Mitt. XV: Struktur und reaktivität von isoanellierten heterocyclischen systemen mit 4nπ- und (4n + 2) π-elektronen. 2-t-butyl-4-methyl-2,4-dihydropyrrolo[3,4-b]indole. reaktionen mit aktivierten CC-dienophilen

Reactions of 2-t-butyl-4-methyl-2,4-dihydropyrrolo[3,4-b]indoles with N-aryl-maleimides have been investigated. The formation of 1:1-cycloadducts is influenced by substituents at 1,3-position. The consecutive transformations of these intermediates can be controlled by nucleophilic solvents or reagents. Ring opening reactions occur at the labile N,O-acetal group of the cycloadducts followed by eliminaton or addition reactions.     

PHOTOSENSITIVITY IN THE SKIN OF THE LIZARD, Anolis carolinensis

Skin of the lizard, Anolis carolinensis, is remarkably sensitive to light. Illuminated in vitro with visible light from a tungsten source (110 W (m-2)), skin changes from brilliant green to dark brown (50% reduction in reflectance) within 2-4 min as a result of dispersion of melanin from a perinuclear position within dermal melanophores into superficial dendritic processes. Reversal of the process, reaggregation of pigment, will occur within 2.0 min upon return to darkness. This photic response can be initiated with light levels as low as 5.0 W m(-2) and is maximized by light levels only 5% that of midwinter sunshine. Pigment dispersion in response to both melanocyte simulating hormone and to light is inhibited by cytochalasin-B, indicating that microfilaments may be the motor element for pigment movement in that direction. Colchicine, but not cytochalasin-B, totally blocks pigment reaggregation following melanocyte stimulating hormone exposure and partially blocks it in the dark phase of the photic response. The results of this study are consistent with a model for pigment movement in A. carolinensis that provides microfilaments for pigment dispersion and microtubule involvement in both dispersion and aggregation. Finally, because it is readily visible, easily quantified, rapid and reversible, photic response in the skin of A. carolinensis is recommended as a valuable model system for the study of saltatory movement of organelles within cells.     

A METHOD FOR MEASURING PHYTOCHROME IN PLANTS GROWN IN WHITE LIGHT

Abstract— Quantitative spectrophotometric measurement of phytochrome in plants grown for relatively long periods of time in white light is not possible due to the presence of chlorophyll. A method is described that prevents the accumulation of chlorophyll permitting such direct spectrophotometric measurement in light-grown tissue. Oat seedlings grown in the presence of the herbicide San 9789† (Norflurazon) for 6 days in constant light have considerably less chlorophyll than etiolated seedlings exposed to 1 min of light. Phytochrome concentrations measured in vivo and in vitro in these herbicide-treated plants were found to be about 2% of the level in etiolated tissue.     

Polymer blends—I. Mechanical and morphological behaviour of polyethylene/polyvinyl chloride blends

As part of a fundamental study of the behaviour of mixed plastics during reprocessing and in service, blends of low density polyethylene (LDPE) and polyvinyl chloride (PVC) have been investigated. It was found that Young's modulus increased steadily from pure LDPE to pure PVC whereas both tensile strength at break and elongation at break passed through a minimum at about 5% PVC. Optical and scanning electron microscope studies have related this mechanical behaviour to morphological changes in the two phase system under stress.     

Reference Energies in Semiempirical Parametrizations

The MNDO scheme has been reparametrized for hydrocarbons using both molecular binding energies and heats of formation at 0 K as experimental reference data. Compared with MNDO, there are only minor changes in the optimized parameters, and the results are essentially of the same accuracy. These tests justify the use of heats of formation at 298 K as reference data in the original MNDO parametrization.     

Esters of 5-carboxyl-5-methyl-1-pyrroline N-oxide: a family of spin traps for superoxide

Apparent rate constants, at acidic pH and neutral pH for the reaction of a family of ester-containing 5-carboxyl-5-methyl-1-pyrroline N-oxides with superoxide (O2*-) were estimated, using ferricytochrome c as a competitive inhibitor. It was of interest to note that the rate constants were similar among the different nitrones and not that significantly different from that found for 5-(diethoxyphosphoryl)-5-dimethyl-1-pyrroline N-oxide. At acidic pH, the rate constant for spin trapping O2*- was 3-fold greater than that at physiological pH. Subsequent experiments determined the half-life of aminoxyls, derived from the reaction of these nitrones with O2*-. The EPR spectra were modeled by using a global analysis method. The results clearly demonstrated that EPR spectra of all the aminoxyls were inconsistent with a model that included a single gamma-hydrogen splitting. A better interpretation modeled them as two diastereomers with identical nitrogen splittings and slightly different beta-hydrogen splittings. Detailed line width analyses slightly favored an equal line width-unequal population ratio for the two diastereomers.     

Structure and oxidation at quasicrystal surfaces

We have investigated the atomic and electronic structure, chemical composition, and oxidation characteristics of the surfaces of icosahedral, Al-rich quasicrystals, using a variety of surface-sensitive techniques (LEED, XPS, STM, AES). We have systematically investigated the way that these traits vary with preparation conditions (e.g. sputtering and then annealing to various temperatures, vs. fracture), with surface symmetry (e.g. 2f vs. 3f vs. 5f surfaces), and with bulk composition (e.g. i-Al–Pd–Mn vs. i-Al–Cu–Fe). We have also compared our results for the quasicrystals with results for crystalline approximants and other related crystalline phases. Our main conclusions are that, under specific conditions of sputter-annealing, the bulk atomic and electronic structures of the clean quasicrystal propagate to the surface. Also, the oxidation chemistry is dominated by that of the primary constituent, aluminum.     

Mechanisms of antioxidant action: Stabilisation of nitrile rubber by interpenetrating networks based on thiol adducts

Nitrile rubbers containing three thiol antioxidants ((I) to (III)) in bound form have been evaluated as masterbatch concentrates by dilution in unstabilised nitrile rubber both at the latex stage and in the polymer melt. Both procedures give effective substantive systems in the case of the hindered phenol (I) and the aromatic thiol amide (II). Both show a high level of antioxidant retention under very severe technological conditions (oil/air oven cyclical test at 150°C). Antioxidant (III), which has only a minor structural difference from (II), is very much less effective as a substantive antioxidant.     

THE EFFECTS OF AGGREGATION ON THE FLUORESCENCE and THE TRIPLET STATE YIELD OF HEMATOPORPHYRIN

Abstract— The fluorescence and triplet state yields of hematoporphyrin have been measured in wuter/methanol mixtures. There is a closely linked response of these yields to aggregation of the hematoporphyrin molecule. The monomer, which is the principal species present at high methanol content, has a triplet state yield of 0.91 and a fluorescence yield of 0.09. By contrast, hematoporphyrin solutions with a high water content containing aggregates have lower fluorescence and triplet state yields, e.g. 0.018 and 0.56, respectively, in water. Static, singlet state quenching in some of the aggregates is responsible for the reduced fluorescence yield. The results also show that in addition to these aggregates there are other types of aggregates where there is an increased singlet to ground state radiative transition probability, resulting from the interaction between transition dipoles in adjacent molecules.