Simultaneous determination of R- and S-prenylamine in plasma and urine by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of R- and S-prenylamine in human plasma and urine is described. It involves a two-step liquid-liquid extraction of prenylamine from biological material and preparation of diastereomeric urea derivatives with R-(-)-naphthylethyl isocyanate, a chiral fluorescence marker. Separation and quantitation of the diastereomeric prenylamine derivatives are carried out by a reversed-phase high-performance liquid chromatographic system with fluorimetric detection. The limit of determination is less than 2 ng of enantiomer per ml of urine and less than 1 ng of enantiomer per ml of plasma. A preliminary kinetic study on one healthy volunteer who had received a single oral dose of racemic prenylamine (100-mg film tablet) showed distinctly higher plasma and urine concentrations of the R-enantiomer.     

Activated alpha-alkyl-alpha-arylacetic acid enantiomers for stereoselective thin-layer chromatographic and high-performance liquid chromatographic determination of chiral amines

The separation of racemic benoxaprofen into the two benoxaprofen enantiomers by preparative high-performance liquid chromatography and the application of the activated enantiomers as derivatization reagents for the simultaneous stereoselective determination of chiral amines in biological material is described. Activated (+)- and (-)-benoxaprofen are both shown to be very sensitive and stable chiral fluorescence markers, applicable to thin-layer chromatography as well as to high-performance liquid chromatography.     

Separation of radioarsenic from irradiated germanium oxide targets for the production of <Superscript>71</Superscript>As and <Superscript>72</Superscript>As

A method for the separation of no-carrier-added arsenic radionuclides from the bulk amount of proton-irradiated GeO₂ targets as well as from coproduced radiogallium was developed. The radionuclides ⁶⁹Ge and ⁶⁷Ga produced during irradiation of GeO₂ were used as tracers for Ge and Ga in the experiments. After dissolution of the target the ratio of As(III) to As(V) was determined via thin layer chromatography (TLC). The extraction of radioarsenic by different organic solvents from acid solutions containing alkali iodide was studied and optimized. The influence of the concentration of various acids (HCl, HClO₄, HNO₃, HBr, H₂SO₄) as well as of KI was studied using cyclohexane. The optimum separation of radioarsenic was achieved using cyclohexane with 4.75 M HCl and 0.5 M KI and its back-extraction with a 0.1% H₂O₂ solution. The separation leads to high purity radioarsenic containing no radiogallium and <0.001% [⁶⁹Ge]Ge. The overall radiochemical yield is 93 ± 3%. The practical application of the optimized procedure in the production of ⁷¹As and ⁷²As is demonstrated and batch yields achieved were in the range of 75–84% of the theoretical values.     

Protein‐Specific,Multicolor and 3D STED Imaging in Cells with DNA‐Labeled Antibodies

Photobleaching is a major challenge in fluorescence microscopy, in particular if high excitation light intensities are used. Signal‐to‐noise and spatial resolution may be compromised, which limits the amount of information that can be extracted from an image. Photobleaching can be bypassed by using exchangeable labels, which transiently bind to and dissociate from a target, thereby replenishing the destroyed labels with intact ones from a reservoir. Here, we demonstrate confocal and STED microscopy with short, fluorophore‐labeled oligonucleotides that transiently bind to complementary oligonucleotides attached to protein‐specific antibodies. The constant exchange of fluorophore labels in DNA‐based STED imaging bypasses photobleaching that occurs with covalent labels. We show that this concept is suitable for targeted, two‐color STED imaging of whole cells.     

Flow-through voltammetry (FTV) with the hanging mercury drop electrode (HMDE)

A flow-through cell with integrated hanging mercury drop electrode for voltammetric, inverse voltammetric, adsorptive voltammetric, and chronoamperometric methods is described. HMDE droplets are automatically formed and renewed. By optimizing the flow-channel the sensitivity could be increased approximately five times in comparison with batch methods using the same deposition conditions.Dedicated to Professor Dr. Rolf Neeb on the occasion of his 65th birthday