Two new water-soluble 1,2,3-triazole-containing
nona-PEG-branched dendrimers are obtained with nine intradendritic
1,2,3-triazoles (trz). Addition of HAuCl4 in water to these
dendrimers quantitatively leads to the intradendritic formation of
AuCl3(trz) moieties subsequent to complete Cl– substitution by trz on Au(III), whereas the analogous complexation
reaction of AuCl3 with a linear PEG trz ligand forms only
an equilibrium between trz-coordinated Au(III) and Au(III) that is
not coordinated to trz. Reduction of the dendrimer-Au(III) complexes
to Au0 by NaBH4 then leads to stabilization
of gold nanoparticles (AuNPs) in water. The sizes of the AuNPs stabilized
by the dendritic macromolecules are further controlled between 1.8
and 12 nm upon selecting the stoichiometry of Au(III) addition per
dendritic trz followed by NaBH4 reduction. With a 1:1 Au/trz
stoichiometry, the AuNP size depends on the length of the PEG tether
of the dendrimer; small dendrimer-encapsulated AuNPs are formed with
PEG2000, whereas large AuNPs are formed with PEG550. With Au/trz stoichiometries
larger than unity, Au(III) is reduced outside the macromolecule, resulting
in the formation of large interdendritically stabilized AuNPs. The
formation of very small and only mildly stabilized AuNPs by neutral
hydrophilic triazole ligands offers an opportunity for very efficient p-nitrophenol reduction by NaBH4 in water at
the AuNP surface.