Determination of Stachys palustris Iridoids by a Combination of Chromatographic Methods

JPC – Journal of Planar Chromatography – Modern TLC - Stachys palustris L. (Lamiaceae) contains the iridoids harpagide and acetylharpagide. The presence of other components, for example...     

Microwave assisted dissolution of aluminium oxide samples

The dependence on time of the efficiency of microwave assisted digestion of Al₂O₃ samples with various physico-chemical properties in H₂SO₄ solution (1 + 1) at a temperature of 170 °C and a pressure of 207 kPa has been investigated. Therefore, the concentrations of Al and that of the impurities in the solutions obtained, as well as the masses of residues after different times have been measured. The efficiency of the dissolution was shown to depend on the specific surface area and on the phase-state of the Al₂O₃. The time demand for total dissolution of the samples ranged from 0.1 to 7 hours.     

New gas chromatographic method for the enantioseparation of β-amino acids by a rapid double derivatization technique

A novel gas chromatographic method was developed for the enantioseparation of valuable acyclic and carbocyclic cis- and trans-β-amino acids, including cispentacin and a number of its analogues and homologues. Excellent (in most cases baseline) separation was achieved for the racemates of these β-amino acids on CP-Chirasil-Dex CB or CP-Chirasil L-Val columns after a simple and rapid double derivatization (esterification followed by N-acylation). The elution sequences were determined in all cases.     

Fast liquid chromatographic determination of radiochemical and chemical purity of [11C]methionine by UPLC technique

Salinity, water logging, high nitrate, fluoride and dissolved uranium concentration in drinking water of southwest Punjab has impacted the local population leading to health issues and additional burden on economy. Though it was known that both U and its daughter products especially Rn contribute to radiological dose to the population through drinking water, there were no correlation studies carried out between these radioactive elements in U impacted regions of southwest Punjab. In this study, an initiative has been taken to assess the doses due to dissolved radon in drinking water. In addition, the U–Rn couple is evaluated in detail along with other hydrochemical parameters. The radon concentration ranges from 360–1700 Bq/m³ for Faridkot and 140–1400 Bq/m³ for Muktsar for both seasons and the related average total dose due to radon for both season of Faridkot and Muktsar are 9.79 µS/year and 7.74 µS/year respectively. The total dissolved uranium is in range of 16–350 µg/L for Faridkot and 14–106 µg/L for Muktsar for both seasons. An inverse correlation was observed between Rn and U, which could be attributed to diverse geochemistry of U and Rn in groundwater.

     

Selective syntheses of novel highly functionalized β-aminocyclohexanecarboxylic acids

Highly functionalized β-aminocyclohexanecarboxylate regio- and stereoisomers were synthetized from racemic unsaturated bicyclic β-lactams via enzymatic resolution, selective transformation of the C–C double bond by stereoselective epoxidation, and regioselective oxirane ring opening with azide or cyanide as nucleophile.     

High‐performance liquid chromatographic enantioseparation of fluorinated cyclic β3‐amino acid derivatives on polysaccharide‐based chiral stationary phases. Comparison with nonfluorinated counterparts

The stereoisomers of five fluorinated cyclic β³‐amino acid derivatives and their nonfluorinated counterparts were separated on chiral stationary phases containing as chiral selectors cellulose tris‐(3,5‐dimethylphenyl carbamate), cellulose tris‐(3‐chloro‐4‐methylphenyl carbamate), cellulose tris‐(4‐methylbenzoate), cellulose tris‐(4‐chloro‐3‐methylphenyl carbamate), amylose tris‐(3,5‐dimethylphenyl carbamate) or amylose tris‐(5‐chloro‐2‐methylphenyl carbamate). The enantioseparations were carried out in normal‐phase mode with n‐hexane/alcohol/alkylamine mobile phases in the temperature range 5–40 °C. The effects of the mobile phase composition, the nature and concentration of the alcohol and alkylamine additives, the structures of the analytes and temperature on the separations were investigated. Thermodynamic parameters were calculated from plots of ln α vs. 1/T. The Δ(ΔH°) values ranged between ?5.0 and +1.6 kJ/mol, while Δ(ΔS°) varied between ?12.6 and +5.7 J/mol/K. The enantioseparation was enthalpically controlled, the retention factor and the separation factor decreasing with increasing temperature, but entropically controlled separation was also observed. The elution sequence was determined for all of the investigated analytes. Copyright © 2016 John Wiley & Sons, Ltd.     

Heterogeneous azide–alkyne cycloaddition in the presence of a copper catalyst supported on an ionic liquid polymer/silica hybrid material

Heterogeneous copper catalysts were prepared by the deposition of CuI on a hybrid material consisting of silica and a polymer with imidazolium moieties. The solid materials were characterised using solid‐phase NMR, Fourier transform infrared, Raman and X‐ray photoelectron spectroscopies and Brunauer–Emmett–Teller measurements. The formation of copper–carbene complexes was proved from Raman spectra and the results were supported by density functional theory calculations. The catalyst could be recycled efficiently with low loss of copper. Metal leaching was proved to be facilitated by the use of conditions typical for a homogeneous system (the presence of a polar solvent or the addition of a tertiary amine). Besides simple model reactions, the best catalyst was found to be suitable for the synthesis of triazoles of more elaborate structure, such as ferrocene or steroid derivatives.     

<Superscript>13</Superscript>C NMR analysis of cellulose samples from different preparation methods

Alpha-cellulose is a part of the wooden material that preserves isotopic composition during tree-growth, and therefore provides important indirect data for paleoclimatological studies. For this reason, it is exceptionally important to extract the alpha-cellulose component from plants, e.g. from tree rings of wood. Since the cell wall of plant cells consists of multicomponent polysaccharides, the extraction of cellulose from wood is not an obvious task. In this paper, we describe, evaluate and compare nine methods, based on the literature and experimental observations, for obtaining cellulose from tree rings of wood. We show that the distortionless enhancement by polarization transfer (DEPT-135) variant of liquid-state ¹³C NMR spectroscopy is a powerful analytical method for monitoring the preparation process. Trifluoroacetic acid was applied as solvent for the NMR analysis. We proved that all the preparation methods give pure cellulose samples without hemicellulose and lignin content, and we propose methods resulting in non-fragmented cellulose. ¹³C and ¹⁸O isotope ratio measurements have shown that all the applied extraction methods result in similar isotope ratios, thus they are suitable for paleoclimatological studies.     

Synthesis of densely functionalized cispentacin derivatives through selective aziridination and aziridine opening reactions: orthogonally protected di- and triaminocyclopentanecarboxylates

A novel substrate-directed synthetic route to a series of highly functionalized, orthogonally protected di- or triaminocyclopentanecarboxylate derivatives with multiple chiral centres from an unsaturated bicyclic β-lactam has been accomplished by applying stereoselective ring C–C double bond aziridination with chloramine-T and phenyltrimethylammonium tribromide, followed by regioselective aziridine opening with different N,O nucleophiles and hydrides. The functionalization strategy was successfully extended for access to enantiomerically pure orthogonally protected triaminocarboxylates.