Adsorption mechanism of water molecules surrounding Au nanoparticles of different sizes

Functionalized Cu-based metal oxide nanoparticles with enhanced Cd+2 adsorption capacity and their ecotoxicity assessment by molecular docking

In the present study, synthesis of eco-friendly Cu-based metal oxides nanoparticles [CuO, Cu₂O, and CuO&Cu₂O nanoparticles (NPs)] without and with functionalization with Diethylene glycol (DEG) has been demonstrated. The synthesized NPs were screened for their ability to adsorb multiple heavy metal ions from an aqueous solution. Based on the maximum Cadmium (Cd⁺²) ion adsorption capacity, functionalized Cu₂O (fCu₂O) NPs were selected for the detailed characterization and batch studies. The average size of fCu₂O NPs was found to be 57.4 ± 6.14 nm in comparison to NPs without capping (72.6 ± 5.19 nm). The experimental parameters viz. contact time, initial pH, and initial concentration were optimized, and the obtained results were interpreted using standard isotherms and kinetic models. The maximum Cd⁺² adsorption on fCu₂O NPs was observed at initial solution pH 7. The adsorption of Cd⁺² was found to be decreased at acidic pH due to the protonation of functional groups present on the NPs surface. A maximum Cd⁺² adsorption capacity of 204 ± 6.2 mg g^-1 was obtained from the Langmuir adsorption isotherm. The crystal structure of NPs was prepared and docked with the protein targets of selected soil microbes in order to determine their ecotoxicity. The obtained results showed that NPs exhibited low affinity towards protein targets in comparison to the standard used. It suggests that NPs have less impact on the functionality of soil microbes and are thus safe for their disposal into the soil micro-environment.

Interaction of nanoparticles with biological macromolecules: a review of molecular docking studies

The high frequency of using engineered nanoparticles in various medical applications entails a deep understanding of their interaction with biological macromolecules. Molecular docking simulation is now widely used to study the binding of different types of nanoparticles with proteins and nucleic acids. This helps not only in understanding the mechanism of their biological action but also in predicting any potential toxicity. In this review, the computational techniques used in studying the nanoparticles interaction with biological macromolecules are covered. Then, a comprehensive overview of the docking studies performed on various types of nanoparticles will be offered. The implication of these predicted interactions in the biological activity and/or toxicity is also discussed for each type of nanoparticles.

Ion-Specific Adsorption on Bare Gold (Au) Nanoparticles in Aqueous Solutions: Double-Layer Structure and Surface Potentials

We study the solvation and electrostatic properties of bare gold (Au) nanoparticles (NPs) of 1-2 nm in size in aqueous electrolyte solutions of sodium salts of various anions with large physicochemical diversity (Cl^-, BF₄^-, PF₆^-, Nip^- (nitrophenolate), 3- and 4-valent hexacyanoferrate (HCF)) using nonpolarizable, classical molecular dynamics computer simulations. We find a substantial facet selectivity in the adsorption structure and spatial distribution of the ions at the AuNPs: while sodium and some of the 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., BF₄^-, PF₆^-, Nip^-) prefer to adsorb strongly on the extended and rather flat (111) facets. In particular, Nip^-, which features an aromatic ring in its chemical structure, adsorbs strongly and perturbs the first water monolayer structure on the NP (111) facets substantially. Moreover, we calculate adsorptions, radially resolved electrostatic potentials as well as the far-field effective electrostatic surface charges and potentials by mapping the long-range decay of the calculated electrostatic potential distribution onto the standard Debye-Hückel form. We show how the extrapolation of these values to other ionic strengths can be performed by an analytical Adsorption-Grahame relation between the effective surface charge and potential. We find for all salts negative effective surface potentials in the range from -10 mV for NaCl down to about -80 mV for NaNip, consistent with typical experimental ranges for the zeta potential. We discuss how these values depend on the surface definition and compare them to the explicitly calculated electrostatic potentials near the NP surface, which are highly oscillatory in the ±0.5 V range.

Molecular Dynamics Studies of Poly(Lactic Acid) Nanoparticles and Their Interactions with Vitamin E and TLR Agonists Pam1CSK4 and Pam3CSK4

Poly(lactic acid) (PLA) nanoparticles (NPs) are widely investigated due to their bioresorbable, biocompatible and low immunogen properties. Interestingly, many recent studies show that they can be efficiently used as drug delivery systems or as adjuvants to enhance vaccine efficacy. Our work focuses on the molecular mechanisms involved during the nanoprecipitation of PLA NPs from concentrated solutions of lactic acid polymeric chains, and their specific interactions with biologically relevant molecules. In this study, we evaluated the ability of a PLA-based nanoparticle drug carrier to vectorize either vitamin E or the Toll-like receptor (TLR) agonists Pam₁CSK₄ and Pam₃CSK₄, which are potent activators of the proinflammatory transcription factor NF-κB. We used dissipative particle dynamics (DPD) to simulate large systems mimicking the nanoprecipitation process for a complete NP. Our results evidenced that after the NP formation, Pam₁CSK₄ and Pam₃CSK₄ molecules end up located on the surface of the particle, interacting with the PLA chains via their fatty acid chains, whereas vitamin E molecules are buried deeper in the core of the particle. Our results allow for a better understanding of the molecular mechanisms responsible for the formation of the PLA NPs and their interactions with biological molecules located either on their surfaces or encapsulated within them. This work should allow for a rapid development of better biodegradable and safe vectorization systems with new drugs in the near future.

