Size controlled, structural characterization and applications of glucopyranoside-based N-heterocyclic carbenes stabilized gold nanoparticles

N-heterocyclic carbenes (NHCs) have evidenced wonderful alternatives as surface ligands, while synthetic challenges have limited their application in chiral gold nanoparticles (AuNPs). To avoid using difficult-tosynthesize and light-sensitive NHC-Au(I) complex, we synthesized four glucopyranoside-based benzimidazolium bromide salts (1a-1d-Br) and their corresponding haloaurate(III) salts (2a-2d-AuCl4). Then, the firstgeneration sugar-substituted NHCs stabilized extra-small and ultra-stable chiral AuNPs (Au@NHCs-sugar NPs, 3a-3d-AuNPs) was synthesized though two mild, efficient, and operation-friendly one-pot chemical reduction methods. The obtained 3a-3d-AuNPs were characterized by UV-Vis, NMR, HR-TEM, TGA, CD, FT-IR, and XPS spectroscopy. The designed 3a-3d-AuNPs with core diameters ranging from 2.3 to 3.8 nm remained stable against glutathione for up to 24 h over a wide temperature range of 95 to -78 degrees C, and over 4 years in air. The absence of NCHN proton in H-1 NMR and FT-IR of 3a-3d-AuNPs confirmed the formation of NHC-Au bond, and clearly showed that all acetyl groups, benzimidazolium heterocycle, and N-substituents maintained. XPS analyses revealed the presence of Au(0) and Au(I) in all Au@NHCs-sugar NPs. This result leads us to postulate that 3a-3dAuNPs exhibit a monolayer of Au(I) surrounding an Au(0) core. These designed 3a-3d-AuNPs were studied for their self-assembly behavior, antibacterial activity against bacterium Xanthomonas citri susp. citri (Xcc), and catalytic activity towards the reduction of nitroarenes. All of them demonstrated strong antibacterial activity against Xcc with minimum inhibitory concentration value <0.03125 mg(.)mL(-1).