The Au containing nanocomposites were synthesized by UV irradiation followed by the thermal treatment of chitosan oligomer solutions doped by HAuCl 4 . The size of the formed gold nanoparti cles depends on the concentration of the dopant, which is proved by UV-Vis absorption spectrosco py and small angle X ray scattering (SAXS). The antioxidant activity of the gold nanoparticles with respect to hydroxy radicals significantly depends on the specific surface of the particles, which was found using the secondary radical spin trapping technique. The change in the • OH radical concen tration was monitored by the intensity of the ESR signal of the adduct of the spin trap (α phenyl N tert butylnitrone) with the Me • radicals formed in the reaction of • OH with DMSO.It is known 1 that gold nanoparticles exhibit high cata lytic activity in some oxidation reactions, such as low temperature CO oxidation, whereas gold as a compact metal is chemically inactive because of both the size effect and the character of interaction of the metal nano particles and support accompanied by the charge transfer between them. A change in the magnetic properties of metals in the nanosized state is of special interest. Previ ously 2 the superparamagnetic behavior of the palladium and gold nanoparticles incorporated into the polymer matrix of polyvinylpyrrolidone has been revealed, al though palladium is weakly paramagnetic and gold in the block state is a typical diamagnetic. Ferromagnetism (ferromagnetic spin polarization) of the gold nanoparticles was experimentally confirmed. 3 Similar changes in the pro perties of the metal on going to the nanosized state can be due to the dependence of the electronic structure on the particle size. The theoretical substantiation of the specif ic features of the electron states of the Au nanoparticles and the calculations proving the dependences of the Fermi energy on the particle size have been presented earlier. 4,5The interaction of the gold nanoparticles and the Au 3 and Au 13 clusters with organic radicals in alkanethiol hybrid systems was theoretically simulated. 4 Some pub lications concern the antioxidation effect of the gold nano particles stabilized by solutions of high molecular weight chitosan 6 and dendrimers 7 with respect to hydroxy radi cals. However, when studying these nanocomposites, a possible decrease in the hydroxy radical concentration due to intense chitosan destruction by hydrogen peroxide via the radical mechanism was ignored. 8,9 To exclude this effect, oligosaccharide of chitosan was used instead of the high molecular weight chitosan itself to stabilize the nanoparticles. Our preliminary experiments showed that the oligomer used underwent no changes under the experimental conditions.The purpose of this work is the ESR spectral study of the antioxidant properties of the gold nanoparticles in oligochitosan solutions depending on the particle size. ExperimentalThe gold nanocomposites were obtained in aqueous solutions of the chitosan oligomer doped by chloroauric acid (HAuCl 4 ) w...

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