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We report a heterogeneous reaction to reduce HAuCl4 solution and form gold nanoparticles (AuNPs) on stainless steel needle surfaces. Through bubbling of nitrogen, AuNPs dispersed into the solution homogeneously. Subsequently, AuNPs were immobilized on the surface of polydimethylsiloxane (PDMS). The immobilized AuNPs exhibit catalase-mimetic activity in a 2 wt% H2O2 solution. [ABSTRACT FROM AUTHOR]

The formation of the electrical double layer (EDL) in an aqueous solution in contact with the charged solid surfaces of a slit-type nanopore has been simulated by grand canonical Monte Carlo (GCMC) and canonical Monte Carlo (CMC) methods. In the GCMC simulations, a primitive EDL model in which water is considered as a continuum and the ions are considered as hard spheres is used. The results are found to be slightly different from those predicted by the Gouy-Chapman model at low electrolyte concentration and low surface charge density. The GCMC results were then used as an initial condition for the CMC sinmulations of a nonprimitive model in which the EDL is composed of molecular water (four-point transferable intermolecular potential, together with fluctuating charge model), cations (Na[SUP+]), and anions (Cl[SUP-]). The nonprimitive model provides a very different view of the EDL at the atomic level. For example, a single layer of water molecules, instead of counterions, is strongly adsorbed on negatively charged surfaces. This feature cannot be observed in the Gouy-Chapman or in the primitive model. Moreover, because the charged surfaces are covered by water molecules, the maximum counterion concentration in a nanopore occurs at the center, instead of on the surfaces, of the pore. This phenomenon is also supported by experimental data and theoretical calculations found in the literature. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations have been performed to study the arrangement of water molecules between charged surfaces. The molecular water used—the four- point transferable intermolecular potential (TIP4P), together with fluctuating charge (FQ)—constitutes the water model TIP4P-FQ. The TIP4P-FQ features the same molecular frame as the TIP4P model; however, with the former, charges on the molecular sites of the same molecule are allowed to fluctuate in response to their environment. Therefore, the induced dipole moment under an external field is inherently considered in the TIP4P-FQ water model. This feature makes it more useful than multipoint fixed-charge models, such as the TIP4P, in studying water arrangement between charged surfaces. The formation of a few ordering layers of water molecules adjacent to a charged surface is confirmed by (N,V,T) Monte Carlo simulations. The preferable orientation of water molecules in this study is found to be similar to previous findings in the literature, with the oxygen atoms pointing to the positively charged surface (oxygen-down) and the hydrogen atoms pointing to the negatively charged surface (oxygen-up). Modeling results also demonstrate that the dominant orientation at the negatively charged surface is one O-H bond pointing to the surface while another O-H bond is aligned parallel to the charged surface. In addition, simulation results using the TIP4P-FQ water model show that the water density in the interfacial region increases ∼8%-14%, which is lower than the density increase observed in experimental data discussed in the literature. [ABSTRACT FROM AUTHOR]

Polybrominated diphenyl ethers (PBDEs), chemicals commonly used as flame-retardants in consumer products, are emerging persistent organic pollutants that are ubiquitous in the environment. In this study, we report a PBDE-respiring isolate - Dehalococcoides mccartyi strain GY50, which debrominates the most toxic tetra- and penta-BDE congeners (∼1.4 µM) to diphenyl ether within 12 days with hydrogen as the electron donor. The complete genome sequence revealed 26 reductive dehalogenase homologous genes ( rdhAs), among which three genes ( pbrA1, pbrA2 and pbrA3) were highly expressed during PBDE debromination. After 10 transfers of GY50 with trichloroethene or 2,4,6-trichlorophenol as the electron acceptor instead of PBDEs, the ssrA-specific genome island ( ssrA-GI) containing pbrA1 and pbrA2 was deleted from the genome of strain GY50, leading to two variants (strain GY52 with trichloroethene, strain GY55 with 2,4,6-trichlorophenol) with identically impaired debromination capabilities (debromination of penta-/tetra-BDEs ceased at di-BDE 15). Through analysis of Illumina paired-end sequencing data, we identified read pairs that probably came from variants that contain ssrA-GI deletions, indicating their possible presence in the original strain GY50 culture. The two variant strains provide real-time examples on rapid evolution of organohalide-respiring organisms. As PBDE-respiring organisms, GY50-like strains may serve as key players in detoxifying PBDEs in contaminated environments. [ABSTRACT FROM AUTHOR]