Photophysical properties of methyl triazone included in MCM-41

Methyl triazone (4,4',4'-[1,3,5-triazine-2,4,6-triyltriimino]tris-trimethyl benzoate) has been included in mesoporous MCM-41 (Mobil's composition of matter-41) silica, and its fluorescence emission has been compared in solution and in the solid state. Although inclusion does not affect significantly the absorption properties, a fluorescence emission shift and a behavior similar to the solid state has been observed by increasing the loading. It is believed that this observation reflects molecular aggregation inside the MCM-41 channels. The potential of formulations of this type for sunscreen applications is discussed.     

Unimolecular photochemistry of 4-thiouracils

Unimolecular phototautomeric reactions in 4-thiouracil, 1-methyl-4-thiouracil and 6-aza-4-thiouracil were studied using the matrix-isolation technique combined with infrared absorption spectroscopy. For monomers of these compounds, isolated in solid argon at 10 K, an intramolecular proton-transfer photoreaction was observed. Upon UV (lambda > 345 nm) irradiation, the initial oxo-thione forms of 4-thiouracils were converted into the corresponding oxo-thiol tautomers. The photogenerated oxo-thiol isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6-311++G(2d,p) level. Good agreement between the observed and predicted pattern of spectral bands allowed a reliable identification. This is the first report on experimental observation of isomeric forms of 4-thiouracils other than the canonical oxo-thione tautomers.     

Synthese und Struktur des ersten ternären Blei(II)-Oxocuprats(I): PbCu2O2

Synthesis and Structure of the First Ternary Lead(II) Copper(I) Oxide: PbCu₂O₂ PbCu₂O₂ can be prepared by solid state reaction or by precipitation from a basic aqueous solution. Single crystals of the new compound were prepared by recrystallisation from a molten mixture (PbO? Cu₂O) and investigated by X-ray diffractometer technique. PbCu₂O₂ crystallizes isotypically with the homologue silver compound PbAg₂O₂ (monoclinic with a = 8.22₃ Å, b = 8.28₉ Å, c = 6.01₅ Å, β = 132.6₂°, Z = 4, space group C? C 1 2/c 1). The crystallographic data from the X-ray investigation are reported. The structure is built by endless [PbO_4/4]- and [CuO_2/4]-chains. Pb²⁺ has a one-sided asymmetric coordination with four next oxygen neighbours and Cu⁺ forms a stretched dumbbell with two oxygen atoms.     

New symmetry properties of a class of Hubbard models

In the Hubbard model for crystals of the AB-type all information on the system is already contained in the set of eigenstates where the number of sites equals the number of electrons or exceeds it by one. We prove this by deriving relations among the eigenstates with different numbers of particles which do not rely on the well-known transformation of electrons to holes. In this context a new good quantum number is identified. We report on results for the one-dimensional case.     

Thermal behaviour of rigid polyurethane foams

By means of a combined thermal analysis technique, the thermal behaviour of rigid polyurethane foams containing additive antipyrenes was studied. The presence of phosphorus- and phosphorus/chlorine-containing antipyrenes based on phosphate and phosphonate and a combination of them led to decreases in the rates of heat and weight loss during heating. More steps of decomposition were formed and the interval of decomposition was widened and shifted to higher temperatures. Some thermal characteristics make it possible to predict the optimum antipyrene compositions and concentrations with minimum time, labour and material consumption under laboratory conditions.

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Zusammenfassung Mittels einer kombinierten Technik wurde das thermische Verhalten eines starren, Antipyrene als Additiv enthaltenden Polyurethanschaumes untersucht. Phosphor und Phosphor/Chlor enthaltende Antipyrene auf Phosphat- und Phosphonatbasis und eine Kombination dieser Substanzen vermindern die Geschwindigkeit der Wärmeentwicklung und des Gewichtsverlustes während des Aufheizvorganges. Es treten mehr Zersetzungsschritte auf und das Temperaturintervall der Zersetzung ist größer und nach höheren Temperaturen hin verschoben. Einige thermische Kennwerte ermöglichen die Voraussage der optimalen Zusammensetzung und Konzentration des Antipyren-Additivs für minimalen Zeit-, Arbeits- und Materialaufwand unter Laboratoriumsbedingungen.

