A Highly Sensitive Sensor Based on Reduced Graphene Oxide,Carbon Nanotube and a Co(II) Complex Modified Carbon Paste Electrode: Simultaneous Determination of Isoprenaline,Captopril and Tryptophan

This paper describes the development of a reduced graphene oxide (RGO), carbon nanotube (CNT) and Co(II) complex (cobalt(II) bis (benzoylacetone) ethylenediimino) (CBE) modified carbon paste electrode (CPE) for simultaneous determination of isoprenaline (IP), captopril (CAP) and tryptophan (Try). A pair of well‐defined redox peaks of Co(II) complex were obtained through a direct electron transfer between the Co(II) complex and the CPE. The proposed sensor showed very efficient electrocatalytic activity for anodic oxidation of IP in a 0.1 M phosphate buffer solution (pH 7.0). Square wave voltammetry (SWV) exhibited two linear dynamic ranges of 0.125–30.0 µM and 30.0–300.0 µM for IP. The detection limit for IP was found to be 50 nM. The proposed sensor was successfully applied for the determination of IP in real samples such as human blood serum, urine and IP ampoule.     

Melamine–formaldehyde resin supported H a mild and inexpensive reagent for synthesis of coumarins under mild conditions

Melamine-formaldehyde resin supported H~+ is used as an efficient catalyst in the Pechmann condensation reaction of phenols withβ-ketoesters,in solvent-free media leading to the formation of coumarin derivatives using conventional heating and microwave irradiation in excellent yields with good purity.     

Experimental and theoretical study on propylene absorption by using PVDF hollow fiber membrane contactors with various membrane structures

Five kinds of asymmetric poly(vinylidene fluoride) (PVDF) hollow fiber membranes with considerable different porosities at the inner and outer surfaces of the membrane were prepared via thermally induced phase separation (TIPS) method and applied for propylene absorption as gas–liquid membrane contactors. A commercial microporous poly(tetrafluoroethylene) (PTFE) hollow fiber membrane was also used as a highly hydrophobic membrane. Experiments on the absorption of pure propylene into silver nitrate solutions were performed and the effects of membrane structure, inner diameter, silver nitrate concentration and absorbent liquid flow rate were investigated at 298 K. PVDF membranes prepared by using nitrogen as bore fluid had lower inner surface porosity than the membranes prepared with solvent as bore fluid. Except the membrane with a skin layer at the outer surface, propylene absorption flux was inversely proportional to the inner diameter of the hollow fiber membrane, and propylene absorption rate per fiber was almost the same. Propylene flux increased with increasing the silver nitrate concentration and also with increasing the absorbent flow rate.A mathematical model for pure propylene absorption in a membrane contactor, which assumes that the membrane resistance is negligibly small and the total membrane area is effective for gas absorption, was proposed to simulate propylene absorption rates. Experimental results were satisfactorily simulated by the model except for the membrane having a skin layer. The model also suggested that propylene is absorbed in silver nitrate solutions accompanied by the instantaneous reversible reaction. This paper may be the first experimental and theoretical study on propylene absorption in membrane contactors.     

A new ytterbium(III) PVC membrane electrode based on 6-methy-4-{[1-(1H-pyrrol-2-yl)methylidene]amino}-3-thioxo-3,4dihydro-1,2,4-triazin-5(2H)-one

This study presents the development of an original electrode, employing 6-methy-4-{[1-(1H-pyrrol-2-yl)methylidene]amino}-3-thioxo-3,4dihydro-1,2,4-triazin-5(2H)-one (PMTO) as a suitable ionophore. Interestingly, the electrode performance provided a very good response for Yb³⁺ in a wide concentration range (from 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ mol L⁻¹) with a detection limit of 4.6 × 10⁻⁷ mol L⁻¹ and a slope of 19.5 ± 0.3 mV per decade of Yb³⁺ concentration. Furthermore, it possessed a fast response time of about 10 s and it functioned in the pH range of 3.3-8.0 with a usage of at least 2 months without observing any deviations. Noticeably, the proposed electrode revealed an excellent selectivity for Yb³⁺ over a broad variety of alkali, alkaline earth, transition and heavy metal ions. The practical applicability of the electrode was demonstrated by its utilization as an indicator electrode in the potentiometric titration of Yb³⁺ ions with EDTA and in the determination of F⁻ in mouth wash samples. Additionally, it was also applied for the determination of Yb³⁺ ions in binary mixtures.     

Synthesis of a novel heterocyclic system—7-methyl-1,2-dihydro-[1,2,4]triazino[3,4-<Emphasis Type="Italic">b</Emphasis>][1,2,4,5]tetrazine-6-thione

4-Amino-6-methyl-3-hydrazino-4,5-dihydro-1,2,4-triazine-5-thione reacted with triethyl orthoformate or triethyl orthoaceate in ethanol to give a novel heterocyclic system, [1,2,4]triazino[3,4-b][1,2,4,5]-tetrazine-6-thione. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 8, pp. 1245–1246. The text was submitted by the authors in English.     

Nuclear quadrupole resonance studies of transparent conducting oxides

We report ^63,65Cu spin–lattice relaxation rates measured by nuclear quadrupole resonance (NQR) in the delafossite compound CuYO₂ and CuYO₂:Ca over a temperature range from 200 to 450 K. CuYO₂:Ca is a prototype transparent oxide exhibiting p-type electrical conductivity. Relaxation rates in CuYO₂:Ca are enhanced by one to two orders of magnitude relative to undoped material, exhibit much stronger temperature dependence, and contain contributions from magnetic and quadrupolar relaxation mechanisms with roughly equal strengths. Relaxation in undoped CuYO₂ is of purely quadrupolar origin and is attributed to interactions with lattice phonons. The main focus of this paper is the magnetic contribution to the relaxation rate in CuYO₂:Ca which is attributed to the hyperfine fields of carriers. It is argued that the dynamics of the hyperfine field are dominated by the hopping rate for carrier transfers between neighboring atoms in the copper planes of the delafossite structure. Comparison of the magnetic relaxation rates with the DC conductivity permits an estimate of the carrier concentration and mobility.     

A CONVENIENT AND GENERAL SYNTHESIS OF A NOVEL HETEROCYCLIC SYSTEM; 5H-[1,3,4]THIADIAZOLO[2,3-d] [1,2,4]TRIAZIN-5-ONES

Abstract

5H-[1,3,4]Thiadiazolo[2,3-d][1,2,4]triazin-5-ones were synthesized by cyclocondensation of 4-amino-5-mercapto-1,2,4-triazin-3-ones with a variety of carboxylic acids in the presence of phosphorus oxychloride.     

Thermodynamic Study of the Binding of Mercury Ion to Human Growth Hormone at Different Temperatures

The interaction of human growth hormone (hGH) with the divalent mercury ion was studied by isothermal titration calorimetry at two temperatures of 27 °C and 37 °C in aqueous solutions. We found that there is a set of two identical and non-interacting binding sites for Hg²⁺ ions. The intrinsic dissociation equilibrium constant and the molar enthalpy of binding are 4.2 mmol⋅L⁻¹ and −14.8 kJ⋅mol⁻¹ at 27 °C and 5.1 mmol⋅L⁻¹ and −14.2 kJ⋅mol⁻¹ at 37 °C, respectively. The results obtained indicate that the stability of the protein increases due to the binding of mercury ions using the extended solvation theory.