Rotational Motion of Ligand-Cysteine on CdSe Magic-Sized Clusters

Abstract

Structure and dynamics of organic ligand capping on the surface of clusters significantly influence the property and function of the clusters. Recently, we revealed that, in cysteine-capped (CdSe) 34 magic-sized cluster (CdSe-Cys), ligandcysteine has two capping structures, namely, monodentate ligand-cysteine with sulfur−cadmium bond and bidentate one with sulfur− and nitrogen−cadmium bonds. In this work, we examine the motion of ligand-cysteine capping on (CdSe) 34 by performing solid-state 2 H nuclear magnetic resonance spectroscopy in CdSe-Cys with the deuterated methanediyl group (−CD 2 −). 2 H quadrupolar Carr−Purcell− Meiboom−Gill (QCPMG) and quadrupolar-echo spectra of CdSe-Cys were measured. Temperature dependence of line width and spin−lattice relaxation time of spikelets in the QCPMG spectra suggested that monodentate ligand-cysteine undergoes molecular motion. The quadrupolar-echo spectra were a sum of a motionally narrowed peak at the center of the spectra and a typical 2 H Pake pattern, which are assigned to monodentate and bidentate ligand-cysteine, respectively. The lineshape analysis for the 2 H quadrupolar-echo spectra obtained at 0−40 °C revealed that the CH 2 group in monodentate ligandcysteine undergoes pseudoisotropic rotation by the combination of two intramolecular rotations around the Cd−S and S−C bonds with the activation energy of ∼19 kJ/mol. Further, no evidence was found for the exchange of the two capping structures.

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.…”

Ligand modification enhanced quantum dot LEDs: principles and methods

“…18b). 92 The trifunctional structure of Cys leads to even better coordination effects, and it has been shown to be effective in dealing with surface defects in CdSe QDs. The adsorption energy of l -phenylalanine ( l -PHE) (3.9 eV) is significantly higher than that of OLA (2.5 eV) and OA (2.3 eV) (Fig.…”

Surface‐Ligand Tuned Reversible Transformations in Aqueous Environments Between CdSe Magic‐Size Clusters and Their Precursor Compounds

“…It has been documented that the purified MSC-420 is capped with 43% Cys via both thiol and amine groups, and with 57% Cys via thiol group only. [55,56] In the presence of excess Cys, a ligand addition reaction occurs. As the thiol group has a much higher binding affinity with Cd than the amine, [57] the amine groups bound with MSC-420 should be replaced by thiol groups from incoming Cys.…”