Solution thermodynamics of Lanthanide–Cryptand 222 complexation processes

The thermodynamics of trivalent cations (Y³⁺, La³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺, Er³⁺, Yb³⁺) and cryptand 222 in acetonitrile at 298.15?K is discussed. Recent reports regarding the behavior of lanthanide(III) trifluoromethane sulfonate salts in acetonitrile are considered. Thus, the experimental work was carried out under conditions in which ions (M³⁺) are predominantly in solution. Therefore, conductiometric titrations were carried out to establish the composition of the cation–cryptand 222 complexes and their ionic behavior in solution. Stability constants and derived standard Gibbs energies, enthalpies and entropies were determined by competitive titration microcalorimetry. Previously reported thermodynamic data for the complexation of cryptand 222 and a few lanthanide cations (La³⁺, Pr³⁺ and Nd³⁺) in acetonitrile are revisited. The medium effect on the stability of complex formation in acetonitrile relative to N,N-dimethylformamide is demonstrated. Thus, a drop in stability by a factor of 8 × 10¹⁰ is observed for the latter relative to the former solvent. The selectivity of cryptand 222 for these cations relative to La³⁺ in acetonitrile is discussed.     

Some problems in adsorption and calorimetric studies of the steps of catalytic processes

Principal side factors as well as technical and procedural peculiarities capable of distorting the results of measurements of adsorbed and desorbed amounts, of falsifying the nature of the processes proceeding in the systems under study, and of promoting artifacts in calorimetric and other studies of gas chemisorption on powders are considered. Modified techniques and procedures allowing the elimination of sources of side phenomena and artifacts and freeing traditional glass static adsorption apparatuses and experimental procedures from undesirable factors and peculiarities are proposed. Some available chemisorption and calorimetric data representing artifacts and also some data that are not artifacts but,due to imperfections of chemisorption techniques, show up as artifacts are presented and discussed. Several applications of the improved techniques and procedures to calorimetric and adsorption studies of the steps of catalytic processes proceeding on the basis of natural gas and of products of its processing are presented and discussed.     

Applicability of Fraser–Suzuki function in kinetic analysis of complex crystallization processes

A modified peak-deconvolution procedure for complex crystallization processes was introduced. The method is based on the constrained curve-fitting technique using the Fraser–Suzuki (FS) function, where the FS asymmetry parameter a ₃ correlates with the value of the Johnson–Mehl–Avrami (JMA) kinetic parameter m. The correlation was verified for an extensive number of theoretically simulated JMA curves; in addition, the dependencies of the a ₃ parameter on other kinetic variables (E, A, q ⁺) were quantified. The suggested deconvolution procedure was tested on two glassy systems with different overlay degree of the involved overlapping surface and bulk crystallization processes. In both cases, the kinetic analysis of deconvoluted data provided reasonable, consistent and accurate results. However, certain level of knowledge and experience was needed in order to correctly recognize and consequently account for all deviations from the theoretical behavior caused by thermal gradients or imperfections of the data acquisition process. As the input data for the fitting procedure can be in any form equivalent to the dα/dT temperature dependence, the method seems to be highly universal and may be applied to data obtained by various TA techniques.     

Modeling of reaction–diffusion processes: part (ii) the theory of catalytic electrode processes at hemi-oblate and prolate ultramicroelectrodes

The analytical solutions of the non-steady-state currents arising from the diffusion of regenerating electroactive species towards a hemi-oblate and prolate electrodes are discussed. This simple new approximate expression is valid for all values of time and all values of rate constant. Tabular compilations of dimensionless current for hemi-oblate and prolate electrodes are reported.     

Some problerns in adsorption and calorimetric studies of the steps of catalytic processes

Principal side factors as well as technical and procedural peculiarities capable of distorting the results of measurements of adsorbed and desorbed amounts, of falsifying the nature of the processes proceeding in the systems under study, and of promoting artifacts in calorimetric and other studies of gas chemisorption on powders are considered. Modified techniques and procedures allowing the elimination of sources of side phenomena and artifacts and freeing traditional glass static adsorption apparatuses and experimental procedures from undesirable factors and peculiarities are proposed. Some available chemisorption and calorimetric data representing artifacts and also some data that are not artifacts but, due to imperfections of chemisorption techniques, show up as artifacts are presented and discussed. Several applications of the improved techniques and procedures to calorimetric and adsorption studies of the steps of catalytic processes proceeding on the basis of natural gas and of products of its pr     

Redox properties of hydrogenated quinoline derivatives — inhibitors in oxidation processes of hydrocarbons

