Development and validation of an HPLC-method for the determination of alkaloids in the stem bark extract of Nauclea pobeguinii

A new method was developed and validated for the quantification of strictosamide in the extract of the stem bark of Nauclea pobeguinii. This plant belongs to the Rubiaceae family and is widely used in the African traditional medicine against malaria and malaria-like symptoms. Alkaloids are suspected to be responsible for the antimalarial activity. One of these alkaloids is strictosamide, already reported to be the major constituent in the root bark of this plant. Because strictosamide was not commercially available another alkaloid, ajmalicine HCl, with comparable properties was used as a secondary standard. The samples of the dried 80% ethanol extract from the stem bark of N. pobeguinii were purified on C(18) solid phase extraction cartridges and analysed using HPLC-UV. The strictosamide used for the validation of the correction factor for response was isolated and purified by means of preparative HPLC and TLC. Although the relative standard deviation (R.S.D.) of 2.6% was still acceptable, the response factor was determined for every analysis based on the ratio of the peak area of strictosamide compared to the peak area of ajmalicine HCl in a concentration of 0.01 mg/ml. The precision of the method according to the time and the concentration, had a R.S.D. value of 2.2% and 2.6%, respectively. The recovery of the method was 92.2% (R.S.D. of 9.4%) which was acceptable. The method has been proven to be suitable for the determination of alkaloids in the extract of the stem bark of N. pobeguinii, according to the ICH guidelines on the validation of analytical methods.     

NHC-Stabilized Iridium Nanoparticles as Catalysts in Hydrogen Isotope Exchange Reactions of Anilines

The preparation of N-heterocyclic carbene-stabilized iridium nanoparticles and their application in hydrogen isotope exchange reactions is reported. These air-stable and easy-to-handle iridium nanoparticles showed a unique catalytic activity, allowing selective and efficient hydrogen isotope incorporation on anilines using D₂ or T₂ as isotopic source. The usefulness of this transformation has been demonstrated by the deuterium and tritium labeling of diverse complex pharmaceuticals.     

Synthesis and cholera toxin binding properties of multivalent GM1 mimics

Dendrimers based on the 3,5-di-(2-aminoethoxy)-benzoic acid branching unit were used to attach multiple copies of a GM1 mimic for inhibition of cholera toxin binding. Systems up to octavalent were synthesized along with relevant reference compounds that contained in one case the ligand in a monovalent format and in another case the scaffold but not the ligand. Using a surface plasmon resonance inhibition assay the prepared inhibitors showed good inhibition. While the monovalent GM1 mimic showed the expected inhibition in the 200 microM range the multivalent scaffolds led to increased binding. The tetravalent compound was shown to be 440-fold more potent than its monovalent counterpart. The octavalent analog, however, was the most potent compound as determined using an ELISA assay.     

On the Stability of Density Stratified Flow Below a Ponded Surface

Transport in Porous Media - Flooding of coastal areas with seawater often leads to density stratification. The stability of the density-depth profile in a porous medium initially saturated with a...     

Spectrophotometric determination of traces of oxygen in water

Winkler's method of determining oxygen in water by titration of the iodine can not be applied with concentrations below 0.03 mg O₂/litre. We studied the spectrophotometric determination of the iodine-starch complex described by bairstow, francis, and wyatt and succeeded in improving its stability by the addition of potassium sulphate. The intensity of the blue colour is very sensitive to variation of temperature. Below 10° C this influence can be neglected. Upwards from 30° C the intensity rapidly decreases. Instead of performing the determination at 10° C we plotted the extinction coefficient of dilute solutions as a function of the iodine concentration for temperatures ranging from 10 to 30° C. With “the aid of this graph the iodine concentration can be found when the extinction coefficient and the temperature of a solution are determined.With this method we can determine oxygen in water in concentrations ranging from 0.005 to 0.4 mg O₂/litre. Duplicates (for water with a low content of oxygen) differ not more than 0.002 mg O2/litre.