Influence of binding groups on molecular junction formation

We study the formation mechanism of molecular junctions using break-junction experiments. We explore the contribution of gold-atom rearrangements in the electrodes by analyzing the junction stretching length, the length of individual plateaus, and the length of the gold one-atom contacts. Comparing the results for alkane dithiols and diamines, we conclude that thiols affect gold electrode dynamics significantly more than amines. This is a vital factor to be considered when comparing different binding groups.     

Amperometric Sniffer for Volatile Amines Based on Paper‐Supported Room Temperature Ionic Liquids Enabling Rapid Assessment of Fish Spoilage

A gas sensors based on a room temperature ionic liquid (RTIL) supported on paper is proposed as amperometric sniffer for monitoring volatile amines (VAs) released from fish samples, in order to gain indication of their state of turning spoiled. It was used as a paper electrochemical detector (PED) for a flow injection system in which controlled headspace volumes in equilibrium with ice‐stored fish samples were directly injected. The performance of this RTIL‐PED sensor was preliminarily tested on synthetic samples of trimethylamine (TMA), dimethylamine (DMA), methylamine (MA) and ammonia (i.e. the main species responsible for the typical flavor of spoiled fish), thus verifying that only TMA, DMA and MA can be detected because NH₃ oxidation occurred beyond the solvent discharge. This notwithstanding, detection of the sole TMA, DMA and MA as a whole turned out to be well suited for the rapid assessment of fish spoilage, since during storage the release enhancement for these amines is largely predominant over that of NH₃. Repeatable (8 % RSD) sharp peaks were detected for all amines above over a wide range (5–1000 nmol) and a detection limit of a little more than 3 nmol was inferred for a signal‐to‐noise ratio of 3. This approach was applied to the detection of VAs released from real fish samples (sardines), in parallel to the determination of their total volatile basic nitrogen (TVBN), which is a conventional indicator frequently adopted for the chemical quality assessment of fish. A substantially satisfactory agreement was found by comparing the data achieved by these two approaches.     

γ-Cyclodextrin/alkylthiol inclusion compounds crystals as substrates for the formation and immobilization of gold nanoparticles produced by magnetron sputtering

In this work, we report the nanodecoration of microcrystals of inclusion compound (IC) of γ-cyclodextrin (γ-CD) that contain octanethiol, decanethiol and dodecanethiol. Crystals of these ICs provide a suitable environment for nucleation, growth and immobilization of gold nanoparticles that were obtained by the magnetron sputtering technique. The use of γ-CD IC substrates with a specific surface morphology (i.e., the functional group of the guest molecule faces outward preferentially from a crystal plane) is an efficient method for the preparation of AuNPs with low size dispersion, which is due to the high affinity between the functional group of the surfactant alkylthiol guest with the metal nanoparticles.     

Compact involutions of semisimple quantum groups

It is proved that a complex cosemisimple Hopf algebra has at most one compact involution modulo automorphisms.     

A digital electronic caliper

A new electronic caliper of unique design is described. The determination of the timing intervals is accomplished by digital means providing an accuracy dependent only upon a single crystal-controlled oscillator. Means has also been provided for varying the display to match different assumed sonic velocities without impairment of accuracy. Two of these units are in routine clinical use with commercially available scanning apparatus.     

Model of the interaction potential of an atom with a hard corrugated surface incorporating a stationary potential well

We propose a new atom-surface interaction potential model which is designed for use in the recent exact theory for the elastic scattering of an atom by a hard corrugated surface model which incorporates a stationary attractive potential well [N. García, F.O. Goodman, V. Celli and N.R. Hill, Phys. Rev. B (1979)]. The model parameters are adjusted to obtain a best-fit to all available experimental data on atom-surface bound-state energies, and comparisons are also made with the latest theoretical data, with satisfactory results.     

Synthesis of flexible, ultrathin gold nanowires in organic media

Gold nanoparticles are very interesting because of their potential applications in microelectronics, optical devices, analytical detection schemes, and biomedicine. Though shape control has been achieved in several polar solvents, the capability to prepare organosols containing elongated gold nanoparticles has been very limited. In this work we report a novel, simplified method to produce long, thin gold nanowires in an organic solvent (oleylamine), which can be readily redispersed into nonpolar organic solvents. These wires have a characteristic flexible, hairy morphology arising from a small thickness (<2 nm) and an enormous length (up to several micrometers), with the possibility of adjusting the dimensions through modification of the growth conditions, in particular, the gold salt concentration. Despite their extreme aspect ratio, the wires are stable in solution for long periods of time but easily break when irradiated with high-energy electron beams during transmission electron microscopy.     

Quantitative electrochemical SERS of flavin at a structured silver surface

In situ electrochemical surface enhanced Raman spectra (SERS) for an immobilized monolayer of a flavin analogue (isoalloxazine) at nanostructured silver surfaces are reported. Unique in the present study, the flavin is not directly adsorbed at the Ag surface but is attached through a chemical reaction between cysteamine adsorbed on the Ag surface and methylformylisoalloxazine. Even though the flavin is held away from direct contact with the metal, strong surface enhancements are observed. The nanostructured silver surfaces are produced by electrodeposition through colloidal templates to produce thin (<1 microm) films containing close-packed hexagonal arrays of uniform 900 nm sphere segment voids. The sphere segment void (SSV) structured silver surfaces are shown to be ideally suited to in situ electrochemical SERS studies at 633 nm, giving stable, reproducible surface enhancements at a range of electrode potentials, and we show that the SER spectra are sensitive to subfemtomole quantities of immobilized flavin. Studies of the SER spectra as a function of the electrode potential show clear evidence for the formation of the flavin semiquinone at the electrode surface at cathodic potentials.