Tuning the chiroptical and morphological properties of steroidal-porphyrin aggregates: a mechanistic, structural, and MM investigation

Synthesis and Direct Observation of Chiral Supramolecular Polymer of Porphyrin Having Cholesteryl Groups

We report the synthesis and microscopic investigations of two chiral helical porphyrin supramolecular polymers with different coordinating metals that are expected to be capable of serving as synthetic macromolecular motors driven by thermal fluctuations. Furthermore, based on their microscopic images, we propose a stepwise process for the formation of higher-order structures. These porphyrins formed completely different association states, and this was reflected in the marked differences in the shapes of the supramolecular polymers. The Cu-TChOAlaCPP supramolecular polymers formed H-aggregate rods in diisopropyl ether, then grew into superhelices and then into ribbons. On the other hand, Zn-TChOAlaCPP supramolecular polymers formed aggregates based on van der Waals interactions in diethyl ether, then grew into fibers and then grew into multiple-helices and ribbons. In addition, we imaged the interaction between long and short chains of the Cu-TChOAlaCPP supramolecular polymer by fast-scanning atomic force microscopy, and we indicated the availability as a macromolecular motor driven by thermal fluctuations.

Tunable Supramolecular Chirogenesis in the Self-Assembling of Amphiphilic Porphyrin Triggered by Chiral Amines

Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of the macrocycle (i.e., D- or L-proline moieties), in the presence of chiral amines as co-solute, such as chiral benzylamine derivatives. The aggregation process, steered by hydrophobic effect, has been studied in aqueous solvent mixtures by combined spectroscopic and topographic techniques. The results obtained pointed out a dramatic effect of these ligands on the morphology and on the supramolecular chirality of the final self-assembled structures. Scanning electron microscopy topography, as well as fluorescence microscopy studies revealed the formation of rod-like structures of micrometric size, different from the fractal structures formerly observed when the self-assembly process is carried out in the absence of chiral amine co-solutes. On the other hand, comparative experiments with an achiral porphyrin analogue strongly suggested that the presence of the prolinate moiety is mandatory for the achievement of the observed highly organized suprastructures. The results obtained would be of importance for unraveling the intimate mechanisms operating in the selection of the homochirality, and for the preparation of sensitive materials for the detection of chiral analytes, with tunable stereoselectivity and morphology.

Porphyrins Through the Looking Glass: Spectroscopic and Mechanistic Insights in Supramolecular Chirogenesis of New Self-Assembled Porphyrin Derivatives

The solvent driven aggregation of porphyrin derivatives, covalently linked to a L- or D-prolinate enantiomer, results in the stereospecific formation of species featuring remarkable supramolecular chirality, as a consequence of reading and amplification of the stereochemical information stored in the proline-appended group. Spectroscopic, kinetic, and topographic SEM studies gave important information on the aggregation processes, and on the structures of the final chiral architectures. The results obtained may be the seeds for the construction of stereoselective sensors aiming at the detection, for example, of novel emergent pollutants from agrochemical, food, and pharmaceutical industry.

The Self-Aggregation of Porphyrins with Multiple Chiral Centers in Organic/Aqueous Media: The Case of Sugar- and Steroid-Porphyrin Conjugates

An overview of the solvent-driven aggregation of a series of chiral porphyrin derivatives studied by optical methods (UV/Vis, fluorescence, CD and RLS spectroscopies) is herein reported. The investigated porphyrins are characterized by the presence in the meso-positions of glycol-, steroidal- and glucosteroidal moieties, conferring amphiphilicity and solubility in aqueous media to the primarily hydrophobic porphyrin platform. Aggregation of the macrocycles is driven by a change in bulk solvent composition, forming architectures with supramolecular chirality, steered by the stereogenic centers on the porphyrin peripheral positions. The aggregation behavior and chiroptical properties of the final aggregated species strongly depend on the number and stereogenicity of the ancillary groups that dictate the mutual spatial arrangement of the porphyrin chromophores and their further organization in larger structures, usually detectable by different microscopies, such as AFM and SEM. Kinetic studies are fundamental to understand the aggregation mechanism, which is frequently found to be dependent on the substrate concentration. Additionally, Molecular Mechanics calculations can give insights into the intimate nature of the driving forces governing the self-assembly process. The critical use of these combined methods can shed light on the overall self-assembly process of chirally-functionalized macrocycles, with important implications on the development of chiral porphyrin-based materials.

Tuning the morphology of mesoscopic structures of porphyrin macrocycles functionalized by an antimicrobial peptide

The aggregation properties of two peptide–porphyrin conjugates were investigated by optical spectroscopy and microscopy imaging with nanometer resolution. Specifically, a tetraphenylporphyrin platform was functionalized by (L)-magainin, a 23-residue long antimicrobial peptide, and by a (L)-magainin analogue differing from the parent peptide by a single residue substitution, [Formula: see text] an Ala vs. Phe replacement in the position 5 of the peptide chain. Spectroscopic and microscopy results show that this single-site substitution has a small effect on the secondary structure attained by the two peptide analogues, but deeply affects the morphology of the mesoscopic structures deposited on hydrophilic mica from methanol/water solutions. In particular, only the Ala-substituted peptide-porphyrin conjugate was shown to be able to form micrometric fibrils, coating homogeneously a hydrophilic mica surface. These results pave the way for potential applications of porphyrin-peptide compounds in localized photodynamic therapy and for designing solid-state stereoselective sensors.

Amphiphilic Porphyrin Aggregates: A DFT Investigation

Owing to the attractive potential applications of porphyrin assemblies in photocatalysis, sensors, and material science, studies presently concerning porphyrin aggregation are widely diffused. π–π stacking, H-bonding, metal coordination, hydrophobic effect, and electrostatic forces usually drive porphyrin interaction in solution. However, theoretical studies of such phenomena are still limited. Therefore, a computational examination of the different porphyrin aggregation approaches is proposed here, taking into account amphiphilic [5-{4-(3-trimethylammonium)propyloxyphenyl}-10,15,20-triphenylporphyrin] chloride, whose aggregation behavior has been previously experimentally investigated. Different functionals have been adopted to investigate the porphyrin dimeric species, considering long-range interactions. Geometry optimization has been performed, showing that for the compound under analysis, H-type and cation–π dimers are the most favored structures that likely co-exist in aqueous solution. Of note, frontier orbital delocalization showed an interesting interaction between the porphyrin units in the dimer at the supramolecular level.

Kinetic and spectroscopic studies on the chiral self-aggregation of amphiphilic zinc and copper (l)-prolinate-tetraarylporphyrin derivatives in different aqueous media

The chiral self-aggregation of (l)-proline porphyrin derivatives depends on both the nature of the media and the coordinated metal ion.

Hierarchical transfer of chiral information from the molecular to the mesoscopic scale by Langmuir–Blodgett deposition of tetrasteroid-porphyrins

Transfer of chiral information from the molecular level to the mesoscale has been obtained by hierarchical self-assembly of tetrasteroid-porphyrins.

β-Substituted ferrocenyl porphyrins: The role of the spacer and of the number of substituents on their structural and spectroscopic characteristics

Mono and bis ethynyl and ethynylphenyl [Formula: see text]-substituted porphyrins have been synthesized and characterized. Their conformational properties have been analyzed through a combination of NMR experiments and molecular mechanic calculations, while UV-Vis absorption and fluorescence measurements together with electrochemical studies allows us to probe the existence of intramolecular electronic processes. The role of the beta-substituents and of the spacer is underlined.