Potentiometry, electronic spectroscopy, and X-ray absorption (XAS) experiments were carried out to monitor the course of the complexation reaction between AuCl4 – and glucosamine moieties (GLA) of chitosan molecules. The disappearance of the ligand (π)–metal (σ*) charge transfer (LMCT) band at 313 nm, characteristic of the AuCl4 – ion, upon the addition of chitosan evidenced the complexation of Au(III) with glucosamine moieties at pH 4. The coordination sphere of Au(III) was determined from the results of XAS experiments in the case of a [GLA]/[Au(III)] ratio equal to 1/4. The Au–Cl and Au–O(N) bond lengths were determined. Finally, preliminary results of gold nanoparticle synthesis by Au(III) reduction under electron beam in the presence of chitosan were presented. The influence of gold speciation on the size of preformed Au(0) clusters was evidenced.

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