When grown in a medium rich in glucose but poor in nitrogen. the algae C/dure/lr protorhecoides excrete a red pigment the structure of which has been proven to correspond IO a product of osydative ring cleavage of the chlorophyll-u chromophore at the C4-C5 methine bridge.Chlorophyll-cr catabolism: l9-Formyl-1[2lH. 22Hlbilinon derivative

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The fibres of the green-lint mutant (Lg) of cotton (Gossypium hirsutum L.) are suberized and contain a large proportion of wax. The unidentified components of the wax were separated into a colourless fluorescent fraction and a yellow pigmented fraction. Using ultraviolet spectroscopy and nuclear-magneticresonance ((1)H-NMR) spectroscopy, esterified trans-caffeic acid was identified as the only phenolic component in the colourless fraction. This fraction was further purified and was shown to contain caffeic acid esterified to fatty acids (mainly ω-hydroxy fatty acids), and glycerol in molar ratios of 4∶5∶5. When 2-aminoindan-2-phosphonic acid (AIP), an inhibitor of phenylalanine ammonia-lyase (EC 4. 3. 1. 5.) was added to ovules cultured in vitro, at the beginning of secondary wall formation, the fibres remained white and the colourless caffeic-acid derivative and the yellow compounds could no longer be detected by ultraviolet spectroscopy. Fibres grown in the presence of AIP were also examined in the electron microscope. Secondary cell walls were present in the treated fibres, but the electron-opaque suberin layers were replaced by apparently empty spaces. This result indicates that cinnamic-acid derivatives are covalently linked to suberin and have a structural role within the polymer or are involved in anchoring the polymer to the cellulosic secondary wall. Purified cell walls of green cotton fibres contained about 1% (of the dry weight) of bound glycerol, 0.9% of the glycerol being extractable with the wax fraction and 0.1% remaining in the cell-wall residue. The corresponding values for white fibres were 0.03% (total), 0.02% (wax), and 0.01% (cell-wall residue). Fibres synthesizing their secondary walls in the presence of AIP contained about normal amounts of bound glycerol in the wax fraction, but glycerol accumulation in the cell-wall residue was inhibited by about 95%. These observations indicate that glycerol is an important constituent of cotton-fibre suberin. Considerable amounts of bound glycerol could also be determined in exhaustively extracted cell walls of the cork layer of potato periderm (1.2%) and smaller amounts in the outer epidermal cell wall of Agave americana L. leaf (0.1%) indicating that the presence of glycerol in suberins and possibly also in cutins may be more widespread than previously thought.

IntroductionExtended polyaromatic hydrocarbons (PAH) are finding increasing interest among other self-assembled supramolecular systems due to their pronounced tendency for formation of extended π-stacked assemblies. These have many potential properties, such as a high electron density which allows their use in promising applications in molecular electronics. 1 However, the main drawback of these rigid polycondensed molecules resides in the difficulty of their synthesis and their very low solubility which prevents their isolation and manipulation. Recently, Müllen and co-workers 2 succeeded in finding a versatile synthesis of hexa-perihexabenzocoronene (HBC), a polycondensed hexagonal molecule containing 13 benzene rings which shows a very high chemical stability 3 and which self-organizes into columnar stacks, by π-stacking, with an outstanding degree of order in the solid state. 4,5 Additionally, its solubility was improved by the addition of peripheral long aliphatic chains which at the same time bestows the molecule with a ditopic property: These HBC derivatives show a liquid crystalline (LC) state over a wide temperature range depending on the length of the aliphatic chain. 6 Moreover, these HBC derivatives exhibit the highest charge carrier mobility recorded so far for an organic molecule both in the solid and in the liquid crystalline states, 7 paving the way toward their application in the domain of electronic 8 and optoelectronic 9-11 devices.Nevertheless, the lateral interaction between the adjacent HBC stacks caused by the crystalline packing of their aliphatic side chains 12 constitutes a major drawback since it interferes with the formation of very long conducting π-stacks. Additionally, most of the HBCs bearing aliphatic chains are liquid crystalline just above room temperature, which leads to a second disadvantage since it induces a drastic decrease of their charge carrier mobilities, 13 which is reported to be due to "lateral" conduction and as a reason for the perturbation or the deterioration of an ideal liquid crystalline mesophase that dominates the conduction process. 14 * To whom correspondence should be addressed. Tel. (Office): +41 (0) Synthesis and characterization of new hexabenzocoronene (HBC) derivatives bearing perfluoroalkylated chains are described. These disc-shaped polycondensed aromatic hydrocarbons are known to self-assemble by π-stacking into columnar architectures. The peripheral decoration with perfluorinated chains, well-known for their low van der Waals forces, leads as expected to reduced intercolumnar interactions. Powder X-ray diffraction and differential scanning calorimetry of these perfluoroalkylated HBCs proved liquid crystalline (LC) properties whose transition temperatures, mesophase stability, and nature depend on the detailed structure of these side chains, i.e., the ratio between aliphatic and perfluorinated parts. On the other hand, the insertion of a phenyl spacer between the aromatic core and the lateral chains increases the LC transition temperature and, sur...