KINETICS OF NON-ISOTHERMAL CRYSTALLIZATION OF POLY (ETHYLENE TEREPHTHALATE) MODIFIED BY POLY (ETHYLENE GLYCOL)

The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship between the reciprocal of t 1/2 ( the half life of crystallization) and the appropriate temperature variable. The parameters such as the activation energy (Ed) for transport, the equilibrium melting temperature (T_m~0),the nucleation parameter (ψ),themaximum crystallization temperature (T_(e, max)), and the kinetic crystallizability (G) for the copolyesters were obtained. The influence of the PEG content in PET chains on the parameters characterizing crystallization kinetics and crystallization thermodynamics was discussed.     

Electrochemical Study of the Lipid‐Transfer Protein

Electrochemical study of barley grain lipid‐transfer protein (LTP) revealed that it may belong to the metal‐binding protein class. Using differential pulse polarography the presence of Cu(II) and Zn(II) ions in the native LTP structure was proved, as well as its affinity for binding Ni(II) ion. Application of a more sensitive electroanalytical technique, such as anodic stripping voltammetry with analyte preconcentration, revealed the presence of Pb(II) and Cd(II) ions and also enabled the following Hg(II) ion binding. Possible biological role of LTP in plant stress response and its contribution to barley phytoextraction potential are discussed.     

On the phase CrTe3

A new phase CrTe₃ was discovered and its existence was confirmed by differential thermal analysis and X-ray investigations. Symmetry and lattice parameters as well as the temperature of its peritectic decomposition were determined.

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Über die PhaseCrTe ₃

Zusammenfassung Eine neue Phase CrTe₃ wurde entdeckt und ihre Existenz wurde mittels differential-thermoanalytischer und röntgenographischer Untersuchungen sichergestellt. Es wurden Symmetrie und Gitterparameter sowie auch die Temperatur des peritektischen Zerfalls bestimmt.

     

铜膜差分脉冲阳极溶出伏安法测定药物中铋的含量

研究了铜膜电极代替汞膜电极测定重金属铋的差分脉冲溶出伏安法。实验了同位镀膜法测定铋的条件。在最佳实验条件下,Bi3+浓度在5×10-8~2×10-5mol/L范围内,其溶出峰峰高与浓度呈线性关系,检出限达到1×10-8mol/L。测定了一些药物中铋的含量,结果准确。     

CURING KINETICS AND PROPERTIES OF ACRYLIC RESIN CURED WITH AZIRIDINE CROSSLINKER

A kind of aziridine crosslinkers was synthesized and used to crosslink acrylate copolymers. The crosslinkingproperties and curing kinetics of the resin were studied. It was found that with the increase of the content of crosslinker in theemulsion, the mechanical properties and solvent resistance of the resin will be apparently improved, but its glass transitiontemperature (T_g) is very low. The lowest amount of crosslinker used in the acrylic resin emulsion is 0.25%. Curing kineticsstudied by DSC show that this curing reaction occurs readily because the apparent activation energy of the reaction is low(65.1 kJ/mol). These results demonstrate that the aziridine crosslinker is indeed a low temperature crosslinking agent and canbe used at room temperature.     

Voltammetric behaviour of bromhexine and its determination in pharmaceuticals

A complete electrochemical study and a novel electroanalytical procedure for bromhexine quantitation are described. Bromhexine in methanol/0.1 mol L⁻¹ Britton–Robinson buffer solution (2.5/97.5) shows an anodic response on glassy carbon electrode between pH 2 and 7.5. By DPV and CV, both peak potential and current peak values were pH-dependent in all the pH range studied. A break at pH 5.5 in E_P versus pH plot revealing a protonation–deprotonation (pK_a) equilibrium of bromhexine was observed. Spectrophotometrically, an apparent pK_a value of 4.3 was also determined.

An electrodic mechanism involving the oxidation of bromhexine via two-electrons and two-protons was proposed. Controlled potential electrolysis followed by HPLC–UV and GC–MS permitted the identification of three oxidation products: N-methylcyclohexanamine, 2-amino-3,5-dibromobenzaldehyde and 2,4,8,10-tetrabromo dibenzo[b,f][1,5] diazocine.

DPV at pH 2 was selected as optimal pH for analytical purposes. Repeatability, reproducibility and selectivity parameters were adequate to quantify bromhexine in pharmaceutical forms. The recovery was 94.50 ± 2.03% and the detection and quantitation limits were 1.4 × 10⁻⁵ and 1.6 × 10⁻⁵ mol L⁻¹, respectively. Furthermore, the DPV method was applied successfully to individual tablet assay in order to verify the uniformity content of bromhexine. No special treatment of sample were required due to excipients do not interfered with the analytical signal. Finally the method was not time-consuming and less expensive than the HPLC one.     

