Under an applied magnetic field, superparamagnetic Fe 3 O 4 nanoparticles with complementary DNA strands assemble into crystalline, pseudo-1D elongated superlattice structures. The assembly process is driven through a combination of DNA hybridization and particle dipolar coupling, a property dependent on particle composition, size, and inter-particle distance. The DNA controls inter-particle distance and crystal symmetry, while the magnetic field leads to anisotropic crystal growth. Increasing the dipole interaction between particles by increasing particle size or external field strength leads to a preference for a particular crystal morphology (e.g., rhombic dodecahedra, stacked clusters, and smooth rods). Molecular dynamics (MD) simulations show that an understanding of both DNA hybridization energetic and magnetic interactions are required to predict the resulting crystal morphology. Taken together, the data show that applied magnetic fields with magnetic nanoparticles can be deliberately used to access nanostructures beyond what is possible with DNA hybridization alone.

Superparamagnetic nanoparticles incorporated into elastic media offer the possibility of creating actuators driven by external fields in a multitude of environments. Here, magnetoelastic membranes are studied through a combination of continuum mechanics and molecular dynamics simulations. We show how induced magnetic interactions affect the buckling and the configuration of magnetoelastic membranes in rapidly precessing magnetic fields. The field, in competition with the bending and stretching of the membrane, transmits forces and torques that drives the membrane to expand, contract, or twist. We identify critical field values that induce spontaneous symmetry breaking as well as field regimes where multiple membrane configurations may be observed. Our insights into buckling mechanisms provide the bases to develop soft, autonomous robotic systems that can be used at micro- and macroscopic length scales.

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Apolipoprotein C-III (ApoC-III) is found on high-density lipoproteins (HDL) and remodels 1,2-dimyristoyl-sn-glycero-3-phosphocholine vesicles into HDL-like particles known as nanodiscs. Using single-Trp containing ApoC-III mutants, we have studied local sidechain environments and interactions in nanodiscs at positions W42, W54, and W65. Using transmission electron microscopy and circular dichroism spectroscopy, nanodiscs were characterized at the ultrastructural and secondary conformational levels, respectively. Nearly identical particles (15 ± 2 nm) were produced from all proteins containing approximately 25 ± 4 proteins per particle with an average helicity of 45–51% per protein. Distinct residue-specific fluorescence properties were observed with W54 residing in the most hydrophobic environment followed by W42 and W65. Interestingly, time-resolved anisotropy measurements revealed that Trp sidechain mobility is uncorrelated to the polarity of its surroundings. W54 is the most mobile compared to W65 and W42, which are more immobile in a nanodisc-bound state. Based on Trp spectral comparisons of ApoC-III in micellar and vesicle environments, ApoC-III binding within nanodiscs more closely resembles a bilayer-bound state. Despite being structurally similar, we found marked differences during nanodisc formation by the Trp variants as a function of temperature with W42 behaving the most similar to the WT protein. Our data suggest that despite the modest mutations of Trp to Phe at two of the three native sites, the interfacial location of W42 is important for lipid binding and nanodisc assembly, which may be biologically meaningful as of the three Trp residues, only W42 is invariant among mammals.