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Solution NMR Methods to Study the Surface Chemistry of Colloidal Nanoparticles from the Ligand’s Point of View

J.C. Martins, Z. Hens
Universiteit Gent, BE

Keywords: NMR, ligand quantification, ligand kinetics, ligand thermodynamics, ligand screening


We show that a portfolio of solution NMR based approaches, including diffusion spectroscopy, transfer NOE and Saturation Transfer Difference (STD) NMR spectroscopy, allows to investigate the chemistry of colloidal nanocrystals in situ by monitoring the capping ligands. Using pfg- diffusion NMR an unequivocal identification of the resonances of the bound ligands as well as the chemical exchange regime displayed by the ligand is possible. This in turn allows the determination of the diffusion coefficient and thus the hydrodynamic radius of the nanocrystals in solution. By calibrating the surface area of the NMR resonances using a solute of known concentration, the density of ligands at the nanocrystal surface can be quantified. The existence of an equilibrium can be established and quantified in certain cases. In complicated mixtures, NMR allows to distinguish binding from non-binding ones, using transfer NOE spectroscopy. For particles with an organic core (pigments, latex, etc..) STD NMR spectroscopy can be applied for this purpose, and has the potential to provide information on the surface alignment of the binding ligand. The results obtained support the generic nature of the approach, given certain prerequisites are taken into account. Recent references for review: 1.Utilising Self-Exchange to Address the Binding of Carboxylic Acid Ligands to CdSe Quantum Dots. B. Fritzinger, R. K.Capek, K. Lambert, J. C. Martins and Z. Hens, J. Am. Chem. Soc. (2010), 132, 10195-10201. 2.In Situ Observation of Rapid Ligand Exchange in Colloidal Nanocrystal Suspensions Using Transfer NOE Nuclear Magnetic Resonance Spectroscopy, Fritzinger, B., I. Moreels, P. Lommens, R. Koole, Z. Hens and J. C. Martins, J. Am. Chem. Soc. (2009), 131, 3024-3032. 3.Widening the View on Dispersant-Pigment Interactions in Colloidal Dispersions with Saturation Transfer Difference NMR-spectroscopy Szczygiel, A., L. Timmermans, B. Fritzinger and J. C. Martins, J. Am. Chem. Soc. (2009), 131, 17756-17758
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