“Click” Synthesis of Nona-PEG-branched Triazole Dendrimers and Stabilization of Gold Nanoparticles That Efficiently Catalyze p-Nitrophenol Reduction

Abstract

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 Au(0) 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.

Theory of Brushes Formed by Ψ-Shaped Macromolecules at Solid–Liquid Interfaces

“…In this case, eq 6 reduces to eq 9. An analytical solution of eq 9 is available when the asymmetry parameter u = n 1 /n 0 is equal to relatively small integer (or inverse integer) numbers (eqs 11,12). For highly branched macromolecules with q ≫ 1, an approximate asymptotic dependence k ≈ (qn 1 n 0 ) −1/2 provides a good estimate for the parameter k at moderate u values, q −1 ≪ u ≪ q (see Figures 2 and 3a).…”

Silver Metallic Cyclodextrin‐Core Star mPEG

“…So far it has been an efficient strategy for incorporation of functional groups into a macromolecular architecture to synthesize metallic polymers in situ or to have metal nanoparticles stabilized by a polymer. The functional groups should be ones, which are able to reduce metal ions into zerovalent, or to coordinate or to electrostatically interact with metal ions, guaranteeing the fact that metal ions are able to be directed onto the target position of a macromolecular architecture and then metal nanoparticles are produced in situ . For example, Black et al .…”

“…The occurrence of the oxidation–reduction reaction suggests that silver nanoparticles should form in situ within III , because resulting SM‐CD‐SPEG aqueous solutions exhibit good stability. It should be mentioned that 1,2,3‐triazole moieties can coordinate metal ions such as gold and silver ions . The interaction may assist in occurrence of the oxidation–reduction reaction as mentioned above, and may also stabilize the silver nanopartilces formed, because the sites of the two types of groups of III are near and are close to the β‐CD core (Scheme ).…”

“…The functional groups should be ones, which are able to reduce metal ions into zerovalent, or to coordinate or to electrostatically interact with metal ions, guaranteeing the fact that metal ions are able to be directed onto the target position of a macromolecular architecture and then metal nanoparticles are produced in situ. [13,20,21,26,27] For example, Black et al [26] synthesized poly(ethylene glycol) (PEG)-coated metal nanoparticles (NPs) through reduction of gold and silver cations with the 3,4-dihydroxyphenylalanine (DOPA) moieties of DOPA-ended PEG polymers. These PEG functionalized metal nanoparticles were stable in physiological ionic strengths and under centrifugation.…”

Iron oxide modified with pyridyl‐triazole ligand for stabilization of gold nanoparticles: An efficient heterogeneous catalyst for A3 coupling reaction in water

“…In recent years ligands such as phosphorus‐ and nitrogen‐based ligands were used for modification and stabilization of Fe 3 O 4 NPs. Very recently, triazoles have been recognized as excellent ligands for metal catalyst stabilization . These highly stable heterocyclic compounds can be produced by the reaction of terminal alkynes with organic azides catalysed by copper (I) complexes …”