Generic Optical Excitations of Correlated Systems: π-tons.

The interaction of light with solids gives rise to new bosonic quasiparticles, with the exciton being-undoubtedly-the most famous of these polaritons. While excitons are the generic polaritons of semiconductors, we show that for strongly correlated systems another polariton is prevalent-originating from the dominant antiferromagnetic or charge density wave fluctuations in these systems. As these are usually associated with a wave vector (π,π,…) or close to it, we propose to call the derived polaritons π-tons. These π-tons yield the leading vertex correction to the optical conductivity in all correlated models studied: the Hubbard, the extended Hubbard model, the Falicov-Kimball, and the Pariser-Parr-Pople model, both in the insulating and in the metallic phase.

Study on the absorption of vinpocetine and apovincaminic acid.

The absorption of vinpocetine (Cavinton) and apovincaminic acid, compounds showing a marked difference in their physico-chemical properties, was studied in rats in in situ loop experiments by using radiolabelled compounds. In the case of apovincaminic acid, the investigations also involved the estimation of the portion of radioactivity excreted in urine and faeces after i.v. and p.o. administration of the compound. According to our results, it can be concluded that both vinpocetine and apovincaminic acid are absorbed from the gastrointestinal tract--apovincaminic acid mainly from the stomach, while vinpocetine is absorbed from the small intestine.

Pharmacokinetics of apovincaminic acid in dogs.

After the oral or intravenous administration of 10 mg vinpocetine to dogs the pharmacokinetics of its main metabolite, apovincaminic acid (AVA) can be described by a two-compartment open model. The apparent half-life of its formation was 0.56 +/- 0.23 h and that of the apparent elimination was 9.6 h which did not significantly differ from the elimination half-life of total radioactivity (8.16 +/- 1.77 h) and from the apparent elimination half-life of vinpocetine itself (8.9 +/- 2.87 h). The volume of distribution of AVA was 2.3 times lower than that of vinpocetine and its clearance value (1.5 +/- 0.77 1 h-1 kg-1) was 2.8 times less than that of vinpocetine. These results suggest that AVA does not undergo further metabolism and its elimination is formation limited.

Determination of apovincaminic acid in biological samples by high-performance liquid chromatography.

A method is described for measuring the concentrations of apovincaminic acid and vincaminic acid (internal standard) in blood plasma and urine by high-performance liquid chromatography using ion pair extraction. The main metabolite of vinpocetine, apovincaminic acid, and vincaminic acid were extracted from 1 ml of plasma and urine into chloroform as an ion pair using tetrabutylammonium hydroxide as counter ion. Analysis was carried out on a reversed-phase column of RP-8 with acetonitrile-0.0075 M phosphate buffer (28:72) at pH 3.5 as mobile phase. The eluted derivatives were detected by UV absorption at 254 nm. The sensitivity of the method is 20 ng/ml for AVA in plasma and urine samples. The relative recovery of these compounds added to plasma was about 50%.

High-performance liquid chromatographic method for the determination of RGH-5702 in plasma samples.

A quick and selective high-performance liquid chromatographic method has been developed for the determination of RGH-5702 in plasma samples. A simple one-step extraction is used followed by reversed-phase chromatography and UV detection. This method allowed the separation of the compound and internal standard within 7 minutes. Validation of the method was performed prior to the assay of samples and continued throughout the study. Acceptable accuracy and precision was achieved at all concentrations investigated. The quantitation limit was 20 ng/ml using 1 ml of plasma. The method has been applied to the analysis of plasma samples from toxicokinetic studies in dogs.