21,24-Dimithylaetiobiliverdin-IV-γ was prepared via excessive methylation of aetiobili. verdin-IV-γ. Its configuration could be established using 1H NMR methods. Photoisomerisation yields the (E,Z,Z) and (E,Z,E) diastereomers which means that the selectivity observed in photoisomerisation of bilatrienes-abc can be removed by making the ligands of the lactame moiety adjacent to exocyclic double bonds nearly equal. The torsional angles at the methine single bonds are approximatly equal in the three diastereomers resulting in much the same UV-VIS spectra. The obviously strong distortion of the conjugated chromophor allows for the deceleration of certain radiationless deexcitation paths thereby allowing for photoisomerisations in homogenous solution.
Methylation of etiobiliverdin-IV-γ yields a ring-A N-methylated product the structure of which was proven by comparison with the corresponding monolactimether and the ring-B methylated product which was synthesized on an independent route. The configura-tion (Z,Z,Z) was deduced by 1H-NMR experiments and a more or less helical conformation which is most twisted at the ring-A methine fragment was found. Photoisomerization exclusively takes place at this position giving the (E,Z,Z) diastereomer, a reaction which is discussed in terms of the correlation of light absorption, methine single bond twist and photochemical selectivity.
Methilation of the aetiobiliverdin-IV-γ-lactimether yields a lactam-N-methylated derivative the structure of which was proven by an ether cleavage and 1H NMR spectroscopy. The configuration (Z,Z,Z) was deduced from 1HNMR experiments. Photo-isomerization exclusively forms the (E,Z,Z) diastereomer. By conformational analysis using the LIS technique and correlations of UV-VIS spectra and PPP-type calculations a more or less helical arrangement for the two diastereomers was confirmed. The twisting is maximal at the methine single bond adjacent to the site of N-methylation, the overall geometry seems to be much more distorted than the non methylated derivatives.
Cellulose microfibrils from the cell wall of the green alga Valonia macrophysa were isolated by enzymatical digestion of the wall matrix and examined in the electron microscope using the negative staining technique. The smallest fibrils obtained after prolonged treatment were found to be flat ribbons with a width about 10—20 nm and a height of 3 to 4 nm. This result is discussed in relation to Frey- Wyssling's concept of an “elementary fibril“ with a cross-section of 3.5 × 3.5 nm. Some alternation of unstained areas along the fibrils was observed. This was interpreted as artificially induced rather than relating to the structure and the arrangement of the cellulose chain molecules.
Flower chromoplasts of Narcissus pseudonarcissus have been isolated in high purity and inte grity by a new procedure. From these chromoplasts circular DNA molecules in supercoiled form have been isolated and demonstrated by electron microscopy to have a contour length of about 44 μm (molecular weight about 92 x 106 daltons)