Surface-Modified Pd/CeO Single-Atom Catalyst Shows Increased Activity for Suzuki Cross-Coupling.

Single-atom catalysts (SACs) comprise catalytically active atoms dispersed on supports; they combine the high activity and site uniformity of homogeneous catalysts with the ease of separability of heterogeneous catalysts. However, SACs lack fine control over the active site, provided by ligands in homogeneous catalysts. In this work, we demonstrate that modification of the support with an organic monolayer is a viable approach to improving the catalytic performance.

Cationic Polymer Coating Increases the Catalytic Activity of Gold Nanoparticles toward Anionic Substrates.

Organic coatings on catalytic metal nanoparticles (NPs) typically hinder their activity due to the blocking of active sites. Therefore, considerable effort is made to remove organic ligands when preparing supported NP catalytic materials. Here, cationic polyelectrolyte coatings are shown to increase the catalytic activity of partially embedded gold nanoislands (Au NIs) toward transfer hydrogenation and oxidation reactions with anionic substrates compared to the activity of identical but uncoated Au NIs.

UV- and Visible-Light Photopatterning of Molecular Gradients Using the Thiol-yne Click Reaction.

The rational design of chemical coatings is used to control surface interactions with small molecules, biomolecules, nanoparticles, and liquids as well as optical and other properties. Specifically, micropatterned surface coatings have been used in a wide variety of applications, including biosensing, cell growth assays, multiplexed biomolecule interaction arrays, and responsive surfaces. Here, a maskless photopatterning process is studied, using the photocatalyzed thiol-yne "click" reaction to create both binary and gradient patterns on thiolated surfaces.

Electron ratchets: State of the field and future challenges.

Electron ratchets are non-equilibrium electronic devices that break inversion symmetry to produce currents from non-directional and random perturbations, without an applied net bias. They are characterized by strong parameter dependence, where small changes in operating conditions lead to large changes in the magnitude and even direction of the resulting current. This high sensitivity makes electron ratchets attractive research subjects, but leads to formidable challenges in their deeper study, and particularly to their useful application.

How To Drive a Flashing Electron Ratchet To Maximize Current.

Biological systems utilize a combination of asymmetry, noise, and chemical energy to produce motion in the highly damped environment of the cell with molecular motors, many of which are "ratchets", nonequilibrium devices for producing directed transport using nondirectional perturbations without a net bias. The underlying ratchet principle has been implemented in man-made micro- and nanodevices to transport charged particles by oscillating an electric potential with repeating asymmetric features. In this experimental study, the ratcheting of electrons in an organic semiconductor is optimized by tuning the temporal modulation of the oscillating potential, applied using nanostructured electrodes.

Light-responsive organic flashing electron ratchet.

Ratchets are nonequilibrium devices that produce directional motion of particles from nondirectional forces without using a bias, and are responsible for many types of biological transport, which occur with high yield despite strongly damped and noisy environments. Ratchets operate by breaking time-reversal and spatial symmetries in the direction of transport through application of a time-dependent potential with repeating, asymmetric features. This work demonstrates the ratcheting of electrons within a highly scattering organic bulk-heterojunction layer, and within a device architecture that enables the application of arbitrarily shaped oscillating electric potentials.

Mechanisms of Symmetry Breaking in a Multidimensional Flashing Particle Ratchet.

Ratcheting is a mechanism that produces directional transport of particles by rectifying nondirectional energy using local asymmetries rather than a net bias in the direction of transport. In a flashing ratchet, an oscillating force (here, an AC field) is applied perpendicular to the direction of transport. In an effort to explore the properties of current experimentally realizable ratchet systems, and to design new ones, this paper describes classical simulations of a damped flashing ratchet that transports charged nanoparticles within a transport layer of finite, non-zero thickness.

Identification of two mechanisms for current production in a biharmonic flashing electron ratchet.

Ratchets rectify the motion of randomly moving particles, which are driven by isotropic sources of energy such as thermal and chemical energy, without applying a net, time-averaged force between source and drain. This paper describes the behavior of a damped electron, modeled by a quantum Lindblad master equation, within a flashing ratchet (a one-dimensional potential that oscillates between a flat surface and a periodic asymmetric surface). By examining the complete space of all biharmonic potential shapes and a large range of oscillation frequencies, two modes of ratchet operation, differentiated by their oscillation frequencies (relative to the rate of electron relaxation), are identified.

