33,352 research outputs found

    Vertical heterogeneity of hydrocarbon-degrading bacteria in a core sediment sample from the Central Indian Ridge

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    Hydrocarbons are ubiquitous in marine environments and might fuel hydrocarbon-metabolizing microbes in the ocean. Numerous studies have documented microbial hydrocarbon degradation in water columns and deep-sea surface sediment. However, the degradation potential and biogeochemical cycling of hydrocarbons in subsurface sediments remain largely unknown. In this study, we used two different hydrocarbons, n-hexadecane (HEX) and methylcyclohexane (MCH), to investigate the distribution and diversity of hydrocarbon-consuming bacteria in a core sediment sample from the Central Indian Ridge (CIR), which is adjacent to mid-ridge hydrothermal vents in the Indian Ocean. We observed different vertical profiles of HEX- and MCH-degrading bacteria in the core sediments. Specifically, HEX-degrading bacteria were universally distributed, while MCH-degrading bacteria were found only in the intermediate layers of the core sediments. Changing factors including dissolved oxygen might affect the natural distribution of different hydrocarbon consumers. We found that a novel species of the genus C1-B045 might play a pivotal role in metabolizing MCH in the CIR deep biosphere. Through amino acid identity comparison with published sequences, we determined that C1-B045 harbors two novel classes of cyclohexanone monooxygenases involved in MCH metabolism. This study sheds light on the structure and function of hydrocarbon-consuming microbes in deep biospheres

    Exposure to a mixture of non-persistent environmental chemicals and neonatal thyroid function in a cohort with improved exposure assessment

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    International audienceBackground: In vitro and toxicological studies have shown that non-persistent environmental chemicals can perturb thyroid hormone homeostasis. Epidemiological studies with improved exposure assessment (i.e., repeated urine samples) are needed to evaluate effects of these compounds, individually or as a mixture, in humans. We studied the associations between prenatal exposure to non-persistent environmental chemicals and neonatal thyroid hormones.Methods: The study population consisted of 442 mother–child pairs from the French SEPAGES mother–child cohort recruited between July 2014 and July 2017. For each participant, four parabens, five bisphenols, tri- closan, triclocarban, benzophenone-3 as well as metabolites of phthalates and of di(isononyl)cyclohexane-1,2- dicarboxylate were assessed in two pools of repeated urine samples (median: 21 spot urines per pool), collected in the 2nd and 3rd trimesters of pregnancy, respectively. Thyroid stimulating hormone (TSH) and total thyroxine (T4) levels were determined in newborns from a heel-prick blood spot. Maternal iodine and selenium were assessed in urine and serum, respectively. Adjusted linear regression (uni-pollutant model) and Bayesian Kernel Machine Regression (BKMR, mixture model) were applied to study overall and sex-stratified associations between chemicals and hormone concentrations.Results: Interaction with child sex was detected for several compounds. Triclosan, three parabens, and one phthalate metabolite (OH-MPHP) were negatively associated with T4 among girls in the uni-pollutant model. BKMR also suggested a negative association between the mixture and T4 in girls, whereas in boys the association was positive. The mixture was not linked to TSH levels, and for this hormone the uni-pollutant model revealed associations with only a few compounds.Conclusion: Our study, based on repeated urine samples to assess exposure, showed that prenatal exposure to some phenols and phthalates disturb thyroid hormone homeostasis at birth. Furthermore, both uni-pollutant and mixture models, suggested effect modification by child sex, while, to date underlying mechanisms for such sex-differences are not well understood

    Reptile volatilome profiling optimisation: A pathway towards forensic applications

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    Reptiles are the most trafficked live taxa in the illegal wildlife trade, in part due to their popularity as an exotic pet. Current methods used to detect these illegally trafficked animals are limited. This study optimised the collection and analysis parameters associated with volatilome collection that will set the foundation for targeted odourant detection methods. This study determined that the dual sorbent type (Tenax® TA and Carbograph 5DT) in combination with 20-min sampling times and 15-min sampling intervals collected the most reproducible reptile volatilome profiles. It was also determined that desorption methods with mid-range desorption flows (20 ml/min), trap temperatures (-15 °C), and mid-range trap desorption (25 ml/min) were most effective in retrieving collected reptile volatilomes. Two-dimensional gas chromatography coupled with time-of-flight mass spectrometry was used for analysis, where combined Rxi-624 Sil MS (mid-polar) first dimension and Stabilwax® (polar) second dimension column sets were selected as the most effective columns for analysing reptile volatilomes. The resultant data collected and analysed using these parameters demonstrated that individual volatilomes from three reptile species were distinct using principal component analysis. In addition, this work highlighted the need for more rigorous statistical methods to determine reptile biomarkers and which compounds most significantly influence volatilome profiles between species

