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Angewandte Chemie (International Ed. in... Sep 2004C(60) has been synthesized by chemical methods in 12 steps. Lessons learned in the author's laboratory during a decade devoted to the synthesis and study of open... (Review)
Review
C(60) has been synthesized by chemical methods in 12 steps. Lessons learned in the author's laboratory during a decade devoted to the synthesis and study of open geodesic polyarenes strongly influenced the strategy and methodology ultimately employed for preparing a suitable 60-carbon precursor and for closing it up to the fullerene ball. This review provides a personal account of how the new synthetic tools were developed and put to use.
Topics: Cyclization; Fullerenes; Molecular Conformation; Organic Chemicals; Temperature
PubMed: 15372546
DOI: 10.1002/anie.200400661 -
Proceedings of the National Academy of... Apr 2004
Topics: Catalysis; Chemistry, Organic; Molecular Conformation; Organic Chemicals; Stereoisomerism
PubMed: 15082833
DOI: 10.1073/pnas.0401811101 -
Environmental Science and Pollution... Jan 2022In this lab-scale study, the POCIS capacity to integrate short contamination peaks of variable intensity and duration was evaluated. POCIS were immersed for 14 days in...
In this lab-scale study, the POCIS capacity to integrate short contamination peaks of variable intensity and duration was evaluated. POCIS were immersed for 14 days in tanks filled with tap water and spiked at different concentrations with 12 pesticides of various polarities (log K = 1.1-4.7) and classes (herbicides, fungicides, and insecticides). Concentrations were kept relatively constant at 1 μg L and 5 μg L, respectively, in two "background" exposure tanks. Three contamination peaks of increasing intensity and decreasing duration were simulated (10 μg L for 24 h, 40 μg L for 6 h, and 60 μg L for 1 h). This lab-scale study demonstrated that ten moderately polar compounds (2 < log K < 4) showed a linear uptake, as observed in previous studies, while a non-linear model fits the data of the two most polar pesticides (log K < 2). Depending on chemical polarity, some compounds exhibited a "burst effect" or "lag effect" during the first 3 days of exposure. After 14 days of exposure, contamination peaks appeared integrated for seven compounds, showing the ability of POCIS to catch very short pollution events and to provide acceptable time-weighted average concentration estimates under laboratory-controlled conditions.
Topics: Environmental Monitoring; Laboratories; Organic Chemicals; Pesticides; Water Pollutants, Chemical
PubMed: 30350144
DOI: 10.1007/s11356-018-3391-2 -
The Science of the Total Environment Aug 2014This study focuses on how Polar Organic Chemical Integrative Samplers (POCIS) work in real environmental conditions. A selection of 23 polar pesticides and 8 metabolites...
This study focuses on how Polar Organic Chemical Integrative Samplers (POCIS) work in real environmental conditions. A selection of 23 polar pesticides and 8 metabolites were investigated by exposure of triplicates of integrative samplers in two rivers in France for successive 14-day periods. The pesticides and metabolites were trapped not only in Oasis HLB sorbent but also in the polyethersulfone (PES) membrane of the POCIS. The distribution of pesticides depended on the molecular structure. The use of the Performance Reference Compound (PRC) is also discussed here. The impact of some environmental parameters and exposure setup on the transfer of pesticides in POCIS sorbent was studied: river flow rate, biofouling on membranes, sampler holding design and position in the stream. Results show a significant impact of river flow velocity on PRC desorption, especially for values higher than 4 cm·s(-1). Some fouling was observed on the PES membrane which could potentially have an impact on molecule accumulation in the POCIS. Finally, the positioning of the sampler in the river did not have significant effects on pesticide accumulation, when perpendicular exposures were used (sampler positioning in front of the water flow). The POCIS with PRC correction seems to be a suitable tool for estimating time-weighted average (TWA) concentrations, for all the molecules except for one of the nine pesticides analyzed in these two French rivers.
