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The mechanism of Au(III) reduction by chitosan has been proposed on the basis of comprehensive study of kinetics of Au(III) reduction and chitosan chain degradation using UV-vis spectroscopy and viscosimetry, and identification of reaction products using colloid titration and (13)C, (1)H NMR spectroscopy. We have shown that formation of gold nanoparticles in H[AuCl4]/chitosan solutions starts with hydrolysis of chitosan catalyzed by Au(III). The products of chitosan hydrolysis rather than chitosan itself act as the main reducing species. According to (13)C and (1)H NMR spectroscopy data, chitosan/Au(0) composites contain chitosan with reduced molecular weight and acetylation degree, whereas water-soluble by-products consist of chitosan oligomers with higher acetylation degree, derivatives of glucosamine acids, and formate ion. Chitosan degradation has significantly contributed to the decrease of its efficiency as a gold nanoparticles stabilizer. The gold particle size increased from 6.9 nm to 16.2 nm, when Au(III)/chitosan molar ratio changed from 1:80 to 1:10., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Highlights: [•] Chitosan based planar optical waveguides (POW) have been fabricated. [•] Chitosan/Ag composites have been obtained by “in situ” reduction of Ag+ ions. [•] Refractive index of Chitosan/Ag composites can be tuned in a range from 1.53 to 1.69. [•] Chitosan/Ag composites can be used as POW up to a silver volume fraction 1.3%. [ABSTRACT FROM AUTHOR]