Determination of the Antibacterial Drug Enrofloxacin by Solid-Phase Spectrofluorimetry

A method for the determination of trace amounts of enrofloxacin based on solid-phase spectrofluorimetry has been developed. The relative fluorescence intensity of enrofloxacin fixed on Sephadex SP C-25 gel was measured directly after packing the gel beads in a 1-mm silica cell, using a solid-phase attachment. The wavelengths of excitation and emission were 277 and 448nm, respectively. The linear concentration range of application was 0.2–4.0ngmL^–1 of enrofloxacin, with a relative standard deviation of 1.2% (for a level of 2.0ngmL^–1) and a detection limit of 0.04ngmL^–1. The method was applied to the determination of enrofloxacin in commercial pharmaceutical formulations and spiked canine serum samples. It was validated using HPLC as a reference method and applying the standard addition methodology. Recovery levels of the method reached 100% in all cases.     

On the selection of the optimal plasticizer for calix[n]arene-based ion-selective electrodes: Possible correlation between the ion selectivity and the ‘softness’ of the plasticizer

A criterion for the selection of a suitable plasticizer for calix[n]arene-based ion-selective electrodes is discussed. The cation selectivity of plasticized membranes without the ligand was first measured as a reference. The membranes can be roughly classified into two groups. The first group shows cation selectivity in the order Cs⁺+>K⁺>Na⁺>Li⁺. The membranes in the second group are made of phosphorus plasticizers, which show a selectivity in the reverse order. The plasticizers in the first group featured a linear relationship between the dipole moment of the plasticizer (calculated by a PM3 method) and the ratio of cesium selectivity to lithium selectivity. The linear relationship supports the view that the polar membrane which includes a soft plasticizer with a large dipole moment shows selectivity for Cs⁺, whereas the nonpolar membrane including the soft plasticizer with the small dipole moment shows much lower selectivity for Cs⁺. Next, 2-fluorphenyl-2-nitrophenyl ether (FPNPE) which showed the highest Cs⁺ selectivity and tris(2-ethylhexyl)phosphate (TEHP) which showed the highest Li⁺ selectivity were mixed in an appropriate ratio to make membranes with a different affinity for hard ions. The metal selectivities of several crown-based and calixarene-based ionophores were examined in these membranes. Although a few exceptions exist, the polar soft membrane is favorable when the interfering metal ion is hard, whereas the hard membrane is favorable when the interfering metal ion is soft.     

The thermal decomposition of ammonium metavanadate,III

The kinetics and thermodynamics of the thermal decomposition of ammonium metavanadate (AMV) are combined with the structural information available for AMV, for the important decomposition intermediate, ammonium hexavanadate (AHV), and for vanadium pentoxide, the product of the decomposition in non-reducing atmospheres, to enable the atomic movements involved in the course of decomposition to be discussed in detail.The decomposition of AMV involves scission of the V-G chains in the AMV structure (accompanied by simultaneous evolution of gaseous ammonia and water) with subsequent rearrangement and cross-linking of discrete units, based on V₃O ₈ ^– , to form AHV. Further decomposition to V₂O₅ is a similar but less ordered process.

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Zusammenfassung Die Kinetik und thermische Zersetzung von Ammoniummetavanadat (AMV) wurden mit der zu erhaltenden Information über die Strukturen des AMV, des wichtigen Zwischenproduktes der Zersetzung, des Ammoniumhexavanadats (AHV) sowie des Vanadiumpentoxids verbunden. Das in nichtreduzierenden Atmosphären erhaltene Zersetzungsprodukt wurde eingehend erörtert um die in der Zersetzung mit inbegriffenen Atombewegungen zu studieren.Bei der Zersetzung von AMV spielt eine Spaltung der V- O-Ketten in der Struktur des AMV mit (welche durch eine gleichzeitige Entwicklung von gasförmigen Ammoniak und Wasser begleitet wird), dieser folgt eine Neuordnung und Raumvernetzung diskreter Einheiten auf V₃O ₈ ^– -Basis um zur Bildung von AHV zu führen. Die weitere Zersetzung zu V₂O₆ ist ein ähnlicher, obwohl weniger geordneter Vorgang.

