Iwona Nierengarten

A Supramolecular Photosynthetic Model Made of a Multiporphyrinic Array Constructed around a C60 Core and a C60–Imidazole Derivative

The photophysical properties of a supramolecular fullerene-porphyrin ensemble resulting from the self-assembly of a pyrrolidinofullerene-imidazole derivative (F1) with a multimetalloporphyrin array constructed around a hexasubstituted fullerene core (F(ZnP)12) have been investigated. The fullerene hexa-adduct core of the host system does not play any active role in the cascade of photoinduced events of the supramolecular ensemble, indeed no intercomponent photoinduced processes could be observed in host F(ZnP)12. In contrast, upon axial coordination with the monosubstituted fullerene guest F1, a quantitative quenching of the fluorescence signal of the metalloporphyrins was observed for the supramolecular complex [F(ZnP)12(F1)n] both in polar and nonpolar solvents. In toluene, the supramolecular ensemble exhibits a charge transfer emission centered around nm, suggesting the occurrence of intramolecular face-to-face interactions of F1 with neighboring metalloporphyrin moieties within the self-assembled photoactive array. This mechanism is supported by the fact that a one order of magnitude increase in the binding constant was observed for the supramolecular complex [F(ZnP)12(F1)n] when compared with a reference system lacking the pyrrolidinofullerene unit. In benzonitrile, a long-lived charge-separated state (τ=0.3 μs) has been detected for the supramolecular adduct.

Polycationic Pillar(5)arene Derivatives: Interaction with DNA and Biological Applications

Dendritic pillar[5]arene derivatives have been efficiently prepared by grafting dendrons with peripheral Boc-protected amine subunits onto a preconstructed pillar[5]arene scaffold. Upon cleavage of the Boc-protected groups, water-soluble pillar[5]arene derivatives with 20 (13) and 40 (14) peripheral ammonium groups have been obtained. The capability of these compounds to form stable nanoparticles with plasmid DNA has been demonstrated by gel electrophoresis, transmission electron microscopy (TEM), and dynamic light scattering (DLS) investigations. Transfection efficiencies of the self-assembled 13/pCMV-Luc and 14/pCMV-Luc polyplexes have been evaluated in vitro with HeLa cells. The transfection efficiencies found for both compounds are good, and pillar[5]arenes 13 and 14 show very low toxicity if any.

Biologically Active Heteroglycoclusters Constructed on a Pillar[5]arene‐Containing [2]Rotaxane Scaffold

Abstract A synthetic approach combining recent concepts for the preparation of multifunctional nanomolecules (click chemistry on multifunctional scaffolds) with supramolecular chemistry (self‐assembly to prepare rotaxanes) gave easy access to a large variety of sophisticated [2]rotaxane heteroglycoclusters. Specifically, compounds combining galactose and fucose have been prepared to target the two bacterial lectins (LecA and LecB) from the opportunistic pathogen Pseudomonas aeruginosa.

Pillar[5]arene-based glycoclusters: synthesis and multivalent binding to pathogenic bacterial lectins

The synthesis of pillar[5]arene-based glycoclusters has been readily achieved by CuAAC conjugations of azido- and alkyne-functionalized precursors. The lectin binding properties of the resulting glycosylated multivalent ligands have been studied by at least two complementary techniques to provide a good understanding. Three lectins were selected from bacterial pathogens based on their potential therapeutic applications as anti-adhesives, namely LecA and LecB from Pseudomonas aeruginosa and BambL from Burkholderia ambifaria. As a general trend, multivalency improved the binding to lectins and a higher affinity can be obtained by increasing to a certain limit the length of the spacer arm between the carbohydrate subunits and the central macrocyclic core.

Metal-atom impact on the self-assembly of cup-and-ball metalloporphyrin-fullerene conjugates.

A fullerene ammonium derivative has been combined with different metalloporphyrin-crown ether receptors to generate very stable supramolecules. The combination of fullerene-porphyrin and ammonium-crown ether interactions leads to a strong chelate effect as evidenced by a high effective molarity (3.16 M). The different parameters influencing the stability of the supramolecular ensembles, in particular the nature of the metal in the porphyrin moiety, have been rationalized with the help of theoretical calculations thus providing new insights into fullerene-porphyrin interactions.

