Ion-selective carbon paste electrode based on new tripodal ligand for determination of cadmium (II)

A new chemically modified carbon paste electrode for Cd(II) ions based on 3,5-dinitro-N-(tri-2-pyridyl methyl) benzamide (DNTPMBA) as an ionophore was prepared. The electrode exhibits a Nernstian response for Cd(II) ions over a wide concentration range (2.16 × 10^?7–1.00 × 10^?1 mol L^?1) with a slope of 30 ± 1 mV per decade. It has a response time of about 50 s and can be used for a period of 3 months with good reproducibility. Detection limit obtained in the optimal conditions was 1.82 × 10^?7 mol L^?1. The electrode was successfully used for potentiometric determination of Cd(II) in well water. The pH influence and interference of some cations were also studied.     

A conductometric study of complexation reaction between dibenzo-24-crown-8 with yttrium cation in some binary mixed non-aqueous solvents

The complexation reaction of macrocyclic ligand, dibenzo-24-crown-8 (DB24C8) with Y⁺³ cation was studied in some binary mixtures of methanol (MeOH), ethanol (EtOH), acetonitrile (AN) and tetrahydrofuran (THF) with dimethylformamide (DMF) at different temperatures using the conductometric method. The conductance data show that in all solvent systems, the stoichiometry of the complex formed between DB24C8 and Y⁺³ cation is 1:1 (ML). The stability order of (DB24C8.Y)⁺³ complex in pure non-aqueous solvents was found to be: AN > EtOH > MeOH > DMF. A non-linear behaviour was observed for changes of log K_f of (DB24C8.Y)⁺³ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the heteroselective solvation of the species involved in the complexation reaction. The obtained results show that the stability of (DB24C8.Y)⁺³ complex is sensitive to the mixed solvents composition. The values of thermodynamic parameters (?H°_c and ?S°_c) for formation of (DB24C8.Y)⁺³ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases, the (DB24C8.Y)⁺³ complex is enthalpy destabilized but entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.     

Spectroscopic, quantum chemical DFT/HF study and synthesis of [2.2.1] hept-2'-en-2'-amino-N-azatricyclo [3.2.1.0(2,4)] octane

The compound 4-N-bicyclo [2.2.1] hept-2'-en-2'-amino-N-azatricyclo [3.2.1.0(2,4)] octane (2) has been synthesized and characterized by elemental analysis, IR, UV-vis, mass and NMR. Density functional theory (DFT) and Hartree-Fock (HF) calculations have been carried out for the title compound by using the standard 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. Predicted vibrational frequencies have been assigned and compared with experimental IR spectra and they complement each other. The theoretical electronic absorption spectra have been calculated by using CIS, TD-DFT and ZINDO methods. The (13)C NMR and (1)H NMR of compound (2) have been calculated by means of Becke 3-Lee-Yang-Parr (B3LYP) density functional method with 6-31G* basis set. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated.     

Imprinted polymer particles for iron uptake: Synthesis, characterization and analytical applications

This work reports the preparation of molecularly imprinted polymer particles for selective extraction and determination of iron ions from aqueous media. The polymer particles were synthesized from Fe(NO₃)₃, morin, 4-vinylpyridine, ethyleneglycoldimethacrylate, and 2,2′-azobisisobutyronitrile and characterized by IR and DSC both prior to and after removing the Fe-morin complex by leaching with HCl. The effect of different parameters, such as pH, adsorption and desorption time, type and minimum amount of eluent for removing the complex from polymer was evaluated and optimized. The proposed method is characterized by the detection limit of 3.1 µg l^?1 anddynamic linear range of 25 to 200 µg l^?1, with the relative standard deviation less than 8.8%. The method was applied to the recovery and determination of iron ions in a few real samples.     

Efficient Synthesis of a New Podand and Application as a Suitable Carrier for Silver Ion‐Selective Electrode

A new podand of 1,1′‐thia‐bis‐[1‐(chloroethan‐2‐acetamid‐α‐oxy)] naphtol was synthesized and used as a suitable carrier for Ag⁺ PVC membrane electrode. The electrode exhibited linear response with a Nernstian slope of (59.5±0.8 mV/decade) within a wide concentration range of 1.0×10^?7 to 1.5×10^?2 mol L^?1 silver ions. The electrode had a fast response time of <10 s and detection limit of 8.6×10^?8 mol L^?1 with a working pH range from 3.7 to 9.0. The electrode was highly selective for Ag(I) ions over a large number of cations such as alkali, alkaline earth, and heavy metal ions. The proposed sensor has been applied as an indicator electrode for indirect determination of vitamin B₁ in tablets by determination of Cl^? ions in this compound with a standard solution of Ag(NO₃).     

