Reaction-diffusion travelling waves in the acidic nitrate-ferroin reaction

A two-variable model proposed for the acidic nitrate-ferroin reaction is considered in the reaction-diffusion context. An initial-value problem in which an amount of nitrate is introduced locally into ferroin at uniform concentration is treated both analytically and numerically. It is shown that the large time structure is a reaction-diffusion travelling wave of permanent form propagating with constant speed. This asymptotic wave speed is shown to be the minimum possible wave speed and the asymptotic approach to this value is estimated. Properties of the permanent-form travelling waves are derived and solutions valid for small and large values of a parameter , involved in the kinetic mechanism, are obtained.     

Electrochemical behaviour of quinazoline in amphiprotic media

The electrochemical behaviour of quinazoline in aqueous methanolic solutions has been studied in detail. In acid solutions two single-electron waves of equal height are obtained whereas in neutral solutions a single two-electron wave is observed. Quinazoline gets reduced to tetrahydroquinazoline in alkaline media and very interestingly gives reverse cathodic peaks during cyclic voltammetric experiments. The polarographic waves are diffusion-controlled and irreversible on the basis of the usual criteria. Based on the results obtained, reduction schemes are given for quinazoline in various buffered media. A comparison of the electrochemical behaviour, between quinazoline and 4-(2-thienyl)quinazoline (4-TQ) has been attempted.

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Das elektrochemische Verhalten von Chinazolin in amphiprotischen Medien

Zusammenfassung Das elektrochemische Verhalten von Chinazolin in wäßrigen methanolischen Lösungen wurde im Detail untersucht. In sauren Lösungen wurden zwei Einelektronenwellen gleicher Höhe erhalten, währenddessen in neutralen Lösungen eine einzige Zweielektronenwelle beobachtet wurde. Chinazolin wird in alkalischem Medium zu Tetrahydrochinazolin reduziert und ergibt interessanterweise kathodische Umkehrpeaks während cyclischer voltammetrischer Experimente. Die polarographischen Wellen sind diffusionskontrolliert und nach den üblichen Kriterien irreversibel. Aufgrund dieser Ergebnisse werden Reduktionsschemata für Chinazolin in verschiedenen Puffermedien angegeben. Es wird ein Vergleich zwischen dem elektrochemischen Verhalten von Chinazolin und 4-(2-Thienyl)-chinazolin (4-TQ) angestellt.

     

Polarography of hexavalent molybdenum in hypophosphorous acid solutions

The polarographic behaviour and determination of Mo(VI) in hypophosphorous acid solutions of concentrations varying from 0.1 to 5.0 mol l^?1 andT=25±0.1 °C have been investigated. It was shown that reduction of MoO ₄ ^2? takes place along a single or two waves depending upon the acid concentration. Microcoulometric experiments have been performed at the limiting region of the different waves obtained at different acid concentrations. A scheme for the mechanism of reduction occuring at theDME has been deduced. A method for analytical determination of Mo(VI) on both the micro- and macro-scales in hypophosphorous acid solutions has been reported. Analysis of a binary mixture Mo(VI)/Cd(II) and a tertiary mixture Mo(VI)/Cd(II)/Zn(II) in mol l^?1 hypophosphorous acid has been investigated.     

Two-quantum photochemistry of the complex <Emphasis Type="Italic">cis</Emphasis>,<Emphasis Type="Italic">trans</Emphasis>-[Pt<Superscript>IV</Superscript>(en)(I)<Subscript>2</Subscript>(CH<Subscript>3</Subscript>COO)<Subscript>2</Subscript>]

The two-quantum photochemistry of aqueous solutions of cis,trans-[Pt^IV(en)(I)₂(CH₃COO)₂] (complex 1) has been studied by laser flash photolysis using an irradiation wavelength of 355 nm. This compound can be considered as a model representative of the mixed-ligand Pt(IV) complexes tested for use in photodynamic therapy. The appearance of transient absorption, presumably due to two consecutively produced Pt(III) complexes, has been revealed. The spectral and kinetic characteristics of the intermediates have been determined. A mechanism of two-quantum photolysis of complex 1 is proposed on the basis of the data obtained.     

