Retinoid chromophores as probes of membrane lipid order

There is a great need for development of independent methods to study the structure and function of membrane-associated proteins and peptides. Polarized light spectroscopy (linear dichroism, LD) using shear-aligned lipid vesicles as model membranes has emerged as a promising tool for the characterization of the binding geometry of membrane-bound biomolecules. Here we explore the potential of retinoic acid, retinol, and retinal to function as probes of the macroscopic alignment of shear-deformed 100 nm liposomes. The retinoids display negative LD, proving their preferred alignment perpendicular to the membrane surface. The magnitude of the LD indicates the order retinoic acid > retinol > retinal regarding the degree of orientation in all tested lipid vesicle types. It is concluded that mainly nonspecific electrostatic interactions govern the apparent orientation of the retinoids within the bilayer. We propose a simple model for how the effective orientation may be related to the polarity of the end groups of the retinoid probes, their insertion depths, and their angular distribution of configurations around the membrane normal. Further, we provide evidence that the retinoids can sense subtle structural differences due to variations in membrane composition and we explore the pH sensitivity of retinoic acid, which manifests in variations in absorption maximum wavelength in membranes of varying surface charge. Based on LD measurements on cholesterol-containing liposomes, the influence of membrane constituents on bending rigidity and vesicle deformation is considered in relation to the macroscopic alignment, as well as to lipid chain order on the microscopic scale.     

Carrier concentration and shallow electron states in Sb-doped hydrothermally grown ZnO

In order to obtain p-type ZnO, the incorporation of group-V elements on oxygen sites has received lots of attention. Recently, the implantation of Sb+ ions into ZnO has been shown to lead to reduced n-type conduction. However, a compensating effect due to implantation damage could not be ruled out. Therefore, single-crystal ZnO has been hydrothermally grown with additional Sb₂O₃, Sb₂O₅, and K(SbO)C₄H₄O₆ in the solution. Schottky barrier contacts have been deposited onto the () face. Capacitance–voltage measurements and thermal admittance spectroscopy have been used for electrical characterization, and secondary ion mass spectrometry was used to measure the Sb content in the samples. Clearly, all samples exhibited n-type conduction. A competition between the incorporation of oxygen and antimony is suggested.     

Oriented crosslinked polyethylene pipes by a novel extrusion method

Crosslinking and stretching (2.5 times along the circumferential direction) of the molten polymer during extrusion produced pipes with dominantly circumferential orientation and a lower degree of axial chain orientation. Differential scanning calorimetry (crystallinity and crystal thickness), density measurements (crystallinity), X-ray diffraction (c-axis orientation), infrared dichroism measurements (crystalline and amorphous chain orientation) and contraction measurements (molecular draw ratio) assessed the microstructure of the pipe material. The mechanical properties of the oriented material were assessed by uniaxial tensile tests. The orientation was biaxial with the main orientation in the circumferential direction and a lesser orientation in the axial direction. The maximum degree of circumferential orientation was obtained at the inner wall of the pipe. The lower degree of crosslinking of the core material allowed slippage of chains during the stretching of the molten polymer and it is suggested that this is the cause of the lower degree of orientation of the core material. The oriented pipe material exhibited a 5-10% higher degree of crystallinity and higher crystal thickness than conventionally crosslinked material. The tensile modulus and the tensile strength of the oriented, cross-linked material was greater along the axial direction than along the circumferential direction. The circumferential and axial moduli for the oriented, crosslinked pipe were greater than the corresponding moduli of the non-oriented cross-linked pipe material. Another pipe based on crosslinked PE that were first circumferentially stretched 2.5 times and later axially stretched 10 times (in the molten state) showed, despite the fact that it exhibited pronounced axial orientation almost a balanced tensile modulus (4.3±0.2 GPa) in the axial-circumferential plane. Atomistic modelling showed that the orientational dependence of the density of the amorphous phase is small.     

