Self-assembling of highly substituted 2-hydroxypropyl-β-cyclodextrin in the presence of in situ-formed iron oxide nanoparticles to produce magnetically ordered water-soluble supramolecular adducts

Abstract

High-substituted 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was shown to self-assemble in aqueous solutions in the presence of in situ-formed insoluble species of iron. Two different types of water-soluble high-molecular compounds were synthesized at room temperature in aqueous aerated alkaline solutions of (NH4)2Fe(SO4)2•6H2O and high-substituted 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) in the presence of NaH2PO2. These substances called adducts proved to be inorganic-organic hybrid nanospecies of iron species, HP-β-CD and encapsulated inorganic salts (sulfates and phosphates of sodium and ammonium). The adducts were established to show different properties and to have diverse compositions depending on the HP-β-CD: Fe molar ratio in starting solution. The first synthesized adduct (I) is characterized by an unambiguous magnetism with lower solubility in water. It gives a homogeneous solution with particles 400 nm in diameter. The second adduct (II) is not magnetic, more soluble in water, and forms nanoparticles of ∼760 nm in diameter. Both adducts are stable in aqueous solutions but totally destroyed in the presence of H2O2, K2S2O8, and AgNO3. By addition of BaCl2 excess to the aqueous solutions of I and II, the residue of BaSO4 is precipitated and dimensions of the particles of both types decrease up to ∼230 and ∼570 nm in diameter, respectively. Solids I and II were characterized by the data of X-ray diffraction (XRD), Mossbauer spectroscopy, SEM, IR-spectra, and magnetic measurements. Aqueous solutions of I and II were studied by means of mass-spectrometry (MALDI-TOF), dynamic light scattering (DLS) measurements, and analyzed by spectrophotometric titration with phenolphthalein.