“Double-Twist”-Based Dynamic Induction of Optical Activity in Multichromophoric System

The electronic circular dichroism (CD)-silent 2,5-bis(biphen-2-yl)terephthalaldehyde has been used as a sensor (reporter) of chirality for primary amines. The through-space inductor–reporter interactions force a change in the chromophore conformation toward one of the diastereomeric forms. The structure of the reporter, with the terminal flipping biphenyl groups, led to generating Cotton effects in both lower- and higher-energy regions of the ECD spectrum. The induction of an optical activity in the chromophore was due to the cascade point-to-axial chirality transmission mechanism. The reporter system turned out to be sensitive to the subtle differences in the inductor structure. Despite the size of the chiral substituent, the molecular structure of the inductor–reporter systems in the solid-state showed many similarities. The most important one was the tendency of the core part of the molecules to adapt pseudocentrosymmetric conformation. Supported by a weak dispersion and Van der Waals interactions, the face-to-face and edge-to-face interactions between the π-electron systems present in the molecule were found to be responsible for the molecular arrangement in the crystal

Photochemical and thermal behavior of light-driven unidirectional molecular motor with long alkyl chains

In order to utilize molecular motors in a molecular device or Smart materials, their dynamic behavior when other groups are introduced at key positions has to be examined. A C(16) hydrocarbon chain has been introduced at the stereogenic centers of the first generation light-driven molecular motor based on sterically overcrowded biphenanthrylidene. It was found that this derivatization does not affect the unidirectional rotary capability of the motor and does not cause a reduction of its speed, opening new possibility for future functionalizations and applications. (C) 2008 Elsevier Ltd. All rights reserved

Enantiopure Tertiary Urea and Thiourea Derivatives of Trianglamine Macrocycle: Structural Studies and Metallogeling Properties

Synthesis and detailed experimental and theoretical study on new urea and thiourea derivatives of chiral trianglamine are presented. In solution, the urea derivative of the trianglamine adopts cone conformation, whereas a respective thiourea derivative exists in solution predominantly as a partial cone conformer. In the crystalline phase, the thiourea trianglamine derivative adapts partial cone conformation. In the solid state, the two symmetry independent molecules of thiourea trianglamine create bilayers, containing molecules arranged in a zipper motif. The bilayers are separated by channels filled with disordered solvent molecules. The thiourea derivative of trianglimine appeared to be a simple, low molecular weight supergelator that formed stable chiral metallogels in <i>N</i>,<i>N</i>-dimethylformamide with Ag­(I), Cu­(I). and Cu­(II) salts. The enantiomeric enrichment of the macrocycle is a necessary condition for effective gelling because neither racemic nor enantiomerically enriched samples (up to 50% ee) form metallogels. The metallogels formed from silver cations and thiourea trianglamine show reversible thixotropic property rarely observed in metallogels

C-hexaphenyl-substituted trianglamine as a chiral solvating agent for carboxylic acids

none5siChiral hexaazamacrocycles with a trianglamine structure and C3-symmetry, containing six ring substituents and twelve stereocenters have been tested as chiral solvating agents (CSAs) for a-substituted carboxylic acids. Excellent results have been obtained with a hexaphenyl-substituted macrocycle. The optimal ratio between the macrocycle and racemic acid, allowing for baseline separation of the enantiomers’ signals in the 1H NMR spectrum, was dependent on the type of acid, in particular on its degree of acidity. The analyte and the CSA could be separated and recovered by a simple acid–base extraction and reused without purification. The conformations of the free and protonated hexaamino macrocycles were inferred by CD spectroscopic studies and DFT calculations.mixedA. Gualandi; S. Grilli; D. Savoia; M. Kwit; J. Gawro´nskiA. Gualandi; S. Grilli; D. Savoia; M. Kwit; J. Gawro´nsk

Synthesis, stereochemistry, and photochemical and thermal behaviour of bis-tert-butyl substituted overcrowded alkenes

In order to study the structural limits in the design of molecular motors, a tert-butyl substituted analogue was prepared. The unexpected photochemical and thermal isomerisation processes and the stereochemistry of a new overcrowded alkene are described. The bis tert-butyl substituted alkenes were synthesised in a five-step sequence with an overall yield of 7.5%. Structural assignments of the isomers based on experimental data were supported by calculations of all four isomers of the alkene. X-Ray crystal analysis showed a strongly twisted alkene (torsion angle 39°) for a less stable photochemically generated cis-isomer.

An unexpected relationship between solvent inclusion and gas sorption properties of chiral calixsalen solids^*

<p>Experimental evidence is provided that tentatively shows a relationship between inclusion and sorption properties within a series of halogenated homochiral calixsalens. Calixsalens with Cl and Br substituents at the C5 position on the aromatic rings display remarkable sorption properties for all of the investigated gases, as well as the ability to form inclusion compounds with chemically different solvents, while unsubstituted (H-) and F-substituted calixsalens do not show any of these properties.</p> <p>There is a tentative relationship between solvent inclusion and gas sorption properties within a series of halogenated homochiral calixsalens. Calixsalens with Cl and Br substituents at the C5 position on the aromatic rings display remarkable sorption properties for a selection of gases, as well as the ability to form inclusion compounds with chemically different solvents, while unsubstituted (H-) and F-substituted calixsalens do not show any of these properties.</p