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

Wang, Shujun ; Peng, Yuling ; Zhang, Chenggen ; Li, Yongbing ; Liu, Chao

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.

Keyword(s)

Coordination chemistry, Theoretical chemistry, Porphyrins, Zinc porphyrins, UV-visible spectroscopy, Fluorescence quenching

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