Comparative Study of Carbon Paste,Screen Printed,and PVC Potentiometric Sensors Based on Copper‐sulphamethazine Schiff Base Complex for Determination of Iodide – Experimental and Theoretical Approaches

New poly vinyl chloride (PVC) membrane, carbon paste (CP), and screen printed (SP) electrodes are constructed for iodide sensing. They are based on copper (II)‐sulphamethazine Schiff base complex as suitable carrier. Mechanism was proved by FT‐IR and UV‐Vis spectroscopy. Computational study involving binding energies calculations at DFT/B3LYP level of theory confirmed the proposed mechanism and agreed the observed selectivity pattern. Responses are near‐Nernstian (?55.0, ?51.0 mV/concentration decade) for PVC, and SP electrodes, and super‐Nernstian (?61.2 mV/concentration decade) for the CP electrode. Lower limit of detection (3.2×10^?6 mol L^?1) and improved selectivity over the highly interfering thiocyanate were obtained in comparison with the previously reported Schiff base complexes‐based iodide sensors.     

Recent Advances in Nanomaterial‐Modified Pencil Graphite Electrodes for Electroanalysis

Pencil graphite electrodes (PGEs) have several advantages over other carbon‐based or commercial metal electrodes, including widespread availability, very low cost, and ease of modification. To make the best use of PGEs in electroanalysis, significant recent advances in the development of different nanomaterial‐PGEs have been observed. The literature published up to mid‐2015 is summarized in the present review, with a focus on the various methodologies used to readily modify graphite pencil electrodes using nanomaterials. This review also touches on the surface characterization of these electrodes and their potential applications in a variety of electrochemical detection applications. The review outlines the scope for further research in this area and discusses the importance of surface modifications of conventional PGE electrodes using nanomaterials or a combination of nanomaterials and electroactive polymers.     

Computational Design,Synthesis and Application of a New Selective Molecularly Imprinted Polymer for Electrochemical Detection

A computational approach was developed to find a suitable functional monomer to design a new molecularly imprinted polymer (MIP), based on which methacyrlic acid (MAA) was selected as a functional monomer to synthesize the molecular imprinted and non‐imprinted polymers. All calculations were carried out using Gaussian 03 software based on the application of Hartree?Fock (HF) method with 6‐31G (d) basis set. The performance of the MIPs prepared with different ratios of MAA was then evaluated using equilibrium rebinding assays. The MIP with the highest binding capacity was chosen as recognition material for the fabrication of new PVC sensors and their responses were compared with each other and with previously reported modifiers in literature. The addition of the ionic surfactant (TFPB) was found to have a synergistic effect on the response mechanism of the electrodes. The results of the MIP modified sensors show that they provide an improved electrode slope, wider pH range and a highly extended life time reaching 7 months compared to 2–4 weeks in case of traditional ion‐exchangers reported in literature, besides, being successfully applied for measurements in biological samples.     

Analysis of vibratinal spectra of 8-hydroxyquinoline and its 5,7-dichloro, 5,7-dibromo, 5,7-diiodo and 5,7-dinitro derivatives based on density functional theory calculations

The geometry, frequency and intensity of the vibrational bands of 8-hydroxyquinoline and its 5,7-dichloro, 5,7-dibromo, 5,7-diiodo and 5,7-dinitro derivatives were obtained by the density functional theory (DFT) calculations with Becke3-Lee-Parr (B3LYP) functional and 6-31G* basis set. The effects of chloride, bromide, iodide and nitro substituent on the vibrational frequencies of 8-hydroxyquinoline have been investigated. The assignments have been proposed with aid of the results of normal coordinate analysis. The observed and calculated spectra are found to be in good agreement.      

A study of primary nucleation of calcium oxalate monohydrate: I‐Effect of supersaturation

There are various organic and inorganic constituents in kidney stones. Among them, calcium oxalate monohydrate (COM) is the primary inorganic constituent of kidney stones. However, the mechanisms of formation of kidney stones are not well understood. In this regard, a basic study is carried out for better understanding of nucleation, crystal growth and/or aggregation of formed COM crystals. The primary nucleation of calcium oxalate monohydrate is studied at the laboratory scale using turbidity measurements. Calcium chloride and potassium oxalate solutions are mixed and then added to a Turbidimeter tube for continuous recording of turbidity. Induction time (time to induce formation of detectable crystals) is estimated from time‐turbidity graphs. The effect of some urinary species, such as oxalate and calcium, on nucleation and crystallization characteristics of COM is determined by particle size distribution analysis, measuring weight of crystals and calculation of relative supersaturation. The classical nucleation theory is applied at high supersaturation ratios (SR) ranging from 1.6 to 2.2. The results indicate that nucleation rate increases with increasing supersaturation ratio from 0.81 × 10²⁸ nuclei/cm³.sec at 1.6 SR, to 18.02 × 10²⁸ nuclei/cm³.sec at 2.2 SR. On the other hand, free energy change and radius of critical nucleus are decreased as supersaturation ratio is increased. The nucleation rates are higher than those reported in literature. Such discrepancy is discussed on the bases of differences in experimental techniques. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization of calcium sulfate dihydrate at different supersaturation ratios and different free sulfate concentrations

