Determination of trace elements in bottled water in Greece by instrumental and radiochemical neutron activation analyses

Summary Four different bottled water brands sold in Greece in the winter of 2001-2002 were analyzed for a wide range of chemical elements, using neutron activation analysis (NAA). The elements Na and Br were determined instrumentally (INAA), whereas the other metals and trace elements radiochemically (RNAA). The results indicated that the mean level of all the elements determined in the samples were well within the European Union (EU) directive on drinking water and accomplish the drinking water standards of the World Health Organisation (WHO) as well as of the Food and Drug Administration (FDA).     

Magnetic, electronic, and structural characterization of nonstoichiometric iron oxides at the nanoscale

We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mossbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements.     

The anomalous Mössbauer fraction of ferritin and polysaccharide iron complex (PIC)

Mössbauer studies of the ubiquitous protein molecule ferritin and its synthetic biomimic polysaccharide iron complex (PIC) exhibit an anomaly in the Mössbauer spectrum wherein the recoil free fraction orf-factor has a sharp drop with respect to temperature as the temperature rises above 30 K for mammalian ferritin and 60 K for PIC. The anomaly coincides with the disappearance of hyperfine splitting, which is due to superparamagnetic relaxation above the blocking temperature. Different absorbers were used to experimentally investigate the effect of absorber thickness on the Mössbauer spectrum. The anomaly persists for thin absorbers. Also, spectra treated with FFT procedures to eliminate the thickness effect still exhibit this anomaly. Motion of the core with respect to the protein shell was also eliminated as a possible source for this phenomenon, by comparing the Debye temperature obtained from the temperature dependence of thef-factor and the isomer shift. A comparison of the magnetic anisotropy constants from magnetization studies with those obtained by relating the hyperfine fieldH of the Mössbauer spectra to the fluctuations of the magnetization imply that the ferritin and PIC molecules possess magnetic anisotropy energy which may not be strictly uniaxial. This, we believe, may be intimately connected with the mechanism causing thef-factor anomaly.This work was carried out in partial fulfilment of the requirements of the PhD degree at Tufts University.     

Neutron activation analysis and natural radioactivity measurements of lignite and ashes from Megalopolis basin,Greece

Elemental concentrations and specific activity values of natural radionuclides were measured in lignite, bottom ash and fly ash samples collected from the Megalopolis power plant A in southern Greece, using nuclear analytical techniques. The results show that the elements As, Br, Mo, Sb, Se, and U were enriched in the lignite samples, the elements Mo, Se and U in bottom ash, while fly ash samples were enriched in As, Mo, Sb, Se and U. Specific activity measurements also show that ²³⁸U (²²⁶Ra) activity values in lignite and both ash samples were high relative to the corresponding data for coal and earth crust given in the literature. As a high quantity of fly ash is produced during the operation of the lignite power plant A, this power plant should be considered as a major source of air particulate pollution and radiation to the population living in the vicinity of lignite burning power plant.     

Functionalization of Graphene Oxide and its Biomedical Applications

Graphene oxide (GO) offers interesting physicochemical and biological properties for biomedicine due to its versatility, biocompatibility, small size, large surface area, and its ability to interact with biological cells and tissues. GO is a two-dimensional material of exceptional strength, unique optical, physical, mechanical, and electronic properties. Ease of functionalization and high antibacterial activity are two major properties identified with GO. Due to its excellent aqueous processability, amphiphilicity, surface functionalization capability, surface enhanced Raman scattering (SERS), and fluorescence quenching ability, GO chemically exfoliated from oxidized graphite is considered a promising material for biological applications. In addition, due to π-π* transitions, a low energy is required for electron movement, a property important in Biosensor and Bioimaging applications of GO. In this article, we present an overview of current advances in GO applications in biomedicine and discuss future perspectives. We conclude that GO is going to play a vital role in Biomedical applications in the near future.     

N−H Bond Formation at a Diiron Bridging Nitride

Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N−H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N−H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E−H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH₃ in high yield through a reaction that engages the redox-activity of the ligand during PCET.     

Determination of fine and hyperfine structure in Fe−Mo(W) dinuclear clusters

The fine and hyperfine structure of two dinuclear sulfide bridged Fe?Mo complex anions and their W homologues have been studied by magnetic susceptibility and Mössbauer measurements. It is shown that, by following a stepwise methodology, it is possible to derive from the low temperature magnetization data the value and sign of the fine structure parametersD andE/D. These parameters are further confirmed by an independent analysis of the Mössbauer data. Magnetic and electric hyperfine interaction parameters are also determined from the Mössbauer results. Both fine and hyperfine parameters point to a valence scheme, for all complexes, of Fe^II?Mo^VI(W^VI) with a varying degree of charge delocalization from the iron to the molybdenum (tungsten) site. The parameterD is negative with an orientation of itsz axis close to theV _zz axis.