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Water-soluble dendritic-conjugated polyfluorenes: Synthesis, characterization, and interactions with DNA Part A Polymer chemistry

Yu, Minghui, Liu, Libing, Wang, Shu
Journal of polymer science 2008 v.46 no.22 pp. 7462-7472
DNA, absorption, dimethyl sulfoxide, dioxane, ethidium, fluorescence, gel chromatography, hydrochloric acid, molecular weight, polymers, solvents
Three generation of Boc-protected dendritic-conjugated polyfluorenes (Boc-PFP-G₀₋₂) were synthesized by Suzuki coupling 1,4-phenyldiboronic ester with dendritic monomers that were synthesized through generation-by-generation approach. The gel permeation chromatography (GPC) analyses showed that the weight-average molecular weight (Mw) of Boc-PFP-G₀₋₂ was in the range of 11,400-20,400 Da with the polydispersity index (PDI) in the range of 1.32-1.96. Treatment of Boc-protected polymers with 6 M HCl in dioxane yielded cationic dendritic-conjugated polyfluorenes (PFP-G₀₋₂). They were soluble in common polar solvents such as DMSO, DMF, and water with absorption maxima between 345 and 379 nm. The solutions of PFP-G₀₋₂ in water were highly fluorescent with emission maxima between 416 and 425 nm. Because higher generation dendrons could prevent the formation of π-stacking aggregates of backbones of conjugated polymer, the fluorescence quantum efficiencies (QEs) of PFP-G₀₋₂ enhance as the dendritic generation grew. The interactions between 25 mer double-stranded DNA (dsDNA) and PFP-G₀₋₂ were studied using ethidium bromide (EB) as fluorescent probe. The electrostatic bindings of PFP-G₀₋₂ with dsDNA/EB complex result in displacement of EB from DNA double helix to the solution accompanying by a quenching of EB fluorescence. The PFP-G₂ with highest generation of dendritic side chains possessed a highest charge density and could form most stable complex with dsDNA.