A Water Solvation Shell Can Transform Gold Metastable Nanoparticles in the Fluxional Regime

Solvated gold nanoparticles have been modeled in the fluxional regime by density functional theory including dispersion forces for an extensive set of conventional morphologies. The study of isolated adsorption of one water molecule shows that the most stable adsorption forms are similar (corners and edges) regardless of the nanoparticle shape and size, although the adsorption strength differs significantly (0.15 eV). When a complete and explicit water solvation shell interacts with gold nanoclusters, metastable in vacuum and presenting a predominance of (100) square facets (ino-decahedra Au₅₅ and Au₁₄₇), these nanoparticles are found unstable and transform into the closest morphologies exhibiting mainly (111) triangular facets and symmetries. The corresponding adsorption strength per water molecule becomes independent of shape and size and is enhanced by the formation of two hydrogen bonds on average. For applications in radiotherapy, this study suggests that the shapes of small gold nanoparticles should be homogenized by interacting with the biological environment.

Molecular-Level "Observations" of the Behavior of Gold Nanoparticles in Aqueous Solution and Interacting with a Lipid Bilayer Membrane

We use coarse-grained molecular dynamics simulations to "observe" details of interactions between ligand-covered gold nanoparticles and a lipid bilayer model membrane. In molecular dynamics simulations, one puts the individual atoms and groups of atoms of the physical system to be "observed" into a simulation box, specifies the forms of the potential energies of interactions between them (ultimately quantum based), and lets them individually move classically according to Newton's equations of motion, based on the forces arising from the assumed potential energy forms. The atoms that are chemically bonded to each other stay chemically bonded, following known potentials (force fields) that permit internal degrees of freedom (internal rotation, torsion, vibrations), and the interactions between nonbonded atoms are simplified to Lennard-Jones forms (in our case) and coulombic (where electrical charges are present) in which the parameters are previously optimized to reproduce thermodynamic properties or are based on quantum electronic calculations. The system is started out at a reasonable set of coordinates for all atoms or groups of atoms, and then permitted to develop according to the equations of motion, one small step (usually 10 fs time step) at a time, for millions of steps until the system is at a quasi-equilibrium (usually reached after hundreds of nanoseconds). We then let the system play out its motions further for many nanoseconds to observe the behavior, periodically taking snapshots (saving all positions and energies), and post-processing the snapshots to obtain various average descriptions of the system. Alkanethiols of various lengths serve as examples of hydrophobic ligands and methyl-terminated PEG with various numbers of monomer units serve as examples of hydrophilic ligands. Spherical gold particles of various diameters as well as gold nanorods form the core to which ligands are attached. The nanoparticles are characterized at the molecular level, especially the distributions of ligand configurations and their dependence on ligand length, and surface coverage. Self-assembly of the bilayer from an isotropic solution and observation of membrane properties that correspond well to experimental values validate the simulations. The mechanism of permeation of a gold NP coated with either a hydrophobic or a hydrophilic ligand, and its dependence on surface coverage, ligand length, core diameter, and core shape, is investigated. Lipid response such as lipid flip-flops, lipid extraction, and changes in order parameter of the lipid tails are examined in detail. The mechanism of permeation of a PEGylated nanorod is shown to occur by tilting, lying down, rotating, and straightening up. The nature of the information provided by molecular dynamics simulations permits understanding of the detailed behavior of gold nanoparticles interacting with lipid membranes which in turn helps to understand why some known systems work better than others and aids the design of new particles and improvement of methods for preparing existing ones.

Understanding nanoparticle cellular entry: A physicochemical perspective

Understanding interactions between nanoparticles (NPs) with biological matter, particularly cells, is becoming increasingly important due to their growing application in medicine and materials, and consequent biological and environmental exposure. For NPs to be utilised to their full potential, it is important to correlate their functional characteristics with their physical properties, which may also be used to predict any adverse cellular responses. A key mechanism for NPs to impart toxicity is to gain cellular entry directly. Many parameters affect the behaviour of nanomaterials in a cellular environment particularly their interactions with cell membranes, including their size, shape and surface chemistry as well as factors such as the cell type, location and external environment (e.g. other surrounding materials, temperature, pH and pressure). Aside from in vitro and in vivo experiments, model cell membrane systems have been used in both computer simulations and physicochemical experiments to elucidate the mechanisms for NP cellular entry. Here we present a brief overview of the effects of NPs physical parameters on their cellular uptake, with focuses on 1) related research using model membrane systems and physicochemical methodologies; and 2) proposed physical mechanisms for NP cellular entrance, with implications to their nanotoxicity. We conclude with a suggestion that the energetic process of NP cellular entry can be evaluated by studying the effects of NPs on lipid mesophase transitions, as the molecular deformations and thus the elastic energy cost are analogous between such transitions and endocytosis. This presents an opportunity for contributions to understanding nanotoxicity from a physicochemical perspective.