Topics: Environmental Monitoring; France; Organic Chemicals; Pesticides; Rivers; Water Pollutants, Chemical
PubMed: 24830931
DOI: 10.1016/j.scitotenv.2014.04.069 -
Journal of Chromatography. A Apr 2010Room temperature ionic liquids are novel solvents with a rather specific blend of physical and solution properties that makes them of interest for applications in... (Review)
Review
Room temperature ionic liquids are novel solvents with a rather specific blend of physical and solution properties that makes them of interest for applications in separation science. They are good solvents for a wide range of compounds in which they behave as polar solvents. Their physical properties of note that distinguish them from conventional organic solvents are a negligible vapor pressure, high thermal stability, and relatively high viscosity. They can form biphasic systems with water or low polarity organic solvents and gases suitable for use in liquid-liquid and gas-liquid partition systems. An analysis of partition coefficients for varied compounds in these systems allows characterization of solvent selectivity using the solvation parameter model, which together with spectroscopic studies of solvent effects on probe substances, results in a detailed picture of solvent behavior. These studies indicate that the solution properties of ionic liquids are similar to those of polar organic solvents. Practical applications of ionic liquids in sample preparation include extractive distillation, aqueous biphasic systems, liquid-liquid extraction, liquid-phase microextraction, supported liquid membrane extraction, matrix solvents for headspace analysis, and micellar extraction. The specific advantages and limitations of ionic liquids in these studies is discussed with a view to defining future uses and the need not to neglect the identification of new room temperature ionic liquids with physical and solution properties tailored to the needs of specific sample preparation techniques. The defining feature of the special nature of ionic liquids is not their solution or physical properties viewed separately but their unique combinations when taken together compared with traditional organic solvents.
Topics: Chemical Fractionation; Ionic Liquids; Organic Chemicals; Osmolar Concentration; Temperature
PubMed: 19766228
DOI: 10.1016/j.chroma.2009.09.011 -
Chemical Research in Toxicology Jul 2020A valuable approach to chemical safety assessment is the use of read-across chemicals to provide safety data to support the assessment of structurally similar chemicals....
A valuable approach to chemical safety assessment is the use of read-across chemicals to provide safety data to support the assessment of structurally similar chemicals. An inventory of over 6000 discrete organic chemicals used as fragrance materials in consumer products has been clustered into chemical class-based groups for efficient search of read-across sources. We developed a robust, tiered system for chemical classification based on (1) organic functional group, (2) structural similarity and reactivity features of the hydrocarbon skeletons, (3) predicted or experimentally verified Phase I and Phase II metabolism, and (4) expert pruning to consider these variables in the context of specific toxicity end points. The systematic combination of these data yielded clusters, which may be visualized as a top-down hierarchical clustering tree. In this tree, chemical classes are formed at the highest level according to organic functional groups. Each subsequent subcluster stemming from classes in this hierarchy of the cluster is a chemical cluster defined by common organic functional groups and close similarity in the hydrocarbon skeleton. By examining the available experimental data for a toxicological endpoint within each cluster, users can better identify potential read-across chemicals to support safety assessments.
Topics: Cluster Analysis; Consumer Product Safety; Cosmetics; Databases, Chemical; Molecular Structure; Odorants; Organic Chemicals; Risk Assessment
PubMed: 32338872
DOI: 10.1021/acs.chemrestox.9b00518 -
Water Research Aug 2018Both nanoparticulate (nZnO and nTiO) and organic chemical ultraviolet (UV) filters are active ingredients in sunscreen and protect against skin cancer, but limited...
Both nanoparticulate (nZnO and nTiO) and organic chemical ultraviolet (UV) filters are active ingredients in sunscreen and protect against skin cancer, but limited research exists on the environmental effects of sunscreen release into aquatic systems. To examine the trade-offs of incorporating nanoparticles (NPs) into sunscreens over the past two decades, we targeted endpoints sensitive to the potential risks of different UV filters: solar reactive oxygen production in water and disruption of zebrafish embryo development. First, we developed methodology to extract nanoparticles from sunscreens with organic solvents. Zebrafish embryos exposed to parts-per-million NPs used in sunscreens displayed limited toxicological effects; nZnO particles appeared to be slightly more toxic than nTiO at the highest concentrations. In contrast, seven organic UV filters did not affect zebrafish embryogenesis at or near aqueous solubility. Second, to simulate potent photo-initiated reactions upon release into water, we examined methylene blue (MB) degradation under UV light. nTiO from sunscreen caused 10 times faster MB loss than nZnO and approached the photocatalytic degradation rate of a commercial nTiO photocatalysts (P25). Organic UV filters did not cause measurable MB degradation. Finally, we estimated that between 1 and 10 ppm of sunscreen NPs in surface waters could produce similar steady state hydroxyl radical concentrations as naturally occurring fluvic acids under sunlight irradiation. Incorporation of NPs into sunscreen may increase environmental concentrations of reactive oxygen, albeit to a limited extent, which can influence transformation of dissolved substances and potentially affect ecosystem processes.
