The solution and liquid crystalline phases formed by dissolution of the dye Edicol Sunset Yellow (ESY) in water have been examined using optical microscopy, multinuclear NMR (1H, 2H, 13C, 23Na), and X-ray diffraction. From the solution 1H and 13C spectra (particularly 13C), it is clear that the tautomeric form present in all these phases is the hydrazone, NH, structure, not the usually given azo, OH, form. Two chromonic mesophases occur: a nematic (N) phase at approximately 30-40 wt % and a hexagonal (M) phase at approximately 40-45 wt %. X-ray diffraction data show that the aggregates in the mesophases are single molecule stacks, with a typical spacing of approximately 3.5 angstroms, as expected for these systems. The NMR quadrupole splittings (2H2O, 23Na) are similar to those observed for surfactant lyotropic mesophases, suggesting that there are no water molecules or counter ions that are tightly bound to the ESY aggregates. An unusual feature of the X-ray diffraction pattern of the mesophases is the occurrence of diffuse off-axis reflections at approximately 6.8 angstroms. It is proposed that these arise from a head-to-tail packing of the molecules within the stacks.
SummaryModi®cations in cell wall pectic polysaccharides are thought to in¯uence cell±cell adhesion and the mechanical properties of plant tissues. Monoclonal antibodies to epitopes occurring in homogalacturonan and side chains of rhamnogalacturonan I have been used in an immunolocalization study of cell wall architecture of developing pea cotyledons. Pectic (1®4)-b-D-galactan appears in cotyledon cell walls at a de®ned stage late in development (approximately 26±30 days after anthesis), whereas homogalacturonan and pectic (1®5)-a-L-arabinan are present in cotyledon cell walls throughout development. (1®4)-b-galactan was restricted to a distinct thin layer at the plasma membrane face of the cell wall. Anion exchange and immunoaf®nity chromatography indicated that the (1®4)-b-galactan was associated with acidic pectic components. Mechanical compressive testing of pea cotyledons, before and after (1®4)-b-galactan appearance, indicated that the cotyledons with the galactan-rich cell wall layer were twice as ®rm as those with no detectable (1®4)-b-galactan.
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