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Thermal decompositions of kaolinite intercalation compounds

Through a combination of X-ray diffraction and thermal analysis (simultaneous TG-DTG-DTA and quasi-isothermal TG), it was shown that the molar ratio intercalation agent/kaolinite in all intercalation compounds is approximately 1. In a saturated atmosphere of the corresponding intercalation agent, the intercalation compounds are stable up to more than 150 °C.Decomposition of the potassium acetate intercalation compound proceeds simultaneously with the dehydroxylation of kaolinite at an extrapolated onset temperature of 360 °C. The high-temperature reactions (dehydroxylation and transformation) of kaolinite obtained through the decomposition of intercalation compounds with volatile intercalation agents depend on the conditions applied during decomposition.

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Zusammenfassung Mittels Röntgenbeugung und thermischer Analyse (simultane TG-DTG-DTA und quasi-isotherme-quasi-isobare TG) konnte gezeigt werden, daß das molare Verhältnis Einlagerungsmedium/Kaolinit in allen Einlagerungsverbindungen etwa 1 ist. In gesättigter Atmosphäre des jeweiligen Einlagerungsmediums ist die Einlagerungsverbindung stabil bis über 150 °C. Die Zersetzung der Kaliumacetat-Einlagerungsverbindung läuft zusammen mit der Dehydroxylation des Kaolinits bei einer extrapolierten onset-Temperatur von 360 °C ab. Die Hochtemperaturreaktionen (Dehydroxylation, Phasenneubildung) von Kaolinit, der aus der Zersetzung von Einlagerungsverbindungen mit flüchtigen Einlagerungsmedien erhalten würde, werden von den Zersetzungsbedingungen beeinflußt.

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Reversed-phase high-performance liquid chromatographic purification and characterization of the adrenocorticotropin/lipotropin precursor and its fragments

Methods are presented for the effective purification by reversed-phase high-performance liquid chromatography (HPLC) of rat adrenocorticotropin/lipotropin (ACTH/LPH) precursor and its two glycosylated forms. Purification of its NH2-terminal segment from human and porcine pituitaries is presented together with microsequencing data confirming the identity of the purified peptides. The effective separation of various native fragments related to ACTH and beta-LPH from sheep pituitaries is presented. A new putative gamma-MSH hormone has been synthesized and purified by reversed-phase HPLC and tryptic peptide mapping performed to establish the identity of the purified peptide.     

Microviscosity of ions and salting-out in the extraction of rare-earth and transplutonium elements

A chemical procedure has been developed for the separation of U, Th, Fe, Sc, Na, Ta and Mo, which interfere in neutron activation analysis of the lanthanide elements in rocks. This methods in based on the extraction of interferents, before irradiation of the samples, using a solution of tetracycline in benzyl alcohol. The lanthanide elements remain in the aqueous phase and are coprecipitated with calcium oxlate or ferric hydroxide for irradiation and subsequent determination by gamma-ray spectrometry. Conditions for the separation of these interferences are examined determining the extraction curves. The chemical separation procedure was applied in the analysis of lanthanides in geological materials and the results showing the accuracy and the reproducibility of the method are presented. The sensitivity for all the lanthanides was determined.     

2,4,6-Tris(tert.butyl)phenyl-substituierte Phosphine

2,4,6-Tris(tert.butyl)phenyl Substituted Phosphines Tris(tert.butyl)phenyl-lithium reacts with PCl₃ to give 2,4,6-tris(tert.butyl)phenyldihalogenophosphine which is reduced by LiAlH₄ yielding 2,4,6-tris(tert.butyl)phenylphosphine. The same reaction by using (CH₃)₃Si? CH₂? PCl₂ leads to 2,4,6-tris(tert.butyl)phenyl-trimethylsilylmethylhalogenophosphine. Thermal treatment of this compound results under elimination of HCl and (CH₃)₃SiCl in the formation of . The nmr data of the compounds synthesized are discussed.