Dispersion State Phase Diagram of Citrate-Coated Metallic Nanoparticles in Saline Solutions

Abstract

The fundamental interactions underlying citrate-mediated chemical stability of metal nanoparticles (NPs), and their surface characteristics dictating particle dispersion/aggregation in aqueous solutions, are largely unclear. Here, we used a newly developed theoretical model to estimate the stoichiometry of citrate molecules chemisorbed onto spherical metallic NPs and define the uncovered solvent-accessible surface area of the NP. Then, we exploited two-body free energy calculations and extended coarse-grained molecular dynamics simulations of citrate-capped metallic NPs in saline solutions to explore an experimentally relevant range of NP charge, as well as the electrolytic medium’s ionic strength, a known trigger for aggregation. In this way, we define dispersion state phase diagrams of citrate-capped metal nanocolloids. UV-vis spectroscopy experiments validated our predictions and extended our results to NPs up to 35 nm. Altogether, our results disclose a complex interplay between the particle size, its surface charge density, and the ionic strength of the medium, which ultimately clarifies how these variables impact colloidal stability. <br>

Two decades of Martini: Better beads, broader scope

“…Citrate capping is particularly relevant since it is often used to increase the colloidal stability of gold NPs and as an intermediate toward the synthesis of Au NPs with other functional groups. The colloidal stability of citrate‐capped Au NPs was also studied by De Vivo and coworkers using experimental and theoretical methods, including Martini CG simulations 312 . The same group also characterized the behavior of more complex metal NPs, bound to multiple copies of a polycationic cell‐penetrating peptide, in contact with a model membrane 313 .…”

“…The colloidal stability of citrate-capped Au NPs was also studied by De Vivo and coworkers using experimental and theoretical methods, including Martini CG simulations. 312 The same group also characterized the behavior of more complex metal NPs, bound to multiple copies of a polycationic cell-penetrating peptide, in contact with a model membrane. 313 Peptide-coated NPs strongly interacted with membranes without affecting their mechanical stability; however, the fixed secondary structure of the peptides in Martini is a significant limitation in predictions of their interaction with lipid membranes.…”

Highly Heterogeneous Polarization and Solvation of Gold Nanoparticles in Aqueous Electrolytes

“…The latter is particularly relevant for modeling electrolytes in solution at room temperature. MD simulations have already been exploited to investigate gold-liquid interfaces, such as the studies of halides and biomolecules in water in contact with planar gold, [27][28][29] adsorption of water on bare 30 or functional AuNPs, 31,32 structure and dispersion state of citrate-coated AuNPs in saline solutions, 33,34 and peptide adsorption on bare AuNPs. 35 In particular, by (nonpolarizable) MD simulations we recently revealed substantial ion-specificity and facet selectivity in the adsorption structure and spatial distribution of various ions on AuNP surfaces: while sodium and some anions (e.g., Cl − , HCF 3− ) adsorb more at the 'edgy' (100) and (110) facets of the NPs, where the water hydration structure is more disordered, other ions (e.g., BF − 4 , PF − 6 , Nip − (nitrophenolate)) prefer to adsorb strongly on the extended and rather flat (111) facets.…”