Andrea Romeo

Scaling the Chirality in Porphyrin J-Nanoaggregates

Chiral porphyrin J-aggregates are confined into microemulsions, achieving a fine control of their size and optical properties. The quality of the circular dichroism signal exhibits a remarkable scaling on the dimension from the nano- up to mesoscopic regime.

Self-organizing functional materials via ionic self assembly: porphyrins H- and J-aggregates on synthetic chrysotile nanotubes.

Positively charged, synthetic chrysotile nanotubes act as inorganic tectons supporting H- and J-type aggregates of anionic porphyrins with markedly different optical properties, making these nanohybrid materials of interest for application in nanotechnology.

Scaling properties in the internal structure of dendrimer systems

In this work, we study the internal density distribution in a dendrimer or “starburst polymers” system at different generations. We have used different techniques like small angle X-ray scattering, quasi-elastic light scattering and a Molecular dynamics simulation. Obtained data, compared with the literature ones, proposed that lower generation dendrimers display an internal self-similar structure, whereas the higher generations tend to exhibit a spherical homogenous dense structure.

Sitting-Atop Metallo-Porphyrin Complexes: Experimental and Theoretical Investigations on Such Elusive Species

The interaction between the sodium cation and two meso-aryl porphyrins (tetraphenylporphyrin, TPP, and tetra(4-methoxyphenyl)porphyrin, TMPP) leads to the formation of new species that have been identified as Sitting-Atop (SAT) complexes, where the metal ion interacts with the N atoms of the porphyrin core without the concomitant deprotonation of the N-H groups. These species have been attained in low polarity solvent through the interaction of the porphyrin free bases with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), and investigated in situ through a combination of spectroscopic techniques, such as UV/vis absorption and fluorescence (static and time-resolved), resonance light scattering, FT-IR, and (1)H NMR. All spectroscopic evidence points to the occurrence of a single equilibrium between each parent compound and its SAT complex, ruling out the presence of other metallo-, protonated, or aggregated porphyrins in solution. The 1:1 stoichiometry of the adducts has been determined via continuous variation method (Jobs plot), and an estimate of the corresponding association constants in CH(2)Cl(2) at 298 K have been obtained by UV/vis titration (K(eq) = (9 +/- 4) x 10(5) L mol(-1) and (5 +/- 2) x 10(6) L mol(-1) for TPP and TMPP, respectively). Density-functional theory (DFT) calculations on SAT model complexes, [NaTPP(PF(6))] and [NaTMPP(PF(6))], have provided information on the molecular structure of these elusive species and on the nature and strength of the sodium-porphyrin interaction. It is found that the sodium ion is bound to the four nitrogen atoms of the porphyrin core. The involvement of the pyrrolic N atoms results in a modest but not negligible elongation of the N-H bonds, pyramidalization of the hydrogen atoms, and blue shift of the N-H stretching frequencies. Electronic structure and energy decomposition analysis reveal that covalent interactions, mainly consisting of porphyrin to sodium charge transfer interactions, are an important component of the sodium-porphyrin bond. Time-dependent DFT (TDDFT) calculations of the lowest excited states of the model systems provide an unambiguous interpretation of the absorption and emission properties of the experimentally identified SAT complexes.

Kinetic control of chirality in porphyrin J-aggregates.

Detailed kinetic investigations demonstrate the fundamental role of kinetic parameters in the expression and transmission of chirality in supramolecular systems. The rate of the aggregation process leading to the formation of J-aggregates strongly affects the size of these nanoassemblies and the chiral induction.

Kinetic effects of tartaric acid on the growth of chiral J-aggregates of tetrakis(4-sulfonatophenyl)porphyrin

The kinetics of growth for chiral J-aggregates of H(4)TPPS(4) porphyrin have been investigated under different experimental conditions in the presence of tartaric acid. The observed rate constants and the anisotropy factor g show a defined dependence on the enantiomer used as a chiral templating agent.

Supramolecular mimetic peroxidase based on hemin and PAMAM dendrimers

An acid-base interaction between hemin and PAMAM dendrimers affords supramolecular non-covalent peroxidase systems whose catalytic activity is enhanced after spontaneous electrostatic self-assembling onto a solid surface.

J-Type Aggregates of the Anionic Meso-Tetrakis(4-Sulfonatophenyl)Porphine Induced by ‚Hindered’ Cationic Porphyrins

Abstract Porphyrin aggregation is a field of wide interest owing to the possible technological and biomedical applications. Under these premises, the possibility of tuning and driving the assembly processes turns out to have a central role in achieving specific structures and, therefore, functions. Recently, we have demonstrated that self-aggregation of water-soluble porphyrins on opposite charged polymeric templates is not simply related to the tendency of a given porphyrin towards aggregation, but is driven by specific molecular recognition processes. 1–3

Micellar aggregates of platinum(II) complexes containing porphyrins

Abstract The complex [Pt(Cy2dim)Me]4(TpyP)(CF3SO3)4 (1) (Cy2dim=dicyclohexyldiimine; TpyP=5,10,15,20-tetrakis(4-pyridyl)-21H,23H-porphine) has been synthesized and characterized with a number of spectroscopic techniques. The solubilization of 1 in anionic (sodium dodecyl sulfate, SDS) and neutral (Triton X-100, TX-100) aqueous surfactant solutions has revealed two different modes of interaction: (i) aggregation in the hydrophobic region of SDS micelles; and (ii) aggregation in the hydrophobic region with partial intercalation in the solvent accessible area of TX-100 micelles. In the case of SDS, the formation of premicellar aggregates has been evidenced by a surfactant concentration range two orders of magnitude lower than the critical micellar concentration (cmc). The metalated Mn(III)TpyP derivative of complex 1 exhibits a moderate peroxidase activity in agreement with the aggregation models proposed for the micellar solutions.

Nucleation effects in the aggregation of water-soluble porphyrin aqueous solutions

Water soluble porphyrins bearing charged groups can be fostered to aggregate by simply screening the repulsive interactions between side-groups with the same charge. We have extensively studied the aggregation of synthetic porphyrins, which on changing the ionic strength give mesoscopic aggregates having a fractal behavior. The resulting structures can be modulated on changing the medium properties. Here we report on a kinetic study of such aggregation behavior on varying the salt concentration, the temperature and the history of the samples, showing the importance of the nucleation step in determining the growth of the aggregates.