Photomechanical vibration of thin crystals of polar semiconductors

It was found that thin crystals of polar (non-centrosymmetric) semiconductors constitute a new type of photo-sensitive system in which incident illumination is converted into mechanical energy: thus, illumination-induced elastic deformation (bending) was observed on thin (00.1) CdS and (111) GaAs crystals; furthermore, by employing chopped light the crystals were excited to their resonant vibration (photomechanical vibration); the dependence of the amplitude of this vibration on the energy of the incident radiation was found to be similar to the dependence of the surface photovoltage on the energy of the incident radiation (surface photovoltage spectrum). The present findings are consistent with a model based on light-induced modulation of the piezoelectric surface stresses.     

Locally conserved currents linearly dependent on the energy-momentum tensor and the polynomial in the position variables

In this note we are considering a symmetrical locally conserved energy-momentum tensor, whose trace vanishes. We show that there are no other combinations of the position variables x and the energy-momentum tensor, whose divergence vanishes except the well-known currents of translations, four-dimensional Lorentz rotations as well as con- formal and dilatational transformations.     

Simultaneous determination of light and heavy lanthanides in their mixture with methylthymol blue as indicator

A method of simultaneous determination of heavy and light lanthanides has been described. In the first stage, the total amount of rare earth elements is determined (complexometrically with EDTA as a titrant and MTB as an indicator, pH = 5.5). Then, on the basis of the proportional relationship between absorbance and molar ratio of the system, concentration of each component is calculated (using the measured absorbance of the system and “the absorbance of the standard” taken from the standard calibration curves). The applicability of the method is limited by r.e.e. concentration equal to 3 × 10^?5M. In the case when the content of one of the metals amounts to at least 15% of their sum, the relative error of determination does not exceed 2%.Results of the determination for selected pairs of lanthanides are presented together with a statistical estimation of errors.     

Ni(II)/N,N-dimethylglycine complex equilibrium study

The complex formation of Ni(II) withN,N-dimethyl-glycine in water and in water-methanol has been studied by computer analysis of potentiometric data.

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Gleichgewichtsuntersuchungen der Komplexbildung von Ni(II) mitN,N-Dimethylglycin (Kurze Mitteilung)

Zusammenfassung Anhand der Computer-Analyse von potentiometrischen Daten wurden die Bildungsgleichgewichte von Nickel(II)-Komplexen mitN,N-Dimethylglycin in Wasser und Wasser — Methanol untersucht.

     

Pillared montmorillonites modified with silver

Alumina, zirconia and titania pillared montmorillonites additionally modified with silver were tested as catalysts of NO reduction with NH₃ or C₂H₄. Ammonia was much more effective reducer of NO than ethylene. The silver containing TiO₂-pillared clay has been found to be the most active catalyst for NO reduction both with NH₃ or C₂H₄. Oxidation of the reducing agents by oxygen limited the NO conversion in the high temperature region. The ammonia and nitric oxide adsorption sites were studied by the temperature programmed desorption methods (TPD). This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the construction of the 2-isooctyl side chain in 17-azasteroids

Summary The transformations of (20R)- and (20S)-3-hydroxy-16-oxo-24-nor-17-azachol-5-eno-23-nitriles towards the 17-aza analogue of cholesterol are described. Attempts of a direct addition of a four carbon atom fragment to nitriles were unsuccessful. Alternately, nitriles were transformedvia carboxylic acids, methyl esters and primary alcohols into iodides. The coupling reaction of (20S)-iodide with (i-Bu)₂CuLi afforded the desired product in low yield but failed in the case of the 20R epimer.

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Untersuchungen zum Aufbau der 2-Isooctyl-Seitenkette in 17-Azasteroiden

Zusammenfassung Die Umsetzungen von (20R)- und (20S)-3-Hydroxy-16-oxo-24-nor-17-azachol-5-eno-23-nitril zum 17-aza-Analogon von Cholesterin werden beschrieben. Versuche einer direkten Addition eines 4-Atom-Fragments an Nitrile verliefen erfolglos. Als Ausweg wurden die Nitrile über Carbonsäuren, Methylester und primäre Alkohole zu den lodiden umgesetzt. Die Kupplungsreaktion von (20S)-lodid mit (i-Bu)₂CuLi ergab das gewünschte Produkt in niedriger Ausbeute; das (20R)-Epimere reagierte nicht.

     

Changes of the affinity between fungal proteins and vanillin bonded to thermally modified porous glass support

Summary The affinity of peroxidase and the fungal proteins to vanillin attached to controlled porous glasses depends on the porosity of the glass and additional thermal treatment of the support. The additional thermal treatment of controlled porous glasses leads to an enrichment in boron atoms of their surface.The results presented in this paper show a better resolution of the analyzed substances when glass with a surface enriched in boron was used as the support for vanillin.     

