Search

Continuous-flow methodologies have been applied to the synthesis of a number of fluorinated alkynyl arenes and heteroarenes. Through a series of optimizations reagent stoichiometry and reaction time were improved and substrate specificity was interrogated. Using optimized conditions under copper-free Sonogashira type couplings readily available arene building blocks were derivatized with fluoroalkynyl side chains in

Silver nanoparticles (Ag NPs) are widely used for their antimicrobial activity and consequently the particles will become environmental contaminants. This study evaluated in sand and soil matrices the toxicity of 10nm spherical Ag NPs (1 and 3 mg Ag/L) toward a beneficial soil bacterium, Pseudomonas chlororaphis O6. In sand, both NP doses resulted in loss in bacterial culturability whereas in a loam soil, no cell death was observed. Amendments of sand with clays (30% v/v kaolinite or bentonite) did not protect the bacterium when challenged with Ag NPs. However, culturability of the bacterium was maintained when the Ag NP-amended sand was mixed with soil pore water or humic acid. Imaging by atomic force microscopy revealed aggregation of single nanoparticles in water, and their embedding into background material when suspended in pore water and humic acids. Zeta potential measurements supported aggregation and surface charge modifications with pore water and humic acids. Measurement of soluble Ag in the microcosms and geochemical modeling to deduce the free ion concentration revealed bacterial culturability was governed by the predicted free Ag ion concentrations. Our study confirmed the importance of Ag NPs as a source of ions and illustrated that processes accounting for protection in soil against Ag NPs involved distinct NP- and ion-effects. Processes affecting NP bioactivity involved surface charge changes due to sorption of Ca²⁺ from the pore water leading to agglomeration and coating of the NPs with humic acid and other organic materials. Removal of bioactive ions included the formation of soluble Ag complexes with dissolved organic carbon and precipitation of Ag ions with chloride in pore water. We conclude that mitigation of toxicity of Ag NPs in soils towards a soil bacterium resides in several interactions that differentially involve protection from the Ag NPs or the ions they produce.

The toxicity of commercially-available CuO and ZnO nanoparticles (NPs) to pathogenic bacteria was compared for a beneficial rhizosphere isolate, Pseudomonas chlororaphis O6. The NPs aggregated, released ions to different extents under the conditions used for bacterial exposure, and associated with bacterial cell surface. Bacterial surface charge was neutralized by NPs, dependent on pH. The CuO NPs were more toxic than the ZnO NPs. The negative surface charge on colloids of extracellular polymeric substances (EPS) was reduced by Cu ions but not by CuO NPs; the EPS protected cells from CuO NPs-toxicity. CuO NPs-toxicity was eliminated by a Cu ion chelator, suggesting that ion release was involved. Neither NPs released alkaline phosphatase from the cells' periplasm, indicating minimal outer membrane damage. Accumulation of intracellular reactive oxygen species was correlated with CuO NPs lethality. Environmental deposition of NPs could create niches for ion release, with impacts on susceptible soil microbes.

This study explores the potential antimicrobial mechanisms of commercial silver nanoparticles (Ag NPs) in the environmental bacterium, Pseudomonas chlororaphis O6. The 10 nm size NPs aggregated in water, as demonstrated by atomic force microscopy. Solubility of the NPs at 10 mg/L was 0.28 mg/L (pH 6) and 2.3 mg/L (pH 7); release from 10 mg/L bulk Ag was below detection. The NPs eliminated cell culturability at 3 mg/L, whereas no effect was observed at 10 mg/L bulk Ag. Zeta potential measurements revealed that the NPs were negatively charged; unlike Ag ions, their addition to the negatively charged cells did not change cell charge at pH 6, but showed a trend to reduce cell charge at pH 7. Isolated extracellular polymeric substances (EPS) from Pc O6 was polydisperse, with negative charge that was neutralized by Ag ions, but not by the NPs. Addition of EPS eliminated Ag NP's toxicity in cells lacking EPS. Intracellular accumulation of OH was not detected in NP-treated cells; however, the use of scavengers suggested the NPs caused extracellular H 2 O 2 production. No evidence was found for loss of membrane integrity upon treatment with the NPs. Our findings indicate that growth of environmental bacteria could be impaired by Ag NPs, depending on the extent of EPS production.