Thermodynamic Properties and Electron Transfer of the Interaction Between Pyropheophorbide a Methyl Ester and Copper: the Nature of Binding Forces

Pyropheophorbide methyl ester (PPME) is clinically used as antitumor drug. Understanding of the strong interaction between PPME and Cu2+ could contribute to understand its pharmacodynamics and pharmacokinetics. The interaction between PPME and Cu2+ was investigated using fluorescence and UV-vis techniques. The binding constants of Cu2+ with PPME were determined at different temperatures depending on the fluorescence quenching results. Furthermore, the thermodynamic functions of standard enthalpy (ΔH0) and standard entropy (ΔS0) for the binding reaction were determined according to the van’t Hoff equation, which indicated that electron transfer, electrostatic, and hydrophobic interactions are important driving forces for PPME-Cu2+ association