title: Synthesis and characterization of novel rhenium(I) complexes towards potential biological imaging applications.
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 by1H 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 complexes1,3, and4were carried out for rat peritoneal cells. Both plant cells (Allium cepabulb cells) and rat peritoneal cells were stained using the maximum non-toxic concentration levels of the compounds, 20.00 mg ml-1for1and3and 5.00 mg ml-1for4to 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.Graphical abstractMicrograph of rat peritoneal cells incubated with novel rhenium complex under epifluorescence microscope.
authors.affiliation: Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka.
authors.forename: Kokila
authors.initials: K
authors.lastname: Ranasinghe
authors.affiliation: Institute of Biochemistry, Molecular Biology and Biotechnology, University of Colombo, Colombo, Sri Lanka.
authors.forename: Shiroma
authors.initials: S
authors.lastname: Handunnetti
authors.affiliation: Department of Zoology and Environmental Sciences, University of Colombo, Colombo, Sri Lanka.
authors.forename: Inoka C
authors.initials: IC
authors.lastname: Perera
authors.affiliation: Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka.
authors.forename: Theshini
authors.identifier: 0000-0002-0624-4984
authors.initials: T
authors.lastname: Perera
keywords: Cytotoxicity; Fluorescent; NMR spectroscopy; Rhenium tricarbonyl