(p, Vm, T) and phase equilibrium measurements for a natural gas-like mixture using an automated isochoric apparatus

We have developed an automatic apparatus for measuring phase equilibrium and (p, V_m, T) properties of gas mixtures in our laboratory. Based upon the isochoric method, the apparatus can operate at temperatures ranging from 100 K to 500 K at pressures up to 35 MPa, and yield absolute results in fully automated operation. Temperature measurements are accurate to 0.01 K and pressure measurements are accurate to 0.002 MPa. The isochoric method utilizes pressure versus temperature measurements along an isomole (near isochore) and detects phase boundaries by locating the change in the slope of the isomoles.We also have developed a strategy that allows us, when using the above isochoric method together with a second apparatus capable of isothermal density measurements, to collect derived densities that are competitive in accuracy with those of the densimeter, but with a procedure and design that is easy to automate. We present data on a natural gas-like mixture. The experimental data indicate that prediction of the dew point curve with current equations of state is unreliable.     

Syntheses, characterization and study of the use of cobalt (II) Schiff-base complexes as catalysts for the oxidation of styrene by molecular oxygen

Schiff-Base complexes of bis-5-phenylazosalicylaldehyde ethylenediimine and bis-5-phenylazosalicylaldehyde-O-phenylenediimine ligands with Co(II) (I and II) have been synthesized and characterized by their IR spectra and elemental analyses. These complexes catalyze the oxidation of styrene in the presence of dioxygen and excess pyridine. The effect of the reaction conditions on the oxidation of styrene was studied by varying solvent, nature and amount of the catalyst and substrate. The catalytic behavior of the studied complexes was shown to be dependent on the conditions applied. In all reactions, acetophenone and 1- phenylethanol were the only observed products.     

An injectable chitosan-based hydrogel reinforced by oxidized nanocrystalline cellulose and mineral trioxide aggregate designed for tooth engineering applications

The complex anatomy of teeth limits the accessibility and efficacy of regenerative treatments. Therefore, the application of well-known inducers as injectable hydrogels for the regeneration of the dentin-pulp complex is considered a promising approach. In this regard, this study aimed to develop an injectable hydrogel containing mineral trioxide aggregate (MTA). The injectable chitosan/oxidized-nanocrystalline cellulose/MTA (CS/OCNC/MTA) hydrogels were prepared, and the physicochemical properties of these hydrogels were evaluated by TGA, FTIR, Rheological analysis, and SEM. Moreover, the effect of MTA on the swelling and degradability of scaffolds was assessed. The proliferative effects of synthesized hydrogels were also determined on human dental pulp stem cells (hDPSCs) by MTT assay. For induction of differentiation and biomineralization in these cells, the alkaline phosphatase activity and Alizarin Red S staining tests were performed in the presence of fabricated scaffolds. The proliferation of hDPSCs was significantly increased in the presence of these hydrogels. Moreover, the addition of MTA to hydrogel structure dramatically improved the differentiation of hDPSCs. These results suggested that this novel injectable hydrogel provides appropriate physiochemical properties and can be considered a promising scaffold for regenerative endodontic procedures.

Graphical abstract

     

An efficient procedure for the synthesis of coumarin derivatives using TiCl4 as catalyst under solvent-free conditions

The ability of titanium(IV) chloride as a catalyst to promote the Pechmann condensation reaction with a range of phenols and β-keto esters is described.The reaction was carried out by addition of TiCl₄ to a mixture of the phenol and the β-keto ester with thorough stirring in the absence of a solvent and represents an improvement on the classical Pechmann conditions. The yields of coumarins obtained via this novel protocol were significantly higher than those using the conventional method and the reaction duration was reduced to a few minutes or even a few seconds.     

Preparation of polypyrrole-coated platinum modified electrode in chloroform in the presence of various supporting electrolytes and its use for the catalytic oxidation of hydroquinone in aqueous and chloroform solutions

Polypyrrole (PPy)-coated platinum modified electrode was prepared electrochemically in chloroform in the presence of tetrabutylammonium perchlorate, tosylate, tetrafluoroborate, periodate, and hydrogen sulphate. Evidence in favour of the occurrence of a redox reaction at the film/solution interface was given by ferrocene oxidation. The electrocatalytic effect of the PPy-coated electrode was revealed by oxidation of hydroquinone on it in water and chloroform. The influence of dopant anion, method of electrosynthesis and operation temperature were demonstrated. The calculated heterogeneous electron transfer rate constant (k(o)) at the PPy-modified Pt electrode at 25 degrees C was 1.4 x 10(-3) cm/sec which is 1000-fold greater than the value (< 10(-6) cm/sec) reported for bare electrode.     

