Interactions of ionic liquids with uranium and its implications on biotransformation

Room temperature ionic liquids (ILs) are pure ionic compounds with melting points below 100°C, which have drawn great attention due to their many unique properties. They have been widely used in organic synthesis, analytical chemistry, and biochemistry. Although ionic liquids have been used to extract metals and radionuclides, there is no systematic study on the interactions of ILs with uranium and their effects on the biotransformation of uranium. My research focused on: (1) the interactions between uranium and ionic liquids in aqueous solution; and (2) biotransformation of uranium in the presence of ILs. The interactions between three representative ionic liquids, [EtPy] [BF4] (N-ethylpyridinium tetrafluoroborate), [EtPy][CF3COO] (N-ethyl pyridinium trifluoroacetate), [BMIM][PF6] (l-butyl-3-methylimidazolium hexafluorophosphate), and uranium were determined by various analytical techniques, such as UV-Vis spectroscopy, potentiometric titration, LCMS and X-ray absorption spectroscopy. Extended X-ray absorption fine structure (EXAFS) analysis showed the formation of monodentate complexes between uranium and [BMIM][PF6][EtPy][BF4] and a biodentate complex with [EtPy][CF3COO]. The effects of ionic liquids on the growth of anaerobic bacterium Clostridium sp. were measured by changes in optical density, pH, and gas production. The ionic liquids inhibited the growth of bacterium to varying degrees. TEM and EDS studies showed that the ILs may affect the cell membrane of the bacterium and thereby its growth. Biosorption of uranium by Clostridium sp. dramatically decreased in the presence of ILs. It decreased in the order of U\u3e U+[BMIM][PF6] \u3e U+[EtPy][BF4] and U+[EtPy][CF3COO]. The bioreduction of U(VI) to U(IV) by Clostridium sp. was affected by the presence of ILs. The rate of reduction of U, in the absence or in the presence of the monodentate complexes U:[EtPy][BF4] and U:[BMIM][PF6] was similar. However, no reduction was observed in the presence of the bidentate U:[EtPy][CF3COO] complex. Also ionic liquids showed different affinities toward reduced U(IV) in solution after bioreduction. In the absence of IL, U(IV) precipitated out rapidly; whereas in the presence of [EtPy][BF4] a substantial amount of U(IV) was present in the solution. This result can be attributed to the complexation of U(IV) with [EtPy][BF4]. Notably, this phenomenon was not observed in the presence of [BMIM][PF6] The formation of U(IV) in solution and in precipitate were confirmed by UV-Vis spectroscope, XANES and EXAFS analysis. Since ILs are relatively resistant to photodegradation and show toxicity at higher concentrations, the persistence in the environment was determined by the investigation of biodegradation of the three ILs. A soil enrichment culture degraded [EtPy][BF4] and [EtPy][CF3COO] to innocuous products, glyoxylate and acetic acid. In the presence of uranium, the rate and extent of biodegradation was slowed. N-ethyl-(4-(carbosyamino)but-3-enoic acid, semialdehyde, and (4-(carbosyamino)but-3-enoic acid were accumulated in medium as biodegradation products. Imidazolium-based ILs [BMIM][PF6] were resistant to biodegradation. This information is useful for the risk assessment of the environmentally friendly compounds

Taraxacum mongolicum extract exhibits antimicrobial activity against respiratory tract bacterial strains in vitro and in neonatal rats by enhancing systemic Th1 immunity

Purpose: To study the antimicrobial activity of the Taraxacum mongolicum extract against respiratory infection-causing bacterial strains in vitro and in neonatal rats.Methods: The in vitro antibacterial activity was assessed by micro-dilution method. Antioxidant activity was determined by ferric reducing antioxidant power (FRAP), nitro blue tetrazolium (NBT) and 2, 2- diphenyl-1-picrylhydrazyl (DPPH) assays. In vivo antimicrobial activity was evaluated in neonatal rat model. Interleukin (IL)-2 (IL-2) and gamma interferon (IFN-γ) were estimated using enzyme-linked immunosorbent assay (ELISA).Results: The hydro-methanol extract of T. mongolicum contained high levels of phenolics and flavonoids, and exhibited strong antimicrobial activity against respiratory infection-causing bacterial species with MICs of 25 - 100 μg/ml, and MBCs of 55 - 215 μg/ml. The highest and lowest antimicrobial activities were observed against Streptococcus pneumonia and Haemophilus influenza, respectively. The extract at doses of 25 and 50 mg/kg exerted protective effects against Streptococcus pneumonia infected neonatal rats by boosting their Th1 immunity. It enhanced the production of interleukin (IL)-2, concomitant with decreased production of interferon (IFN)-γ in neonatal rats. The extract contained isoetin, hesperidin, naringenin, kaempferol, sinapinic and gallic acid.Conclusion: These results suggest that the hydro-methanolic extract of Taraxacum mongolicum and its constituents can be potentially developed for use in the management of respiratory bacterial infections.Keywords: Respiratory tract infection, Interleukin, Taraxacum mongolicum, Immunity, Neonatal rat

Spatial-temporal Graph Based Multi-channel Speaker Verification With Ad-hoc Microphone Arrays

The performance of speaker verification degrades significantly in adverse acoustic environments with strong reverberation and noise. To address this issue, this paper proposes a spatial-temporal graph convolutional network (GCN) method for the multi-channel speaker verification with ad-hoc microphone arrays. It includes a feature aggregation block and a channel selection block, both of which are built on graphs. The feature aggregation block fuses speaker features among different time and channels by a spatial-temporal GCN. The graph-based channel selection block discards the noisy channels that may contribute negatively to the system. The proposed method is flexible in incorporating various kinds of graphs and prior knowledge. We compared the proposed method with six representative methods in both real-world and simulated environments. Experimental results show that the proposed method achieves a relative equal error rate (EER) reduction of $\mathbf{15.39\%}$ lower than the strongest referenced method in the simulated datasets, and $\mathbf{17.70\%}$ lower than the latter in the real datasets. Moreover, its performance is robust across different signal-to-noise ratios and reverberation time

Recovering Greater Fungal Diversity from Pristine and Diesel Fuel Contaminated Sub-Antarctic Soil Through Cultivation Using Both a High and a Low Nutrient Media Approach

Novel cultivation strategies for bacteria are widespread and well described for recovering greater diversity from the “hitherto” unculturable majority. While similar approaches have not yet been demonstrated for fungi it has been suggested that of the 1.5 million estimated species less than 5% have been recovered into pure culture. Fungi are known to be involved in many degradative processes, including the breakdown of petroleum hydrocarbons, and it has been speculated that in Polar Regions they contribute significantly to bioremediation of contaminated soils. Given the biotechnological potential of fungi there is a need to increase efforts for greater species recovery, particularly from extreme environments such as sub-Antarctic Macquarie Island. In this study, like the yet-to-be cultured bacteria, high concentrations of nutrients selected for predominantly different fungal species to that recovered using a low nutrient media. By combining both media approaches to the cultivation of fungi from contaminated and non-contaminated soils, 91 fungal species were recovered, including 63 unidentified species. A preliminary biodegradation activity assay on a selection of isolates found that a high proportion of novel and described fungal species from a range of soil samples were capable of hydrocarbon degradation and should be characterized further