Mode-resolved Fabry-Perot experiment in low-loss Bragg-reflection waveguides.

Based on the interaction between different spatial modes, semiconductor Bragg-reflection waveguides (BRWs) provide a highly functional platform for non-linear optics. For achieving any desired quantum optical functionality, we must control and engineer the properties of each spatial mode. To reach this purpose we extend the Fabry-Perot technique and achieve a detailed linear optical characterization of dispersive multimode semiconductor waveguides. With this efficient broadband spectral method we gain direct experimental access to the relevant modes of our BRWs and determine their group velocities. Furthermore, we show that our waveguides have lower than expected loss coefficients. This renders them suitable for integrated quantum optics applications.

Replacement of acetonitrile by ethanol as solvent in reversed phase chromatography of biomolecules.

Acetonitrile, which is a by-product of acrylonitrile synthesis, is the commonly used solvent in ion-pair reversed phase chromatography. In consequence of the decreasing demand for acrylonitrile due to the financial crisis, a worldwide shortage of acetonitrile is observed. Therefore, the aim of this study was to establish ion-pair reversed phase chromatographic assays using alternative eluents for acetonitrile and to decrease costs incurred hereby. We compared the performance of ion-pair reversed phase chromatography using acetonitrile with the alternative eluents methanol, ethanol and n-propanol, using monolithic reversed phase C5 as well as C18 chromatography columns. We used triethylammonium acetate (TEAA) and tetrabutylammonium sulfate (TBA) as representative cationic ion-pair reagents and trifluoroacetic acid (TFA) as representative anionic ion-pair reagent. For covering a large field of applications, we fractionated representative low, middle and high-molecular weight biomolecules, in particular dinucleoside polyphosphates, peptides, proteins and tryptic digested human serum albumin. Whereas the chromatographic characteristics of both methanol and n-propanol were partly insufficient, ethanol was characterised equally or partly even better in the matter of elution strength and separation quality compared to the eluent water-acetonitrile. In conclusion, ethanol is an appropriate alternative for acetonitrile in ion-pair reversed phase chromatography of biomolecules.

Uridine adenosine tetraphosphate acts as an autocrine hormone affecting glomerular filtration rate.

Recently, uridine adenosine tetraphosphate (Up(4)A) was described as a strong vasoconstrictor released from endothelial cells after stimulation with mechanical stress. In this study, we isolated and identified Up(4)A from kidney tissue, and we characterized the essential varying effects of Up(4)A on the afferent and efferent arterioles. Porcine and human kidney tissue was fractionated by size exclusion chromatography, affinity chromatography, anion exchange chromatography and reverse phase chromatography. In fractions purified to homogeneity, Up(4)A was identified by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS), MALDI-LIFT fragment mass spectrometry (MALDI-TOF/TOF MS), retention-time comparison and enzymatic cleavage analysis. We analysed the release of Up(4)A from cultivated renal proximal tubule cells after stimulation of protein kinase C with oleoyl-2-acetyl-sn-glycerol (OAG). Up(4)A was identified in renal tissue, and the effect of Up(4)A on the vascular tone of isolated perfused afferent and efferent arterioles was tested. Stimulation of tubule cells with OAG increased the release rate of Up(4)A from tubule cells about tenfold. Up(4)A acts as a strong vasoconstrictive mediator on afferent arterioles, but has no significant effect on the tone of efferent arterioles, suggesting a functional role of Up(4)A as an autocrine hormone for glomerular perfusion. Because of the predominant effect of the Up(4)A on afferent arterioles, we assume that Up(4)A may decrease glomerular perfusion, intra-glomerular pressure and, hence, glomerular filtration rate. The release of Up(4)A from renal tubular cells may be an additional mechanism whereby tubular cells could affect renal perfusion. Up(4)A release may further contribute to renal vascular autoregulation mechanisms. In conclusion, as Up(4)A occurs in renal tissue and has marked effects on afferent but not efferent arterioles, Up(4)A may play a role in renal hemodynamics and possibly blood pressure regulation.