A comparative study of trace enrichment of chlorophenols in water by extraction with C6 and C8 alkanes and by C18 reversed-phase adsorption

The efficiency, reproducibility and sensitivity ofn-hexane and iso-octane extraction and of C₁₈ reversed-phase adsorption for accumulation of 4-chloro-, 2,4-dichloro-, 2,4,5- and 2,4,6-trichloro-, 2,3,4,6-tetrachloro- and pentachlorophenol from aqueous solutions were compared. In extraction procedures the acetyl and pentafluorobenzoyl derivatives of chlorophenols were extracted from water. In adsorption procedure chlorophenols adsorbed on a Sep-Pak C₁₈ cartridge were eluted with acetone and after that derivatized analogously.All three procedures were found to be applicable for an efficient trace enrichment of chlorophenols in water, the proper choice being dependent on the required sensitivity of the analysis. Lower detection limits of single compounds at 10 ng·1^–1 levels were achieved by adsorption procedure owing to the more uniform and for most chlorophenols higher adsorption than extraction recoveries as well as owing to the possibility of treating larger volumes of water samples. The extraction procedure could be successfully applied to the concentrations of chlorophenols in water 1g·1^–1.Owing to its higher efficiency and better sensitivity the C₁₈ reversed-phase adsorption procedure was chosen as the more suitable one for the determination of chlorophenol levels in surface, ground and drinking waters. The conversion of chlorophenols accumulated from a water sample parallel to both acetyl and pentafluorobenzoyl derivatives and the analysis of both types of derivatives on two basically different gas Chromatographic columns were recommended for a more reliable identification and quantitation of the compounds analyzed.     

Identification of SARS-CoV-2 Papain-like Protease (PLpro) Inhibitors Using Combined Computational Approach**

In the current pandemic, finding an effective drug to prevent or treat the infection is the highest priority. A rapid and safe approach to counteract COVID-19 is in silico drug repurposing. The SARS-CoV-2 PLpro promotes viral replication and modulates the host immune system, resulting in inhibition of the host antiviral innate immune response, and therefore is an attractive drug target. In this study, we used a combined in silico virtual screening for candidates for SARS-CoV-2 PLpro protease inhibitors. We used the Informational spectrum method applied for Small Molecules for searching the Drugbank database followed by molecular docking. After in silico screening of drug space, we identified 44 drugs as potential SARS-CoV-2 PLpro inhibitors that we propose for further experimental testing.     

A cooperative hyper-heuristic search framework

In this paper, we aim to investigate the role of cooperation between low level heuristics within a hyper-heuristic framework. Since different low level heuristics have different strengths and weaknesses, we believe that cooperation can allow the strengths of one low level heuristic to compensate for the weaknesses of another. We propose an agent-based cooperative hyper-heuristic framework composed of a population of heuristic agents and a cooperative hyper-heuristic agent. The heuristic agents perform a local search through the same solution space starting from the same or different initial solution, and using different low level heuristics. The heuristic agents cooperate synchronously or asynchronously through the cooperative hyper-heuristic agent by exchanging the solutions of the low level heuristics. The cooperative hyper-heuristic agent makes use of a pool of the solutions of the low level heuristics for the overall selection of the low level heuristics and the exchange of solutions. Computational experiments carried out on a set of permutation flow shop benchmark instances illustrated the superior performance of the cooperative hyper-heuristic framework over sequential hyper-heuristics. Also, the comparative study of synchronous and asynchronous cooperative hyper-heuristics showed that asynchronous cooperative hyper-heuristics outperformed the synchronous ones.     

A note on regularity of the pressure in the Navier–Stokes system

In this note we improve the standard regularity of the dynamic part of the pressure in the Navier–Stokes system. Using the theory of elliptic equations with \(L^1\) right-hand side we prove that, in addition to be in \(L^2\), the dynamic pressure belongs to \(W^{1,\alpha }_{loc} \) with \(1<\alpha <\frac{n}{n-1}\), in case of Dirichlet boundary condition. For pressure boundary condition the dynamic pressure is proved to be in \(W^{1,\alpha } \). As a consequence, for the force \(\mathbf{f} \in L^q (\Omega )^n \) and \(q>n /2 \) the pressure turns out to be continuous.     

The oxyfunctionalization of 4‐methylcoumarins using dimethyldioxirane

The kinetic study of the efficient regioselective oxidation of the C? C double bond of 4‐methylcoumarins with isolated dimethyldioxirane was investigated using UV–vis spectroscopy methods. In the excess of dimethyldioxirane, the pyrone ring of a coumarin skeleton is selectively epoxidated and hydroxylated in neutral media, in high yields. Kinetic analyses demonstrate two independent reaction pathways, epoxidation and hydroxylation, respectively, which was also confirmed using kinetic isotope effect methods. Both reaction products were isolated, and their structures were determined by NMR and mass spectra. The position of methyl groups attached at the aromatic part of coumarin molecule shows significant influence on kinetic rate constants and activation parameters. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 414–420, 2009     

Use of electrochemical impedance spectroscopy to characterise the physical properties of ex situ reconstructed sea surface microlayer

The objective of this work was to develop electrochemical impedance spectroscopy (EIS) to characterise the physical properties of the sea surface microlayer ( ssm ). Samples from Lake Rogoznica in Croatia were extracted by n-hexane and dichloromethane (dcm) respectively and transferred to mercury electrodes. The EIS results were compared with those of a model phospholipid, dioleoyl phosphatidylcholine (DOPC) which forms near defect-free monolayers on a mercury surface. The ssm extracts formed inhomogeneous monolayers on the mercury surface and the dcm ssm extract monolayer showed greater surface roughness than the hexane ssm extract. The hexane ssm extract introduced defects and a greater surface roughness into mixed DOPC- ssm extract monolayers than the dcm ssm extract due to the lower compatibility of the non-polar hexane extract with the DOPC than that of the polar ssm extract. In addition, the dcm ssm component in the mixed DOPC- ssm monolayer showed an association with pyrene added to the solution.     

Pt/C nanocatalysts for methanol electrooxidation prepared by water-in-oil microemulsion method

Journal of Solid State Electrochemistry - Pt nanoparticles supported on Vulcan XC-72R were synthesized by water-in-oil microemulsion method. By incorporating different amounts of HCl as a capping...     

Global Controllability for Quasilinear Nonnegative Definite System of ODEs and SDEs

Journal of Optimization Theory and Applications - We consider exact and averaged control problem for a system of quasilinear ODEs and SDEs with a nonnegative definite symmetric matrix of the...