Factors affecting electrical conductivity of carbon black-loaded rubber. II. Effect of concentration and type of carbon black on electrical conductivity of SBR

Effect of the concentration of four types of carbon black, namely, HAF, FEF, ISAF and GPF, on the electrical conductivity of SBR (1502) was studied. The anomalous behavior of conductivity [σ_min in σ(T) curves] becomes more pronounced as we approach a characteristic value of carbon concentration, F₀, at which maximum anomaly occurs; F₀ was found to depend on the type of carbon black. Moreover, the depth of the valley shape of the σ(T) curve increases with the particle size of carbon black used.     

Ternary complexes in solution. Comparison of the coordination tendency of some polybasic oxygen acids toward the binary complexes of Cu(II) andAMP,ADP orATP

Summary Potentiometric equilibrium measurements have been made at 25±0.1°C (=0.1 mol dm^–3 KNO₃) for the interaction of adenosine-5-mono-, -di- and -triphosphate (AMP,ADP andATP) and Cu(II) with biologically important secondary ligand acids (malic, maleic, succinic, tartaric, citric and oxalic acids) in a 1:1:1 ratio and the formation of various 1:1:1 mixed ligand complex species inferred from the potentiometricpH titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP, and secondary ligand acid, have been refined with the SUPERQUAD computer program. In some systems logK values are positive, i.e. the ternary complexes are found to be more stable than the corresponding binary complexes. In some Cu(II) ternary systems the interligand interactions between the coordinate ligands, possibly H bond formation, have been found to be most effective in deciding the stability of the ternary complexes formed in solution. Stabilities of mixed ligand complexes increase in the orderAMP <ADP <ATP. With respect to the secondary ligands, the formation constants of the mixed ligand complexes decrease in the order succinic > maleic > tartaric > malic > citric > oxalic acid.

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Ternäre Komplexe in Lösung. Vergleich der Koordinationstendenz einiger polybasischer Sauerstoffsäuren gegenüber binären Komplexen von Cu(II) mitAMP,ADP oderATP

Zusammenfassung Es wurden potentiometrische Gleichgewichtsmessungen bei 25±0.1°C bei =0.1 mol dm^–1 KNO₃ durchgeführt, um die Wechselwirkung von Adenosin-5-mono-, -di- und triphosphat mit Cu(II) und biologisch relevanten Sekundärliganden wie Äpfel-, Malein-, Bernstein-, Wein-, Zitronen- und Oxalsäure im Verhältnis 1:1:1 festzustellen. Aus den potentiometrischenpH-Titrationskurven ergaben sich verschiedene 1:1:1 gemischte Ligandenkomplexe. Anfänglich abgeschätzte Komplexbildungskonstanten der Komplexe und Säuredissoziationskonstanten vonAMP,ADP undATP und den Sauerstoffsäuren wurden mittels des Computerprogramms SUPERQUAD verfeinert. In einigen Systemen ist logK positiv, demzufolge sind die ternären Komplexe stabiler als die korrespondierenden binären. In einigen ternären Cu(II)-Komplexen bestehen zwischen den Liganden Wechselwirkungen, vermutlich auf der Basis von stabilitätsfördernden Wasserstoffbrückenbindungen. Die Stabilitäten der gemischten Komplexe steigen in der ReihenfolgeAMP <ADP <ATP. Bezüglich der Sekundärliganden ergibt sich für die Bildungskonstanten der ternären Komplexe die Reihung Bersteinsäure > Maleinsäure > Weinsäure > Äpfelsäure > Zitronensäure > Oxalsaure.

     

The physical properties of pressure sensitive rubber composites

Nitrile butadiene rubber, NBR, structural foam of different apparent densities was obtained by using different concentrations of foaming agent, azodicarbonamide, ADC/K. The true stress-strain characteristics, in case of compression, of foamed samples after the application of cyclic stress-strain were measured. The effect of the cyclic stress-strain on strain energy density of ADC/K foaming agent-filled NBR rubber composites was studied. The mechanical parameters were found to depend on the foaming agent concentration and on the pre-cyclic fatigue number. Results also indicated that the strain energy decreased with filler concentration.The effects of the cyclic stress-strain on the conductivity of ADC/K foaming agent-filled NBR rubber composites were studied. The electrical properties were found to depend on the foaming agent concentration, the strain amplitude and the number of stress-strain cycles of pre-strain. This study was assisted by the current-voltage characteristics which were measured under the effect of different compression ratios: 0%, 5%, 10%, 15%, 20%, 25% and 30%. The free current carrier mobility and the equilibrium concentration of charge carriers in the conduction band were produced as functions of compressive strain. Results also indicate that there is a linear variation between pressure and conductivity for all samples, which means that these samples can be used as a pressure sensor.     

