Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

http://nanotubes.rutgers.edu/PDFs/nchem_TMDs_2013.pdf

The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets

Here, we present a review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms. For purpose of this review, silver nanomaterials include silver nanoparticles, stabilized silver salts, silver–dendrimer, polymer and metal oxide composites, and silver-impregnated zeolite and activated carbon materials. While there is some evidence that silver nanoparticles can directly damage bacteria cell membranes, silver nanomaterials appear to exert bacteriocidal activity predominantly through release of silver ions followed (individually or in combination) by increased membrane permeability, loss of the proton motive force, inducing de-energization of the cells and efflux of phosphate, leakage of cellular content, and disruption DNA replication. Eukaryotic cells could be similarly impacted by most of these mechanisms and, indeed, a small but growing body of literature supports this concern. Most antimicrobial studies are performed in simple aquatic media or cell culture media without proper characterization of silver nanomaterial stability (aggregation, dissolution, and re-precipitation). Silver nanoparticle stability is governed by particle size, shape, and capping agents as well as solution pH, ionic strength, specific ions and ligands, and organic macromolecules—all of which influence silver nanoparticle stability and bioavailability. Although none of the studies reviewed definitively proved any immediate impacts to human health or the environment by a silver nanomaterial containing product, the entirety of the science reviewed suggests some caution and further research are warranted given the already widespread and rapidly growing use of silver nanomaterials.

https://link.springer.com/content/pdf/10.1007%2Fs11051-010-9900-y.pdf

A review of the antibacterial effects of silver nanomaterials and potential implications for human health and the environment

Molecular conductance junctions are structures in which single molecules or small groups of molecules conduct electrical current between two electrodes. In such junctions, the connection between the molecule and the electrodes greatly affects the current-voltage characteristics. Despite several experimental and theoretical advances, including the understanding of simple systems, there is still limited correspondence between experimental and theoretical studies of these systems.

/pdf/electron-transport-in-molecular-wire-junctions-2m2v92jao5.pdf

Electron transport in molecular wire junctions.

The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Most of the energy deposited in cells by ionizing radiation is channeled into the production of abundant free secondary electrons with ballistic energies between 1 and 20 electron volts. Here it is shown that reactions of such electrons, even at energies well below ionization thresholds, induce substantial yields of single- and double-strand breaks in DNA, which are caused by rapid decays of transient molecular resonances localized on the DNA's basic components. This finding presents a fundamental challenge to the traditional notion that genotoxic damage by secondary electrons can only occur at energies above the onset of ionization, or upon solvation when they become a slowly reacting chemical species.

http://science.sciencemag.org/content/sci/287/5458/1658.full.pdf

Resonant Formation of DNA Strand Breaks by Low-Energy (3 to 20 eV) Electrons

Dry films of platinum chemotherapeutic drugs covalently bound to plasmid DNA (Pt-DNA) represent a useful experimental model to investigate direct effects of radiation on DNA in close proximity to platinum chemotherapeutic agents, a situation of considerable relevance to understand the mechanisms underlying concomitant chemoradiation therapy In the present paper we determine the optimum conditions for preparation of Pt-DNA films for use in irradiation experiments Incubation conditions for DNA platination reactions have a substantial effect on the structure of Pt-DNA in the films The quantity of Pt bound to DNA as a function of incubation time and temperature is measured by inductively coupled plasma mass spectroscopy Our experiments indicate that chemical instability and damage to DNA in Pt-DNA samples increase when DNA platination occurs at 37°C for 24 hours, the condition which has been extensively used for in vitro studies Platination of DNA for the formation of Pt-DNA films is optimal at room temperature for reaction times less than 2 hours By increasing the concentration of Pt compounds relative to DNA and thus accelerating the rate of their mutual binding, it is possible to prepare Pt-DNA samples containing known concentrations of Pt while reducing DNA degradation caused by more lengthy procedures

/pdf/dna-platinum-thin-films-for-use-in-chemoradiation-therapy-juh7s07lwa.pdf

DNA-Platinum Thin Films for Use in Chemoradiation Therapy Studies

O− electron stimulated desorption from O2 in CO and N2 matrices

The impact of low-energy electrons (7--19 eV, \ensuremath{\Delta}E=60 meV) is found to induce desorption of metastable particles (${\mathrm{N}}_{2}^{\mathrm{*}}$ and ${\mathrm{CO}}^{\mathrm{*}}$) from condensed multilayer ${\mathrm{N}}_{2}$ and CO films. For ${\mathrm{N}}_{2}$ films, the yield function of the metastable-particle signal, which shows two regions (below and above 11 eV) of large intensity difference, is assigned to excitations to the valence state ${\mathit{B}}^{3}$${\mathrm{\ensuremath{\Pi}}}_{\mathit{g}}$ and to the Rydberg state ${\mathit{E}}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$, respectively. Desorption of ${\mathrm{N}}_{2}^{\mathrm{*}}$ above 11 eV is believed to be due to the repulsive interaction between the excited molecules and the solid surface. The desorption yield of ${\mathrm{CO}}^{\mathrm{*}}$, which is much weaker than that for ${\mathrm{N}}_{2}^{\mathrm{*}}$, is discussed in terms of vibrational energy transfer from the vibrational excited a${\ensuremath{'}}^{3}$${\mathrm{\ensuremath{\Sigma}}}^{+}$ state.

Low-energy-electron stimulated desorption of metastable particles from condensed N 2 and CO

We present a comparison between the electron stimulated desorption (ESD) of anions from DNA samples prepared by lyophilization (an example of poorly organized or nonuniform films) and molecular self-assembly (well-ordered films). The lyophilization (or freeze- drying) method is perhaps the most frequently employed technique for forming DNA films for studies of low-energy electron (LEE) interactions leading to DNA damage; however, this technique usually produces nonuniform films with considerable clustering which may affect DNA configuration and enhance sample charging when the film is irradiated. Our results confirm the general validity of ESD measurements obtained with lyophilized samples, but also reveal limitations of lyophilization for LEE studies on DNA films. Specifically we observe some modulation of structures, associated with dissociative electron attachment, in the anion yield functions from different types of DNA film, confirming that conformational factors play a role in the LEE induced damage to DNA.

Effect of morphology of thin DNA films on the electron stimulated desorption of anions

Well-ordered films of molecular DNA can be formed by the attachment of thiolated DNA oligonucleotides to a supporting gold substrate. The gold substrate represents a significant fraction of the total cost of preparing such films, and it is thus important to determine whether such substrates can be reused. Here, we investigate with X-ray photoelectron spectroscopy the suitability of UV/ozonolysis previously employed to remove alkanethiols from gold, for removing 40-mer, single- and double-stranded synthetic DNA. We find that while UV/O3 can indeed remove thiolated DNA from gold slides, the treatment times required permit the implantation of additional organic contaminants.

/pdf/x-ray-photoelectron-spectroscopy-analysis-of-gold-surfaces-2ogpqyo326.pdf

Léon Sanche

Papers

DNA-Platinum Thin Films for Use in Chemoradiation Therapy Studies

O− electron stimulated desorption from O2 in CO and N2 matrices

Low-energy-electron stimulated desorption of metastable particles from condensed N 2 and CO

Effect of morphology of thin DNA films on the electron stimulated desorption of anions

X-ray photoelectron spectroscopy analysis of gold surfaces after removal of thiolated DNA oligomers by ultraviolet/ozone treatment.