Copper metallic nanoparticles capped with PEGylated PAMAM-G3 dendrimers for the catalytic reduction of low solubility nitroarenes of pharmaceutical interest

摘要

Copper nanoparticles (Cu NPs) were synthesized using NaBH4 as reducing agent and increasing molar ratios of 50 % PEGylated polyamidoamine dendrimer of the third generation (PEG-PAMAM-G3) as a capping agent. The dendrimer-stabilized Cu NPs were evaluated as novel catalysts for the reduction of poorly soluble nitrocompounds in aqueous media. The nanocatalysts were characterized using transmission electron microscopy (TEM), ultraviolet-visible light (UV-vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and dynamic light scattering (DLS). UV-vis revealed the presence of localized surface resonance plasmon at 560 nm, whereas TEM analysis confirmed disperse and spherical Cu NPs of around 2.6-3.7 nm. The catalysts were successfully tested in the efficient aqueous reduction of 4-(4-nitrophenyl)morpholine as model low solubility substrate using NaBH4 as reducing agent. The best catalytic performance was attained by the catalyst having a PAMAM:Cu ratio of 0.4, which retained its activity throughout four catalytic cycles. The catalyst was also efficient in the aqueous reduction of two pharmaceutically relevant building blocks such as 4-(2-fluoro-4nitrophenyl)morpholine) and 4-(4-nitrophenyl)morpholin-3-one. Our results suggest that PEG-PAMAM-G3 prevents Cu NPs agglomeration and flocculation, and enhances their stability in aqueous solution thus enabling their use in environmentally friendly catalytic processes.