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

In a previous article of this book, it has been shown that the concept developed in the gas phase to explain the behavior of electrons scattered from isolated atoms and molecules could be utilized to explain several electron scattering phenomena occurring in the solid phase. The results presented clearly indicated that many of the electron resonances (i.e., transient anions) present in the gas-phase were also found in the various scattering cross sections of solids. Transient molecular anions are not only involved in electron scattering, in the sense that they do not necessarily reemit the captured electron. They can also be stabilized into a permanent molecular anion or they can dissociate producing a stable anion fragment and a neutral atom, molecule or radical. In the present article, it is shown that these processes are present near the surface of solids where they can be observed by detecting stable anion emission in vacuum or charge accumulation on the surface. The mechanisms responsible for resonance stabilization and dissociative attachment (DA) in the condensed phase can be linked to those responsible for similar processes in the gas phase, by comparison between experimental results obtained in the two phases and, with those of the dipolar dissociation (DD) process which does not involve the initial formation of an anion resonance.

Effects of the Solid Phase on Resonance Stabilization, Dissociative Attachment and Dipolar Dissociation

Purpose Assessment of the radiation dose delivered to a tumor and different organs is a major issue when using radiolabelled compounds for diagnostic imaging or endoradiotherapy. The present article reports on a study to correlate the mean 18F-fluorodeoxyglucose (18F-FDG) activity in different tissues measured in a mouse model by positron emission tomography (PET) imaging, with the dose assessed in vitro by Fricke dosimetry. Methods The dose-response relationship of the Fricke dosimeter and PET data was determined at different times after adding 18F-FDG (0–80 MBq) to a Fricke solution (1 mM ferrous ammonium sulfate in 0.4 M sulfuric acid). The total dose was assessed at 24 h (~13 half-lives of 18F-FDG). The number of coincident events produced in 3 mL of Fricke solution or 3 mL of deionized water that contained 60 MBq of 18F-FDG was measured using the Triumph/LabPET8TM preclinical PET/CT scanner. The total activity concentration measured by PET was correlated with the calculated dose from the Fricke dosimeter, at any exposure activity of 18F-FDG. Results The radiation dose measured with the Fricke dosimeter increased rapidly during the first 4 h after adding 18F-FDG and then gradually reached a plateau. Presence of non-radioactive-FDG did not alter the Fricke dosimetry. The characteristic responses of the dosimeter and PET imaging clearly exhibit linearity with injected activity of 18F-FDG. The dose (Gy) to time-integrated activity (MBq.h) relationship was measured, yielding a conversion factor of 0.064 ± 0.06 Gy/MBq.h in the present mouse model. This correlation provides an efficient alternative method to measure, three-dimensionally, the total and regional dose absorbed from 18F-radiotracers. Conclusions The Fricke dosimeter can be used to calibrate a PET scanner, thus enabling the determination of dose from the measured radioactivity emitted by 18F-FDG in tissues. The method should be applicable to radiotracers with other positron-emitting radionuclides.

Estimation of the Internal Dose Imparted by 18F-Fluorodeoxyglucose to Tissues by Using Fricke Dosimetry in a Phantom and Positron Emission Tomography

Metal nanoparticles are considered as highly promising radiosensitizers in cancer radiotherapy. Understanding their radiosensitization mechanisms is critical for future clinical applications. This review is focused on the initial energy deposition by short-range Auger electrons; when high energy radiation is absorbed by gold nanoparticles (GNPs) located near vital biomolecules; such as DNA. Auger electrons and the subsequent production of secondary low energy electrons (LEEs) are responsible for most the ensuing chemical damage near such molecules. We highlight recent progress on DNA damage induced by the LEEs produced abundantly within about 100 nanometers from irradiated GNPs; and by those emitted by high energy electrons and X-rays incident on metal surfaces under differing atmospheric environments. LEEs strongly react within cells; mainly via bound breaking processes due to transient anion formation and dissociative electron attachment. The enhancement of damages induced in plasmid DNA by LEEs; with or without the binding of chemotherapeutic drugs; are explained by the fundamental mechanisms of LEE interactions with simple molecules and specific sites on nucleotides. We address the major challenge of metal nanoparticle and GNP radiosensitization; i.e., to deliver the maximum local dose of radiation to the most sensitive target of cancer cells (i.e., DNA). To achieve this goal the emitted electrons from the absorbed high energy radiation must be short range, and produce a large local density of LEEs, and the initial radiation must have the highest possible absorption coefficient compared to that of soft tissue (e.g., 20–80 keV X-rays).

/pdf/mechanisms-of-nanoscale-radiation-enhancement-by-metal-3petcblb.pdf

Mechanisms of Nanoscale Radiation Enhancement by Metal Nanoparticles: Role of Low Energy Electrons

The study of chlorine-containing molecules, especially chlorofluoro-carbons (CFCs), has received continued interest mainly because of their well-known association with the ozone depletion in the Earth’s stratosphere. It was first proposed1 that chlorine atoms are produced by photolysis of such species as CF2C12 (CFC-12) and CFCl3 (CFC-11). For the former species, the reaction is: CF2Cl2 + hv→Cl + CF2Cl. The resultant Cl atom destroys ozone via a (Cl, C1O) reaction chain. The significance of CFCs to the ozone depletion has been well recognized since the discovery of the Antarctic ozone hole.2 Nevertheless, the above photodissociation model predicts a maximum rate of Cl atom production in the upper stratosphere at altitudes of 30∼40 km and a negligible rate below 20 km.1 However, the ozone hole is found at the lower polar stratosphere at an altitude of ∼15 km. It is known that the creation of the ozone hole is closely related to the existence of polar stratospheric clouds (PSCs) that form in the Antarctic stratosphere due to the extreme cold temperature; these PSCs consist mainly of condensed-phase water ice and nitric acid/ice.3,4 The formation of the ozone hole has been attributed to heterogeneous reactions occurring on surfaces of PSC ice particles, which convert chlorine from the inactive compounds (HCl and ClONO2) into reactive Cl2: HCl + ClONO2 → Cl2 + HNO3.3,4 Upon photolysis, Cl2 releases chlorine to destroy O3.

Léon Sanche

Papers

Effects of the Solid Phase on Resonance Stabilization, Dissociative Attachment and Dipolar Dissociation

Estimation of the Internal Dose Imparted by 18F-Fluorodeoxyglucose to Tissues by Using Fricke Dosimetry in a Phantom and Positron Emission Tomography

Mechanisms of Nanoscale Radiation Enhancement by Metal Nanoparticles: Role of Low Energy Electrons

Large Enhancements in Dissociative Electron Attachment to Chlorine Containing Molecules Adsorbed on H2O Ice

Absolute vibrational and electronic cross sections for low-energy electron scattering from condensed Thymidine