Distance-dependent fluorescence of tris(bipyridine)ruthenium(II) on supported plasmonic gold nanoparticle ensembles.

Metal surfaces and nanostructures interact with fluorescent materials, enhancing or quenching the fluorescence intensity, modifying the fluorescent lifetime, and changing the emission frequency and linewidth. These interactions occur via several mechanisms, including radiationless energy transfer, electric field enhancement, and photonic mode density modification. The interactions display a strong dependence on the distance between the fluorophore and the metal structures.

Stabilization of metal nanoparticle films on glass surfaces using ultrathin silica coating.

Metal nanoparticle (NP) films, prepared by adsorption of NPs from a colloidal solution onto a preconditioned solid substrate, usually form well-dispersed random NP monolayers on the surface. For certain metals (e.g.

Improved Sensitivity of Localized Surface Plasmon Resonance Transducers Using Reflection Measurements.

The refractive index sensitivity (RIS) of a localized surface plasmon resonance (LSPR) transducer is one of the key parameters determining its effectiveness in sensing applications. LSPR spectra of nanoparticulate gold films, including Au island films prepared by evaporation on glass and annealing as well as immobilized Au nanoparticle (NP) films, were measured in the transmission and reflection modes. It is shown that the RIS, measured as the wavelength shift in solvents with varying refractive index (RI), is significantly higher in reflection measurements.

Sensitivity and optimization of localized surface plasmon resonance transducers.

Gold nanoisland films displaying localized surface plasmon resonance optical response were constructed by evaporation on glass and annealing. The surface plasmon distance sensitivity and refractive index sensitivity (RIS) for island films of different nominal thicknesses and morphologies were investigated using layer-by-layer polyelectrolyte multilayer assembly. Since the polymer forms a conformal coating on the Au islands and the glass substrate between islands, the relative sensitivity of the optical response to adsorption on and between islands was evaluated.

Graded Autocatalysis Replication Domain (GARD): kinetic analysis of self-replication in mutually catalytic sets.

A Graded Autocatalysis Replication Domain (GARD) model is proposed, which provides a rigorous kinetic analysis of simple chemical sets that manifest mutual catalysis. It is shown that catalytic closure can sustain self replication up to a critical dilution rate, lambda c, related to the graded extent of mutual catalysis. We explore the behavior of vesicles containing GARD species whose mutual catalysis is governed by a previously published statistical distribution.

Continuous ethanol production by immobilized yeast reactor coupled with membrane pervaporation unit.

A system comprised of an immobilized yeast reactor producing ethanol, with a membrane pervaporation module for continuously removing and concentrating the produced ethanol, was developed. The combined system consisted of two integrated circulation loops: In one the sugar-containing medium is circulated through the membrane pervaporation module. The two loops were interconnected in a way allowing for separate parameter optimization (e.

Some peculiarities of water transport through plasticized nonporous membranes.

"Liquid" and "plasticized" solvent membranes are of interest as possible analogues of biological systems. Semipermeable homogeneous films are prepared by plasticizing polyvinylchloride with organic phosphates. Water permeability of such films is relatively high.

Flux ratio and driving forces in a model of active transport.

In order to analyze the energetics of active transport, a hypothetical carrier model is considered in which the active transport process is reduced to a minimal number of elementary steps. The relation between the following three quantities is examined: The affinity of the reaction driving the active transport, the ratio of isotope fluxes between identical solutions ("short-circuit"), and the maximal chemical potential difference which the active transport system can maintain. The interdependence of isotopeinteraction and the degree of coupling between transport and chemical reaction is shown explicitly: when the transport and chemical reaction are completely coupled, there is marked isotope interaction.

The coupling of an enzymatic reaction to transmembrane flow of electric current in a synthetic "active transport" system.

If a chemical reaction is constrained to occur within an asymmetric structure, e.g. by the presence of bound or otherwise trapped enzyme, coupling of the reaction to the flow of one or more solutes, or to the flow of electric current, becomes possible.