Determination of the coumarin derivative cloricromene acid in rabbit plasma and platelets.

Two methods for the determination of cloricromene acid in biological samples are described. Cloricromene acid is a catabolite of cloricromene, a coumarin derivative which is active in the cardiovascular system. After oral administration of cloricromene to a rabbit, plasma and platelets were taken at different times and cloricromene acid was then isolated by solid-phase extraction with Sep-Pak C18 cartridges using acetonitrile-tetrahydrofuran-20% aqueous acetic acid (15:11:74, v/v/v) as eluent. The analyses were performed by reversed-phase high-performance liquid chromatography (RP-HPLC) combined with fluorescence detection with excitation at 310 nm and emission at 390 nm. The limit of quantification by RP-HPLC was about 50 pg. The catabolite in the plasma was identified by continuous-flow fast atom bombardment mass spectrometry (CF-FAB-MS), also used as a complementary means of RP-HPLC determination. The results obtained by RP-HPLC and CF-FAB-MS showed good agreement.     

Characterization of polysaccharide production of Haemophilus influenzae type b and its relationship to bacterial cell growth

Haemophilus influenzae type b (Hib) causes invasive infections in infants and young children. Vaccines consisting of Hib capsular polysaccharide (polymer of ribosylribitol phosphate [PRP]) conjugated to a protein are effective in the prevention of such infections. The production of capsular polysaccharide type b was studied in three cultivation conditions: single, glucose pulse, and repeated batch. Specific polysaccharide production (Y _p/x ) was calculated for all experiments, showing the following values: 67 (single-batch cultivation), 71 (glucose pulse), 75 (repeated-batch cultivation, first batch), and 87 mg of PRP/g of dry cell weight (DCW) (repeated-batch cultivation, second batch). Biomass concentration reached ∼1.8 g of DCW/L, while polysaccharide concentration was about ∼132 mg/L in the three fermentation runs. Polysaccharide synthesis is associated with cell growth in all studied conditions as established by Kono's analysis and Luedeking-Piret's model.     

Experimental calibration and field investigation of the oxygen isotopic fractionation between biogenic aragonite and water

Marine molluscs have long been recognised as potential records of palaeoclimate change using the patterns and differences in the stable isotopic composition of the carbonate shells. The aim of this study is to improve the robustness of this approach for aragonitic molluscs by completing the first experimental calibration of the fractionation between water and biogenic aragonite. Fractionation factors were calibrated by growing specimens of the freshwater mollusc Lymnaea peregra under controlled conditions of water temperature and isotopic composition. Fifteen populations of L. peregra were maintained at constant temperature and isotopic conditions for five months (at five different temperatures and using three different water compositions). Water samples and temperature measurements were taken regularly throughout the experiment. The temperature dependence of the fractionation factor, between 8 and 24 degrees C, is given by: 1000 ln alpha=16.74x(1000T(-1))-26.39 (T in Kelvin) and the relationship between temperature (T), delta(18)O(carb) and delta(18)O(wat) is given by: T=21.36-4.83xdelta(+ degrees )O(carb)-delta(+ degrees )O(wat) (T is in degrees C, delta(18)O(carb) is with respect to Vienna Pee Dee Belemnite (PDB), the International Atomic Energy Agency (IAEA) replacement standard for PDB, and delta(18)O(wat) is with respect to Vienna standard mean ocean water (VSMOW)) The outcome of the controlled experiment is compared with previous studies on synthetic, and biogenic, calcite and aragonite from field and laboratory investigations. These comparisons suggest that although a vital offset exists between the fractionation of isotopes in synthetic and biogenic aragonite for molluscs in general, there is no vital effect that is specific either to freshwater, or to individual, genera. Therefore, the calibrated relationship may be used for any freshwater or marine mollusc to derive palaeotemperatures providing the isotopic composition of the environmental water can be reliably constrained. Copyright 1999 John Wiley & Sons, Ltd.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.