Antioxidant-potentiality of gold–chitosan nanocomposites
Introduction
Preparation of noble metal nanoparticles by reducing metal salts has been extensively studied [1]. To stabilize dispersion of nanoparticles, it is necessary to use protective agents, such as polymers, surfactants, and chelating agents. These nanoparticles have widely been studied with a view to improve the quality of catalysts.
All living organisms are suffered from the damage caused by the free-radical oxygen species. Free-radical oxygen species damage cells by attacking unsaturated fatty acids in the cell membrane. Fortunately, a protective enzyme, superoxide dismutase, completely converts these free-radical oxygen species into two water molecules and oxygen [2], [3]. However, it is known that superoxide dismutase tissue levels decrease with aging. So, it is a challenging task to develop new catalysts for the elimination of active radical species.
Chitin, poly-B-(1,4)-n-acetyl-d-glucosamine, is a cellulose-like biopolymer widely distributed in nature, especially in marine invertebrates, insects, fungi, and yeasts. Chitin also has unique properties, including toughness, bioactivity, and biodegradability. Recently, chitosan, which is deacetylated chitin, has been attractive [4], [5], because the free amino groups in this modified product contribute polycationic, chelating, and film-forming properties, along with ready solubility in dilute acetic acid. In particular, partially deacetylated chitin is water soluble, and is similar in behavior to hydrophilic polymers that adsorb on metal particle surfaces and form complexes.
In this study, gold–chitosan nanocomposites were prepared and their catalytic activities were evaluated from elimination of hydroxyl radicals using a spin trapping technique.
Section snippets
Materials
Chitosan was obtained from Wako Pure Chemicals Co. Chloroauric acid was obtained from Wako Pure Chemicals Co. Milli-Q water (Millipore Co.) was used in all experiments. The other chemicals were of analytical grade.
Preparation of gold–chitosan nanocomposites
Preparation of gold nanoparticles in aqueous solution was conducted by chemical reduction of HAuCl4–chitosan mixtures with sodium borohydride. For a typical experiment, 0.2 cm3 of freshly prepared 20 mmol dm−3 HAuCl4 solution was added to 19.7 cm3 of chitosan of various
Results and discussion
Fig. 1 shows UV spectra of HAuCl4 aqueous solutions in the presence of chitosan after addition of sodium borohydride. All the spectra exhibit an absorption band at around 510–520 nm which is a typical plasmon band, suggesting the formation of gold nanoparticles [9]. When the concentration of chitosan added is increased, the intensity of the absorption band decreases and then increases again with a further increase of the chitosan concentration. This result indicates that the size of gold
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