First chemical study of anaspidean Syphonota geographica: structure of degraded sterols aplykurodinone-1 and -2

Two unprecedented degraded sterols, aplykurodinone-1 (1) and -2 (2), have been isolated from the skin of the marine anaspidean Syphonota geographica, collected along the coasts of Greece. The structures and the relative stereochemistry were established by spectroscopic analysis and confirmed by chemical correlation with related known compounds.     

Simulation of13C NMR chemical shifts for polychlorinated and polybrominated oxybenzenes with two-particle increment scheme

A two-particle system of OY-Cl and OY-Br mixed increments for predicting¹³C NMR chemical shifts of polyhalogenated polyoxybenzenes has been developed. It has been found that only theortho- and para-interactions of the OY and Hal substituents contribute significantly to the¹³C chemical shifts and that theortho-effects of the OY located between Ha1 and H and those of the OY located between two Ha1 atoms are different. Additional effects are due to solvating solvents. The increment scheme is predictive over the whole class of compounds under consideration and may be realized on personal computers.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 617–624, April, 1994.     

Miniaturization of separation techniques using planar chip technology

Miniaturization of separation columns implies equally reduced vol- umes of injectors, detectors, and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron-sized structures such as channels. This is demonstrated by two examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical path length cell despite its volume of 1 nL. A capillary electrophoresis device allows integrated injections of 100 pL samples, efficiencies of 70,000 to 160,000 theoretical plates in 10 to 20 seconds, and external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm.     

Selection of thermotolerant yeasts for simultaneous saccharification and fermentation (SSF) of cellulose to ethanol

A total of 27 yeast strains belonging to the groupsCandida, Saccharomyces, andKluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45°C. K. marxianus andK. fragilis were found to be the best ethanol producing organisms at the higher temperature tested and, so, were selected for subsequent simultaneous saccharification and fermentation (SSF) studies.     

Preparation of apolar glass capillary columns by the barium carbonate procedure

As an extension of previous reports, the barium carbonate procedure has been optimized in detail for the preparation of apolar columns. The aim was to produce optimum overall column characteristics, and to maintain them unchanged under the prolonged influence of the highest possible temperature. The main parameters under optimization were glass variety, leaching of glass surface with aqueous HCl, and amount of barium carbonate deposited, while deactivation and coating were kept constant. The basic column characteristics were adsorption properties and thermostability of deactivation, acid/base behaviour and separation efficiency. They were determined by a new, quantitative testing procedure. Intense leaching was able to eliminate almost totally the differences between glass varieties and to create a well-defined glass surface. While untreated glass, leached glass, and barium carbonate treated glass showed specific weak points in the respective column quality, the combination of leaching and barium carbonate treatment yielded the highest and most stable quality. Some technical modifications of the preparation procedure are described, including deactivation in the gas phase, and use of pentane as a solvent for static coating.     

Acid-catalyzed attack of the dinitrogen ligand in thecis-(Me2PhP)4Mo(N2)2 andtrans-(Ph2PCH2CH2PPh2W(N2)2 complexes by nitronium and nitrosonium cations with the formation of nitrogen oxides

The interaction of labeled dinitrogen complexescis-(Me₂PhP)₄Mo(¹⁵N₂)₂ andtrans-(dppe)₂W(¹⁵N₂)₂ with non-labeled nitronium and nitrosonium fluoroborates,¹⁴NO₂BF₄ and¹⁴NOBF₄, in sulfolane at room temperature in the presence of H₂SO₄ results in rapid formation of labeled nitrous and nitric oxides (¹⁵N¹⁴NO,¹⁵NO), as well as¹⁵N¹⁴N. The yield of the products depends on the reagent ratio and reaches 10–20 mol. % per mole of a complex under optimum conditions. The mechanism of the reactions found is proposed. It involves the step of protonation of the dinitrogen ligand to form the corresponding hydrazido(2–) derivatives, which are then attacked by nitronium or nitrosonium cations. In accordance with the mechanism proposed, it was established that the hydrazido(2–) complexes, (Me₂PhP)₃Mo(¹⁵N₂H₂)Cl₂ and (dppe)₂W(¹⁵N₂H₂)Cl₂, are capable of forming¹⁵N¹⁴NO,¹⁵NO, and¹⁵N¹⁴N under the action of¹⁴NO₂BF₄ and¹⁴NOBF₄ in the absence of an acid.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 13–13, July, 1995.     

Solid-phase extraction-liquid chromatography-fluorimetry for organotin speciation in natural waters

Summary A method is reported for the determination of dibutyltin (DBT), diphenyltin (DPhT), tributyltin (TBT), and triphenyltin (TPhT) species at the nanogram per litre concentration level in natural water samples. Analytes were isolated from samples by solid-phase extraction and analysed both off-line and on-line by reversed-phase high-performance liquid chromatography with post-column derivatization and fluorimetric detection. Several SPE cartridges and eluents were evaluated; C₁₈ enrichment and elution with a mixture of methanol, acetic acid, and water was found most suitable. Preconcentration factors up to 250 can be achieved when a 500-mL sample is processed. Detection limits, recovery rates, and the precision of the whole process have been determined. The method has been applied to the determination of organotin species in spiked natural water samples collected on the NW Mediterranean coast. Recovery rates range from 75 to 110% and detection limits are at the low ng L⁻¹ level (1–3 ng Sn L⁻¹ for DPhT, DBT, and PhT and 40 ng Sn L⁻¹ for TBT when 250 mL spiked sea water is processed.)     

Graph—theoretical approach to the calculation of physico-chemical properties of polymers

A topological extrapolation method for the calculation of various properties (melting points, refractive indices, specific rotation, etc.) of infinite linear polymers is developed. The rapid convergence of the oligomer extrapolation series results in very good agreement between calculated and experimental values. Comparison between the proposed method and other empirical or semi-empirical methods (the group addition method and the Pade-approximation) is also presented.     

Development and validation of a stability-indicating HPLC method for the determination of degradation products in dipyridamole injection

Summary The development and subsequent validation of an isocratic high-performance liquid chromatographic (HPLC) procedure employing ultraviolet (UV) detection for the determination of degradation products in Dipyridamole Injection is reported. The development of this assay involved the evaluation of several factors including buffer type, ionic strength, pH, organic composition, and column type. The described method is simple, reproducible, accurate, and selective. The precision, relative standard deviation (RSD), amongst five sample preparations for total degradation products was not more than (NMT) 10.2 %, while the individual degradation products were NMT 12.1%. Intermediate precision, as determined from fifteen sample preparations, generated by two Analysts on different HPLC systems over three days, exhibited an RSD for total and individual degradation products of 8.2 % and NMT 27.5 %, respectively. The mean absolute recovery of dipyridamole using the described method is 102.1±1. 9%, (mean±SD, n=12) over the concentration range of 0.03 % to 5.0 % of its label claim of 5 mg mL⁻¹. The limit of detection and limit of quantitation were 0.1 and 0.3 μg mL⁻¹, respectively. The linearity of the peak response was verified with respect to dipyridamole concentration over a range of 0.3 and 50 μg mL⁻¹ (0.03 % to 5.0 % label claim). The Standard and Assay Preparations are stable for up to 48 hours at room temperature. The selectivity was evaluated by subjecting the finished product (Dipyridamole Injection) to thermal, acidic, basic, oxidative and fluorescent radiation stress conditions. No interference in the analysis of degradation products was observed, showing the method is stability-indicating.