Fig. 4. Schematic illustration of (a) 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) conjugation reaction, (b) ion-pairing reaction, and (c) CH–π interaction occurring on the SR ligands of metal NCs. (a) illustrates the EDC conjugation between folic acid (FA) and Au22(SG)18 (SG = glutathione ligand), where the –NH2 groups of SG ligands are protected by benzyl chloroformate (CBz) prior to the EDC reaction; reproduced with permission from ref. 122. Copyright 2017, Wiley-VCH. (b) illustrates the production of amphiphilic Au25(MHA)18@xCTA NCs (x = 6–9) by the phase-transfer-driven ion-pairing reaction, where MHA denotes 6-mercaptohexanoic acid and CTA denotes cetyltrimethylammonium; reproduced with permission from ref. 129. Copyright 2015, American Chemical Society. (c) exhibits inter-cluster CH–π interactions (top panel) and the “herringbone pattern” of –S-Nap ligands in the supercrystals of Au103S2(S-Nap)41 NCs, where HS-Nap denotes 2-naphthalenethiol (colour code: light blue, motif Au(i); yellow, S; light grey, H; blue/magenta, C); reproduced with permission from ref. 55. Copyright 2017, American Chemical Society.
