Analysis of 51 persistent organic pollutants in soil by means of ultrasonic solvent extraction and stir bar sorptive extraction GC-MS

A novel method based on ultrasonic solvent extraction and stir bar sorptive extraction (SBSE) for the analysis of 51 persistent organic pollutants including organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and polybrominated diphenylethers (PBDEs) in soil samples was developed. The different parameters that affect both the extraction of analytes from the soil samples, such as solvent selection, solvent volume, mass of soil, and extraction time, and the partitioning from the solvent/water mixture to the PDMS were studied. The final selected conditions consisted of the extraction of 1 g of soil with 15 mL methanol by sonication for 30 min. The methanol extract was mixed with 85 mL of Milli-Q water and extracted by means of SBSE for 14 h at 900 rpm. The stir bars were analyzed by thermal desorption-GC-mass spectometry (TD-GC-MS). The effects of the matrix on the recovery of the various pollutants under the developed method were studied using two soils with very different physicochemical properties. Method sensitivity, linearity, repeatability, and reproducibility were also studied. Validation and accuracy of the method were conducted by analyzing two commercial certified reference materials (CRMs). The main advantage of this method resides in the fact that a small amount of a nontoxic solvent (methanol) is needed for the extraction of only 1 g of solid sample allowing LODs ranging from 0.01 to 2.0 microg/kg. Repeatability and reproducibility variations were lower than 20% for all investigated compounds. Results of the CRMs verify the high accuracy of this method.     

Intake and excretion of disodium monomethylarsonate in horses: a speciation study

Capillary electrophoresis coupled to inductively coupled plasma mass spectrometry was used in a speciation study on disodium monomethylarsonate (DS-MMA^V) and its metabolites in horses, to which the drug was administered by intramuscular injection on five consecutive days at a single arsenic dosage of 270 mg day⁻¹. Samples of urine, whole blood, plasma, and mane hair were analyzed before, during, and after drug administration. The data show that blood clearing and urinary excretion of MMA is a fast process following first-order kinetics with biological half-lives of about 38 h and 44 h for urine and plasma, respectively. In the time period of 9 days studied, the only metabolite detected in urine was dimethylarsinic acid (DMA^V), which 4 days after the last drug administration accounted for up to 75% of the total excreted arsenic species. This shows, for the first time, that biomethylation of MMA^V to DMA^V is the principal metabolic pathway of this drug in horses. Although DS-MMA^V was administered only during a short 5-day period, an up to six fold increase of arsenic could be measured in the newly grown mane hair.     

Rapid and quantitative evaluation of the effect of process variables on the kinetics of photocatalytic degradation of phenol using experimental design techniques and parallel factor (PARAFAC) analysis

A 2³ factorial design has been used to analyze the effect of pH, the nature of the catalyst, and the concentration of the substrate on the rate constant of the photodegradation reaction of phenol. The main effects of the considered variables and their interaction are discussed. The significance of the effects has been corroborated using an ANOVA test. The values of phenol concentrations, used to calculate the rate constant, and the concentrations of intermediates were obtained by applying parallel factor (PARAFAC) analysis to the data obtained from monitoring the process by means of excitation–emission fluorescence (EEM). The proposed methodology, which combines experimental design and multivariate techniques, is a rapid alternative for study of chemical kinetics.     

Strong asymptotics for Sobolev orthogonal polynomials in the complex plane

We obtain the strong asymptotics for the sequence of monic polynomials minimizing the norm

     

Application of renormalized coupled-cluster methods to potential function of water

The goal of this paper is to examine the performance of the conventional and renormalized single-reference coupled-cluster (CC) methods in calculations of the potential energy surface of the water molecule. A comparison with the results of the internally contracted multi-reference configuration interaction calculations including the quasi-degenerate Davidson correction (MRCI(Q)) and the spectroscopically accurate potential energy surface of water resulting from the use of the energy switching (ES) approach indicates that the relatively inexpensive completely renormalized (CR) CC methods with singles (S), doubles (D), and a non-iterative treatment of triples (T) or triples and quadruples (TQ), such as CR-CCSD(T), CR-CCSD(TQ), and the recently developed rigorously size extensive extension of CR-CCSD(T), termed CR-CC(2,3), provide substantial improvements in the results of conventional CCSD(T) and CCSD(TQ) calculations at larger internuclear separations. It is shown that the CR-CC(2,3) results corrected for the effect of quadruply excited clusters through the CR-CC(2,3)+Q approach can compete with the highly accurate MRCI(Q) data. The excellent agreement between the CR-CC(2,3)+Q and MRCI(Q) results suggests ways of improving the global potential energy surface of water resulting from the use of the ES approach in the regions of intermediate bond stretches and intermediate energies connecting the region of the global minimum with the asymptotic regions. Contribution to the Mark S. Gordon 65th Birthday Festschrift Issue.     

Synthesis and biological activity of analogues of vanchrobactin, a siderophore from Vibrio anguillarum serotype O2

Several analogues of vanchrobactin, a catechol siderophore isolated from the bacterial fish pathogen Vibrio anguillarum serotype O2 strain RV22, have been synthesized. The biological evaluation of these novel compounds showed that most of them are active as siderophores, as determined by growth promotion assays using the producer strain, as well as V. anguillarum serotype O1, Salmonella enterica, and Erwinia chrysanthemi. These compounds also gave a positive chrome azurol-S (CAS) test. On the basis of these results, we were able to deduce some structure-activity relationships. Furthermore, we found an analogue with siderophore activity that has appropriate functionality (an amino group) for use as an antibiotic vector to be employed in a "Trojan horse strategy".     

Molecular fibers and wires in solid-state and solution self-assemblies of cyclodextrin [2]rotaxanes

Cyclodextrin [2]rotaxanes have been prepared by coupling dimethylanilines with dicarboxylic acids using DMT-MM, in aqueous solutions of alpha-cyclodextrin, and the example illustrated shows unusual fluorescence emission and other spectroscopic behavior characteristic of the formation of molecular wires in solution, similar to the fibers observed in the solid state.     

Catalytic asymmetric vinylogous mannich reaction of N-(2-thienyl)sulfonylimines

Both cyclic and acyclic silyl dienol ethers participate efficiently in the asymmetric vinylogous Mannich reaction of N-2-thienylsulfonylimines catalyzed by copper(I) complexes of Fesulphos ligands. This procedure displays wide imine and nucleophile versatility, high enantiocontrol, and complete gamma-regioselectivity in most cases examined. The mild sulfonamide deprotection allows the resulting products to be readily transformed into optically active delta-lactams or 5-hydroxy-2-piperidone derivatives.     

Design of Furan-Based Acceptors for Organic Photovoltaics

We explore a series of furan-based non-fullerene acceptors and report their optoelectronic properties, solid-state packing, photodegradation mechanism and application in photovoltaic devices. Incorporating furan building blocks leads to the expected enhanced backbone planarity, reduced band gap and red-shifted absorption of these acceptors. Still, their position in the molecule is critical for stability and device performance. We found that the photodegradation of these acceptors originates from two distinct pathways: electrocyclic photoisomerization and Diels–Alder cycloaddition of singlet oxygen. These mechanisms are of general significance to most non-fullerene acceptors, and the photostability depends strongly on the molecular structure. Placement of furans next to the acceptor termini leads to better photostability, well-balanced hole/electron transport, and significantly improved device performance. Methylfuran as the linker offers the best photostability and power conversion efficiency (>14 %), outperforming all furan-based acceptors reported to date and all indacenodithiophene-based acceptors. Our findings show the possibility of photostable furan-based alternatives to the currently omnipresent thiophene-based photovoltaic materials.