Evaluation of sphingomyelin,cholester, and phosphatidylcholine-based immobilized artificial membrane liquid chromatography to predict drug penetration across the blood-brain barrier

Over the past decades, several in vitro methods have been tested for their ability to predict drug penetration across the blood-brain barrier. So far, in high-performance liquid chromatography, most attention has been paid to micellar liquid chromatography and immobilized artificial membrane (IAM) LC. IAMLC has been described as a viable approach, since the stationary phase emulates the lipid environment of a cell membrane. However, research in IAMLC has almost exclusively been limited to phosphatidylcholine (PC)-based stationary phases, even though PC is only one of the lipids present in cell membranes. In this article, sphingomyelin and cholester stationary phases have been tested for the first time towards their ability to predict drug penetration across the blood-brain barrier. Upon comparison with the PC stationary phase, the sphingomyelin- and cholester-based columns depict similar predictive performance. Combining data from the different stationary phases did not lead to improvements of the models. Figure

Schematic representation of how IAM-LC is used to predict drug penetration across the blood-brain barrier.     

A practical comparison of MQMAS techniques

A systematic experimental evaluation of several approaches to multiple-quantum MAS NMR was performed for spin-5/2 nuclei using (27)Al NMR of the aluminosilicate andalusite and the porous aluminum phosphate AlPO(4)-14 as model. Experiments were conducted in the fields of 9.4 and 17.6T using magic-angle spinning frequencies up to 30kHz and rf-field strengths of 250 and 120kHz. Numerical SIMPSON optimizations of the NMR parameters were performed alongside the experimental evaluations. Both theory and experiment show that the optimization is most critical for the species in the sample that have the largest quadrupolar coupling constant. For 5QMAS experiments it could be confirmed that the highest available rf-field strength and rotation frequency are favorable for the efficiency of the experiments. For 3QMAS experiments of sites with moderate quadrupolar coupling constants optimum results were obtained at less stringent conditions. The comparison of a FAM II-modification and DFS gave the expected improvement by a factor of about two with respect to a rectangular pulse. No significant difference between these techniques concerning the signal-to-noise ratios was obtained. An actual improvement of the isotropic resolution by a factor of about two was obtained going from 3QMAS to 5QMAS. In addition the resolution of the spectra increases by a factor of about two going from 9.4 to 17.6T.     

Formation of H3+ in Collisions of H2+ with H2 Studied in a Guided Ion Beam Instrument

In order to study collisions between ions and neutrals, a new Guided Ion Beam (GIB) apparatus, called NOVion, has been assembled and tested. The primary purpose of this instrument is to measure absolute cross sections at energies relevant for technical or inter- and circumstellar plasmas. New and improved results are presented for forming H₃⁺ in collisions of H₂⁺ with H₂. Between 0.1 eV and 2 eV, our measured effective cross sections are in good overall agreement with most previous measurements. However, at higher energies, our results do not show the steep decline, recommended in the standard literature. After critical evaluation of all experimental and theoretical data, a new analytical function is proposed, describing properly the dependence of the title reaction on the collision energy up to 10 eV.     

Cycloaddition reactions of 2H-benzo[b]thiete and conjugated cyclic dienes

2H-Benzo[b]thiete 1 reacts with cyclopentadiene 3 in consecutive [8π + 2π]cycloadditions yielding the condensed heterocycles 6–8 . Tetracyclone 9 on the other hand gives only the monoadduct 10 . An [8π + 8π]cycloaddition can be observed for 1 and diphenylisobenzofuran 11 . The related π system 13 shows again consecutive [477π + 27π]processes ( 1 + 13 ← 14, 15 ).     

In-line Particle Size Analysis in the fines outlet of an air classifier

Laser diffraction (LD), with reference to the analysis time, is highly advantageous for the automation of particle size analysis. The high measuring frequencies alloy quasi-continous measuring operation. The fineness values obtained form the particle size distribution (PSD) can be transformed into electrical signals for automatic process control. For industrial purposes, an encapsulated measuring cell was developed where the laser beam penetrates the dispersed fines stream via two optical windows. Thus, hazardous materials can also be measured, specifically pharmaceutical or chemical products, or applications requiring explosion-proof plant design are possible. Great efforts had to be made to keep the inner side of the windows clean form product dust. Ultimately, batches running for more than 8 h could be analysed continuously without any contamination of the windows. For the PSD measurements, a standard LD instrument was used with a measuring range of 0.5/0.9–175 μm. As product fineness is monitored continuously in-stream, and virtually without delay, any changes in the fineness during classifier operation can be detected immediately. On the one hand, this opens up a new field for studies of classifier performance. On the other, immediate quality control of even very small batches is possible during the micronization process. The results demonstrate very clearly, for example, the importance of controlling the feed rate to the classifier. Therefore, fineness control by means of this in-line technique gives superior advantages for direct adjustment of the classifier speed.