Half-wave potentials of the one-electron electrochemical oxidation (E _1/2 ^ox) of hydroquinolines with different degrees of heterocycle hydrogenization as well as containing substituents of various natures in the benzene ring and heterocycle have been measured. Linear correlations betweenE _1/2 ^ox and the values of the Hammett polar -constants form- andp-substituents in dihydroquinolines and related sulfur-containing dithiolthiones were established. The character of the variation ofE _1/2 ^ox in the series of hydroquinolines was found to correlate with the characteristic features of the inhibiting action of these compounds in the liquid-phase oxidation of various hydrocarbons. However, in contrast to phenolic antioxidants for hydroquinolines, there is no dependence of the retardation period onE _1/2 ^oxin the oxidation of hydrocarbons at temperatures higher than 100 °C.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 610–613, April, 1994.     

Characterization of adsorption processes in analytical liquid–solid chromatography

This review discusses nonlinear chromatographic methods of importance for proper characterization of the adsorption processes in analytical chromatographic systems, with focus on reversed-phase liquid chromatography. Linear methods such as the linear solvation energy relationship (LSER) method and the Snyder–Dolan hydrophobic-subtraction model will also be reviewed briefly. The nonlinear methods for adsorption isotherm determination and the tools for further treatment of the nonlinear adsorption data will be extensively treated in a way suitable for the general chromatographer. Applications of the various methods will be given and the outcome and conclusions will be discussed. Special emphasis will be placed on discussing the possibilities of combining linear and nonlinear methods in order to obtain a deeper and more complete investigation of the interactions in the actual phase system.     

Analysis of decomposition processes of ausferrite in copper–nickel austempered ductile iron

Analysis of thermal decomposition processes of the ausferrite obtained during simulation of austempering heat treatment was performed on austempered ductile iron (ADI). The analysis method consisting in investigation of inverse phase transformations was applied. The material with specified phase composition and well-defined thermophysical properties, both resulting from the conducted heat treatment cycle, was heated under controlled conditions and the thermal effects—enthalpy change and volume change were recorded by means of differential scanning calorimetry (DSC) and differential dilatometry. The process of ausferrite decomposition in the range of 100–800 °C was discussed; the identification scheme and temperature sequence of phase transformations accompanying the ausferrite decomposition were established. The elaborated decomposition scheme allows selection of the ADI heat treatment and its optimization by means of the non-isothermal thermal analysis methods.     

Applications of microwave-assisted processes (MAP™) to environmental analysis

The use of microwave-assisted extraction has gained wide acceptance as a powerful tool for the recovery of environmental contaminants and their subsequent analysis. This paper reviews the historical and fundamental basis of the technology. It also provides a cursory review of the current state-of-the-art and literature (2000–2006) in the area of environmental analysis in addition to providing a critical review of the level of efforts being devoted to its further development. MAP is a Trademark of Her Majesty the Queen in Right of Canada as represented by the Minister of the Environment.     

NMR titration and molecular model MOPAC calculation of protonation processes of two MRI ligands

The protonation process of two DTPA bis(amide) derivatives,DTPA-BDMA and DTPA-BDEA,was studied by using 1H NMR titration and MOPAC calculation.Their protonation process was proposed in the order of the central amine,the terminal amines,the central carboxyl,the terminal carboxyl,the other terminal carboxyl and central amine.During the protonation of the terminal amine,there existed a large fraction of proton transfer from the central amine to the other terminal amine.     

Padé approximation of ECE and DISP processes at channel electrodes

A two-point Padé approximation is derived for ECE and DISP1 reactions occurring at channel electrodes for all rate constants. These are shown to be in excellent agreement with previous studies.     

Solubilization and Hydrolysis of Ovotransferrin Solubilization of α-chymotrypsin. Enthalpy changes for three processes

At 298.15 K, the solubilization of hen ovotransferrin at buffered pH 7.8 (0.08 M Tris⋅HCl buffer, containing 0.1 M CaCl₂) and the solubilization of α-chymotrypsin (from bovine pancreas) at non-buffered pH 3.0 (0.001 M HCl) both resulted in large exothermic reactions, being the apparent ΔHs –2485 in the first case and –780.1 kJ mol^–1 in the second case, respectively. By contrast, the complete hydrolysis of ovotransferrin (pH 7.8) achieved by using a-chymotrypsin (pH 3.0) gave an endothermic reaction with ΔH=+31.84 kJ mol^–1. This revised version was published online in July 2006 with corrections to the Cover Date.     

