Twisted baskets

Cryogels Based on Poly(2-oxazoline)s through Development of Bi- and Trifunctional Cross-Linkers Incorporating End Groups with Adjustable Stability

1,4-Bis(iodomethyl)benzene and 1,3,5-tris(iodomethyl)benzene were used as initiators for the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) and its copolymerization with tert-butyl (3-(4,5-dihydrooxazol-2-yl)propyl)carbamate (BocOx) or methyl 3-(4,5-dihydrooxazol-2-yl)propanoate (MestOx). Kinetic studies confirmed the applicability of these initiators. Termination with suitable nucleophiles resulted in two- and three-armed cross-linkers featuring acrylate, methacrylate, piperazine-acrylamide, and piperazine-methacrylamide as polymerizable ω-end groups. Matrix-assisted laser desorption/ionization mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy confirmed the successful attachment of the respective ω-end groups at all initiation sites for every prepared cross-linkers. Except for acrylate, each ω-end group remained stable during deprotection of BocOx containing cross-linkers. The cryogels were prepared using EtOx-based cross-linkers, as confirmed by solid-state NMR spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Stability tests revealed a complete dissolution of the acrylate-containing gels at pH = 14, whereas the piperazine-acrylamide-based cryogels featured excellent hydrolytic stability.

The role of chlorine position in the electronic circular dichroism of chlorophenyl-ethanol investigated by vibronic calculations

(R)-1-phenyl-ethanol (PhEtOH) and the different isomers of (R)-1-(chlorophenyl)ethanol (ClPhEtOH) exhibit very interesting electronic circular dichroism (ECD) in methanol. In all cases, the spectrum shows clear vibronic features, but it is monosignated and negative for PhEtOH and meta-ClPhEtOH, positive for the ortho isomer and bisignated for the para isomer. We used computational chemistry to rationalise this behaviour adopting CAM-B3LYP/def2-TZVP, describing the bulk solvent effects with polarizable continuum models and solute-solvent specific interactions with clusters comprising the solute and two solvent molecules. We adopted harmonic vibronic models to compute the ECD spectral shapes of all stable conformers, and we obtained the room-temperature spectra by Boltzmann average. Simulated spectra are in very good agreement with experiment and allow us to rationalise their difference in terms of the relevance of Franck-Condon (FC) and Herzberg-Teller (HT) intensity-borrowing contributions, modulated by the substituent effect. The bisignated shape of the spectrum of para-ClPhEtOH arises from the competition of opposite-sign FC and HT bands, promoted by different vibrational modes. Due to the challenges we document in computing its ECD spectrum, para-ClPhEtOH represents a good test case to help the development of novel methodologies for an improved description of weak vibronic ECD spectra of flexible systems in explicit solvents.

Supramolecular chiroptical switching of helical-sense preferences through the two-way intramolecular transmission of a single chiral source

Complexation-induced reversal of helical-sense preferences is demonstrated with a simple molecule with a pair of exciton-coupled chromophores.

Assembly and Folding of Twisted Baskets in Organic Solvents

A synthetic method for obtaining enantiopure and twisted baskets of type (P)-3 is described. These chiral cavitands were found to fold quinoline gates, at the rim of their twisted platform, in acetonitrile and give molecular capsules that assemble into large unilamellar vesicles. In a less polar dichloromethane, however, cup-shaped (P)-3 packed into vesicles but with the quinoline gates in an unfolded orientation. The ability of twisted baskets to form functional nanostructured materials could be of interest for building stereoselective sensors and catalysts.