Mass spectrometric investigation of gallium and zirconium complexes with octaethylporphyrin and tetraphenylporphyrin

Gallium and zirconium octaethylporphyrin (OEP) and tetraphenylporphyrin (TPP) were examined by electrospray ionization (ESI) mass spectrometry. All systems were prepared in dichloromethane with addition of a stabilizing lipophilic anionic agent, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB). In the solutions examined both monomeric and dimeric metalloporphyrins were observed. In the gallium-OEP mass spectrum the ion registered at m/z 601 was attributed to monomeric [Ga(OEP)](+) and that at m/z 1219 to the dimeric form, [[Ga(OEP)](2)OH](+). Peaks appearing in the ESI mass spectra of zirconium systems were substantially less intense, probably owing to the relatively low stability of complexes of this metal caused by its different geometry preferences. The most abundant monomeric zirconium-OEP complexes were [[Zr(OEP)OH]](+) (m/z 639) and [Zr(OEP)Cl](+) (m/z 657), and dimeric [[Zr(OEP)OH](2)](2+) (m/z 639). Analogous species were observed in the Zr(TPP) system: monomeric [[Zr(OEP)OH]](+) (m/z 719) and [Zr(TPP)Cl](+) (m/z 737) and dimeric [[Zr(TPP)OH](2)](2+) (m/z 719). In both cases series of other dimers, e.g. [[Zr(OEP)](2)O(2)H](+) (m/z 1277), [[Zr(OEP)OH](2)Cl](+) (m/z 1313), [Zr(TPP)(2)O(2)H](+), (m/z 1437), [[Zr(TPP)OH](2)OH](+) (m/z 1455) and [[Zr(TPP)OH](2)Cl](+) (m/z 1473), appeared. The results obtained confirmed the hypothesis concerning the formation of dimeric metalloporphyrins in solutions containing stabilizing lipophilic anions. It also allowed us to explain the super-Nernstian slopes of the calibration curves towards primary anions of ion-selective electrodes with membranes containing the examined metalloporphyrins.     

Semifluorinated chains in 2D-(perfluorododecyl)-alkanes at the air/water interface

Langmuir monolayers of a homologous series of perfluorododecyl-n-alkanes (general formula F(CF2)12(CH2)nH, abbreviated as F12Hn, where n = 6-20) are investigated through isotherms of surface pressure (pi) and electric surface potential (DeltaV) versus area (A) and quantitative Brewster angle microscopy. The investigated monolayers are found to be liquid in nature. The negative sign of the measured surface potential evidences the orientation of all the investigated molecules with their perfluorinated parts directed toward the air regardless of the length of the hydrogenated unit. Analysis of the direction of the molecular dipole moment with respect to the main axis indicates that the minimum effective dipole moment is achieved for a molecule oriented at an angle of about 35 degrees to the surface normal. The film thickness was evaluated from the relative intensity measurements. The results suggest that the F12Hn molecules are tilted to the interface in the vicinity of collapse, which is in accordance with the liquid character of their monolayers.     

Effect of composition and gelation conditions on structural changes accompanying the gelation of PAN,PVA and gelatin solutions

Summary For three types of polymer-solvent systems: polyacrylonitrile in dimethylformamide, polyvinyl alcohol in water and gelatin in water the isothermal gelation process was followed with viscometry, light scattering and X-ray diffraction techniques. Effects of thermal history (quenching, melting) and solvent composition were investigated. It was found that the variation of structure as revealed by these methods (molecular aggregation, crystallization etc.) is not specific for the gelation itself but associated with some side-processes which result from retarded phase separation. The molecular mechanism of “pure gelation” proceeding at unchanged supramolecular structure is discussed.

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Zusammenfassung Für drei Systeme Polymer/L?sungsmittel, n?mlich für Polyacrylnitril in Dimethylformamid, für Polyvinylalkohol in Wasser und für Gelatine in Wasser, wurde die isotherme Gelierung viskosimetrisch, mit Lichtstreuung und mit R?ntgenbeugung beobachtet. Die Wirkungen der thermischen Vorgeschichte (Abschrecken, Schmelzen) und der L?sungsmittelzusammensetzung wurden untersucht. Es ergab sich, da? die ?nderung der Struktur, wie sie mit diesen Methoden aufgedeckt wurde (Molekularaggregation, Kristallisation usw.) nicht spezifisch für die Gelatinierung ist, sondern mit einigen Nebenprozessen, die aus verz?gerter Phasentrennung resultieren, verknüpft ist. Der molekulare Mechanismus einer reinen Gelatinierung, der bei unver?nderter Supermolekularstruktur stattfindet, wird diskutiert.