Fluidity modulation of phospholipid bilayers by electrolyte ions: insights from fluorescence microscopy and microslit electrokinetic experiments

Fluidity and charging of supported bilayer lipid membranes (sBLMs) prepared from 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) were studied by fluorescence recovery after photobleaching (FRAP) and microslit electrokinetic measurements at varying pH and ionic composition of the electrolyte. Measurements in neutral electrolytes (KCl, NaCl) revealed a strong correlation between the membrane fluidity and the membrane charging due to unsymmetrical water ion adsorption (OH(-) ? H(3)O(+)). The membrane fluidity significantly decreased below the isoelectric point of 3.9, suggesting a phase transition in the bilayer. The interactions of both chaotropic anions and strongly kosmotropic cations with the zwitterionic lipids were found to be related with nearly unhindered lipid mobility in the acidic pH range. While for the chaotropic anions the observed effect correlates with the increased negative net charge at low pH, no correlation was found between the changes in the membrane fluidity and charge in the presence of kosmotropic cations. We discuss the observed phenomena with respect to the interaction of the electrolyte ions with the lipid headgroup and the influence of this process on the headgroup orientation and hydration as well as on the lipid packaging.     

Catching gaseous SO2 in cone-type lanthanide complexes: an unexpected coordination mode for SO2 in f-element chemistry

Easy come, easy go: the first molecular SO(2) complexes of the lanthanides (Ln=Sm, Eu) have been prepared. The compounds can reversibly coordinate gaseous SO(2). Concomitant with the addition and removal of SO(2), the color of the complexes changes reversibly. The structures of the SO(2) compounds could be confirmed in solution and in the solid state.     

Heteronuclear NOE spectroscopy of ionic liquids

(19)F,(1)H HOESY experiments with three ionic liquids ([bmim]BF(4), [bmim]PF(6) and [emim]BF(4)) were run in two different solvents and neat. The results give preferred probabilities of presence and enable us to systematically study interactions between the cations and the anions in the ionic liquid phase by NMR spectroscopy. The influence of different solvents and of the presence or absence of air (i.e. oxygen) is discussed. This enabled us to substantially speed up the NMR experiments and to develop a more precise method for the investigation of liquid-phase structures in ionic liquids.     

Continuous and reversible mixing or demixing of nanoparticles by dielectrophoresis

Mixing and demixing (separation) are essential tasks in microfluidic devices, which seem to be contrary in nature. Accordingly, completely different strategies and devices are usually employed for their realization. We here present a microfluidic device which is capable of performing both these tasks as it can be operated in either mixing or demixing mode. The mixing and demixing processes are reversible and are accomplished by continuous operation of the device. An asymmetric S-shaped ridge extends over the full width of a microfluidic channel (200 μm) creating a constriction of 620 nm in height with an aspect ratio of 1 : 500. Appropriate AC and DC voltages generate electrodeless dielectrophoresis at the constriction as well as (linear) electrokinetic driving forces along the channel. These de/mixing parameters can be adapted in real time in such a way that continuous separation and mixing efficiencies of 85-100% can be achieved. As a proof of concept we demonstrate continuous mixing and demixing of polystyrene nanoparticles (20 and 100 nm). The experimental results are complemented by numerical simulations illustrating the particles' motion under the influence of the electrokinetic effects and thermal noise (diffusion). The monolithic one-step fabrication process by soft lithography (with PDMS in our case) will make integration and combination of several mixing and demixing functions into a more complex lab-on-a-chip device possible.     

Fluoride-ion acceptor properties of WSF4: synthesis, characterization, and computational study of the WSF5(-) and W2S2F9(-) anions and 19F NMR spectroscopic characterization of the W2OSF9(-) anion

The new [N(CH(3))(4)][WSF(5)] salt was synthesized by two preparative methods: (a) by reaction of WSF(4) with [N(CH(3))(4)][F] in CH(3)CN and (b) directly from WF(6) using the new sulfide-transfer reagent [N(CH(3))(4)][SSi(CH(3))(3)]. The [N(CH(3))(4)][WSF(5)] salt was characterized by Raman, IR, and (19)F NMR spectroscopy and [N(CH(3))(4)][WSF(5)]·CH(3)CN by X-ray crystallography. The reaction of WSF(4) with half an aliquot of [N(CH(3))(4)][F] yielded [N(CH(3))(4)][W(2)S(2)F(9)], which was characterized by Raman and (19)F NMR spectroscopy and by X-ray crystallography. The WSF(5)(-) and W(2)S(2)F(9)(-) anions were studied by density functional theory calculations. The novel [W(2)OSF(9)](-) anion was observed by (19)F NMR spectroscopy in a CH(3)CN solution of WOF(4) and WSF(5)(-), as well as CH(3)CN solutions of WSF(4) and WOF(5)(-).     

