Encapsulation and Stabilization of Gold Nanoparticles with “Click” Polyethyleneglycol Dendrimers

Abstract

Water-soluble arene-cored "clicked" and non-"clicked" dendrimers terminated by 27, 81, and 243 triethyleneglycol (TEG) tethers (respectively generations G0, G1, and G2) have been synthesized and shown to form dendrimer-encapsulated gold nanoparticles (DEAuNPs) and dendrimer-stabilized gold nanoparticles (DSAuNPs). The dendrimers have been characterized by IR, (1)H NMR, (13)C NMR, size-exclusion chromatography, elemental analysis, MALDI-TOF mass spectroscopy, DOSY NMR, and dynamic light scattering. The AuNPs have been generated and stabilized by these PEGylated dendrimers using a variety of reduction modes, including NaBH(4) in methanol, various single-electron metallocene-type reductants, and even in the absence of additional reductants. The active role of the "clicked" triazole rings, dendrimer generation, stoichiometry of Au precursor, and nature of the reductant and of the solvent are delineated, leading to DSAuNPs with the G0 dendrimer and smaller DEAuNPs with the G1 and G2 dendrimers. Altogether, AuNPs in the size range from 1.8 to 42 nm were formed and characterized by transmission electron microscopy (TEM), high resolution TEM (HRTEM) and UV-vis spectroscopy. Both 1,2,3-triazole and PEGylated Percec-type dendrons are required in the dendrimer structure for the stabilization of AuNPs upon NaBH(4) reduction of HAuCl(4) in methanol. On the other hand, in the absence of other reductant in water, only PEGylated Percec-type dendrons in dendrimers were found to be indispensable, because of their semicavitand shape, for the spontaneous reduction of HAuCl(4) and stabilization of DSAuNPs.

Template Synthesis of Subnanometer Gold Clusters in Interfacially Cross-Linked Reverse Micelles Mediated by Confined Counterions

“…In the literature, spontaneous reduction of aurate was reported to be assisted by the dehydration of aurate within block copolymer micelles 28 or by encapsulation within dendrimers. 29 Although similar dehydration and encapsulation could have occurred in our system, we were unable to identify the reducing agent in our previous investigation. Herein, we report that it was the bromide ions that reduced the aurate during the template synthesis and the microenvironment of the ICRM core was responsible for the decreased reduction potential.…”

“…In the literature, when dehydrated within block copolymer micelles 28 or encapsulated within dendrimers, aurate was reported to be reduced by otherwise unlikely functional groups such as poly(ethylene glycol). 29 Although the ICRM core contains a nanosized water pool, the entrapped aurate is not expected to be fully solvated as in aqueous solution. Quite likely, similar dehydration and encapsulation lowered the reduction potential of the ICRM-encapsulated aurate and promoted the otherwise difficult reaction.…”

PEGylated Inorganic Nanoparticles

“…The gold nanoclusters can grow in the intermolecular space of PEGylated PAM dendrons. [82,83] Complete coreshell type morphology can be achieved by increasing the number of dendron generations. For a narrow size distribution of gold NPs hemispherical shaped dendrons gave the best results.…”

Gold Nanoparticle Surface Functionalization: A Necessary Requirement in the Development of Novel Nanotherapeutics

“…An alternate method 'Click' chemistry typically refers to the Husigen 1,3-dipolar cyloaddition of azides and terminal amides providing fast, simple and irreversible reactions for the attachment of structural units, and has also been used for GNP functionalization [32]. Boisselier et al (2010) used 'click' chemistry to successfully synthesize encapsulate and stabilize GNPs with PEG dendrimers using a variety of reduction methods including NaBH 4 in methanol [33]. Highly functionalized GNPs are achievable through this technique with Gadolinium III enriched DNA-GNP conjugates being formed, which demonstrating high HeLa cell uptake for magnetic resonance imaging [34].…”