Metal Dipicolylamines and their Biomedical Applications: A Mini Review

Abstract

Research in synthetic inorganic chemistry demonstrates that metal complexes are widely utilized as therapeutic as well as diagnostic agents. Due to the coordinative saturation, substitutional inertness, and unique redox characteristics, metal polypyridyl complexes have ignited attention and have been exploited in a number of biological and biomedical fields. The polypyridyl ligand, dipicolylamine (DPA) is a symmetrical secondary amine with two pyridyl rings. Delocalization of excited electrons occurs throughout the ligand system due to its conjugated character and the metal-to-ligand charge transfer transitions, resulting in a strong fluorescence signal. The high lipophilic nature of this ligand has proven to improve metal-DPA complex absorption by cell membranes. The N–H amine group in DPA and its analogues have the additional function of allowing hydrogen bonds to form, and deprotonation of this amine has allowed the creation of mononuclear and polynuclear species, with deprotonation of the bridging amine nitrogen also playing a significant role in the coordination sequence. DPA-appended metal complexes have garnered attention in the quest for linkages between magnetic, spectroscopic, structural, and coordination geometries. A number of mononuclear metal-DPA complex crystal structures with four, five, or six coordinated metal centers have been synthesized and explored for their biological properties. This study reviews DPA-derivatized ligand-linked metal complexes as promising cancer, microbial, and fungal inflammatory therapeutics, as well as potential diagnostic agents for fluorescence imaging and radiopharmaceuticals. Keywords: Dipicolylamine, metal complexes, coordination geometries, fluorescent agents