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

Abstract

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(CH 2CH 2C(O)NHCH 2CH 2NR 2) 3 ( 3a, R = CH 2CH 2C(O)OCH 2CH 2OCH 3; 3b, R = CH 2CH 2C(O)O(CH 2CH 2O) 2C 2H 5; 3c, R = CH 2CH 2C(O)O(CH 2CH 2O) 9CH 3), [CH 2N(CH 2CH 2C(O)NHCH 2CH 2NR 2) 2] 2 ( 4, R = CH 2CH 2C(O)O(CH 2CH 2O) 2C 2H 5) and (R 2NCH 2CH 2NHC(O)CH 2CH 2)N[CH 2CH 2N(CH 2CH 2C(O)NHCH 2CH 2NR 2) 2] 2 ( 5a, R = CH 2CH 2C(O)OCH 2CH 2OCH 3; 5b, R = CH 2CH 2C(O)O(CH 2CH 2O) 2C 2H 5; 5c, R = CH 2CH 2C(O)O(CH 2CH 2O) 9CH 3) 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(C 3H 7)R 2 ( 1, R = CH 2CH 2C(O)O(CH 2CH 2O) 2C 2H 5) and [CH 2NR 2] 2 ( 2, R = CH 2CH 2C(O)O(CH 2CH 2O) 2C 2H 5) were also synthesised to estimate the minimum required donating capabilities of the stabiliser. Loading the appropriate dendritic templates with H[AuCl 4] ( 12) and subsequent reduction of the respective metallodendrimers with Na[BH 4] 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.