Synthesis and Biological Evaluation of New Fused Thiazolo[4,5-d] Pyridazine Derivatives

The synthesis of thiazolo[4,5-d]pyridazines and the unknown ring systems, thiazolo[4,5-d]-1,2,4-triazolo- and tetrazolo[4,3-b]pyridazines as well as thiazolo(4,5-d]pyridazino[2,3-c]2H triazines, has been achieved according to different pathways. Biological testing of the new tricyclic heterocycles revealed that some of these compounds possess remarkable antibacterial activity.     

New spectrophotometric method for the determination of trace amounts of palladium

Summary A simple, rapid, selective, and sensitive method for the spectrophotometric determination of palladium is developed based on the reaction of Pd(II) with 1-amino-4-hydroxyanthraquinone (AMHA). The reaction is carried out atpH 3.8 in 50% (v/v) ethanol-water medium. The molar absorptivity of the complexed ligand is 1.1 · 10⁴ l mol^–1 cm^–1 at 620 nm. Calibration plots are linear up to 17 µg Pd cm^–3. The optimum concentration range (Ringbom plot) is between 3–14.5 µg cm^–3. The spectral study of the reaction in solutions containing equimolar concentrations or an excess of one component, in thepH range 0.3–6.5, indicate the possible complex transitions that occur in solution. Complete graphical and logarithmic analysis of the absorbance-pH graphs was performed to demonstrate and characterize the complexation equilibria in solution. Under the optimum conditions, palladium can be determined as the noncharged complex Pd(AMHA)₂ in the presence of a large number of foreign ions. Interferences caused by zirconium(IV) could be masked with fluoride ions.

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Eine neue spektrophotometrische Methode für die Bestimmung von Palladium in Spuren

Zusammenfassung Eine einfache, schnelle und empfindliche Methode für die spektrophotometrische Bestimmung von Palladium wurde auf der Basis der Reaktion von Pd(II) mit 1-Amino-4-hydroxyanthrachinon (AMHA) entwickelt. Die Reaktion wird in 50% (v/v) Ethanol/Wasser beipH 3.8 ausgeführt. Die molare Absorption des komplexierten Liganden beträgt 1.1 · 10⁴ l mol^–1 cm^–1 bei 620 nm. Kalibrierungskurven verlaufen bis zu 17 µg Pd cm^–3 linear. Der optimale Konzentrationsbereich (Ringbom-Plot) liegt zwischen 3 und 14.5 µg cm^–3. Spektroskopische Untersuchungen der Reaktion in Lösungen, entweder mit equimolaren Konzentrationen oder mit einem Überschuß an einer Komponente impH-Bereich 0.3–6.5, lassen Rückschlüsse auf mögliche Komplex-Übergänge in Lösung zu. Es wurde eine vollständige graphische, logarithmische Analyse der Absorptions-pH-Graphen durchgeführt, um die Komplexgleichgewichte in Lösung aufzuklären und zu charakterisieren. Unter den Optimalbedingungen kann Palladium als nichtgeladener Komplex Pd(AMHA)₂ in Gegenwart einer großen Anzahl an Fremd-Ionen bestimmt werden. Schwierigkeiten mit Zirkonium(IV) konnte durch Maskierung mit Fluorid-Ionen umgangen werden.

     

Effect of sodium oxide doping on solid-solid interactions between V2O5 AND Al2O3

A V₂O₅/Al₂O₃ mixed solids sample was prepared with a molar ratio of 0.41 Na₂O (4 and 10 mol%) was added in the form of sodium nitrate prior to calcination in air in the temperature range 500–1000C. Solid-solid interactions between V₂O₅ and Al₂O₃ were studied using DTA and TG curves and their derivatives together with XRD techniques.The results obtained showed that Na₂O interacted with V₂O₅ at temperatures starting from 500C to yield a sodium/vanadium compound, Na_0.3V₂O₅ which remained stable and decomposed in part by heating at 1000C. V₂O₅ exists in orthorhombic and monoclinic forms in the case of pure mixed solids and those containing 4 mol% of Na₂O and preheated at 500C, and in monoclinic form in the case of the mixed solid doped with 10 mol% of Na₂O.Heating of pure and doped mixed oxide solids at 650C resulted in the conversion of most of the V₂O₅ into AlVO₄. Doping with sodium oxide enhanced the solid-solid interaction between V₂O₅ and Al₂O₃ at 650C to produce AlVO₄. The produced AlVO₄ decomposed completely on heating at 700C to form -Al₂O₃ and V₂O₅, (orthorhombic and monoclinic forms).The presence of Na₂O was found to decrease the relative intensity of the diffraction lines of -Al₂O₃ (corundum) produced at 750C which indicated some kind of hindrance of the crystallization process.Heating of pure and doped mixed solids at 1000C resulted in a further crystallization of acorundum together with V₂O₅ and sodium vanadate, Na_0.3V₂O₅. However, the intensities of diffraction lines relative to those of the sodium vanadium compound were found to decrease markedly by heating at 1000C, indicating partial thermal decomposition into vanadium and aluminium oxides.     

