title: Mechanism of Au(III) reduction by chitosan: comprehensive study with 13C and 1H NMR analysis of chitosan degradation products.
abstract: 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.
authors.affiliation: I. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of RAS, 20, S. Kovalevskoy str., Yekaterinburg 620990, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Pestov
authors.affiliation: Institute of Chemistry, Far East Branch of RAS, 159, prosp.100-letiya Vladivostoka, Vladivostok 690022, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Nazirov
authors.affiliation: Far Eastern Federal University, 8, Sukhanova St., Vladivostok 690950, Russia.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Modin
authors.affiliation: Institute of Chemistry, Far East Branch of RAS, 159, prosp.100-letiya Vladivostoka, Vladivostok 690022, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Mironenko
authors.affiliation: Institute of Chemistry, Far East Branch of RAS, 159, prosp.100-letiya Vladivostoka, Vladivostok 690022, Russia. Electronic address: sbratska@ich.dvo.ru.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Bratskaya
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy; D048271:Chitosan / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D066244:Proton Magnetic Resonance Spectroscopy
chemical_list: D006046:Gold; D048271:Chitosan
keywords: Chitosan; Decarboxylation; Depolymerization; Formate; Gold nanoparticles; Metal/polymer ratio