Protonation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine in water

Abstract

Protonation equilibriums of the porphyrin core H2P in H2P(PhSO3-)4 with perchloric acid in water are investigated by methods of spectropotentiometry and computer chemistry (DFT/B3LYP and PM3). It is shown that leveling of step constants is caused by formation of aquacomplex [H4P2+(PhSO3-)4](H2O)2 of diprotonated porphyrin platform showing properties of anion-molecular receptor. Values of K1 (4.85 ± 0.03), K2·K3(1.22 ± 0.03) are defined, and rough value of K2 (-0.23) for reactions H2P + H+ H3P+ (1); H3P+ + H+ H4P2+ (2); H4P2+ + 2H2O [H4P2+](H2O)2 (3) is calculated. Molecular parameters [H4P2+(PhSO3-)4](H2O)2 are calculated and it is established that receptor H4P2+ possesses very high complementarity concerning two water molecules. © ISUCT Publishing.