The very-high-temperature pyrolysis of ethane: Evidence against high rates for dissociative recombination reactions of methyl radicals

The pyrolysis of 1 and 2% ethane in krypton has been studied in shock waves by the laser-schlieren technique over 1700–4800 K. For 2400–2800 K an effective zero density gradient is seen following the rapid dissociation of the ethane. Through simulation with various mechanisms it is evident that the high rates for the dissociative recombination reactions of methyl radicals obtained in recent shock-tube studies, are incompatible with this observation; these rates must be reduced at least an order of magnitude. On the basis of theory and previous low-temperature (T) measurements, k = 7.8 × 10¹¹ (-6562/T) (cm³/mol s) is recommended for the second of these reactions.     

Alizarin Red S as a colored agent for the extraction-photometric and color measurement determination of some local anesthetic organic compounds

The possibility has been considered for using 1,2-dihydroxyantraquinonone-3-sulfoacid (Alizarin Red S, ARS) as a colored agent for the determination of organic bases as of their ion associates. Spectrophotometric and colorimetric properties of the ion associates of cetyltrimethylammonium bromide and local anesthetics Novocaine and Lidocaine with ARS have been studied in aqueous solutions at pH 2–6; the optimal conditions for the formation of ion associates have been determined and the extraction mechanism has been revealed. Calibration curve equations have been obtained for the dependences of the absorbance of extracts and back extracts of organic bases in aqueous and organic phases, as well as the chromaticity functions (CF) of the ion associates on the concentration of the organic bases in aqueous and organic phases. Molar absorption coefficients and CF of the considered ion associates have been determined. The advantages of the color measurement over spectrophotometry for the determination of molar absorption coefficients and CF have been demonstrated. An application of the developed procedure has been proposed.     

Processing,structure, microstructure,and transport properties of the oxygen-conducting ceramics (La,Sr)(Ga,M)O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> (M=Mg,Fe, Ni)

The structure, microstructure, and dielectric and transport properties of (La,Sr)(Ga,M)O_y (M=Mg, Fe, and Ni) ceramic solid solutions have been studied by X-ray diffraction, thermogravimetry, and dilatometry in various gas atmospheres. Enhancement of conductivity and an increase of the thermal expansion coefficient have been confirmed to correlate with an increasing concentration of oxygen vacancies at high temperatures in the samples studied. Transformation from pure ionic to mixed conductivity has been revealed in the samples with increasing iron or nickel content.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Research in the isoxazole series. 38. Polarographic reduction of 4-arylazoisoxazoles

The indicated compounds are reduced on a dropping-mercury electrode in aqueous alcohol solutions at pH > 7 in one two-electron wave to 1,2-disubstituted hydrazines; four-electron reduction with the formation of amines takes place in acidic media. Two one-electron reduction waves are observed in dimethylformamide (DMF). Satisfactory E_1/2– correlation equations were obtained for 4-arylazo-3,5-dimethyloxazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1320–1323, October, 1980.     

Crystal hydrates: an investigation of the use of crystal hydrates as stationary phases in gas chromatography

Summary The use of crystallohydrates, crystallohydrate solutions and melts as stationary phases in gas chromatography has been proposed. Crystallohydrates have been shown to display high selectivity in the separation of polar organic compounds when use is made of water vapours as the mobile phase. Some aspects of gas-liquid chromatography in water vapours and with the stationary phase comprising crystallohydrates have been studied, and the preliminary results obtained point to the desirability of further progress in this field.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Removal of contaminated oxide layer on carbon steel in hydrochloric acid disodium citrate solutions

The removal of contaminated high temperature grown magnetite on carbon steel in buffered HCl-disodium citrate solutions has been studied. Decontamination factors higher than 200 concomitantly with a dissolution of metal substrate lower than 1 m after 1 hour treatment have been obtained.     

