Influence of pH on dendritic structure of strongly fluorescent persulfate-treated poly(amidoamine) dendrimer

The influence of pH on the dendritic structure of strongly fluorescent ammonium persulfate (APS)-treated poly(amidoamine) (PAMAM) dendrimers was examined. The APS-treated PAMAM dendrimers were prepared by aging of 0.2 mM aqueous solutions of a hydroxyl groups-terminated, generation-five PAMAM (G5OH) dendrimer together with 200 μl of 0.1 M APS solutions. The G5OH dendrimer showed an absorbance at 280 nm, which was red-shifted to 360 nm after APS treatment. The APS-treated G5OH dendrimer solutions emitted much stronger fluorescence than the pristine G5OH dendrimer solutions when irradiated at 360 nm. The pH of the G5OH dendrimer solution is 7.6 while that of the APS-treated G5OH dendrimer solution is 5.2. The pore surface of both pristine and fluorescent G5OH dendrimers was altered more significantly under acidic than basic conditions. The tertiary amine groups of the pore surface of the fluorescent G5OH dendrimers were protonated by APS treatment as well as under the acidic condition; therefore, the pore surface of the G5OH dendrimer was filled with tertiary ammonium cations, which were, however, further deprotonated under basic conditions. The sulfur anions (VI and II) were generated during the hydrolysis of APS, which were interacted with the G5OH dendrimers under both acidic and basic conditions.