Invertion and methylation of pyrrole ring in tetrasulfophenylporphyrin: basicity, aggregation properties, chirality

Abstract

Equilibria of methylated N-confused platform of 2-N-methyl-5,10,15,20-tetrakis-(4′-sulfophenyl)-2-aza-21-carbaporphyrin tetraanion HMeIP(PhSO3H)4 platform diprotonation by perchloric acid in water, H– and J-aggregates self-assembly were investigated using synchronous UV–Vis-fluorescence-pH titration and DFT/B3LYP/6-31++G(d,p) calculations. Methylation of inverted pyrrole ring in H2IP(PhSO3−)4 allows to fix the tautomer HMeIP(PhSO3−)4 with external NH-proton. Intramolecular tightness causes formation of two bifurcated NHN IMHB between pyrrole hydrogen and pyrrolenine nitrogen of platform HMeIP(PhSO3−)4. IMHB protect intramolecular centers of hydrogen bonding from intermolecular interactions. First stage of HМеIP(PhSO3−)4 protonation is accompanied by bifurcated IMHB type change from NHN to HNH. On the second protonation stage IMHB are broken and intermolecular hydrogen bonds with solvent molecules are formed. Diprotonated H3МеIP2+(PhSO3−)4 platform is a flexible 1,3-alternate, possessed molecular and anion receptor properties. Equilibrium in the second stage of protonation in water is completely shifted to the aquacomplex, which is formed due to hydrogen and electrostatic binding of the solvent molecules at the both receptor sites. Methylation and invertion of pyrrole ring leads to HMeIP(PhSO3−)4 proton affinity increasing and eliminated the phenomena of synchronous H2P(PhSO3−)4 porphyrin platform diprotonation, which is due to more stable aquacomplex [H4P2+(PhSO3−)4](H2O)2 formation. Initial tetraanion HMeIP(PhSO3−)4 and aquacomplex [H4IP2+(PhSO3−)4](H2O)2 are monomers of H- and J-aggregates self-assembly. Driving force of H-aggregates formation is the ionic self-assembly between sulfonate groups of monomers and spacer cations. J-aggregates self-assembly is due to formation of more stable anion complexes as a result of water molecules intermolecular substitution in [H3MeIP2+(PhSO3−)4](H2O)2 by monomers sulfonate groups. Protonated chitosan was used as a inducer and chiral scaffold of CW-H- and tubular CW-J-aggregates (porphyrin nanotubes) self-assembly. Parameters of CW-H- and CW-J-dimers geometry were calculated and 3D models of H-aggregates and porphyrin nanotubes were developed on their basis.