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Ligand displacement exposes binding site heterogeneity on CdSe nanocrystal surfaces

Emile Drijvers (UGent) , Jonathan De Roo (UGent) , José Martins (UGent) , Ivan Infante and Zeger Hens (UGent)
(2018) CHEMISTRY OF MATERIALS. 30(3). p.1178-1186
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Abstract
Nanocrystal ligand interactions and ligand exchange processes are usually described by a uniform distribution of equal binding sites. Here, we analyze this assumption by a quantitative study of the displacement of Z-type cadmium oleate ligands from CdSe nanocrystals by addition of L-type ligands. First, we determined the stoichiometry of the displacement reaction by analyzing the equilibrium upon dilution using solution nuclear magnetic resonance spectroscopy. We found that 1 equiv of tetramethylethylene-I,2-diamine (TMEDA) or 2 equiv of n-butylamine or benzylamine bind to the displaced cadmium oleate. We only reached a comprehensive description of the displacement isotherm by including two types of binding sites with a different equilibrium constant. We corroborated this finding by density functional theory calculations on a CdSe model nanocrystal, which show that even single facets contain a broad variety of binding sites. Finally, we analyzed the thermodynamics of the displacement equilibrium for the weaker binding sites by constructing van't Hoff plots for the different displacers. Whereas displacement with TMEDA appears to be enthalpically neutral, it is entropically favorable. In contrast, displacement with the primary amines is entropically unfavorable but is associated with a negative change in enthalpy. Since the distribution of binding energy emanates from the large fraction of edge and vertex sites on a nanocrystal facet, these findings are most likely inherent to nanocrystals in general and should be considered when analyzing surface reactions on such materials.
Keywords
QUANTUM-DOT SOLIDS, COLLOIDAL NANOCRYSTALS, SELENIDE NANOCRYSTALS, THIN-FILMS, CHEMISTRY, EXCHANGE, CARBOXYLATE, ACID, TRANSPORT

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Chicago
Drijvers, Emile, Jonathan De Roo, José Martins, Ivan Infante, and Zeger Hens. 2018. “Ligand Displacement Exposes Binding Site Heterogeneity on CdSe Nanocrystal Surfaces.” Chemistry of Materials 30 (3): 1178–1186.
APA
Drijvers, E., De Roo, J., Martins, J., Infante, I., & Hens, Z. (2018). Ligand displacement exposes binding site heterogeneity on CdSe nanocrystal surfaces. CHEMISTRY OF MATERIALS, 30(3), 1178–1186.
Vancouver
1.
Drijvers E, De Roo J, Martins J, Infante I, Hens Z. Ligand displacement exposes binding site heterogeneity on CdSe nanocrystal surfaces. CHEMISTRY OF MATERIALS. 2018;30(3):1178–86.
MLA
Drijvers, Emile, Jonathan De Roo, José Martins, et al. “Ligand Displacement Exposes Binding Site Heterogeneity on CdSe Nanocrystal Surfaces.” CHEMISTRY OF MATERIALS 30.3 (2018): 1178–1186. Print.
@article{8547456,
  abstract     = {Nanocrystal ligand interactions and ligand exchange processes are usually described by a uniform distribution of equal binding sites. Here, we analyze this assumption by a quantitative study of the displacement of Z-type cadmium oleate ligands from CdSe nanocrystals by addition of L-type ligands. First, we determined the stoichiometry of the displacement reaction by analyzing the equilibrium upon dilution using solution nuclear magnetic resonance spectroscopy. We found that 1 equiv of tetramethylethylene-I,2-diamine (TMEDA) or 2 equiv of n-butylamine or benzylamine bind to the displaced cadmium oleate. We only reached a comprehensive description of the displacement isotherm by including two types of binding sites with a different equilibrium constant. We corroborated this finding by density functional theory calculations on a CdSe model nanocrystal, which show that even single facets contain a broad variety of binding sites. Finally, we analyzed the thermodynamics of the displacement equilibrium for the weaker binding sites by constructing van't Hoff plots for the different displacers. Whereas displacement with TMEDA appears to be enthalpically neutral, it is entropically favorable. In contrast, displacement with the primary amines is entropically unfavorable but is associated with a negative change in enthalpy. Since the distribution of binding energy emanates from the large fraction of edge and vertex sites on a nanocrystal facet, these findings are most likely inherent to nanocrystals in general and should be considered when analyzing surface reactions on such materials.},
  author       = {Drijvers, Emile and De Roo, Jonathan and Martins, Jos{\'e} and Infante, Ivan and Hens, Zeger},
  issn         = {0897-4756},
  journal      = {CHEMISTRY OF MATERIALS},
  language     = {eng},
  number       = {3},
  pages        = {1178--1186},
  title        = {Ligand displacement exposes binding site heterogeneity on CdSe nanocrystal surfaces},
  url          = {http://dx.doi.org/10.1021/acs.chemmater.7b05362},
  volume       = {30},
  year         = {2018},
}

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