Electron paramagnetic resonance and spin trapping investigations of the photoreactivity of human lens proteins

Oxidation of cysteine, glutathione and ascorbate by photoexcited proteins from normal and cataractous lenses was investigated using electron paramagnetic resonance in combination with spin trapping. We report that illumination of these proteins in pH 7 buffer with light > 300 nm in the presence of thiols (RSH) and a spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), afforded DMPO/S-cysteine and DMPO/SG adducts, suggesting the formation of the corresponding thiyl radicals. In a nonbuffered aqueous solution, illumination of the proteins and glutathione also produced superoxide detected as a DMPO/O2H adduct. Irradiation of these proteins in the presence of ascorbate generated ascorbate radical. We conclude that chromophores present in the natural normal and cataractous lenses are capable of initiating photooxidative processes involving endogenous thiols and ascorbic acid. This observation may be pertinent to UV-induced development of cataract.     

THE FLUORESCENT PRODUCT OF SCALEWORM BIOLUMINESCENT REACTION: AN IN VITRO STUDY

Abstract— The fluorescence of scaleworms has been attributed by Harvey (1952) to a product of the bioluminescent reaction confined in the scales of these worms. We have purified this fluorescent molecule by gel filtration. This compound has an apparent low molecular weight as shown by polyacrylamide gel clectrophoresis in the presence of SDS. The yield of the fluorescent product, after gel filtration, varies with the stimulation of the bioluminescence, triggered either chemically or enzymatically. The fluorescence spectrum of the purified product is similar to the one observed in vivo , with a maximum centered at 520 nm. Consequently, the fluorescent compound isolated is likely the reaction product of the bioluminescent reaction.     

Constitution moleculaire d'α,ω-difluoropolydimethylsiloxanes equilibres obtenus par une reaction de redistribution

α,ω-Difluoropolydimethylsiloxanes F[(CH₃)₂SiO]_n(CH₃)₂SiF have been prepared by reaction of (CH₃)₂SiF₂ with cyclic dimethylsiloxanes [(CH₃)₂SiO]_n (n = 3 or 4). An equilibrium is reached in the redistribution of fluorine vs. oxygen atoms after ca. 24 h at 200°C or 15 days at 150°C when catalysed by AlCl₃. 16 equilibrated samples of varied (R = F/Si) overall compositions have been analysed by ¹H and ¹⁹F NMR and by VPC. The presence of rings has been established for the lower values of R. The molecular constitution of the equilibrated samples is described by a set of constants. The abundance of the end units

is slightly larger than expected from random distribution. The good resolution of the spectra permits the distinguishing of the 9th order of environment of the end units and the 5th order for the middle units and the verification that there is no preferential association among the building units, and thus the proportion of chains of various lengths obeys Flory's random distribution mode. The equilibrium molecular constitution of these α,ω-difluorosiloxanes is close to that of their dichloro analogs; the substitution of chlorine by fluorine atoms at the end of the chains thus appears to cause little perturbation. On the other hand, the kinetic evolution of the reaction appears to be different, since the first species which forms is always the pyro molecule

instead of long chains and large rings as in the case of the chloro analogs.     

Solvatation preferentielle dans les systemes ternaires polyvinylpyrrolidone/solvant halogene/solvant donneur de proton—III: Confrontation des resultats obtenus par diffusion de la lumiere et par spectroscopie infra-rouge

We have compared the experimental results of study of the preferential solvation of polyvinylpyrrolidone in halogenated solvent/proton-donor solvent mixtures, obtained by light scattering and i.r. spectroscopy and described in the two preceding papers. The preferential adsorption of the proton-donor solvent is explained by the formation of a hydrogen-bond complex of polymer with proton-donor solvent, on which other proton-donor molecules are bound by induced autoassociation. This complexing occurs even in mixtures where the “inert” solvent (1,2-dichloroethane) is preferentially adsorbed; this is experimental proof of a differing solvation of the chains in their close neighbourhood and within short range of them.     

Enumeration of resonance structures

Simple MO techniques are described that can be used to count resonance structures for unsaturated hydrocarbons, ions, and radicals. Alternant or non-alternant unsaturated species can be treated accurately and rapidly. The relationship of the structure count to the calculated values of highest filled and lowest vacant HMO energy levels is discussed. A qualitative relationship of the structure count with reactivity and stability if exemplified with several cases. A known correspondence of resonance theory and perturbational MO theory, previously limited to benzenoid and acyclic systems, is expanded to include all pi molecular systems.     

