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

Abstract

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.

Chirality induction to achiral molecules by silica‐coated chiral molecular assemblies

“…For such ICD to be observed, the dye molecules need to be closely packed, giving an exponential growth of the signal versus surface concentration of the dye. This is also confirmed by the recent results reported by us and others on the chiral aggregation of porphyrin‐based systems, which feature sensibly larger g values, that scales with the dimensions of the aggregates 27–29 . In contrast, when the dyes are incorporated inside the surfactant assembly, the chiral organization of the dyes is induced by the chiral environment of the surfactant 19 .…”

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

“…The chirality of the self-assembled structures still depends on the stereochemistry of the amine present in solution, but with CD bands of reduced intensities of about one order of magnitude, and of simple bisignated pattern. Finally, it is important to mention, as reported in our previous studies [32], that the aggregation of (L)ZnP(-) and (D)ZnP(-) carried out without chiral amines proceeds through alike biphasic autocatalytic mechanism, leading to final architectures featuring intense supramolecular chirality, depending on the stereochemistry of the proline appended functionality.…”

“…This material could be carefully collected and placed onto an aluminum stub surface for an SEM topographic investigation, or drop casted onto a microscope glass slide, for a fluorescence or fluorescence microscopy analysis. Both techniques showed the formation of peculiar structures, in the form of dense bundles of weed-like nanorod-type species with about 10 µm in length, and ca 150-200 nm width (Figure 4a-c), strikingly different from those obtained for the aggregation carried out without chiral amine dopants [32]. resulted in a fast aggregation step, virtually completed within the time of samples preparation, both in the absence and in the presence of external co-ligands.…”

“…Synthesis of the porphyrins was accomplished by following procedures reported by our group [8,32], which relies on straightforward procedures used in peptide chemistry. As a first stage, the 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (H 2 pCTPP) was reacted with (L)-or (D)-proline tert-butyl ester using the EDCl/HOBT coupling reagents, providing the corresponding prolinated derivatives which were subsequently hydrolyzed in a TFA/CH 2 Cl 2 mixture to give the amphiphilic compounds (L)H 2 P(-) and (D)H 2 P(-).…”

“…Along this line, we were interested in the study of the aggregation process of amphiphilic tetraphenylporphyrin derivatives, functionalized by chiral polar or ionic functionalities such as sugars [22][23][24], steroids [25][26][27][28] or charged proline derivatives [29][30][31], acting as stereochemical information to be recognized and efficiently transmitted during the stereospecific formation of the final supramolecular mesoscopic structures. Very recently, we investigated the self-assembly behavior of intrinsically chiral zinc-tetraphenylporphyrin derivatives, characterized by the presence of covalently linked enantiomers of anionic Lor D-prolinate groups on the molecular frame [32] (Chart 1).…”