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  • 1
    Electronic Resource
    Electronic Resource
    Microtubular Structures in Macronuclei of Synchronously Dividing Tetrahymena pyriformis (1968)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 15 (1968), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SYNOPSIS. When heat-synchronized cultures of Tetrahymena pyriformis, amicronucleate strain GL, were examined by electron microscopy, intramacronuclear microtubules were observed in dividing cells. These tubules have a diameter of 180–230 A and occur either singly or packed together in bundles. They are predominantly associated with outpocketings and invaginations of the nucleus. Sections as well as negatively stained preparations of isolated macronuclear envelopes indicate that the microtubules are inserted at the inner nuclear membrane.The findings suggest that microtubules of the spindle type participate in the process of macronuclear division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1968.tb02212.x
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  • 2
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 24. Mitt. Über die Beziehung zwischen Lichtabsorption und Struktur von Bilatrienen-abc (1978)
    Springer
    Monatshefte für Chemie 109 (1978), S. 1429-1449 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using the recently established solution structure of a bilatriene-abc derivative the parameter set of thePPP-SCF-LCAO-MO-Cl model was refined. The general trend, that molecular configuration itself does not so much determine the absorption spectra as was deduced by investigation of partial bile pigment structures, was confirmed for the bilatrienes-abc. Instead, the configuration at a particular double bond induces a certain torsional angle at the adjacent single bond which leads to dramatic spectral changes on isomerization of this double bond. Isomerization without this torsional effect brings about different relative intensities of the two main spectral bands. Comparing measured spectra of several bilatrienes-abc and calculated spectra a helicalsyn, syn, syn-conformation with three torsional angles at the methine fragments of appr. 20° was deduced for systems with (Z, Z, Z)-configuration. For a recently prepared (E, Z, Z)-derivative a nearly helicalsyn, syn, syn-conformation with torsional angles of 40°, 20° and 20° at the methine single bonds is the most probable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00906056
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  • 3
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 25. Mitt. Die diastereomeren (geometrisch isomeren) Biliverdindimethylester—Struktur, Konfiguration und Konformation (1978)
    Springer
    Monatshefte für Chemie 109 (1978), S. 1451-1473 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Photoisomerization of the symmetrically substituted bilatrienes-abc1 and2 adsorbed on aluminum oxide yields the photoisomers1′ and2′, whereas the biliverdindimethylester (3) gives rise to two isomers3′ and3″. By X-ray photoelectron spectrometry of the N1s-level all these diastereomers were shown to have a bislactam structure. From1H-NMR experiments (chemical shifts, Lanthanide induced shifts, double resonance experiments) the configurations (Z,Z,Z) at the methin positions were assigned to the educts—the photoisomers1′ and2′ having the configurations (Z,Z,E). The configurations (Z,Z,E) and (E,Z,Z) could be assigned to the diastereomers3′ and3″. The conformational aspects within these series are discussed and on the basis of several studies asyn-syn-syn-helical arrangement is deduced for the systems of configuration (Z,Z,Z). For the (Z,Z,E) isomers in the region of (Z)-configuration a conformation resembling the (Z,Z,Z)-systems is reasonable, but in the region of configuration (E) a stronger twisting at the methin single bond due to steric crowding should be favoured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00906057
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  • 4
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 26. Mitt.: Zur anaeroben Photochemie von Gallenpigmenten: Die Lumineszenz von Gallenpigment-Partialstruktursystemen und integralen Farbstoffen (1979)
    Springer
    Monatshefte für Chemie 110 (1979), S. 987-1001 
    Details
    ISSN: 1434-4475
    Keywords: Anaerobic photochemistry ; Bile pigments ; Luminescence ; Radiationless deexcitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The luminescence properties of about twentyfive model compounds representing the three main partial structures of bile pigments (namely pyrromethenes, pyrromethenones and methylenepyrrolylmethylenepyrrolinones) as well as tripyrrines and the geometrical isomers of aetiobiliverdin-IV-γ are reported. In these compounds there is usually only a very faint or even no fluorescence and phosphorescene as the pathway of deexcitation. Vibrational internal conversion and photoisomerizations at the exocyclic double bonds are the main anaerobic paths of radiationless decay of the excited states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00906694
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  • 5
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 19. Mitt.: Die elektrochemische Oxidation von Pyrromethenonen und Pyrromethenen (Gallenpigment-Partialstrukturen) (1978)
    Springer
    Monatshefte für Chemie 109 (1978), S. 183-192 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electrochemical oxidation of arylmethylene-pyrrolinones, pyrromethenones and pyrromethenes as representative bile pigment partial structure models was investigated by means of a rotating disc platinum electrode using acetonitrile as the solvent. Two different oxidation reactions were found. The first reaction being a reversible one-electron oxidation with compounds of the arylmethylene-pyrrolinone series and pyrromethenones which are unsubstituted in position 5 of the pyrrole ring. A two step reaction (the first one reversible, the second irreversible) on the other hand was found to be typical for pyrromethenones bearing a methyl group in this position. Through protonation the first step is at a higher potential, whereas the second one is lowered and becomes reversible. The resulting oxidation pattern can be interpreted analogous to the oxidation of hydroquinones in aprotic solvents. The geometrical isomers of a pyrromethenone were oxidized at appr. the same potential, but there is a strong dependence of the potential of the first oxidation step on the substitution: a higher degree of alkylation favours oxidation by lowering the oxidation potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00911959
