Synthesis of zinc porphyrins and effect of peripheral substituents on the coordination reaction

Abstract

Three free-base porphyrins, modified with Boc-d-threonine and their zinc porphyrins have been synthesized using benzaldehyde, 4-chlorobenzaldehyde, and 4-methoxybenzaldehyde. The effects of peripheral substituents on the coordination reactions between zinc porphyrins and imidazole derivatives have been studied by UV-visible spectroscopy, fluorescence spectrometry, and theoretical calculations. The results show that the coordination reaction forms a Zn-N bond between zinc porphyrins involving different peripheral substituents and imidazole derivatives. The association coordination constants decrease (N-MeIm > Im) due to the change in enthalpy; the zinc porphyrin synthesized using 4-chlorobenzaldehyde and N-methylimidazole shows the largest association constant. Fluorescent quenching is observed during the coordination process with the zinc porphyrin synthesized using 4-methoxybenzaldehyde and N-methylimidazole showing the largest Stern-Volmer quenching rate constant. In addition, theoretical calculations have been used to investigate essential characteristics of the reaction, charges, bond lengths, and bond energies for each system.