Pyrazolat und Tetrazolat als Brückenliganden in [Pt(pz)2]3, [Pt(pz)2]∞ und [Pt(tz)2]∞ Die Kristallstruktur von [Pt(pz)2]3

Pyrazolat and Tetrazolat as Bridging Ligands in [Pt(pz)₂]₃, [Pt(pz)₂]_∞, and [Pt(tz)₂]_∞ Crystal Structure of [Pt(pz)₂]₃ . [Pt(pz)₂(Hpz)₂]₂ (Hpz = pyrazole) suspended in mesitylene decomposes at 185°C in a sealed tube to [Pt(pz)₂]₃ and [Pt(pz)₂]_∞. The reaction of K₂PtCl₄ with K(pz) under hydrothermal conditions at 150°C yields [Pt(pz)₂H₂O]_∞. [Pt(tz)₂ H₂O]_∞ (Htz = tetrazole) is obtained at 25°C from K₂PtCl₄ and Li(tz) in water. [Pt(pz)₂]₃ crystallizes in the tetragonal space group I4₁/a with a = 1694.9 pm, c = 3127.5 pm and Z = 16. It forms a ring structure with the symmetry D_3h. In the structure the Pt atoms are each bridged by two pyrazolato ligands. Short but nonbonding Pt? Pt distances range from 303.4 pm to 306.7 pm. The average Pt? N distance is 201 pm.     

The Influence of the Axial Chirality of Dibenzo[a,c]cyclooctene on the Configuration of Its Photo-Diels-Alder Adducts

Triazole-diones and naphthoquinone are shown to add in a photochemical [4+2] reaction to the strongly twisted title diene 1 . With 1, 4-naphthoquione, the process is also accompanied by a [2+2] cycloaddition. When the pure atropisomer (?)- 1 is irradiated in presence of 2, 3-dichloro- 1, 4-naphthoquinone ( 9 ), the axial chirality of the diene is preserved. Moreover, it is found to exert complete control over the chirality induced in the resulting spiro-dihydropyrane 10 . Absolute configuration are determined by X-ray crystallography. In absence of a photo-dienophile, the axially chiral, dextrorotatory 6-phenyldibenzo[a,ccyclootene] ((++)- 11 ) undergoes a stereospecific electrocyclization to give levorotatory 4b,6a-dihydro-5-phenylcyclobuta[l]phenanthrene ((?)- 13 ). Thus, only one out of two possible, disrotatory modes of ring closure is preferred.     

Inorganic-Organic Polymers as Migration Barriers Against Liquid and Volatile Compounds

In addition to the barrier properties against water vapor and oxygen, inorganic-organic polymers can also function as protection layers against unwanted migration of chemical substances in two ways. First, hybrid polymers prevent components from migrating out of polymer substrates. This is of special interest for polymeric materials containing substances like plasticizing agents, unreacted monomers or catalysts. Thus the olfactory nuisance and the toxicological emission are decreased. The plastics are also prevented from becoming prematurely brittle. Second, the coated materials are also protected against the interaction of dyes or dirt staining the material.These functions can be achieved by thermally or UV curable coating materials, synthesized by the sol-gel technique. Since several polymer materials show only a low heat resistance (e.g. PVC, polyolefines), this publication is focussed on the development of new migration barriers based on photochemically curable sols.Another advantage of the UV process in comparison to thermal treatments are the short curing times and low power consumption which make this process even more attractive for industrial applications. The coatings were characterized by IR and solid state NMR spectroscopy. The migration barrier properties were tested according to industrial standards.Due to the choice of specific functional groups, these hybrid polymers can be further modified in order to combine the migration barrier function with additional properties: scratch and abrasion resistance, hydrophobicity, antistatic effects. Examples of feasible combinations of properties are also given.     

NO as temporary guanidino-protecting group provides efficient access to Pbf-protected argininic acid

Pbf-protected argininic acid [H-OArg(Pbf)-OH], a building block for Fmoc-solid phase peptide synthesis, is obtained in high yield when a large excess of nitrosating agent is used in conjunction with intermediate N^δ-nitrosyl protection and N^δ-denitrosation in aqueous acidic medium.     

Untersuchungen im Dreistoff: Ni−Al−Si sowie von Mono- und Disilicidsystemen einiger Übergangsmetalle

Zusammenfassung An Hand von Schmelzproben wird das Mischungsverhalten einiger Disilicidpaare (V, Cr, Mn, Fe, Co und Ni) festgestellt. VSi₂–CrSi₂ bilden eine lückenlose Mischreihe; CrSi₂ löst rund 25 Molproz. MnSi₂; in etwa gleichem Ausmaße lösen einander MnSi₂ und FeSi₂. Alle übrigen Paare: CrSi₂–FeSi₂, –CoSi₂ bzw.–NiSi₂ und MnSi₂–CoSi₂ bzw.–NiSi₂ zeigen nur geringe Mischbarkeit. Auch die Löslichkeit von CrSi₂ in MnSi₂ ist nicht ausgeprägt.Im Dreistoff Ni–Al–Si werden die ternären Kristallarten Ni(Al_0,5Si_0,5) mit FeSi-Typ (a=4,52₈ kX·E.) und Ni₃ (Al, Si)₇ mit Ir₃Ge₇-Type (a=8,27₄ kX·E.) aufgefunden. Der weitgehende Übergang von NiAl nach NiSi₂ wird vom Standpunkt der Strukturverwandtschaft diskutiert. Auch in der Phase Ni₂Al₃ erfolgt ein merklicher Austausch Al/Si.Mit 2 Abbildungen     