Spectrofluorimetric study of host-guest complexation of ibuprofen with beta-cyclodextrin and its analytical application

The characteristics of host-guest complexation between beta-cyclodextrin (beta-CD) and two forms of ibuprofen (protonated and deprotonated) were investigated by fluorescence spectrometry. 1:1 stoichiometries for both complexes were established and their association constants at different temperatures were calculated by applying a non-linear regression method to the change in the fluorescence of ibuprofen that brought about by the presence of beta-CD. The thermodynamic parameters (deltaH, deltaS and deltaG) associated with the inclusion process were also determined. Based on the obtained results, a sensitive spectrofluorimetric method for the determination of ibuprofen was developed with a linear range of 0.1-2 microg ml(-1) and a detection limit of 0.03 microg ml(-1). The method was applied satisfactorily to the determination of ibuprofen in pharmaceutical preparations.     

Highly Selective Ion-Sensitive Electrodes Based on Dibenzo-Crown Ethers Containing Functional Groups for the Determination of Potassium in Biological Fluids

The electrochemical properties of membranes based on dibenzo-crown ethers bearing hydroxyl and chloromethyl groups in polyether rings were studied. These substances were tested as membrane ionophores for ion-selective electrodes (ISEs) reversible to potassium ion. The developed ISEs were used for determining potassium in blood plasma samples. The generalized results of determining potassium in the blood of different patients with cardiovascular diseases revealed quantitative regularities that allowed the diseases to be diagnosed early.     

Nickel pentacyanonitrosylferrate film modified aluminum electrode for electrocatalytic oxidation of hydrazine

The electrocatalytic oxidation of hydrazine at the aluminum electrode, modified by electroless deposition of nickel pentacyanonitrosylferrate (NiPCNF) on the surface of the electrode has been studied by cyclic voltammetry, chronoamperometry and rotating disk electrode voltammetry and the kinetics of the catalytic reaction were investigated. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. It was found that a one-electron charge-transfer process is rate limiting and that the average values of the rate constant for the catalytic reaction and the diffusion coefficient, evaluated by different approaches, are 5.2×10³ M^–1s^–1 and 8.5×10^–6 cm²s^–1, respectively. Further examinations of the modified electrodes show that the modifying layers (NiPCNF) on the aluminum substrate have reproducible behavior and a high level of stability, after exposing them in air and hydrazine solutions for a long time. Electronic Publication     

Electroless preparation and electrochemical behavior of a platinum-doped nickel hexacyanoferrate film–zinc modified electrode: catalytic ability of the electrode for electrooxidation of methanol

The use of a zinc substrate as an electrode and the modification of its surface by means of a thin film of platinum-doped nickel hexacyanoferrate (Pt-NiHCF) were developed. The modification conditions of the zinc surface including the electroless deposition of metallic nickel on the electrode surface from NiCl₂ solution, chemical derivatization of the deposited nickel to the NiHCF film in 0.5 M K₃[Fe(CN)₆] solution, and electrochemical penetration of metallic platinum into the modified film are described. The modified zinc electrodes prepared under optimum conditions show a well-defined redox couple due to the [Ni^IIFe^III/II(CN)₆]^1–/2– system. The effects of pH, the alkali metal cation, and the anion of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied in detail. The diffusion coefficients of hydrated alkali metal cations in the film (D), the transfer coefficient (), and the transfer rate constant for the electron (k_s) were calculated in the presence of some alkali metal cations. The electrocatalytic activity of the modified electrode for methanol oxidation was demonstrated. The stability of the modified electrode under various experimental conditions was investigated.     

Electrocatalytic oxidation of methanol on a glassy carbon modified electrode by bis(1,2-phenylenediamine) nickel(II) complex

Electrocatalytic oxidation of methanol on a glassy carbon electrode coated with Ni(II)-(1,2-phenylendiamine)₂ (GC/NiOPD), conditioned by the potential recycling in a potential range of 100–650 mV (vs. SCE) is studied by cyclic voltammetry in an alkaline medium (0.10 M NaOH). The results show that the NiOPD layer formed at the surface of the electrode behaves as an efficient electrocatalyst for the oxidation of methanol in the alkaline medium via the Ni(III) species with a cross exchange reaction occurring throughout the layer at a low concentration of methanol. The effects of various parameters such as potential scan rates, methanol concentration and NiOPD surface concentration on the electro-oxidation of methanol are also investigated.