Physicochemical Properties of Gold Nanostructures Deposited on Glass

Properties of gold films sputtered onto borosilicate glass substrate were studied. UV-Vis absorption spectra were used to investigate optical parameters. XRD analysis provided information about the gold crystalline nanostructure, the texture, and lattice parameter and biaxial tension was also determined by the XRD method. The surface morphology was examined by atomic force microscopy (AFM); chemical structure of sputtered gold nanostructures was examined by X-ray photoelectron spectroscopy (ARXPS). The gold crystallites are preferentially [111] oriented on the sputtered samples. Gold deposition leads to dramatic changes in the surface morphology in comparison to pristine glass substrate. Oxygen is not incorporated into the gold layer during gold deposition. Experimental data on lattice parameter were also confirmed by theoretical investigations of nanoclusters using tight-binding potentials

Accurate Binding of Sodium and Calcium to a POPC Bilayer by Effective Inclusion of Electronic Polarization

Binding affinities and stoichiometries of Na+ and Ca2+ ions to phospholipid bilayers are of paramount significance in the properties and functionality of cellular membranes. Current estimates of binding affinities and stoichiometries of cations are, however, inconsistent due to limitations in the available experimental and computational methods. In this work, we improve the description of the binding details of Na+ and Ca2+ ions to a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) bilayer by implicitly including electronic polarization as a mean field correction, known as the electronic continuum correction (ECC). This is applied by scaling the partial charges of a selected state-of-the-art POPC lipid model for molecular dynamics simulations. Our improved ECC-POPC model reproduces not only the experimentally measured structural parameters for the ion-free membrane, but also the response of lipid headgroup to a strongly bound cationic amphiphile, as well as the binding affinities of Na+ and Ca2+ ions. With our new model, we observe on the one side negligible binding of Na+ ions to POPC bilayer, while on the other side stronger interactions of Ca2+ primarily with phosphate oxygens, which is in agreement with the previous interpretations of the experimental spectroscopic data. The present model results in Ca2+ ions forming complexes with one to three POPC molecules with almost equal probabilities, suggesting more complex binding stoichiometries than those from simple models used to interpret the NMR data previously. The results of this work pave the way to quantitative molecular simulations with realistic electrostatic interactions of complex biochemical systems at cellular membranes.Peer reviewe

Dipole time correlation functions of the Stockmayer fluid in the microcanonical and canonical ensembles

Computer simulations of Stockmayer fluids were performed to generate dipole time correlation functions (TCF) at three temperatures and three dipole moments in both the microcanonical and canonical ensembles. The effect of Nos&eacute; constant-temperature dynamics on time-dependent quantities is discussed, and empirical results are given to show that the choice of thermal inertia parameter influences the speed with which a system moves through its phase space. The time correlation functions from the simulations were analyzed in terms of current theories for dipolar systems. A functional form is proposed to cover both the longtime and short-time behavior of the time correlation functions of dipoles. The relationship between this functional form and the dielectric function of the Stockmayer system is also discussed.<br /