Elastic π±-d and π±-4He scattering below 70 MeV

Elastic scattering differential cross section data of ^± d at 65 MeV and ^{± 4}He at 51 MeV are presented and compared respectively to fully relativistic 3-body and optical potential calculations including true pion absorption.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Segregation of separate steps in chromium-catalyzed reactions for convenience and mechanistic analysis

[structure: see text] We have developed an apparatus for carrying out redox-coupled chromium-manganese or chromium-zinc reactions on solid-supported substrates which allows recycling of the stoichiometric reductant. In addition to providing a greatly simplified procedure for these reactions, we observe striking differences in the recyclability of Mn and Zn. A preliminary extension of the methodology to the catalytic coupling of allylchromium reagents with solid-supported aldehydes is also reported.     

Synthesis and structure of Ta4SI11: disorder and mixed valency in the first tantalum sulfide iodide

The new compound Ta(4)SI(11) has been prepared by direct reaction of the elements at 430 degrees C for 2 weeks in evacuated Pyrex ampules and characterized by single-crystal X-ray diffraction, X-ray photoelectron spectroscopy, magnetic susceptibility measurements, and semiempirical electronic structure calculations. Ta(4)SI(11) crystallizes with orthorhombic symmetry in space group Pmmn; a = 16.135(3) A, b = 3.813(1) A, c = 8.131(2) A, and Z = 1. The disordered structure involves two crystallographically distinct sites for Ta atoms, both of which are 50% occupied as well as a bridging anion site that is 50% S and 50% I. Magnetic susceptibility above 100 K gives micro (eff) = 1.53 micro (B) to suggest one unpaired electron per formula unit. X-ray photoelectron spectroscopy and extended Hückel calculations suggest that the structure consists of Ta(3) triangles and "isolated" Ta atoms, leading to the formulation (Ta(3))(9+)(Ta(4+))(S(2)(-))(I(-))(11) and we hypothesize that each Ta(3) is capped by a sulfur atom.     

Dynamics of protein and mixed protein/surfactant adsorption layers at the water/fluid interface

The adsorption behaviour of proteins and systems mixed with surfactants of different nature is described. In the absence of surfactants the proteins mainly adsorb in a diffusion controlled manner. Due to lack of quantitative models the experimental results are discussed partly qualitatively. There are different types of interaction between proteins and surfactant molecules. These interactions lead to protein/surfactant complexes the surface activity and conformation of which are different from those of the pure protein. Complexes formed with ionic surfactants via electrostatic interaction have usually a higher surface activity, which becomes evident from the more than additive surface pressure increase. The presence of only small amounts of ionic surfactants can significantly modify the structure of adsorbed proteins. With increasing amounts of ionic surfactants, however, an opposite effect is reached as due to hydrophobic interaction and the complexes become less surface active and can be displaced from the interface due to competitive adsorption. In the presence of non-ionic surfactants the adsorption layer is mainly formed by competitive adsorption between the compounds and the only interaction is of hydrophobic nature. Such complexes are typically less surface active than the pure protein. From a certain surfactant concentration of the interface is covered almost exclusively by the non-ionic surfactant. Mixed layers of proteins and lipids formed by penetration at the water/air or by competitive adsorption at the water/chloroform interface are formed such that at a certain pressure the components start to separate. Using Brewster angle microscopy in penetration experiments of proteins into lipid monolayers this interfacial separation can be visualised. A brief comparison of the protein adsorption at the water/air and water/n-tetradecane shows that the adsorbed amount at the water/oil interface is much stronger and the change in interfacial tension much larger than at the water/air interface. Also some experimental data on the dilational elasticity of proteins at both interfaces measured by a transient relaxation technique are discussed on the basis of the derived thermodynamic model. As a fast developing field of application the use of surface tensiometry and rheometry of mixed protein/surfactant mixed layers is demonstrated as a new tool in the diagnostics of various diseases and for monitoring the progress of therapies.     

ELLIPSOMETRY OF BLACK LIPID MEMBRANES OF EGG LECITHIN AND CHLOROPLAST EXTRACTS

Abstract— Ellipsometric angles and reflectivity of black lipid membranes containing either egg lecithin or chloroplast extracts were measured at a wavelength of 6328 Å. Evidence was found for positive uniaxial anisotropy in membranes of lecithin. If the thickness of those films is assumed to be 62 Å, the refractive index normal to the film surface is 1.471 ± 0.004, and the refractive index parallel to the film surface is 1.454 ± 0.003. The results for membranes of chloroplast extracts also indicate a positive anisotropy in the indices of absorption.     

Ternary mutual diffusion coefficients of ZnCl2−KCl−H2O at 25°C by Rayleigh interferometry

Mutual diffusion coefficients and densities were measured for aqueous ZnCl₂–KCl mixtures at 25° by using free-diffusion Rayleigh interferometry and pycnometry, respectively. The ZnCl₂ concentrations were fixed at 1.5 mol-dm^–3, whereas those of KCl were 0.5, 1.25, 2.0, or 4.0 mol-dm^–3. This corresponds to a half charged zinc-chlorine storage battery at various suporting electrolyte concentrations. The main-term coefficient of ZnCl₂ only varies by 10% with KCl concentration, whereas that of KCl varies by about 22%. The ZnCl₂ cross-term coefficient remains small and positive; in contrast the KCl cross-term coefficient goes through a maximum and is negative at high and low KCl concentrations. At KCl concentrations of 0.5 and 4.0 mol-dm^–3, solutions with the KCl c0 are statically and dynamically (diffusively) unstable at the top and bottom of the boundary. Evaluation of the parameters of the non-linear least-squares solution to the diffusion equation is difficult for the 1.25 mol-dm^–3 KCl case, since this system has nearly equal eigenvalues in its diffusion coefficient matrix.     

NON-NUCLEAR DAMAGE AND CELL LYSIS ARE INDUCED BY UVA, BUT NOT UVB OR UVC, RADIATION IN THREE STRAINS OF L5178Y CELLS

The potential to induce non-nuclear changes in mammalian cells has been examined for (1) UVA1 radiation (340–400 nm, UVASUN 2000 lamp), (2) UVA + UVB (peak at 313 nm) radiation (FS20 lamp), and (3) UVC (254 nm) radiation (GI5T8 lamp). The effects of irradiation were monitored in vitro using three strains of L5178Y (LY) mouse lymphoma cells that markedly differ in sensitivity to UV radiation. Comparisons were made for the effects of approximately equitoxic fluences that reduced cell survival to 1–15%. Depending on the cell strain, the fluences ranged from 830 to 1600 kJ/m² for the UVASUN lamp, 75 to 390 J/m² for the FS20 lamp and 3.8 to 17.2 J/m² for the G15T8 lamp. At the exposure level used in this study, irradiation with the UVASUN, but not the FS20 or G15T8, lamp induced a variety of non-nuclear changes including damage to cytoplasmic organelles and increased plasma membrane permeability and cell lysis. Cell lysis and membrane permeabilization were induced by the UVA1 emission of the UVASUN lamp, but not by its visible + IR components (>400 nm). The results show that the plasma membrane and other organelles of LY cells are highly sensitive to UVA1 but not to UVB or UVC radiation. Also UVA1, but not UVB or UVC radiation, causes rapid and extensive lysis of LY cells. In conclusion, non-nuclear damage contributes substantially to UVA cytotoxicity in all three strains of LY cells.