Urea vs. carbamate groups: a comparative study in a chiral C2 symmetric organogelator.

The effect of the replacement of molecular moieties (carbamates vs. urea) that drive self-assembly for two organogelators with an identical C(2) symmetric molecular structure is described. The main properties of the gels obtained from the urea-based organogelators are also discussed. The proposed organogelators are chiral molecules and are able to express chirality also at the supramolecular level, thus allowing the employment of electronic circular dichroism to gain insight into the molecular-scale structure of fibrillar aggregates. With the same technique, the behavior of enantiomeric mixtures of the urea-based organogelators was investigated, revealing the occurrence of different self-sorting phenomena at the molecular and supramolecular scale. The urea-based organogelators demonstrated to be more efficient gelators with respect to the carbamate-based analogues, showing a high gel-to-sol transition temperature (up to 66 °C) and a very low minimum gelling concentration (0.85 mg mL(-1)). This study is a starting point for a deeper investigation of structure/property relationships and, taking into account the peculiar behavior detected for the enantiomeric mixtures, also of self-sorting and molecular recognition phenomena.

Separation of Enantiomers of a Phospholipid in Langmuir Monolayers by a New Selector.

Chiral discrimination in a racemic mixture of dipalmitoylphosphatidylcholine (DPPC) is induced by a new selector at the water-air interface: L-DPPC is segregated in the condensed phase of a Langmuir monolayer upon interactions with an enantiopure amphiphilic compound.

Ultrafast resonance energy transfer in the umbelliferone-alizarin bichromophore.

In this work we present the synthesis, time-resolved spectroscopic characterization and computational analysis of a bichromophore composed of two very well-known naturally occurring dyes: 7-hydroxycoumarin (umbelliferone) and 1,2-dihydroxyanthraquinone (alizarin). The umbelliferone donor (Dn) and alizarin acceptor (Ac) moieties are linked to a triazole ring viaσ bonds, providing a flexible structure. By measuring the fluorescence quantum yields and the ultrafast transient absorption spectra we demonstrate the high efficiency (∼85%) and the fast nature (∼1.5 ps) of the energy transfer in this compound. Quantum chemical calculations, within the density functional theory (DFT) approach, are used to characterize the electronic structure of the bichromophore (Bi) in the ground and excited states. We simulate the absorption and fluorescence spectra using the TD-DFT methods and the vertical gradient approach (VG), and include the solvent effects by adopting the conductor-like polarizable continuum model (CPCM). The calculated electronic structure suggests the occurrence of weak interactions between the electron densities of Dn and Ac in the excited state, indicating that the Förster-type transfer is the appropriate model for describing the energy transfer in this system. The average distance between Dn and Ac moieties calculated from the conformational analysis (12 Å) is in very good agreement with the value estimated from the Förster equation (∼11 Å). At the same time, the calculated rate constant for energy transfer, averaged over multiple conformations of the system (3.6 ps), is in reasonable agreement with the experimental value (1.6 ps) estimated by transient absorption spectroscopy. The agreement between experimental results and computational data leads us to conclude that the energy transfer in Bi is well described by the Förster mechanism.

Chirality driven self-assembly in a fluorescent organogel.

In this work, we present the characterization of an enantiomeric pair of fluorescent dye organogelators and the properties of their stable gel at low concentration in organic solvents. The gels of both enantiomers and of their mixtures were analyzed by differential scanning calorimetry, circular dichroism (CD), atomic force microscopy, UV-vis absorption, and fluorescence. The acquired data were supported by molecular modeling of the helical assembly of the gelators and by the simulation of their CD spectra by means of DeVoe method, and suggested the occurrence of an enantiomeric discrimination process during the formation of the gels.

A halogen bond-donor amino acid for organocatalysis in water.

Herein we report a halogen bond-donor amino acid, 4-iodotetrafluorophenylalanine, which behaves as a catalyst for the aqueous synthesis of bis-(heterocyclic)methanes. We also provide experimental evidence that halogen bonding is a plausible explanation for the observed catalytic effect.

A new organogelator based on an enantiopure C2 symmetric pyrrolidine.

The synthesis and the properties of a new chiral organogelator based on a C(2) symmetric pyrrolidine, are described together with its use for the synthesis of other functionalised organogelators.

Can nitrones functionalize carbon nanotubes?

An unprecedented functionalization of multi-walled carbon nanotubes (MWCNTs) has been conveniently achieved by the 1,3-dipolar cycloaddition of a cyclic nitrone. This organic functionalization yields materials with a great solubility in DMF (close to 10 mg per mL of DMF) preferentially occurring at the defects of the MWCNT sp(2) network.