Tridiagonal treatment for the Schr?dinger equation with a noncentral electric dipole ring-shaped potential

A noncentral potential is proposed in which the noncentral electric dipole and a ring-shaped component ${\cos ^{2}\theta/r^{2}\sin^{2}\theta}$ are included. The exactly complete solutions of the Schr?dinger equation with this potential is investigated by working in a complete square integrable basis that supports an infinite tridiagonal matrix representation of the wave operator. The solutions obtained are for all energies, the discrete (for bound states) as well as the continuous (for scattering states). The expansion coefficients of the wavefunctions (both angular and radial) are written in terms of orthogonal polynomials satisfying three-term recursion relation. The discrete spectrum of the bound states is obtained by diagonalization of the radial recursion relation.     

Molecular correlation integrals. Two center one electron integrals containing a function of interparticle distance in one center expansion approximation

Two-center one-electron integrals needed in certain molecular correlated wave function calculations, using one-center expansion approximation, have been studied. The form of the basic correlated function used in this study is The parent integral is expressed in terms of an angular integral, and an auxiliary radial integral depending upon the variables r₁, r₂, and r₁₂. Several analytical formulas, and a recursive formula are derived for the auxiliary integral, and other related integrals. All these formulas are given in computationally useful forms. Logical flow charts and FORTRAN programs were constructed for computing the basic integrals discussed in the paper. Numerical values of some integrals, thus obtained, are tabulated for comparisons.     

Acid-base properties and stability of pyrylium polymethine dyes in chlorohydrocarbon solutions

The reactions of pyrylocyanine dyes with aqueous alcoholic alkali and with acetic acid have been studied. It has been shown that decoloration of such dyes in chlorohydrocarbon solutions only occurred under the action of alkali and was linked with the formation of an intermediate acyclic form of the dye which was the addition product of hydroxyl ion at the position of the pyrylium ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 312–314, March, 1986.     

Polarographic behaviour of phenyl-2-picolylketone-2-pyridylhydrazone and its copper (II) complexes

The polarographic behaviour of phenyl-2-picolylketone-2-pyridylhydrazone, PPKPyH, has been studied in aqueous-ethanol mixtures of different pH's using DC and DP polarographic method. In the pH range 3.7–6.2, the observed single irreversible reduction wave is assigned to the splitting of the N—N bond and reduction of C=N centre. In alkaline medium, a second wave appears at more negative potential due to the reduction of the phenyl-2-picolylketone which is formed from the hydrolysis of PPKPyH. The optimum conditions for the analytical determination of PPKPyH was reported. Differential pulse polarography have been used to elucidate the complexation reaction between PPKPyH and copper(II) in unbuffered solutions. Two complexes are formed with log ₁ = 4.42 and log ₂ = 8.87.     

Volumetric and Viscometric Analyses for l-Glutamic Acid in NaCl Aqueous Solutions at Different Temperatures

The physico-chemical property data for l-glutamic acid in aqueous NaCl solutions were obtained at 0, 0.5, 1.0 and 2.0 mol·kg^?1 NaCl and amino acid molalities from 0 to 0.0669 mol·kg^?1 between 293.15 and 323.15 K. The influence of NaCl addition on the volumetric and viscometric properties of the amino acid has been studied. From the experimental densities, the apparent molar volumes and transfer volumes of l-glutamic acid in aqueous electrolyte solutions have been calculated. The viscosity data in the studied domain of amino acid molalities have led to the evaluation of the Falkenhagen and Jones–Dole viscosity coefficients of l-glutamic acid in NaCl aqueous solutions. The results have been discussed in terms of interactions occurring in the systems.     