Spectrophotometric assay of retinol via charge-transfer complexes

Simple and sensitive spectrophotometric methods for the assay of retinol have been presented. The first method was based on the reaction of retinol with iodine to give a molecular charge-transfer complex, the retinol acting as n-donor and iodine as -electron acceptor. The second method depends on the formation of a highly coloured stable radical anion between retinol and 7,7,8,8-tetracyanoquinodimethane (TCNQ as a -electron acceptor. The molecular ratios of the reactants in the complexes have been established and the experimental conditions leading to maximum charge-transfer bands were also studied. Beer's law is obeyed over the retinol concentration range 2.5–26 µg/ml. The proposed procedures have been applied successfully to the analysis of drug formulation. The average recovery and average standard deviation was 99.99 ±1.13% with retinol-iodine and 100.001 ± 1.31% with retinol-TCNQ. A kinetic study was performed by heating retinol at 50°C for different periods of time, the result obtained by plotting log c against time indicates that thermal decomposition of retinol is of first order. The results obtained by both methods were in good agreement with those obtained by the official method. The developed procedures were found to be simple, accurate and precise and can be used for the determination of retinol in presence of its degradation products.     

Synthesis,Characterization, and an ab initio Study of a Manganese(II) Macrocyclic Schiff-Base Complex with Two 2-Aminoethyl Pendant Arms

The cyclocondensation of 2,6-diformylpyridine with N,N,N,N-tetrakis(2-aminoethyl)ethane-1,2-diamine (pentene) in the presence of Mn^II forms the [1 + 1] pendant arm Schiff-base macrocyclic complex, [MnL³]²⁺. The ligand is a 15-membered pentaaza macrocycle having two 2-aminoethyl pendant arms {L³= 6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentene}. The complex, investigated by analytical, spectroscopic and magnetic techniques, supports the formation of a highly symmetrical pentagonal bipyramid complex with the Mn^II ion located within a pentaaza macrocycle and two pendant amines coordinating on opposite sides of a plane defined by the macrocycle and the metal ion. The structure of the complex was also verified by ab initio HF-MO calculations using a standard 3-21G basis set.     

Comparative study on the inclusion behaviour of cyclodextrin derivatives with venoruton and rutin by thin layer chromatography

The interaction of rutin and venoruton (troxerutin), with alpha-, beta- and gamma-cyclodextrin (CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and methyl-beta-cyclodextrin (M-beta-CD) was investigated by reversed-phase thin layer chromatography on polyamide plates. A mobile phase consisted of NH(4)OH; NH(4)Cl buffer solution containing various CD concentrations (pH = 9.7, 20 degrees C) was used as mobile phase. The equilibrium constants (K(f)) and the retention factor (R(f)) were determined and used to study the inclusion process. The in fluence of CDs on the solubility of rutin and venoruton was characterized by R(M) values and the increasing hydrophilicity of drugs. The results show that the inclusion capacity of cyclodextrins follows the order HP-beta-CD > M-beta-CD > beta-CD > gamma-CD, and rutin is more easily included by the studied cyclodextrins than venoruton. In addition, the thermodynamic parameters (Delta H, Delta S) for the formation of complexes were obtained from the van't Hoff equation, displaying the enthalpy-entropy compensation effect.     

Thermodynamics of Ion-Association of NaClO4 in Aqueous-Methanol and Aqueous-Glycerol Using Conductance Measurements

The conductance of NaClO₄ at (25–45)°C in methanol-H₂O, and glycerol-H₂O mixtures in a concentration range up to 10^?2 M has been measured. The association constant, K_A, values have been determined, where the conductometric data were analysed by a M S X computer using the Fuoss-Aprano method. The K_A values for NaClO₄ in methanol-H₂O are higher than in glycerel-H₂O mixtures, Also K_A values increase as the proportional of methanol or glycerol increases in mixture. The thermodynamic parameters ΔH°, ΔG°, and ΔS° were also calculated. It is obvious that the entire process of the ionic association in those systems are endothermic ones. The Walden products, Λ_oη were calculated for all systems investigated.