Chiral Amphiphilic Secondary Amine-Porphyrin Hybrids for Aqueous Organocatalysis

Abstract

Two chiral proline-derived amphiphilic 5-substituted-10,15,20-tris(4-sulfonatophenyl)porphyrins were prepared, and their pH-dependent supramolecular behavior was studied. In neutral aqueous solutions, the free-base form of the hybrids is highly soluble, allowing enamine-based organocatalysis to take place, whereas under acidic conditions, the porphyrinic protonated core of the hybrid leads to the formation of self-assembled structures, so that the hybrids flocculate and their catalytic activity is fully suppressed. The low degree of chirality transfer observed for aqueous Michael and aldol reactions strongly suggests that these reactions take place under true “in water” organocatalytic conditions. The highly insoluble catalyst aggregates can easily be separated from the reaction products by centrifugation of the acidic reaction mixtures, and after neutralization and desalting, the sodium salts of the sulfonated amine-porphyrin hybrids, retaining their full catalytic activity, can be recovered in high yield.

Synthesis, Characterization, X-ray Molecular Structure, Antioxidant, Antifungal and Allelopathic Activity of a new Isonicotinate-derived meso-Tetraarylporphyrin

“…This procedure is somewhat more practical than the one described a few years ago by V. I. Potkin and co-workers [24], that involves the previous preparation of isonicotinoyl chloride hydrochloride. Spectroscopic data for 4 ( 1 H and 13 C NMR, HRMS-ESI) fully coincided with those in the literature [24]. Condensation of this aldehyde with freshly distilled pyrrole was performed according to the Adler and Longo method (reflux in propionic acid under open air, followed by chromatographic purification; silica gel, DCM/methanol 93:7) [16], afforded the free base porphyrin 1 in a remarkable 29% yield.…”

“…This compound was fully characterized by IR, 1 H-NMR, and 13 C-NMR spectroscopy, and by HRMS-ESI spectrometry. A detailed discussion of its spectroscopic properties can be found in the Supporting Information.…”

“…The presence of porphyrins in myriad biological systems, coupled with the ability to finely tune their chemical and physical properties, position both free base porphyrins and metalloporphyrins as adaptable materials and as crucial for scientific investigations. The deep-rooted biological importance of these tetrapyrrolic macrocycles and their exceptional electronic and structural properties have spurred their widespread utilization, encompassing their use as photosensitizers in photodynamic therapy [1,2] and in functionalization reactions [3,4], as sensors [5,6], in solar cells [7,8], and more recently, as organocatalysts [9][10][11][12][13] and as photoredox catalysts [4,14,15]. The availability of a large number of porphyrins and metalloporphyrins in these applications is made possible mainly thanks Disclaimer/Publisher's Note: The statements, opinions, and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s).…”

Synthesis of New Amino-Functionalized Porphyrins:Preliminary Study of Their Organophotocatalytic Activity

“…In the context of our research program on novel catalytic applications of porphyrins, [ 24 , 25 , 26 ] we have disclosed that the organocatalytic activity of both achiral [ 27 ] and of chiral [ 28 ] cyclic secondary amines linked to a 4-sulfonatophenylporphyrin scaffold can be efficiently regulated by the pH of the medium, which controls the aggregation state of the amphiphilic porphyrin moiety ( Figure 1 ).…”

Photocatalytic Water Splitting Promoted by 2D and 3D Porphyrin Covalent Organic Polymers Synthesized by Suzuki-Miyaura Carbon-Carbon Coupling

“…Neutral porphyrin ring (H 2 P) can protonate or deprotonate the nitrogen present in the pyrrole rings that form the porphyrin moieties and thus, this causes a change in their photophysical and electrochemical properties. It is described in the literature that at pH under 4.5, meso-porphyrins protonate (H 4 P 2+ ), and at pH above 10, porphyrin rings lose the two initial protons (P 2− ) [57,58]. After screening pH dependence in the hydrogen formation rate, it has been obtained that the optimal pH for water splitting reaction is between pH 6 and 8.…”