Fluorescent zinc(ii) complexes for gene delivery and simultaneous monitoring of protein expression

Two new zinc(ii) complexes, [Zn(l-His)(NIP)]⁺(1) and [Zn(acac)₂(NIP)](2) (where NIP is 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, acac = acetyl acetone), have been synthesized and characterized by elemental analysis, UV-vis, fluorescence, IR, ¹H NMR and electron spray ionization mass spectroscopies. Gel retardation assay, atomic force microscopy and dynamic light scattering studies show that 1 and 2 can induce the condensation of circular plasmid pBR322 DNA into nanometer size particles under ambient conditions. Treatment of 2 with 5 mM EDTA restored 30% of the supercoiled form of DNA, revealing partial reversibility of DNA condensation. The in vitro transfection experiment demonstrates that the complexes can be used to deliver pCMV-tdTomato-N1 plasmid which expresses red fluorescent protein. The confocal studies show that the fluorescent nature of complexes is advantageous for visualizing the intracellular delivery of metal complexes as well as transfection efficiency using two distinct emission windows.