Die Ausnutzung der Adsorption in der polarographischen Analyse

Zusammenfassung Allgemein gültige Regeln zur Unterdrückung (Maskierung) polarographischer Stufen werden aufgestellt. Die theoretischen Grundlagen zur Wahl des geeigneten Maskierungsmittels werden angegeben. Dabei werden die Einflüsse der Struktur adsorbierbarer Stoffe, der Zusammensetzung des Depolarisators und der Zusammensetzung der Lösung diskudiert und die analytischen Möglichkeiten gezeigt.In einigen Fällen entsteht durch die Reaktion zwischen dem adsorbierbaren Liganden mit dem Kation eine Stufe, die analytisch ausgenützt werden kann, da sie sehr kleine Ligandenkonzentrationen zu bestimmen erlaubt. Als Beispiel wird das System Nickel(II)-Cystein in Puffer von pH 6–8 in 10^–5 M Cysteinlösungen beschrieben.

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Summary Rules of general validity for the suppression (masking) of polarographic waves have been established. The theoretical principles making possible to select a suitable masking agent have been given. The influences of structure of the surface-active substances, the composition of the depolarizer, and the composition of the solution have been discussed and analytical possibilities have been pointed out.In some cases a reaction of adsorbed ligand with a cation can produce a new wave which can be used for analytical purposes, since a very small concentration of a ligand can be determined. As an example the system nickel(II)-cysteine in buffer solutions of pH 6–8 with 10^–5 M solutions of cysteine has been described.

     

Capillary Flow of Cationic Polyelectrolyte Solutions

The flow rates and the dynamic contact angles of aqueous solutions of cationic polyelectrolyte (CPE) in quartz capillaries with radius of 3–4 m are measured. It is shown that the surface tension and viscosity of CPE solutions with concentrations from 10^–1 to 10^–5 g/l are the same as for water. Surface inactivity of CPE leads to the substantial difference between the capillary properties of their solutions and those of surfactant solutions. It is established that, as the solution concentration increases, the advancing contact angles are reduced from 83° to 75°; the receding contact angles lie between 10° and 20°. Large hysteresis of contact angle can probably be related to the formation of metastable wetting film behind the receding meniscus. Surface hydrophobization occurs as a result of the adsorption of CPE molecules on the negatively charged quartz surface. The specific features of the application of CPE solutions in the deposition technology of hydrophobic coatings, the capillary imbibition and displacement of oils from hydrophobic pores are discussed.     

Particlelike excitations in the polypeptide chain model

The α-helical protein molecule is modeled by a one-dimensional crystal chain with three peptide groups in the lattice cell and with the nearest and third neighbor interactions. Three types of solitonlike solutions describing excitation motion along the model have been obtained. The first one is three modulated waves which are in phase. The other two are modulated waves with phase shifts equal to ?π and \documentclass{article}\pagestyle{empty}\begin{document}$ {\textstyle{4 \over 3}} $\end{document}π, respectively.     

The vibrational excitation of hydrogen fluoride behind incident shock waves

The vibrational excitation of HF occurring behind incident shock waves has been studied in the temperature range of 1400°K to 4100°K. The extent of excitation was determined as a function of time by continuously monitoring the emission intensity from the 1–0 band of HF centered at 2.5 μ. The data were interpreted in terms of the process and gave a value of for M = HF. The corresponding result for (τp)^?1_Ar was found to be insignificant in comparison to this result. Data were also obtained for the effect of F atoms upon the relaxation rate, i.e., it was found that      

Chemical wave studies in the bromate–pyrocatechol beads system

We studied the chemical wave activity of the pyrocatechol‐acidic bromate system in the presence of ferroin‐loaded beads. The wave activity lasted for more than 24 h while meandering spirals continued for up to 10 h. Rigid and meandering spiral waves were investigated. We have analyzed the wave propagation speed and spiral tip trajectory versus the initial concentrations of all reagents as well as the age of the solution. Wave velocity depends on [H⁺] and [BrO] concentrations by the relationship v=k[H⁺]^1/2[BrO]^1/2, which is in agreement with other studies. This system is ideal to study wave activity and spiral waves as it does not produce precipitates under the studied conditions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 198–203, 2011