Gas Chromatographic Method for Routine Determination of Oleanolic and Ursolic Acids in Medicinal Plants

Summary A rapid and simple gas chromatographic method has been established for routine analysis of free oleanolic and ursolic acids in dried samples of medicinal herbs. Soxhlet extraction of triterpenes was followed by solid-phase extraction (SPE). Amounts of the compounds were measured by gas chromatography after silylation of the purified samples. Experiments were performed to establish the optimum conditions (e.g. solvent, and mode and duration of extraction) for calibration curve linearity, sensitivity, reproducibility, and recovery. The conditions used for derivatization and gas chromatographic analysis resulted in an improvement on literature data. The method devised enables accurate routine measurement of many samples in quite a short time (e.g. for chemotaxonomical screening, or quality control of herbal drugs). The practical application of the method was illustrated on five Lamiaceae species.     

Enthalpies of solution and of crystallization of lithium nitrate and of lithium nitrate trihydrate in water at 25°C

The enthalpies of crystallization of LiNO₃ and LiNO₃–3H₂O from aqueous solutions at 25°C, measured by a calorimetric method and determined from the previously published data on the concentration dependence of the enthalpy of solution, are reported. The results are compared with the values obtained from the concentration dependences of the activity coefficients and from the temperature dependences of the solubilities. The enthalpy of solution at infinite dilution and the enthalpy of hydration are given.     

UV spectra of vinyl chalcogenides: Correlation with the photoelectron spectra

The electron absorption spectra of alkylvinyl chalcogenides (CH₂=CHEAlk, E = S, Se, Te) were analyzed with consideration of the photoelectron spectroscopic data. The following sequence of electronic transitions was found in their UV spectra:

Metal Chelates of Hydrazo-Dimedon Dyes. Chelating Tendencies of 5,5-Dimethylcyclohexane-2-(2-Carboxyphenyl,and 3-Carboxyphenyl)-Hydrazono 1,3-Dione (DC-2-CPHD and DC-3-CPHD)

The consecutive stepwise formation constants of 1:1 and 1:2 chelate species formed by the interaction of DC-2-CPHD and DC-3-CPHD anions with tripositive lanthanon and divalent copper, nickel, cobalt, zinc, manganese, and cadmium cations were determined potentiometrically at ionic strengh of 0.1 (KNO₃) and 30°C. The results indicate that two different coordination modes, one tridentate (DC-2-CPHD), and one bidentate (DC-3-CPHD), are in evidence.     

The structure of cyclopentene oxide determined by gas phase electron diffraction

The r_g structure of cyclopentene oxide has been determined by the simultaneous least squares analysis of electron diffraction and microwave spectroscopic data. The investigation has reaffirmed previous studies indicating that the molecule prefers a boat conformation. The methylene and epoxide flap angles obtained are 152.3±2.1° and 104.7±1.0° respectively. Other structural parameters determined are: r_g (C-H avg.) = 1.120±0.004 Å; r_g (C-C avg.) = 1.538±0.002 Å; r_g (C-O) = 1.443±0.003 Å, and r_g (C-C) = 1.482±0.004 Å for the carbon-carbon bond in the three membered epoxide ring. These results compare favorably with the reported structures of ethylene oxide and cyclohexene oxide. A tentative rationalization of the unusual boat conformation is also offered.     

The vibrational spectra and normal coordinate analysis of tetracyclopropyllead

All the fundamental frequencies observed in IR and Raman spectra have been assigned to the normal modes of the molecule (C₃H₅)₄Pb (C₃H₅ = cyclopropyl). The calculated force field is compared to that of (C₃H₅)₂Hg and the Cmetal stretching force constants are discussed along with those of Me₄Pb and Me₂Hg; The similarity of the spectra of cyclopropyllead and cyclopropyl-mercury proves that the vibrations of cyclopropyl structural units are isolated in both molecules.     

Some observations concerning the direct titration of nitrite with cerium(IV)

Direct titration of nitrite with cerium (IV), with ferroin as indicator, is shown to give satisfactory results if the acidity is kept between 0.033 and 0.055M at the end-point. Loss of nitrous acid owing to volatilization and decomposition is discussed. From 10 to 60 mg of sodium nitrite can be estimated with a standard deviation of 5 mug and an average error of 0.2%.     

Characterization of proteins separated by displacement chromatography using low angle laser light scattering photometry

Summary -Lactoglobulin A and B (-LACT) were separated by displacement chromatography (DSC) on an ionexchange column using dextran sulfate as the displacer. A LALLS photometer and a UV detector, in series, were used to determine the molecular weight (MW) of the proteins, on-line. The results indicate that both, -LACT A and B, were present as dimers in the buffer used for the mobile phase. The MWs of the proteins were about 6–8% higher than the theoretical MW of a dimer (37,000). Additional control studies have shown the presence of a high molecular weight species in both the proteins, which could possibly be an aggregate. This species was observed in the LALLS signal but was nearly absent in the UV signal. Our work has demonstrated the feasibility of interfacing LALLS with displacement chromatography for detecting impurities or aggregates which may be difficult to detect by conventional detectors used for chromatography.     

Preparation and properties of poly(vinyl alcohol)/silica nanocomposites derived from copolymerization of vinyl silica nanoparticles and vinyl acetate

Nanocomposites of poly(vinyl alcohol)/silica nanoparticles (PVA-SNs) were prepared by in-situ radical copolymerization of vinyl silica nanoparticles functionalized by vinyltriethoxysilane (VTEOS) and vinyl acetate with benzoyl peroxide (BPO, i.e., initiator), subsequently saponified via direct hydrolysis with NaOH solution. The resulting vinyl silica nanoparticles, PVA-SNs were characterized by means of fourier transformation spectroscopy (FTIR), transmission electron microscopy (TEM) and the elemental analysis method. Effects of silica nanoparticles on viscosity and alcoholysis of PVA-SNs were studied by a ubbelohode capillary viscometer and the back titration method. The morphological structure of PVA-SN films was investigated by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile test were used to determine the thermal and mechanical properties of PVA-SN films. The results indicated that the content of vinyl groups on the surface of the vinyl silica nanoparticles was up to 3.02 mmol/g and vinyl silica nanoparticles had been successfully copolymerized with vinyl acetate. Furthermore, compared to pure PVA, silica nanoparticles bonded with polymer matrix in a low concentration affected the viscosity and alcoholysis of the PVA-SNs materials. At the same time, it resulted in the improvement of the thermal and mechanical properties of the PVA-SN materials due to a strong interaction between silica nanoparticles and the polymer matrix via a covalent bond. It could be found that the optical clarity of the membrane was changed through UV-Vis absorption spectrum due to the introduction of silica nanoparticles.