    Extractive desulfurization of fuel oils using ionic liquids

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    The sulphur content of transportation fuels must be reduced in high-sulphur crude oil by desulfurization. Traditionally, desulfurization methods have required harsh reaction conditions and are not very effective at removing refractory sulfur compounds such as benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). Alternative methods, such as ionic liquid (IL)-mediated desulfurization, are both effective and environmentally friendly. Isolants ideal for desulfurization are required to be recyclable, insoluble in oil, selective for compounds containing sulphur, and eco-friendly. These properties are offered by ILs based on pyridinium. Therefore, the primary objectives of this thesis were to: (1) investigate the properties of N-butyl-pyridinium tetrafluoroborate ([BPy][BF₄]) and N-carboxymethyl pyridinium hydrogen sulfate ([CH₂COOHPy][HSO₄]); (2) understand the effects of reaction parameters (temperature, volume ratio, oxidant dosage, quantities of sulphur compound extracted, etc.) on desulfurization efficiency; (3) clarify the interactions between ILs and sulphur compounds; and (4) investigate the recycling and regeneration of ILs. Experimental results showed that the desulfurization efficiency of [BPy][BF₄] increased with temperature and oxidant dosage and declined with IL to fuel volume ratio. It was observed that at 30゚C, 1:1 ration of IL to model fuel [BPy][BF₄] could remove up to 79% of DBT in 80 min in the presence of oxidant H₂O₂. [CH₂COOHPy] [HSO₄] was found to be more effective in desulfurization, capable of removing up to 99.9% of DBT in the presence of oxidant H₂O₂ within 40 min at 25゚C, 1:1 ratio of IL to model fuel. The recycled [CH₂COOHPy][HSO₄] marginally lost effectiveness after 8 recycles. It was also found that the effectiveness of both ILs was lower in real diesel compared to model fuels. Computational density functional theory-based structural analysis revealed that there were two types of possible π-π interactions between [BPy] [BF₄] and DBT/DBTO₂, resulting in the formation of complexes with different geometries. [CH₂COOHPy][HSO₄] also exhibits similar potential π−π interactions with DBT/DBTO₂. Moreover, both ILs undergo the same oxidative mechanism of desulfurization, as they involve π-π interactions and hydrogen bonds

    Application Directed Synthesis of Multifunctional Fullerene Derivatives

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    This thesis presents work on the synthesis and characterisation of functionalised fullerene derivatives designed specifically for applications in energy storage, supramolecular assembly and lithographic patterning. Chapter 1 provides an introduction to fullerene, fullerene chemistry, the examples of structurally complex fullerene derivatives and their corresponding applications. Chapter 2 describes the synthesis of highly soluble fullerene derivatives as charge carriers for redox flow batteries, achieving a remarkably high solubility of ~336 mM in oDCB, and exhibiting a wide potential window, 1.78 V, in an electrolyte consisting of oDCB/tetrabutylammonium tetrafluoroborate. The synthesis of a series of tris-fullerene CTG molecules that can be used for developing supramolecular arrays is introduced in Chapter 3, in which a synthetic strategy of using tris-amino acid derivatised CTG as the starting material in a one-pot Prato reaction was proposed and investigated to yield the target molecule. In Chapter 4, a fullerene-platinum complex is explored as a resist material to develop the lithographic pattern, in which a sub-13 nm line width was achieved. The presence of Pt atoms enhances the secondary electron scattering and thus increased the energy deposition efficiency resulting in better lithographic patterning capability. Overall, this thesis acts as a guide to efficient and targeted fullerene derivative synthesis, providing insight and strategy into fullerene functionalisation which will help push forward the exploitation of fullerene as a nanosized building block to be utilised in applied, functional materials in the future