Stereoselective synthesis of (3S,4S)-tert-butyl-N-Boc-3-ethyl-4-hydroxy-l-prolinate and (3S,4R)-tert-butyl-N-Boc-3-ethyl-4-hydroxy-l-prolinate

Diastereomers of tert-butyl-N-Boc-3-ethyl-4-hydroxy-l-prolinate 1 and 2 have been synthesized in six steps starting from readily available Boc-protected trans-4-hydroxy-l-proline. The key reactions in the synthesis are asymmetric reductions, firstly on the 4-ketoproline intermediate 6 and secondly on the 3-exocyclic olefin bond of the resulting allylic alcohol 7 or 8. Reaction conditions were optimized in order to control the stereochemistry of the three chiral centers.     

PHOTODYNAMIC INACTIVATION OF R3230AC MAMMARY CARCINOMA IN VITRO WITH HEMATOPORPHYRIN DERIVATIVE: EFFECTS OF DOSE, TIME, and SERUM ON UPTAKE and PHOTOTOXICITY

Abstract Primary cultures of the R3230AC mammary adenocarcinoma were used for pharmacokinetic studies of hematoporphyrin derivative (HPD), a preparation containing several porphyrin species and useful as a photoactivatable anti-tumor agent. Uptake of HPD in vitro was shown to be time-, dose- and temperature-dependent with an apparent plateau reached at 2 - 4 h. An increase in the amount of serum in the medium progressively reduced the amount of HPD taken up by the cells; at a level of 10% serum, uptake of HPD was reduced by >95%. The time-course of efflux of HPD from these cells demonstrated a complex pattern, with an initial rapid component followed by a more gradual rate of efflux up to 4 h. Assessment of photoradiation-induced cytotoxicity was performed by a method developed to quantitatively measure trypan blue exclusion. Relative cytotoxicity was determined by use of heat-killed cells as a standard. At two different concentrations of HPD, cytotoxicity was dependent on light exposure time. The presence of serum, which reduced uptake of HPD was correctable to reduced cytotoxicity. Based on the amount of light exposure to produce 50% cell kill, an order of potency was obtained for HPD > hematoporphyrin > hydroxyethylvinyldeuteroporphyrin in vitro. This order of potency correlated with the relative proportion of hydrophobic components as estimated by HPLC analysis. The results indicate that HPD is an effective cytotoxic agent in vitro in a well-differentiated mammary adenocarcinoma model.     

Bioactivity screening by chromatography-bioluminescence coupling

Summary Because luminescent microorganisms change their light emission in the presence of bioactive substances, they provide an effective way of monitoring toxicity. Here we report the direct coupling of bioluminescence to chromatography which is capable of detecting single toxic components in complex mixtures. Two approaches were investigated, utilizing thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). The TLC-bioluminescence imaging technique was developed into a versatile and rugged method and proved to be superior to the HPLC-based design. Employing genetically engineered luminescent bacteria gives customized selectivity of bioactivity detection. The combination of analytical separation technology with the biospecific sensing ability of living cells provides a novel screening tool for targeting bioactive components in complex samples.     

Untersuchungen über Molekulargewichtsverteilungen von Hochpolymeren

Zusammenfassung Es wurde die Molekulargewichtsverteilung von Polystyrolen untersucht, die durch Polymerisation von unverdünntem Styrol mit Azoisobutyronitril als Starter (0,5 bis 6·10^–3 Mole pro Mol Styrol) im Temperaturbereich von 30–90°C erhalten worden waren. Unter diesen Bedingungen kann die Beteiligung der Kettenübertragung an der Beendigung des Wachstums einer Kettenmolekel vernachlässigt werden. Es wird gezeigt, daß aus den erhaltenen Molekulargewichtsverteilungen der Anteil der Kettenaddition und der Kettendisproportionierung an der Abbruchsreaktion berechnet werden kann. Bei allen untersuchten Proben überwiegt zwar der Additionsanteil, doch ist stets auch eine Radikaldisproportionierung mit Sicherheit festzustellen. Unerwarteterweise nimmt der Additionsanteil mit steigender Polymerisationstemperatur zu. Eine Erklärungsmöglichkeit wird diskutiert.Mit 8 Abbildungen     

Domino Reactions with Fluorinated Five-membered Heterocycles – Syntheses of Trifluoromethyl Substituted Butenolides and γ-Ketoacids

A new approach to trifluoromethyl substituted butenolides and their thioanalogues is described starting from 2-fluoro-3-trifluoromethylfurans and -thiophenes, respectively. The reaction sequence includes three steps – nucleophilic displacement reaction, Claisen, and finally Cope rearrangement – which can be run as domino reaction. A modification of the domino reaction (transesterification instead of Cope rearrangement) provides a concise access to α-trifluoromethyl-γ-ketoacids.