Chiara M. A. Gangemi

Applications of supramolecular capsules derived from resorcin[4]arenes, calix[n]arenes and metallo-ligands: from biology to catalysis

Supramolecular architectures developed after the initial studies of Cram, Lehn and Pedersen have become structurally complex but fascinating. In this context, supramolecular capsules based on resorcin[4]arenes, calix[n]arenes or metal–ligand structures are dynamic assemblies inspired by biological systems. The reversible formation of these assemblies, combined with the possibility to modify their dimensions and shapes in the presence of a guest (concepts of reversibility and adaptivity) make them similar to biological macromolecules, such as proteins and enzymes. The small space inside a supramolecular capsule is characterized by different properties compared to the bulk solution. This review describes concrete applications of capsular supramolecular self-assemblies in the biomedical field, in catalysis and in material science.

Hierarchically controlled protonation/aggregation of a porphyrin–spermine derivative

We designed and synthesized a new porphyrin–spermine derivative that self-assembles under hierarchical control. Its aggregation processes depend on the protonation of both the spermine units and central core nitrogen atoms. Therefore, the time duration of pH titrations and/or the direct protonation of a specific site allow for choosing the desired aggregation state of the system.

Chiral Zn–salen complexes: a new class of fluorescent receptors for enantiodiscrimination of chiral amines

The first example of fluorescent chiral Zn–salen hosts, able to efficiently recognise chiral amines via non-covalent interactions, is reported here. The host–guest interactions have been characterised by 2D-NMR spectroscopy in order to elucidate the origin of enantioselectivity.

(Salen)Mn(III) Catalyzed Asymmetric Epoxidation Reactions by Hydrogen Peroxide in Water: A Green Protocol

Enantioselective epoxidation reactions of some chosen reactive alkenes by a chiral Mn(III) salen catalyst were performed in H2O employing H2O2 as oxidant and diethyltetradecylamine N-oxide (AOE-14) as surfactant. This procedure represents an environmentally benign protocol which leads to e.e. values ranging from good to excellent (up to 95%).

The interaction of a β-fused isoindoline–porphyrin conjugate with nucleic acids

A diiminoisoindolo-pyrazino unit was annulated to the β-pyrrolic position of the Zn complex of tetraphenylporphyrin, giving a macrocycle with an expanded π system in satisfactory yields. The crystal structure of this derivative evidenced the formation of a hydrogen bond network. The interaction of the β-fused isoindoline porphyrin derivative with nucleotides and nucleic acids has been investigated.

The memory-driven order–disorder transition of a 3D-supramolecular architecture based on calix[5]arene and porphyrin derivatives

A 3D supramolecular polymer based on calix[5]arene tethered poly(p-phenyleneethynylene) with a complementary porphyrin endowed with alkanediyldiammonium functions is prepared in solution but collapses when transferred to a chemically inert solid matrix forming a dispersion of de-phasing porphyrin aggregates. We found that a short thermal shock induces the de-aggregation of the porphyrin aggregates, and a partial restoration of the original 3D-supramolecular architecture.

Combined Approach To Remove and Fast Detect Heavy Metals in Water Based on PES–TiO2 Electrospun Mats and Porphyrin Chemosensors

Hybrid poly(ether sulfones) (PES)–TiO2 electrospun mats are used as selective filters to remove lead and zinc ions from water. Presence of TiO2 is functional to trigger fiber’s surface charge that allows for better performances in terms of ionic adsorption with respect to bare PES mats. Temperature increase promotes a speed up of ion removal. Ability of electrospun mats to retain adsorbed ions is proven by washing procedures, which confirm the lack of released Pb2+ in solution, even after sonication. To detect presence of metal ions in aqueous solutions, water-soluble porphyrins are used as chemosensors, which are able to provide fast, in-field, and real-time analysis. In particular, cationic H2T4 metalation, occurring both in solution or at transparent glass surface, allows for a straightforward spectrophotometric (UV–vis) detection of metal ions in solution.

Easy sensing of lead and zinc in water using smart glass based on cationic porphyrin layers

Spontaneous formation of meso-tetra(N-methyl-4-pyridyl)porphyrin (H2T4) layers on a glass surface is proven effective to assess the sensitivity and selectivity of solid chemosensors for spectrometric detection (at sub-ppm levels) of Pb2+ and Zn2+ ions in water. The obtained results, achieved by a simple, low cost and repeatable non-covalent glass surface functionalization, are suitable for application in water management and control where detection of contaminants at micromolar or even submicromolar concentrations is required. The most striking result is represented by the high sensitivity towards Zn2+ ions, unusual for cationic porphyrins in solution, herein associated with macrocycle ring distortion caused by immobilization onto a glass surface. Moreover, the co-presence of Pb2+ and Zn2+ in water promotes a trans-metalation process responsible for a peculiar fingerprint of contaminant abundance in solution within the selected (short) analysis time. The defined sensing strategy is extendible to other metal ions, thus making these H2T4 functionalised glass slides ideal for the rapid on site-real time detection of heavy metal ions in water.

Driving Coordination Polymer Monolayer Formation by Competitive Reactions at the Air/Water Interface

We have developed a novel approach enabling us to follow and facilitate the formation of two-dimensional coordination polymer monolayers directly at the air/water interface without the need of complex instrumentation. The method is based on the use of a surface active ligand that, when spread at the air/water interface, progressively undergoes hydrolysis with consequent gradual decrease in surface pressure. Notably, if the aqueous subphase contains metal ions capable of coordinating the ligand, coordination competes with hydrolysis, resulting in a lower surface pressure decrease. As a consequence, the formation of the coordination polymer monolayer can be verified simply by surface pressure measurements. Competition between hydrolysis and coordination was investigated as a function of the main experimental parameters affecting the two reactions, enabling the formation of stable coordination polymer monolayers with controlled density. Finally, the formation of continuous rigid 2D layers was confirmed by compression isotherms and ex situ morphological characterization. This work will simplify the verification of coordination polymer monolayer formation; thus, it will boost the synthesis of novel and innovative 2D materials.

A novel porphyrin-based molecular probe ZnTCPPSpm4 with catalytic, stabilizing and chiroptical diagnostic power towards DNA B-Z transition

In this work we have designed a new zinc(II) porphyrin with four spermines conjugate in the meso positions, meso-tetrakis-(4-carboxysperminephenyl)porphyrin, ZnTCPPSpm4) with the aim of acting as a chiroptical probe for the Z-form of DNA, a high energy transient conformation of DNA. In addition to monitor by Electronic Circular Dichroism chiroptical response the formation of Z-DNA in the presence of micromolar concentration of spermine, this porphyrin based molecular probe is also able to catalyze and stabilize this important DNA structure. The ZnTCPPSpm4 conjugate represents a perfect example of single molecule, which possesses all these three properties at the same time. The increased stability of Z-DNA in the presence of this derivative opens possibility for further studies on the mechanism of B- to Z-DNA transition, and on the design of new probes with improved efficiency.