Adiabatic corrections for thei 3Π g state of the hydrogen molecule

Summary The adiabatic corrections of thei ³_g state of H₂ are calculated for a wide range of internuclear distances using an explicitly correlated wavefunction. The vibrational structure of this state is calculated in the adiabatic approximation. It is shown that forN=1 levels of the – substate, for which the nonadiabatic corrections are negligible, the agreement between theory and experiment is excellent; the small mass independent discrepancy of the order of 0.5–3 cm^–1 is due to the convergence error in the Born-Oppenheimer calculations. For higherN the discrepancy is much larger. However, it is mass andN-dependent and it is almost entirely due to the nonadiabatic effects caused by³_g-³_g interactions. The still larger discrepancy for the + substate of thei state is evidently caused by additional interactions of thei state with close-lying states of³ _g ⁺ symmetry.Dedicated to Prof. Klaus Ruedenberg on the occasion of his 70th birthday     

Proton induced X-ray emission (PIXE) analysis on thick samples exemplified on the rare earth elements

Summary Proton Induced X-ray Emission (PIXE) analysis calibration curves (i.e. intensity of analytical signal as a function of concentration c _i ) are determined on thick solid samples with rare earth element concentrations c _i 0.3g/g. The calibration curves are linear at low concentrations c _i 0.3 weight% at proton energies 1.7E _PO 2.5MeV. The precision of the quantitative analysis amounts to ±4 %. The shape of the curves at higher concentrations may be understood by simple qualitative considerations.Distortions by interelement-effects caused by additional other rare earth elements j in concentrations c _j 2 weight% are not detectable. The agreement between the experimental and the calculated intensities for different matrices is very good at low concentrations c _i 1 weight% of analyte.

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Protoneninduzierte Röntgenspektralanalyse (PIXE) dicker Proben am Beispiel der Seltenen ErdelementeI. Experimentelle Bestimmung von Eichkurven, Genauigkeit und Matrixeffekten

Zusammenfassung Es werden Eichkurven (d. h. Intensität des Analysensignals in Abhängigkeit von der Analytkonzentration c _i ) für die protoneninduzierte Röntgenspektralanalyse (PIXE) dicker Festkörperproben mit Seltenen Erdelementen im Konzentrationsbereich c _i 0,3g/g aufgenommen. Diese Eichkurven verlaufen bei niedrigen Konzentrationen c _i 0,3 Gewichts-% und Protonenenergien 1,7E_PO2,5MeV linear. Die Genauigkeit der quantitativen Analyse beträgt ±4 %. Der Verlauf der Eichkurven bei höheren Konzentrationen kann durch einfache qualitative Überlegungen verstanden werden.Es werden keine Störungen durch Interelementeffekte beobachtet, die durch zusätzliche andere Seltene Erdelemente j in Konzentrationen c _j 2 Gewichts-% hervorgerufen werden. Die Übereinstimmung der experimentellen und berechneten Intensitäten für verschiedene Matrices ist bei niedrigen Analytkonzentrationen c _i 1 Gewichts-% sehr gut.

Dedicated to Karl Gleu at the occasion of his 80th birthday     

Methane and butane oxidation on aluminoplatinum catalysts

Methane and butane oxidation by oxygen (air) on once used AP-56 reforming catalyst has been studied at temperatures 663–773 and 493–533 K, respectively. Kinetic equations for these reactions are proposed and the difference in their oxidation mechanisms is discussed.

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-56 663–773 493–533 K, . . CH₄ C₄H₁₀.

     

Dinuclear Complexes Contributing to Softness of Metal Acceptors

Since emf measurements with amalgam electrodes have been used, in most studies of the stabilities of complexes between soft metal acceptors and halide ions a series of investigations of the kinetics of electrode reactions were accomplished with halide systems of metal ions in the Groups 11 and 12 in aqueous and/or DMSO solutions. The aim was to establish which complexes contribute to the exchange current density, i _o. Such measurements are found to be a very sensitive method for identifying dinuclear complexes that can display much higher charge transfer rate constants than mononuclear complexes can. From these results it can be stated that hard acceptors do not show any tendency to form dinuclear halide complexes, whereas soft acceptors are apt to do so. This fact leads to the conclusion that dinuclear complexes have a strong internuclear bond. In determinations of the overall stability constant _j of a complex ML _j there is an influence from a complex M₂L _j with a constant _j , resulting in the substitution of _j for ( _j + 2a _{j j} ), where a _j = [M] when the ligand number n = (C _L – [L])/C _M has the value j. An approximate value of the association constant, K _ass, of the internuclear bond can be calculated from _j if _j is known. On the basis of these measurements the most probable types of the internuclear bonds are discussed.     