The determination of10B by prompt proton spectrometry

Boron was analysed in ore and glass samples by prompt proton spectrometry, using deuterons of 2.7 MeV to coincide with a region where the excitation function of the¹⁰B(d, p)¹¹B reaction did not vary appreciably with energy. Targets of approximately 300 μg/cm² thick of powdered samples were prepared by centrifugation. Concentrations down to 0.2% were determined. Possible interference by other elements, particularly nitrogen, magnesium and titanium, was investigated.     

Ligand exchange reactions of ferrocene with phenanthrene or 9,10-dimethylphenanthrene in the presence of aluminum chloride and aluminum

Ligand exchange reactions between phenanthrene or 9,10-dimethylphenanthrene with ferrocene effected in the presence of AlCl₃-Al were carried out under a variety of conditions. With phenanthrene (I), hydrogenation at the C-9 and C-10 positions could take place during the reaction and the cationic products obtained were the η⁶-phenanthrene-η⁵-cyclopentadienyliron and η⁶-9,10-dihydro-phenanthrene-η⁵-cyclopentadienyliron moncations (II and III), and the η⁶-phenanthrene-$\text{trans}$-$\text{bis}$-η⁵-cyclopentadienyliron and η⁶-9,10-dihydrophenanthrene-$\text{trans}$-$\text{bis}$-η⁵-cyclopentadienyliron dications (IV and V). With 9,10-dimethylphenanthrene (VI), reactions carried out in refluxing cyclohexane gave the non-hydrogenated η⁶-9,10-dimethylphenanthrene-η⁵-cyclopentadienyliron monocation (VII) and η⁶-9,10-dimethylphenanthrene-$\text{trans}$-$\text{bis}$-η⁵-cyclopentadienyliron dication (VIII). When higher temperatures were used in an attempt to promote hydrogenation, decomposition predominated and no cationic product could be obtained. These finding are discussed and contrasted with previous results obtained from similar reactions using anthracene or 9,10-dimethylanthracene.     

Cohesive energy densities of polyethers: Poly(hexamethylene oxide)

The solubility parameter of poly(hexamethylene oxide) has been estimated by measuring solution viscosities and by turbidimetric titrations in a series of solvents. From both experimental methods, a value of $\text{δ}{}_{\mathrm{<mtext>p</mtext>}}\text{= 33.9}\text{J}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{cm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ ($\text{8.1}\text{cal}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{cm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$) was obtained, whence the cohesive energy density is 274.5 J cm^?3 (65.6 cal cm^?3). These experimental values are compared with those calculated by empirical methods.     

New sesquiterpenoids from the sponge axinella cannabina

The structures of three sesquiterpenoids, axisothiocyanate-2(4), axamide-1(5) and axamide-2(6), present in the marine sponge Axinella cannabina, have been determined on the basis of chemical and spectral evidences.     

Der Einfluß von Vanadin und Niob auf feste Subcarbidlösungen in den Systemen Tantal-Wolfram-Kohlenstoff und Tantal-Molybdän-Kohlenstoff

Zusammenfassung Röntgenbeugungsfilme von Pulveraufnahmen wärmebehandelter Proben wurden zur Untersuchung der Phasengleichgewichte der pseudo-ternären Subcarbidsysteme Ta₂C–Mo₂C(W₂C)–V₂C(Nb₂C) bei 1650° und 2000°C herangezogen. Es werden in jedem System die Zusammensetzungs-bereiche festgestellt, in denen die bekannte Disproportionierungsreaktion zu erwarten ist. Es ist dies ein erster Schritt, um zu ermöglichen, diese Legierungen zur Herstellung von Schneide-werkzeugen heranzuziehen. In allen Systemen bilden die Subcarbidphasen ausgedehnte Einphasenbereiche. In den Nb₂C enthaltenden Systemen gibt es Legierungen mit engen Zusammensetzungsbereichen, die möglicherweise als Legierungen für die Erzeugung von Schneidewerkzeugen herangezogen werden können.

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The effect of vanadium and niobium on the subcarbide solid solution in the tantalum-tungsten-carbon and tantalum-molybdenum-carbon systems

The phase equilibria of the pseudo-ternary subcarbide systems Ta₂C–Mo₂C(W₂C)–V₂C(Nb₂C) at 1650 and 2000°C have been investigated using X-ray powder diffraction films of heat treated samples. The compositional regions in each system where the known disproportionation reaction is expected to occur have been defined as an initial step towards the utilization of these alloys for cutting tools. The subcarbide phases form extended single phase regions in all systems. Alloys from small compositional regions in those systems containing Nb₂C are possible candidates for preliminary cutting tool alloy evaluation.

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Mit 4 Abbildungen

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Herrn Prof.H. Nowotny gewidmet.