    Functional Polymers as Innovative Tools in the Delivery of Antimicrobial Agents

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    This Special Issue explored different topics concerning recent progress in the synthesis and characterization of suitable innovative macromolecular systems, proposed as carriers of specific antimicrobial molecules, to be employed in the biomedical and pharmaceutical fields. Many infectious diseases are induced by omnipresent micro-organisms, including bacteria, viruses, protozoa, fungi, and algae, and, consequently, are very common, accounting for a significant share of the global disease burden. Unfortunately, antimicrobial resistance, adverse effects, and the high cost of antimicrobials are crucial health challenges worldwide. One of the common efforts in addressing this issue lies in improving the existing antimicrobial delivery systems. In this regard, nanoparticles as well as three-dimensional hydrophilic systems represent valuable tools able to ensure excellent performances. Biocompatible polymeric particles, entrapping these bioactive molecules, are capable of releasing them over a desired period of time, thereby decreasing the frequency of their administration. At the same time, these systems are able to protect antimicrobial drugs from degradation, enhancing their bioavailability. This Special Issue serves to highlight and capture the contemporary progress recorded in this field

    Metal Promoted Cyclocarbonylation Reactions in the Synthesis of Heterocycles

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    This book is focused on metal-catalyzed cyclocarbonylation reactions applied to the synthesis of heterocyclic rings of different sizes, including diastereoselective and enantioselective approaches, homogeneous and heterogeneous metal catalysis, and the application of these reactions to the total synthesis of natural products

    Enhancing catalytic properties of ligand-protected gold-based 25-metal atom nanoclusters by silver doping

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    Herein, engineering metal composition of metal nanoclusters (NCs) by foreign metal doping was used as an approach to synthesize gold (Au)-based 25-metal NC catalysts, without compromising the presence of their ligands and unique structure of 25 metal atoms. The Au-based 25-metal atom NCs with silver doping which can also be called as bimetallic AuAg NCs (i.e., Au25-xAgx(SR)18 NCs with x = 4–12) were successfully synthesized by co-reduction method with various feeding ratios (RAu/Ag = 24/1, 22/3 and 18/7). The Ag dopants favorably replaced Au(0) atom on the vertex of the icosahedral core and enhanced the catalytic activity of bimetallic Au25-xAgx(SR)18 NCs due to combination of several factors. As compared to monometallic Au25(SR)18 NCs, Au25-xAgx(SR)18 NCs have (1) synergistic effects of Au and Ag atoms; (2) better ligands removal's and active sites exposure due to weaker Ag-SR bond than Au-SR bond based on DFT analysis; (3) weaker Ag-H than Au-H bond based on DFT analysis; and (4) better stability as smaller metal NCs during the catalytic reaction. The study reveals a wider opportunity to tailor the catalytic properties of atomically precise Au-based 25-metal atom NC by engineering its metal composition

    Nanostructured piezoelectric materials for the design and development of self-sensing composite materials and energy harvesting devices

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    The work activities reported in this PhD thesis regard the functionalization of composite materials and the realization of energy harvesting devices by using nanostructured piezoelectric materials, which can be integrated in the composite without affecting its mechanical properties. The self-sensing composite materials were fabricated by interleaving between the plies of the laminate the piezoelectric elements. The problem of negatively impacting on the mechanical properties of the hosting structure was addressed by shaping the piezoelectric materials in appropriate ways. In the case of polymeric piezoelectric materials, the electrospinning technique allowed to produce highly-porous nanofibrous membranes which can be immerged in the hosting matrix without inducing delamination risk. The flexibility of the polymers was exploited also for the production of flexible tactile sensors. The sensing performances of the specimens were evaluated also in terms of lifetime with fatigue tests. In the case of ceramic piezo-materials, the production and the interleaving of nanometric piezoelectric powder limitedly affected the impact resistance of the laminate, which showed enhanced sensing properties. In addition to this, a model was proposed to predict the piezoelectric response of the self-sensing composite materials as function of the amount of the piezo-phase within the laminate and to adapt its sensing functionalities also for quasi-static loads. Indeed, one final application of the work was to integrate the piezoelectric nanofibers in the sole of a prosthetic foot in order to detect the walking cycle, which has a period in the order of 1 second. In the end, the energy harvesting capabilities of the piezoelectric materials were investigated, with the aim to design wearable devices able to collect energy from the environment and from the body movements. The research activities focused both on the power transfer capability to an external load and the charging of an energy storage unit, like, e.g., a supercapacitor