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Eingeladener Vortrag
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The X-ray crystallographic study of the macrocyclic tetrakis-N[N-2-hydroxyethyl-piperazino]calix[4]resorcinarene·3CH3CH2OH·H2O (3) reveals a self-assembled dimeric capsule-like complex held together by an array of intermolecular hydrogen bonds. Pairs of concave molecules associate directly in bowl-to-bowl fashion and enclose an accessible supramolecular cavity of Å3 hosting one water and three ethanol molecules. The supramolecular arrangement displays alternating layers of facing bowls and interlocking lower rim aliphatic moieties. The helical conformation of the 2-hydroxyethyl piperazinomethyl moieties displays chirality of a bimolecular capsule frozen in the solid state. 3 crystallises in the triclinic space group P-1 with two symmetry independent molecules in the asymmetric unit. Two enantiomeric capsules form a racemic pair in the unit cell.
Synthesis and Reactions of (1E,2Z)-2-N,N-Dialkylhydrazono-2-phenylethanal N,N-Dimethylhydrazones
(2003)
(1E,2Z)-2-N,N-Dialkylhydrazono-2-phenylethanal N,N-dimethylhydrazones 3a-e weresynthesised by the reaction of 1,4,5-triazapentadienium salts 2 with N,N-dimethylhydrazine. The compounds 3a and 3d didnot react with tosyl isocyanate in an electrophilic substitutionreaction at the azomethine C-1 as aza-enamines, but they reactedat room temperature in benzene in a 1,4-dipolar cycloaddition toyield 1,3,5-triazinan-2,4-diones 5a and 5d, whereas at 70 °Coctahydroimidazoimidazol-2,5-dione 6a wasformed via criss-cross addition reaction. With dimethyl sulfatein DMF, 3a was transformed into the trimethylhydrazoniumsalts 7a and 8a,isolated as co-crystallised perchlorates (molar ratio 1:1).
Aza-enamines X - Formylation of Pyrazole-4-carbaldehyde Hydrazones at the Hydrazonoazomethine C-Atom
(2003)
1,3-Disubstituted 1H-pyrazole-4-carbaldehyde-N,N-dimethylhydrazones 1 reacted with the Vilsmeier-Haackreagent, corresponding to the aza-enamine concept, in an electrophilicsubstitution reaction at the azomethine C-atom yielding the 1,4,5-triaza-pentadieniumsalts 2. These were hydrolysed to give2-hydrazono-2-(1H-pyrazole-4-yl)ethanals 3. The electrophilic attack did not takeplace at the vinylogous position 5' of the pyrazoles.
For the highly selective and sensitive sensing of Hg2+ in water, a new design concept was realized where the selectivity of the probe's binding site is amplified by electronic properties of the chromophore. The molecular architecture of this phenoxazinone-type sensor molecule combines two potential coordination sites via an amino-keto conjugative backbone. These structural prerequisites allow only the most preferred mercuric ion to bind to the dithia dioxa monoaza crown unit, while other heavy, transition, and main group metal ions as well as protons are trapped at the keto group, inducing opposite spectral effects due to interaction with either the donor (Hg2+) or the acceptor group (other cations) of the probe. Besides these advantageous features, the probe operates well within the visible range of the spectrum and displays rather intense molar absorptivities as well as fluorescence quantum yields.
The photophysical properties of several newly synthesized 1-benzothiazole-3-(4-donor)-phenyl-substituted prop-2-en-1-ones (substituted chalcones) are studied as a function of solvent polarity, temperature, and metal ion by employing steady-state and time-resolved spectroscopy. To investigate the effect of bulkiness and donor strength of the anilino moiety on the spectroscopic properties of these dyes, the spectroscopic behavior of the 4-N-dimethylamino (DMA), the 4-N-tetraoxa-monoaza-15-crown-5 (A15C5), and the 4-N-tetrathia-monoaza-15-crown-5 (AT415C5) derivatives as well as the 3-julolidino (Jul) analogue is compared. Absorption and fluorescence measurements reveal that the strength of the intramolecular charge transfer (ICT) process increases on the order of AT415C5 < A15C5 ~ DMA < Jul. The slight but significant differences between the two crowned dyes are well-supported by the results of the X-ray structure analysis, where oxa aza and thia aza crowns show essentially different geometries. For both fluoroionophores, this variation of heteroatom substitution pattern of the receptor induces specific cation selectivities. The spectroscopic effects accompanying complexation and the different binding sites are studied by steady-state and time-resolved optical spectroscopy as well as NMR spectroscopy. Whereas the probe carrying a tetraoxa monoaza 15-crown-5 receptor shows cation-induced fluorescence enhancement in the presence of alkali and alkaline-earth metal ions, its tetrathia analogue binds selectively to HgII, AgI, and CuII in acetonitrile. Moreover, an increase in fluorescence is observed for the latter probe even upon coordination to the widely known fluorescence quencher HgII. Besides receptor complexation, chelate formation in the benzothiazole-carbonyl acceptor part of these intrinsic fluorescent probes is possible, leading to a chromoionophoric signaling behavior in the near-infrared (NIR).