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At least 685 records · Page 38Linked to original sources
PubMed2004

Development and validation of a method to determine the unbound paclitaxel fraction in human plasma.

Paclitaxel is pharmaceutically formulated in a mixture of Cremophor EL and ethanol (1:1, v/v). The unbound fraction of the anticancer drug paclitaxel in plasma is dependent on both plasma protein binding and entrapment in Cremophor EL micelles. We have developed a simple and reproducible method for the quantification of the unbound paclitaxel fraction in human plasma. Human plasma was spiked with [3H]paclitaxel and [14C]glucose (unbound reference) and incubated at 37 degrees C for 30 min. Plasma ultrafiltrate was prepared by a micropartition system (MPS-1) and collected in a sample cup containing 100 microl of plasma to prevent the loss of paclitaxel due to adsorption. The radionuclides were separated after combustion of the biological samples using a sample oxidizer and the radioactivity was determined by liquid scintillation counting. The unbound fraction of paclitaxel was calculated by dividing the ratios of 3H and 14C in plasma ultrafiltrate and in plasma. The method was thoroughly validated using human plasma spiked with pharmacologically relevant concentrations of paclitaxel (10-1000 ng/ml) and Cremophor EL (0.25-2.0%). The method was precise, with a within-day precision ranging from 3.9 to 11.0% and a between-day precision ranging from 5.8 to 13.1%. In patient plasma with low serum albumin values containing 1% of Cremophor EL, the unbound fraction appeared to be significantly higher than that in plasma with normal albumin values. The determination of the unbound fraction of paclitaxel proved to be stable during a 10-week storage at -20 degrees C. Furthermore, the assay was applicable in patient samples. This assay can be used to determine the unbound fraction of paclitaxel in plasma. Moreover, its design should allow the determination of the unbound concentrations of other hydrophobic drugs.

Aged↗
PubMed2004

Bacillus subtilis alpha-amylase: interactions of a partially folded conformer with small unilamellar vesicles.

We studied the interactions between conformers of exocellular alpha-amylase and small unilamellar vesicles (SUV) composed of the major membrane lipids of Bacillus subtilis under physiological conditions of pH, temperature and ionic strength. Using fluorescence spectroscopy, surface plasmon resonance (SPR) and phase separation, we show that the native alpha-amylase has no affinity for the SUV, whereas a partially folded form, displaying structural properties in common with the competent state for secretion, binds to the vesicles (KA approximately 10(5) M(-1)). This association prevented its subsequent folding. The complex was destabilized in the presence of PrsA, a major peripheric lipoprotein of B. subtilis which displays a strong affinity for SUV (KA approximately 1.5x10(8) M(-1)). Vesicles coated with PrsA lost their ability to bind the partially folded conformer. The approach in vitro, in which our aim was to mimic the last stage of alpha-amylase translocation, indicates that PrsA possibly helps, in vivo, the secreted protein to acquire its native conformation by modulating the interaction between the latter and the lipid polar heads on the trans side of the cytoplasmic membrane.

Bacillus subtilis↗
PubMed2005

Direct Yellow and Methylene Blue liquid-liquid extraction with alkylene carbonates.

Propylene and 1,2-butylene carbonates enable very effective extraction of Methylene Blue. The use of a more hydrophobic 1,2-butylene carbonate is preferred for practical application. Separation is enhanced by addition of an electrolyte (NaCl). Partition coefficients for solutions containing Methylene Blue and 1M NaCl are at least a hundred times higher than for Direct Yellow solutions. The recovery of Methylene Blue with propylene and 1,2-butylene carbonates is significantly better, compared with the cloud point technique. Cloud point technique yields to almost 100% only in the case of low concentrations of Methylene Blue in the feed (0.5mg dm(-3)). For higher initial concentrations (0.01-0.25 g dm(-3)) of Methylene Blue, this method of recovery provides low extraction percentages (10-40%). Alkylene carbonates are not appropriate extractants for recovery of very hydrophilic Direct Yellow.

Alkenes↗
PubMed2003

Improved spiral disk assembly for high-speed counter-current chromatography.

The spiral disk for type-J high-speed counter-current chromatography (HSCCC) has been improved by placing short segments of PTFE (tetrafluoroethylene) tubing into the channel at regular intervals. The best results were obtained with a four-channel spiral column using 600 spacers, which significantly improved stationary phase retention and partition efficiency in both n-butanol-acetic acid-water (4:1:5) and poly(ethylene glycol) 1000-dibasic phosphate polymer phase systems. Based on these findings, a "bead-chain spiral disk" was designed and its performance tested with a type-J HSCCC centrifuge. This new column design substantially improved the separation of both dipeptide and protein samples in terms of stationary phase retention and partition efficiency.

Countercurrent Distribution↗
PubMed2003

Application of high-speed counter-current chromatography to the preparative separation and purification of baicalin from the Chinese medicinal plant Scutellaria baicalensis.

Baicalin was separated and purified for the first time from the traditional Chinese medicinal plant Scutellaria baicalensis Georgi by high-speed counter-current chromatography. Crude baicalin was obtained by extraction with methanol-water (70:30, v/v) from S. baicalensis Georgi. The separation was performed in two steps with a two-phase solvent system composed of n-butanol-water (1:1, v/v), in which the lower phase was used as the mobile phase at a flow-rate of 1.0 ml min(-1) in the head-to-tail elution mode. A total of 37.0 mg of baicalin at 96.5% purity was yielded from 200 mg of the crude baicalin (containing 21.6% baicalin) with 86.0% recovery as determined by HPLC analysis.

