Luisa Lascialfari

Self-sorting chiral organogels from a long chain carbamate of 1-benzyl-pyrrolidine-3,4-diol

(3S,4S)-1-benzylpyrrolidine-3,4-diyl bis(dodecylcarbamate), a pyrrolidine ring bearing two long carbon chains connected by carbamate functionalities, is the origin of stable gels in both polar and apolar solvents. Several experimental and theoretical techniques (cryo-TEM, AFM, DSC, circular dichroism (CD), molecular mechanics calculations and CD simulations) were used to describe the formation and the characteristics of the chiral supramolecular structures and fibers constituting the gel. The chirality at both supramolecular and microscopic level depends on the configuration of the stereogenic centers of the pyrrolidine unit. The gels formed by the two enantiomers of the gelator and their mixtures display enantiomeric discrimination resulting in a self-sorting process. In fact, separate fibers of opposite helicity are obtained, which suggests this class of compounds has strong potential for realizing functionalized chiral architectures.

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.

Preparation of small size palladium nanoparticles by picosecond laser ablation and control of metal concentration in the colloid

We assessed a method for the preparation of small, highly stable and unprotected Pd nanoparticles by picosecond laser ablation in 2-propanol. The nanoparticles can be extracted from 2-propanol by centrifugation and redispersed in water, where a strongly negative ζ-potential assures long term stability. The proposed procedure permits reduction of particle size down to 1.6nm and optimization of the Pd(0):Pd(II) ratio which, in the best cases, was of the order of 6:1. The increase of this ratio with ablation times has been correlated to the high temperature conversion of PdO to metallic Pd by a simple theoretical model. A study of the relationship between colloid absorption at 400nm and Pd concentration permitted the role of PdO in the determination of the UV-vis spectra to be clarified and the limits of the Mie theory for the evaluation of colloid concentration to be established. The absorption at 400nm can be used as a fast method to estimate the Pd content in the colloids, provided that a calibration of the ablation process is preliminarily performed.

Soft matter nanocomposites by grafting a versatile organogelator to carbon nanostructures

The organic functionalization of either [60]fullerene or MWCNTs with a highly efficient organogelator has allowed the production of novel and homogeneously dispersed soft-nanocomposites. While the nanostructured carbon materials produced by simple mixing do not homogeneously disperse into a preformed gel, C60- and MWCNT-containing gels have been conveniently obtained by covalent functionalization of the carbon lattice with reactive organogelator derivatives. The present study, while emphasizing the gelling properties of a selected class of organogelators, allows the conjugation of the properties of gels and nanostructured carbon materials yielding novel soft-nanocomposites.

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.

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.

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.

Metal-clad optical waveguide fluorescence device for the detection of heavy metal ions

Abstract. We developed Hg2+-sensing chips by decorating the external surface of metal-clad optical waveguides with a monolayer of Hg2+-sensitive fluorescent molecular probes. The emission properties of the original water-soluble form of the molecule were previously found to be selectively quenched in the presence of Hg2+ ions. The fabricated samples were tested with optical waveguide fluorescence spectroscopy by putting them in contact with a 5-μM water solution of Hg2+ ions and recording the emission spectra versus incubation time. The estimate of the limit of detection was 150 nM. A preliminary evaluation of the selectivity of the structure was also performed by using Cd2+ as possible interfering analytes.

Five-Membered Ring Systems with O & N Atoms

Abstract This review covers the work published in the calendar year 2013. Novel reaction chemistry and new ring synthetic methods for isoxazoles, isoxazolines, isoxazolidines, oxazoles, oxazolines, oxazolidines, and oxadiazoles are reviewed.

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.