Topics: Animals; Ecosystem; Embryo, Nonmammalian; Embryonic Development; Nanoparticles; Organic Chemicals; Reactive Oxygen Species; Sunscreening Agents; Titanium; Ultraviolet Rays; Water Pollutants, Chemical; Zebrafish; Zinc Oxide
PubMed: 29656193
DOI: 10.1016/j.watres.2018.03.062 -
Organic & Biomolecular Chemistry Mar 2005The field of asymmetric organocatalysis is rapidly developing and attracts an increasing number of research groups around the world. Here we present a brief overview of... (Review)
Review
The field of asymmetric organocatalysis is rapidly developing and attracts an increasing number of research groups around the world. Here we present a brief overview of this area, guided by a mechanistic classification. Accordingly, organocatalysts are categorized as either Lewis base, Lewis acid, Brønsted base, or Brønsted acid catalysts.
Topics: Acids; Catalysis; Molecular Conformation; Molecular Structure; Organic Chemicals; Stereoisomerism
PubMed: 15731852
DOI: 10.1039/b415217b -
Chemical Reviews Mar 2014
Review
Topics: Alkynes; Cyclization; Free Radicals; Hydrogen; Kinetics; Nitriles; Organic Chemicals; Silicon; Sulfhydryl Compounds; Thermodynamics
PubMed: 24383397
DOI: 10.1021/cr400441m -
Ecotoxicology and Environmental Safety Oct 2020Organophosphate ester contaminants, including organophosphate pesticides (OPPs) and organophosphate flame retardants (OPFRs) are ubiquitous in surface water and pose a...
Organophosphate ester contaminants, including organophosphate pesticides (OPPs) and organophosphate flame retardants (OPFRs) are ubiquitous in surface water and pose a significant risk to aquatic organisms, thus it is important to develop effective methods for long-term monitoring of these emerging compounds. Polar organic chemical integrative sampler (POCIS) has become a promising monitoring tool for waterborne contaminants, yet recent studies found that the commonly used polyethersulfone (PES) membrane strongly sorbed some moderately hydrophobic compounds, resulting in long lag-phase for chemical accumulation in POCIS. In the present study, 0.45-μm nylon membranes was selected as POCIS diffusion-limiting membrane to design a new POCIS-Nylon configuration for analyzing moderately hydrophobic OPPs and OPFRs in water. The POCIS-Nylon had negligible lag-phase due to low sorption of OPPs and OPFRs to nylon membrane. Meanwhile, linear accumulation time and sensitivity for target contaminants using POCIS-Nylon retained similar to the traditional POCIS. Water velocity and chemical concentration had little impact on sampling rate (R), validating that the POCIS-Nylon was suitable for various water conditions. Finally, the occurrence of OPPs and OPFRs in urban waterways of Guangzhou, China was evaluated using the POCIS-Nylon with R values that were calibrated in the laboratory. The average concentration of OPPs was 4.97 ± 1.35 ng/L (range: 2.64 ± 1.28-6.54 ± 0.18 ng/L) and the average concentration of OPFRs was 400 ± 88 ng/L (range: 316 ± 24-615 ± 36 ng/L) across nine sampling sites. The present study provides a way to resolve the inherent challenge of accumulating hydrophobic substances by POCIS.
Topics: Calibration; China; Environmental Monitoring; Flame Retardants; Hydrophobic and Hydrophilic Interactions; Nylons; Organic Chemicals; Organophosphates; Polymers; Sulfones; Water Pollutants, Chemical
PubMed: 32593097
DOI: 10.1016/j.ecoenv.2020.110891