Chromatography, High Pressure Liquid↗
PubMed2003

Improved apparatus for solid-liquid multi-stage counter-current extraction.

An improved apparatus for solid-liquid multi-stage counter-current extraction (SLME) was developed. The apparatus has a set of 24 extraction vessels. Each extraction vessel unit is composed of a piston-cylinder in which the solid phase is placed, and a cup-cylinder in which the liquid phase is set. Of the 24 extraction vessels, 20 were used for the separation stage, and the other 4 were used for the back-extraction stage. (+/-)-Troger's base was selected as a racemic model compound for the continuous enantioseparation by the apparatus, and a cellulose derivative was used as the chiral separator. After 50 cycles of the operation (in 9 h), 0.1 g of (-)-enantiomer (85% in purity) was recovered from the solid phase by back-extraction with ethanol, whereas 1.1 g of (+)-isomer (75% in purity) was collected from the liquid phase (ethanol).

Chromatography, High Pressure Liquid↗
PubMed2003

Preparative separation of rhein from Chinese traditional herb by repeated high-speed counter-current chromatography.

High-speed counter-current chromatography (HSCCC) was repeatedly used for isolation and purification of rhein from Rheum officinale Baill (Dahuang) with a two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water (3:7:5:5, v/v), which had been selected by analytical (HSCCC). Using two preparative units of the HSCCC centrifuge, about a 500 mg amount of the crude extract was separated, yielding 6.7 mg of rhein at a high purity of over 97%.

Anthraquinones↗
PubMed2003

Supercritical fluid extraction of grape seed oil and subsequent separation of free fatty acids by high-speed counter-current chromatography.

Supercritical fluid extraction (SFE) of grape seed oil was performed to study the effect of various parameters such as pressure, temperature and the particle size of the sample on the yield and composition of oil using an analytical-scale SFE system. Then the extraction was scaled up by 125 times using a preparative SFE system under the optimized conditions of high pressure (30-40 MPa) and low temperature (35-40 degrees C) with medium particle size (20-40 mesh). The maximum yield of the oil can reach 6.2% with pure supercritical CO2 and 4.0% more oil can be obtained by adding 10% of ethanol as modifier. The unsaturated fatty acids (UFSs) make up about 70% in the oil on the basis of free fatty acids. The grape seed oil was then subjected to separation and purification for free fatty acids after saponification by high-speed counter-current chromatography coupled with evaporative light scattering detection (ELSD). The separation of 1.0 g of oil can yield about 430 mg pure linoleic acid at 99% purity. The fatty acids were analyzed by HPLC-ELSD.

Chromatography, High Pressure Liquid↗
PubMed2004

Preparative high-speed counter-current chromatography for purification of shikonin from the Chinese medicinal plant Lithospermum erythrorhizon.

The bioactive compound shikonin was successfully isolated and purified from the crude extract of the traditional Chinese medicinal plant Lithospermum erythrorhizon Sieb. et Zucc. by preparative high-speed counter-current chromatography (HSCCC). The preparative HSCCC was performed using a two-phase solvent system composed of n-hexane-ethylacetate-ethanol-water (16:14:14:5 (v/v)). A total amount of 19.6 mg of shikonin at 98.9% purity was obtained from 52 mg of the crude extract (containing 38.9% shikonin) with 96.9% recovery. The preparative isolation and purification of shikonin by HSCCC was completed in 200 min in a one-step separation.

Countercurrent Distribution↗
PubMed2004

Comparison of high-speed counter-current chromatography and high-performance liquid chromatography on fingerprinting of Chinese traditional medicine.

Active constituents of Chinese traditional medicine (CTM) are influenced by soils, climates, and growth stages. Therefore, fingerprint is important in quality control of CTM. Our studies showed for the first time that high-speed counter-current chromatography (HSCCC) could be applied in the development of fingerprint of CTM. Twelve components were separated from extracts of three crude samples of Salvia miltiorrhiza Bunge, which were collected from different growth locations. All 12 components of each sample were isolated within 13 h coming with good correspondence by using HSCCC. Relative standard deviation (R.S.D.) values of the retention time in HSCCC separation was less than 3% satisfied the precision requirements of national standards in the fingerprint development. As a new approach, HSCCC was compared to the conventional approach-HPLC in our experiments. The fingerprint developed by HPLC comprised 11 peaks that collected within 45 min. R.S.D. values of retention times of the corresponding peaks in HPLC analysis were very small (maximum 0.66% and average 0.10%). In conclusion, HSCCC was a feasible method to be used in the development of fingerprint of CTM.

Chromatography, High Pressure Liquid↗
PubMed2004

Isolation of high purity 1-[2',4'-dihydroxy-3',5'-di-(3"-methylbut-2"-enyl)-6'-methoxy] phenylethanone from Acronychia pedunculata (L.) Miq. by high-speed counter-current chromatography.

Following an initial clean-up step on silica, high-speed counter-current chromatography (HSCCC) was used to purify an aryl ketone, 1-[2',4'-dihydroxy-3',5'-di-(3"-methylbut-2"-enyl)-6'-methoxy] phenylethanone from an extract of the stem bark of the shrub Acronychia pedunculata. The two-phase solvent system used was composed of n-heptane-ethyl acetate-methanol-water at an optimized volume ratio of 4:1:4:1 (v/v/v/v). Target compound (58.1 mg) with a purity of 98.9% was obtained after HSCCC of 183.5 mg sample with a purity of 35.7% recovered after the silica clean-up step. Identification of the target compound was performed by 1H NMR, 13C NMR, two-dimensional NMR and LC-electrospray ionization MS.

Alkenes↗