Liquid chromatography/electrospray time-of-flight mass spectrometry for the characterisation of cyclic phosphazenes

Cyclic phosphazenes with different substituents were synthesised and investigated by liquid chromatography (LC) and electrospray ionisation mass spectrometry (ESI-MS). Hexachlorocyclotriphosphazene was functionalised with aliphatic substituents as alcohols and amines, leading to product mixtures, which were subsequently analysed. In contrast to classical methods of structural analysis such as nuclear magnetic resonance (NMR) spectroscopy or X-ray crystallography, which are restricted to pure compounds, these complex mixtures can favourably be analysed by means of LC/ESI-MS. The main products could be separated from by-products and, moreover, all the components of the unknown mixture were unambiguously identified by accurate mass measurements. For all compounds with different side-chain ratios, remaining chlorine atoms or hydroxyl groups and even for spiro or ansa products, molecular structures could be suggested.     

Preparation and characterization of cellulose microspheres

The aim of this work was to synthesize and characterize cellulose microspheres with a particle size below 5 μm and narrow size distribution. After activation and functionalization with antibodies, these particles shall be applied as adsorbents in suspension-based extracorporeal blood purification systems, such as the Microspheres-Based Detoxification System. In the frame of this work such microspheres were developed and synthesized with reproducible properties. Besides using well-established methods for characterization of this kind of bead cellulose, additional procedures for the examination of its properties were developed and applied.     

Membrane-mediated induction and sorting of K-Ras microdomain signaling platforms

The K-Ras4B GTPase is a major oncoprotein whose signaling activity depends on its correct localization to negatively charged subcellular membranes and nanoclustering in membrane microdomains. Selective localization and clustering are mediated by the polybasic farnesylated C-terminus of K-Ras4B, but the mechanisms and molecular determinants involved are largely unknown. In a combined chemical biological and biophysical approach we investigated the partitioning of semisynthetic fully functional lipidated K-Ras4B proteins into heterogeneous anionic model membranes and membranes composed of viral lipid extracts. Independent of GDP/GTP-loading, K-Ras4B is preferentially localized in liquid-disordered (l(d)) lipid domains and forms new protein-containing fluid domains that are recruiting multivalent acidic lipids by an effective, electrostatic lipid sorting mechanism. In addition, GDP-GTP exchange and, thereby, Ras activation results in a higher concentration of activated K-Ras4B in the nanoscale signaling platforms. Conversely, palmitoylated and farnesylated N-Ras proteins partition into the l(d) phase and concentrate at the l(d)/l(o) phase boundary of heterogeneous membranes. Next to the lipid anchor system, the results reveal an involvement of the G-domain in the membrane interaction process by determining minor but yet significant structural reorientations of the GDP/GTP-K-Ras4B proteins at lipid interfaces. A molecular mechanism for isoform-specific Ras signaling from separate membrane microdomains is postulated from the results of this study.     

Optical waveguides for the evanescent wave-induced cleavage of photolabile linker compounds

Functional surfaces and especially the control of surface properties depending on external parameters such as light illumination have gained increasing importance in the last few years. We present the characterization of polymers from the cycloolefin (co)polymer class (COC/COP) functionalized with an aminosilane as a basis for the further immobilization of compounds. In a first step, an assay using AlexaFluor?647 fluorescent dye was used to assess surface homogeneity and reproducibility. A coefficient of variation of less than 15% for dot-to-dot and less than 25% for chip-to-chip could be achieved. The same amino-functionalized surfaces were then used to immobilize a biotinylated photolabile linker compound, binding AlexaFluor?647-labeled streptavidin. The linker was photocleaved with high efficiency at λ = 365 nm and P = 0.15 mW/cm². Fluorescence measurements show that polymers of the COC/COP class can be used as versatile surfaces for the photoinduced release of compounds immobilized via photolabile linkers.     

The hydrated electron: a seemingly familiar chemical and biological transient

Since the discovery of the hydrated electron in bulk water in 1962, the species has been the subject of intense research and speculation. For many decades even the basic features of the simplest of all chemical and biological transients and reactants--such as its structure, binding motifs, lifetimes, and binding energies--remained elusive. Recently, another milestone in the research of the hydrated electron was the determination of its vertical binding energy (VBE). Also a long-lived hydrated electron near the surface of liquid water has been discovered. The present Minireview discusses the implications and consequences of this and other new findings in addition to the emerging complex picture of a solvated electron in water.     

Dynamic flow in a realistic model of the upper human lung airways

The objective of the study is an analysis of lung ventilation during breathing under rest conditions and for high frequency ventilation (HFV). The measurements include investigations of the flow using an endotracheal tube. A transparent model of the upper human lung airways down to the 6th generation was generated, and the oscillatory flow through the branching network was studied by DPIV. The method of refractive index matching of the fluid (water/glycerin) and the model (silicone) allows an unobstructed view into the internal flow network. The mass flow rate and the frequency were adapted to the characteristic flow parameters, the Reynolds- and the Womersley-number. The comparison of the results for normal breathing and HFV shows that a mass exchange occurs for higher frequencies known as Pendelluft, which could not be seen during normal breathing. This mass exchange between the daughter tubes is a consequence of the asymmetric impedance in the successive daughter branches. The lung topology determines the local pressure loss in the model and therefore the local mass flow direction of the Pendelluft. At higher frequencies we observed an increase in exchange between the daughter branches. The transformation of the velocity profiles between inspiration and expiration suggests a net mass flow which is created into the model along the centerline and the inner walls of the bifurcations. This flow is compensated with a net mass outflow to the trachea along the outer walls of the branches.