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

We report the results of a study on the influence of organic salts on the induction of single strand breaks (SSBs) and double strand breaks (DSBs) in DNA by electrons of 1 eV to 60 keV. Plasmid DNA films are prepared with two different concentrations of organic salts, by varying the amount of the TE buffer (Tris-HCl and EDTA) in the films with ratio of 1:1 and 6:1 Tris ions to DNA nucleotide. The films are bombarded with electrons of 1, 10, 100, and 60 000 eV under vacuum. The damage to the 3197 base-pair plasmid is analyzed ex vacuo by agarose gel electrophoresis. The highest yields are reached at 100 eV and the lowest ones at 60 keV. The ratios of SSB to DSB are surprisingly low at 10 eV (∼4.3) at both salt concentrations, and comparable to the ratios measured with 100 eV electrons. At all characteristic electron energies, the yields of SSB and DSB are found to be higher for the DNA having the lowest salt concentration. However, the organic salts are more efficient at protecting DNA against the damage induced by 1 and 10 eV electrons. DNA damage and protection by organic ions are discussed in terms of mechanisms operative at each electron energy. It is suggested that these ions create additional electric fields within the groove of DNA, which modify the resonance parameter of 1 and 10 eV electrons, namely, by reducing the electron capture cross-section of basic DNA units and the lifetime of corresponding transient anions. An interstrand electron transfer mechanism is proposed to explain the low ratios for the yields of SSB to those of DSB produced by 10 eV electrons.

Influence of organic ions on DNA damage induced by 1 eV to 60 keV electrons

Lifetime of Negative Ion Resonances and the Density of Free Electron States: O 2 Isolated in an Argon Matrix

We report absolute electron scattering cross sections σp for the production of CO within thin solid film of carbon dioxide (CO2) condensed on a solid Ar substrate. The CO fragments, which remain trapped within the bulk of the carbon dioxide film, are detected in situ by recording energy losses to their lowest triplet electronic state a 3Π using high-resolution electron-energy-loss spectroscopy. The production of CO is studied as a function of the electron exposure, film thickness, and incident electron energy between 2 and 30 eV, a range within which most of the secondary electrons are created in systems irradiated by high-energy particles. The energy dependence is characterized by a feature around 4 eV with σp=(7.0±4.0)×10−18 cm2, a minimum around 7 eV, a strong rise up to a large and broad maximum around 15 eV with σp=(5.4±2.5)×10−17 cm2, a decrease to a minimum around 18.5 eV, and finally a monotonous increase up to 30 eV. The CO production is discussed in terms of the formation of electron resonances ...

Low-energy electron scattering cross section for the production of CO within solid films of carbon dioxide.

This chapter addresses the nanoscale dynamics involved in the sensitization of biological cells to ionizing radiation. More specifically, it describes the role of low energy electrons (LEE) in radiosensitization by gold nanoparticles and chemotherapeutic agents, as well as potential applications to radiotherapy. The basic mechanisms of action of the LEE generated within nanoscopic volumes by ionizing radiation are described in solid water ice and various forms of DNA. These latter include the subunits (i.e., a base, a sugar or the phosphate group), short single strands (i.e., oligonucleotides) and plasmid and linear DNA. By comparing the results from experiments with the different forms of the DNA molecule and theory, it is possible to determine fundamental mechanisms that are involved in the dissociation of the subunits, base release and the production of single, double-strand breaks and cross-links. Below 15 eV, LEE localize on DNA subunits to form transient negative ions. Such states can damage DNA by dissociating into a stable anion and radical fragment(s), via dissociative electron attachment, or by decaying into dissociative electronically excited states. LEE can also transfer from one DNA subunit to another, particularly from a base to the phosphate group, where they can induce cleavage of the C-O bond (i.e., break a strand). DNA damage and the corresponding nanoscale dynamics are found to be modified in the presence of other cellular constituents. For example, condensing on DNA the most abundant cellular molecule, H2O, induces the formation of a new type of transient anion whose parent is a H2O-DNA complex.

Nanoscale Dynamics of Radiosensitivity: Role of Low Energy Electrons

Vacuum experiments with monoenergetic low-energy electrons (LEEs) impacting on biomolecules have revealed basic mechanisms of radiobiological damage. To move closer to cellular conditions, we explore the possibility of damaging DNA at standard atmospheric pressure with electrons of 0–1.5 eV. These electrons are produced by UV light incident on a tantalum or n-Si substrate, onto which a five-monolayer film of DNA is deposited. Total conformational damage, cross-links, and double- and single-strand breaks (SSBs) are measured as a function of LEE fluence. The photoelectron energy distribution can be modified by changing the work function of the substrate or the photon energy. In a N2 atmosphere with a tantalum substrate, the yields of SSBs (5 ± 2 × 10–14 electron–1 molecule–1) and their number per energy deposited (46 ± 36 × 10–4/eV) are in good agreement with those obtained, under similar conditions, by monoenergetic 0.5–1.0 eV electron impact in vacuo and 1.5 KeV X-ray photoelectrons at atmospheric pressur...

Léon Sanche

Papers

Influence of organic ions on DNA damage induced by 1 eV to 60 keV electrons

Lifetime of Negative Ion Resonances and the Density of Free Electron States: O 2 Isolated in an Argon Matrix

Low-energy electron scattering cross section for the production of CO within solid films of carbon dioxide.

Nanoscale Dynamics of Radiosensitivity: Role of Low Energy Electrons

DNA Strand Breaks Induced by 0–1.5 eV UV Photoelectrons under Atmospheric Pressure