Mechanistic Insights into Nanoparticle Surface Adsorption by Solution NMR Spectroscopy in an Aqueous Gel
Engineering nanoparticle (NP) functions at molecular level requires a detailed understanding of the dynamic processes occurring at the NP surface. Here we show that the combined analysis of Dark state Exchange Saturation Transfer (DEST) and Relaxation Dispersion (RD) NMR experiments acquired on gel-stabilized samples of NP allows for accurate determination of the kinetics and thermodynamics of adsorption. We used the former approach to describe the interaction of cholic acid (CA) and phenol (PhOH) with ~200 nm ceria NP. We show that, while CA forms weak interactions with the NP, PhOH is tightly bound to the NP surface. Interestingly, we found that adsorption of PhOH proceeds through an intermediate, weakly bound state in which the small molecule has residual degrees of rotational diffusion. We believe the use of aqueous gels for stabilizing NP samples will increase the applicability of solution NMR methods to characterization of nanomaterials.
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