Catalytic hydrogenation of carbon monoxide on RuFe/SiO2 catalysts

The H₂+CO reaction on silica supported Ru, Fe and RuFe catalysts prepared from metal carbonyl clusters has been investigated under atmospheric and 20 bar pressure. According to the change of selectivity values with temperature and with pressure, the participation of surface carbon proposed earlier by several authors seems to be confirmed by this work.

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H₂+CO Ru, Fe RuFe, , 20 . , , , .

     

Mathematical structure of chromatographic optimization based on information theory: I. Effect of mobile phase composition on precision

Summary The influence of mobile phase composition X on the precision of liquid-chromatographic analysis is interpreted in terms of the derivate of the mutual information for peak j with respect to X, d_j/dX. The sign and magnitude of d_j/dX depend on the operational conditions of X or on the details of chromatograms (e.g., resolutions R_s), but d_j/dX always indicates the direction of X toward more information _j. The sensitivity function s_j(=1/(k_j+1)) is examined on the basis of information theory. Optimization is formulated as a nonlinear programming problem.     

Isomerization and secondary metathesis of 2-butenes over a MoO3/Al2O3 catalyst

Transformation of cis- and trans-2-butene at 40°C was investigated over a MoO₃/A₂O₃ catalyst reduced with hydrogen and subjected to different pretreatments. Isomerization is accelerated by hydrogen preadsorbed either at low or high temperatures. The cometathesis of 2-butenes with the 1-butene intermediate, however, is enhanced only by hydrogen preadsorbed at low and suppressed by hydrogen adsorbed at high temperatures.

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- -2- 40°C MoO₃/Al₂O₃, . , , . 2- 1- , ; , .

     

Percolation Effects on the Surface of a Polyimide Film Modified with Aqueous Solutions of an Alkali and Acid

A cluster structure of the surface of a polypyromellitimide film was studied by the electron microscopy and ATR IR spectroscopy methods at different steps of consecutive treatment with aqueous solutions of an alkali and acid. The effective size and fractal dimension D of polyamidoacid clusters, as well as the degree _s of the filling of the surface with the latter were calculated from the data of the electron microscopy as a function of the degree of imide group conversion into amidoacid units on the film surface. The _s and D parameters were shown to increase with a rise in : _s = 0.1–0.3 and D = 1.3–1.4 at < _cr and _s 0.6 and D 1.7 at > _cr, where _cr is a critical degree of conversion, which corresponds to the formation of a continuous physical network of polyamidoacid macromolecules or a percolation cluster. In a region close to _cr (at < _cr), the correlation length land the concentration C of the clusters vary according to the laws of the percolation theory for two-dimensional lattices: l (_cr – )^– and C (_cr – ), where = 1.3 ± 0.1 and = 0.67 ± 0.05.     

Application of the MIMS Technique to Study the Stability Constants of Small Organic Guest Molecules into Cyclodextrin Hosts in Aqueous Medium

In this work the potential of MIMS (Membrane Introduction Mass Spectrometry) for studying the inclusion of small organic guest molecules into cyclodextrin hosts in aqueous medium was investigated. MIMS profiles showed that the inclusion of benzene in cyclodextrins is favored in the following order: -CD HO-propyl--CD> -CD> -CD with equilibrium constants of K -CD = 404; K_HO-propyl-CD = 395, K _-CD = 335 and K _-CD = 210 M^-1 at 25 °C. Kinetic experiments suggested that under the conditions employed the inclusion process has a pseudo first-order dependence on the guest benzene concentration with the following order: -CD > -CD HO-propyl--CD> -CD. MIMS inclusion profiles of chlorobenzene and toluene showed that the presence of substituents in benzene makes the inclusion in -CD more difficult. Experiments with ferrocene--CD have also been carried out, showing that the complex rapidly dissociates in water and the resulting free -CD can complex with benzene present in the solution.     

