Einfluß der thermischen Vorgeschichte auf die Phasenumwandlungen von Dipalmitoyllecithin/Wasser-Mischungen

1. The influence of the thermal pretreatment (first and second heating run, annealing process) on the phase transition temperaturesT _m, enthalpiesΔ¯H _m and the specific heatc _sp of 1,2-dipalmitoyllecithin-water-mixtures was studied by differential scanning calonmetry.
2. The differences in theT _m- andΔ¯H _m-data of the main transition of the first and second heating run were found in the concentration rangex ^w<0,75. In the concentration rangex _W>0.75 these differences disappear.
3. The annealing process of a 1,2-dipalmitoyllecithin-water-mixturex _W=0,89 leads to a splitting of the main transition peak in two separate peaks with a different shape. This behaviour may imply that 1,2-dipalmitoyllecithin coexists in two different hydration states.

     

Hydrogen-bonding contributions to the lattice energy of salts for second harmonic generation

The lattice energies of a series of organic dihydrogenphosphate salts capable of second harmonic generation (SHG) have been calculated. These calculations, coupled with empirical data, indicate that a minimum of 20–25% of the lattice energy arises from hydrogen-bond interactions. Hydrogen bonding is shown to be a strong enough force to have a profound effect on the overall packing and crystal geometry of such ionic materials, and is thus an important factor to consider for crystal engineering.     

Temperature-induced structural transitions and vibrational properties of microclusters: ab-initio molecular dynamics studies

We present the results of ab-initio molecular dynamics studies of selected microclusters of sodium, silicon and magnesium at finite temperatures, and especially discuss those obtained around room temperature. In particular, from the analysis of the atomic trajectories we can identify in some cases the existence of different isomers and the isomerization pathways. We have also calculated vibrational spectra at low temperatures and find that they can be used as a very sensitive structural probe also in sodium clusters, where the electronic properties are quite insensitive to the geometry.     

Untersuchungen zurFriesschen Verschiebung von Estern derortho- undpara-Methoxybenzoesäure

TheFries rearrangement of different methoxy benzoates has been investigated. Frompara-methoxy benzoates the corresponding hydroxy-4-methoxy benzophenones could be obtained in good yields by treatment withLewis acids (especially TiCl₄) in nitromethane at 20°C (4-hydroxy derivatives) or without solvent at 120°C (2-hydroxy derivatives). Under the same conditions only demethylation occurs withortho-methoxy benzoates leading to the corresponding salicylates. Small amounts of hydroxy-2-methoxy benzophenones were obtained by treatment with polyphosphoric acid.

     

Eine neue photometrische Eisenbestimmung mit Äthylendiamintetraessigsäure

Zusammenfassung Es wird gezeigt, daß man mit Hilfe von Komplexon-III Eisen-III-Verbindungen nach Überführung in gelbgefärbte Komplexverbindungen, deren Absorptionsmaximum unterhalb 366 m liegt, photometrisch bestimmen kann. Die Extinktion ist bei gleicher Eisenkonzentration vomph-Wert abhängig und in denph-Bereichen zwischen 0,80 und 2,80 sowie zwischen 3,92 und 5,10 konstant, so daß beide Bereiche zur Bestimmung geeignet sind. Es ist beachtlich, daß die komplexe Bindung erst oberhalbph 10,5 zerfällt und Eisenhydroxyd ausflockt. DasLambert-Beersche Gesetz ist in dem Konzentrationsbereich zwischen 4g und 500g Eisen/ml streng erfüllt. Die Bestimmung ist vielen anderen bisher bekannten photometrischen Eisenbestimmungsverfahren überlegen, da schwächere Komplexbildner (z. B. Weinsäure) und sonstige Lösungspartner nicht stören.

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Summary It was found that iron (III) compounds can be determined photometrically by the aid of complexone III. The yellow complex compound has an absorption maximum below 366 m. The extinction, at equal iron concentration, is dependent on theph value. It is constant inph ranges between 0.80 and 2.80 and also between 3.92 and 5.10, so that either of these ranges is suitable for this determination. It should be noted that the complex decomposes only aboveph = 10.5; iron hydroxide separates. TheLambert-Beer law is strictly followed in the concentration range 4g and 500g iron/ml. This method of determination is far superior to many familiar photometric procedures for iron because weaker complex-formers (e. g. tartaric acid) and other cosolutes do not interfere.

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Résumé On montre que les composés du fer-III peuvent être dosés photométriquement à l'aide de la complexone-III après transformation en un complexe coloré en jaune dont l'absorption maximum se trouve au-dessous de 366 m. L'extinction dépend duph pour des concentrations égales en fer et se montre constante entre 0,80 et 2,80, de même qu'entre 3,92 et 5,10, de sorte que ces deux domaines conviennent pour le dosage. Il faut remarquer que le complexe ne se détruit qu'au-dessus deph 10,5 et l'hydroxyde ferrique flocule. La loi deLambert-Beer est satisfaite dans le domaine de concentration entre 4 g et 500 g de fer/ml. La méthode de dosage est de beaucoup supérieure aux méthodes connues jusqu'ici pour la détermination colorimétrique du fer du fait que les complexants les plus faibles, comme l'acide tartrique, ne gênent pas.

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Jetzt: Riedel De Haën A.-G., Chemische Fabriken Seelze bei Hannover.     

The Adsorption of Polyvinylpyrrolidone on Kaolinite Saturated with Sodium Chloride

The adsorption of two different molecular weights of polyvinylpyrrolidone (PVP) (M(w)=44,000 and M(w)=360,000 g mol(-1)) from water on kaolinite saturated with sodium chloride has been studied. The adsorption of PVP increases slowly as temperature increases. The adsorption of PVP on the kaolinite was studied by considering Fourier transform infrared (FTIR) spectra, X-ray diffraction patterns, and dielectric constants. During the adsorption process, PVP interacts with saturating sodium cations and possibly forces some of them onto the edges of the kaolinite; thus, the dielectric constant of saturated kaolinite is reduced after PVP adsorption. Copyright 2001 Academic Press.     

Radioanalytical quality control of11C,18F and123I-labelled compounds and radiopharmaceuticals

Radiochemical quality control using high performance high pressure liquid chromatography and, to some extent, gas chromatography is described for a variety of carrier-free¹¹C-,¹⁸F-and¹²³I-labelled compounds and radiopharmaceuticals. The particular problems associated with the handling of carrier-free compounds labelled with short-lived radionuclides are outlined, and chromatographic data are given for the separation and purification of such products.     

The correction for the counting yield in nuclear spectroscopy

Pulser and live timer are alternate tools. Dead time effects can be expressed in terms of a pulse rate dependent factor of the counting yield. The task of their correction should be shifted from the live timer of the ADC to a central timing unit. A new method is proposed, combining the advantages of the pulser and the live timer, where by each selected and accepted event is adjoined to a clock time interval and each selected but not accepted event to a dead time interval. The length of each interval is determined by the arrival of the next selected event.