Free Sulfate is a major parameter affecting gypsum crystallization during phosphoric acid production. Gypsum crystal size, shape and filtration rate are significantly affected by the concentration of free sulfate. It is, therefore, important to evaluate the effectiveness of different sulfate levels from 1.5% to 3.5% on induction time and gypsum morphology. The crystallization of gypsum was carried out under simulated conditions of phosphoric acid production by the dihydrate process. Calcium hydrogen phosphate and sulfuric acid were mixed with dilute phosphoric acid at 80 °C, and the turbidity of the reaction mixture was measured at different time periods to calculate the induction time of gypsum crystals formation. With increasing free sulfate concentration, the induction time was significantly decreased. Chemical processing of Central and South Florida phosphate concentrates under different concentrations of free sulfate from 1.5% to 5.5% was carried out. The change on crystal size distribution and filtration rate were traced with free sulfate concentrations. The results show that, filtration rate of phosphogypsum was correlated to the mean diameter of crystals. In addition, induction time and co‐crystallized (lattice) P₂O₅ % in gypsum are decreased with increasing free sulfate content from 1.5% to 3.5%. Morphology of formed gypsum crystals at different sulfate contents and different supersaturation ratios are investigated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mössbauer spectroscopy of Al substituted Fe in holmium iron garnet

A Mössbauer spectroscopy study was made on Ho₃Fe_5-xAl_xO₁₂ (x=0.0, 0.05, 0.7). X‐ray diffraction patterns indicate that the samples with x=0.0 and 0.05 have the garnet structure, while the sample with x=0.7 has an additional noncubic structural phase. The room temperature spectrum for samples with x=0.0 and 0.05 consists of two magnetic components corresponding to the octahedral and tetrahedral sites with hyperfine magnetic fields (B_hf) of 50 T and 40 T, respectively. For x=0.7 we observe a new magnetic component with B_hf= 45 T, a reduction in the intensity and broadening of the tetrahedral component, and the evolution of a nonmagnetic central component. These variations are evidently due to the addition of aluminium to the system. At liquid nitrogen temperature the samples with x=0.0 and 0.05 are nearly identical. It was also observed that the increase in B_hf for the octahedral site is smaller than that for the tetrahedral site as the temperature is lowered to 80 K.     

Synthesis of hindered hydrazones and their reaction with thionyl chloride

Hydrazones 12a–c and ketazines 13a–c were prepared by the reaction of ketones 11a–c with hydrazine hydrate depending on the temperature and the reaction time. Some ketone (aryl)hydrazone derivatives 14a,c,e reacted with thionyl chloride to afford the chlorothiadiazoline derivatives 15a–c . Surprisingly, the chlorine atom in the latter compounds was found to undergo smooth nucleophilic substitution, and by boiling these compounds in absolute ethanol gave the corresponding ethoxythiadiazoline derivatives 16a–c . The structure of the ethoxythiadiazoline 16b was confirmed by single crystal X‐ray determination. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:223–228, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10125     

Photosensitized Generation of Singlet Oxygen from (Substituted Bipyridine)ruthenium(II) Complexes

Photophysical properties in dilute MeCN solution are reported for seven Ru^II complexes containing two 2,2′‐bipyridine (bpy) ligands and different third ligands, six of which contain a variety of 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridines, for one complex containing no 2,2′‐bipyridine, but 2 of these different ligands, for three multinuclear Ru^II complexes containing 2 or 4 [Ru(bpy)₂] moieties and also coordinated via 4,4′‐carboxamide‐disubstituted 2,2′‐bipyridine ligands, and for the complex [(Ru(bpy)₂(L)]²⁺ where L is N,N′‐([2,2′‐bipyridine]‐4,4′‐diyl)bis[3‐methoxypropanamide]. Absorption maxima are red‐shifted with respect to [Ru(bpy)₃]²⁺, as are phosphorescence maxima which vary from 622 to 656 nm. The lifetimes of the lowest excited triplet metal‐to‐ligand charge transfer states ³MLCT in de‐aerated MeCN are equal to or longer than for [Ru(bpy)₃]²⁺ and vary considerably, i.e., from 0.86 to 1.71 μs. Rate constants k_q for quenching by O₂ of the ³MLCT states were measured and found to be well below diffusion‐controlled, ranging from 1.2 to 2.0⋅10⁹ dm³ mol⁻¹ s⁻¹. The efficiencies f of singlet‐oxygen formation during oxygen quenching of these ³MLCT states are relatively high, namely 0.53 – 0.89. The product of k_q and f gives the net rate constant k for quenching due to energy transfer to produce singlet oxygen, and k_q−k equals k, the net rate constant for quenching due to energy dissipation of the excited ³MLCT states without energy transfer. The quenching rate constants were both found to correlate with ΔG^CT, the free‐energy change for charge transfer from the excited Ru complex to oxygen, and the relative and absolute values of these rate constants are discussed.