Microprobe sampling—Photo ionization-time-of-flight mass spectrometry for in situ chemical analysis of pyrolysis and combustion gases: Examination of the thermo-chemical processes within a burning cigarette

A microprobe sampling device (μ-probe) has been developed for in situ on-line photo ionization mass spectrometric analysis of volatile chemical species formed within objects consisting of organic matter during thermal processing. With this approach the chemical signature occurring during heating, pyrolysis, combustion, roasting and charring of organic material within burning objects such as burning fuel particles (e.g., biomass or coal pieces), lit cigarettes or thermally processed food products (e.g., roasting of coffee beans) can be investigated. Due to its dynamic changes between combustion and pyrolysis phases the cigarette smoking process is particularly interesting and has been chosen as first application. For this investigation the tip of the μ-probe is inserted directly into the tobacco rod and volatile organic compounds from inside the burning cigarette are extracted and real-time analyzed as the glowing front (or coal) approaches and passes the μ-probe sampling position. The combination of micro-sampling with photo ionization time-of-flight mass spectrometry (PI-TOFMS) allows on-line intrapuff-resolved analysis of species formation inside a burning cigarette. Monitoring volatile smoke compounds during cigarette puffing and smoldering cycles in this way provides unparalleled insights into formation mechanisms and their time-dependent change. Using this technique the changes from pyrolysis conditions to combustion conditions inside the coal of a cigarette could be observed directly. A comparative analysis of species formation within a burning Kentucky 2R4F reference cigarette with μ-probe analysis reveals different patterns and behaviors for nicotine, and a range of semi-volatile aromatic and aliphatic species.     

Supramolecular Hydrogel Capsules Based on PEG: A Step Toward Degradable Biomaterials with Rational Design

Supramolecular microgel capsules based on polyethylene glycol (PEG) are a promising class of soft particulate scaffolds with tailored properties. An approach to fabricate such particles with exquisite control by droplet‐based microfluidics is presented. Linear PEG precursor polymers that carry bipyridine moieties on both chain termini are gelled by complexation to iron(II) ions. To investigate the biocompatibility of the microgels, living mammalian cells are encapsulated within them. The microgel elasticity is controlled by using PEG precursors of different molecular weights at different concentrations and the influence of these parameters on the cell viabilities, which can be optimized to exceed 90% is studied. Reversion of the supramolecular polymer cross‐linking allows the microcapsules to be degraded at mild conditions with no effect on the viability of the encapsulated and released cells.

     

A combinatorial formula for rank 2 cluster variables

Let r be any positive integer, and let x ₁,x ₂ be indeterminates. We consider the sequence {x _n } defined by the recursive relation $$x_{n+1} =\bigl(x_n^r +1\bigr)/{x_{n-1}}$$ for any integer n. Finding a combinatorial expression for x _n as a rational function of x ₁ and x ₂ has been an open problem since 2001. We give a direct elementary formula for x _n in terms of subpaths of a specific lattice path in the plane. The formula is manifestly positive, providing a new proof of a result by Nakajima and Qin.     

Convergence of Lowest Order Semi-Lagrangian Schemes

We consider generalized linear transient advection-diffusion problems for differential forms on a bounded domain in ? ^d . We provide comprehensive a priori convergence estimates for their spatiotemporal discretization by means of a first-order in time semi-Lagrangian approach combined with a discontinuous Galerkin method. Under rather weak assumptions on the velocity underlying the advection we establish an asymptotic L ²-estimate of order $O(\tau+h^{r}+h^{r+1}\tau^{-\frac{1}{2}}+\tau^{\frac{1}{2}})$ , where h is the spatial meshwidth, τ denotes the time step, and r is the polynomial degree of the forms used as trial functions. This estimate can be improved considerably in a variety of special settings.