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Résumé On a rapproché les données structurales du métavanadate d'ammonium (MVA) avec celles relatives à la cinétique et à la thermodynamique de la décomposition thermique du MVA, pour étudier le produit intermédiaire important de la décomposition, l'hexavanadate d'ammonium (HVA) et le pentoxyde de vanadium. On discute en détail le produit de la décomposition obtenu en atmosphère non réductrice afin d'obtenir des données sur les mouvements atomiques mis en jeu pendant la décomposition.La décomposition du MVA s'effectue avec scission des chaines V—O dans la structure du MVA, accompagnée d'un dégagement de gaz ammoniac et d'eau et suivie d'un réarrangement et d'une réticulation d'unités discrètes V₃O ₈ ^– , pour former HVA. La décomposition ultérieure en V₂O₅ suit un processus similaire mais moins bien ordonné.

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() , , ( ) . , . - ( ) , V₃O ₈ ^– . V₂O₅ , .

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Financial support from the National Institute for Metallurgy, Johannesburg, and the South African Council for Scientific and Industrial Research is gratefully acknowledged.     

Coupled hydrogenation of arenes and alkenes or dienes with cobalt phosphine complexes

Coupled hydrogenation of arenes with alkenes and dienes proceeds under mild conditions in the presence of a phosphine-modified cobalt system as well as of H₃Co[P(C₄H₉)₃]₃. Benzene hydrogenation products are cyclohexene (up to 25%) and cyclohexane. By the ESR method, a Co(0) complex containing P(C₄H₉)₃, an arene molecule and AlR₃ as ligands has been identified in the catalytic system Al(C₂H₅)₃+Co(C₅H₇O₂)₂+P(C₄H₉)₃. The nature of the active complex and the possible mechanism of the coupled process are discussed.

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, , H₃Co[P(C₄H₉)₃]₃ . ( 25%) . Al(C₂H₅)₃+Co(C₅H₇O₂)₂+P(C₄H₉)₃ Co(0), P(C₄H₉)₃, AlR₃. .

     

Transient response study of the participation of adsorbed forms of ammonia in propene ammoxidation

On the basis of transient response studies, it is suggested that ammonia on the surface of a Mo–Si–Bi–P oxide catalyst forms a compound that is stable at the reaction temperature and whose reaction with propene yields acrylonitrile.

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, Mo–Si–Bi–P , .

     

Structure of vanadium phosphate anion in solutions from17O,51V and31P NMR data

¹⁷O,⁵¹V and³¹P NMR studies indicate that the anion structure of sodium vanadophosphate in an aqueous solution is close to that in crystals of the (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O salt.

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¹⁷O,⁵¹V,³¹P , (CN₃H₆)₈HPV₁₄O₄₂ 7H₂O.

     

Evolved gas analysis for examination of surface oxides on alloys

Temperature programmed reduction in a hydrogen flow with simultaneous evolved gas analysis was employed to determine surface oxides on oxide dispersion strengthened (ODS) nickel containing TiO₂, A1₂O₃ or Cr₂O₃ particles, and on a Ni-2OCr alloy, after exposure to air at elevated temperatures. Oxides on particles of water-atomized (WA) Ni-2OCr powder were analysed similarly. Significant differences in starting temperatures of the reaction between hydrogen and phases present in oxide layers made identification of the phases possible. NiO or NiO doped with Ti, Al or Cr are the major constituents of the scale formed on ODS Ni. NiTiO₃, NiCr₂O₄ and NiAl₂O₄ are formed as a result of a reaction between TiO₂, A1₂O₃ or Cr₂O₃ particles in the scale with NiO. The oxide layer formed on Ni-2OCr alloy consists of Cr₂O₃ and of NiO doped with Cr. Surface oxides on WA Ni-2OCr contain Cr₂O₃ and a small amount of NiO.

