Antioxidant-potentiality of gold–chitosan nanocomposites

doi:10.1016/S0927-7765(03)00151-6

Colloids and Surfaces B: Biointerfaces

Volume 32, Issue 2, 15 October 2003, Pages 117-123

https://doi.org/10.1016/S0927-7765(03)00151-6 Get rights and content

Abstract

Gold nanoparticles were prepared in the presence of chitosan via reduction of HAuCl₄ with sodium borohydride. The average particle size of gold nanoparticles was significantly affected with the concentration of chitosan added and was ranged between 6 and 16 nm. The gold–chitosan nanocomposites are formed by adsorbing chitosan molecules on the gold nanoparticles. The catalytic activity of gold–chitosan nanocomposites upon elimination of hydroxyl radicals formed in an H₂O₂/FeSO₄ system was examined using a spin-trapping method. The catalytic activity increased with the concentration of chitosan added and showed a maximum and then decreased with a further concentration of chitosan added, although a strict correlation between the average diameter of gold and the catalytic activity was not found. In addition, the activity of gold–chitosan was 80 times higher than that of ascorbic acid, which is well known as an antioxidant.

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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