Dμ—A new concept in industrial low-energy electron dosimetry

Irradiation with low-energy electrons (100–300 keV) results in dose gradients across the thickness of the dosimeters that are typically used for dose measurement at these energies. This leads to different doses being measured with different thickness dosimeters irradiated at the same electron beam, resulting in difficulties in providing traceable dose measurements using reference dosimeters. In order to overcome these problems a new concept is introduced of correcting all measured doses to the average dose in the first micrometer—D_μ. We have applied this concept to dose measurements with dosimeters of different thickness at two electron accelerators operating over a range of energies. The uncertainties of the dose measurements were evaluated, and it was shown that the dose in terms of D_μ was the same at each energy for all dosimeters within the measurement uncertainty. Using the concept of D_μ it is therefore possible to calibrate and measure doses from low-energy electron irradiations with measurement traceability to national standards.     

Amphiphilic comb-shaped polymers from poly(ethylene glycol) macromonomers

Comb-shaped amphiphilic graft copolymers composed of hydrophobic backbones and hydrophilic side chains were prepared by radical copolymerization of poly(ethylene glycol) monomethacrylate macromonomers, and methacrylate and acrylate comonomers in toluene. The copolymerizations were very sensitive to the reaction conditions, and insoluble cross-linked gels were easily formed. The yields of soluble copolymers were affected by the initiator concentration, the macromonomer concentration, and the choice of chain transfer agents and comonomers. Solubilities of the copolymers in water or methanol were found to depend on the sizes and the numbers of the PEG side chains. The copolymers showed surface activity with CMC:s in the order of 0.1–1.5 g/L and surface tensions of 36–56 dyn/cm. When tested as emulsifiers most of the copolymers gave oil-in-water type emulsions at room temperature. Polymers carrying MPEG 2000 side chains were crystalline with melting points of 38–44°C, while those based on PEG 400 and 1000 were mostly amorphous with glass transition temperatures between -55 and -60°C. © 1992 John Wiley & Sons, Inc.     

Efforts to improve detection sensitivity for capillary electrophoresis coupled to atmospheric pressure photoionization mass spectrometry

Electrospray ionization performs best with volatile buffers. However, generally the best separation performance for capillary electrophoresis (CE) is achieved with non‐volatile buffers. Hyphenation of CE with mass spectrometry (MS) utilizing atmospheric pressure photoionization (APPI) enables use of a wider range of separation buffers without compromising detection sensitivity. As APPI is considered to be mass flow sensitive, the use of a larger inner diameter separation capillary (75 µm) allows larger volumes to be injected, without decreased separation performance, thus providing improved sensitivity (approx. a factor of 10), compared to the use of a 25 µm capillary. However, nebulizing gas flow and position of capillary tip in the sprayer have to be carefully optimized to prevent excessive band broadening. Further improvement in sensitivity (approx. a factor of 2) was obtained by decreasing the distance between the sprayer and ionization region, indicating that a specially designed CE/APPI‐MS interface for low flow rates will be favourable. Copyright © 2010 John Wiley & Sons, Ltd.     

Adsorption and spontaneous rupture of vesicles composed of two types of lipids

To analyze the adsorption of single vesicles composed of two types of lipids (e.g., zwitterionic and positively charged lipids or zwitterionic and negatively charged lipids), we propose a statistical model taking into account lipid-surface interactions, lipid-lipid lateral interactions, and vesicle bending energy. Our treatment specifies how these parameters govern vesicle adsorption, shows how the radius of the vesicle-surface contact area may depend on the vesicle composition, and clarifies the conditions for vesicle rupture.     

A simple model for the water o-H2 complex

The infrared spectrum of the complex between o-H2 and H2O, D2O, or HDO, isolated in a matrix of solid p-H2, has been studied between 20 and 4500 cm(-1). In addition the infrared spectrum of the complex between p-D2 and H2O in solid o-D2 has been studied. The spectral shifts are interpreted as the result of the quadrupole-dipole interaction between hydrogen and water.