Acetylcholinesterase-based biosensors for quantification of carbofuran, carbaryl, methylparaoxon, and dichlorvos in 5% acetonitrile

Amperometric acetylcholinesterase biosensors have been developed for quantification of the pesticides carbofuran, carbaryl, methylparaoxon, and dichlorvos in phosphate buffer containing 5% acetonitrile. Three different biosensors were built using three different acetylcholinesterase (AChE) enzymes—AChE from electric eel, and genetically engineered (B394) and wild-type (B1) AChE from Drosophila melanogaster. Enzymes were immobilized on cobalt(II) phthalocyanine-modified electrodes by entrapment in a photocrosslinkable polymer (PVA-AWP). Each biosensor was tested against the four pesticides. Good operational stability, immobilisation reproducibility, and storage stability were obtained for each biosensor. The best detection limits were obtained with the B394 enzyme for dichlorvos and methylparaoxon (9.6 × 10⁻¹¹ and 2.7 × 10⁻⁹ mol L⁻¹, respectively), the B1 enzyme for carbofuran (4.5 × 10⁻⁹ mol L⁻¹), and both the B1 enzyme and the AChE from electric eel for carbaryl (1.6 × 10⁻⁷ mol L⁻¹). Finally, the biosensors were used for the direct detection of the pesticides in spiked apple samples.     

Quantification of refractory organic substances in freshwaters: further insight into the response of the voltammetric method

A recently published method for quantifying refractory organic matter (often referred to as humic substances) in freshwaters was applied to a wide range of International Humic Substance Society (IHSS) humic compounds in order to (i) gain a better understanding of the mechanism of the voltammetric response which is the basis of the analytical method and (ii) provide guidance on choosing the optimal standard to be used. At the same time, the sensitivity of the technique has been increased by switching from the pulse mode initially proposed to the square-wave mode. The results obtained show that (i) differences in adsorption onto the electrode rather than differences in complexation strength are responsible for the differences in the intensity of the signal obtained for the different humic compounds, (ii) carboxylate, N- and S-containing groups do not play a role in the voltammetric signal.     

Synthesis of 4-aminotropones from [(sulfinyl or sulfonyl)methyl]-substituted p-quinamines

An efficient synthesis of 4-aminotropones has been achieved in excellent yields by simple treatment of 4-amino-4-[(p-tolylsulfinyl)methyl]-2,5-cyclohexadienones (p-quinamines) with NaH. The method allowed regiocontrolled access to 3-methyl, 5-methyl- and 3,5-dimethyl-substituted derivatives starting from p-quinamines with adequate substituents at the cyclohexadienone moiety and/or at the carbon linked to the sulfur function. The p-quinamines in turn were easily accessible from N-Boc p-anisidines (Boc=tert-butoxycarbonyl) by electrochemical oxidation in MeOH to quinone imine monoketals, followed by addition of a alpha-lithium sulfinyl carbanion to the imino group, and ketal hydrolysis. Oxidation of the sulfoxide gave the sulfonyl-substituted p-quinamines that, upon basic treatment, behave similarly. The p-quinamine 55 and bis-p-quinamine 56, resulting in the addition of the anion derived from dimethyl sulfone to the p-quinonimine ketal 14, also gave the 4-aminotropone. The mechanism involves the initial formation of a alpha-sulfonyl carbanion, which intramolecularly attacks the cyclohexadienone giving a norcaradiene-like enolate intermediate, the evolution of which through a ring-expansion process, pushes off a methyl sulfinate anion or SO2. This efficient process fulfils the criteria of atom economy. The introduction of a proline substituent in the nitrogen of the starting p-quinamine allowed the synthesis of an enantiopure 4-aminotropone, the asymmetric Diels-Alder reactions of which with maleimide occurred in a highly endo and pi-facial diastereoselective manner.     

