Optical properties of a paramagnetic metalloporphyrin hematoporphyrin monomethyl ether coordinated to divalent manganese metal ion

Metalloporphyrins with paramagnetism are becoming research focus because their potential use in biomedical field as fluorescence probes and the magnetic resonance imaging (MRI) contrast agents. Divalent manganese metal ion (Mn 2+ ) has a half-filled 3d shell with a strong paramagnetic effect. To investigate whether porphyrins coordinated to Mn 2+ can serve as multiple functional probes, hematoporphyrin monomethyl ether coordinated to Mn 2+ (Mn-HMME) was synthesized and its characterization, MRI enhancement property, luminescence property and photosensitivity were studied. Mn-HMME was characterized by UV-visible spectrum and Fourier transform infrared spectrum. It was found that the number of Q bands in the absorption spectrum of Mn-HMME reduced to two compared to free HMME. From the Fourier transform infrared spectrum of Mn-HMME, the characteristic infrared absorption peak of N-H bond in HMME at 970 cm -1 disappears, but the nitrogen-metal characteristic absorption peaks (1114 cm -1 and 1093 cm -1 ) were observed. The MRI of Mn-HMME indicates that Mn-HMME has relatively strong MRI enhancement effect. From luminescence spectroscopic analysis, the fluorescence emission of Mn-HMME was weaker than that of free HMME but still detectable. This may be caused by the energy transfer from free HMME to Mn 2+ . The test of photosensitivity of Mn- HMME denotes that the photosensitivity of Mn-HMME disappears. Our results indicate that Mn-HMME has the potential as a multiple functional probe in both fluorescence imaging and MRI.