Protonation of 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphine in Water

Abstract

Protonation equilibriums of the porphyrin core H 2 P in H 2 P(PhSO 3 - ) 4 with perchloric acid in water are investigated by methods of spectropotentiometry and computer chemistry (DFT/B3LYP and РМ3). It is shown that leveling of step constants is caused by formation of aquacomplex [H 4 P 2+ (PhSO 3 - ) 4 ](H 2 O) 2 of diprotonated porphyrin platform showing properties of anion-molecular receptor. Values of lgK 1 (4.85 ± 0.03), lg(K 2 ·K 3 )(1.22 ± 0.03) are defined, and rough value of lgK 2 (-0.23) for reactions H 2 P + H + H 3 P + (1); H 3 P + + H + H 4 P 2+ (2); H 4 P 2+ + 2H 2 O [H 4 P 2+ ](H 2 O) 2 (3) is calculated. Molecular parameters [H 4 P 2+ (PhSO 3 - ) 4 ](H 2 O) 2 are calculated and it is established that receptor H 4 P 2+ possesses very high complementarity concerning two water molecules.