Cellulose oligomers

Moulthrop, J. S., Swatloski, R. R, Moyna, G. et al.. High-resolution NMR studies of cellulose and cellulose oligomers in ionic liquid solutions, Chem. Commun., 1557,2005. 

Longer cellulose oligomers have been modeled with MD as well. Two studies have attempted to discuss the molecular shapes in aqueous solution as well as the solvent llo-dextrin and cellodextrin llodextrin interactions [191,192]. The first of these studies showed that chains were heavily solvated and not fully extended or in contact with other cellulose fragments. The simulation was proposed as a model for freshly prepared cellophane. The latter study was more in agreement regarding chain shapes with the results in Figure 5.16. In addition, that work showed, unlike the simulated cellotetraose molecules in the same study. 

The cellulose oligomers, beginning with methyl cellotrioside, yield powder diffraction patterns that are very similar to those of cellulose II. The NMR studies of the cellulose oligomers further establish the extensive analogy between cellotetraose and cellulose II. Work by both Gessler et al. [222] and Raymond et al. [223] has shown that the 06 atoms in cellotetraose and methyl cellotrioside [224] all take the gt position, consistent with the diffraction and NMR results for cellulose II. Because the chains in the methyl cellotrioside and cellotetraose are antiparallel, this work adds support to the above results on cellulose II. On the other hand, molecules in crystalline a-lactose, a related disaccharide, have parallel packing [225]. 

A method for depolymerisation of cellulose in [C2mim][Cl] using solid acid catalysts produced cellulose oligomers in high yield, which are readily precipitated by the addition of water [209], The advantage of this method was that it avoided... 

Moyna and Rogers have studied cellulose being dissolved in [bmim]Cl with the help of 13C NMR [78] (Fig. 15). As the main result, the cellulose oligomers are dissolved in the IL as they are in H20, which demonstrated again the potential of this technology. The authors claim that NMR spectroscopy can help explaining... 

Fig. 15 13C NMR spectra of various cellulose oligomers in [bmim]Cl/DMSO-d6 [78]. Reproduced by permission of The Royal Society of Chemistry...

Figure 17 C NMR spectra of cellulose oligomer (DP 7) In DMSO and cellouronic acid Na salt, (1 —>4)-/3-linked polyglucuronate, In D2O. Cellouronic acid Na salt was prepared from viscose rayon by the TEMPO-mediated oxidation.

Figure 7. CP/MAS C NMR spectra of some cellulose oligomers recorded at 50.36 MHz a/ cellobiose, b/ methyl 0-D-cello-bioside, c/ cellotetraose and d/ methyl 6-D-cellotrioside.

Linear Homotetrasaccharides - Cellulose oligomers up to the 20-mer have been assembled from a key tetrasaccharide glycoside which was converted into the glycosyl trichloroacetimidate and separately to a derivative with 0-4 of the non-reducing end deprotected. Several specifically deoxygenated derivatives of P-maltosyl-(l- 4)-a,a-trehalose have been specifically prepared, sulfated and tested for smooth muscle cell antiproliferative activity. Iterative methods have been applied to make the a-(l ->2)-D-mannose tetramer and di- to tetra-... 

A study of the conformations of amylose and cellulose oligomers using vibrational spectroscopies has been reported. At the same conference, the use of FTIR (near, mid and far IR), and EXAFS, for spectroscopic characterization of mono- and disaccharides and coordination transition metal complexes was described. IR has been applied to characterize l,2 3,4-di-0-isopropylidene-6-0-triphenylstannylmethyl-a-D-galactopyranose. ... 

Table 15-5. Rate Constants ki for the Hydrolysis of Cellulose Oligomers ...

NMR can be employed effectively for examination of many modification processes for cellulose. Studies on acetylation have been reviewed by Usmanov [101]. The quantitative analysis of NMR data relies upon information derived from specifically modified model analogues. Similarly, C chemical shift data for various cellulose oligomers permit the analysis of the spectra of samples of cellulose acetate. Quantitative analyses for the distribution of acetate groups in cellulose acetates of various types have been achieved. 

Cellulose oligomers containing less than ten monomers are water-soluble (Atalla et al., 2008). It is expected that the cellulose chains are hydrated at the elementary nanofibril level and that cellulose processing at high temperature reduces the hydration. Thus, an increase in temperature changes the state of aggregation of native celluloses. Water aids in the relative motion of nanofibrils, while removal of water causes dryness and stimulates formation of hydrogen bonds between nanofibrils. This... 

Dudley R.L., Fyfe C.A., Stephenson P.J., Deslandes Y., Hamer G.K., and Marchessault R.H. 1983. High-resolution carbon-13 CP/MAS NMR spectra of solid cellulose oligomers and the structure of cellulose II. J Am Chem Soc 105 2469-2472. 

Solid state C-n.m.r. spectroscopy using CP-MAS methods on cellulose oligomers up to cellohexaose has been reported. 

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