DSC study of cold and heat denaturation processes of β-lactoglobulin A with guanidine hydrochloride

The cold and heat denaturations of bovine β-lactoglobuhn A (β-lg A) has been studied in solutions of guanidine hydrochloride (GuHCl) by differential scanning calorimelry (DSC) The experimental results are presented and discussed.It is shown that the number of protons bound by the monomeric molecules of β-lg A was unchanged before and after its heat denaturation below pH 3,and that the activation energy of the heat denaturation was depressed owing to the presence of GuHCl.In the solutions with 2.50 and 3.06 mol/L of GuHCl,both the cold and heat denat-urations of β-lg A were observed.In comparison with the heat denaturation,the activation energy of cold denaturation was far lower and the number of GuHCl molecules bound by the unfolded polypeptide chains after cold denaturation increased a lot.The absolute value of the enthalpy of cold denaturation was larger than that of heat denaturation It was found by the analysis that the contribution to the total denaturational enthalpy of conformational change i     

Study of α- and β-relaxation processes in supercooled sucrose liquids

The relaxation map of highly concentrated sucrose water mixtures was built using mechanical and impedance spectroscopies. Data of - and -relaxation processes obtained with both techniques complete calorimetric and rheological measurements. The temperature evolutions of the relaxations were extrapolated using the measured data and the equations commonly used to describe the relaxations: Arrhenius and WLF behaviours for respectively the - and -relaxations. The temperature/frequency domain when and processes merge for 99% sucrose solution is discussed with respect to scenery proposed in the literature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Mechanistic studies of Fc-PNA(⋅DNA) surface dynamics based on the kinetics of electron-transfer processes

N‐Terminally ferrocenylated and C‐terminally gold‐surface‐grafted peptide nucleic acid (PNA) strands were exploited as unique tools for the electrochemical investigation of the strand dynamics of short PNA(?DNA) duplexes. On the basis of the quantitative analysis of the kinetics and the diffusional characteristics of the electron‐transfer process, a nanoscopic view of the Fc‐PNA(?DNA) surface dynamics was obtained. Loosely packed, surface‐confined Fc‐PNA single strands were found to render the charge‐transfer process of the tethered Fc moiety diffusion‐limited, whereas surfaces modified with Fc‐PNA?DNA duplexes exhibited a charge‐transfer process with characteristics between the two extremes of diffusion and surface limitation. The interplay between the inherent strand elasticity and effects exerted by the electric field are supposed to dictate the probability of a sufficient approach of the Fc head group to the electrode surface, as reflected in the measured values of the electron‐transfer rate constant, k⁰. An in‐depth understanding of the dynamics of surface‐bound PNA and PNA?DNA strands is of utmost importance for the development of DNA biosensors using (Fc‐)PNA recognition layers.     

Hydration and dehydration processes of β-cyclodextrin: A raman spectroscopic study

A linear relationship between the integrated intensity of the Raman OH stretching band (I_OH) and ambient humidity in equilibrium with a sample of a crystalline -Cyclodextrin (CD) hydrate, for humidities between 15% and 100%, was obtained. In addition, hydration and dehydration processes were monitored by measuring I_OH as a function of time. For the normally hydrated crystal, both hydration and dehydration processes present essentially continuous and similar variations with hysteresis for times shorter than 20 min.     

The specific feature of photochemical processes in molecules of 3,3′-dialkylthiacarbocyanines in binary solvent mixtures

The effect of the composition of the dimethyl sulfoxide (DMSO)-toluene mixture on the photochemical processes of 3,3′-diethylthiacarbocyanine (DETCC) iodide and 3,3′-dimethylthiacarbocyanine (DMTCC) chloride was studied. In the mixtures with the DMSO content more than 20 vol %, DETCC iodide and DMTCC chloride molecules are characterized by a high efficiency of both trans → cis photoisomerization and fluorescence, in contrast to intersystem crossing to the triplet state. With decreasing the DMSO content to 3 vol %, the relative quantum yield of DETCC iodide intersystem crossing increases by two orders of magnitude, which is accompanied by a decrease in the lifetime of DETCC iodide triplet molecules from 1.1 × 10^?4 to 2.4 × 10^?7 s and a decrease in the yield of the cis-isomers. To explain the results, the concepts of “external heavy atom (iodide) effect” and hyperfine coupling (HFC mechanism) in radical pairs that could be formed via electron transfer between the iodide and an excited dye molecule were used.     

“Matrix effects” in the activation of compounds with a system of conjugation in the inhibition of oxidative processes

Russian Chemical Bulletin -