The Impact of Copper‐Catalyzed Alkyne–Azide 1,3‐Dipolar Cycloaddition in Fullerene Chemistry

Click reactions largely cross the borders of organic synthetic chemistry and are now at the forefront of many interdisciplinary studies at the interfaces between chemistry, physics, and biology. As part of this research, our group is involved in a program on the development of clickable fullerene building blocks and their application in the preparation of a large variety of new advanced materials and bioactive compounds. Importantly, the introduction of the click chemistry concept in fullerene chemistry allowed us to produce compounds that would barely be accessible by using the classical tools of fullerene chemistry. This is particularly the case for the conjugation of fullerenes with other carbon nanoforms, such as carbon nanohorns and graphene. It is also the case for most of the sophisticated molecular ensembles constructed from clickable fullerene hexa-adduct building blocks. In this paper, we have summarized our ongoing progress in this particular field.

Conjugated Porphyrin Dimers: Cooperative Effects and Electronic Communication in Supramolecular Ensembles with C60

Two new conjugated porphyrin-based systems (dimers 3 and 4) endowed with suitable crown ethers have been synthesized as receptors for a fullerene-ammonium salt derivative (1). Association constants in solution have been determined by UV–vis titration experiments in CH2Cl2 at room temperature. The designed hosts are able to associate up to two fullerene-based guest molecules and present association constants as high as ∼5 × 108 M–1. Calculation of the allosteric cooperative factor α for supramolecular complexes [3·12] and [4·12] showed a negative cooperative effect in both cases. The interactions accounting for the formation of the associates are based, first, on the complementary ammonium-crown ether interaction and, second, on the π–π interactions between the porphyrin rings and the C60 moieties. Theoretical calculations have evidenced a significant decrease of the electron density in the porphyrin dimers 3 and 4 upon complexation of the first C60 molecule, in good agreement with the negative cooperativity found in these systems. This negative effect is partially compensated by the stabilizing C60–C60 interactions that take place in the more stable syn-disposition of [4·12].

Piling Up Pillar[5]arenes To Self‐Assemble Nanotubes

New liquid-crystalline pillar[5]arene derivatives have been prepared by grafting first-generation Percec-type poly(benzylether) dendrons onto the macrocyclic scaffold. The molecules adopt a disc-shaped structure perfectly suited for self-organization into a columnar liquid-crystalline phase. In this way, the pillar[5]arene cores are piled up, thus forming a nanotubular wire encased within a shell of peripheral dendrons. The capability of pillar[5]arenes to form inclusion complexes has been also exploited. Specifically, detailed binding studies have been carried out in solution with 1,6-dicyanohexane as the guest. Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Colh mesophase has been deduced from X-ray diffraction data and found to be similar to that observed within the crystal lattice of a model inclusion complex prepared from 1,4-dimethoxypillar[5]arene and 1,6-dicyanohexane.

Langmuir and Langmuir–Blodgett Films from Amphiphilic Pillar[5]arene‐Containing [2]Rotaxanes

Amphiphilic pillar[5]arene-containing [2]rotaxanes have been prepared and fully characterized. In the particular case of the [2]rotaxane incorporating a 1,4-diethoxypillar[5]arene subunit, the structure of the compound was confirmed by X-ray crystal structure analysis. Owing to a good hydrophilic/hydrophobic balance, stable Langmuir films have been obtained for these rotaxanes and the size of the peripheral alkyl chains on the pillar[5]arene subunit has a dramatic influence on the reversibility during compression-decompression cycles. Indeed, when these are small enough, molecular reorganization of the rotaxane by gliding motions are capable of preventing strong π-π interactions between neighboring macrocycles in the thin film.

From Pillar[n]arene Scaffolds for the Preparation of Nanomaterials to Pillar[5]arene-containing Rotaxanes.

Pillar[n]arenes are a new class of macrocycles that are efficiently prepared from readily available building blocks. In this particular field, our research teams became interested in the use of a pillar[5]arene core as a compact scaffold for the synthesis of nanomaterials with a controlled distribution of functional groups on both rims of the macrocyclic framework. Such compounds have found applications in biology as multivalent ligands for specific lectines or as polycationic compounds for gene delivery. Liquid-crystalline derivatives have been prepared by grafting mesogenic subunits on the pillar[5]arene core. On the other hand, we also became interested in the preparation of pillar[5]arene-containing [2]rotaxanes. In particular, we have shown that pillar[5] arene-based [2]rotaxanes can be obtained from the reaction of amine stoppers with pseudo-rotaxanes resulting from the association of a pillar[5]arene derivative with a diacyl chloride reagent. Finally, amphiphilic [2]rotaxanes have been prepared and incorporated in thin ordered films at the air-water interface.