Self-Assembly of Nanoparticle Amphiphiles with Adaptive Surface Chemistry

Abstract

We investigate the self-assembly of amphiphilic nanoparticles (NPs) functionalized with mixed monolayers of hydrophobic and hydrophilic ligands in water. Unlike typical amphiphilic particles with "fixed" surface chemistries, the ligands used here are not bound irreversibly but can rearrange dynamically on the particles' surface during their assembly from solution. Depending on the assembly conditions, these adaptive amphiphiles form compact micellar clusters or extended chain-like assemblies in aqueous solution. By controlling the amount of hydrophobic ligands on the particles' surface, the average number of nearest neighbors--that is, the preferred coordination number--can be varied systematically from ∼ 1 (dimers) to ∼ 2 (linear chains) to ∼ 3 (extended clusters). To explain these experimental findings, we present an assembly mechanism in which hydrophobic ligands organize dynamically to form discrete patches between proximal NPs to minimize contact with their aqueous surroundings. Monte Carlo simulations incorporating these adaptive hydrophobic interactions reproduce the three-dimensional assemblies observed in experiment. These results suggest a general strategy based on reconfigurable "sticky" patches that may allow for tunable control over particle coordination number within self-assembled structures.

Nonadditivity of nanoparticle interactions

“…Nonspherically symmetric interactions owing to uneven ligand densities also play a role (119). Collective restructuring of the oligomers coating NPs maximizing hydrophobic interactions is implicated in the formation of chains of end-modified gold nanorods (120) and hexagonally packed mesoscale capsules (Fig.…”

Modified Lipid Extraction Methods for Deep Subsurface Shale

“…Such mineral-lipid interactions have been shown to depend on a combination of the isoelectric point of the minerals, physical adsorption, electrostatic, van der Waals, and chemical bonding (Stevens et al, 2009; Oleson et al, 2010; Sahai et al, 2017). Amphipathic compounds (11-mercaptoundecanoic acid, MUA and 1-dodecanethoil, DDT) have been used to minimize the interference of such mineral-lipid interactions through self-assembly of lipid molecules in solution (Lee et al, 2014). In the presence of these compounds, the lipid molecules aggregated, while in their absence the lipid molecules remained un-aggregated in solution.…”

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges

“…The method we describe is based on gold NPs (6.2 AE 0.8 nm in diameter) functionalized with mixed monolayers of hydrophilic (TMA) and hydrophobic (ODT or DDT) ligands in ar atio of 77:23 unless otherwise stated (Figure 1a;s ee Supporting Information for experimental details). [11] As shown below,addition of these particles to solutions containing open bilayer structures resulted in the selective adsorption of particles at the hydrophobic edge of the membrane.T he resulting NP capped bilayers were stable against further growth and remained unaggregated in solution for several weeks.T od emonstrate the generality of this mechanism, we investigated the effects of amphiphilic NPs on three different bilayer-forming materials:1 )hollow tubules of DC 8,9 PC lipid, [4] 2) helical ribbons of cholesterol, [3] and 3) sheared vesicles of DPPC lipid. [13] Each material is used to highlight adifferent opportunity for applying these NP surfactants 1) to precisely control the dimensions of lipid nanostructures,2)to inhibit the growth of undesirable assemblies such as cholesterol gallstones,and 3) to stabilize lipid microdiscs used in the study of membrane proteins.T aken together,t hese results suggest that amphiphilic NPs can act as versatile supramolecular surfactants,w hich bind to select surfaces and control their growth.…”

“…Nanoparticles (NPs) with appropriate surface chemistries are attractive candidates for stabilizing such structures,a st heir size can be made commensurate with the bilayer thickness, thereby facilitating multivalent interactions with the bilayer edge.S urface-active nanoparticles are known to adsorb strongly at oil-water interfaces [9] and to various types of bilayer membranes. [10] In particular, amphiphilic nanoparticles with hydrophilic and hydrophobic domains on their surface can form stable dispersions in water [11] and interact strongly with the hydrophobic core of bilayer membranes. [11a, 12] Here,w es how that amphiphilic NPs can bind selectively to the open edge of bilayer membranes to stabilize otherwise transient structures and inhibit their further growth.…”