Spin probe studies on high temperature (T >T g) microdynamics of polyamide 66 fibers

Summary Short-range segmental motions of the amorphous phase of polyamide 66 were studied by means of spin probe radicals. In a dry sample the relaxation in the temperature range 366–426 with an activation energy 27.6 kJ/mol was found. In a sample containing traces of water two processes, and relaxations, with activation energies 47.0 kJ/mol and 22.0 kJ/mol, respectively, were found. relaxation was dominant in the higher temperature range (410–460 K) while relaxation was active at lower temperatures (365–410 K).

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Zusammenfassung Die inneren, lokalen Drehbewegungen in den amorphen Bereichen des Polyamid 66 wurden mit Hilfe der Paramagnersondenmethode untersucht. Wasserfreies Polyamid 66 zeigt den-Relaxations-prozeß (die Aktivierungsenergie 27.6 kJ/Mol) im Temperaturbereich von 366 K bis 426 K, wasserhaltiges Polyamid 66 zeigt zwei Prozesse,- und-Relaxationen, deren Aktivierungsenergien 47.0 kJ/Mol und 22.0 kJ/Mol sind. Die-Relaxation dominiert in dem höheren Temperaturbereich (von 410 K bis 460 K) und die-Relaxation in dem niederen Temperaturbereich (von 365 K bis 410 K).

     

PIXE and EMP analyses of volcanites from Nea Kameni island (Aegean Sea,Greece)

The major and trace element compositions of several minerals and their surrounding groundmass in the volcanic rocks from the post-caldera Nea-Kameni island of the Santorini volcanic complex, Aegean Sea, have been determined, in-situ with particle-induced X-ray emission (PIXE) and wavelength dispersive X-ray analysis with an electron microprobe (EMP).The lavas are typically calc-alkaline dacites. All samples are porphyritic with a phenocryst mineralogy dominated by plagioclase, augite, hyperstene and Ti-magnetite. The phenocrysts range in size from 200 m to 2.5 mm.The PIXE and EMP analyses were done on sections polished with diamond paste. They were sufficiently thick ( 100 m) to stop the 2.7 MeV protons used for the analysis and yet thin enough for individual minerals to be seen with transmitted light. The specific minerals and groundmass areas to be analyzed had been selected and marked through conventional microscopic examination prior to analysis.Solid/liquid partition coefficients, which depend much less significantly on the method for determining the concentrations, were calculated from the element abundances in phenocrysts and corresponding groundmass.     

Multiconformational Method for Analyzing the Biological Activity of Molecular Structures

A multiconformational method for analyzing the biological activity of compounds is proposed that combines conformer search algorithms and a 3DQSAR receptor modeling procedure. The method allows one to find highactivity and lowactivity conformers and determine the receptor shape. The biological activity of a substance is determined as a superposition of the activities of its conformers with allowance for their proportions in the substance. Agreement between calculated and experimental conformations and between calculated and experimental biological activities pIC _50%) is demonstrated by the example of agonists of the 5HT_1A receptor.     

Rearrangement ofα -trifluoromethyl-β-dialkylamino-β-fluoroacrylic acid N.N-dialkylamides

Conclusions When heated in the presence of a catalytic amount of BF₃ etherate,-trifluoromethyl--diethylamino--fluoroacrylic acid N, N-dimethylamide is reversibly isomerized to-trifluoromethyl--dimethylamino--fluoroacrylic acid N, N-diethylamide. The methyl esters of-trifluoromethyl--diethylammo--fluoroacrylic acid and-trifluoromethyl--phenoxy--fluoroacrylic acid N,N-dimethylamide are not isomerized under the same conditions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.1, pp.137–141, January, 1976.     