Direct and simultaneous voltammetric analysis of heavy metals in tap water samples at Assiut city: an approach to improve the analysis time for nickel and cobalt determination at mercury film electrode

Tap water samples (Assiut city, lie in the middle north of upper Egypt, approx. 370 km from Cairo, January-March, 2002) were taken from the eight sampling sites of different locations at Assiut city. The samples are analyzed to determine the total content of cadmium, copper, lead and zinc by differential pulse anodic stripping voltammetry (DPASV) while nickel and cobalt are determined by a new simple differential pulse adsorptive stripping voltammetry (DPAdSV), using dimethylglyoxime (DMG) as the complexing agent. This method uses sodium sulfite as the supporting electrolyte, which facilitates the removal of oxygen interference without the traditional necessity of purging with inert gas. The effect of various parameters was studied using DPASV (for Cd, Pb, Cu and Zn) and AdSV (for Ni and Co) methods. Subsequently, under the so found experimental conditions, the stability of calibration curves and the detection limits (μg/l) have been determined. The data achieved (for all metals utility) are comparable to those measured by the graphite furnace atomic absorption spectrophotometric (GF-AAS) method. The effects of the interferences between these metal ions have been investigated. Moreover, the effect of storage was discussed and the obtained results were compared favorably with standard official methods. Statistical analysis of the database exhibits applicability and the accuracy of the techniques. The results obtained from the two techniques (Voltammetry and GF-AAS) are in very good agreements in the most tap water samples.     

Determining the wax content of crude oils by using differential scanning calorimetry

By the use of differential scanning calorimetry (DSC), a new method to measure the wax content of crude oil has been developed. In this paper, the wax content of a crude oil is proposed and proved to be the Q (total thermal effect of wax precipitation in sample) ratio of the crude oil and its corresponding wax obtained by using standard acetone method, i.e. Q_oil/Q_wax. For the 14 studied crude oils with the wax content ranging from 1 to 27 wt.%, the wax contents determined by the presented method are in good agreement with those determined by standard acetone method, with an absolute average deviation of only 0.82 wt.%. This method has an advantage over reported DSC methods in which the exact dissolution or precipitation enthalpy of wax is a must. It is also found that the wax contents determined by either of the two methods show good linear relationship with the total thermal effect Q_oil, with the correlation coefficients over 0.96. According to the empirical correlations, the wax content of a crude oil can be easily determined by using the DSC total thermal effect Q_oil. In addition and more significantly, the new method can be applied to improve the accuracy in determining the amount of precipitated wax in a waxy crude oil at different temperatures.     

Comparison between potentiostatic and galvanostatic intermittent titration techniques for determination of chemical diffusion coefficients in ion-insertion electrodes

Using well-cycled, thin composite graphite electrodes we analyze carefully the limitations of potentiostatic and galvanostatic intermittent titration techniques (PITT and GITT, respectively) for determination of the differential (incremental) intercalation capacitance, C_dif, and the chemical diffusion coefficient, D, of Li ions in these ion-insertion electrodes (IIEs). We demonstrate the superiority of the GITT over PITT to determine these quantities as the former technique allows for a more accurate determination of C_dif and hence D which closely approach to the spinodal domain related to the first-order phase transition during ion-insertion. We show that GITT is also more effective in eliminating the parasitic contributions of background currents to the total measured response. A pronounced difference in the initial, intrinsic kinetics of formation of a new phase in the bulk of the old one has been observed depending on the direction of titration (phases less saturated with Li are formed faster during deintercalation than the Li-rich phases in the course of intercalation).     

Two-state irreversible thermal denaturation of anionic peanut (Arachis hypogaea L.) peroxidase

Detailed differential scanning calorimetry (DSC), steady-state tryptophan fluorescence and far-UV circular dichroism (CD) studies, together with enzymatic assays, were carried out to monitor the thermal stability of anionic peanut peroxidase (aPrx) at pH 3.0. The spectral parameters were seen to be good complements to the highly sensitive but integral method of DSC. Thus, changes in far-UV CD corresponded to changes in the overall secondary structure of the enzyme, while changes in intrinsic tryptophan fluorescence emission corresponded to changes in the tertiary structure of the enzyme. The results, supported with data concerning changes in enzymatic activity with temperature, show that thermally induced transitions for aPrx are irreversible and strongly dependent upon the scan rate, suggesting that denaturation is under kinetic control. It is shown that the process of aPrx denaturation can be interpreted with sufficient accuracy in terms of the simple kinetic scheme, , where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation; N is the native state, and D is the denatured state. On the basis of this model, the parameters of the Arrhenius equation were calculated.