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Zusammenfassung Temperaturprogrammierte Reduktion im Wasserstoffstrom wurde zusammen mit gleichzeitiger Analyse des in Freiheit gesetzten Gases dazu benutzt, um Oberflächenoxide an Nickel enthaltenden TiO₂-, A1₂O₃- oder Cr₂O₃-Partikeln mit verstärkter Oxiddispersion (ODS) und an einer Ni-2OCr-Legierung nach Behandlung in Luft bei erhöhten Temperaturen zu bestimmen. Oxide auf Partikeln von wasser-zerstäubtem (WA) Ni-2OCr-Pulver wurden auf ähnliche Weise analysiert. Signifikante Unterschiede in der Starttemperatur der Reaktionen zwischen Wasserstoff und der in den Oxidschichten vorliegenden Phasen ermöglichen die Identifikation der Phasen. NiO oder mit Ti, Al oder Cr gedoptes NiO sind die Hauptbestandteile des auf ODS-Ni gebildeten Belags. NiTiO₃, NiCr₂O₄ und NiAl₂O₄ treten als Produkte der Reaktion von TiO₂-, Al₂O₃- oder Cr₂O₃-Partikeln mit NiO im Belag auf. Die auf der Ni-2OCr-Legierung gebildete Oxidschicht besteht aus Cr₂O₃ und aus mit Cr gedoptem NiO. Oberflächenoxide auf WA-Ni2OCr enthalten Cr₂O₂ und geringe Mengen an NiO.

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- , , , , , , Ni-2r, . Ni-2OCr. , , . , , , , . NiTiO₃, NiCr₂O₄ NiAl₂O₄ , , . , Ni-2r, , . Ni-2r .

     

Kinetics and mechanism of redox reactions of U(III) ions with 2-chloro and 2-bromopropanoic acids

The kinetics and mechanism of redox reactions of U³⁺ ions with 2-chloro and 2-bromopropanoic acids were studied. The influence of pH led to the determination of the rate constants corresponding to two parallel steps. The influence of binary mixtures on the reaction rate was followed. The kinetic results for halogen-substituted carboxylic acids forming an isokinetic series have been compared.

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U⁺³ 2-- 2- . pH . . , .

     

High resolution solid state1H NMR spectra of hydroxy groups in aluminas

Using magic angle spinning technique, the¹H NMR spectra of surface hydroxy groups of different alumina modifications (-, -, and -Al₂O₃) have been studied. Several types of hydroxy groups that differ in their chemical shifts are tentatively attributed to different types of coordination of OH groups to aluminium atoms.

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¹H (-, -, -Al₂O₃). , , , .

     

Temperature programmed reduction and oxidation of Ir/Al2O3 catalysts

3 % Ir/Al₂O₃ catalysts have been studied by means of temperature programmed reduction and oxidation. With growing degree of metal oxidation (higher T_ox) reducibility of the catalysts at low temperatures decreases.

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3% Ir/Al₂O₃ . ( ) .

     

Alcohol formation from synthesis gas: A thermodynamic study

A thermodynamic study is presented for the simultaneous synthesis of C₁–C₄ alcohols from synthesis gas. The equilibrium composition was calculated for the gaseous mixture containing Co, H₂, CH₃OH, C₂H₅OH, C₃H₇OH, n-C₄H₉OH and H₂O. Operating industrial conditions were specifically considered.

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C₁–C₄ -. , CO, H₂, CH₃OH, C₂H₅OH, C₃H₇OH, -C₄H₉OH H₂O. .

     

Reaction of triphenyl phosphite ozonide with thioacetals

Kinetic regularities in the reaction of triphenyl phosphite ozonide with several thioacetals in CH₂Cl₂ solution at –15°C have been studied. The consumption rate of ozonides is described by the kinetic equation W=k₀[(C₆H₅O)₃P·O₃]+k₁[(C₆H₅O)₃P·O₃][R₁R₂C(SR₃)₂] Rate constants k₀ and k₁ for the thioacetals: (CH₃H₇S)₂CH₂, (C₆H₅S)₂CH₂, (C₆H₅CH₂S)₂CH, (n=C₁₂H₂₅–S)₂CH₂, (C₃H₇S)₂C(H)CH₃, (C₃H₇S)₂C(H)C₆H₅, (C₃H₇S)₂C(CH₃)C₆H₅ and (C₃H₇S)₂C(H)C₁₀H₉, increases with increasing the electron-donating power of subtituents R_i.