Die Anwendung Thermoanalytischer Methoden zur Charakterisierung Faserbildender Organischer Hochpolymerer

Zusammenfassung An Hand von Literaturbeispielen und eigenen Arbeiten wird eine Übersicht über Anwendungsmöglichkeiten der Thermogravimetrie (TG) auf dem Gebiete der faserbildenden organischen Hochpolymeren gegeben. Die Untersuchung der relativen Thermostabilität, deren Veränderung durch Modifizierung der Polymeren oder den Zusatz von Stabilisatoren und die Ableitung kinetischer Daten werden besonders herausgestellt. Die Vorteile der Differentialthermogravimetrie sowie die Notwendigkeit isothermer thermogravimetrischer Untersuchungen zur Charakterisierung des thermischen Langzeitverhaltens werden erläutert. Abschließend werden allgemeine Einschränkungen und Empfehlungen für die Anwendung der TG, z. B. die Kombination mit anderen Charakterisierungsmethoden, genannt.

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A review on the application of thermogravimetry (TG) in the field of fiber-forming organic high polymers is given by examples from the literature and from the work of the author. The investigation of the relative thermostability, their changes by modification of the polymers or by addition of stabilizers and the calculation of kinetic values are particularly stressed. The advantage of derivative thermogravimetry and the necessity for isothermal thermogravimetric investigation to characterize the longtime behaviour of polymers are explained. Finally, general limitations of, and recommendations for, the application of TG, e.g. the combination with other methods of investigation, are mentioned.

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Résumé On donne une vue d'ensemble sur les possibilités d'application de la thermogravimétrie (TG) dans le domaine des hauts polymères organiques fibriformes, en se servant d'exemples pris dans la littérature et de travaux personnels. On dégage les données relatives à la stabilité thermique et aux changements qui s'y rapportent si l'on modifie le polymère ou si on le traite par des stabilisateurs; on présente également le calcul des paramètres cinétiques. On montre les avantages de la thermogravimétrie différentielle ainsi que la nécessité d'effectuer des essais thermogravimétriques isothermes pour caractériser le comportement thermique de longue durée. Enfin, on mentionne les limites et les avantages dans l'emploi de la TG, par exemple, l'emploi combiné avec d'autres méthodes de caractérisation.

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() . , , , . , . () .

     

Effects of cyclodextrin on hydrolysis and the Smiles rearrangement of salicylic acid esters

The effect of -cyclodextrin (-CD) on aqueous hydrolysis of methyl,p-, andm-nitrophenyl salicylates as well as on the Smiles rearrangement ofp-nitrophenyl salicylate was studied. No effect of -CD on the pH-independent rate constant of aqueous hydrolysis of methyl ester was observed, while -CD accelerated aqueous hydrolysis of nitrophenyl esters byca. 10 times. The inclusion of these esters into the cavity of -CD is accompanied by a change in the mechanism of hydrolysis: free ester in the deprotonated form undergoes hydrolysis through the mechanism of intramolecular general base catalysis, while the ester bound to cyclodextrin is hydrolyzed due to the nucleophilic attack of the deprotonated hydroxyl group of -CD at a neutral substrate molecule. The effects of cyclodextrin on the rate constant of borate-catalyzed hydrolysis were interpreted by assuming that the substrate bound to -CD undergoes borate-assisted attack at the deprotonated cyclodextrin hydroxyl group. The Smiles rearrangement, which is an intramolecular nucleophilic substitution reaction, is accelerated in the presence of -CD.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2658–2665, November, 1996.     

Hydrogen bonding in ε-caprolactam dimer: a quantum-chemical study

The equilibrium geometries, vibrational frequencies, and IR band intensities were calculated for the monomer and hydrogen-bonded cyclic dimer of -caprolactam (1) by the density functional B3LYP/6-311++G(d,p) method and compared with the experimental data. The gas phase IR spectrum of monomer of 1 was first measured. The calculated hydrogen bonding enthalpy H/2 in the hydrogen-bonded dimer in the gas phase (–5.93 kcal/mol) is consistent with the published data. The computed scaled (scaling factor 0.97) vibrational frequencies of the monomer and dimer are in good agreement with the experimental data. The geometry of the -caprolactam monomer remains nearly unchanged in its dimer except for the N-H, C-O, and C-N bond lengths that respectively change from 1.012, 1.230, and 1.369 in the former to 1.029, 1.246, and 1.350 in the latter. The frequencies, eigenvectors, and IR intensities of the amide modes of the monomer and dimer differ dramatically. The calculated NH and CO frequency shifts due to hydrogen bonding are in good agreement with the experimental data, but theoretical intensification of the NH IR band is much greater than that observed experimentally (by nearly 69 times vs. 11 times, respectively). The calculated N...O intermolecular distance in the structure of -caprolactam dimer equals the experimental value (2.89 ). The influence of the basis set employed on the results of calculations is discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1818–1825, September, 2004.     

