Interaction between silica nanoparticles in binary liquid mixtures: the effect of polarity on adhesion

In order to explore the relationship between selective liquid sorption and the stability of dispersed silica particles, we carried out studies in ethanol–cyclohexane binary mixtures as well as in partially miscible 1-butanol–water mixtures. In ethanol–cyclohexane, adsorption excess isotherms were determined on hydrophilic and hydrophobic aerosil particles. The volume and the thickness of the adsorption layer were derived from the isotherms. Knowing the layer thickness and Hamaker constants, interparticle interaction potentials were calculated at various mixture compositions. At low ethanol concentration, where hydrophilic surfaces are considerably enriched in ethanol, interparticle interaction is enhanced and the high shear stress calculated from rheological measurements indicates the development of a three-dimensional network of aggregated particles. In contrast, hydrophobic aerosil particles in ethanol–cyclohexane approach each other without ensuing aggregation because interparticle interactions are weak, a fact well demonstrated by rheological measurements. It was also established that interactions between silica particles with hydrophilic surfaces are weak in butanol–water mixtures. Since water is preferentially adsorbed on the surface of hydrophilic particles to the azeotropic composition (\( x_{\rm{1}}^{\rm{a}} \)=0.62), within this wide composition range the Hamaker constant of the interfacial layer is identical with that of water.     

Seasonal Variations of Polycyclic Aromatic Hydrocarbons in Air Particulate Extracts

Aroma-active volatile organic compounds (VOCs) present in brandies produced in the Slovak Republic have been identified by gas chromatography–olfactometry (GC–O) and GC–MS. GC–O data treatment was based on a concept of detection frequency. Direct injection of samples was used due to its simplicity and the fact that determined composition is that of the original samples. This is especially important for correlation of results obtained by sensory evaluation and gas chromatographic measurements. Among 200 organic compounds found by GC only 71 showed olfactive properties at the given concentration levels. In order to identify aroma-active substances, linear retention indices (LRI) have been calculated and compared with available LRI libraries. The most aroma-active compounds have been found in samples of Frucon brandy, while Vinovica showed their minimal content. The results obtained by gas chromatography have been compared with sensory evaluation of brandy odor.     

Structural characterization of the crystalline diastereomeric complexes of enantiopure dimethylacridino-18-crown-6 ether and the enantiomers of 1-(1-naphthyl)ethylamine hydrogen perchlorate

This paper describes the X-ray crystal structure of the diastereomeric complexes formed by enantiopure dimethyl-substituted acridino-18-crown-6 ether (R,R)-1 and the enantiomers of 1-(1-naphthyl)ethylammonium perchlorate. We found that the heterochiral complex (R,R)-1–(S)-1-NEA is more stable than the homochiral one (R,R)-1–(R)-1-NEA. In the case of the heterochiral complex, the X-ray studies revealed a strong intermolecular π–π interaction between the naphthyl unit and the acridine moiety. However, in the case of the homochiral complex, π–π interaction was not found. We suggest that the existence or absence of the π–π interaction and the difference in steric repulsions in the diastereomers is responsible for the enantiomeric discrimination.     

On triazoles XLIII. Synthesis of 1,2,4‐triazolyl isoquinolinium zwitter ions

Type 8 isoquinolinium zwitter ions were synthesised by the reaction of type 1 diketones or type 2 pyrylium salts with different 5‐amino‐3‐Q‐1H‐1,2,4‐triazoles. Spectroscopic and X‐ray diffraction evidence was given for the zwitter ion structure of the products obtained. The position of the negative charge on the 1,2,4‐tiazolium ring was proved by comparison of the cmr and uv spectra of the products obtained with the three possible N‐benzyl derivatives 14–16 prepared for this purpose.     

Effect of Culture Conditions on Fatty Acid Profiles of Bacteria and Lipopolysaccharides of the Genus Pseudomonas—GC-MS Analysis on Ionic Liquid-Based Column

The profiling of bacterial fatty acids is a well-established technique in identifying and classifying bacteria. Cultivation conditions may affect the biosynthesis, thereby, changing the fatty acid profile in bacteria. The effect of the culture conditions on the fatty acid components of Pseudomonas aeruginosa PAO1, Pseudomonas aeruginosa ATCC 27853, Pseudomonas aeruginosa polyresistant and Pseudomonas putida all are aligned to the genus Pseudomonas. The fatty acids in the lipopolysaccharides of Pseudomonas aeruginosa PAO1 were also examined. The effects of the cultivation conditions were followed by using agar and blood agar media at the characteristic temperatures, 25 °C, 37 °C and 42 °C, respectively, and an analysis was made during the 1st, 3rd and 5th day following inoculation. In addition to quantitative differences, we also experienced qualitative differences in the fatty acid profiles which detect newly appearing fatty acids, due to changes in environmental factors. The application of ionic liquid-based column unveils new possibilities for the analyses of fatty acids in GC-MS experiments for bacterial fatty acid profiling. The validation results (response linearity, limit of detection, limit of quantification, system suitability, intraday and interday repeatability and accuracy) show the high separation efficiency of the ionic liquid-based column in the analyses.     

