The role of electric interactions in the retention index concept; Implications in quantitative structure-retention studies

Summary A new equation is derived relating the retention index to the molecular polarizabilities, ionization potentials and permanent dipole moments of the stationary phase and the solute.Various implications of this equation to quantitative structure-retention relationships are discussed.     

Influence of substrate and product concentrations on the production of cyclodextrins by CGTase of Bacillus firmus,strain no. 37

The influence of substrate or product level on the initial velocity of cyclodextrin (CD) production by cyclodextringlycosyltransferase from a Brazilian isolate of Bacillus firmus was studied. Our results indicate that the product γ-CD is a stronger inhibitor to the reaction than β-CD. Small saccharides could also inhibit CD production, although to a lesser extent than the products, and maltose was the strongest inhibitor among small saccharides. Increasing substrate concentration resulted in greater reduction on enzyme activity for the formation of β-CD than for γ-CD. We modeled the kinetics of CD production with a set of four reversible reactions including the cyclization/coupling reaction that forms/opens CDs, and three disproportionation reactions. Our model on the initial velocity data explained well the substrate inhibition phenomenon. Kinetic parameters were determined by fitting the initial velocity data into our model.     

咪唑类化合物-CuCl络合催化剂在甲醇氧化羰基化反应中的催化性能

研究了咪唑及其衍生物配合CuCl对甲醇液相氧化羰化合成碳酸二甲酯的催化性能。筛选出溶解性好、腐蚀性小且催化活性高的多功能助催剂。实验结果表明，反应体系中加入N-甲基咪唑后，CuCl可以完全溶解。当催化剂的浓度为0.2 mol/L, N-甲基咪唑与CuCl的量为4∶1，反应温度为120 ℃，反应压力为2.40 MPa，CO与O2的进气比2∶1，反应3 h的条件下甲醇的摩尔转化率为15.4%，选择性为98%以上。从腐蚀性试验结果看，50 ℃时，加入N-甲基咪唑化合物后，Q235钢在CuCl/CH3OH/H2O/CO/O2体系中的腐蚀速率为0.22mm/a，缓蚀效率为94.5%。动力学研究表明，反应近似为一级，加入N-甲基咪唑后，反应速率常数为0.15 min－1。     

Error Levels of Different Methods of Evaluation of TG Measurements

It follows from an analysis of the error levels of TG evaluation methods that it is a conceptual error to disregard the analogies of mass, energy and momentum streams of subordinate partial processes. This error is bypassed by means of the introduced method of dimensionless analysis and by determining the characteristic, constants-like data of thermal processes by using the measured data directly. These methods are very suitable for increasing the consistency of the calculated results by seeking for similarity, even in comparisons of measurements made under very different conditions and for emphasizing the differences too, quantitatively. With this new interpretation of TG processes, the idea of the kinetic compensation effect becomes only a consequence of the discussed conceptual error. This revised version was published online in August 2006 with corrections to the Cover Date.     

Activation thermodynamic parameters of binary mixtures of propionic acid ando-substituted anilines

Variations of densities and viscosities with temperature and composition are reported for binary liquid mixtures containing propionic acid+aniline (I),+o-toluidine (II),+o-anisidine (III), and+o-chloroaniline (IV). Entropies S _m and enthalpies H _m of activation as functions of the composition of the mixtures, as well as free energies of activation G _m at 10, 20, 30, 40, and 50°C and different compositions were calculated by means of Eyring's equation. The formation of activated complexes between the components of these binary mixtures is postulated and claimed to result from acid-base and hydrogen bonding exchange interactions.     

Determination of L-tryptophan-serum albumin binding by high-performance liquid chromatography

Summary Two high-performance liquid chromatography (HPLC) techniques were developed for the determination of binding constants in the interaction of serum albumin with L-tryptophan: internal calibration and external calibration. The results obtained were compared with those obtained by the classical method of equilibrium dialysis and by gel filtration. While all the methods are equally reliable, the internal and external calibration techniques seem to be superior in their simplicity, speed and convenience.     

Kinetics parameters in Mg2SiO4:Tb thermoluminescent material

This paper reports a first approach on the kinetics parameters of terbium-activated magnesium orthosilicate using various methods. A deconvolution has also used for taking into account a more complex glow-curve structure.

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Zusammenfassung Mittels verschiedener Methoden werden in erster Näherung die kinetischen Parameter von terbiumaktiviertem Magnesiumorthosilikat ermittelt Zur Berücksichtigung einer komplexeren Thermolumineszenzkurve wurde auch eine Dekonvolution angewendet.

     

Two-beam interference detection of the changes in fibre structural parameters during low drawing process

A Pluta polarizing interference microscope with a fibre stretching device attached was used to detect the changes in molecular structure that occur during the fibre cold drawing process. Fibres drawn with low draw ratios show different types of deformation mechanisms. The interference patterns recorded at different draw ratios are used to relate the deformation mechanisms with the measured structural parameters. Some optical parameters are measured such as; refractive indices nand n birefringence n, the polarizability per unit volume , the orientation distribution function f(θ), the angle θ between the stretching direction and the chain axis, and the angle θ_m which the transition dipole moment of the molecular species makes with the molecular axis (chain axis). Three polymeric fibres (Polyethylene terephthalate PET, Polypropylene PP and Polyamide PA) were used in this study and their interferograms are illustrated.     

Complexation behaviour of benzilmono(Iepidyl)hydrazone (BLH) toward bivalent metal ions: A potentiometric study

Potentiometric investigations on metal complexes of various bivalent metal ions, viz. UO₂(II), Cu(II), Ni(II), Co(II), Cd(II), Pb(II), Zn(II) and Mn(II) with benzilmonol(lepidy!)hydrazone (BLH) have been carried out at different ionic strengths and at different temperatures in order to determine stability constants of the complexes. Thermodynamic parameters ΔC, ΔH and ΔS have also been evaluated from temperature coefficient data. The effect of varying the dielectric constant of the medium on the stability constants of complexes has also been investigated at 30±0.5°C and μ = 0.1MNaCl. Thermodynamic stability constants and thermodynamic stabilization energies for the first transition metals have also been discussed.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.