Puroindoline-a, a lipid binding protein from common wheat, spontaneously forms prolate protein micelles in solution

The self-assembly in solution of puroindoline-a (Pin-a), an amphiphilic lipid binding protein from common wheat, was investigated by small angle neutron scattering, dynamic light scattering and size exclusion chromatography. Pin-a was found to form monodisperse prolate ellipsoidal micelles with a major axial radius of 112 ± 4.5 ? and minor axial radius of 40.4 ± 0.18 ?. These protein micelles were formed by the spontaneous self-assembly of 38 Pin-a molecules in solution and were stable over a wide pH range (3.5-11) and at elevated temperatures (20-65 °C). Pin-a micelles could be disrupted upon addition of the non-ionic surfactant dodecyl-β-maltoside, suggesting that the protein self-assembly is driven by hydrophobic forces, consisting of intermolecular interactions between Trp residues located within a well-defined Trp-rich domain of Pin-a.     

Fluorescence lifetime imaging of oxygen in living cells

The usefulness of the fluorescent probe ruthenium tris(2,2′-dipyridyl) dichloride hydrate (RTDP) for the quantitative imaging of oxygen in single cells was investigated utilizing fluorescence lifetime imaging. The results indicate that the fluorescence behavior of RTDP in the presence of oxygen can be described by the Stem-Volmer equation. This shows that fluorescence quenching by oxygen is a dynamic quenching process. In addition, it was demonstrated that the fluorescence lifetime of RTDP is insensitive to pH, ion concentration, and cellular contents. This implies that a simple calibration procedure in buffers can be used to quantify oxygen concentrations within cells. First fluorescence imaging experiments on J774 macrophages show a nonuniform fluorescence intensity and a uniform fluorescence lifetime image. This indicates that the RTDP is heterogeneously partitioned throughout the cells, while the oxygen concentration is constant.     

Generation of ultraviolet broadband light in a single-mode fiber

Ultraviolet broadband light spanning 337–405 nm was produced in a single-mode optical fiber primarily by stimulated Raman scattering. Pulses of 4 ns duration at 337 nm were coupled into a 50 m long ultraviolet-grade fiber featuring single-mode operation in the 320–450 nm range. Significant spectral broadening was achieved with pulses of only ∼10 W peak power. Our experiments demonstrate the potential for a source with ∼10⁴ times the spectral radiance of a quartz tungsten halogen lamp, which is currently used for many applications in this wavelength range. PACS 42.65.Ky; 42.81.Wg     

Circuit preserving edge maps

It is proved that any one-to-one edge map f from a 3-connected graph G onto a graph G′, G and G′ possibly infinite, satisfying f(C) is a circuit in G′ whenever C is a circuit in G is induced by a vertex isomorphism. This generalizes a result of Whitney which hypothesizes f(C) is a circuit in G′ if and only if C is a circuit in G.     

Expanding diversity in dynamic combinatorial libraries: simultaneous exchange of disulfide and thioester linkages

Dynamic combinatorial libraries have been prepared which feature two simultaneous covalent exchange reactions in aqueous solution at neutral pH. This allows for diversity, not only of the subunits that are linked, but also of the linkage itself.     

Circular dichroism of 5α-deuteriocholesta-1,3-diene

Replacement of the 5α-hydrogen by deuterium in 5α-cholesta-1,3-diene decreased the Δ at 262 nm (in hexane) from ?2.37 ± 0.06 to ?2.18 ± 0.04.