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Reports: UR7 49407-UR7: Synthesis of Nanoparticle-Cored Dendrimers with Single Molecular Weight Using Dendritic Functionalization of Monodisperse Gold Nanoparticles
The primary goal of this research is to synthesize monodisperse nanoparticle-cored dendrimers (NCDs) using our new synthetic strategy in which dendrons are linked to functionalized nanoparticles by single coupling reaction. Currently known NCDs are quite polydisperse and unlike dendrimers that have uniform molecular weight and uniform density. The availability of highly monodisperse NCDs will allow us to further elucidate the relationships between primary structural elements in these nanostructures and their optical and/or electronic properties.
During the first year of this grant, the progress was made on the separate syntheses of functionalized monodisperse nanoparticles and dendrons with different size and composition. They will be put together by ester or amide coupling reactions to produce various monodisperse NCDs in the future.
In an effort to synthesize monodisperse gold NCDs with different sized particle cores, we have prepared monodisperse phenylethanethiolate-protected Au25 nanoparticles (1.1 nm) and Au140 nanoparticles (1.8 nm). The formation of Au25 nanoparticles were confirmed by UV-vis absorbance spectra that displays the distinct peaks at 670, 460, and 400 nm, which are indicative of molecule-like electronic levels of Au25 nanoparticles. In comparison, Au140 nanoparticles show only an exponential decay in UV spectra without any gold surface plasmon bands. By incorporation of w-functional groups to the monolayer, the nanoparticles obtain specific reactivities. New thiolate ligand was incorporated into Au25 and Au140 NPs by mixing the p-mercaptobenzoic acid and phenylethanethiolate-protected Au NPs in acetone and the reactions were confirmed by FT-IR analyses. The number of COOH groups on nanoparticle surfaces after ligand exchange was determined by 1H NMR integration analysis. A combination of MALDI-TOF/TOF-MS spectroscopy, transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) will be used for the detailed characterization of monodisperse nanoparticles.
The HO-functionalized polypropyleneimine (PPI) dendrons (G2 and G3) were synthesized from ethylenediamine by multistep reactions. The multiple HO-functional groups in the exterior provides high solubility in polar solvent including water and the more reactive NH2-focal point will be directed to COOH groups on gold nanoparticles for amide coupling reaction. The polyarylether dendrons with HO-focal point (G1, G2, and G3) were also prepared. The dendrons shown in Figure 1 are now currently in stock and will be covalently bonded to gold nanoparticles. The diffraction peaks of XRD will confirm the monodispersity of the NCDs. Mass measurements of NCDs will also be performed using MALDI-TOF/TOF-MS spectrometer.
