Rajai H. Atalla

Native Cellulose: A Composite of Two Distinct Crystalline Forms

Multiplicities in the resonances of chemically equivalent carbons, which appear in the solid-state carbon-13 nuclear magnetic resonance spectra of native celluloses, have been examined at high resolution. The patterns of variation are consistent with the existence of two distinct crystalline forms. One form is dominant in bacterial and algal celluloses, whereas the other is dominant in celluloses from higher plants.

The 13c-n.m.r. spectra of the xylo- and cello-oligosaccharides

Abstract The 13 C-n.m.r. spectra have been recorded and assigned for the xylo- and cello-oligosaccharides, the former up to xylopentaose, and the latter up to cello-tetraose. A spectrum of a low-d.p. cellulose in dimethyl sulfoxide- d 6 was also assigned. In every instance, the spectra of the higher oligosaccharides closely parallel those of the corresponding disaccharides. Variations in line intensities permitted assignment of peaks to both terminal groups and internal residues. A particularly important difference was observed between the chemical shifts at the internal C-4 atoms for the two series of oligomers. This difference has been interpreted as evidence for significant differences in average linkage-orientation or solvation, which is related to the absence of C-6 in the xylo-oligosaccharides.

The complex of amylose and iodine

Abstract The organization of polyiodide chains in the amylose-iodine complex was investigated by Raman spectroscopy, by UV/vis, and by second-derivative UV/vis spectroscopies complemented by semiempirical calculations based on a simple structural model. The Raman spectra indicate that the primary substructures of the polyiodide chains are I3− and I5− sub-units. The second derivatives of the UV/vis spectra reveal four absorption peaks that can be attributed to the four polyiodide species I93−, I113−, I133−, and I153− on the basis of AM1 calculations and a polyiodide structural model. In an amylose-iodine-iodide solution, the polyiodides within the amylose helices exist in equilibrium with iodine and iodide. Changing the iodide concentration causes changes in the relative population of the different polyiodide chains and their substructures. The change in population of the various polyiodide species is accompanied by a corresponding shift in the positions of the UV/vis absorption maxima. The Raman spectra reflect parallel changes in the population of the I3− and I5− subunits. The proposed polyiodide chain lengths are consistent with previously reported observations concerning changes in the color characteristics of iodine-amylose complexes with the length of the amylose molecule up to a dp between 40 and 50.

Solid state NMR spectroscopy of specifically 13C-enriched lignin in wheat straw from coniferin

Abstract Three coniferins, specifically 13 C-enriched at side chain α, β and γ carbons, and natural abundance (unenriched) coniferin were administered to internode cavities of lignifying culms of dwarf wheat. Difference 13 C CP/MAS spectra were obtained between the spectra of the coniferin-fed and the unfed wheat straws, or between the spectra of straws fed with enriched coniferin and unenriched coniferin. The difference spectra indicated that, although the feeding of coniferin increased the lignin content slightly, the normal lignification process was not affected seriously by feeding of the precursor. The lignin derived from the coniferin in the wheat stalk was specifically 13 C-enriched at the positions corresponding to the fed precursors. It is estimated that of the total lignin associated with the bottom and top sections of the wheat straws, respectively, 15.4±2.0 and 9.5±2.5% of the lignin originated from the labelled coniferin. The percentages of the major dimeric substructures of enriched lignin in the top and bottom of internodes, respectively, are: β - O -4 including β - O -4/ α - O - R (R = carbohydrates and lignols), 74±1.5 and 65±1.5%; combined β-5, β-β and β-1 structures, 18±1.5 and 28±1.5%; and combined coniferyl alcohol and aldehyde end groups, 8±1.5 and 6±1.5%.

Non-Chlorine Bleaching of Wood Pulps Mediated by Heteropolyoxometalates

Wood consists primarily of carbohydrates (cellulose and some hemicelluloses) and lignin. In the production of chemical pulps, used in the manufacture of high quality paper, most of the lignin is removed by reaction with alkaline sulfide. At the elevated temperatures used in pulping, chemical reactions of lignin give rise to highly colored conjugated aromatic structures that remain within the wood cell (fiber) walls. The purpose of bleaching is to degrade or remove these chromophores along with remaining lignin.