The effect of mechanical grinding on the formation and crystallinity changes of the inclusion complex of acetaminophen andβ-cyclodextrin

The effect of mechanical grinding on the physicochemical properties of acetaminophen in the presence of three additives,- or-cyclodextrin and microcrystalline cellulose, was studied by using TLC, powder X-ray diffraction analysis, infrared spectroscopy and differential scanning calorimetry. The results indicate that the crystallinity of physical mixtures of acetaminophen and the described additives decreased with increased grinding time and formed an amorphous state when mixtures containing- or-cyclodextrin were ground with acetaminophen. We also found that the acetaminophen molecules could be included step-by-step into the cavity of-cyclodextrin molecules and formed an amorphous inclusion complex.-Cyclodextrin and microcrystalline cellulose did not form an inclusion complex with acetaminophen, but acted only to decrease the crystallinity of the ground mixtures. The mechanical grinding efficiency for acetaminophen was improved in the order of-cyclodextrin -cyclodextrin > microcrystalline cellulose.This paper is part XI of Drug Interaction in Pharmaceutical Formulations.     

Determination of trace heavy metals associated with suspended particulate matter in pond water by microscale anodic stripping voltammetry

Summary Less than 1 milligram of suspended particulate matter in a 50-ml water sample was separated by centrifugation, decomposed with 22l of 21010 perchloric-nitric-hydrofluoric acid mixture, and analyzed for copper, lead, cadmium and zinc by microscale differential pulse anodic stripping voltammetry with a hanging mercury drop electrode in 300l of 0.06M perchloric acid. The procedure was simple and rapid, because a single Teflon microvessel was used throughout the whole procedure.

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Bestimmung von Schwermetallspuren in suspendierten Teilchen in Teichwasser durch Anodic Stripping Voltammetry im Mikromaßstab

Zusammenfassung Weniger als 1 mg suspendierter Teilchenmaterie wurde durch Zentrifugieren abgetrennt, mit 22l eines Gemisches HClO₄HNO₃HF (21010) zersetzt und darin Cu, Pb, Cd und Zn durchDifferential-Pulse-Anodic-Stripping-Voltammetrymit hängender Hg-Tropfelektrode in 300 l 0.06M Perchlorsäure bestimmt. Das Verfahren ist einfach und schnell, es bedarf dazu nur eines Mikrokölbchens aus Teflon.

     

Potentiometric Studies on Binary and Ternary Complexes of Di- and Trivalent Metal Ions Involving Some Hydroxamic Acids, Amino Acids, and Nucleic Acid Components

Summary. Formation of binary and ternary complexes of Cu^II, Co^II, Ni^II, Zn^II, Fe^III, Al^III, and Cr^III metal ions with some selected aliphatic and aromatic hydroxamic acids and some biologically important amino acids or nucleic acid components was investigated using the potentiometric technique at 25°C and I=0.10moldm^–3 NaNO₃. The acid-base properties of the ligands were investigated and discussed. The acidity constants of the ligands were determined and used for determining the stability constants of the complexes formed in aqueous medium under the experimental conditions. The ternary complex formation was found to occur in a stepwise manner. The stability constants of these binary and ternary systems were calculated. The order of stability of the ternary complexes in terms of the nature of hydroxamic acid, amino acid, nucleic acid component and metal ions was investigated and discussed as well as the values of log K and log X for the ternary systems. The concentration distribution of the various complex species in solution was evaluated. In addition, evaluation of the effect of temperature of the medium on the stability of the ternary system M^III – benzohydroxamic acid – L-histidine or adenine (M^III=Fe^III, Al^III, and Cr^III) has been studied. The thermodynamic parameters were calculated and discussed.