A new polaronic order-disorder phase transition in magnetite as observed through μSR

Recent μSR measurements on the Mott-Wigner glass, magnetite, as a function of temperature and external magnetic field have shown the existence of two inequivalent magnetic sites below T_A=247K. These data are being interpreted in terms of the onset or destruction of local order manifested as local atomic correlations (molecular polarons).     

Cyclosporin A,ein immunsuppressiv wirksamer Peptidmetabolit aus Trichoderma polysporum (LINK ex PERS.) Rifai

Cyclosporin A, a Peptide Metabolite from Trichoderma polysporum (LINK ex PERS .) Rifai, with a remarkable immunosuppressive activity Two antifungal metabolites, cyclosporins A and C, were isolated from a strain of Trichoderma polysporum (LINK ex PERS .) Rifai. Cyclosporin A, the main component, has the molecular formula C₆₂H₁₁₁N₁₁O₁₂ as deduced by NMR. and mass spectra. Hydrolytic cleavage of cyclosporin A furnished 11 amino acids as fragments, among them an artefact of a new C₉-amino acid. The amino acid sequence was determined by Edman degradation of iso-cyclosporin A, a basic rearrangement product formed from cyclosporin A by N, O-acyl migration. In an independent investigation an X-ray analysis of the iodo derivative 10 was performed (see the following paper). On the basis of the chemical, spectroscopic and crystallographic evidence the complete structure of cyclosporin A was elucidated as the neutral cyclic oligopeptide 1 . Cyclosporin A and C show remarkable immunosuppressive and antiphlogistic activities in several pharmacological models.     

Hydrogen defect-level pinning in semiconductors: the muonium equivalent

We have determined locations for the donor and acceptor levels of muonium in six semiconductor materials (Si, Ge, GaAs, GaP, ZnSe, and 6H-SiC) as a test of defect-level pinning for hydrogen. Within theoretical band alignments, our results indicate a common energy for the equilibrium charge-transition level Mu(+/-) to within experimental uncertainties. However, this is nearly 0.5 eV higher than the energy at which the equivalent level for hydrogen was predicted to be pinned. Corrections for zero-point energy account for only about 10% of this difference. We also report experimental results for the (negative-U) difference between donor and acceptor levels for Mu to be compared with calculated values for H impurities in the same materials.     

Observation of muonium in solid hydrogen

A small fraction (∼ 15%) of positive mouns stopped in condensed H₂ form muonium (Mu) atoms. We have observed the characteristic MSR precession signal of these Mu atoms and measured their relaxation as a function of temperature in pure parahydrogen as well as in natural (≃75% ortho) hydrogen. Our longitudinal field spin relaxation results show clear evidence for Mu diffusion. Work supported by NRC and NSERC.     

The growth of polymer colloids

The traditional theoretical approach to emulsion polymerization is extended to include effects due to the size of each polymer latex particle. Specific account can thus be taken of the particle size distribution in considering the growth of the colloid. Coupled partial differential equations are derived to describe the system and shown to reduce to the conventional Smith-Ewart equations under certain limits. Solutions are presented for simple models for the emulsion polymerization of styrene and vinyl acetate.     

GERMICIDAL ULTRAVIOLET LIGHT INDUCES ORNITHINE DECARBOXYLASE IN MOUSE EPIDERMAL CELLS AND MODIFIES THE INDUCTION CAUSED BY PHORBOL ESTER TUMOR PROMOTERS

Germicidal ultraviolet light (UVC. 8–10 J/m²) induces ornithine decarboxylase (ODC) in mouse epidermal cells in vitro in a biphasic manner with maxima of 2–3 fold induction at 4–6 h and of 10–20 fold induction at 15–18 h after irradiation. At this dose of UVC overall protein synthesis is inhibited by 10–30% and RNA synthesis by 40–50%. Induction of both ODC peaks is prevented by actinomycin D or cycloheximide. Similar culture factors appear to influence the extent of ODC induction by UVC and by the tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA), since the ratio of peak activities is approximately constant at 2, whereas absolute values vary considerably between experiments. If cells are irradiated with UVC and then exposed to TPA, the effects are additive at 10 J/m², less than additive at higher and enhanced at lower doses of UVC.     

Molecular weight distribution in emulsion polymerizations

A mathematical formulation is given which describes the evolution of the number distribution of the molecular weight (MWD) of linear polymer chains that grow in emulsion polymerization systems. The resulting set of coupled ordinary differential equations takes into account the microscopic events of free radical entry, exit, chain annihilation, bimolecular termination (by combination and disproportionation), and chain transfer in a mono- or polydisperse system. Simple analytic solutions are presented for systems in which the number of particles, as well as the average number of free radicals per particle, is constant and in which the rate coefficients are size independent. These solutions indicate that compartmentalization of the free radicals in the latex particles results in a significant increase in the polydispersity of the polymer produced by emulsion polymerization, compared with that in bulk systems. The theory shows that significant mechanistic information may be obtained from experimental MWDs and that, in principle, experimental conditions may be prescribed to grow a desired MWD. The MWDs are presented in a novel manner that facilitates the comparison of theory with experiment.     

Die vermutliche Struktur der Anodendroside. Glykoside und Aglykone, 331. Mitteilung

Five crystalline compounds (anodendrosides) have been isolated from Anodendron paniculatum (Roxb.)A. DC. (Apocynaceae). They represent glycosides containing unusual sugars. Tentative structures for anodendroside-A ( 155 ), ?E₁ ( 3 ), ?E₂ ( 84 ), ?F ( 144 ) and ?G ( 115 ) are now presented. These structures are based on UV., IR., but mostly on high resolution mass spectra. NMR.-spectra could be performed with A, O-acetyl-E₂ and O-acetyl-G, which are in good agreement with the suggested structures. The unusual methylendioxy group postulated in the sugar moiety of A, E₁ and E₂ was also established by chemical methods, yielding approximately 1 Mol. equiv. of formaldehyde after acid hydrolysis of anodendroside-E₂.     

Styrene emulsion polymerization: Kinetics and particle size distributions in highly swollen latex systems

The results are reported of studies on the kinetics and the time evolution of the particle size distribution in seeded styrene emulsion polymerization systems wherein the seed latex particles were highly swollen with monomer as a result of prior swelling by dodecane. Conditions were such that no new latex particles were formed nor was a significant number of monomer droplets present (“Interval III”). The data were fitted to obtain values for the rate coefficients for entry and exit (desorption) of free radicals. It was found that, during the early part of the polymerization (when the polymer:monomer ratio in the latex particles is considerably less then in an equivalent emulsion polymerization system without dodecane), the entry rate coefficient was much smaller than that measured in systems without dodecane. This effect is consistent with an entry mechanism wherein entering free radicals must displace surfactant molecules from the latex particles.