Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

OXYGEN DIFFUSION THROUGH HORSERADISH PEROXIDASE

The quenching by molecular oxygen of the fluorescence from a protoporphyrin IX adduct of horseradish peroxidase has been investigated using both intensity and time-resolved techniques. The bimolecular quenching rate constant determined for this process, as evaluated by the conventional Stern-Volmer analysis, was 2 x 10(8) M-1 s-1, among the lowest observed for protein systems. This result suggests that the heme binding site in horseradish peroxidase is relatively inaccessible to oxygen, which may account for the observation of room temperature phosphorescence in aerated solutions from enzymatically created triplet states.     

High-performance liquid chromatographic determination of naltrexone in plasma of hemodialysis patients

A simple, sensitive, selective and reliable reversed-phase high-performance liquid chromatographic (HPLC) method with UV detection is described for the determination of naltrexone in plasma samples. Naltrexone and the internal standard, naloxone, were isolated from plasma either with a liquid-liquid extraction method using ethyl acetate or with a solid-phase extraction method using Sep-Pack C18 cartridge before chromatography. The extracts were dried under a stream of nitrogen and the samples were reconstituted in the mobile phase, then 20 microL were injected on a Waters Symmetry C18 column (5 microm particle size, 4.6 x 150 mm). The mobile phase consisted of 0.06% triethylamine (pH 2.8)-acetonitrile (92:8, v/v) pumped at 1 mL/min. The peak-area ratio versus plasma concentration was linear over the range of 10-500 ng/mL and the detection limit was less than 8 ng/mL. Quantification was by ultra-violet detection at 204 nm. The present method was applied to the determination of the plasma concentration of naltrexone in dialyzed patients. Patients (n = 8) with severe generalized pruritus received 50 mg of naltrexone orally per day for 2 weeks. The variability in the therapeutic response in treated patients required plasma concentration investigations of this opioid antagonist.     

Preparation of clarithromycin. Selective 6-O-methylation of the novel erythromycin A 9-O-(2-pyrimidyl)oxime

A new method for the preparation of clarithromycin is described through the highly regioselective O-methylation at C(6)-OH of the novel derivative 9-pyrimidyloxime erythromycin A. The facile synthesis of 6,11-O-dimethyl- and 6,11,12-O-trimethyl erythromycin A is also reported. These compounds are useful as standards to assess clarithromycin purity in quality control processes.     

Vibration-induced climbing of drops

We report an experimental study of liquid drops moving against gravity, when placed on a vertically vibrating inclined plate, which is partially wetted by the drop. The frequency of vibrations ranges from 30 to 200 Hz, and, above a threshold in vibration acceleration, drops experience an upward motion. We attribute this surprising motion to the deformations of the drop, as a consequence of an up or down symmetry breaking induced by the presence of the substrate. We relate the direction of motion to contact angle measurements. This phenomenon can be used to move a drop along an arbitrary path in a plane, without special surface treatments or localized forcing.