Poly acrylic acid sodium salt paa

Quercetin (Que) (purity ≥ 95%, HPLC), cobalt(II) perchlorate hexahydrate (purity ≥ 98%), 4-morpholinepropanesulfonic acid (MOPS) (purity ≥ 99.5%, titration), dimethyl sulfoxide for spectroscopy (DMSO) (purity ≥ 99.8%), and poly(acrylic acid sodium salt) (PAA) (average Mw ~5100, GPC, purity ≥ 99%) were purchased from Sigma-Aldrich and used without purification. Stock solutions of Que were prepared in pure DMSO and then properly diluted in a buffered aqueous solution (pH 7.4, MOPS 10 mM) to have a final organic solvent content of only 5% v/v. Buffer solutions were prepared by weighing proper amounts of MOPS and titrating with a sodium hydroxide solution to the desired pH. All Que solutions were always freshly prepared and stored in the dark to avoid possible light-induced alterations. The cobalt(II) stock solution was prepared by dissolving the corresponding perchlorate salt in water and titrating the resulting solution with standard EDTA, using orange xylenol as an indicator [60 ]. Poly(acrylic acid) stock solutions were prepared at pH 7.4 in MOPS 10 mM; the concentration of the polymer was expressed per monomer unit of acrylic acid. High-purity water (Millipore, Milli-Q Element A 10 ultrapure water) and A-grade glassware were employed throughout.