Influence of Surface Ligand Molecular Structure on Phospholipid Membrane Disruption by Cationic Nanoparticles.

Cationic nanoparticles are known to interact with biological membranes and often cause serious membrane damage. Therefore, it is important to understand the molecular mechanism for such interactions and the factors that impact the degree of membrane damage. Previously, we have demonstrated that spatial distribution of molecular charge at cationic nanoparticle surfaces plays an important role in determining the cellular uptake and membrane damage of these nanoparticles.

Interfacial water and ion distribution determine ζ potential and binding affinity of nanoparticles to biomolecules.

The molecular features that dictate interactions between functionalized nanoparticles and biomolecules are not well understood. This is in part because for highly charged nanoparticles in solution, establishing a clear connection between the molecular features of surface ligands and common experimental observables such as ζ potential requires going beyond the classical models based on continuum and mean field models. Motivated by these considerations, molecular dynamics simulations are used to probe the electrostatic properties of functionalized gold nanoparticles and their interaction with a charged peptide in salt solutions.

Molecular Dynamics Simulation of Interaction between Functionalized Nanoparticles with Lipid Membranes: Analysis of Coarse-Grained Models.

We compare atomistic and two popular coarse-grained (POL- and BMW-MARTINI) models by studying the interaction between a cationic gold nanoparticle functionalized with primary alkane amines and a lipid bilayer that consists of either zwitterionic lipids or a mixture of zwitterionic and anionic lipids. In the atomistic simulations, the nanoparticle does not exhibit any notable affinity to the zwitterionic bilayer but readily binds to the 9:1 zwitterionic:anionic bilayer, and nanoparticle adsorption leads to local segregation of anionic lipids and slowing down of their diffusion. At the coarse-grained level, the POL-MARTINI model does not lead to nanoparticle-membrane binding for either bilayer system, while the BMW-MARTINI model leads to nanoparticle binding to both bilayers; with the BMW-MARTINI model, nanoparticle binding leads to much less demixing of zwitterionic and anionic lipids and moderately rates of lipid diffusion.

Hydration of diblock copolymer micelles: Effects of hydrophobicity and co-solvent.

Diblock polymer micelles dispersed in an aqueous environment are being actively investigated for various applications, but there is only a qualitative understanding of the effect of the chemical structure on the micelle hydration and water dynamics as these properties are difficult to assess experimentally. Using all-atom molecular dynamics simulations, we investigate aqueous solutions of three comparable in size diblock copolymer micelles with core-forming blocks of different hydrophobicity: polybutadiene (PB), polycaprolactone (PCL), and polytetrahydrofuran (pTHF) with the same hydrophilic block, polyethylene oxide (PEO). We found that core-block hydrophobicity and ability to form hydrogen bonds with water strongly affect the water dynamics near the core: water molecules spend considerably less time in contact with the PB block than with PCL and pTHF blocks.

The dynamics of solvation dictates the conformation of polyethylene oxide in aqueous, isobutyric acid and binary solutions.

Polymers hydrogen-bonding with solvent represent an important broad class of polymers, properties of which depend on solvation. Using atomistic molecular dynamics simulations with the OPLS/AA force field we investigate the effect of hydrogen bonding on PEO conformation and chain mobility by comparing its behavior in isobutyric acid and aqueous solutions. In agreement with experimental data, we found that in isobutyric acid PEO forms a rather rigid extended helical structure, while in water it assumes a highly flexible coil conformation.

Spontaneous Insertion, Helix Formation, and Hydration of Polyethylene Oxide in Carbon Nanotubes.

Hydration strongly affects macromolecular conformation in solution and under nanoconfinement as encountered in nature and nanomaterials. Using atomistic molecular dynamics simulations we demonstrate that polyethylene oxide spontaneously enters single wall carbon nanotubes (CNTs) from aqueous solutions and forms rodlike, helix, and wrapped chain conformations depending on the CNT diameter. We show that water organization and the stability of the polyethylene oxide hydration shell under confinement is responsible for the helix formation, which can have significant implications for nanomaterial design.