Planar and distorted indigo as the core motif in novel chromophoric liquid crystals

Symmetrically bis-substituted indigo derivatives with long peripheral alkyl chains were synthesised by the reductive condensation of corresponding isatin derivatives. Their thermotropic mesomorphism was investigated with respect to different substitution patterns, which include the position and lateral modifications of the substituents. A systematic investigation of structure-property relationships revealed that only substitution at the 6 and 6' positions affords the calamitic shape necessary to form smectic or nematic liquid crystalline phases. This finding is rationalised on the basis of a structural analysis of N,N'-diacetyl indigo and the consequences for 5,5'- and 6,6'-bis-substituted derivatives are discussed. Some of the liquid crystalline substances exhibit dichroism, which is especially pronounced in highly ordered phases. In addition, the 6,6' substitution leads to significantly enhanced activity with respect to the photochemical trans-cis isomerization of N, N'-diacetylated indigo derivatives

A new fluorinated inositol-based surfactant

Carbohydrates are versatile materials of natural origin and thus they are interesting hydrophilic head groups for surfactants. Especially myo-inositol derivatives have advantages over pyranosidic or furanosidic sugar derivatives, namely a higher thermal and chemical stability. The main disadvantage turned Out to be the poor water solubility of myo-inositol surfactants, which, however, can be overcome by introducing an oligoethylene oxide group between the inositol head group and the apolar chain. Our goal was to combine the favourable properties of surfactants based on myo-inositol with those of fluorinated surfactants, which are becoming increasingly important as CO2 solvation mediators or stabilizers for reverse water-in-fluorocarbon microemulsions. Thus we synthesized a new surfactant which combines the three units of interest, namely an inositol head group, an oligoethylene oxide linker to provide sufficient solubility and a fluorinated chain. We studied the thermotropic and lyotropic liquid crystalline behaviour as well as the surface tension and compared these results with those of a fully protonated surfactant which has a similar structure. (C) 2012 Elsevier B.V. All rights reserved

Enantioselective Total Synthesis and Structural Revision of Dysiherbol A

A 12-step total synthesis of the natural product dysiherbol A, a strongly anti-inflammatory and anti-tumor avarane meroterpene isolated from the marine sponge Dysidea sp., was elaborated. As key steps, the synthesis features an enantioselective Cu-catalyzed 1,4-addition/enolate-trapping opening move, an Au-catalyzed double cyclization to build up the tetracyclic core-carbon skeleton, and a late installation of the C5-bridgehead methyl group via proton-induced cyclopropane opening associated with spontaneous cyclic ether formation. The obtained pentacyclic compound (corresponding to an anhydride of the originally suggested structure for dysiherbol A) showed identical spectroscopic data as the natural product, but an opposite molecular rotation. CD-spectroscopic measurements finally confirmed that both the constitution and the absolute configuration of the originally proposed structure of (+)-dysiherbol A need to be revised

Less is more: Unstable foams clean better than stable foams

Hypothesis: Foamed surfactant solutions can clean surfaces! We hypothesise that the cleaning efficiency depends on the liquid fraction and on the stability of the foam. We also hypothesise that the cleaning efficiency is the better the smaller the average bubble size is. Experiments: The double syringe technique was used to generate foams with varying liquid fractions but the same, very small bubble sizes with and without perfluorohexane in the gas phase. We performed cleaning tests in which the foams were applied to glass substrates contaminated with a fluorescent oil. Findings: We found that unstable foams clean better than stable foams. Three cleaning mechanisms were identified: (1) imbibition at low liquid fractions, (2) wiping, i.e., shifting of the contact line between oil, foam and glass, at all liquid fractions, and (3) drainage at high liquid fractions. The change of the liquid fraction and of the foam stability lead to different combinations of these mechanisms and thus to different cleaning results. CO 2021 Elsevier Inc. All rights reserved

1,2,5,10,11,14-Hexaoxadispiro[5.2.5.2]hexadecanes: Novel Spirofused Bis-Trioxane Peroxides

A set of new bis-spirofused 1,2,4-trioxanes 4a-d was obtained from the reaction of cyclohexane-1,4-dione with allylic hydroperoxides 2a-d, bearing an additional hydroxy group in the homoallylic position, by diastereoselective photooxygenation of allylic alcohols 1a-d and subsequent BF3-catalyzed peroxyacetalization with the diketone. From the reaction of a monoprotected cyclohexane-1,4-dione 5 with the allylic hydroperoxide 6 derived from the singlet oxygenation of methyl hydroxytiglate, one monospiro compound was obtained, the 1,2,4-trioxane ketone 7, as well as a mixture of the diastereoisomeric syn- and anti bis-1,2,4-trioxanes 8. The structures of bis-1,2,4-trioxanes were examined theoretically by DFT methods and compared with X-ray structural data in order to evaluate the preferential trioxane ring conformational orientation