Controlled vesicle self-assembly in microfluidic channels with hydrodynamic focusing

Traditional liposome preparation methods are based on mixing of bulk phases, leading to inhomogeneous chemical and/or mechanical conditions during formation; hence liposomes are often polydisperse in size and lamellarity. Here we show the formation of liposomes that encapsulate reagents in a continuous two-phase flow microfluidic network with precision control of size from 100 to 300 nm by manipulation of liquid flow rates. We demonstrate that by creating a solvent-aqueous interfacial region in a microfluidic format that is homogeneous and controllable on the length scale of a liposome, we can facilitate the fine control of liposome size and polydispersity.     

The search for a new model structure of β-Factor XIIa

We present the search for a new model of -factor XIIa, a blood coagulation enzyme, with an unknown experimental 3D-structure. We decided to build not one but three different models using different homologous proteins as well as different techniques and different modellers. Additional studies, including extensive molecular dynamics simulations on the solvated state, allowed us to draw several conclusions concerning homology modelling, in general, and -factor XIIa, in particular.     

Use of thermomagnetometry in the study of iron-containing pyrotechnic systems

Thermal analysis is routinely used to characterize pyrotechnic fuels, oxidants and fuel/oxidant mixtures [1]. Thermomagnetometry (TM) can provide additional information if the magnetic properties of the materials change during reaction. TG, TM and DTA results for the iron/potassium permanganate, iron/barium peroxide, and iron/strontium peroxide systems as loose powders or pressed pellets indicate predominantly solid-gas mechanisms for reactions in these systems.     

Ξ Resonances in Ξ− Be interactions II. Properties of Ξ(1820) and Ξ(1960) in the\Lambda \bar K^0 and\Sigma ^0 \bar K^0 channels

In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive \(\Lambda \bar K^0 \) and \(\Sigma ^0 \bar K^0 \) final states formed in Ξ^? Be interactions. In the \(\Lambda \bar K^0 \) channel, we observe a signal at 1826 MeV/c² which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c², Г=12±14 MeV/c². A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the \(\Lambda \bar K^0 \) channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c², Г=25±15 MeV/c². This state, which we call Ξ(1960), is not observed in the \(\Sigma ^0 \bar K^0 \) channel, leading to an upper limit on the ratio of partial widths \(\Sigma \bar K/\Lambda \bar K\) of 2.3 (90% confidence level). A moment analysis of the \(\Lambda \bar K^0 \) final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2⁺, 7/2^?, etc.     

Kinetics and mechanism of rhenium-catalyzed O atom transfer from epoxides

O atom transfer from epoxides cis-stilbene oxide and styrene oxide to triphenylphosphine catalyzed by Tp'ReO(3) (Tp' = hydridotris(3,5-dimethylpyrazolyl)borate) is shown to proceed via an unexpectedly complex combination of mechanisms. Reduction of Tp'ReO(3) with PPh(3) in THF is rapid above room temperature to form a highly reactive species suggested to be Tp'ReO(2). Spectroscopic examination and attempts to isolate this by chromatography lead only to Tp'Re(O)(OH)(2) (1); exposure of the crude reduction mixture to ethanol results in formation of Tp'Re(O)(OEt)(OH) (3). Both 1 and 3 are as efficient catalysts for O atom transfer as the unpurified mixture resulting from reaction of PPh(3) with Tp'ReO(3); all three rhenium reactants give the same turnover frequency to within 10% at identical [Re](total) and [epoxide]. The kinetic behavior of the catalytic system (epoxide:Re = 20) is complex; an initial "burst" of alkene production is seen, which quickly tapers off and falls into a pseudo-zero-order reaction. The majority of rhenium is observed to exist as the syn-Tp'Re(O)(diolate) complex, formed by ring expansion of the epoxide. However, cycloreversion of this diolate is incapable of accounting for the observed catalytic turnover frequency. An additional intermediate, a coordinated epoxide, is proposed to form and partition between ring expansion and direct fragmentation to alkene; eventually a steady-state concentration of diolate forms. Competition between direct atom transfer and ring expansion followed by diolate cycloreversion is demonstrated by reaction of 3 with excess cis-stilbene oxide and styrene oxide in the absence of reductant to give a 4:1 mixture of alkene and syn-diolate from cis-stilbene oxide or a 5.5:1 mixture of alkene and syn-diolate from styrene oxide under conditions where diolate cycloreversion is a negligible contributor.     

Liposomes as signal amplification reagents for bioassays in microfluidic channels

Liposomes with encapsulated carboxyfluorescein were used in an affinity-based assay to provide signal amplification for small-volume fluorescence measurements. Microfluidic channels were fabricated by imprinting in a plastic substrate material, poly(ethylene terephthalate glycol) (PETG), using a silicon template imprinting tool. Streptavidin was linked to the surface through biotinylated-protein for effective immobilization with minimal nonspecific adsorption of the liposome reagent. Lipids derivatized with biotin were incorporated into the liposome membrane to make the liposomes reactive for affinity assays. Specific binding of the liposomes to microchannel walls, dependence of binding on incubation time, and nonspecific adsorption of the liposome reagent were evaluated. The results of a competitive assay employing liposomes in the microchannels are presented.