Au nanoparticles stabilised by PEGylated low generation PAMAM dendrimers: Design, characterisation and properties

The preparation and characterisation of a series of well-defined low generation (poly)amidoamine (PAMAM)-based dendrimers with end-grafted ethylene glycol ether moieties of type N(CH2CH2C(O)NHCH2CH2NR2)3 (3a, R = CH2CH2C(O)OCH2CH2OCH3; 3b, R = CH2CH2C(O)O(CH2CH2O)2C2H5; 3c, R = CH2CH2C(O)O(CH2CH2O)9CH3), [CH2N(CH2CH2C(O)NHCH2CH2NR2)2]2 (4, R = CH2CH2C(O)O(CH2CH2O)2C2H5) and (R2NCH2CH2NHC(O)CH2CH2)N[CH2CH2N(CH2CH2C(O)NHCH2CH2NR2)2]2 (5a, R = CH2CH2C(O)OCH2CH2OCH3; 5b, R = CH2CH2C(O)O(CH2CH2O)2C2H5; 5c, R = CH2CH2C(O)O(CH2CH2O)9CH3) and their application for the stabilisation of gold nanoparticles (Au NPs) is described. These dendrimers were prepared by a consecutive divergent synthesis methodology including Michael addition and amidation cycles. For comparison, amidoamine related model compounds N(C3H7)R2 (1, R = CH2CH2C(O)O(CH2CH2O)2C2H5) and [CH2NR2]2 (2, R = CH2CH2C(O)O(CH2CH2O)2C2H5) were also synthesised to estimate the minimum required donating capabilities of the stabiliser. Loading the appropriate dendritic templates with H[AuCl4] (12) and subsequent reduction of the respective metallodendrimers with Na[BH4] produced dendrimer encapsulated gold colloids. The dendrimeric scaffold, the length of the ethylene glycols, the adjusted stabilizer:gold ratio and the duration of reaction time affects the average Au particle diameter in a range of 4.0 (±0.9) to 58.5 (±14.5) nm. Furthermore, depending on the nature of the stabiliser, nanoparticles were formed having spherical or multiple morphologies. Characterisation by transmission electron microscopy (TEM), dynamic light scattering (DLS), UV/vis, and IR spectroscopy revealed that Au NPs are formed and protected inside the dendrimer scaffold.

Graphical abstractThe preparation and characterisation of a series of well-defined low generation (poly)amidoamine-based dendrimers with end-grafted ethylene glycol ether units is discussed. Loading the dendritic templates with Au(III) ions led to the formation of the appropriate metallodendrimers. Subsequent reduction using Na[BH4] produced dendrimer-encapsulated Au NPs.Figure optionsDownload full-size imageDownload high-quality image (62 K)Download as PowerPoint slideHighlights► Low generation (amidoamine)-based dendrimers are synthesised. ► Various (poly)ethylene glycol termini are attached. ► Compounds act as stabilisers in gold nanoparticle formation. ► Influence on particle size and morphology is presented.