Rosalba Randazzo

Vortexes and Nanoscale Chirality

Contents: • Experimental details of the CD experiments on the halved cuvettes.

Reversible “Chiral Memory” in Ruthenium Tris(phenanthroline)–Anionic Porphyrin Complexes

In the last few years, transfer and memory of chirality have been attracting growing interest for potential technological applications. In general, this phenomenon occurs through two steps: 1) transfer of chirality from a chiral template to an achiral covalent or noncovalent “polymeric” species and 2) “removal” of the chiral cast which leaves its chirality permanently imprinted on the “polymer”. The chiral memory relies on the kinetic inertness of the “polymeric” species and most examples rely on systems that have a “static” memory: that is, once imprinted and memorized, chirality becomes an intrinsic but nontunable feature of the complex. Only recently has a system with a “dynamic memory” for which it is possible to cyclically store and release the “memorized chirality” been reported. We report herein a new and more intriguing “dynamic” supramolecular memory system (SuMe). We have recently reported that the L and D enantiomers of [Ru(1,10-phenanthroline)3] 2+ ([Ru(phen)3] , lmax = 262 nm, Figure 1) induce chiral aggregation of various achiral anionic porphyrins. Our interest in this complex system stems from two considerations. Firstly, porphyrins are ideal building blocks for supramolecular architectures because of their unique spectroscopic properties (extinction coefficients of ca. 10 and intense emission signals, the position and intensity of which can be tuned by insertion of a central metal ion) and the possibility of modulation of their self-aggregation. Secondly, ruthenium (II) complexes can transfer two kind of molecular information—energy and chirality—to porphyrins and their aggregates. 5] The interaction between meso-tetrakis(4-sulfonatophenyl)porphine (H2TPPS4, lmax = 412 nm, Figure 1) and an equimolar amount of [Ru(phen)3] 2+ (pH 6.0, NaCl (0.3m)) is indicated by variations in the absorption spectra of both [Ru(phen)3] 2+ and H2TPPS4. The strongest evidence of interaction, however, comes from the appearance of an induced circular dichroism (ICD) band in the absorption region (Soret band) of the achiral porphyrin (Figure 2). The relationship between chirality of the cationic metal complex and that transferred to the anionic porphyrins is straightforward because interactions of H2TPPS4 with the Land D[Ru(phen)3] 2+ lead to mirror-image ICD signals (Figure 2). At a pH value lower than 3 and in the presence of millimolar concentration of salt, the protonated species of H2TPPS4 (H4TPPS4, pKa 5, lmax = 436 nm) is zwitterionic and self-assembles to give both face-to-face (H, lmax = 422 nm) and edge-to-edge aggregates (J, lmax = 490 nm, Figure 3). Yashima and co-workers have shown very Figure 1. Structure of the anionic porphyrin H2TPPS4 and of the L and D enantiomers of [Ru(phen)3] .

Hierarchical Effect behind the Supramolecular Chirality of Silver(I)–Cysteine Coordination Polymers

Cysteine is a sulfur-containing amino acid that easily coordinates to soft metal ions and grafts to noble metal surfaces. Recently, chiroptical activity of Ag(+)/cysteine coordination polymers has been widely studied, while, on the other hand, the appearance of a plasmon-enhanced circular dichroic signal (PECD) at the plasmonic spectral region (λ > 400 nm) has been observed for AgNPs capped with chiral sulfur-containing amino acids. These two events are both potentially exploited for sensing applications. However, the presence of Ag(+) ions in AgNP colloidal solution deals with the competition of cysteine grafting at the metal NP surface and/or metal ion coordination. Herein we demonstrate that the chiroptical activity observed by adding cysteine to AgNP colloids prepared by pulsed laser ablation in liquids (PLAL) is mainly related to the formation of CD-active Ag(+)/cysteine supramolecular polymers. The strict correlation between supramolecular chirality and hierarchical effects, driven by different chemical environments experienced by cysteine when different titration modalities are used, is pivotal to validate cysteine as a fast and reliable probe to characterize the surface oxidation of AgNPs prepared by pulsed laser ablation in liquids by varying the laser wavelengths.

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.

Spontaneous deposition of polylysine on surfaces: Role of the secondary structure to optimize noncovalent coating strategies

Understanding the factors that governs spontaneous molecular transfer from solution to solid surface is fundamental to control noncovalent surface functionalization strategies, both in term of robustness and reproducibility. The comprehension of the nature of interaction involved in the mechanism of spontaneous adsorption will allow for a fine modulation of the deposition process. Herein, we provide experimental evidences to demonstrate that poly-lysine secondary structure represents a crucial factor profoundly influencing the outcome of its spontaneous deposition on quartz surfaces. In particular, random coil to α-helix transition is required to drive an effective transfer of the poly-l-lysine at the liquid-solid interface. β-sheet deposition requires longer times to be accomplished, while random-coil deposition is highly unfavored. Accordingly, polylysine deposition on quartz and silicon is effective when α-helix is formed in solution (pH>10). This surface noncovalent functionalization represents a simple strategy to fabricate hybrid organic-inorganic or biocompatible materials. In fact, the proposed methodology is proven robust and repeatable and compatible for combination with solution or vapor phases (i.e. MOCVD) nanomaterial deposition approaches.

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.

Vortexes tune the chirality of graphene oxide and its non-covalent hosts

Graphene oxide (GO) is one of the most appealing bidimensional materials able to interact non-covalently with achiral molecules and to act as chiral inducers. Vortexes can tune chirality and, consequently transfer a specific handedness to non-covalent host molecules, either when dispersed in water or when deposited on a solid surface.

Interactions of Λ and Δ enantiomers of ruthenium(II) cationic complexes with achiral anionic porphyrins

The interactions between Lambda and Delta enantiomers of ruthenium(II)-phenanthroline cationic complex ([Ru(phen)(3)](2+)) and three anionic porphyrins have been characterized by absorption, circular dichroism (CD), fluorescence, and resonance light scattering (RLS). The three porphyrins used in this study have been chosen for the different number (two or four) and reciprocal (symmetrical, cis or trans) disposition of the anionic (4-sulphonatophenyl) peripheral groups in the meso positions. All the techniques evidence the formation of inorganic-organic hybrids. In particular, CD and fluorescence measurements show that the inorganic moiety is able to transfer to porphyrins not only chirality (as shown from the appearance of an induced CD signal (ICD) in the absorption region of porphyrins) but, most likely, also energy.

ZnTPPS demetalation: Role of polyelectrolytes on aggregation after protonation in acid

Acid-base properties of tetra-anionic zinc meso-5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin (ZnTPPS) in presence of cationic and anionic polyelectrolytes are studied by UV-visible spectroscopy...

Spectroscopic characterization of water soluble phosphonato corrole: The effect of H-bounds on the self-assembled species

Hierarchical self-assembly of porphyrins is an intrigue research field, which can lead to the design of functional materials. Porphyrin derivatives self-assembling under hierarchical control allows to understand the principles governing molecular recognition processes, as demonstrated for meso-tetrakis(4-phosphonatophenyl)porphyne (H2TPPP) whose polyprotic nature is responsible for a pH-dependent hierarchical aggregation. Herein, self-assembly of meso-tris(4-phosphonatophenyl)corrole (TPPC) in aqueous solution has been spectroscopically studied and compared to that of TPPP. The corrole aggregation does not follow the hierarchical rules that govern the porphyrin counterpart due to the accessibility of the core of the macrocycle to protons, promoted by the reduced number of involved intermolecular H-bonds.