Capping Structure of Ligand–Cysteine on CdSe Magic-Sized Clusters

Abstract

Ligand molecules capping on clusters largely affect the formation and stabilization mechanism and the property of clusters. In semiconductor CdSe clusters, cysteine is used as one of the ligands and allows the formation of ultrastable (CdSe) 34 magic-sized clusters. Cysteine has sulfhydryl, amine, and carboxylate groups, all of which have coordination ability to the CdSe surface, and the bonding states of the three functional groups of ligand–cysteine on the CdSe core have not been determined. In this work, the capping structure of ligand–cysteine is examined by performing Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and multinuclear solid-state nuclear magnetic resonance (NMR) spectroscopy. FT-IR, XPS, and 1 H, 13 C, and 23 Na magic-angle spinning NMR show that the sulfhydryl group of ligand–cysteine forms a sulfur–cadmium bond with a cadmium atom at the CdSe surface, while the carboxylate group does not contribute to the protection of the CdSe core and binds to a sodium ion contained as a counterion. 15 N–{ 77 Se} through-bond J -single quantum filtered NMR experiment reveals that the amine group of ligand–cysteine has no coordination to selenium atoms. By considering the N–Cd bond forming ratio (∼43%) revealed in our previous work, which is confirmed in this work by analyzing 13 C α signal intensity (∼42%), we concluded that cysteine capping on (CdSe) 34 occurs in two ways: one involves both the sulfur–cadmium and nitrogen–cadmium bonds, and the other bears only the sulfur–cadmium bond.

Effect of Chiral Ligand Concentration and Binding Mode on Chiroptical Activity of CdSe/CdS Quantum Dots

“…Some investigations of Cys binding modes on the surface of Cd-based clusters and nanoparticles have been previously reported. For example, by performing multinuclear ( 1 H, 13 C, 77 Se, 15 N, 113 Cd, and 23 Na) solid-state NMR techniques, Takegoshi et al have shown that the Cys ligand binds with CdSe 34 magic clusters via coordination to Cd 2+ ions as S – –NH 2 bidentate and S – monodentate ligand, in amounts of 43% and 57%, respectively. − In another study using 13 C solid-state NMR, it was demonstrated that Cys binds to the surface of 2.9 nm CdSe QDs as a S – –COO – bidentate ligand. Density functional theory (DFT) calculations revealed that the interaction patterns between Cys and (CdSe) n vary with the cluster size and medium.…”

Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials

“…Most of the elements found in main group inorganic semiconductors have NMR active nuclei, potentially making solid-state NMR an ideal tool for probing the structure of NPs. Solid-state NMR has previously been applied to a number of different NP systems, such as cadmium chalcogenides (CdX, X = S, Se, Te), [26][27][28][29][30][31][32][33][34] indium phosphide (InP), [35][36][37] silicon (Si), [38][39][40][41][42] etc., [43][44][45][46] to determine both the surface and bulk structure. Direct excitation solid-state NMR experiments mainly probe the bulk of the NPs, although surface NMR signals are visible in small diameter NP NMR spectra.…”

Enhanced Light-Driven Charge Separation and H2 Generation Efficiency in WSe2 Nanosheet–Semiconductor Nanocrystal Heterostructures

“…l -Cysteine, with sulfhydryl and carboxylate functional groups, facilitates the binding of CdSe/CdS DIRs to WSe 2 (as shown in Figure S5). , The TEM image of the mixture (Figure d) confirms that CdSe/CdS DIRs are indeed in contact with WSe 2 NSs.…”