Nanoimpacts at Active and Partially Active Electrodes: Insights and Limitations

While the electrochemical nanoimpact technique has recently emerged as a method of studying single entities, it is limited by requirement of a catalytically active particle impacting an inert electrode. We show that an active particle-active electrode can provide mechanistic insight into electrochemical reactions. When an individual Pt electrocatalyst adsorbs to the surface of a partially active electrode, further reduction of electrode-produced species can proceed on the nanocatalyst. Current transients obtained during hydrogen evolution allow simultaneous measurement of the Pt catalyst over different length scales, size dependency suggests H atom intercalation as a catalytic deactivation mechanism. Although results show that outer-sphere redox probes are unproductive for particle characterization, the breadth of inner-sphere electrochemical reactions makes this a promising method for understanding the properties of catalytic nanomaterials, one at a time.     

Automatic detection of peculiar galaxies in large datasets of galaxy images

We propose an image analysis unsupervised learning algorithm that can detect peculiar galaxies in datasets of galaxy images. The algorithm first computes a large set of calculated characteristics reflecting different aspects of the visual content, and then weighs them based on the σ of the values computed from the galaxy images. The weighted Euclidean distance of each galaxy image from the median is measured, and the peculiarity of each galaxy is determined based on that distance. Experimental results using irregular galaxy images show that the method can effectively detect peculiar galaxies. Code and data used in the experiments are freely available.     

Whole-Object Fluorescence Lifetime Setup for Efficient Non-Imaging Quantitative Intracellular Fluorophore Measurements

In the present study we introduce a Whole-Object Fluorescence Life Time (wo-FLT) measurement approach for ease and a relatively inexpensive method of tracing alterations in intracellular fluorophore distribution and in the physical-chemical features of the microenvironments hosting the fluorophore. Two common fluorophores, Rhodamine 123 and Acridine Orange, were used to stain U937 cells which were incubated, with and without either Carbonyl cyanide 3-chlorphenylhydrazon or the apoptosis inducer H₂O₂. The wo-FLT, which is a non-imaging quantitative measurement, was able to detect several fluorescence decay components and corresponding weights in a single cell resolution. Following cell treatment, both decay time and weight were altered. Results suggest that the prominent factor responsible for these alterations and in some cases to a shift in emission spectrum as well, is the intracellular fluorophore local concentration. In this study it was demonstrated that the proposed wo-FLT method is superior to color fluorescence based imaging in cases where the emission spectrum of a fluorophore remains unchanged during the investigated process. The proposed wo-FLT approach may be of particular importance when direct imaging is impossible.     

Enzyme-free amplified detection of DNA by an autonomous ligation DNAzyme machinery

The Zn(2+)-dependent ligation DNAzyme is implemented as a biocatalyst for the amplified detection of a target DNA by the autonomous replication of a nucleic acid reporter unit that is generated by the catalyzed ligation process. The reporter units enhance the formation of active DNAzyme units, thus leading to the isothermal autocatalytic formation of the reporter elements. The system was further developed and applied for the amplified detection of Tay-Sachs genetic disorder mutant, with a detection limit of 1.0 × 10(-11) M. Besides providing a versatile paradigm for the amplified detection of DNA, the system reveals a new, enzyme-free, isothermal, autocatalytic mechanism that introduces means for effective programmed synthesis.     

pH-programmable DNAzyme nanostructures

Two engineered DNA nanostructures consisting of a nucleic acid functional hairpin and a DNA "tweezers" assembly act as pH-switchable devices for the "ON-OFF" activation/deactivation of the horseradish-peroxidase-mimicking DNAzyme.     

Synthesis and Reactivity of Allylic and Propargylic Trichloromethanesulfinates

Abstract

The synthesis and rearrangement of the title compounds to sulfones are discussed. A facile isomerization of the allylic trichloromethyl sulfones to the corresponding vinyl sulfones is also described.     

Resonance absorption of coherent infrared radiation by thin polypropylene films and its technological applications

Tunable CO₂ and non-tunable CO₂ lasers were used for the irradiation of thin polypropylene films. The wavelength of the IR radiation was adjusted in such a way that it coincided exactly with the absorbance peak in the spectrum of the polypropylene pattern. In this way, conditions of resonance absorption of IR radiation by polymer films were produced. Strong thermal effects in PP were observed under irradiation at the resonance wavelength. The threshold value of IR power, which causes thermal phenomena in irradiated films was established. We pulled films exposed to established threshold values with a constant speed in the plane normal to the laser beam. Highly developed relief and thin traces were formed depending on the pulling speed. Traces with a width smaller than the wavelength of the incident laser beam were obtained. The IR spectra of irradiated PP films were studied with a FTIR spectrometer. Changes in the spectra of PP films were established using correlation analysis of spectral data. The phenomenon could be applied for obtaining highly developed surface relief, storage of information in polymer films and welding of polymer materials.     

Synthesis and characterization of micrometer‐sized homo and composite polyacrylonitrile particles of narrow size distribution on the basis of single‐step swelling of uniform polystyrene template microspheres

Polyacrylonitrile/polystyrene micrometer‐sized composite particles of narrow size distribution were prepared by a single‐step swelling of uniform polystyrene template microspheres with emulsion droplets of methylene chloride containing the monomer acrylonitrile and the initiator benzoyl peroxide. Methylene chloride was then evaporated carefully, followed by polymerization of acrylonitrile at 70 °C within the shrunken template particles. Polymerization of acrylonitrile also occurred at the particles' surface due to the interaction of surface polyacrylonitrile oligoradicals with acrylonitrile dissolved in the aqueous phase. Uniform polyacrylonitrile particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, TGA‐DSC, XRD, XPS, advancing contact angle, light microscope, SEM and cross‐sectional TEM. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4847–4861, 2004