Vibrational spectra of cyclooctatetraenyl alkali metal complexes [C8H8M2 (M = Na, K)]: A theoretical study

The cyclooctatetraenyl dianion (C₈H₈²⁻) π-conjugated system forms a stable complex system with alkali and some transition metals. The results of vibrational analysis for C₈H₈M₂ (M = Na, K) complexes were reported here. The geometries of C₈H₈M₂ (M = Na, K) were optimized using ab initio (HF, MP2, CCSD(T)) and DFT (B3LYP) methods with 6-311G** and 6-311++G** basis sets and the harmonic frequencies were obtained. To reproduce and compare with the experimental values the structurally similar molecules C₅H₅M (M = Na, K) and benzene were studied. The scale factors obtained from these systems were applied to predict the experimental frequencies of C₈H₈M₂ (M = Na, K). The force field and vibrational spectra are analyzed and the most probable assignments are proposed for all the fundamentals based on the potential energy distribution.     

Recommendations for oversight of nanobiotechnology: dynamic oversight for complex and convergent technology

Federal oversight of nanobiotechnology in the U.S. has been fragmented and incremental. The prevailing approach has been to use existing laws and other administrative mechanisms for oversight. However, this “stay-the-course” approach will be inadequate for such a complex and convergent technology and may indeed undermine its promise. The technology demands a new, more dynamic approach to oversight. The authors are proposing a new oversight framework with three essential features: (a) the oversight trajectory needs to be able to move dynamically between “soft” and “hard” approaches as information and nano-products evolve; (b) it needs to integrate inputs from all stakeholders, with strong public engagement in decision-making to assure adequate analysis and transparency; and (c) it should include an overarching coordinating entity to assure strong inter-agency coordination and communication that can meet the challenge posed by the convergent nature of nanobiotechnology. The proposed framework arises from a detailed case analysis of several key oversight regimes relevant to nanobiotechnology and is informed by inputs from experts in academia, industry, NGOs, and government.     

Estimation of surface area concentration of workplace incidental nanoparticles based on number and mass concentrations

Surface area was estimated by three different methods using number and/or mass concentrations obtained from either two or three instruments that are commonly used in the field. The estimated surface area concentrations were compared with reference surface area concentrations (SA_REF) calculated from the particle size distributions obtained from a scanning mobility particle sizer and an optical particle counter (OPC). The first estimation method (SA_PSD) used particle size distribution measured by a condensation particle counter (CPC) and an OPC. The second method (SA_INV1) used an inversion routine based on PM1.0, PM2.5, and number concentrations to reconstruct assumed lognormal size distributions by minimizing the difference between measurements and calculated values. The third method (SA_INV2) utilized a simpler inversion method that used PM1.0 and number concentrations to construct a lognormal size distribution with an assumed value of geometric standard deviation. All estimated surface area concentrations were calculated from the reconstructed size distributions. These methods were evaluated using particle measurements obtained in a restaurant, an aluminum die-casting factory, and a diesel engine laboratory. SA_PSD was 0.7–1.8 times higher and SA_INV1 and SA_INV2 were 2.2–8 times higher than SA_REF in the restaurant and diesel engine laboratory. In the die casting facility, all estimated surface area concentrations were lower than SA_REF. However, the estimated surface area concentration using all three methods had qualitatively similar exposure trends and rankings to those using SA_REF within a workplace. This study suggests that surface area concentration estimation based on particle size distribution (SA_PSD) is a more accurate and convenient method to estimate surface area concentrations than estimation methods using inversion routines and may be feasible to use for classifying exposure groups and identifying exposure trends.     

Attenuation studies near K-absorption edges using Compton scattered <Superscript>241</Superscript>Am gamma rays

We have carried out photon attenuation measurements at several energies in the range from 49.38 keV to 57.96 keV around the K-absorption edges of the rare earth elements Sm, Eu, Gd, Tb, Dy and Er using 59.54 keV gamma rays from ²⁴¹Am source after Compton scattering from an aluminium target. Pellets of oxides of the rare earth elements were chosen as mixture absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. The scattered gamma rays were detected by an HPGe detector. The results are consistent with theoretical values derived from the XCOM package.