Supramolecular Chirality in Solvent‐Promoted Aggregation of Amphiphilic Porphyrin Derivatives: Kinetic Studies and Comparison between Solution Behavior and Solid‐State Morphology by AFM Topography

Abstract

The solvent-promoted aggregation behavior of some amphiphilic porphyrin derivatives bearing chiral functionality in the form of a charged L-proline group has been investigated by UV/Vis, resonance light scattering, fluorescence and circular dichroism spectroscopy. The investigated macrocycles give rise to aggregates featuring supramolecular chirality with high ellipticity. Kinetic studies reveal peculiar differences in the fashion of aggregation, depending on the intimate nature of the chiral functionality, namely, cationic (nitrogen-quaternized L-proline, 3H(2)) or anionic (carboxylate residue, 6H(2)) group. Formation of anionic 6H(2) aggregates shows a diffusion-limited kinetic behavior. AFM topography studies show formation of tighter globular structures. On the other hand, the corresponding 3H(2) aggregates are formed by a cooperative, fractal-type decay, and appear as long-fibrous, looser structures. In the templated aggregation of 3H(2) over preformed 6H(2) aggregates, AFM images show formation of globular structures with reduced sizes, as a likely consequence of shorter interchromophore distances, due to favorable Coulombic interactions. The results obtained show an interesting parallelism between the solution behavior and the solid-state aggregate structures, corroborating the sergeant-soldier effect observed in the templated aggregation. The results presented give important insights for understanding the complex mechanisms involved in these issues, which are of key importance for the development of chiral supramolecular materials and stereoselective sensors and devices.

AFM imaging, fractal analysis and in vitro cytotoxicity evaluation of Zn(II) vs. Cu(II) porphyrins

“…Atomic force microscopy (AFM) measurements of various type of porphyrinic compounds [6,7] and in particular on metalloporphyrins [8] proved to be an important tool for investigating their nanometric scale aggregates and self assembly. In order to quantitatively characterize the morphology of complex surfaces it can be used one of the modern conceptsscaling.…”

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

“…For many years, we have focused on the possibility to build up chiral porphyrin suprastructures by assembling inherently chiral porphyrin derivatives having single or multiple stereogenic centers peripherally located on the macrocycle thanks to the conjugation with diverse biomolecules, as amino acids, glucosides or steroids [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. The self-aggregation of these compounds was induced in organic/aqueous mixtures by the so-called “good-bad” solvent protocol, in which porphyrins solubilization in a “good” solvent is followed by the addition of the proper amount of a “bad” one, where typically the macrocycle is insoluble, even at low concentrations.…”

Amphiphilic Porphyrin Aggregates: A DFT Investigation

“…Operating carefully within the experimental parameters, i.e., concentration of porphyrin solutions, type, and order of addition of the two solvents and time, assemblies with different structures can be achieved [27,28]. We typically used ethanol/water or dimethylacetamide/water solvent combinations at proper water contents to drive the formation of ordered porphyrin suprastructures by hydrophobic effect [21,[29][30][31][32].…”