Homogeneous polymeric proanthocyanidins have been isolated from 22 plant sources and all are based on a C(4)-C(8) [or C(S)] linked polyflavan-3-01 structure. I3C N.m.r. spectroscopy in 2[H,]acetone-water is used to calculate the ratio of procyanidin to prodelphinidin monomer units, the average heterocyclic ring stereochemistry of the monomers, and the ratio of monomers to chain-terminating units. The majority of polymers isolated in this study possess monomers with predominantly a 2,3-cis stereochemistry [the same configuration as (-) -epicatechin],The number-average molecular weight, calculated from monomer to terminal unit ratios, of the polymers is 1 500-5 000. The structure of the chain-terminating group is established by thiolysis degradation and g.1.c. analysis of the products.
A synchrotron wide-angle x-ray scattering study of mung bean (Vigna radiata) primary cell walls was combined with published solid-state nuclear magnetic resonance data to test models for packing of (1→4)-b-glucan chains in cellulose microfibrils. Computersimulated peak shapes, calculated for 36-chain microfibrils with perfect order or uncorrelated disorder, were sharper than those in the experimental diffractogram. Introducing correlated disorder into the models broaden the simulated peaks but only when the disorder was increased to unrealistic magnitudes. Computer-simulated diffractograms, calculated for 24-and 18-chain models, showed good fits to experimental data. Particularly good fits to both x-ray and nuclear magnetic resonance data were obtained for collections of 18-chain models with mixed cross-sectional shapes and occasional twinning. Synthesis of 18-chain microfibrils is consistent with a model for cellulose-synthesizing complexes in which three cellulose synthase polypeptides form a particle and six particles form a rosette.
Soil samples from long-term plots annually fertilized with superphosphate since 1952 and also unfertilized (control) plots of an irrigated and intensively grazed pasture in Canterbury, New Zealand, were subjected to a sequential extraction procedure followed by "P nuclear magnetic resonance (NMR) analysis of the soil phosphorus (P) forms present.Overall, 80% of the total organic P (as determined by ignition) was removed from the soil by the sequential extraction procedure. Most of the organic P (900/) detected by NMR was in the monoester fraction. Small quantities of diester and pyrophosphate were also found. Choline phosphate constituted a significant proportion (18-25%) of the monoester P in the acetylacetone and 0.5 M NaOH extracts. Long-term superphosphate additions resulted in almost all of the P accumulated in the monoester P fraction (up to 99Yo).
SummaryNative cellulose in higher plants forms crystalline ®brils a few nm across, with a substantial fraction of their glucan chains at the surface. The accepted crystal structures feature a¯at-ribbon 2 1 helical chain conformation with every glucose residue locked to the next by hydrogen bonds from O-3¢ to O-5 and from O-2 to O-6¢. Using solid-state NMR spectroscopy we show that the surface chains have a different C-6 conformation so that O-6 is not in the correct position for the hydrogen bond from O-2. We also present evidence consistent with a model in which alternate glucosyl residues are transiently or permanently twisted away from the¯at-ribbon conformation of the chain, weakening the O-3¢ ± 0-5 hydrogen bond. Previous molecular modelling and the modelling studies reported here indicate that this translational' chain conformation is energetically feasible and does not preclude binding of the surface chains to the interior chains, because the surface chains share the axial repeat distance of the 2 1 helix. Reduced intramolecular hydrogen bonding allows the surface chains to form more hydrogen bonds to external molecules in textiles, wood, paper and the living plant.
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