Search results for "Solvent"

Effect of Stiffness on the Micellization Behavior of Model H4T4 Surfactant Chains

2006

The micellization behavior of a series of model surfactants, all with four head and tail groups (H4T4) but with different degrees of chain stiffness, was studied using grand canonical Monte Carlo simulations on a cubic lattice. The critical micelle concentration, micellar size, and thermodynamics of micellization were examined. In all cases investigated, the critical micelle concentration was found to increase with increasing temperature as observed for nonionic surfactants in apolar or slightly polar solvents. At a fixed reduced temperature and increasing chain stiffness, in agreement with previous observations, it was found that the critical micelle concentration decreased and the average…

Research on Acute Toxicity and the Behavioral Effects of Methanolic Extract from Psilocybin Mushrooms and Psilocin in Mice

2015

The pharmacological activities and acute toxicity of the psilocin (PC) and dried residues of the crude extracts of psychotropic mushrooms were investigated in mice. The hallucinogenic substances were effectively isolated, by using methanol, from the species of Psilocybe semilanceata and Pholiotina cyanopus, that were collected in the north-east region of Poland. The chemical analysis of these extracts, which was performed by liquid chromatography with mass spectrometry detection (LC-MS), indicated the presence of psilocin and other hallucinogenic substances, including indolealkylamines and their phosphorylated analogues. When the pure psilocin or fungal extracts were used, slight difference…

Sampling and analysis of pesticides in ambient air.

2008

Developments in the sampling and determination of pesticides in ambient air have been discussed and data on the occurrence of pesticides in atmosphere have been presented. Developments in active sampling methods were reviewed and the different materials used for trapping pesticides from gas and particulate phases were discussed. Likewise, the use and developments of passive air samplers were reviewed. This article pays special attention to the analysis of pesticides trapped from ambient air, and recapitulate the procedures for extraction, clean-up and determination of these substances. Improvements in sampling procedures, analytical methods and monitoring activities are necessary to advance…

Conformational studies into N-methylation of alanine diamide models: A quantitative approach

2006

Abstract A systematic theoretical analysis was performed on N -acetyl- l -alanine N ′-methylamide (Ac- l -Ala-NHMe) and the analogues methylated on the N-terminus (Ac- l -(Me)Ala-NHMe), C-terminus (Ac- l -Ala-NMe 2 ), and both N/C-termini (Ac- l -(Me)Ala-NMe 2 ), to evaluate the influence of methylation of the amide group on the conformational properties of the affected residues. The ϕ , ψ potential energy surfaces were calculated at the B3LYP/6-31+G**//HF/3-21G level of theory with inclusion of the solvent (water) effect (SCRF method). The conformers localised were fully optimised at the B3LYP/6-31+G** in vacuo. The accessible areas of the potential energy surfaces; the number of conformer…

Aminoacid zwitterions in solution : Geometric, energetic, and vibrational analysis using density functional theory-continuum model calculations

1998

Glycine and alanine aminoacids chemistry in solution is explored using a hybrid three parameters density functional (B3PW91) together with a continuum model. Geometries, energies, and vibrational spectra of glycine and alanine zwitterions are studied at the B3PW91/6-31+G∗∗ level and the results compared with those obtained at the HF and MP2/6-31+G∗∗ levels. Solvents effects are incorporated by means of an ellipsoidal cavity model with a multipolar expansion (up to sixth order) of the solute’s electrostatic potential. Our results confirm the validity of the B3PW91 functional for studying aminoacid chemistry in solution. Taking into account the more favorable scaling behavior of density funct…

Liquid gas techniques for GC trace analysis

1990

Liquid gases (LG), i.e. low boiling compounds with vapor pressures below 5 bar at room temperature, are introduced as solvents for trace analyses. A system for preparin, diluting and handling LG solutions safely and conveniently in 5 to 500 μl amounts was developed as well as a syringe for direct injection of μl-LG samples into capillary GC. Even technical grade LG are of high purity. GC/FID of LG solutions (starting at −60°C) allows the separation of volatile traces from the solvent peak: e.g., dichloromethane can be measured in the picogram range.

Characterization and quantitation of mixtures of alkyl ether sulfates and carboxylic acids by capillary electrophoresis with indirect photometric det…

2003

The separation, characterization, and determination of mixtures of alkyl ether sulfates (AES) and fatty acids (C10-C16) in background electrolytes (BGEs) containing acetonitrile (ACN)-water mixtures is addressed. Due to inhibition of the ionization of the carboxylate groups, the migration time and the resolution between the fatty acids decreased when the water content of the BGE was reduced, but efficiency and resolution between the AES oligomers improved. The migration times increased and resolution improved by substituting 5% ACN by an equivalent amount of dioxane. A complete separation of the two surfactant classes, up to the AES oligomers with 8 ethylene oxide units (EOs) with respect t…

Selective Extraction and Efficient Binding in a Protic Solvent of Contact Ion Triplets by Using a Thiourea-Based Bis-Calix[6]arene Receptor

2013

We report a D3h-symmetric tail-to-tail bis-calix[6]thiourea 5 that displays two divergent cavities triply connected by thiourea linkages. This calix[6]tube was efficiently synthesized through a [1+1] macrocyclization reaction and characterized by X-ray diffraction analysis. The binding properties of this heterotritopic receptor were evaluated in a protic environment (i.e., CD3OD/CDCl3) through NMR studies. Thus, bis-calix[6]thiourea 5 exhibits a remarkable ability in the cooperative complexation of an anion sandwiched between two ammonium ions, a high selectivity for ammonium sulfate salts being observed. The anion is bound through multiple hydrogen-bonding interactions at the thiourea bind…

Some aspects of the recovery of chlorinated residues (DDT-type compounds and PCB) from fish tissue by using different extraction methods

1974

Tuning the selectivity of molecularly imprinted polymer extraction of arylcyclohexylamines: From class-selective to specific

2020

Abstract A molecularly imprinted polymer (MIP) has been prepared in presence of 3-hydroxy phencyclidine (3-OH PCP) as template by bulk polymerization using N,N-dimethylformamide, as porogenic solvent, for the selective solid-phase extraction (SPE) of arylcyclohexylamines from oral fluids. Experimental variables of the extraction procedure have been studied in order to increase both, extraction recovery of 3-OH PCP, used as model analyte, and imprinting factor. By modifying the composition of the washing solvent, the selectivity of the MIP extraction procedure can be tuned, moving from an arylcyclohexylamine selective method to a 3-OH PCP specific method. The applicability of the synthesized…