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  • 6
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 20. Mitt.: Untersuchungen über das Deprotonierungsgleichgewicht und die Bildung von Metallkomplexen von Gallenpigment-Partialstrukturen (1978)
    Springer
    Monatshefte für Chemie 109 (1978), S. 883-897 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract By spectrophotometric measurements in the systemDMSO/H2O/Me 4NOH pK a-values for several model compounds representing bile pigment partial structures were established. The acidic protons of pyrrole and lactame type nitrogen atoms are removed by bases governed by the electronic properties of the substituents on these ring systems. The pK a-values for both types lie in the same region. In the pyrromethenones the lower one corresponds to the lactame type NH as was deduced by comparison with specifically methylated derivatives. The complexation of these ligands is determined by the possibility of removing an acidic proton and achieving a chelate structure by means of an adjacent pyrrolinone type nitrogen atom. Complexes are favoured in the series pyrromethenes 〉 lactim ethers 〉 pyrromethenones. With the latter there are two possibilities: one observed with BF2-chelation where the lactime form becomes stabilized, the other one with zink where both acidic centers are involved in the bonding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00907309
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  • 7
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 42. Mitt. Kraftfeldrechnungen an Gallenfarbstoffen: Die Energiehyperfläche rubinoider Pigmente (1981)
    Springer
    Monatshefte für Chemie 112 (1981), S. 1325-1332 
    Details
    ISSN: 1434-4475
    Keywords: Bilirubin ; Conformational analysis ; Force field calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The energy hypersurface of rubinoid bile pigments is calculated using a force field model previously described. Two cases are observed. I: The pigment is substituted symmetrically or unsymmetrically by apolar groups. This results in a very shallow energy valley containing several enantiomeric conformers of approximately equal energies. II: Substitution by polar groups, especially in position 8 and 12 of the rubin skeleton, (e.g.−CH2−CH2−COOH) is followed by a “lock in” bonding between such groups and the lactam ring functions. Thereby only two enantiomeric conformers, which are energetically stabilized, are possible. The barrier between these species amounts to about 40 kJ/mol. These results are compared with the experimental facts available so far. An analysis of the corresponding energy hypersurfaces of the diastereomeric forms of (Z,Z)-, (E,Z)-, (Z,E)- and (E,E)-configurations is given as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00904684
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  • 8
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 39. Mitt.: Ein Kraftfeldmodell zur konformationsanalytischen Untersuchung von Gallenfarbstoffen (1981)
    Springer
    Monatshefte für Chemie 112 (1981), S. 391-403 
    Details
    ISSN: 1434-4475
    Keywords: Bilatrienes-abc ; Pyrromethenes ; Pyrromethenones ; Tripyrrines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A force field model was designed with respect to the special needs of bile pigments. It is parametrized and tested using partial structures of bile pigments as well as an integral pigment; the solution structures of the molecules were previously deduced using independent experimental methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00900769
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  • 9
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 40. Mitt.: Azafulvene, Schlüsselstellen beim Aufbau von Pyrrolpigmenten? —Eine neue Synthese von verdinoiden und rubinoiden Gallenfarbstoffen (1981)
    Springer
    Monatshefte für Chemie 112 (1981), S. 501-510 
    Details
    ISSN: 1434-4475
    Keywords: Azafulvenes ; Biladienes-ac ; Bilatrienes-abc ; DDQ ; Synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Substituted azafulvenes were generated by dehydrogenation of 5′-methyl-substituted pyrromethenones withDDQ and characterized by UV- and1H-NMR-spectroscopy. Their electrophilic properties were demonstrated using several quenchers and furthermore they were used for a synthesis of verdinoid bile pigments (which easily can be converted to rubinoid systems by the action of NaBH4) with nearly any desired unsymmetrical alkyl substitution patter: The azafulvene spezies was generated by the action ofDDQ on a 5′-methylpyrromethenone and was quenched by an 5′-unsubstituted pyrromethenone. The resulting rubinoid adduct was dehydrogenated immediatly byDDQ — yields were good to high.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00901829
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  • 10
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 43. Mitt. (1982)
    Springer
    Monatshefte für Chemie 113 (1982), S. 111-121 
    Details
    ISSN: 1434-4475
    Keywords: Association ; Bilirubin and derivatives ; Tautomerism ; Variable temperature UV-VIS spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract ByLambert−Beer-experiments at different temperatures in the range from 290 to 80K of solutions containing Bilirubin (2), its dimethylester3, its dimethoxydimethylester derivative4 and aetiobilirubin-IV-γ (1) in 2-methyltetrahydrofurane the preponderance of an association equilibrium determining the spectral changes upon cooling in the case of1 and3 was deduced. By protonation studies of partial structures5 and6 as well as of the integral pigments3 and4 the lactam-lactim equilibrium was proved to be on the side of the lactam tautomer at low temperatures as well. Upon cooling a zwitterionic species was detected in case of compound2. The conformational aspects in cases where a disturbance by the equiblibria given above could be ruled out are discussed. A warning is given to use low temperatures measurements of absorption and luminescence properties to gain structural and photochemical informations without previously establishing the nature of the solutions very carefully.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814344
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