Studies on the sulfation of cellulose α-lipoate and ability of the sulfated product to stabilize colloidal suspensions of gold nanoparticles

A versatile method for the synthesis of cellulose a-lipoate with a low degree of substitution (DS) has been developed using N,N-dimethylacetamide (DMA)/LiCl as a solvent and N,N'-carbonyldiimidazole (CDI) as an esterification reagent. The cellulose a-lipoate with DS of alpha-lipoate groups of 0.26 was converted with sulfur trioxide pyridine complex in dimethyl sulfoxide (DMSO) as solvent. The sulfation is accompanied by an unexpected partial oxidation of the disulfide moiety leading to the formation of the corresponding stereoisomers of S-oxides. The resulting mixture of water-soluble cellulose alpha- and beta-lipoate sulfate possesses a DS of sulfuric acid half ester groups of 1.78. This cellulose-alpha/beta-lipoate sulfate derivative can be used as an effective stabilizer and solubilizer for the formation of colloidal suspensions of gold nanoparticles formed in situ in aqueous solution. (C) 2015 Elsevier Ltd. All rights reserved,