presence of squalene in the active methanol extract, chloroform fraction, and subfraction-1. In silico analysis revealed a higher affinity of squalene against protein receptors that control lipid metabolism than metformin. (4) Conclusions: Data obtained from the present work suggested the crude methanol extract exerted the highest hypoglycemic effect compared to fraction, subfraction, and squalene, confirming synergistic effect may be responsible for the hypoglycemic activity of S. polyanthum.     

Catalytic Transesterification of Coconut Oil in Biodiesel Production: A Review

Catalysis Surveys from Asia - Biodiesel is one of the renewable energy (RE) sources that has received much interest due to its promising properties. Recently, the use of coconut oil as biodiesel...     

Dynamic Calibration and Performance of Reliable and Fast-Response Coaxial Temperature Probes in a Shock Tube Facility

An experimental dynamic calibration technique of reliable, rugged, low-cost, and fast-response coaxial temperature probes is presented. These probes were successfully designed and fabricated in-house, in conjunction with its signal processing circuit, which can be used for transient heat transfer measurements in a hypersonic testing facility. These probes have a response time less than 50 μs with a rise time less than 0.3 μs. Two types of scratches were used, mainly abrasive papers with different grit sizes and scalpel blades with different thicknesses to form the probe junction. The effect of the scratch technique on the probe's thermal product is investigated. The probes were tested and calibrated in the test section and end wall of the UNITEN shock tube facility at different axial and radial locations. The effects of placing the coaxial temperature probe at different axial and radial distances, different working fluids, and different Mach numbers on the transient surface temperature rise were examined. It was observed from the dynamic calibration results that the thermal product of a particular coaxial temperature probe depends on Mach number, junction scratch technique, and junction location, as well as on the enthalpy conditions. It was also noticed that the calibrated coaxial temperature probe using the scalpel blade technique with a particular blade size gives consistent thermal product values. Thus, it does not require an individual calibration. However, for a coaxial temperature probe whose junction was created using the abrasive paper technique with different grit sizes, a calibration for each coaxial temperature probe is likely to be needed.     

Responsive vesicles from the self-assembly of crystalline-coil polyferrocenylsilane-block-poly(ethylene oxide) star-block copolymers

We demonstrate the synthesis and characterization of star‐shaped crystalline‐coil block copolymers with four arms consisting of an inner block of poly(ethylene oxide) and an outer semicrystalline compartment of poly(ferrocenyldimethylsilane), [PEO₅₀‐b‐PFDMS₃₅]₄. The materials were synthesized by transition‐metal‐catalyzed ring‐opening polymerization of dimethylsila[1]ferrocenophane in the presence of silane‐functionalized four‐arm PEO stars as macroinitiators and they exhibited a moderate polydispersity (PDI?1.4). Self‐assembly in mixtures of THF and different alcohols as selective solvents for the PEO block resulted in the formation of semicrystalline vesicles (ethanol, 1‐butanol) or large, rather ill‐defined, spherical structures (methanol). Further, both the rate of addition of the selective co‐solvent and the overall solvent/non‐solvent ratio drastically affected the size and stability of the self‐assembled particles. We could also show that a photoacid generator, as a model for an active substance, can be encapsulated and the UV‐induced generation of HCl resulted in a straightforward degradation of the organometallic vesicles.     

Quantitative and physical evaluation of patchouli essential oils obtained from different sources of Pogostemon cablin

Patchouli essential oil can be obtained from fresh, dried and fermented plant material. It is a highly valuable product in the fragrance industry and its quality changes depending upon raw material age and oil storage. In this work, patchouli essential oils derived from different treatments have been subjected to GC-FID quantitative analysis using an internal standard (ISTD) method with response factors (RF). Samples were obtained from i) fresh plants; ii) hydrodistillation of one year mature and fermented plants; iii) hydrodistillation of one year mature plants; iv) commercial products from Indonesia and Malaysia. Linear Retention Indices (LRI) for both polar and non-polar GC-MS analyses were also measured as a tool for qualitative analysis towards a homologous series of C7-C30 n-alkanes. The results obtained confirmed that, in all samples, patchouli alcohol was the main volatile constituent, with higher amount in lab-scale produced oils, compared with commercial samples. Other major compounds, in lab oils and commercial samples respectively, were: delta-guaiene, alpha-guaiene, pogostol, seychellene and alpha-patchoulene. Another 36 compounds were also found.     

Multi-wavelength fiber laser based on nonlinear polarization rotation in semiconductor optical amplifier and photonic crystal fiber

A nonlinear polarisation rotation (NPR) based multi-wavelength laser source is demonstrated using a semiconductor optical amplifier (SOA) and photonic crystal fiber (PCF). The SOA acts as not only the gain medium but also the phase retarder for multi-wavelength oscillation in conjunction with an isolator. The incorporation of PCF improves the NPR effect and thus assists in the multiwavelength generation. The wavelength spacing reduces from 4.82 to 2.76 nm as the PCF length increases from 50 to 100 m. With a 100 m long PCF, the proposed laser produces at least 42 lasing wavelengths with optical signal to noise ratio of more than 10 dB.     

Determination of Vanadium(IV) and Vanadium(V) in Benfield Samples by IEC with Conductivity Detection

In this study, the determination of vanadium valence state, V(IV) and V(V) has been achieved using ion-exchange chromatography with conductivity detector. In this method, V(IV) was determined as V(IV)-EDTA complex and V(V) as vanadate ion. Determination of V(IV) was successfully done using 3 mM carbonate/bicarbonate/EDTA at pH 8.6 as the eluent. The additive, EDTA in the mobile phase did not seem to interfere with the V(IV) analysis. The detection of V(V) was achieved with 5 mM disodium hydrogen phosphate buffer at pH 10.4. A linear calibration graph over VO₃ ^? and V(IV) with concentration ranges 5–15 mg L^?1 gave the detection limit at 0.09 and 0.1 mg L^?1, respectively. Both V(IV) and V(V) were successfully determined in Benfield sample, with concentrations of V(IV) and V(V) at 4 and 11,000 mg L^?1, respectively.     

A glassy carbon electrode modified with SnO2 nanofibers,polyaniline and hemoglobin for improved amperometric sensing of hydrogen peroxide

Microchimica Acta - The authors describe a glassy carbon electrode (GCE) modified with a multiporous nanofibers prepared from SnO2, polyaniline and hemoglobin, and its application to the...