Global Optimization of 8–10 Atom Palladium–Iridium Nanoalloys at the DFT Level

The global optimization of PdnIr(N–n) N = 8–10 clusters has been performed using the Birmingham Cluster Genetic Algorithm (BCGA). Structures were evaluated directly using density functional theory (DFT), which has allowed the identification of Ir and Ir-rich PdIr cubic global minima, displaying a strong tendency to segregate. The ability of the searches to find the putative global minimum has been assessed using a homotop search method, which shows a high degree of success. The role of spin in the system has been considered through a series of spin-restricted reoptimizations of BCGA-DFT minima. The preferred spin of the clusters is found to vary widely with composition, showing no overall trend in lowest-energy multiplicities

Alkyl Isocyanide-Derivatized Platinum Nanoparticles

Alkyl Isocyanide-Derivatized Platinum Nanoparticle

Effect of Molecular Structure on Electrochemical Phase Behavior of Phospholipid Bilayers on Au(111)

Lipid bilayers form the basis of biological cell membranes, selective and responsive barriers vital to the function of the cell. The structure and function of the bilayer are controlled by interactions between the constituent molecules and so vary with the composition of the membrane. These interactions also influence how a membrane behaves in the presence of electric fields they frequently experience in nature. In this study, we characterize the electrochemical phase behavior of dipalmitoylphosphatidylcholine (DPPC), a glycerophospholipid prevalent in nature and often used in model systems and healthcare applications. DPPC bilayers were formed on Au(111) electrodes using Langmuir–Blodgett and Langmuir–Schaefer deposition and studied with electrochemical methods, atomic force microscopy (AFM) and in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). The coverage of the substrate determined with AFM is in accord with that estimated from differential capacitance measurements, and the bilayer thickness is slightly higher than for bilayers of the similar but shorter-chained lipid, dimyristoylphosphatidylcholine (DMPC). DPPC bilayers exhibit similar electrochemical response to DMPC bilayers, but the organization of molecules differs, particularly at negative charge densities. Infrared spectra show that DPPC chains tilt as the charge density on the metal is increased in the negative direction, but, unlike in DMPC, the chains then return to their original tilt angle at the most negative potentials. The onset of the increase in the chain tilt angle coincides with a decrease in solvation around the ester carbonyl groups, and the conformation around the acyl chain linkage differs from that in DMPC. We interpret the differences in behavior between bilayers formed from these structurally similar lipids in terms of stronger dispersion forces between DPPC chains and conclude that relatively subtle changes in molecular structure may have a significant impact on a membrane’s response to its environment

Synthesis of an Achiral Isomer of Lipoic Acid As an Anchor Group for SAM Formation on Gold Surfaces

Isolipoic acid, a symmetrical and achiral isomer of the commonly used α-lipoic acid, has previously been overlooked as a tether group for the formation of self-assembled monolayers (SAMs). Here its ready synthesis through a new route and its functionalization with ferrocenyl groups for redox-active SAM formation on gold electrodes are described

Macrocyclic Metal Complex–DNA Conjugates for Electrochemical Sensing of Single Nucleobase Changes in DNA

The direct incorporation of macrocyclic cyclidene complexes into DNA via automated synthesis results in a new family of metal-functionalized DNA derivatives that readily demonstrate their utility through the ability of one redox-active copper­(II)-containing strand to distinguish electrochemically between all four canonical DNA nucleobases at a single site within a target sequence of DNA

Macrocyclic Metal Complex–DNA Conjugates for Electrochemical Sensing of Single Nucleobase Changes in DNA

The direct incorporation of macrocyclic cyclidene complexes into DNA via automated synthesis results in a new family of metal-functionalized DNA derivatives that readily demonstrate their utility through the ability of one redox-active copper­(II)-containing strand to distinguish electrochemically between all four canonical DNA nucleobases at a single site within a target sequence of DNA

A Selective Blocking Method To Control the Overgrowth of Pt on Au Nanorods

A method for the preparation of smooth deposits of Pt on Au nanorods is described, involving sequential deposition steps with selective blocking of surface sites that reduces Pt-on-Pt deposition. The Au–Pt nanorods prepared by this method have higher long-term stability than those prepared by standard Pt deposition. Electrochemical data show that the resulting structure has more extended regions of Pt surface and enhanced activity toward the carbon monoxide oxidation and oxygen reduction reactions

Influence of the Lipid Backbone on Electrochemical Phase Behavior

Sphingolipids are an important class of lipids found in mammalian cell membranes with important structural and signaling roles. They differ from another major group of lipids, the glycerophospholipids, in the connection of their hydrocarbon chains to their headgroups. In this study, a combination of electrochemical and structural methods has been used to elucidate the effect of this difference on sphingolipid behavior in an applied electric field. N-Palmitoyl sphingomyelin forms bilayers of similar coverage and thickness to its close analogue di-palmitoyl phosphatidylcholine. Grazing incidence diffraction data show slightly closer packing and a smaller chain tilt angle from the surface normal. Electrochemical IR results at low charge density show that the difference in tilt angle is retained on deposition to form bilayers. The bilayers respond differently to increasing electric field strength: chain tilt angles increase for both molecules, but sphingomyelin chains remain tilted as field strength is further increased. This behavior is correlated with disruption of the hydrogen-bonding network of small groups of sphingomyelin molecules, which may have significance for the behavior of molecules in lipid rafts in the presence of strong fields induced by ion gradients or asymmetric distribution of charged lipids

Effect of Anionic Lipids on Mammalian Plasma Cell Membrane Properties

The effect of lipid composition on models of the inner leaflet of mammalian cell membranes has been investigated. Grazing incidence X-ray diffraction and X-ray and neutron reflectivity have been used to characterize lipid packing and solvation, while electrochemical and infrared spectroscopic methods have been employed to probe phase behavior in an applied electric field. Introducing a small quantity of the anionic lipid dimyristoyl­phosphatidyl­serine (DMPS) into bilayers of zwitterionic dimyristoyl­phosphatidyl­ethanolamine (DMPE) results in a significant change in the bilayer response to an applied field: the tilt of the hydrocarbon chains increases before returning to the original tilt angle on detachment of the bilayer. Equimolar mixtures, with slightly closer chain packing, exhibit a similar but weaker response. The latter also tend to incorporate more solvent during this electrochemical phase transition, at levels similar to those of pure DMPS. Reflectivity measurements reveal greater solvation of lipid layers for DMPS > 30 mol %, matching the greater propensity for DMPS-rich bilayers to incorporate water. Taken together, the data indicate that the range of 10–35 mol % DMPS provides optimum bilayer properties (in flexibility and function as a barrier), which may explain why the DMPS content of cell membranes tends to be found within this range