Counterintuitive Solid-State Syntheses of Indium-Thiolate-Phen Cations as Efficient and Selective Fluorescent Biosensors for HIV-1 ds-DNA and Sudan Ebolavirus RNA Sequences

Coordination compounds [In(Tab)(2)(Phen)(2)](PF6)(3) (2), [In(Tab)(2) (Phen)(2) , In(Tab)(4)(Phen)](OAc)(6) (3) and [In(Tab)(4)(Phen)](OAc)(3) (4) (Tab= 4-(Trimethylammonio) benzenethiolate; Phen-1,10-Phenanthroline) are formed via a counterintuitive solid-state synthesis involving the mix of In(OAc)(3), TabHPF(6) and Phen in various stoichiometries. The Tab-to-Phen ratios of 2 - 4 are opposite to the TabHPF(6)-to-Phen ratios of the starting materials. By comparison, the corresponding solution-state reactions provide 4 exclusively at high concentrations, and otherwise the Phen-free [In(Tab) (4)](OAc) (3) (1). Reaction of In(OAc) (3), TabHPF(6) and a bulkier Dpphen (Dpphen= 4,7-Diphenyl-1,10-phenanthroline) ligand in the solid state give [In(Tab)(2)(Dpphen)(2)](PF6)(3) (5) exclusively, regardless of the reaction stoichiometry. Compounds 2, 4 and 5 associate with two fluorophore carboxyfluorescein (FAM) probe labelled DNA fragments (P-DNAs) through electrostatic, p-stacking and/or hydrogen-bonding interactions, forming P-DNA@ 2, P-DNA@ 4 and P-DNA@ 5 hybrids that quench the fluorescence of FAM via a photo-induced electron transfer process. These hybrids are further used as efficient and selective "turn-on" fluorescent sensors for HIV-1 ds-DNA and Sudan Ebolavirus RNA sequences with detection limits in the pM-nM range.