Abstract:
Background: Re(I) tricarbonyl complexes exhibit immense potential as fluorescence imaging agents. However, only
a handful of rhenium complexes have been utilized in biological imaging. The present study describes the synthesis
of four novel rhenium complexes, their characterization and preliminary biological studies to assess their potential as
biological imaging agents.
Results: Four facial rhenium tricarbonyl complexes containing a pyridyl triazine core, (L1 = 5,5′(3-(2-pyridyl)-1,2,4-
triazine-5,6-diyl)-bis-2-furansulfonic acid disodium salt and L2 = (3-(2- pyridyl)-5,6-diphenyl-1,2,4-triazine-4′,4′′-
disulfonic acid sodium salt) have been synthesized by utililzing two different Re metal precursors, Re(CO)5Br and
[Re(CO)3(H2O)3]OTf in an organic solvent mixture and water, respectively. The rhenium complexes [Re(CO)3(H2O)
L1]+ (1), Re(CO)3L1Br (2), [Re(CO)3(H2O)L2]+ (3), and Re(CO)3L2Br (4), were obtained in 70–85% yield and characterized
by 1H NMR, IR, UV, and luminescence spectroscopy. In both H2O and acetonitrile, complexes display a weak absorption
band in the visible region which can be assigned to a metal to ligand charge transfer excitation and fluorescent
emission lying in the 650–710 nm range. Cytotoxicity assays of complexes 1, 3, and 4 were carried out for rat peritoneal
cells. Both plant cells (Allium cepa bulb cells) and rat peritoneal cells were stained using the maximum non-toxic
concentration levels of the compounds, 20.00 mg ml−1 for 1 and 3 and 5.00 mg ml−1 for 4 to observe under the
epifluorescence microscope. In both cell lines, compound concentrated specifically in the nuclei region. Hence, nuclei
showed red fluorescence upon excitation at 550 nm.
Conclusions: Four novel rhenium complexes have been synthesized and characterized. Remarkable enhancement
of fluorescence upon binding with cells and visible range excitability demonstrates the possibility of using the new
complexes in biological applications.