Spectrophotometric studies of the thermodynamics of sitting-atop complexation between free base meso-tetraarylporphyrins and titanium(IV) chloride

Titanium(IV) chloride reacts with free base meso-tetraarylporphyrin and its ortho, meta and para-substituted derivatives (H₂T(X)PP; X: OCH₃, CH₃ and Cl) for formation of sitting-atop (SAT) complexes, [TiCl₄(H₂T(X)PP)]. The computer fitting of the variation of the absorbance versus mole ratio by KINFIT program was used for calculation of the formation constants of these complexes in chloroform. Thermodynamic parameters, ΔG°, ΔH°, ΔS°, have been determined and the influence of the temperature and the substituted aryl groups (electronic and steric effects) in the free base porphyrins on the stability of the SAT complexes was studied.     

On strongly (<Emphasis Type="Italic">P</Emphasis>)-cyclic acts

By a regular act we mean an act such that all its cyclic subacts are projective. In this paper we introduce strong (P)-cyclic property of acts over monoids which is an extension of regularity and give a classification of monoids by this property of their right (Rees factor) acts.     

Engineering of a <Emphasis Type="Italic">Bacillus</Emphasis> α-Amylase with Improved Thermostability and Calcium Independency

Successful industrial use of amylases requires that they are sufficiently stable and active at application conditions, e.g., at high temperature in starch-liquefaction process. In the present study, site-directed mutagenesis was used to enhance the thermal stability and calcium independency of a mesophilic α-amylase from Bacillus megaterium WHO. Mutations (A53S and H58I) were designed at the calcium-binding site based on the sequence alignment. Kinetic and thermostability parameters of the mutants were analyzed and compared with that of the wild type. In the presence of calcium, the affinity of the enzymes (wild type and mutants) toward starch was increased. In comparison to the wild type, calcium ion had more effect on the catalytic efficiency, k _cat/K _m, and half-life (at 60 °C) of A53S mutant. In A53S, the dependence of half-life on calcium concentration showed that the enhanced calcium binding is likely to be responsible for the increased stability. In contrast, calcium-independent mutant (H58I) possessed high thermostability. In addition, thermodynamic parameters of amylolytic reaction exhibited an increase in the activation energy and the entropy of the system. Kinetics of irreversible thermal inactivation suggests that the activation energy increased by 1.4-fold in the most stable variant.     

The gas phase hydrogen‐bonded dimers of HOCl: A high‐level quantum chemical study

The O···H? O and Cl···H? O hydrogen bonding interactions were analyzed for HOCl dimers by using B3LYP, MP2, CCSD, and MP4(SDTQ) methods in conjunction with the various basis sets. Five isomers were found for the HOCl dimer. The ZPE and BSSE corrected binding energies were computed at the different levels of theory. At the optimized geometries obtained at CCSD/AUG‐cc‐pVDZ level, energies were re‐evaluated at MP4(SDTQ)/AUG‐cc‐pVTZ and CCSD(T)/cc‐pVTZ levels of theory. We found an average of ?20.9 and ?9.6 kJ/mol for the strength of the O···H and Cl···H hydrogen bonding interactions, respectively. Excitation and vertical ionization energies as well as rotational constants were computed at different levels of theory. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were used to elucidate the nature of the interactions of HOCl dimers. The interaction energies were decomposed by Morokuma methodology. We have computed Δ_fH°(HOCl) and Δ_fH°(HOCl⁺) using the atomization reactions. The Δ_fH°₂₉₈(HOCl) values are ?17.85 and ?18.05 kcal/mol by using CBS‐Q and CBS‐QB3 extrapolation models, respectively, in good agreement with the results given in JANAF tables. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Three-dimensional Brownian diffusion of rod-like macromolecules in the presence of randomly distributed spherical obstacles: molecular dynamics simulation

Brownian diffusion of rod-like polymers in the presence of randomly distributed spherical obstacles is studied using molecular dynamics simulations. It is observed that dependence of the reduced diffusion coefficient of these macromolecules on the available volume fraction can be described reasonably by a power law function. Despite the case of obstructed diffusion of flexible polymers in which reduced diffusion coefficient has a weak dependence on the polymer length, this dependence is noticeably strong in the case of rod-like polymers. Diffusion of these macromolecules in the presence of obstacles is observed that is anomalous at short time scales and normal at long times. Duration time of the anomalous diffusion regime is found that increases very rapidly with increasing both the polymer length and the obstructed volume fraction. Dynamics of diffusion of these polymers is observed that crosses over from Rouse to reptation type with increasing the density of obstacles.