A Solution NMR Toolbox for Characterizing the Surface Chemistry of Colloidal Nanocrystals

Abstract

The possibilities offered by 1 H solution NMR for the study of colloidal nanocrystal ligands are reviewed. Using CdSe and PbSe nanocrystals with tightly bound oleate ligands as examples, the solution NMR toolbox for ligand analysis is introduced, highlighting 1D 1 H, diffusion ordered (DOSY) and nuclear Overhauser effect (NOESY) spectroscopy as NMR techniques that enable bound ligands to be distinguished from free ligands. For each of the toolbox techniques, it is outlined how dynamic stabilization in the fast exchange regime affects the spectra obtained. Next, it is shown how the perturbation of a purified dispersion by dilution or the addition of excess ligands can be used to analyze the binding of ligands to a nanocrystal. Finally, saturation transfer difference (STD) spectroscopy is presented as an NMR technique that may complement the established toolbox.

Fast and Tunable Synthesis of ZrO2 Nanocrystals: Mechanistic Insights into Precursor Dependence

“…47 The resonances at 5.3 ppm are characteristic of the alkene resonance of oleic acid, while their broadening in both spectra and the presence of very clear negative nOe cross-peaks to the methylene resonances of the alkyl chain in the 2D NOESY spectra (dashed circle in Figure 7B and C) confirm that OAc is bound to the NCs surface before and after purification. 47 In spectrum A (before purification) a second, sharper resonance is present superimposed upon the broad alkene resonance of bound OAc. Although the narrow width of the peak suggests that this feature corresponds to free OAc, very clear negative NOE cross-peaks emanating from this resonance can also be observed, indicating the proximity of OAc to the NCs surface in sample A.…”

“…Oleic acid was selected because the well-resolved alkene resonance of OAc strongly facilitates the interpretation in NMR spectra. 47 Two 1D 1 H NMR spectra corresponding to samples with c-ZrO2 NCs treated at 230°C for 6 hours prior to (spectrum A) and after five purifications (spectrum B) are compared in Figure 7. Bound ligands typically feature peak broadening due to excessive T2 relaxation.…”

One-pot organometallic synthesis of well-controlled gold nanoparticles by gas reduction of Au(I) precursor: a spectroscopic NMR study

“…However, no NMR resonance for the amine extremity, notably the α-CH 2 at 2.93 ppm of HDA, was observed. Disappearance of NMR signals, related to fast relaxation processes, for nuclei close to the binding site of NPs is a common observation for ligands involved in "intermediate" or slow exchange between the NP surface and the solution [36].…”

Structural characterization of functionalized gold nanoparticles for drug delivery in cancer therapy: a NMR based approach

“…Nowadays, a number of important spectroscopic and imaging techniques can be used for physicochemical characterization of nano-formulations for DD. 32,33 Among them, Nuclear Magnetic Resonance (NMR) spectroscopy holds a prominent place for being non-destructive, highly reproducible and sensitive to structural details of molecules and molecular conjugates, which can be used for both qualitative and quantitative characterization purposes. A variety of well-established NMR experiments can provide valuable information on the molecular size, shape, dynamics, chemical structure, intermolecular interactions, binding and exchange processes in complex nano-systems.…”

“…A variety of well-established NMR experiments can provide valuable information on the molecular size, shape, dynamics, chemical structure, intermolecular interactions, binding and exchange processes in complex nano-systems. [33][34][35] NMR allows for the in situ nondestructive analysis of nano-systems and can be particularly useful in distinguishing between free and interacting with and/or bound to NP species, and to quantify the distribution of these species. In this context, diffusion ordered spectroscopy (DOSY) and nuclear Overhauser effect (NOE) spectroscopy, being particularly sensitive to structural and dynamical changes, have become invaluable tools for studies of the molecular transport, interactions and binding processes in complex systems.…”