Fluorescent UO2(II) and ZrO(II) complexes: Synthesis, structural characterization, fluorescence, DNA binding studies and biological applications in cell probing

A new series of UO2(II) and ZrO(II) azo-complexes based on 5-nitro-8-hydroxyquinoline; [UO2(H2L1)(NO3)EtOH] (1), [ZrO(H2L1)(NO3)H2O] (2), [UO2(HL2)(NO3)EtOH]3H(2)O (3), [ZrO(HL2)(NO3)EtOH] (4), [UO2(HL3)(NO3)(H2O)(3)]2H(2)O (5) and [ZrO(HL3)(NO3)EtOH] (6); have been synthesized. The structure of these complexes has been characterized using elemental analysis, thermal analysis, molar conductance, UV-vis, IR, electron impact mass, X-ray powder diffraction and NMR spectra. The results revealed the formation of non-electrolyte mononuclear complexes via the N atom of the azo group or of the quinoline ring and the oxygen atom of the deprotonated OH. Fluorescence properties of the synthesized complexes have been examined and the fluorescence quantum yield (phi(f)) has been determined. The complexes have been tested as cell staining and imaging under the fluorescent microscope. The data showed that complexes 1 and 2 efficiently stain the nuclei in addition to some focal cytoplasmic areas. Other than complexes 3 and 4 exclusively stained the nuclei. On the other hand, complexes 5 and 6 stained the cytoplasm exclusively. It has been demonstrated that complex 4 was the most effective in cell staining. The binding constant (Kb) with DNA was calculated using UV-vis absorption titration and fluorescence spectral methods. It was concluded that complex 4 can be used effectively as fluorescent probes in studying cell biology.