Organophosphate esters by GC–MS: An optimized method for aquatic risk assessment

Organophosphate esters used as flame retardants and plasticizers are ubiquitous contaminants in surface waters. Many studies indicate that these compounds are neurotoxicants, endocrine disruptors, and may affect reproduction and development of aquatic organisms. Thus, analytical methods that allow accurate quantification of these contaminants at environmentally relevant concentrations are desirable for risk assessment studies. In this study, a method based on solid phase extraction and gas chromatography coupled to mass spectrometry was developed for determination of organophosphate esters in river water extracts. Multivariate optimization was used to determine the best conditions for injection of larger volumes of sample in a Programmable Temperature Vaporization inlet. Furthermore, the matrix effect on the instrumental response was evaluated and compensated by association of extraction‐blank‐matched calibration and isotopically labeled focus standards. The method quantification limits ranged from 0.009 to 0.11 µg/L, staying below the predicted non‐effect concentration for the aquatic compartment for all analytes, which is a requisite for using in risk assessment studies. The method was applied to freshwater samples collected in rivers from the Sao Paulo State, Brazil, and eight out of the ten target organophosphate esters were quantified, being tris(2‐chloroisopropyl) phosphate and tris(phenyl) phosphate the most frequently detected compounds.     

Classification problems for shifts on modules over a principal ideal domain

In this paper we study symbolic dynamics over alphabets which are modules over a principal ideal domain, considering topological shifts which are also submodules. Our main result is the classification, up to algebraic and topological conjugacy, of the torsion-free, transitive, finite memory shifts.

     

Chromotropic acid-formaldehyde reaction in strongly acidic media. The role of dissolved oxygen and replacement of concentrated sulphuric acid

The procedure for formaldehyde analysis recommended by the National Institute for Occupational Safety and Health (NIOSH) is the Chromotropic acid spectrophotometric method, which is the one that uses concentrated sulphuric acid. In the present study the oxidation step associated with the aforementioned method for formaldehyde determination was investigated. Experimental evidence has been obtained indicating that when concentrated H₂SO₄ (18 mol l⁻¹) is used (as in the NIOSH procedure) that acid is the oxidizing agent. On the other hand, oxidation through dissolved oxygen takes place when concentrated H₂SO₄ is replaced by concentrated hydrochloric (12 mol l⁻¹) and phosphoric (14.7 mol l⁻¹) acids as well as by diluted H₂SO₄ (9.4 mol l⁻¹). Based on investigations concerning the oxidation step, a modified procedure was devised, in which the use of the potentially hazardous and corrosive concentrated H₂SO₄ was eliminated and advantageously replaced by a less harmful mixture of HCl and H₂O₂.     

Copper Complexes as Alternative Redox Mediators in Dye-Sensitized Solar Cells

Thirty years ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the sun’s energy and converting it into electricity. Since then, a lot of work has been dedicated to improving their global photovoltaic efficiency and their eco-sustainability. Recently, various articles showed the great potential of copper complexes as a convenient and cheap alternative to the traditional ruthenium dyes. In addition, copper complexes demonstrate that they can act as redox mediators for DSSCs, thus being an answer to the problems related to the I₃⁻/I⁻ redox couple. The aim of this review is to report on the most recent impact made by copper complexes as alternative redox mediators. The coverage, mainly from 2016 up to now, is not exhaustive, but allows us to understand the great role played by copper complexes in the design of eco-sustainable DSSCs.     

Homochiral [2.2]Paracyclophane Self‐Assembly Promoted by Transannular Hydrogen Bonding

[2.2]paracyclophane (pCp), unlike many π‐building blocks, has been virtually unexplored in supramolecular constructs. Reported here is the synthesis and characterization of the first pCp derivatives capable of programmed self‐assembly into extended cofacial π‐stacks in solution and the solid state. The design employs transannular (intramolecular) hydrogen bonds (H‐bonds), hitherto unstudied in pCps, between pseudo‐ortho‐positioned amides of a pCp‐4,7,12,15‐tetracarboxamide (pCpTA) to preorganize the molecules for intermolecular H‐bonding with π‐stacked neighbors. X‐ray crystallography confirms the formation of homochiral, one‐dimensional pCpTA stacks helically laced with two H‐bond strands. The chiral sense is dictated by the planar chirality (R_p or S_p) of the pCpTA monomers. A combination of NMR, IR, and UV/Vis studies confirms the formation of the first supramolecular pCp polymers in solution.     

Transannular Hydrogen Bonding in Planar‐Chiral [2.2]Paracyclophane‐Bisamides

A series of [2.2]paracyclophane‐bisamide regioisomers and alkylated comparators were designed, synthesized, and characterized in order to better understand the transannular hydrogen bonding of [2.2]paracyclophane‐based molecular recognition units. X‐Ray crystallography shows that transannular hydrogen bonding is maintained in the solid‐state, but no stereospecific self‐recognition is observed. The assignment of both transannularly and intermolecularly hydrogen bonded N?H stretches could be made by infrared spectroscopy, and the effect of transannular hydrogen bonding on amide bond rotation dynamics is observed by ¹H‐NMR in nonpolar solvents. The consequences of transannular hydrogen bonding on the optical properties of [2.2]paracyclophane is observed by comparing alkylated and non‐alkylated pseudo‐ortho 4,12‐[2.2]paracyclophane‐bisamides. Finally, optical resolution of 4‐mono‐[2.2]paracyclophane and pseudo‐ortho 4,12‐[2.2]paracyclophane‐bisamides was achieved through the corresponding sulfinyl diastereoisomers for circular dichroism studies. Transannular hydrogen bonding in [2.2]paracyclophane‐amides allows preorganization for self‐complementary intermolecular assembly, but is weak enough to allow rapid rotation of the amides even in nonpolar solvents.     

High resolution laser-based detection of ammonia

In the present paper we compare the response of two types of photoacoustic cells (resonant and nonresonant) to determine the amount of ammonia volatilized from biological liquid samples at constant temperature, pressure and pH. The home made detector was a photoacoustic spectroscopy apparatus developed by Molecular Spectroscopy Laboratory staff at ENEA Frascati Research Centre in Italy. The sensor makes use of photo-acoustic cells equipped with commercially available high sensitivity miniaturized microphones. The radiation source was a line-tunable stabilized 10 W CW CO₂ laser. Ammonia measurements were performed by tuning the laser source on the 9R30 laser line (9.2197 µm radiation wavelength). Ammonium chloride standard solutions were prepared by us in laboratory, to serve as reproducible ideal samples. The photoacoustic response of the two type of photoacoustic cells was determined and compared. The feasibility study was reported.