Identification and Quantification of Lignans,Carboxylic Acids and Sugars in the Leaves of Forsythia Species and Cultivars

Lignans, carboxylic acids and sugars were determined by gas chromatography (GC) with mass selective detection, the lignans also by high-performance liquid chromatography with UV detection in the leaf extracts of four species and four cultivars of Forsythia plant. Three methods were used to optimize the extraction of the main lignan constituents (arctiin, arctigenin), which possess significant pharmaceutical effects. Supercritical fluid extraction (SFE) proved to be the most efficient method compared to sonication and refluxation. The total lignan content of the leaves varied from 31.6 (F. ovata ‘Tetragold’) to 113.8 mg g⁻¹ (F. ovata ‘Robusta’).

     

Steric complementarity in carboxylate anion recognition

A 2,6 pyridino-linked aminocryptand acts as a good host for carboxylate anions, oxalate, malonate, acetate and lactate at low protonation levels as shown by aqueous complexation constants. With oxalate, at the hexaprotonated level of the host, the crystal structure shows formation of a dimeric unit linked by an oxalate/semioxalate short (2.474 A) H-bond. The protonated cryptand uses a cleft-binding mode in preference to the cavity-binding mode used by other aminocryptand hosts.     

Retention behavior of resorcinarene‐based cavitands on C8 and C18 stationary phases

The understanding of the retention behavior of large molecules is an area of interest in liquid chromatography. Resorcinarene‐based cavitands are cavity‐shaped cyclic oligomers that can create host–guest interactions. We have investigated the chromatographic behavior of two types of cyclic tetramers as analytes in high‐performance liquid chromatography. The experiments were performed at four different temperatures (15, 25, 35, 45°C) on two types of reversed stationary phases (C₈ and C₁₈) from two different manufacturers. We have found a huge difference between the retention of resorcinarenes and cavitands. In some cases, the retention factor of cavitands was even a hundred times larger than the retention factor of resorcinarenes. The retention of methylated derivates was two to four times larger compared to that of demethylated compounds on every column. The opposite retention behavior of the resorcinarenes and cavitands on the two types of stationary phases showed well the difference of the selectivity of the XTerra and BDS Hypersil columns. The retention mechanism was studied by the thermodynamic parameters calculated from the van't Hoff equation.     

Profiling the Concentration of Reduced and Oxidized Glutathione in Rat Brain Using HPLC/DAD Chromatographic System

This study aimed to develop a HPLC/DAD method in order to determine and quantify the reduced glutathione (GSH) and oxidized glutathione (GSSG) levels in rat brain. Due to the presence of the thiol group (-SH), GSH can interact with the Ellman′s reagent (DTNB), with which it forms a reaction product through which the level of GSH can be quantified, using the DAD detection system. Chromatographic separation was achieved after a derivatization process by using a mobile phase acetonitrile (A) and phosphate buffer (20 mM, pH = 2.5) (B). The compounds of interest were detected at 330 nm using a chromatographic C8 column. The method of determination met the validation criteria, specified by the regulatory bodies. The applicability of the method was demonstrated in a chronic toxicology study of central nervous system (CNS), following different treatment regimens with haloperidol.     

Simultaneous capillary GC of acids and sugars as their silyl(oxime) derivatives: Quantitation of chlorogenic acid,raffinose, and pectin substances

Our GC-MS method for the simultaneous quantitation of sugars and acids as their silyl(oxime) derivatives, from one solution by one injection, has been extended to the reproducible determination of high molecular weight compounds sensitive to decomposition yet requiring a high evaporation temperature (e.g. chlorogenic acid and rffinose) and for the quantitation of the decomposition products of pectin (i.e., for the determination of galacturonic acid at low ng levels in the presence of a 10–100 fold excess of glucose eluting just before the acid). The optimized GC procedure has been used for quantitation of the sugar and acid (including chlorogenic acid) composition of potato samples, and for the determination of the increasing amount of the decomposition products of pectin substances in apple pulp after different storage times.