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CH₂Cl₂ –15°C. : W=k₀[(C₆H₅O)₃P·O₃]+k₁[(C₆H₅O)₃P·O₃][R₁R₂C(SR₃)₂] k₀ k₁ (C₃H₇S)₂CH₂, (C₆H₅S)₂CH₂, (C₆H₅CH₂S)₂CH₂, (n-C₁₂H₂₅S)₂CH₂, (C₃H₇S)₂C(H)CH₃, (C₃H₇S)₂C(H)C₆H₅, (C₃H₇S)₂C(CH₃)C₆H₅, (C₃H₇S)₂C(H)C₁₀H₉. .

     

Determination of radioactive nuclides of uranium and thorium series and estimation of α-flux in LSI constituent materials

Gamma-rays of nuclides of uranium and thorium series in silicone resin and ceramics were measured with a Ge(Li) detector. The state of radioactive equilibrium was determined by comparing the concentrations of uranium and thorium with the radioactive concentrations of²¹⁴Pb and²¹²Pb. The radioactive equilibrium was attained in silicone resin but not in ceramics. The -flux was calculated from the concentrations of uranium and thorium and their daughter nuclides. The calculated values of -flux agreed with that of -flux measured.     

Adsorption calorimetric studies of copper(I) halides

Adsorption properties of CuBr and CuI with respect to O₂ and CO₂ at 298 K have been examined. Two forms of CO₂ adsorption with adsorption heats of q=28 and 10 kJ/mol for CuBr and q=14 and 9 kJ/mol for CuI have been found. Low values of the adsorption entropy indicate the high mobility of CO₂ molecules in the adsorption layer.

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CuBr CuI CO₂ 298 . CO₂ 28 10 / CuBr 14 9 / CuI. CO₂ .

     

Reduction of alkenes by hydrogen transfer over a Pd/sepiolite catalyst. Compensation effect

This paper shows the occurrence of a linear relationship between the activation energy (E_A) and the logarithm of the pre-exponential factor (ln A) in the Arrhenius equation, and between the enthalpy increment (H) and the entropy increment (S) in the Eyring equation for the reduction of olefinic double bonds by hydrogen transfer over a Pd/sepiolite catalyst. Such a relationship is known as the compensation effect or isokinetic relationship.

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Pd/ (E_a) (ln A) (H) (S) . .

     

Some aspects of the thermal behaviour of In2Se3

On the basis of measurements of the specific heat capacity from 7 to 525 K and of DTA investigations from 300 K up to the melting point, it was possible to clarify the problem of the occurrence of the two room-temperature modifications of In₂Se₃.

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Zusammenfassung Anhand von DTA-Untersuchungen im Bereich zwischen 300 K. und dem Schmelzpunkt und durch Messung der spezifischen WÄrmekapazitÄt im Bereich von 7 K bis 525 K. konnte eine KlÄrung hinsichtlich des Auftretens von zwei In₂Se₃-Raumtemperatur-Modifikationen gegeben werden.

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, 300 , 7–525 , .

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The authors thank St. Budurov (Sofia) for helpful discussions.     

Formation of the active component of a vanadium complex catalyst for the oxidation of anthracene to anthraquinone

The phase composition in various stages of preparation of the active material coating the catalyst for the partial oxidation of anthracene to anthraquinone was studied. The presence of an active phase was evidenced in the final active material as well in a precursor.

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, . , .

     

On the mechanism of alcohol insertion into the carbonyl group in the coordination sphere of Fe(III) tris-hexafluoroacetylacetonate

The kinetics of formation of hemiacetals in the Fe(III) coordination sphere resulting from the reaction of Fe(III) tris-hexafluoroacetylacetonate with methanol has been studied by the stopped-flow method. Two molecules of methanol and coordinated hexafluoroacetylacetonate anion (HFA^–) take part in the rate-determining step. The effect of the second molecule of alcohol can be attributed to catalysis of proton transfer from methanol to the HFA^– ligand through the chain of hydrogen bonds in 6-membered cyclic structures.

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stopped-flow Fe(III). , -. , , .