Self-assembly reactions between the cis-protected metal corners (N-N)MII (N-N = ethylenediamine, 4,4'-substituted 2,2'-bipyridine; M = Pd, Pt) and the fluorinated edge 1,4-bis(4-pyridyl)tetrafluorobenzene

The self-assembly reactions between the fluorinated ditopic ligand 1,4-bis(4-pyridyl)tetrafluorobenzene (A) and different nitrogen-protected palladium(II) and platinum(II) complexes have been investigated. While dynamic equilibria between molecular triangles and squares were observed when the diimine compounds 4,4'-R2bipy (bipy = 2,2'-bipyridine; R = H, Me, t-Bu) were employed as ancillary ligands, only square species were obtained from ethylenediamine (en) derivatives. Characterization of the obtained metallomacrocycles was accomplished by 1H and 19F NMR spectroscopy in combination with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR). Molecular dynamics simulations (UFF) have been performed to interpret the influence of the fluorinated ring on the square/triangle relative stability. Density functional calculations using the GIAO method have been employed for the interpretation of the chemical shift assignments. The study of the ability of these compounds to act as hosts of electron-rich aromatic guests has shown that the palladium ethylenediamine square is capable of establishing this type of intermolecular interaction exclusively in aqueous media. The host-guest stoichiometry and association constants have been determinated by 1H NMR spectroscopy.     

Palladium catalyzed Suzuki C-C couplings in an ionic liquid: nanoparticles responsible for the catalytic activity

A new family of functionalized ligands derived from norborn-5-ene-2,3-dicarboxylic anhydride has been used in Suzuki C-C cross-couplings between aryl boronic acids and aryl bromide derivatives in [BMI][PF(6)] (BMI=1-n-butyl-3-methyl-imidazolium), using palladium acetate as catalytic precursor. High conversions and yields are obtained when amine ligands containing hydroxy groups are involved. TEM analyses after catalysis show the formation of small nanoparticles, in contrast to the agglomerates observed when nanoparticles are intentionally preformed, with a consequent decrease in the catalytic activity in the latter case. Some tests, including the correlation effect between solvent and ligand, are carried out to try to identify the true nature of the catalyst. All the results obtained suggest that formation of nanoparticles is required to lead to a catalytically active system.     

Deconvolution of Molecular Weight Distributions Using Dynamic Flory‐Schulz Distributions

Summary: The deconvolution of molecular weight distributions (MWDs) may be useful for obtaining information about the polymerization kinetics and properties of catalytic systems. However, deconvolution techniques are normally based on steady‐state assumptions and very little has been reported about the use of non‐stationary approaches for the deconvolution of MWDs. In spite of this, polymerization reactions are often performed in batch or semi‐batch modes. For this reason, dynamic solutions are proposed here for simple kinetic models and are then used for deconvolution of actual MWD data. Deconvolution results obtained with dynamic models are compared to deconvolution results obtained with the standard stationary Flory‐Schulz distributions. For coordination polymerizations, results show that dynamic MWD models are able to describe experimental data with fewer catalytic sites, which indicates that the proper interpretation of the reaction dynamics may be of fundamental importance for kinetic characterization. On the other hand, reaction dynamics induced by modification of chain transfer agent concentration seem to play a minor role in the shape of the MWD in free‐radical polymerizations.

This Figure illustrates that MWDs obtained at unsteady conditions should not be deconvoluted with standard steady‐state Flory‐Schulz distributions.     

Analysis of organic compounds of water-in-crude oil emulsions separated by microwave heating using comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry

In this work the higher peak capacity and resolution of comprehensive two-dimensional gas chromatography (GCxGC) has been successfully applied, for the first time, to tentatively identify several polar organic compounds of organic extracts of aqueous phases resulting from microwave demulsification process of water-in-crude oil emulsions. Results have shown that higher temperatures and longer exposure time to microwave irradiation produced water phases with a wider variety of polar organic compounds. The microwave process showed to be suitable for the extraction of several polar compounds classes of petroleum. The proposed microwave extraction method and GCxGC identification of polar compounds of petroleum samples are of practical interest for the petrochemical industry due to corrosion and related problems associated with these polar compounds in refinery equipments. The GCxGC/time-of-flight MS technique shows to be very important in the total separation of different classes of compounds and allows the identification of many compounds in these classes.