Abstract
BackgroundRe(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.ResultsFour 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.ConclusionsFour 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.Graphical abstractMicrograph of rat peritoneal cells incubated with novel rhenium complex under epifluorescence microscope. Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-016-0218-4) contains supplementary material, which is available to authorized users.
Highlights
Re(I) tricarbonyl complexes exhibit immense potential as fluorescence imaging agents
Many Re(I) carbonyl complexes synthesized in recent years exhibit luminescent properties [7, 14, 20–24, 26] which is believed to originate from the metal-to-ligand charge transfer (MLCT) transitions [20–22, 28]
Strong peaks in the 2035 to 1880 cm−1 range in FTIR spectra obtained for metal complexes are characteristic to the three carbonyl peaks in the metal coordination sphere and confirm the presence of the fac-Re(CO)3+ core [1]
Summary
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 in the nuclei region. Nuclei showed red fluorescence upon excitation at 550 nm
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