title: Interfacial Hydrogen Atom Transfer by nanohybrids based on Humic Acid Like Polycondensates.
abstract: Novel nanohybrid materials were prepared by covalent grafting of a polyphenolic polymer [Humic Acid Like Polycondensate (HALP)] on SiO2 nanoparticles. Four nanohybrids were so-produced, using four different types of SiO2 i.e. three Aerosil flame-made nanoparticles with nominal specific surface area of 50, 90 and 300 m(2)/g, herein codenamed OX50, A90, A300 respectively, plus a colloidal SiO2[S300] with SSA=300 m(2)/g. The antioxidant activity of the SiO2-HALP nanohybrids was evaluated by assessing their kinetics for Hydrogen Atom Transfer [HAT] to DPPH radicals. When normalized per same HALP concentration, bigger NPs SiO2[OX50]-HALP NPs can scavenge 280 μmoles of DPPH radicals per gram of HALP, while [A90]-HALP and [A300]-HALP NPs can scavenge 514 and 832 μmoles of DPPH radicals per gram of HALP, respectively. The colloidal SiO2[S300]-HALP can scavenge fewer DPPH radicals (252 μmoles) per gram of HALP. Based on detailed kinetic data it is shown that (i) surface grafted HALPs perform 300% better HAT than non-grafted HALP in solution. (ii) By controlling the particle type and grafting-loading, we can control/optimize the HAT performance: when grafted on the appropriate SiO2 surface the HALP macromolecules are able to quench up to 0.8 mmoles of DPPH-radical per gram of HALP.
authors.affiliation: Department of Physics, University of Ioannina, GR-45110 Ioannina, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Bletsa
authors.affiliation: Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
authors.forename: Panagiota
authors.initials: P
authors.lastname: Stathi
authors.affiliation: Department of Materials Science & Engineering, University of Ioannina, GR-45110 Ioannina, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Dimos
authors.affiliation: Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Louloudi
authors.affiliation: Department of Physics, University of Ioannina, GR-45110 Ioannina, Greece. Electronic address: ideligia@cc.uoi.gr.
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Deligiannakis
mesh_terms: D001713:Biphenyl Compounds / Q000037:antagonists & inhibitors / Q000737:chemistry; D003102:Colloids; D016166:Free Radical Scavengers / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis*; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D053758:Nanoparticles / Q000737:chemistry*; D010851:Picrates / Q000037:antagonists & inhibitors / Q000737:chemistry; D059808:Polyphenols / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D001713:Biphenyl Compounds; D003102:Colloids; D016166:Free Radical Scavengers; D006812:Humic Substances; D010851:Picrates; D059808:Polyphenols; D012822:Silicon Dioxide; D006859:Hydrogen; C004931:1,1-diphenyl-2-picrylhydrazyl
keywords: EPR; HALP; Hydrogen-Atom-Transfer; Nanohybrid; PCET; SiO(2)