"Chelating molecular imaging probe amino polycarboxylic acid-manganese (II) complexes: as potent photoluminescent materials for imaging"

Abstract

Background: The most used gadolinium and manganese-based contrast agents improve the visibility of internal cell body structures in MRI. To overcome the nephrogenic systemic fibrosis (NSF) related to renal impairment, we are in the race to find safer MRI contrast agents. The utilization of some paramagnetic transition metal ions, Mn²⁺ and Fe³⁺ that may effectively relax the water protons is a potential strategy for developing substitute contrast agents for Gd³⁺chelates and these metals are less harmful than Gd³⁺. This investigation concentrates on synthesis of DTPA and EDTA-based manganese complexes with two different poly amino carboxylic acids to enhance as potential contrast agents with further studies.

Methods: DTPA/EDTA anhydrides and respective amino substituted ligands were prepared under nitrogen atmosphere and complexes were prepared by reflux method at pH 8.4 using 1N NaHCO₃ solution which was characterized by UV-visible, FTIR, ¹H NMR, ESR, and TGA studies.

Results: FT-IR analysis shown 510 cm^-1 M-O bond and shifting of the ranges observed on comparing ligand and metal studies which confirmed the metal complex formation. 10.5 – 10.6 ppm for COOH group and 5.8 – 5.9 ppm for N-H group confirm the formation of poly amino carboxylic acid ligands with DTPA/EDTA. Nuclear spin I=5/2 reveals the 3d⁵ electronic configuration for Mn. The Mn complexes have shown good thermal stability, and EDTA complexes have good bacterial-resistant activity. Both DTPA/EDTA complexes have good fluorescence activities.

Conclusion: The manganese-based complexes showed good resistance against both Gram positive and Gram negative bacteria which are well-suited to human body, with excellent emissions of complexes that may lead to further studies for imaging agents.