Single channel recordings of alpha-hemolysin reconstituted in S-layer-supported lipid bilayers.

Previous studies demonstrated that lipid membranes attached to a proteinaceous crystalline surface-layer (S-layer) revealed a prolonged lifetime and showed a reduced tendency to rupture in the presence of membrane active molecules. In addition, comparative studies on folded and S-layer-supported lipid membranes (SsLM) revealed an uniform capacitance of 0.64 +/- 0.04 microF/cm(2) for both composite membranes. In the present study, the feasibility to reconstitute the channel-forming protein alpha-hemolysin (alpha HL) into SsLM at single channel resolution was investigated. Single alpha HL channels could be recorded and the intrinsic properties like unitary conductance, current-voltage characteristics, and closure was found to be similar at both membranes. Thus, the tightly attached S-layer allowed complete reconstitution of alpha HL channels in SsLM.     

Ultrafast electron transfer, localization and solvation at ice–metal interfaces: Correlation of structure and dynamics

The interaction of an excess electron with a polar molecular environment is well known as electron solvation. This process is characterized by an energetic stabilization and by changes of the electronic spatial extent due to screening of the localized charge through molecular rearrangement. At metal–ice interfaces we photo-inject delocalized electrons from the metal substrate into adsorbed ice layers and analyze the ultrafast dynamics of electron transfer, localization and solvation by femtosecond time- and angle-resolved two-photon photoemission spectroscopy. To acquire further understanding of the individual steps of the complex process we vary the interfacial structure. The substrate is changed between Cu(1 1 1) and Ru(0 0 1) and the electron dynamics in ice islands are compared to closed D₂O layers. Contrasting crystalline and amorphous ice we found that electron solvation is mediated through electron localization at favorable structural sites, which occurs very efficiently in amorphous ice, but is less likely in a crystalline layer. Next, we find that in an open ice structure like ice islands the energetic stabilization due to electron solvation proceeds at a rate of 1 eV/ps which is three times faster than in a closed ice layer. We attribute this behavior to differences in the molecular coordination, which determines the molecular mobility and, thus, the transfer rate of electronic energy to solvent modes. The substrate’s electronic structure, on the other hand, is important to understand the transfer rates from electrons in ice back to the metal. First experiments on trapped electrons in crystalline ice underline the potential to study electron solvation not only during the equilibration process, but also in quasi-static conditions, where we find that the stabilization continues, although at much weaker rates.     

Influence of solvents on the insertion of methacrolein into zirconacyclopropenes

The reaction of Cp₂Zr(L)(η²-Me₃SiC₂) (L = THF, py) with equimolar amounts of H₂C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product

Full-size image

1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [

Full-size image

2 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively.

Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination.     

Interatomic Coulombic decay in mixed NeKr clusters

We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A well-defined feature ranging from 9 to 12 eV in kinetic energy is observed in coincidence with the Ne 2s photoelectrons. It derives from an ICD process, in which an initial Ne 2s vacancy is filled by a Ne 2p electron and an electron is emitted from a 4p level on a neighboring Kr atom. We have studied the dependence of the effect on photon energy, cluster composition, and cluster size. Interestingly, the ICD electron energy increases slightly and grows a shoulder on going from 2% to 5% Kr in the coexpansion process, which we interpret in terms of surface versus bulk effects.     

On the Origin of Primitive Cells: From Nutrient Intake to Elongation of Encapsulated Nucleotides

Recent major discoveries in membrane biophysics hold the key to a modern understanding of the origin of life on Earth. Membrane bilayer vesicles have been shown to provide a multifaceted microenvironment in which protometabolic reactions could have developed. Cell‐membrane‐like aggregates of amphiphilic molecules capable of retaining encapsulated oligonucleotides have been successfully created in the laboratory. Sophisticated laboratory studies on the origin of life now show that elongation of the DNA primer takes place inside fatty acid vesicles when activated nucleotide nutrients are added to the external medium. These studies demonstrate that cell‐like vesicles can be sufficiently permeable to allow for the intake of charged molecules such as activated nucleotides, which can then take part in copying templates in the protocell interior. In this Review we summarize recent experiments in this area and describe a possible scenario for the origin of primitive cells, with an emphasis on the elongation of encapsulated nucleotides.     

Hydroxide and hydronium ion adsorption — A survey

The propensity of hydroxide and hydronium ions to accumulate at interfaces is the subject of ongoing scientific debate. Electrokinetic and surface force measurements suggest elevated interfacial concentrations of hydroxide ions across a wide range of pHs. Contrary to this, however, surface-sensitive spectroscopic techniques and molecular dynamic (MD) simulations indicate that hydronium ions have strong surface affinity under similar conditions. Here we review results obtained for gas/water, oil/water and solid/water interfaces. Emphasis is placed on ion adsorption phenomena occurring on polymer films of different hydrophobicity and structure. The results clearly show that asymmetric water ion adsorption is independent of the hydrophobicity of the solid surface. Recently obtained data reveal significant effects of the hydroxide and hydronium ions even on the charging of hydrophobic polymers in the presence of multivalent electrolytes and on the charging of zwitterionic lipid membranes.