Synthesis and Characterization of oligosaccharides tethered to gold films and gold nanoparticles

Abstract

The goal of this research was to stereoselectively synthesize α- and β- linked glucopyranosylamide derivatives utilizing the modified Staudinger methodology and to tether these derivatives to gold films and gold nanoparticles. The key step in the synthesis of the glucopyranosyl conjugates is the coupling of a glycosylazide to an acid derivative in the presence of either triphenylphosphine or trimethylphosphine. The synthesis proceeds via the in situ generation of glucosyl isoxazoline intermediate. The characterization of the resulting films and particles has been performed using Fourier-Transform Infrared (FT-IR), Atomic Force Microscopy (AFM), and X-Ray Photoelectron Spectroscopy (XPS). The XPS and AFM analyses have shown evidence for monolayer and multilayered films depending on the derivative used. Glucopyranosyl derivatives with free hydroxyl groups gave well ordered, self-assembled monolayers (SAMs). FT-IR and XPS analysis of the SAMs demonstrated that the resulting monolayers were comprised of a hydrogen bonded network between amides on adjacent sites. Glycoconjugates have also been attached to gold nanoparticles and evidence for aggregation of gold nanoparticles when bound to hydroxylated glycosylamides having thiolated/disulfide side chains has been observed. There is evidence for an enhancement in the aggregation of the gold nanoparticles in the presence of the lectin Concanavalin A which binds specifically to α-linked gluco and mannopyranosides.