Role of phenol derivatives in the formation of silver nanoparticles.

We demonstrate that dihydroxy benzenes are excellent reducing agents and may be used to reduce silver ions to synthesize stable silver nanoparticles in air-saturated aqueous solutions. The formation of Ag nanoparticles in deaerated aqueous solution at high pH values suggests that the reduction of silver ions occurs due to oxidation of dihydroxy benzenes and probably on the surface of Ag2O. Pulse radiolysis studies show that the semi-quinone radical does not participate in the reduction of silver ions at short time scales. Nevertheless, results show that primary intermediates undergo slower transformation in the presence of dihydroxy benzenes than in their absence. This slow transformation eventually leads to the formation of silver nanoparticles. The Ag nanoparticles were characterized by UV-vis absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and TEM techniques showed the presence of Ag nanoparticles with an average size of 30 nm.

Radical scavenging and catalytic activity of metal-phenolic complexes.

A series of metal-ligand complexes were prepared by the reaction of various metal ions, namely, Cu(II), Mn(II), or Fe(II) with phenolic derivatives of [catechol, chlorogenic acid (CGA), n-propyl gallate (nPG), 3-hydroxy anthranilic acid, resveratrol, and rutin] and characterized by UV-vis spectroscopy. The metal/ligand complexing ratio and complexation constants have been determined. The complexes were probed for their reactivity toward various free radicals (e aq-, CO2*-, and O2*-). Pulse radiolysis studies showed that the one-electron reduction of metal/phenol complexes by CO2*- radicals was metal-centered, and this was confirmed by the formation of an initial adduct with CO2*- radicals. Rate constants for the scavenging of superoxide anions with metal complexes ranged between 10(7)-10(9) dm3 mol(-1) s(-1) and those for the reaction of e aq- with the metal complexes were in the range of (1-5) x 10(9) dm3 mol(-1) s(-1), depending on the pH of the solution. Cyclic and differential pulse voltammetric studies showed that the reduction potential of the complexes are found to range between -0.022 to 0.45 V vs normal hydrogen electrode.